Abstract The maintenance of hydrologic function on grazing lands is an important management objec... more Abstract The maintenance of hydrologic function on grazing lands is an important management objective to sustain forage production during low moisture supply, safeguard other ecosystem goods and services and build resilience to a warming climate. Hydrologic function can be influenced by grazing patterns, as represented by variation in the timing, intensity and frequency of livestock use. While rotational, adaptive grazing (a short-duration, multi-paddock grazing system that emphasises plant recovery between grazing events) is growing in popularity and has the potential to influence grassland hydrological processes such as water infiltration, few studies have comprehensively examined infiltration in relation to on-ranch grazing practices. We examined water infiltration in grasslands on 52 ranches (set up as matched pairs) to examine whether adaptive grazing alters water infiltration in the Great Plains of western Canada, as compared to conventional grazing management employed on neighbouring ranches. We also used producer survey information to test for the influence of ongoing nuanced grazing practices on water infiltration rates, over and above the biophysical effects of soil texture, soil bulk density and plant litter, as well as cultivation history and climate. Overall, adaptive grazing, and specifically the use of higher rest-to-grazing ratios early in the growing season (prior to August 1), led to increased water infiltration in grassland soils. Water infiltration was positively associated with increased litter mass under adaptive grazing, whereas higher bulk density (and sandier) soils were associated with decreased infiltration rates. This study highlights the potential of specialised rotational grazing systems using cattle to improve soil hydrologic function in grazed grasslands.
Tredennick et al. criticize one of our statistical analyses and emphasize the low explanatory pow... more Tredennick et al. criticize one of our statistical analyses and emphasize the low explanatory power of models relating productivity to diversity. These criticisms do not detract from our key findings, including evidence consistent with the unimodal constraint relationship predicted by the humped-back model and evidence of scale sensitivities in the form and strength of the relationship.
Land-use change is one of the most important factors influencing soil microbial communities, whic... more Land-use change is one of the most important factors influencing soil microbial communities, which play a pivotal role in most biogeochemical and ecological processes. Using agroforestry systems as a model, this study examined the effects of land-uses and edaphic properties on bacterial communities in three agroforestry types covering a 270 km soil-climate gradient in Alberta, Canada. Our results demonstrate that land-use patterns exert stronger effects on soil bacterial communities than soil zones in these agroforestry systems. Plots with trees in agroforestry systems promoted greater bacterial abundance and to some extent species richness, which was associated with more nutrient rich soil resources. While Acidobacteria, Actinobacteria and Alphaproteobacteria were the dominant bacterial phyla and sub-phyla across land-uses, Arthrobacter, Acidobacteria_Gp16, Burkholderia, Rhodanobacter and Rhizobium were the keystone taxa in these agroforestry systems. Soil pH and carbon contents emerged as the major determinants of bacterial community characteristics. We found non-random co-occurrence and modular patterns of soil bacterial communities, and these patterns were controlled by edaphic factors and not their taxonomy. Overall, this study highlights the drivers and co-occurrence patterns of soil microbial communities in agroforestry-systems.
The search for predictions of species diversity across environmental gradients has challenged eco... more The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.
Adaptive multi-paddock (AMP) grazing is a form of rotational grazing in which small paddocks are ... more Adaptive multi-paddock (AMP) grazing is a form of rotational grazing in which small paddocks are grazed with high densities of livestock for short periods, with long recovery periods prior to regrazing. We compared the fluxes of greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), from soils of AMP-grazed grasslands to paired neighboring non-AMP-grazed grasslands across a climatic gradient in Alberta, Canada. We further tested GHG responses to changes in temperature (5 °C vs. 25 °C) and moisture levels (permanent wilting point (PWP), 40% of field capacity (0.4FC), or field capacity (FC)) in a 102-day laboratory incubation experiment. Extracellular enzyme activities (EEA), microbial biomass C (MBC) and N (MBN), and available-N were also measured on days 1, 13, and 102 of the incubation to evaluate biological associations with GHGs. The 102-day cumulative fluxes of CO2, N2O, and CH4 were affected by both temperature and moisture content (p &...
Recent evidence indicates that many native bee species are in decline due to the cumulative effec... more Recent evidence indicates that many native bee species are in decline due to the cumulative effects of multiple human‐induced stressors such as habitat loss, pesticide exposure, pathogens, and climate change. These declines have raised interest in the status of native bees and in developing tools that support management of bee communities and the ecosystem services they deliver. Native bees were surveyed using pan traps and netting over 2 years at 68 locations in croplands and rangelands across three ecological regions of Alberta's prairies – the Grassland, Parkland, and Boreal Natural Regions – to evaluate patterns in bee communities in response to disturbance and ecological gradients. Bee community composition was different across land use and ecoregions. While several cavity‐nesting species had a strong association with rangelands, cavity‐nesting bees tended to be less common in croplands and may be more sensitive to loss of rangeland habitat. Response patterns in overall bee abundance and richness were driven by interactions between region and land use, highlighting the need for regional studies to understand how bee communities respond to these factors. This survey is one of the first to sample the response of bee communities to landscape disturbance across a broad spatial area of the Canadian prairies. Large‐scale compositional studies are essential for understanding the status of native bee communities, and for monitoring long‐term trends over time. We recommend subsequent coordinated surveys using standardised methods across broad spatial scales.
