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Significant interest exists in the potential for specialized grazing systems, including adaptive multipaddock (AMP) grazing, to enhance grassland health and function. However, specific pasture management practices associated with AMP grazing at the ranch level remain poorly understood in comparison with more regionally representative management systems. As part of a larger study examining grazing effects on soil carbon, greenhouse gases, and other ecosystem attributes, here we report on differences in disturbance history and grazing management practices on a sample of AMP operators and their neighboring (n-AMP) ranches at 32 paired sites across the prairie provinces of western Canada. Most ranches studied (77.5%) relied on pastures composed of introduced (seeded) forage. On average, the AMP ranches surveyed were larger in size, supported greater animal numbers, and were more likely to use seeded forages comprising diverse mixes. Relative to n-AMP ranches, AMP ranches used 18.6-fold higher average stock densities in smaller paddocks (22.3 vs. 120.7 ha) while grazing over a grazing season that was 76 d longer, although computed stocking rates remained similar (P ≥ 0.10). AMP operators specifically used much shorter grazing periods (2.8 d) during the early growing season (i.e., before August 1) that were followed by a prolonged rest period (69 d) and could be used to compute a rest-to-grazing ratio for the first half of the grazing season for all ranches. This ratio, along with cattle stock density computed at the pasture scale, exhibited the greatest potential to differentiate the two groups of ranchers. Finally, both groups, and in particular ranchers within the AMP group, demonstrated high variability in management practices among individual operators, highlighting the importance of using specific management metrics rather than generalized descriptors of “grazing system type” to interpret their influence.

Management intensive grazing (MIG) may not maximize plant productivity on rangelands because of morphophysiological traits of grassland vegetation. We examined defoliation and moisture effects on the biomass yield of rhizomatous and caespitose grass pairs that were either phylogenetically similar or of similar agroclimatic adaptation, including two agronomic grasses. From relatively low to high moisture regime adaptation, species pairs included western wheatgrass (Pascopyrum smithii [Rydb.] A. Love) and needle-and-thread (Hesperostipa comata [Trin. & Rupr.] Barkw.), northern wheatgrass (Elymus lanceolatus [Scribn. & J.G. Sm.]) and western porcupine grass (H. curtiseta [Hitchc.] Barkw.), plains and foothills rough fescue (Festuca hallii [Vasey] and F. campestris Rydb.), and smooth and meadow brome (Bromus inermis Leyss. and B. riparius Rehm). Response variables were shoot yield, root-shoot ratio, and water-use efficiency. We hypothesized that caespitose grasses, regardless of their origin or adaptation to agroclimate regime, would respond more determinately in biomass accumulation. Defoliation effects on shoot biomass were more pronounced under high moisture. Low intensity − high frequency defoliation yielded similarly to deferred controls in all grasses, and the same was true for high-intensity − low-frequency (HILF) defoliation in 1 rhizomatous grass. Three of the 4 rhizomatous grasses and 1 caespitose grass yielded greater under HILF defoliation compared with high-intensity − high-frequency defoliation. Caespitose grasses allocated more biomass to roots under low moisture conditions. Water-use efficiency decreased under high moisture conditions and more intense and/or frequent defoliation and peaked in agronomic grasses. Overall, our results suggested that growth patterns corresponded more with phylogenetic similarity as opposed to growth form. A conceptual model from these results showed that across all species, only the introduced bromes generated greater biomass under HILF defoliation, and this may explain why past research consistently concludes that MIG does not enhance plant productivity on rangelands.

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.

