Cattle grazing management affects soil microbial diversity and community network complexity in the Northern Great Plains

Soil microbial communities play a vital role in the biogeochemical cycling and ecological functioning of grassland, but may be affected by common land uses such as cattle grazing. Changes in microbial diversity and network complexity can affect key ecosystem functions such as nutrient cycling. However, it is not well known how microbial diversity and network complexity respond to grazing in the Northern Great Plains. Consequently, it is important to understand whether variation in grazing management alters the diversity and complexity of grassland microbial communities. We compared the effect of intensive adaptive multi-paddock (AMP) grazing and conventional grazing practices on soil microbial communities using 16S/ITS amplicon sequencing. Samples were collected from grasslands in 13 AMP ranches and 13 neighboring, conventional ranches located across the Canadian prairies. We found that AMP grazing increased fungal diversity and evenness, and led to more complex microbial associations. Acidobacteria, Actinobacteria, Gemmatimonadetes, and Bacteroidetes were keystone taxa associated with AMP grazing, while Actinobacteria, Acidobacteria, Proteobacteria, and Armatimonadetes were keystone taxa under conventional grazing. Besides overall grazing treatment effects, specific grazing metrics like cattle stocking rate and rest-to-grazing ratio affected microbial richness and diversity. Bacterial and fungal richness increased with elevated stocking rate, and fungal richness and diversity increased directly with the rest-to-grazing ratio. These results suggest that AMP grazing may improve ecosystem by enhancing fungal diversity and increasing microbial network complexity and connectivity.

Extreme drought impacts have been underestimated in grasslands and shrublands globally

Climate change is increasing the frequency and severity of short-term (~1 y) drought events-the most common duration of drought-globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function-aboveground net primary production (ANPP)-was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought.

Light to moderate long-term grazing enhances ecosystem carbon across a broad climatic gradient in northern temperate grasslands

Grasslands are globally abundant and provide many ecosystem services, including carbon (C) storage. While grasslands are widely subject to livestock grazing, the influence of grazing on grassland ecosystem C remains unclear. We studied the effect of long-term livestock grazing on C densities of different ecosystem components in 110 northern temperate grasslands across a broad agroclimatic gradient in Alberta, Canada. These grasslands stored 50 to 180 t ha^-1C in live and dead vegetation, as well as soil C to 30 cm depth, with the majority as soil organic C (SOC). The mulch layer comprised a large amount of C (~18 t ha^-1C) especially within humid grasslands. Although grazing reduced C densities in litter mass, total ecosystem C was 8.5 % greater under grazing (127.8 t ha^-1) compared to those non-grazed (117.8 t ha^-1), primarily due to increases in SOC and roots. Increases in SOC were consistently observed in the 0-15 cm layer across all climatic conditions, with changes in SOC of the 15-30 cm layer inversely related to aridity. A structural equation model revealed that increased SOC under grazing was indirectly attributed to increases in eudicot rather than graminoid biomass. In addition, SOC increased with graminoid quality (i.e., a reduced carbon to nitrogen ratio), which together with elevated eudicots, increased litter and mulch C, and ultimately enhanced SOC densities. When applied to spatial maps of habitat type and land use (livestock grazing) activity across the region, an area of ~3.8 M ha of grassland was projected to contain an additional 17.1 M t of C under grazing, primarily in mesic grasslands, worth an estimated $3.1 B (Cdn.) under current C valuation guidelines in Canada. Overall, these results highlight the importance of grasslands for C storage and establishing policies that maintain and promote their sustainable use, including light to moderate grazing.

Agroforestry perennials reduce nitrous oxide emissions and their live and dead trees increase ecosystem carbon storage