Long-term livestock grazing (here after 'grazing') affects carbon (C) and nutrient cyclin... more Long-term livestock grazing (here after 'grazing') affects carbon (C) and nutrient cycling in grassland ecosystems, in part by altering the quantity and quality of litter inputs. Despite their spatial extent and size of carbon and nutrient stocks, the effect of grazing on grassland biogeochemical cycling through the mediation of microbial activity remains poorly understood. To better understand the relationship between grazing and C and nutrient cycling in litter, we conducted an 18-month long study in paired grasslands previously grazed and nongrazed by cattle for 25 years, measuring extracellular enzyme activity (EEA) in various plant litter samples. Litter sources, including seven grass species dominant in one or more subregions and possessing divergent responses to grazing, as well as a community mix of litter sourced from each site, were tested at 15 sites spanning three grassland subregions in Alberta, Canada. We quantified EEAs associated with C cycling (β-glucosidase, β-Cellobiosidase and β-xylosidase), nitrogen (N) cycling (N-acetyl-glucosaminidase) and phosphorus (P) cycling (phosphatase). In general, litter in grasslands exposed to grazing had greater activity of C-liberating and P-liberating enzyme (β-xylosidase and phosphatase) in the mesic grasslands of the Foothills Fescue subregion (P ≤ 0.10). Observed EEAs were strongly mediated by litter type, with greater EEAs in litter of grass species known to increase in abundance under long-term grazing, including Poa pratensis in the Foothills Fescue subregion, and Bouteloua gracilis in arid grasslands of the Mixedgrass Prairie. In contrast, Pascopyrum smithii litter had the lowest enzyme activities in all subregions. We also found that EEAs changed through time (0-18 months) with consistently high levels detected at 1 (June 2014), 6 (October 2014) and 18 months (October 2015) after placement. Overall, these findings indicate grazing enhances EEA, and thus C and N-cycling, in northern temperate grasslands.
Abstract Agricultural land management practices have the potential to reduce carbon emissions fro... more Abstract Agricultural land management practices have the potential to reduce carbon emissions from soils, especially when a reduction in microbial (heterotrophic respiration, RH) rather than root respiration (autotrophic, RA) is achieved. Soil RA and RH and their sensitivity to temperature changes were determined in the forestland and neighboring herbland (area without trees) soils of three agroforestry systems (hedgerow, shelterbelt, and silvopasture) over two growing seasons (May through September in 2013 and 2014). Over the two growing seasons, mean RA from the forestland was 32% greater than that from the herbland, while the RH in the forestland was 22% lower than that in the herbland. The sensitivity of RA to temperature was consistently greater in the forestland (3.6) than in the herbland (3.4), though the opposite was found for RH. Effects of agroforestry system on RA and RH also varied seasonally. The contribution of RH to total soil respiration was greater in each of the hedgerow (59%) and shelterbelt (55%) systems than in the silvopasture system (51%), reflecting the high RH from annual cropland within the hedgerow and shelterbelt systems. We found stronger control of RH by temperature in the hedgerow and shelterbelt, suggesting that an increase in soil temperature in response to future climatic warming could reduce the amount of carbon held in these systems as compared to the silvopasture system. Overall, the inclusion or maintenance of perennial vegetation (forest and grassland) in an annually cropped agricultural landscape could result in a net reduction in soil RH, and thereby mitigate losses of carbon from agricultural soils.
While northern temperate grasslands are important for supporting beef production, it remains uncl... more While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p 0.05). Forb crude protein concentrations were lower (p 0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking...
A survey of Alberta beef producers was conducted at sites overlapping with a province-wide networ... more A survey of Alberta beef producers was conducted at sites overlapping with a province-wide network of permanent biodiversity monitoring plots to characterize focal pastures and their management, including estimates of stocking rates. Overall, greater stocking rates were reported in the boreal compared with the parkland and grassland natural regions, coinciding with an increased reliance on tame forage on relatively small land areas of largely deeded land. Higher stocking rates were also associated with earlier starting dates of grazing in the season, higher mean annual precipitation, and lower mean annual temperature.
