Introduction. Animal consumers have important roles in ecosystems (Chew 1974, 1976), determining plant species composition and structure (Harper 1969, Pacala and Crawley 1992, Crawley 1983, 1989), regulating rates of plant production and nutrient cycling (Naiman 1988, McNaughton et al. 1989, Holland et al. 1992), and altering soil structure and chemistry (Milchunas et al. 1993, Huntly 1991). Desertification of semi-arid grasslands in the Southwest United States by domestic livestock provides an important example of herbivore regulation of ecosystem structure and function (Schlesinger et al. 1990). The species composition and physical structure of these desert grassland ecosystems were significantly altered by alien herbivores about 100 years ago (Bahre 1991, York and Dick-Peddie 1968, Gardner 1951, Hastings and Turner 1980, Buffington and Herbel 1965, Dick-Peddie 1993). To what extent the spatial patterns of semi-arid shrubland and grassland plant production and soil characteristics are currently controlled by plant resource use, abiotic factors, or consumers is not known. Desertification is an ecosystem-level phenomenon occurring on a global scale with great relevance to human welfare (Nelson 1988). In order to understand the processes that contribute to desertification, we must fully understand interactions among the components of arid-land ecosystems. Schlesinger et al. (1990) suggest that in the absence of continued livestock perturbations, plant resource use and abiotic factors appear to be the principal factors accounting for the persistence of desert shrublands in desertified semi-arid grasslands. However, Brown and Heske (1990a) provide evidence that indigenous small mammal consumers may also have a major role in determining vegetation structure in those desert ecosystems. Brown and Heske (1990a, Heske et al. 1993) found that the exclusion of rodents from Chihuahuan Desert creosotebush shrubland areas resulted in a significant increase in grass cover over a 12 year period. Brown and Heske (1990a) concluded that rodents were keystone species in those desert shrub communities, greatly influencing vegetation structure. Rodents are also known to have significant influences on plant species composition and diversity in desert communities (Inouye et al. 1980, Heske et al. 1993, Brown et al. 1986). Several species of granivorous rodents (Family: Heteromidae, genera: Dipodomys, Perognathus, Chaetodipus) appear to have the greatest influence on vegetation herbivory. Soil disturbance through the digging activities of rodents can have profound local effects on plant species composition and vegetation structure in the Chihuahuan Desert (Moroka et al. 1982). Digging activities of desert rodents intermix surface soils with subsurface soils (Abaturov 1972), and increase rainfall infiltration (Soholt 1975). Reported measures of the percentage of desert soil surface areas disturbed by rodent digging activities in desert enviroments range from 10% (Abaturov 1972) to 4.5% (Soholt 1975). Burrowing activities increase local soil nutrient and water status, creating favorable sites for increased plant densities, biomass production, and increased species diversity (Morehead et al. 1989, Mun and Whitford 1990). Rabbits (Lagomorpha: Black-tailed jackrabbits, Lepus californicus, and desert cottontail rabbits, Sylvilagus aduboni) are also important consumers of desert vegetation (Brown 1947, Johnson & Anderson 1984, Steinberger and Whitford 1983, Ernest 1994). Rabbits can have significant effects on plant species composition and structure resulting from selective herbivory (Gibbens et al. 1993, Clark and Wagner 1984, Norris 1950, Zeevalking and Fresco 1977). Gibbens et al. (1993) found that excluding rabbits from Chihuahuan Desert creosotebush (Larrea tridentata) communities over a period of 50 years increased the canopy cover of some grasses, and also increased canopy cover of some shrub species. Small mammal (rodent and rabbit) populations may fluctuate considerably with variation in climate and annual plant production (Brown et al. 1979, Brown & Heske 1990, Brown & Zeng 1989, Whitford 1976, Johnson & Anderson 1984). Reproduction in desert rodents is known to be induced by plant foliage production (Reichman and Van De Graff 1975, Beatley 1969). If small mammals are keystone species affecting plant species composition and structure in desert ecosystems, then the impacts of small mammals on vegetation are probably linked with variation in climate and plant production. A reciprocal plant-herbivore/granivore feedback system may result, where small mammal populations and thus impacts on vegetation, are initially determined by climate influences on plant food resource availability to the small mammals. Thus, the effects of small mammals during dry years will probably be different from the effects during wet years because of different population sizes. If this is so, one should be able to measure differential effects of small mammals on plant communities over series of wet or dry years, such as El Nino and La Nina cycles (Nicholls 1988). Such reciprocal interactions should also occur in relation to long-term (decades) climate change. The effects of any one small mammal species population on the biotic community will be complicated by competitive interactions with other mammal species (Munger & Brown 1981, Brown & Zeng 1989, Brown & Heske 1990), however overall impacts on vegetation and soils by the combined effects of all small mammal species may be closely linked with variation in precipitation and plant production. Depending upon the persistence of plant food resources such as foliage or seeds, lag times in consumer impacts may be expected following periods of precipitation and plant production. In desert ecosystems, widely scattered shrubs produce a patch pattern of fertile islands with high plant biomass production and soil nutrients, surrounded by relatively unproductive barren soil (West and Klemmedson 1978, Crawford and Gosz 1982). Researchers at the Jornada Long-Term Ecological Research site in New Mexico have proposed a desertification model suggesting that perturbations caused by domestic livestock grazing and climate change initiated processes transforming grasslands with relatively homogeneous resource distributions to shrubland environments with relatively heterogenous resource distributions (Schlesinger et al. 1990). This patchy vegetation/resource distribution pattern is stable under present climate regimes, and appears to be maintained by plant resource use and abiotic soil processes (Schlesinger et al. 1990). However, Wagner (1976, page 195) suggested that small mammals were probably maintaining shrubland dominated ecosystems at the Jornada by suppressing grasses through selective herbivory. Research Hypotheses. The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan Desert shrublands and grasslands. What role if any do indigenous small mammal consumers have in maintaining desertified landscapes in the Chihuahuan Desert? Additionally, how do the effects of small mammals interact with changing climate to affect vegetation patterns over time? This study will provide long-term experimental tests of the roles of consumers on ecosystem pattern and process across a latitudinal climate gradient. The following questions or hypotheses will be addressed. 1) Do small mammals influence patterns of plant species composition and diversity, vegetation structure, and spatial patterns of vegetation canopy cover and biomass in Chihuahuan Desert shrublands and grasslands? Are small mammals keystone species that determine plant species composition and physiognomy of Chihuahuan Desert communities as Brown and Heske (1990a) and Gibbens et al. (1993) suggest? Do small mammals have a significant role in maintaining the existence of shrub islands and spatial heterogeneity of creosotebush shrub communities? 2) Do small mammals affect the taxonomic composition and spatial pattern of vegetation similarly or differently in grassland communities as compared to shrub communities? How do patterns compare between grassland and shrubland sites, and how do these relatively small scale patterns relate to overall landscape vegetation patterns? 3) Do small mammals interact with short-term (annual) and long-term (decades) climate change to affect temporal changes in vegetation spatial patterns and species composition? Other Consumers. Ants are important consumers in Chihuahuan Desert ecosystems (MacKay 1991), and granivorous ants are known to have competitive interactions with rodents (Brown & Davidson 1977, Brown et al. 1979) for plant seed resources. Termites are important detritivores in Chihuahuan Desert ecosystems (MacKay 1991) and appear to have key roles in plant litter decomposition and nutrient cycling (Whitford et al. 1982, Schaefer & Whitford 1981), and in altering soil structure and hydrologic processes (Elkins et al. 1986). Grasshoppers are important herbivores in Chihuahuan Desert ecosystems (Rivera 1986, Wisdom 1991, Richman et al. 1993), with various species specializing on most of the different plant species present in any location (Otte 1976, Joern 1979). Since manipulations of small mammals will probably affect these arthropod consumers, we will monitor these other consumers on the measurement plots to document any changes. Documentation of changes or lack of changes in ant, termite, and grasshopper consumer groups will be needed to interpret the results of small mammal manipulations on vegetation and soils. For example, if removal of rodents results in an increase of seed-harvesting ants, changes or lack of changes in vegetation and soils may be attributed to compensatory granivory from the increase in ants. Small mammals are the consumer group that appears to have the greatest influence on Chihuahuan Desert communities (see literature citations above). Given the known ecological importance of small mammals and the complexity and difficulties that would be associated with manipulating small mammals and arthropods, we have chosen to start with experiments on small mammals first. If these other consumer groups appear to have important interactions with small mammals, we will pursue additional experiments in the future to focus on those interactions, and to elucidate the ecological roles of these arthropod consumers.