Agroforestry systems (AFS) contribute to carbon (C) sequestration and reduction in greenhouse gas emissions from agricultural lands. However, previously understudied differences among AFS may underestimate their climate change mitigation potential. In this 3-year field study, we assessed various C stocks and greenhouse gas emissions across two common AFS (hedgerows and shelterbelts) and their component land uses: perennial vegetated areas with and without trees (woodland and grassland, respectively), newly planted saplings in grassland, and adjacent annual cropland in central Alberta, Canada. Between 2018 and 2020 (~April-October), nitrous oxide emissions were 89% lower under perennial vegetation relative to the cropland (0.02 and 0.18 g N m^-2  year^-1 , respectively). In 2020, heterotrophic respiration in the woodland was 53% lower in shelterbelts relative to hedgerows (279 and 600 g C m^-2  year^-1 , respectively). Within the woodland, deadwood C stock was particularly important in hedgerows (35 Mg C ha^-1 or 7% of ecosystem C) relative to shelterbelts (2 Mg C ha^-1 or <1% of ecosystem C), and likely affected C cycling differences between the woodland types by enhancing soil labile C and microbial biomass in hedgerows. Deadwood C stock was positively correlated with annual heterotrophic respiration and total (to ~100 cm depth) soil organic C, water-soluble organic C, and microbial biomass C. Total ecosystem C was 1.90-2.55 times greater within the woodland than all other land uses, with 176, 234, 237, and 449 Mg C ha^-1 found in the cropland, grassland, planted saplings treatment, and woodland, respectively. Shelterbelt and hedgerow woodlands contained 2.09 and 3.03 times more C, respectively, than adjacent cropland. Our findings emphasize the importance of AFS for fostering C sequestration and reducing greenhouse gas emissions and, in particular, retaining hedgerows (legacy woodland) and their associated deadwood across temperate agroecosystems will help mitigate climate change.

Timing and duration of access mat use impacts their mitigation of compaction effects from industrial traffic

Grasslands are declining worldwide and are often impacted by industrial activities, including infrastructure development. Current best management practices for low-disturbance development on grasslands include the use of wooden access mats as temporary work platforms and roadways to mitigate soil compaction and rutting due to heavy traffic. We assessed the impacts of heavy traffic (TON), and the impacts of the same heavy equipment driven over top of access mats (AM), on soil physical, hydrological, and nutrient responses in sandy and loamy soils in the Dry Mixedgrass prairies over a 2-year period. We also assessed how the timing (early vs. late in the growing season) and duration (6 vs. 12 vs. 24 weeks) of AM and TON affected the same metrics. Compared to undisturbed soils, TON increased soil penetration resistance (15 cm depth) up to 93% in loamy and up to 101% in sandy soils, and decreased water infiltration rates from 53 to 71%, respectively. Notably, the negative impacts of TON on soil physical characteristics and hydrology were larger in sandy vs. loamy soils, and when moist soils were exposed to traffic early in the growing season. AMs were effective at mitigating soil compaction from industrial traffic when used on sandy soils. However, AM use increased the supply of total nitrogen and other plant macro- and micro-nutrients, particularly in soils subject to longer (12-24 wk) mat placement. Results indicate TON may have long-lasting effects on grassland (particularly sandy) soils, and that AM use represents an effective tool to mitigate traffic impacts. Further, early-season traffic should be avoided when soils are moist (whether with AM or not), and AMs should be placed on soils for limited durations (≤6 wk) to minimize potential nutrient losses.

Biochar and its manure-based feedstock have divergent effects on soil organic carbon and greenhouse gas emissions in croplands

Applying organic amendments to soil can increase soil organic carbon (SOC) storage and reduce greenhouse gas (GHG) emissions generated by agriculture, helping to mitigate climate change. However, it is necessary to determine which type of amendment produces the most desirable results. We conducted a 3-y field study comparing one-time addition of manure compost and its biochar derivative to a control to assess their effects on SOC and GHG emissions at ten annually cropped sites in central Alberta, Canada. Manure compost and biochar were applied at equivalent carbon rates (7 Mg ha^-1) and tilled into the surface 10 cm of soil. Two years post-treatment, biochar addition increased surface (0-10 cm) SOC by 12 and 10 Mg ha^-1 relative to the control and manure addition, respectively. Therefore, biochar addition led to the sequestration of SOC at a rate of 2.5 Mg ha^-1 y^-1 relative to the control. No treatment effect on deeper (10-100 cm) or cumulative SOC was found. In 2018 and 2019, manure addition increased cumulative GHG (sum of CO₂, CH₄, and N₂O) emissions by 33%, on average, due to greater CO₂ emissions relative to both the control and biochar addition. In contrast, in 2020, biochar addition reduced cumulative GHG emissions by an average of 21% due to lower CO₂ emissions relative to both the control and manure addition. Our study shows that the application of biochar, rather than its manure compost feedstock, increased surface SOC sequestration and had either no effect on (first two years) or reduced GHG emissions (year three) relative to the control. We recommend that policy and carbon sequestration initiatives focus on optimizing biochar production-application systems to fully realize the potential of biochar application as a viable climate change mitigation practice in agriculture.