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 microorganisms play critical roles in maintaining ecological functions of the northern mixed-grass prairie. While defoliation regimes and elevated precipitation affect plant community composition and primary productivity in these grasslands, their effects on soil microbiome and interactome have not been studied. We examined the response of soil microbiome and interactome to long-term (2010–2015) treatments of varying defoliation regimes (low vs. high intensity and low vs. high frequency) and two precipitation conditions (ambient vs. elevated) on two contrasting sites (a dry vs. a mesic site) in a northern mixed-grass prairie. High intensity defoliation reduced alpha-diversity and altered the beta-diversity of soil microbial communities in the mesic site but not in the dry site, while elevated precipitation reduced alpha-diversity and altered the beta-diversity of soil microbial communities in both sites. Defoliation and precipitation did not show interaction effects on overall alpha- and beta-diversity, but did combine to influence the interactome network. High intensity defoliation promoted the oligotrophic genera Spartobacteria (Verrucomicrobia), Pseudonocardia (Actinobacteria), and Conexibacter (Actinobacteria), while elevated precipitation promoted the copiotrophic genera Nitrososphaera (Thaumarchaeota), Anderseniella (Proteobacteria), Sphingomonas (Proteobacteria), and Acidobacteria Gp16 (Acidobacteria). High intensity defoliation increased the number of linkages for Alphaproteobacteria and Acidobacteria, and decreased the number of linkages for Gemmatimonadetes and Spartobacteria in the interactome networks. However, elevated precipitation increased the number of linkages for Actinobacteria and Gemmatimonadetes and decreased the number of linkages for Spartobacteria and Acidobacteria. Our results show that defoliation intensity and elevated precipitation affected the microbiome and associated interactome network within soils of the northern mixed-grass prairie by affecting different functional taxonomic groups, indicating distinct scenarios for defoliation and precipitation in affecting soil microbial communities.

Our understanding of the effect of agroforestry systems on soil organic carbon (SOC) is largely limited to the upper layer of the mineral soil, while LFH (litter, partially decomposed litter and humus) and deeper soil layers are poorly studied. In this study, the effects of three different agroforestry systems (hedgerow, shelterbelt, and silvopasture) and their component land-cover types (treed area and adjacent herbland) on SOC stock in LFH and mineral soil layers (0–75 cm) were investigated across 36 sites in central Alberta, Canada. The SOC stock of mineral soil (0–75 cm) was not affected by agroforestry systems but by land-cover type. The treed area had greater (p

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.

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.

How land-use and soil depth affect soil organic carbon (SOC) quality and stability, properties that are key to the long-term storage of C, is poorly understood in agroforestry systems. We examined the effects of land-use (forest vs. annual cropland) and soil depth (0–10 vs. 10–30 cm) on the quality (availability of C for decomposition), structural stability (composition of C functional groups), and thermal stability (energy yield and temperature characteristics during thermal oxidation) of SOC in a hedgerow system in central Alberta, using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and thermal analysis methods. The SOC quality (proportion of O-alkyl C) was higher, while the proportion of H- and C-substituted aromatic C and structural stability (hydrophobicity index (HB/HI), aromaticity index (ARM), and alkyl index (A/OA)) were all lower in the forest than in the cropland. The SOC also had lower thermal stability (higher energy density and lower temperature at which 50% of the mass was lost (TG-T50)) in the forest than in the cropland. Between the two soil depths, SOC quality (proportion of N-alkyl C, O-alkyl C and di-O-alkyl C) was higher, but the proportion of H- and C-substituted aromatic C and structural and thermal stabilities were lower, within the surficial 0–10 cm layer than in the 10–30 cm soil. We conclude that while the forest land-use within the hedgerow system had a higher SOC quality, it had lower SOC structural and thermal stabilities, suggesting that SOC under the forest land-use may be more susceptible to decline under climate change or other forms of anthropogenic disturbance.

Livestock grazing is an important driver of the carbon (C) cycle in grasslands and could be a decisive factor determining whether grasslands are a net sink or source of C. However, short-term C dynamics in grassland ecosystems and its response to different grazing intensities remain unclear, especially under field conditions. Here we test the hypothesis that photosynthetic C allocation in the plant-soil system of grasslands is differentially affected by the intensity of grazing that occurred in the prior growing season. We studied the fate of new C assimilates, using a 13CO2 pulse-labeling technique, as they move from shoots to roots and soil in vegetation previously exposed to different defoliation (emulated grazing) intensities in two semiarid Mixed Prairie grassland ecosites having contrasting soil textures (sandy vs. loamy). Within 24 h after photosynthetic uptake, 34.5% of the labeled C was translocated out of shoots, with 21% of the labeled C found in the mineral soil. Plant communities treated with high intensity defoliation during the previous growing season had more of the newly fixed 13C translocate into live roots at both ecosites throughout the 25-day chase period, indicating a higher demand for photosynthetic C by the root system of heavily defoliated plants. Twenty-five days after labeling, 13C transfer into the top 30 cm mineral soil was consistently greater at the loamy (26% of total 13C remaining) than at the sandy ecosite (10.4% of 13C remaining). We conclude that conditioning with high intensity defoliation the prior growing season stimulated short-term C allocation to roots in these semi-arid grasslands. Although this response was independent of soil texture, more C was translocated belowground overall in the loamy ecosite. The effect of defoliation intensity and ecosite in regulating short-term C allocation in the plant-soil system in temperate grasslands should be incorporated into future models describing C cycling in grasslands when predicting C dynamics under different management strategies employing contrasting grazing intensities.