Date Production: 2019
SMES rabbit survey data
Introduction. Animal consumers have important roles in ecosystems (Chew 1974, 1976), determining plant species composition and structure (Harper 1969, Pacala and Crawley 1992, Crawley 1983, 1989), regulating rates of plant production and nutrient cycling (Naiman 1988, McNaughton et al. 1989, Holland et al. 1992), and altering soil structure and chemistry (Milchunas et al. 1993, Huntly 1991). Desertification of semi-arid grasslands in the Southwest United States by domestic livestock provides an important example of herbivore regulation of ecosystem structure and function (Schlesinger et al. 1990). The species composition and physical structure of these desert grassland ecosystems were significantly altered by alien herbivores about 100 years ago (Bahre 1991, York and Dick-Peddie 1968, Gardner 1951, Hastings and Turner 1980, Buffington and Herbel 1965, Dick-Peddie 1993). To what extent the spatial patterns of semi-arid shrubland and grassland plant production and soil characteristics are currently controlled by plant resource use, abiotic factors, or consumers is not known. Desertification is an ecosystem-level phenomenon occurring on a global scale with great relevance to human welfare (Nelson 1988). In order to understand the processes that contribute to desertification, we must fully understand interactions among the components of arid-land ecosystems. Schlesinger et al. (1990) suggest that in the absence of continued livestock perturbations, plant resource use and abiotic factors appear to be the principal factors accounting for the persistence of desert shrublands in desertified semi-arid grasslands. However, Brown and Heske (1990a) provide evidence that indigenous small mammal consumers may also have a major role in determining vegetation structure in those desert ecosystems. Brown and Heske (1990a, Heske et al. 1993) found that the exclusion of rodents from Chihuahuan Desert creosotebush shrubland areas resulted in a significant increase in grass cover over a 12 year period. Brown and Heske (1990a) concluded that rodents were keystone species in those desert shrub communities, greatly influencing vegetation structure. Rodents are also known to have significant influences on plant species composition and diversity in desert communities (Inouye et al. 1980, Heske et al. 1993, Brown et al. 1986). Several species of granivorous rodents (Family: Heteromidae, genera: Dipodomys, Perognathus, Chaetodipus) appear to have the greatest influence on vegetation herbivory. Soil disturbance through the digging activities of rodents can have profound local effects on plant species composition and vegetation structure in the Chihuahuan Desert (Moroka et al. 1982). Digging activities of desert rodents intermix surface soils with subsurface soils (Abaturov 1972), and increase rainfall infiltration (Soholt 1975). Reported measures of the percentage of desert soil surface areas disturbed by rodent digging activities in desert enviroments range from 10% (Abaturov 1972) to 4.5% (Soholt 1975). Burrowing activities increase local soil nutrient and water status, creating favorable sites for increased plant densities, biomass production, and increased species diversity (Morehead et al. 1989, Mun and Whitford 1990). Rabbits (Lagomorpha: Black-tailed jackrabbits, Lepus californicus, and desert cottontail rabbits, Sylvilagus aduboni) are also important consumers of desert vegetation (Brown 1947, Johnson & Anderson 1984, Steinberger and Whitford 1983, Ernest 1994). Rabbits can have significant effects on plant species composition and structure resulting from selective herbivory (Gibbens et al. 1993, Clark and Wagner 1984, Norris 1950, Zeevalking and Fresco 1977). Gibbens et al. (1993) found that excluding rabbits from Chihuahuan Desert creosotebush (Larrea tridentata) communities over a period of 50 years increased the canopy cover of some grasses, and also increased canopy cover of some shrub species. Small mammal (rodent and rabbit) populations may fluctuate considerably with variation in climate and annual plant production (Brown et al. 1979, Brown & Heske 1990, Brown & Zeng 1989, Whitford 1976, Johnson & Anderson 1984). Reproduction in desert rodents is known to be induced by plant foliage production (Reichman and Van De Graff 1975, Beatley 1969). If small mammals are keystone species affecting plant species composition and structure in desert ecosystems, then the impacts of small mammals on vegetation are probably linked with variation in climate and plant production. A reciprocal plant-herbivore/granivore feedback system may result, where small mammal populations and thus impacts on vegetation, are initially determined by climate influences on plant food resource availability to the small mammals. Thus, the effects of small mammals during dry years will probably be different from the effects during wet years because of different population sizes. If this is so, one should be able to measure differential effects of small mammals on plant communities over series of wet or dry years, such as El Nino and La Nina cycles (Nicholls 1988). Such reciprocal interactions should also occur in relation to long-term (decades) climate change. The effects of any one small mammal species population on the biotic community will be complicated by competitive interactions with other mammal species (Munger & Brown 1981, Brown & Zeng 1989, Brown & Heske 1990), however overall impacts on vegetation and soils by the combined effects of all small mammal species may be closely linked with variation in precipitation and plant production. Depending upon the persistence of plant food resources such as foliage or seeds, lag times in consumer impacts may be expected following periods of precipitation and plant production. In desert ecosystems, widely scattered shrubs produce a patch pattern of fertile islands with high plant biomass production and soil nutrients, surrounded by relatively unproductive barren soil (West and Klemmedson 1978, Crawford and Gosz 1982). Researchers at the Jornada Long-Term Ecological Research site in New Mexico have proposed a desertification model suggesting that perturbations caused by domestic livestock grazing and climate change initiated processes transforming grasslands with relatively homogeneous resource distributions to shrubland environments with relatively heterogenous resource distributions (Schlesinger et al. 1990). This patchy vegetation/resource distribution pattern is stable under present climate regimes, and appears to be maintained by plant resource use and abiotic soil processes (Schlesinger et al. 1990). However, Wagner (1976, page 195) suggested that small mammals were probably maintaining shrubland dominated ecosystems at the Jornada by suppressing grasses through selective herbivory. Research Hypotheses. The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan Desert shrublands and grasslands. What role if any do indigenous small mammal consumers have in maintaining desertified landscapes in the Chihuahuan Desert? Additionally, how do the effects of small mammals interact with changing climate to affect vegetation patterns over time? This study will provide long-term experimental tests of the roles of consumers on ecosystem pattern and process across a latitudinal climate gradient. The following questions or hypotheses will be addressed. 1) Do small mammals influence patterns of plant species composition and diversity, vegetation structure, and spatial patterns of vegetation canopy cover and biomass in Chihuahuan Desert shrublands and grasslands? Are small mammals keystone species that determine plant species composition and physiognomy of Chihuahuan Desert communities as Brown and Heske (1990a) and Gibbens et al. (1993) suggest? Do small mammals have a significant role in maintaining the existence of shrub islands and spatial heterogeneity of creosotebush shrub communities? 2) Do small mammals affect the taxonomic composition and spatial pattern of vegetation similarly or differently in grassland communities as compared to shrub communities? How do patterns compare between grassland and shrubland sites, and how do these relatively small scale patterns relate to overall landscape vegetation patterns? 3) Do small mammals interact with short-term (annual) and long-term (decades) climate change to affect temporal changes in vegetation spatial patterns and species composition? Other Consumers. Ants are important consumers in Chihuahuan Desert ecosystems (MacKay 1991), and granivorous ants are known to have competitive interactions with rodents (Brown & Davidson 1977, Brown et al. 1979) for plant seed resources. Termites are important detritivores in Chihuahuan Desert ecosystems (MacKay 1991) and appear to have key roles in plant litter decomposition and nutrient cycling (Whitford et al. 1982, Schaefer & Whitford 1981), and in altering soil structure and hydrologic processes (Elkins et al. 1986). Grasshoppers are important herbivores in Chihuahuan Desert ecosystems (Rivera 1986, Wisdom 1991, Richman et al. 1993), with various species specializing on most of the different plant species present in any location (Otte 1976, Joern 1979). Since manipulations of small mammals will probably affect these arthropod consumers, we will monitor these other consumers on the measurement plots to document any changes. Documentation of changes or lack of changes in ant, termite, and grasshopper consumer groups will be needed to interpret the results of small mammal manipulations on vegetation and soils. For example, if removal of rodents results in an increase of seed-harvesting ants, changes or lack of changes in vegetation and soils may be attributed to compensatory granivory from the increase in ants. Small mammals are the consumer group that appears to have the greatest influence on Chihuahuan Desert communities (see literature citations above). Given the known ecological importance of small mammals and the complexity and difficulties that would be associated with manipulating small mammals and arthropods, we have chosen to start with experiments on small mammals first. If these other consumer groups appear to have important interactions with small mammals, we will pursue additional experiments in the future to focus on those interactions, and to elucidate the ecological roles of these arthropod consumers.