Soil greenhouse gas emissions and grazing management in northern temperate grasslands

Adaptive multi-paddock (AMP) grazing, a grazing system in which individual paddocks are grazed for a short duration at a high stock density and followed by a long rest period, is claimed to be an effective tool to sustainably manage and improve grasslands and enhance their ecosystem services. However, whether AMP grazing is superior to conventional grazing (n-AMP) in reducing soil greenhouse gas (GHG) emissions is unclear. Here, we measured CO₂, CH₄, and N₂O fluxes between August 2017 and August 2019 in 12 pairs of AMP vs. n-AMP ranches distributed across an agro-climatic gradient in Alberta, Canada. We found that field GHG fluxes did not differ between AMP and n-AMP grazing systems, but instead were regulated by specific management attributes, environmental conditions, and soil properties, including cattle stocking rate, cultivation history, soil moisture content, and soil bulk density. Specifically, we found that seasonal mean CO₂ emissions increased with increasing cattle stocking rates, while CH₄ uptake was lower in grasslands with a history of cultivation. Seasonal mean CO₂ emissions increased while CH₄ uptake decreased with increasing soil moisture content. In addition, CH₄ uptake decreased with increasing soil bulk density. Observed N₂O emissions were poorly predicted by the management, environmental conditions, and soil properties investigated in our study. We conclude that AMP grazing does not have an advantage over n-AMP grazing in reducing GHG fluxes from grasslands. Future efforts to develop optimal management strategies (e.g., the use of sustainable stocking rates and avoided cultivation) that reduce GHG emissions should also consider the environmental conditions and soil properties unique to every grassland ecosystem.

Shrub Encroachment Following Wetland Creation in Mixedgrass Prairie Alters Grassland Vegetation and Soil

Wetland decline under post-European settlement and land use change across western Canada has led to mitigation strategies, including wetland creation. Created wetlands can trigger environmental change, including woody species encroachment, in turn altering vegetation and soil. We quantify changes in shrub abundance from prior to wetland creation (1949) until 60 years later (2012) within a Mixedgrass ecosystem of the Verger watershed in Alberta, Canada. In addition, we compare remaining grassland with areas colonized by shrubland on similar ecosites for differences in (1) plant composition, including native and introduced flora, (2) herbage yield and forage accessibility for livestock, and (3) soil properties (surface organic depth, bulk density, mineral nitrogen (N), and carbon (C) concentration). Repeat photos show Shepherdia argentea shrublands increased from 0 to 88 ha (to 1.15% of study area) following wetland creation, with the greatest increase in the last 20 years. Relative to grasslands, shrublands had lower total plant diversity but greater presence of introduced plant species. Shrub patches were 94% lower in herbaceous production, with 77% of shrublands non-utilized by cattle, collectively leading to reduced grazing capacity. Relative to grasslands, shrublands had a thicker soil surface mulch layer, and where cattle were present, had increased mineral soil N and C. Overall, shrub encroachment following wetland creation has markedly altered vegetation and soils in this once grassland landscape, with negative impacts on native plant diversity, herbage production and forage accessibility, and has implications for the management of shrub encroachment.

Modelling spatio-temporal patterns of soil carbon and greenhouse gas emissions in grazing lands: Current status and prospects

The sustainability of grazing lands lies in the nexus of human consumption behavior, livestock productivity, and environmental footprint. Due to fast growing global food demands, many grazing lands have suffered from overgrazing, leading to soil degradation, air and water pollution, and biodiversity losses. Multidisciplinary efforts are required to understand how these lands can be better assessed and managed to attain predictable outcomes of optimal benefit to society. This paper synthesizes our understanding based on previous work done on modelling the influences of grazing of soil carbon (SC) and greenhouse gas emissions to identify current knowledge gaps and research priorities. We revisit three widely-used process-based models: DeNitrification DeComposition (DNDC), DayCent, and the Pasture Simulation model (PaSim) and two watershed models: The Soil & Water Assessment Tool (SWAT) and Variable Infiltration Capacity Model (VIC), which are widely used to simulate C, nutrient and water cycles. We review their structures and ability as process-based models in representing key feedbacks among grazing management, SOM decomposition and hydrological processes in grazing lands. Then we review some significant advances in the use of models combining biogeochemical and hydrological processes. Finally, we examine challenges of incorporating spatial heterogeneity and temporal variability into modelling C and nutrient cycling in grazing lands and discuss their weakness and strengths. We also highlight key research direction for improving the knowledge base and code structure in modelling C and nutrient cycling in grazing lands, which are essential to conserve grazing lands and maintain their ecosystem goods and services.