Abstract The maintenance of hydrologic function on grazing lands is an important management objec... more Abstract The maintenance of hydrologic function on grazing lands is an important management objective to sustain forage production during low moisture supply, safeguard other ecosystem goods and services and build resilience to a warming climate. Hydrologic function can be influenced by grazing patterns, as represented by variation in the timing, intensity and frequency of livestock use. While rotational, adaptive grazing (a short-duration, multi-paddock grazing system that emphasises plant recovery between grazing events) is growing in popularity and has the potential to influence grassland hydrological processes such as water infiltration, few studies have comprehensively examined infiltration in relation to on-ranch grazing practices. We examined water infiltration in grasslands on 52 ranches (set up as matched pairs) to examine whether adaptive grazing alters water infiltration in the Great Plains of western Canada, as compared to conventional grazing management employed on neighbouring ranches. We also used producer survey information to test for the influence of ongoing nuanced grazing practices on water infiltration rates, over and above the biophysical effects of soil texture, soil bulk density and plant litter, as well as cultivation history and climate. Overall, adaptive grazing, and specifically the use of higher rest-to-grazing ratios early in the growing season (prior to August 1), led to increased water infiltration in grassland soils. Water infiltration was positively associated with increased litter mass under adaptive grazing, whereas higher bulk density (and sandier) soils were associated with decreased infiltration rates. This study highlights the potential of specialised rotational grazing systems using cattle to improve soil hydrologic function in grazed grasslands.
Tredennick et al. criticize one of our statistical analyses and emphasize the low explanatory pow... more Tredennick et al. criticize one of our statistical analyses and emphasize the low explanatory power of models relating productivity to diversity. These criticisms do not detract from our key findings, including evidence consistent with the unimodal constraint relationship predicted by the humped-back model and evidence of scale sensitivities in the form and strength of the relationship.
Land-use change is one of the most important factors influencing soil microbial communities, whic... more Land-use change is one of the most important factors influencing soil microbial communities, which play a pivotal role in most biogeochemical and ecological processes. Using agroforestry systems as a model, this study examined the effects of land-uses and edaphic properties on bacterial communities in three agroforestry types covering a 270 km soil-climate gradient in Alberta, Canada. Our results demonstrate that land-use patterns exert stronger effects on soil bacterial communities than soil zones in these agroforestry systems. Plots with trees in agroforestry systems promoted greater bacterial abundance and to some extent species richness, which was associated with more nutrient rich soil resources. While Acidobacteria, Actinobacteria and Alphaproteobacteria were the dominant bacterial phyla and sub-phyla across land-uses, Arthrobacter, Acidobacteria_Gp16, Burkholderia, Rhodanobacter and Rhizobium were the keystone taxa in these agroforestry systems. Soil pH and carbon contents emerged as the major determinants of bacterial community characteristics. We found non-random co-occurrence and modular patterns of soil bacterial communities, and these patterns were controlled by edaphic factors and not their taxonomy. Overall, this study highlights the drivers and co-occurrence patterns of soil microbial communities in agroforestry-systems.
The search for predictions of species diversity across environmental gradients has challenged eco... more The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.
Adaptive multi-paddock (AMP) grazing is a form of rotational grazing in which small paddocks are ... more Adaptive multi-paddock (AMP) grazing is a form of rotational grazing in which small paddocks are grazed with high densities of livestock for short periods, with long recovery periods prior to regrazing. We compared the fluxes of greenhouse gases (GHGs), including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), from soils of AMP-grazed grasslands to paired neighboring non-AMP-grazed grasslands across a climatic gradient in Alberta, Canada. We further tested GHG responses to changes in temperature (5 °C vs. 25 °C) and moisture levels (permanent wilting point (PWP), 40% of field capacity (0.4FC), or field capacity (FC)) in a 102-day laboratory incubation experiment. Extracellular enzyme activities (EEA), microbial biomass C (MBC) and N (MBN), and available-N were also measured on days 1, 13, and 102 of the incubation to evaluate biological associations with GHGs. The 102-day cumulative fluxes of CO2, N2O, and CH4 were affected by both temperature and moisture content (p &...
Recent evidence indicates that many native bee species are in decline due to the cumulative effec... more Recent evidence indicates that many native bee species are in decline due to the cumulative effects of multiple human‐induced stressors such as habitat loss, pesticide exposure, pathogens, and climate change. These declines have raised interest in the status of native bees and in developing tools that support management of bee communities and the ecosystem services they deliver. Native bees were surveyed using pan traps and netting over 2 years at 68 locations in croplands and rangelands across three ecological regions of Alberta's prairies – the Grassland, Parkland, and Boreal Natural Regions – to evaluate patterns in bee communities in response to disturbance and ecological gradients. Bee community composition was different across land use and ecoregions. While several cavity‐nesting species had a strong association with rangelands, cavity‐nesting bees tended to be less common in croplands and may be more sensitive to loss of rangeland habitat. Response patterns in overall bee abundance and richness were driven by interactions between region and land use, highlighting the need for regional studies to understand how bee communities respond to these factors. This survey is one of the first to sample the response of bee communities to landscape disturbance across a broad spatial area of the Canadian prairies. Large‐scale compositional studies are essential for understanding the status of native bee communities, and for monitoring long‐term trends over time. We recommend subsequent coordinated surveys using standardised methods across broad spatial scales.