SMES Leaf Litter Data
Introduction. Animal consumers have important roles in ecosystems (Chew 1974, 1976), determining plant species composition and structure (Harper 1969, Pacala and Crawley 1992, Crawley 1983, 1989), regulating rates of plant production and nutrient cycling (Naiman 1988, McNaughton et al. 1989, Holland et al. 1992), and altering soil structure and chemistry (Milchunas et al. 1993, Huntly 1991). Desertification of semi-arid grasslands in the Southwest United States by domestic livestock provides an important example of herbivore regulation of ecosystem structure and function (Schlesinger et al. 1990). The species composition and physical structure of these desert grassland ecosystems were significantly altered by alien herbivores about 100 years ago (Bahre 1991, York and Dick-Peddie 1968, Gardner 1951, Hastings and Turner 1980, Buffington and Herbel 1965, Dick-Peddie 1993). To what extent the spatial patterns of semi-arid shrubland and grassland plant production and soil characteristics are currently controlled by plant resource use, abiotic factors, or consumers is not known. Desertification is an ecosystem-level phenomenon occurring on a global scale with great relevance to human welfare (Nelson 1988). In order to understand the processes that contribute to desertification, we must fully understand interactions among the components of arid-land ecosystems. Schlesinger et al. (1990) suggest that in the absence of continued livestock perturbations, plant resource use and abiotic factors appear to be the principal factors accounting for the persistence of desert shrublands in desertified semi-arid grasslands. However, Brown and Heske (1990a) provide evidence that indigenous small mammal consumers may also have a major role in determining vegetation structure in those desert ecosystems. Brown and Heske (1990a, Heske et al. 1993) found that the exclusion of rodents from Chihuahuan Desert creosotebush shrubland areas resulted in a significant increase in grass cover over a 12 year period. Brown and Heske (1990a) concluded that rodents were keystone species in those desert shrub communities, greatly influencing vegetation structure. Rodents are also known to have significant influences on plant species composition and diversity in desert communities (Inouye et al. 1980, Heske et al. 1993, Brown et al. 1986). Several species of granivorous rodents (Family: Heteromidae, genera: Dipodomys, Perognathus, Chaetodipus) appear to have the greatest influence on vegetation herbivory. Soil disturbance through the digging activities of rodents can have profound local effects on plant species composition and vegetation structure in the Chihuahuan Desert (Moroka et al. 1982). Digging activities of desert rodents intermix surface soils with subsurface soils (Abaturov 1972), and increase rainfall infiltration (Soholt 1975). Reported measures of the percentage of desert soil surface areas disturbed by rodent digging activities in desert enviroments range from 10% (Abaturov 1972) to 4.5% (Soholt 1975). Burrowing activities increase local soil nutrient and water status, creating favorable sites for increased plant densities, biomass production, and increased species diversity (Morehead et al. 1989, Mun and Whitford 1990). Rabbits (Lagomorpha: Black-tailed jackrabbits, Lepus californicus, and desert cottontail rabbits, Sylvilagus aduboni) are also important consumers of desert vegetation (Brown 1947, Johnson & Anderson 1984, Steinberger and Whitford 1983, Ernest 1994). Rabbits can have significant effects on plant species composition and structure resulting from selective herbivory (Gibbens et al. 1993, Clark and Wagner 1984, Norris 1950, Zeevalking and Fresco 1977). Gibbens et al. (1993) found that excluding rabbits from Chihuahuan Desert creosotebush (Larrea tridentata) communities over a period of 50 years increased the canopy cover of some grasses, and also increased canopy cover of some shrub species. Small mammal (rodent and rabbit) populations may fluctuate considerably with variation in climate and annual plant production (Brown et al. 1979, Brown & Heske 1990, Brown & Zeng 1989, Whitford 1976, Johnson & Anderson 1984). Reproduction in desert rodents is known to be induced by plant foliage production (Reichman and Van De Graff 1975, Beatley 1969). If small mammals are keystone species affecting plant species composition and structure in desert ecosystems, then the impacts of small mammals on vegetation are probably linked with variation in climate and plant production. A reciprocal plant-herbivore/granivore feedback system may result, where small mammal populations and thus impacts on vegetation, are initially determined by climate influences on plant food resource availability to the small mammals. Thus, the effects of small mammals during dry years will probably be different from the effects during wet years because of different population sizes. If this is so, one should be able to measure differential effects of small mammals on plant communities over series of wet or dry years, such as El Nino and La Nina cycles (Nicholls 1988). Such reciprocal interactions should also occur in relation to long-term (decades) climate change. The effects of any one small mammal species population on the biotic community will be complicated by competitive interactions with other mammal species (Munger & Brown 1981, Brown & Zeng 1989, Brown & Heske 1990), however overall impacts on vegetation and soils by the combined effects of all small mammal species may be closely linked with variation in precipitation and plant production. Depending upon the persistence of plant food resources such as foliage or seeds, lag times in consumer impacts may be expected following periods of precipitation and plant production. In desert ecosystems, widely scattered shrubs produce a patch pattern of fertile islands with high plant biomass production and soil nutrients, surrounded by relatively unproductive barren soil (West and Klemmedson 1978, Crawford and Gosz 1982). Researchers at the Jornada Long-Term Ecological Research site in New Mexico have proposed a desertification model suggesting that perturbations caused by domestic livestock grazing and climate change initiated processes transforming grasslands with relatively homogeneous resource distributions to shrubland environments with relatively heterogenous resource distributions (Schlesinger et al. 1990). This patchy vegetation/resource distribution pattern is stable under present climate regimes, and appears to be maintained by plant resource use and abiotic soil processes (Schlesinger et al. 1990). However, Wagner (1976, page 195) suggested that small mammals were probably maintaining shrubland dominated ecosystems at the Jornada by suppressing grasses through selective herbivory. Research Hypotheses. The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan Desert shrublands and grasslands. What role if any do indigenous small mammal consumers have in maintaining desertified landscapes in the Chihuahuan Desert? Additionally, how do the effects of small mammals interact with changing climate to affect vegetation patterns over time? This study will provide long-term experimental tests of the roles of consumers on ecosystem pattern and process across a latitudinal climate gradient. The following questions or hypotheses will be addressed. 1) Do small mammals influence patterns of plant species composition and diversity, vegetation structure, and spatial patterns of vegetation canopy cover and biomass in Chihuahuan Desert shrublands and grasslands? Are small mammals keystone species that determine plant species composition and physiognomy of Chihuahuan Desert communities as Brown and Heske (1990a) and Gibbens et al. (1993) suggest? Do small mammals have a significant role in maintaining the existence of shrub islands and spatial heterogeneity of creosotebush shrub communities? 2) Do small mammals affect the taxonomic composition and spatial pattern of vegetation similarly or differently in grassland communities as compared to shrub communities? How do patterns compare between grassland and shrubland sites, and how do these relatively small scale patterns relate to overall landscape vegetation patterns? 3) Do small mammals interact with short-term (annual) and long-term (decades) climate change to affect temporal changes in vegetation spatial patterns and species composition? Other Consumers. Ants are important consumers in Chihuahuan Desert ecosystems (MacKay 1991), and granivorous ants are known to have competitive interactions with rodents (Brown & Davidson 1977, Brown et al. 1979) for plant seed resources. Termites are important detritivores in Chihuahuan Desert ecosystems (MacKay 1991) and appear to have key roles in plant litter decomposition and nutrient cycling (Whitford et al. 1982, Schaefer & Whitford 1981), and in altering soil structure and hydrologic processes (Elkins et al. 1986). Grasshoppers are important herbivores in Chihuahuan Desert ecosystems (Rivera 1986, Wisdom 1991, Richman et al. 1993), with various species specializing on most of the different plant species present in any location (Otte 1976, Joern 1979). Since manipulations of small mammals will probably affect these arthropod consumers, we will monitor these other consumers on the measurement plots to document any changes. Documentation of changes or lack of changes in ant, termite, and grasshopper consumer groups will be needed to interpret the results of small mammal manipulations on vegetation and soils. For example, if removal of rodents results in an increase of seed-harvesting ants, changes or lack of changes in vegetation and soils may be attributed to compensatory granivory from the increase in ants. Small mammals are the consumer group that appears to have the greatest influence on Chihuahuan Desert communities (see literature citations above). Given the known ecological importance of small mammals and the complexity and difficulties that would be associated with manipulating small mammals and arthropods, we have chosen to start with experiments on small mammals first. If these other consumer groups appear to have important interactions with small mammals, we will pursue additional experiments in the future to focus on those interactions, and to elucidate the ecological roles of these arthropod consumers.
Data from: Starch and dextrose at 2 levels of rumen-degradable protein in iso-nitrogenous diets: Effects on lactation performance, ruminal measurements, methane emission, digestibility, and nitrogen balance of dairy cows.
This feeding trial was designed to investigate two separate questions. The first question is, “What are the effects of substituting two non-fiber carbohydrate (NFC) sources at two rumen-degradable protein (RDP) levels in the diet on apparent total-tract nutrient digestibility, manure production and nitrogen (N) excretion in dairy cows?”. This is relevant because most of the N ingested by dairy cows is excreted, resulting in negative effects on environmental quality. The second question is, “Is phenotypic residual feed intake (pRFI) correlated with feed efficiency, N use efficiency, and metabolic energy losses (via urinary N and enteric CH4) in dairy cows?”. The pRFI is the difference between what an animal is expected to eat, given its level of productivity, and what it actually eats. The goal was to determine whether production of CH4, urinary N or fecal N is a driver of pRFI.
This experiment was conducted at the Dairy Cattle Center of University of Wisconsin-Madison. The use and care of animals was approved by the University of Wisconsin-Madison Research Animal and Resource Committee.