Extracellular enzyme activity in grass litter varies with grazing history, environment and plant species in temperate grasslands

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.

Survey of cattle and pasture management practices on focal pastures in Alberta

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.

Access Matting Reduces Mixedgrass Prairie Soil and Vegetation Responses to Industrial Disturbance

Substantial interest exists in understanding the role of low-disturbance construction methods in mitigating industrial impacts to native grassland soils and vegetation. We assessed soil and vegetation responses to conventional high-disturbance sod-stripping and revegetation on sandy soils, and the alternative practice of low-disturbance access matting to provide a temporary work surface on sandy and loamy soils. Treatments were associated with high-voltage transmission tower construction during 2014 within the Mixedgrass Prairie. High-disturbance sites were hydroseeded in May of 2015, while low-disturbance sites recovered naturally. We assessed soil physical (bulk density, water infiltration) and chemical properties (organic matter, pH, and electrical conductivity) after construction and herbage biomass for three growing seasons. Sod-stripping led to 53% greater soil bulk density and 51% less organic matter than nondisturbed controls, while water infiltration increased by 32% in these high-sand (>80%) soils. In contrast, access matting led to minimal soil property changes regardless of the texture. While total herbage biomass was unaffected by all construction treatments, sod-stripping reduced grass biomass by 80% during the first growing season, which coincided with a 119% increase in forb mass. Root biomass (0-15 cm) also declined 77% with sod-stripping. Vegetation biomass on sites with access matting remained largely unaffected by the disturbance. Overall, low-disturbance construction methods using access matting were more effective than sod-stripping in mitigating the negative impacts of industrial development on Mixedgrass soil properties, as well as vegetation biomass, and are recommended as a best management practice during industrial disturbance.

Introducing trees to agricultural lands increases greenhouse gas emission during spring thaw in Canadian agroforestry systems

The role of agroforestry systems in mitigating greenhouse gas (GHG) emission from agricultural soils during spring thaw (early April to mid-May) has been poorly studied. Soil CO₂, CH₄ and N₂O fluxes were measured from treed areas and adjacent herblands (areas without trees) during spring thaw in 2014 and 2015 at 36 agroforestry sites (12 hedgerow, 12 shelterbelt and 12 silvopasture) in central Alberta, Canada. Fluxes of those GHGs varied with agroforestry systems and land-cover types. We found greater CO₂ emission (P < 0.001) and CH₄ uptake (P < 0.05), but lower N₂O emission (P < 0.01) in the silvopasture than in the hedgerow and shelterbelt systems, with no difference between the last two systems. Treed areas in general had greater CO₂ emissions (P < 0.001) and CH₄ uptake (P < 0.01), and lower N₂O emissions (P < 0.001) than the herblands. Soil temperature, moisture content, organic C content and soil available N concentration affected GHG fluxes. The global warming potential (GWP) was greater (P < 0.05) in the silvopasture than in the hedgerow or shelterbelt systems over the two spring thaw seasons examined, and greater (P < 0.05) in the treed areas than in the herblands during the cool spring in 2015. However, the GWP per unit soil organic C was lower in the treed areas (0.004-0.101%) than in the herblands (0.005-0.225%). As compared to previously reported mean growing season GHG emission (15.4 g CO₂-eq m^-2 day^-1), the GWP of these land uses during spring thaw was small (<5% of the annual GWP) due to the short spring period (6 weeks) and the small GHG emission (2.5 g CO₂-eq m^-2 day^-1). Although GHG emissions during spring thaw were small compared to those in the growing season, they should not be ignored.

Asynchrony among local communities stabilises ecosystem function of metacommunities

Temporal stability of ecosystem functioning increases the predictability and reliability of ecosystem services, and understanding the drivers of stability across spatial scales is important for land management and policy decisions. We used species‐level abundance data from 62 plant communities across five continents to assess mechanisms of temporal stability across spatial scales. We assessed how asynchrony (i.e. different units responding dissimilarly through time) of species and local communities stabilised metacommunity ecosystem function. Asynchrony of species increased stability of local communities, and asynchrony among local communities enhanced metacommunity stability by a wide range of magnitudes (1–315%); this range was positively correlated with the size of the metacommunity. Additionally, asynchronous responses among local communities were linked with species’ populations fluctuating asynchronously across space, perhaps stemming from physical and/or competitive differences among local communities. Accordingly, we suggest spatial heterogeneity should be a major focus for maintaining the stability of ecosystem services at larger spatial scales.