Long-term livestock grazing (here after 'grazing') affects carbon (C) and nutrient cyclin... more Long-term livestock grazing (here after 'grazing') affects carbon (C) and nutrient cycling in grassland ecosystems, in part by altering the quantity and quality of litter inputs. Despite their spatial extent and size of carbon and nutrient stocks, the effect of grazing on grassland biogeochemical cycling through the mediation of microbial activity remains poorly understood. To better understand the relationship between grazing and C and nutrient cycling in litter, we conducted an 18-month long study in paired grasslands previously grazed and nongrazed by cattle for 25 years, measuring extracellular enzyme activity (EEA) in various plant litter samples. Litter sources, including seven grass species dominant in one or more subregions and possessing divergent responses to grazing, as well as a community mix of litter sourced from each site, were tested at 15 sites spanning three grassland subregions in Alberta, Canada. We quantified EEAs associated with C cycling (β-glucosidase, β-Cellobiosidase and β-xylosidase), nitrogen (N) cycling (N-acetyl-glucosaminidase) and phosphorus (P) cycling (phosphatase). In general, litter in grasslands exposed to grazing had greater activity of C-liberating and P-liberating enzyme (β-xylosidase and phosphatase) in the mesic grasslands of the Foothills Fescue subregion (P ≤ 0.10). Observed EEAs were strongly mediated by litter type, with greater EEAs in litter of grass species known to increase in abundance under long-term grazing, including Poa pratensis in the Foothills Fescue subregion, and Bouteloua gracilis in arid grasslands of the Mixedgrass Prairie. In contrast, Pascopyrum smithii litter had the lowest enzyme activities in all subregions. We also found that EEAs changed through time (0-18 months) with consistently high levels detected at 1 (June 2014), 6 (October 2014) and 18 months (October 2015) after placement. Overall, these findings indicate grazing enhances EEA, and thus C and N-cycling, in northern temperate grasslands.
Abstract Agricultural land management practices have the potential to reduce carbon emissions fro... more Abstract Agricultural land management practices have the potential to reduce carbon emissions from soils, especially when a reduction in microbial (heterotrophic respiration, RH) rather than root respiration (autotrophic, RA) is achieved. Soil RA and RH and their sensitivity to temperature changes were determined in the forestland and neighboring herbland (area without trees) soils of three agroforestry systems (hedgerow, shelterbelt, and silvopasture) over two growing seasons (May through September in 2013 and 2014). Over the two growing seasons, mean RA from the forestland was 32% greater than that from the herbland, while the RH in the forestland was 22% lower than that in the herbland. The sensitivity of RA to temperature was consistently greater in the forestland (3.6) than in the herbland (3.4), though the opposite was found for RH. Effects of agroforestry system on RA and RH also varied seasonally. The contribution of RH to total soil respiration was greater in each of the hedgerow (59%) and shelterbelt (55%) systems than in the silvopasture system (51%), reflecting the high RH from annual cropland within the hedgerow and shelterbelt systems. We found stronger control of RH by temperature in the hedgerow and shelterbelt, suggesting that an increase in soil temperature in response to future climatic warming could reduce the amount of carbon held in these systems as compared to the silvopasture system. Overall, the inclusion or maintenance of perennial vegetation (forest and grassland) in an annually cropped agricultural landscape could result in a net reduction in soil RH, and thereby mitigate losses of carbon from agricultural soils.
While northern temperate grasslands are important for supporting beef production, it remains uncl... more While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p 0.05). Forb crude protein concentrations were lower (p 0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking...
A survey of Alberta beef producers was conducted at sites overlapping with a province-wide networ... more A survey of Alberta beef producers was conducted at sites overlapping with a province-wide network of permanent biodiversity monitoring plots to characterize focal pastures and their management, including estimates of stocking rates. Overall, greater stocking rates were reported in the boreal compared with the parkland and grassland natural regions, coinciding with an increased reliance on tame forage on relatively small land areas of largely deeded land. Higher stocking rates were also associated with earlier starting dates of grazing in the season, higher mean annual precipitation, and lower mean annual temperature.
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Papers by Cameron Carlyle