Prior to the beginning of the study, 24 multiparous Holstein dairy cows were trained for 7 days to adapt to the GreenFeed (C-Lock Inc., Rapid City, SD) system: a mobile, open circuit gas quantification system that measures CH4 emission with minimal animal disturbance (Dorich et al., 2015). The machine continuously analyzes the CH4 concentration from the exhaled air when the cow consumes delivered feed treats at the trough of the unit. During the GreenFeed adaptation, the 24 cows were fed the herd diet once daily at 0730 h. At each training, each cow was assigned with a score of 1 to 5 depending on how well the cow adapted to the GreenFeed unit (1 = poor; 5 = very good). After the 7-day adaptation to the equipment, the 18 cows that adapted best (18 highest total scores) to the system were selected to conduct the study. All 18 cows were fed the same herd diet during the week before the commencement of this study.
The eighteen cows in the experiment were 148 ±10 days in milk, 3 ± 0.6 parity, 42.3 ± 4.1 kg/day milk yield, 644 ± 41kg body weight (BW) at the commencement of the study (mean + standard deviation). Cows were housed in a tie-stall barn and fed once (starting at 0730 h) and milked twice (0430 and 1630 h) daily. All cows were injected with 500 mg of bST (Posilac; Monsanto, St. Louis, MO) at the beginning of experiment and at 14-day intervals throughout the experiment. The experiment was conducted as a split-plot study. Subplot treatments were 3 refined NFC treatments: 10% refined starch (S), 5% dextrose, 5% refined starch (H), and 10% dextrose (D), as percent of dietary dry matter (DM). Both refined starch (Cargill, Minneapolis, MN) and dextrose (ADM, Decatur, IL) were food-grade products refined from corn starch. The NFC treatments were randomly allocated in three 3 x 3 Latin squares with 3 cows per square. The replicated Latin squares were then randomly assigned to either 11% rumen degradable protein (RDP), 5% rumen un-degraded protein (RUP) (11:5 RDP:RUP ratio) or 9% RDP, 7% RUP (9:7 RDP:RUP ratio), respectively (on a DM basis) in a completely randomized design. The treatments differing in RDP:RUP ratios were achieved by substitution of soybean meal with expeller soybean meal (SoyPLUS, West Central Soy, Ralston, IA) and blood meal. The feeding periods were 28 days in length, with 14 days for adaptation and 14 days for sample collection. The milk production for cows that were fed 11:5 and 9:7 RDP:RUP ratio diets were 43.1 and 41.3 kg/d, respectively.
Experimental diets were offered as total mixed ration (TMR) composed of forage and concentrate at 61:39 ratio (DM basis). The diets were formulated to contain the same concentration of forage (alfalfa silage, corn silage, and wheat straw), to be iso-nitrogenous, and to contain similar concentration of NFC and neutral detergent fiber (NDF). The concentrate for each diet was fed as a customized premix. Due to the availability of forages, different cuts of alfalfa silage were used for each period and corn silage was changed at the beginning of the third period. Due to the minor differences in chemical compositions such as CP and NDF among cuts, the diets were adjusted at the beginning of each period to standardize the chemical compositions.
The cows were fed at 0730 h during the first 2 weeks of each period, whereas during the 3rd and 4th weeks of each period, the 9:7 and 11:5 RDP:RUP ratio diets were offered once daily at 0730 and 0900 h, respectively. The enteric CH4 measurement was staggered between the cows fed the two RDP:RUP ratios accordingly due to the time needed for feed delivery and measurement of CH4 from each RDP:RUP ratio group. All cows were fed ad libitum with TMR adjusted daily to yield 10% orts. The TMR for all the diets were sampled weekly, refusal samples from each of the 18 cows were collected daily during the 3rd and 4th weeks of each period. Forages were sampled for moisture weekly and adjustment in diet was made accordingly to keep the offered diets consistent in each period. All feed samples were stored at -20 oC until dried for further analysis.
Milk yield was recorded daily and milk samples were collected for 4 consecutive milkings from day 18 to day 20, and day 25 to day 27 in each period. Milk was analyzed for milk solids (fat, true protein, and lactose) and milk urea-nitrogen (MUN) concentrations with infrared analysis (Agsource Milk Analysis Laboratory, Menomonie, WI) with a Foss FT6000 (Foss Electric, Hillerød, Denmark). The fat-and-protein-corrected milk (FPCM) was computed based on the equations of International Dairy Federation (IDF, 2015). Body weight (BW) of the cows was taken at 0630 h on days 18,19, 25 and 26 of each period and averaged by week to represent the BW of the cow for the respective week. The average BW of two measurements during the 4th week for each cow was used in estimating the daily urine volume. Feed efficiency (FE) was calculated as FPCM divided by DMI. Dietary nitrogen use efficiency (NUE) was calculated as total nitrogen in milk divided by nitrogen intake (kg of milk true protein/6.38) / (kg of DMI × dietary CP %/6.25).
Eleven spot samplings of enteric CH4 spread over the 24 h feeding cycle were conducted over a 4-day interval during the 3rd week of each period for each cow. The GreenFeed unit was moved from cow to cow fed the same dietary treatment in random order with a minimum of 5 minutes measurement, and 2 minutes interval between samplings for background gas concentration determination. At each sampling, concentrate mix of the corresponding RDP:RUP ratio was delivered into the feed trough to keep the cow’s head inside the trough during analysis of the exhaled breath of the cow. For each sampling, approximately 100 g of concentrate mix was delivered. This amount is less than 2% of the total daily DMI and thus was not included in the DMI calculation, however, it may introduce a source of variation in the substrate available for CH4 production. As a result, CH4 emission measurement was conducted at 1, 2.5, 4, 5.5, 10, 11.5, 13, 14.5, 16, 17.5, and 22.5 h after feeding for both groups of cows. Morning milking was between 5.5 and 10 h; evening milking was between 17.5 and 22.5 h. The GreenFeed unit was zero- and span-calibrated before the start of each sampling period with pure nitrogen carrier gas, CH4 and CO2 (474 and 4497 ppm, respectively). The daily enteric CH4 emission was calculated as the average of the 11 spot samplings for each cow. The hourly emission rate was calculated as the CH4 emission at each of the 11 spot samplings divided by 24.
Feed samples were dried at 60 oC in a forced draft oven for 48 hours. Dried samples were then ground to pass a 1-mm Wiley mill screen (Arthur H. Thomas, Philadelphia, PA). Each feed ingredient (alfalfa silage, corn silage, wheat straw, and concentrate mixes) was composited by the last 2 weeks of each period. Samples were analyzed at Dairyland Laboratories (Arcadia, WI) for nutrient composition. All feed samples were analyzed for total N (AOAC, 1995), amylase-treated NDF (Mertens et al., 2002), ADF and lignin (AOAC, 2000), ether extract (Thiex et al., 2003), ash and OM (Thiex et al., 2012). In addition, starch and water-soluble carbohydrate content of feed samples were analyzed according to Vidal et al. (2009) and Deriaz (1961), respectively. In-situ ruminal incubation was done for each feed ingredient, refusals and fecal samples using 2 ruminally cannulated cows to determine indigestible NDF (iNDF). Duplicate bags were inserted into a nylon laundry mesh bag (38.1 cm x 45.7 cm) (Home Products International, Chicago, IL), which was inserted into the rumen via the rumen cannula of each cow. After 288 hours of incubation, the mesh bags were taken out of the rumen and submerged in cold water and rinsed to remove particles on the surface of bags. Bags were then rinsed with washing machine with cold water for two 12-min rinse cycles. After dried at 55 ºC in a forced-air oven, the bags were washed with α-amylase (Sigma chemical Co., St. Louis, MO) and sodium sulfide to determine the iNDF using an Ankom 200 Fiber Analyzer (Ankom Technology, Fairport, NY).
Blood samples (~10 mL) were collected for each cow from the coccygeal venipuncture with Vacutainer tubes at 4 h after feeding on day 26 of each period. The blood samples were immediately centrifuged at 10,000 × g at 4 °C for 10 minutes and the serum fraction was analyzed for urea nitrogen concentration (SUN, serum urea-nitrogen) with a 96-well plate reader (Synergy H1 Multi-Mode Reader, BioTek, Winooski, VT).
Ruminal fluid of each cow was collected by rumenocentesis at 4 h after feeding on day 27 and day 28 of each period for cows on the 9:7 and 11:5 RDP:RUP ratio diets, respectively, according to the procedure by Nordlund and Garrett (1994). Approximately 10 mL of ruminal fluid was taken from the ventral sac area of the rumen and instantly tested for pH (Laqua Twin pH-meter model B-713; Spectrum Technologies Inc., Plainfield, IL). Then 1-mL aliquots of ruminal fluid were pipetted into microfuge tubes, acidified with 50% trichloroacetic acid solution and stored at – 20 °C for later analysis. For determination of the concentration of volatile fatty acids (VFA), the frozen samples were thawed to room temperature and centrifuged at 10,000 × g at 4 °C for 3 minutes. The supernatant was transferred to gas-chromatography (GC) vials for analysis of VFA concentration using GC (Clarus 500 Gas Chromatograph, PerkinElmer Inc. Shelton, CT). Ammonia nitrogen (NH3-N) concentration of the ruminal fluid was analyzed by a procedure modified from Chaney and Marbach (1962).