Forest and grassland cover types reduce net greenhouse gas emissions from agricultural soils

Western Canada's prairie region is extensively cultivated for agricultural production, which is a large source of greenhouse gas emissions. Agroforestry systems are common land uses across Canada, which integrate trees into the agricultural landscape and could play a substantial role in sequestering carbon and mitigating increases in atmospheric GHG concentrations. We measured soil CO2, CH4 and N2O fluxes and the global warming potential of microbe-mediated net greenhouse gas emissions (GWPm) in forest and herbland (areas without trees) soils of three agroforestry systems (hedgerow, shelterbelt and silvopasture) over two growing seasons (May through September in 2013 and 2014). We measured greenhouse gas fluxes and environmental conditions at 36 agroforestry sites (12 sites for each system) located along a south-north oriented soil/climate gradient of increasing moisture availability in central Alberta, Canada. The temperature sensitivity of soil CO2 emissions was greater in herbland (4.4) than in forest (3.1), but was not different among agroforestry systems. Over the two seasons, forest soils had 3.4% greater CO2 emission, 36% higher CH4 uptake, and 66% lower N2O emission than adjacent herbland soils. Combining the CO2 equivalents of soil CH4 and N2O fluxes with the CO2 emitted via heterotrophic (microbial) respiration, forest soils had a smaller GWPm than herbland soils (68 and 89kgCO2ha(-1), respectively). While emissions of total CO2 were silvopasture>hedgerow>shelterbelt, soils under silvopasture had 5% lower heterotrophic respiration, 15% greater CH4 uptake, and 44% lower N2O emission as compared with the other two agroforestry systems. Overall, the GWPm of greenhouse gas emissions was greater in hedgerow (88) and shelterbelt (85) than in the silvopasture system (76kgCO2ha(-1)). High GWPm in the hedgerow and shelterbelt systems reflects the greater contribution from the monoculture annual crops within these systems. Opportunities exist for reducing soil greenhouse gas emissions and mitigating climate change by promoting the establishment of perennial vegetation in the agricultural landscape.

Effects of supplemental dietary tannins on the performance of white-tailed deer (Odocoileus virginianus)

Tannins are natural and nutritionally significant components of the diets of browsing ungulates. In trials on supplemented pastures and in drylots, we estimated dry matter intake (DMI), weight gain, and urea N, potassium, cortisol and creatinine in urine of captive white-tailed deer fed pelleted diets that differed only in the respective quebracho tannin (QT) content. The low control, medium and high QT rations were 3.6, 63 and 152 g/kg DM respectively. There was no tannin-free pellet option. Trials were divided into winter pasture, restricted choice and spring growth. In winter pasture trial on pasture using QT, deer reduced QT intake relative to that expected under random foraging. This aversion was also apparent during the spring growth trial. While DMI in the winter pasture trial remained similar among treatments (p > 0.05), averaging 130 g/kg(0.75)/day, deer gained more weight (p < 0.05) when given a choice that included the high QT ration. During subsequent spring growth, DMI and weight gains generally exceeded those of the winter period. Unlike the winter pasture trial, weight gains in spring growth trial were higher (p < 0.05) in the low-control QT treatment. In the restricted choice trial, weight gain was again higher (p < 0.05) for deer fed a low-control QT diet. The urea N/creatinine ratio of deer fed the low-control QT diet (0.0357) was over three times that of deer fed the high QT diet (0.0107). Neither potassium/creatinine nor cortisol/creatinine ratios were affected by diet (p > 0.05). Collectively, these results suggest that although deer do not avoid tannins, and even ingested up to 5% under the choice options in these trials, the effect of tannins on deer performance may vary by season as well as by foraging opportunities.

Performance and dietary preferences of white-tailed deer grazing chicory, birdsfoot trefoil or alfalfa in north central Alberta