Spot urine and feces samples from each cow were collected during the 4th week of each period. The urine and feces were collected at 6 time points on 4-hour intervals to cover the 24 h clock over 3 days (2 spot samples per day for a total of 6 samples for each cow). The urine was obtained through vulval stimulation. Urine samples were acidified with 0.072 M H2SO4 with a 4:1 ratio of acid to urine by volume. At each fecal sampling, approximately 100 g of fresh feces were collected from the rectum of the cow and the feces from the 6 spot samplings were composited for each cow. Both collected urine and feces samples were frozen at -20 °C for later analysis. After thawing at room temperature, urine samples were composited for each cow by period and analyzed for total N (Leco FP-2000 Nitrogen Analyzer, Leco Instruments Inc., St. Joseph, MI). In addition, urinary urea-nitrogen (UUN) concentration and creatinine concentration was analyzed with a colorimetric assay and a picric acid assay (Oser, 1965) adapted to flow-injection analysis, respectively, both using Lachat Quik-Chem 8000 FIA (Lachat Instruments, Milwaukee, WI). Total daily urine volume was estimated with creatinine as internal marker, and using the constant creatinine excretion rate of 29 mg/kg of BW from the 4th week according to Valadares et al. (1999). Concentrations of allantoin and uric acid in urine samples were determined by a colorimetric method (Chen and Gomes, 1992) and InfinityTM uric acid liquid stable reagent (Thermo Fisher Scientific Inc., Middletown, VA), respectively, both with a 96-well plate reader (Synergy H1 Multi-Mode Reader, BioTek, Winooski, VT). Urinary allantoin and uric acid excretions were calculated from the respective concentrations multiplied by estimated total daily urine volume. Urinary purine derivatives (PD) were calculated as the sum of daily allantoin and uric acid excreted in the urine. Fecal samples of each cow were dried at 60 °C in a forced draft oven until for 96 h and then ground through 1-mm Wiley mill screen (Arthur H. Thomas Co., Philadelphia, PA), and analyzed for fecal NDF (with Ankom instrument described above), fecal starch (Vidal et al., 2009) (Dairyland Laboratories, Arcadia, WI), and total N (Leco FP-2000 Nitrogen Analyzer). Fecal crude protein (CP) was calculated as fecal total nitrogen * 6.25. Manure N was calculated as the sum of fecal N and urinary N. Nitrogen retained was calculated as the difference between N intake and N excretion (milk true protein N, fecal N, and urinary N). In addition to iNDF content, feces were also analyzed for total ash by igniting the dry, ground feces sample in a furnace at 600 ºC for 2 hours, the same method used to determine ash in feed samples. Fecal organic matter (OM) was calculated as the difference between feces DM output and ash in feces.
Indigestible NDF served as an internal marker for estimation of feces DM output and in determination of amount of nutrient digested. The marker method was based on the assumption that iNDF present in feed consumed is not digested by the cow and thus equals the amount of iNDF excreted in feces. The iNDF intake is calculated from the iNDF concentration in feed ingredients (measured using the 288-hour rumen incubation described above), multiplied by the daily DMI for each cow. Feces output (DM basis) was estimated with iNDF intake divided by iNDF concentration in feces, which was also determined from the rumen incubation (Cochran et al., 1986). The amount of nutrient intake (OM, NDF, CP, and starch) was calculated from the respective nutrient concentration in feed ingredient multiplied by DMI. Amount of nutrient apparently digested was calculated as the difference of nutrient intake and nutrient in feces for each cow in each period. Total-tract apparent digestibility of nutrients was determined from amount of nutrient in fecal excretion and daily nutrient intake during the 4th week of each period.
This experiment was part of “Climate Change Mitigation and Adaptation in Dairy Production Systems of the Great Lakes Region,” also known as the Dairy Coordinated Agricultural Project (Dairy CAP), funded by the United States Department of Agriculture’s National Institute of Food and Agriculture (award number 2013-68002-20525). The main goal of the Dairy CAP is to improve understanding of the magnitudes and controlling factors over GHG emissions from dairy production in the Great Lakes region. Using this knowledge, the Dairy CAP has improved life cycle analysis (LCA) of GHG production by Great Lakes dairy farms, developing farm management tools, and conducting extension, education and outreach activities.
SMES Soil Surface Disturbance
Introduction. Animal consumers have important roles in ecosystems (Chew 1974, 1976), determining plant species composition and structure (Harper 1969, Pacala and Crawley 1992, Crawley 1983, 1989), regulating rates of plant production and nutrient cycling (Naiman 1988, McNaughton et al. 1989, Holland et al. 1992), and altering soil structure and chemistry (Milchunas et al. 1993, Huntly 1991). Desertification of semi-arid grasslands in the Southwest United States by domestic livestock provides an important example of herbivore regulation of ecosystem structure and function (Schlesinger et al. 1990). The species composition and physical structure of these desert grassland ecosystems were significantly altered by alien herbivores about 100 years ago (Bahre 1991, York and Dick-Peddie 1968, Gardner 1951, Hastings and Turner 1980, Buffington and Herbel 1965, Dick-Peddie 1993). To what extent the spatial patterns of semi-arid shrubland and grassland plant production and soil characteristics are currently controlled by plant resource use, abiotic factors, or consumers is not known. Desertification is an ecosystem-level phenomenon occurring on a global scale with great relevance to human welfare (Nelson 1988). In order to understand the processes that contribute to desertification, we must fully understand interactions among the components of arid-land ecosystems. Schlesinger et al. (1990) suggest that in the absence of continued livestock perturbations, plant resource use and abiotic factors appear to be the principal factors accounting for the persistence of desert shrublands in desertified semi-arid grasslands. However, Brown and Heske (1990a) provide evidence that indigenous small mammal consumers may also have a major role in determining vegetation structure in those desert ecosystems. Brown and Heske (1990a, Heske et al. 1993) found that the exclusion of rodents from Chihuahuan Desert creosotebush shrubland areas resulted in a significant increase in grass cover over a 12 year period. Brown and Heske (1990a) concluded that rodents were keystone species in those desert shrub communities, greatly influencing vegetation structure. Rodents are also known to have significant influences on plant species composition and diversity in desert communities (Inouye et al. 1980, Heske et al. 1993, Brown et al. 1986). Several species of granivorous rodents (Family: Heteromidae, genera: Dipodomys, Perognathus, Chaetodipus) appear to have the greatest influence on vegetation herbivory. Soil disturbance through the digging activities of rodents can have profound local effects on plant species composition and vegetation structure in the Chihuahuan Desert (Moroka et al. 1982). Digging activities of desert rodents intermix surface soils with subsurface soils (Abaturov 1972), and increase rainfall infiltration (Soholt 1975). Reported measures of the percentage of desert soil surface areas disturbed by rodent digging activities in desert enviroments range from 10% (Abaturov 1972) to 4.5% (Soholt 1975). Burrowing activities increase local soil nutrient and water status, creating favorable sites for increased plant densities, biomass production, and increased species diversity (Morehead et al. 1989, Mun and Whitford 1990). Rabbits (Lagomorpha: Black-tailed jackrabbits, Lepus californicus, and desert cottontail rabbits, Sylvilagus aduboni) are also important consumers of desert vegetation (Brown 1947, Johnson & Anderson 1984, Steinberger and Whitford 1983, Ernest 1994). Rabbits can have significant effects on plant species composition and structure resulting from selective herbivory (Gibbens et al. 1993, Clark and Wagner 1984, Norris 1950, Zeevalking and Fresco 1977). Gibbens et al. (1993) found that excluding rabbits from Chihuahuan Desert creosotebush (Larrea tridentata) communities over a period of 50 years increased the canopy cover of some grasses, and also increased canopy cover of some shrub species. Small mammal (rodent and rabbit) populations may fluctuate considerably with variation in climate and annual plant production (Brown et al. 1979, Brown & Heske 1990, Brown & Zeng 1989, Whitford 1976, Johnson & Anderson 1984). Reproduction in desert rodents is known to be induced by plant foliage production (Reichman and Van De Graff 1975, Beatley 1969). If small mammals are keystone species affecting plant species composition and structure in desert ecosystems, then the impacts of small mammals on vegetation are probably linked with variation in climate and plant production. A reciprocal plant-herbivore/granivore feedback system may result, where small mammal populations and thus impacts on vegetation, are initially determined by climate influences on plant food resource availability to the small mammals. Thus, the effects of small mammals during dry years will probably be different from the effects during wet years because of different population sizes. If this is so, one should be able to measure differential effects of small mammals on plant communities over series of wet or dry years, such as El Nino and La Nina cycles (Nicholls 1988). Such reciprocal interactions should also occur in relation to long-term (decades) climate change. The effects of any one small mammal species population on the biotic community will be complicated by competitive interactions with other mammal species (Munger & Brown 1981, Brown & Zeng 1989, Brown & Heske 1990), however overall impacts on vegetation and soils by the combined effects of all small mammal species may be closely linked with variation in precipitation and plant production. Depending upon the persistence of plant food resources such as foliage or seeds, lag times in consumer impacts may be expected following periods of precipitation and plant production. In desert ecosystems, widely scattered shrubs produce a patch pattern of fertile islands with high plant biomass production and soil nutrients, surrounded by relatively unproductive barren soil (West and Klemmedson 1978, Crawford and Gosz 1982). Researchers at the Jornada Long-Term Ecological Research site in New Mexico have proposed a desertification model suggesting that perturbations caused by domestic livestock grazing and climate change initiated processes transforming grasslands with relatively homogeneous resource distributions to shrubland environments with relatively heterogenous resource distributions (Schlesinger et al. 1990). This patchy vegetation/resource distribution pattern is stable under present climate regimes, and appears to be maintained by plant resource use and abiotic soil processes (Schlesinger et al. 1990). However, Wagner (1976, page 195) suggested that small mammals were probably maintaining shrubland dominated ecosystems at the Jornada by suppressing grasses through selective herbivory. Research Hypotheses. The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan Desert shrublands and grasslands. What role if any do indigenous small mammal consumers have in maintaining desertified landscapes in the Chihuahuan Desert? Additionally, how do the effects of small mammals interact with changing climate to affect vegetation patterns over time? This study will provide long-term experimental tests of the roles of consumers on ecosystem pattern and process across a latitudinal climate gradient. The following questions or hypotheses will be addressed. 1) Do small mammals influence patterns of plant species composition and diversity, vegetation structure, and spatial patterns of vegetation canopy cover and biomass in Chihuahuan Desert shrublands and grasslands? Are small mammals keystone species that determine plant species composition and physiognomy of Chihuahuan Desert communities as Brown and Heske (1990a) and Gibbens et al. (1993) suggest? Do small mammals have a significant role in maintaining the existence of shrub islands and spatial heterogeneity of creosotebush shrub communities? 2) Do small mammals affect the taxonomic composition and spatial pattern of vegetation similarly or differently in grassland communities as compared to shrub communities? How do patterns compare between grassland and shrubland sites, and how do these relatively small scale patterns relate to overall landscape vegetation patterns? 3) Do small mammals interact with short-term (annual) and long-term (decades) climate change to affect temporal changes in vegetation spatial patterns and species composition? Other Consumers. Ants are important consumers in Chihuahuan Desert ecosystems (MacKay 1991), and granivorous ants are known to have competitive interactions with rodents (Brown & Davidson 1977, Brown et al. 1979) for plant seed resources. Termites are important detritivores in Chihuahuan Desert ecosystems (MacKay 1991) and appear to have key roles in plant litter decomposition and nutrient cycling (Whitford et al. 1982, Schaefer & Whitford 1981), and in altering soil structure and hydrologic processes (Elkins et al. 1986). Grasshoppers are important herbivores in Chihuahuan Desert ecosystems (Rivera 1986, Wisdom 1991, Richman et al. 1993), with various species specializing on most of the different plant species present in any location (Otte 1976, Joern 1979). Since manipulations of small mammals will probably affect these arthropod consumers, we will monitor these other consumers on the measurement plots to document any changes. Documentation of changes or lack of changes in ant, termite, and grasshopper consumer groups will be needed to interpret the results of small mammal manipulations on vegetation and soils. For example, if removal of rodents results in an increase of seed-harvesting ants, changes or lack of changes in vegetation and soils may be attributed to compensatory granivory from the increase in ants. Small mammals are the consumer group that appears to have the greatest influence on Chihuahuan Desert communities (see literature citations above). Given the known ecological importance of small mammals and the complexity and difficulties that would be associated with manipulating small mammals and arthropods, we have chosen to start with experiments on small mammals first. If these other consumer groups appear to have important interactions with small mammals, we will pursue additional experiments in the future to focus on those interactions, and to elucidate the ecological roles of these arthropod consumers.
SMES termite casing data
Introduction. Animal consumers have important roles in ecosystems (Chew 1974, 1976), determining plant species composition and structure (Harper 1969, Pacala and Crawley 1992, Crawley 1983, 1989), regulating rates of plant production and nutrient cycling (Naiman 1988, McNaughton et al. 1989, Holland et al. 1992), and altering soil structure and chemistry (Milchunas et al. 1993, Huntly 1991). Desertification of semi-arid grasslands in the Southwest United States by domestic livestock provides an important example of herbivore regulation of ecosystem structure and function (Schlesinger et al. 1990). The species composition and physical structure of these desert grassland ecosystems were significantly altered by alien herbivores about 100 years ago (Bahre 1991, York and Dick-Peddie 1968, Gardner 1951, Hastings and Turner 1980, Buffington and Herbel 1965, Dick-Peddie 1993). To what extent the spatial patterns of semi-arid shrubland and grassland plant production and soil characteristics are currently controlled by plant resource use, abiotic factors, or consumers is not known. Desertification is an ecosystem-level phenomenon occurring on a global scale with great relevance to human welfare (Nelson 1988). In order to understand the processes that contribute to desertification, we must fully understand interactions among the components of arid-land ecosystems. Schlesinger et al. (1990) suggest that in the absence of continued livestock perturbations, plant resource use and abiotic factors appear to be the principal factors accounting for the persistence of desert shrublands in desertified semi-arid grasslands. However, Brown and Heske (1990a) provide evidence that indigenous small mammal consumers may also have a major role in determining vegetation structure in those desert ecosystems. Brown and Heske (1990a, Heske et al. 1993) found that the exclusion of rodents from Chihuahuan Desert creosotebush shrubland areas resulted in a significant increase in grass cover over a 12 year period. Brown and Heske (1990a) concluded that rodents were keystone species in those desert shrub communities, greatly influencing vegetation structure. Rodents are also known to have significant influences on plant species composition and diversity in desert communities (Inouye et al. 1980, Heske et al. 1993, Brown et al. 1986). Several species of granivorous rodents (Family: Heteromidae, genera: Dipodomys, Perognathus, Chaetodipus) appear to have the greatest influence on vegetation herbivory. Soil disturbance through the digging activities of rodents can have profound local effects on plant species composition and vegetation structure in the Chihuahuan Desert (Moroka et al. 1982). Digging activities of desert rodents intermix surface soils with subsurface soils (Abaturov 1972), and increase rainfall infiltration (Soholt 1975). Reported measures of the percentage of desert soil surface areas disturbed by rodent digging activities in desert enviroments range from 10% (Abaturov 1972) to 4.5% (Soholt 1975). Burrowing activities increase local soil nutrient and water status, creating favorable sites for increased plant densities, biomass production, and increased species diversity (Morehead et al. 1989, Mun and Whitford 1990). Rabbits (Lagomorpha: Black-tailed jackrabbits, Lepus californicus, and desert cottontail rabbits, Sylvilagus aduboni) are also important consumers of desert vegetation (Brown 1947, Johnson & Anderson 1984, Steinberger and Whitford 1983, Ernest 1994). Rabbits can have significant effects on plant species composition and structure resulting from selective herbivory (Gibbens et al. 1993, Clark and Wagner 1984, Norris 1950, Zeevalking and Fresco 1977). Gibbens et al. (1993) found that excluding rabbits from Chihuahuan Desert creosotebush (Larrea tridentata) communities over a period of 50 years increased the canopy cover of some grasses, and also increased canopy cover of some shrub species. Small mammal (rodent and rabbit) populations may fluctuate considerably with variation in climate and annual plant production (Brown et al. 1979, Brown & Heske 1990, Brown & Zeng 1989, Whitford 1976, Johnson & Anderson 1984). Reproduction in desert rodents is known to be induced by plant foliage production (Reichman and Van De Graff 1975, Beatley 1969). If small mammals are keystone species affecting plant species composition and structure in desert ecosystems, then the impacts of small mammals on vegetation are probably linked with variation in climate and plant production. A reciprocal plant-herbivore/granivore feedback system may result, where small mammal populations and thus impacts on vegetation, are initially determined by climate influences on plant food resource availability to the small mammals. Thus, the effects of small mammals during dry years will probably be different from the effects during wet years because of different population sizes. If this is so, one should be able to measure differential effects of small mammals on plant communities over series of wet or dry years, such as El Nino and La Nina cycles (Nicholls 1988). Such reciprocal interactions should also occur in relation to long-term (decades) climate change. The effects of any one small mammal species population on the biotic community will be complicated by competitive interactions with other mammal species (Munger & Brown 1981, Brown & Zeng 1989, Brown & Heske 1990), however overall impacts on vegetation and soils by the combined effects of all small mammal species may be closely linked with variation in precipitation and plant production. Depending upon the persistence of plant food resources such as foliage or seeds, lag times in consumer impacts may be expected following periods of precipitation and