Little information exists on the performance of deer on alternative forage species in northern temperate environments during summer and fall, the period of inherent maximum growth in deer. In performance and choice experiments, we compared live weight gain (g/kg(0.75)/day), absolute [kg/ha dry matter (DM)] and relative (% DM) herbage utilization, relative preference index (RPI) as well as plant community visitation of white-tailed deer grazing alfalfa (Medicago sativa), birdsfoot trefoil (Lotus corniculatus) or chicory (Cichorium intybus) in north central Alberta, Canada. Herbage phytomass and quality was also measured on the grazed pastures. Alfalfa had higher dry matter yields and crude protein concentrations than chicory and trefoil. Chicory had lower neutral detergent fiber concentrations than the other forages. Tannin concentrations were greatest in birds foot trefoil (nearly 55 g/kg DM), well above those in the other forages (<5 g/kg DM). Live weight gain was similar among deer feeding within the paddocks seeded to birds foot trefoil and chicory, and more than two times higher (p < 0.05) than deer feeding in paddocks seeded to alfalfa. Deer spent more grazing time (about 40%) on chicory pastures than on alfalfa and birds foot trefoil pastures. RPI values were greatest for birds foot trefoil at 2.11, intermediate for chicory at 1.40, and lowest for alfalfa at <0.60. Absolute herbage utilization remained similar (p > 0.05) among the three forage species. In contrast, relative herbage utilization was greater from birds foot trefoil (52% DM) than chicory (40% DM) or alfalfa (25% DM). These results suggest that the use of alfalfa with other alternative forages may prove beneficial to deer production, rather than using alfalfa pasture alone.

Shrub encroachment impacts the potential for multiple use conflicts on public land

Public rangelands in North America are typically managed under a multiple use policy that includes livestock grazing and wildlife management. In this article we report on the landscape level extent of grassland loss to shrub encroachment in a portion of the Rocky Mountain Forest Reserve in southwestern Alberta, Canada, and review the associated implications for simultaneously supporting livestock and wildlife populations while maintaining range health on this diminishing vegetation type. Digitized aerial photographs of 12 km of valley bottom from 1958 and 1974 were co-registered to ortho-rectified digital imagery taken in 1998, and an un-supervised classification used to determine areas associated with grassland and shrubland in each year. Field data from 2002 were over-layed using GPS coordinates to refine the classification using a calibration-validation procedure. Over the 40-year study period, open grasslands declined from 1,111 ha in 1958 to 465 ha in 1998, representing a 58% decrease. Using mean production data for grass and shrub dominated areas we then quantified aggregate changes in grazing capacity of both primary (grassland) and secondary (shrubland) habitats for livestock and wildlife. Total declines in grazing capacity from 1958 to 1998 totaled 2,744 Animal Unit Months (AUMs) of forage (-39%), including a 58% decrease in primary (i.e., open grassland) range, which was only partly offset by the availability of 1,357 AUMs within less productive and less accessible shrubland habitats. Our results indicate shrub encroachment has been extensive and significantly reduced forage availability to domestic livestock and wildlife, and will increase the difficulty of conserving remaining grasslands. Although current grazing capacities remain marginally above those specified by regulated grazing policies, it is clear that continued habitat change and decreases in forage availability are likely to threaten the condition of remaining grasslands. Unless shrub encroachment is arrested or grassland restoration initiated, reductions in aggregate ungulate numbers may be necessary.

Populus forest characterization in Elk Island National Park relative to herbivory, prescribed fire, and topography

Wild ungulate herbivory and prescribed fire can modify the vegetational characteristics of Populus forest plant communities and alter their potential to meet conservation objectives. Effective management of these areas depends on understanding the impact of these disturbances across natural landscapes. Our objective was to quantify various overstory and understory plant community characteristics in the Populus forests in and around Elk Island National Park, Alberta, under different disturbance regimes. Vegetation from 36 sites, stratified by four topographic positions and three historical treatment combinations of fire and native ungulate herbivory, were sampled. In these sites, we quantified tree density, basal area and cover, understory species richness and diversity, shrub density and height, as well as grass, forb, and browse annual net primary production (ANPP). Although tree canopy characteristics were similar under all three disturbances, small-diameter trees (< 5 cm) were nearly absent within the Park. The reference area outside the Park had greater browse-leaf and -twig ANPP, as well as shrub height, but lower grass ANPP. Inside the Park, burned areas had greater shrub density and ANPP of grass and forb components. Topographically, tree stand basal area, cover, and shrub height were greatest on the northern slope, as was browse-leaf ANPP. Species diversity and richness were relatively greater on the toe slope. Within the plant community variables examined, the disturbances and positions frequently interacted, particularly the burned treatment with the crest position and level of herbivory with the south-facing and north-facing slopes. The structure, composition, and ANPP of Populus forest in Elk Island National Park has been significantly affected by both ungulate herbivory and prescribed burning. These factors, along with topography, influence the vegetation and are consequently important for management of the park's habitat and ungulate populations. Key words: ANPP, national park, prescribed fire, structure, topography, ungulate herbivory.