plant production. In desert ecosystems, widely scattered shrubs produce a patch pattern of fertile islands with high plant biomass production and soil nutrients, surrounded by relatively unproductive barren soil (West and Klemmedson 1978, Crawford and Gosz 1982). Researchers at the Jornada Long-Term Ecological Research site in New Mexico have proposed a desertification model suggesting that perturbations caused by domestic livestock grazing and climate change initiated processes transforming grasslands with relatively homogeneous resource distributions to shrubland environments with relatively heterogenous resource distributions (Schlesinger et al. 1990). This patchy vegetation/resource distribution pattern is stable under present climate regimes, and appears to be maintained by plant resource use and abiotic soil processes (Schlesinger et al. 1990). However, Wagner (1976, page 195) suggested that small mammals were probably maintaining shrubland dominated ecosystems at the Jornada by suppressing grasses through selective herbivory. Research Hypotheses. The purpose of this study is to determine whether or not the activities of small mammals regulate plant community structure, plant species diversity, and spatial vegetation patterns in Chihuahuan Desert shrublands and grasslands. What role if any do indigenous small mammal consumers have in maintaining desertified landscapes in the Chihuahuan Desert? Additionally, how do the effects of small mammals interact with changing climate to affect vegetation patterns over time? This study will provide long-term experimental tests of the roles of consumers on ecosystem pattern and process across a latitudinal climate gradient. The following questions or hypotheses will be addressed. 1) Do small mammals influence patterns of plant species composition and diversity, vegetation structure, and spatial patterns of vegetation canopy cover and biomass in Chihuahuan Desert shrublands and grasslands? Are small mammals keystone species that determine plant species composition and physiognomy of Chihuahuan Desert communities as Brown and Heske (1990a) and Gibbens et al. (1993) suggest? Do small mammals have a significant role in maintaining the existence of shrub islands and spatial heterogeneity of creosotebush shrub communities? 2) Do small mammals affect the taxonomic composition and spatial pattern of vegetation similarly or differently in grassland communities as compared to shrub communities? How do patterns compare between grassland and shrubland sites, and how do these relatively small scale patterns relate to overall landscape vegetation patterns? 3) Do small mammals interact with short-term (annual) and long-term (decades) climate change to affect temporal changes in vegetation spatial patterns and species composition? Other Consumers. Ants are important consumers in Chihuahuan Desert ecosystems (MacKay 1991), and granivorous ants are known to have competitive interactions with rodents (Brown & Davidson 1977, Brown et al. 1979) for plant seed resources. Termites are important detritivores in Chihuahuan Desert ecosystems (MacKay 1991) and appear to have key roles in plant litter decomposition and nutrient cycling (Whitford et al. 1982, Schaefer & Whitford 1981), and in altering soil structure and hydrologic processes (Elkins et al. 1986). Grasshoppers are important herbivores in Chihuahuan Desert ecosystems (Rivera 1986, Wisdom 1991, Richman et al. 1993), with various species specializing on most of the different plant species present in any location (Otte 1976, Joern 1979). Since manipulations of small mammals will probably affect these arthropod consumers, we will monitor these other consumers on the measurement plots to document any changes. Documentation of changes or lack of changes in ant, termite, and grasshopper consumer groups will be needed to interpret the results of small mammal manipulations on vegetation and soils. For example, if removal of rodents results in an increase of seed-harvesting ants, changes or lack of changes in vegetation and soils may be attributed to compensatory granivory from the increase in ants. Small mammals are the consumer group that appears to have the greatest influence on Chihuahuan Desert communities (see literature citations above). Given the known ecological importance of small mammals and the complexity and difficulties that would be associated with manipulating small mammals and arthropods, we have chosen to start with experiments on small mammals first. If these other consumer groups appear to have important interactions with small mammals, we will pursue additional experiments in the future to focus on those interactions, and to elucidate the ecological roles of these arthropod consumers.
Data from: Agro-environmental consequences of shifting from nitrogen- to phosphorus-based manure management of corn.
This experiment was designed to measure greenhouse gas (GHG) fluxes and related agronomic characteristics of a long-term corn-alfalfa rotational cropping system fertilized with manure (liquid versus semi-composted separated solids) from dairy animals. Different manure-application treatments were sized to fulfill two conditions: (1) an application rate to meet the agronomic soil nitrogen requirement of corn (“N-based” without manure incorporation, more manure), and (2) an application rate to match or to replace the phosphorus removal by silage corn from soils (“P-based” with incorporation, less manure). In addition, treatments tested the effects of liquid vs. composted-solid manure, and the effects of chemical nitrogen fertilizer. The controls consisted of non-manured inorganic N treatments (sidedress applications). These activities were performed during the 2014 and 2015 growing seasons as part of the Dairy Coordinated Agricultural Project, or Dairy CAP, as described below. The data from this experiment give insight into the factors controlling GHG emissions from similar cropping systems, and may be used for model calibration and validation after careful evaluation of the flagged data.
The experiment was conducted at Cornell University’s Musgrave Research Farm near in Aurora, NY (https://cuaes.cals.cornell.edu/farms/musgrave-research-farm/). Soils are high-pH glacial tills, approximately 55% Lima silt loam (fine-loamy, mixed, active, mesic oxyaquic hapludalfs) and 45% Kendaia and Lyons soils. Slopes range from 0-8%, and there is imperfect tile drainage. Experimental plots were not irrigated. Weather observations from Musgrave Farm can be found at http://newa.cornell.edu/index.php?page=all-weather-data . Manure for the experiment was collected from Aurora Ridge Farm, a commercial dairy. Effluent from an anaerobic manure digester was separated into liquid and solid components using a screw-press, and then solids were further composted (Gooch and Pronto, 2009).
For all experimental plots, seedbeds were prepared by one-time disking followed by rolling with a culti-mulcher. All manure was surface applied. Liquid manure in the “P-based” treatment was immediately incorporated by chisel plow (20 cm depth) to conserve ammonia nitrogen. Liquid manure in the “N-based” treatment and all solid manures were incorporated by chisel plow seven days after application to allow nitrogen volatilization. Starter fertilizer was applied at 5 cm depth and 5 cm to the side of the seed furrow. In 2014, pesticides for general weed control were applied on June 20 to all plots. Single tank mix included S-metolachlor (CAS No. 87392-12-9, 0.94 kg/ha); atrazine (CAS No. 1912-24-9, 0.63 kg/ha); mesotrione (CAS No. 104206-82-8, 0.09kg/ha); isopropylamine salt of glyphosate (CAS No. 38641-94-0, 1.68 kg/ha). In 2015, pesticides were applied on June 25 to all plots. Single tank mix included S-metolachlor (0.93 kg/ha); atrazine (0.75 kg/ha); mesotrione (0.18 kg/ha); isopropylamine salt of glyphosate (2.12 kg/ha). At harvest, crop residue from 10 cm cutting height was left in all plots.
Gas fluxes from soil (CO2, CH4, N2O) were measured on 32 dates in 2014 and 22 dates in 2015, using vented chambers (Dell et al., 2014) and following standard measurement protocols (Parkin and Venterea, 2010). The gas flux measurement chamber was placed between rows. For plots receiving urea and ammonium nitrate fertilizer (UAN), the measurement chamber was placed on the UAN band after application. Chamber deployment time was 45 minutes with sampling intervals of 15 minutes. Samples were analyzed by gas chromatography (GC), and the gas flux rates were calculated by linear regression. Soil samples were treated with the Cornell “Morgan extraction” (Morgan, 2941) to measure available nitrate-nitrogen, phosphorus and potassium. Soil pH and organic matter were also measured, but no soil physical characteristics are available. Organic matter was measured as loss-on-ignition with exposure to 500 degrees Celsius.
This experiment was part of “Climate Change Mitigation and Adaptation in Dairy Production Systems of the Great Lakes Region,” also known as the Dairy Coordinated Agricultural Project (Dairy CAP), funded by the United States Department of Agriculture – National Institute of Food and Agriculture (award number 2013-68002-20525). The main goal of the Dairy CAP is to improve understanding of the magnitudes and controlling factors over GHG emissions from dairy production in the Great Lakes region. Using this knowledge, the Dairy CAP has improved life cycle analysis (LCA) of GHG production by Great Lakes dairy farms, developed farm management tools, and conducted extension, education and outreach activities.
Carbon Dioxide, Methane, Nitrous Oxide, and Ammonia Emissions from Digested and Separated Dairy Manure during Storage and Land Application
This data set includes measurements of greenhouse gas (GHG) and ammonia fluxes from dairy manure, with accompanying measurements of manure physical and chemical characteristics. The manure was collected from two farms in the Great Lakes region and subjected to varying treatments of anaerobic digestion and liquid-solid separation. Farm 1 was a private farm with a 2,560-cow diary herd. Manure was collected three times daily using skid steers. Both digestion and separation of manure were performed at Farm 1. Farm 2 was the USDA Dairy Forage Research Center in Prairie du Sac, WI with a 350-cow herd and manure collected by scrape daily. Farm 2 had a separator but no digester.
Gas fluxes from manure of each treatment type were monitored both from manure storage barrels ("Storage_GHG" tab of dataset), and from field-applied manure ("Field_GHG" tab). The "Manure" tab gives information about the manure chemical and physical characteristics after treatment (i.e. after digestion and/or separation) and during barrel storage. The "Soil" tab gives information about soil chemical contents during the time period of flux measurements from field-applied manure. Manure storage was during November 2013 – May 2014. In May 2014 the stored manure was surface-applied and immediately incorporated on 3.3 m^2 plots at Farm 2 in a randomized block design, at a rate of 320 kg N/ha. Field corn (maize) was planted in the plots. Note that gas fluxes are given as cumulative mass flux over the monitoring period, with sampling approximately once a week during storage (November 2013 – May 2014) and field monitoring (May 2014 – September 2014). The instrument used to measure both storage barrel and field fluxes was a "Gasmet" brand Fourier Transform Infrared (FTIR) Spectroscopy gas analyzer. Each flux sample was taken over 7 minutes with gas concentrations measured every 20 seconds. Flux data from different manure fraction "treatments" are reported as the measured fluxes, and also as the fluxes normalized to a raw manure (i.e. whole, wet manure) weight basis.
This experiment is part of the project called “Climate Change Mitigation and Adaptation in Dairy Production Systems of the Great Lakes Region,” also known as the Dairy Coordinated Agricultural Project (Dairy CAP). The Dairy CAP is funded by the United States Department of Agriculture – National Institute of Food and Agriculture (award number 2013-68002-20525). The main goal of the Dairy CAP is to improve understanding of the magnitudes and controlling factors over GHG emissions from dairy production in the Great Lakes region. Using this knowledge, the Dairy CAP is improving life cycle analysis (LCA) of GHG production by Great Lakes dairy farms, developing farm management tools, and conducting extension, education and outreach activities.
Manure application methods for alfalfa-grass
The MAMA experiment (Manure Application Methods for Alfalfa-Grass) was designed to evaluate nutrient and pathogen losses with conventional and improved liquid dairy manure management practices for alfalfa-grass production. Observations from MAMA have also been used for parameterization and validation of computer simulation models of greenhouse gas (GHG) emissions from dairy farms (Gaillard et al., in preparation). The experiment included five treatments: shallow injection of manure, aerator/banded manure (subsurface deposition), banded manure (trailing foot application), broadcast manure, and no manure (i.e. control). The five treatments were replicated three times in a randomized complete block design. This experiment was performed as part of the Dairy CAP, described below.
The experiment was conducted at the Marshfield Research Station of the University of Wisconsin and the USDA Agricultural Research Service (ARS) in Marshfield, WI (Wood County, Latitude 44.641445, Longitude -90.133526). Soils at the research station are from the Withee soil series, fine-loamy, mixed, superactive, frigid Aquic Glossudalf, with 2% slope. Each of the fifteen experimental plots was approximately 7.3 x 12.8 meters, oriented across slope. A weather station was at the south edge of the research field and centered east-west. A weather station for snow data was located 420 meters south of the field.
The experiment was initiated on May 16, 2013 by planting alfalfa (Medicago sativa) on plots that were in a corn (Zea mays) and soybean (Glycine max) rotation during the previous five years. All plots were planted with cultivar “Nexgrow-6422Q 19,” using a 10-foot Brillion forage seeder. Planting rate was 19 kg seed per hectare. Alfalfa forage was harvested by cutting at 3 inches (~8 cm) height. Alfalfa was harvested once in 2013, three times in 2014 and 2015, and four times in 2016. Forage characteristics were measured at the University of Wisconsin Soil and Forage Lab in Marshfield (total P and total K) and at the Marshfield ARS (dry matter, total N and total C)
The manure applied in this experiment was from the dairy herd at the Marshfield Research Station. Cows were fed a diet of 48% dry matter, 17.45% protein, and 72.8% total digestible nutrients. Liquid slurry manure, including feces, urine, and bedding, was collected and stored in a lagoon on the site. Manure was withdrawn from the lagoon, spread on the plots and sampled for analysis all on the same day, once per year shortly after an alfalfa harvest. Manure samples were analyzed at the University of Wisconsin Soil and Forage Lab in Marshfield (NH4-N, total P and total K) and at the Marshfield ARS (pH, dry matter, volatile solids, total N and total C).
GHG fluxes from soil (CO2, CH4, N2O) were measured using static chambers as described in Parkin and Venterea (2010). In addition, ammonia fluxes (NH3) from soil were measured using a dynamic chamber method (Svensson, 1994; Misselbrook and Hansen, 2001). Additional soil chemical and physical characteristics were measured as noted in the data dictionary and other metadata of the MAMA data set, included here.
This experiment was part of “Climate Change Mitigation and Adaptation in Dairy Production Systems of the Great Lakes Region,” also known as the Dairy Coordinated Agricultural Project (Dairy CAP), funded by the United States Department of Agriculture – National Institute of Food and Agriculture (award number 2013-68002-20525). The main goal of the Dairy CAP was to improve understanding of the magnitudes and controlling factors over GHG emissions from dairy production in the Great Lakes region. Using this knowledge, the Dairy CAP has improved life cycle analysis (LCA) of GHG production by Great Lakes dairy farms, developing farm management tools, and conducting extension, education and outreach activities.
Data from: Underestimation of N2O emissions in a comparison of the DayCent, DNDC, and EPIC 1 models
Process-based models are increasingly used to study mass and energy fluxes from agro-ecosystems, including nitrous oxide (N2O) emissions from agricultural fields. This data set is the output of three process-based models – DayCent, DNDC, and EPIC – which were used to simulate fluxes of N2O from dairy farm soils. The individual models’ output and the ensemble mean output were evaluated against field observations from two agricultural research stations in Arlington, WI and Marshfield, WI. These sites utilize cropping systems and nitrogen fertilizer management strategies common to Midwest dairy farms.
The models were calibrated and validated using data collected at Arlington and Marshfield over five years (nine years for crop yield). Calibration and validation used observations of soil temperature (n = 887), volumetric soil water content (VSWC, n = 880), crop yield (n = 67), and soil N2O flux (n = 896). The observed data are presented here with the model output to document model calibration and validation; most of these observed data are also held by Ag Data Commons in separate data sets from field experiments at Arlington and Marshfield (http://dx.doi.org/10.15482/USDA.ADC/1361194, http://dx.doi.org/10.15482/USDA.ADC/1401975, http://dx.doi.org/10.15482/USDA.ADC/1399470). The remaining observed data is described in Osterholz et al. 2014.
Model simulations were run from 2010-2015 for the Arlington site and 2013-2015 for the Marshfield site. The three models were parameterized (i.e. calibrated) for each site using the same climate, initial soil physical and chemical conditions, hydraulic properties, initial soil carbon, and management schedules. Weather data for each site (daily minimum and maximum temperature, precipitation, relative humidity, wind speed, and solar radiation) was reconstructed using the NOAA online climate database (NOAA, 2016). Initial soil physical and chemical properties were constructed from available on-site measurements and supplemented using the Web Soil Survey (Soil Survey Staff, 2016). Soil carbon data was available for each site, and to prioritize model agreement initial soil carbon for the 0-20cm layer was set at 55.7 Mg C ha-1 for Arlington (Sanford et al., 2012), and at 52.6 Mg C ha-1 for Marshfield. Following parameterization of soil C, a 17 year spin-up period (1993-2009) at each site was simulated prior to the years during which data was collected (2010-2015). While DayCent developers typically recommend a spin-up of at least 1000 years, DNDC has been run with spin-up periods as low as 2 years (Zhang et al., 2015). Given that observations of soil C were available, a 17 year spin-up was chosen to reflect the duration between initial soil C sampling (Sanford et al., 2012) and the first measurement of N2O in our data set (Osterholz et al., 2014). Management and input schedules were constructed from on-site data and record-keeping; these are available in the supplementary online data of the primary journal paper. All other initial parameters, such as crop-specific productivity or soil carbon turnover rate, were independently established by each model in calibration.
This work was part of “Climate Change Mitigation and Adaptation in Dairy Production Systems of the Great Lakes Region,” also known as the Dairy Coordinated Agricultural Project (Dairy CAP), funded by the United States Department of Agriculture – National Institute of Food and Agriculture (award number 2013-68002-20525). The main goal of the Dairy CAP was to improve understanding of the magnitudes and controlling factors over greenhouse gas (GHG) emissions from dairy production in the Great Lakes region. Using this knowledge, the Dairy CAP has improved life cycle analysis (LCA) of GHG production by Great Lakes dairy farms, developing farm management tools, and conducting extension, education and outreach activities.