To evaluate mechanisms by which defoliation alters grassland productivity, we examined mixed grass prairie herbage yields under recurring treatments that included hand-clipping of plots over five growing seasons at high intensity and low frequency (HILF), low intensity and high frequency (LIHF), high intensity and high frequency (HIHF), or the end of the growing season (deferred control), combined with water treatments of ambient rainfall or water addition. The study was repeated in a drier upland and mesic lowland range site. Yield was assessed as annual accumulated herbage production and, for HILF and control treatments in 2012 (year 3), evaluated separately for forbs and major graminoids. Temporal changes in the proportional yield during the growing season were also examined for the HILF and HIHF treatments. Moisture addition increased accumulated herbage, especially in the upland, and exacerbated differences among defoliation effects in select years. Productivity was greatest in the deferred controls, suggesting no treatment led to overcompensation, even with moisture addition. Among growing season treatments, yields under HILF exceeded that of the HIHF in 6 of 10 different combinations of site and year, particularly early in the study and under high moisture. Observed herbage yields suggest deferred patches of grassland may boost productivity and limit the ability of HILF defoliation to increase production, a pattern magnified by a reduction in Pascopyrum smithii in lowlands before mid-July. Accumulated herbage yield did respond favorably to HILF defoliation in uplands due to increased yields of Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths. Overall, these results suggest that any growing season defoliation reduces yields, although where defoliation is necessary at that time, production may be more likely to be maintained under HILF defoliation. More studies examining long-term growth responses to defoliation that include variation in vegetation types, environmental conditions, and defoliation regime are warranted.

Conversion of native grassland to other agricultural land uses can alter soil properties such as organic matter, but little is known about how this impacts soil physical quality indicators in the mixedgrass and aspen parkland natural subregions of the Canadian prairies. This study evaluated soil physical properties in three land use systems (native grasslands, introduced pastures and annual croplands) at seven sites across south-central Alberta, Canada. Hydraulic conductivity (K), pore size fractions and S-index were derived from moisture retention curves measured using a HYPROP system. Fractal aggregation was determined from the mass-diameter relationship of soil aggregates (0.25–8 cm diameter) using 3D laser scanning. All our results, except for K, showed a consistent trend of soil quality differences in the following ranking: native grassland > introduced pasture > annual cropland. Relative to croplands, introduced pastures led to an increase from 9 to 12% in medium-size pores (as median volume fraction of 9–50 μm diameter), whereas this pore fraction in native grassland was 19% (Ps

Grazing lands provide many goods and ecosystem services, such as forage, livestock, soil carbon (C) storage, biodiversity, and recreational opportunities. Ensuring the long-term sustainability of grazing lands requires optimal management to simultaneously balance livestock productivity for sustaining human food and nutritional demands while reducing environmental impacts, such as greenhouse gases (GHG) emissions and soil degradation. In this paper, we revisit grazing management in grazing lands exposed to different grazing systems. In Section 2, we briefly review parameterization and multi-faceted goals for sustainability of grazing systems considering broader sustainability from economic to environmental aspects. We also discuss the inconsistencies between grazing researchers and ranchers’ practices. In Section 3, we review the separate experimental data to examine the impacts of multi-paddock rotational grazing on soil carbon, nutrient and GHGs. In Section 4, we present status and upcoming challenges in monitoring and upscaling of grazing ecosystem research and management. In Section 5, new concepts of multiple source monitoring networks are presented that enable the analysis of scale-dependent processes. Finally, we point out future directions for monitoring and assessment of managing soil C and GHG emissions from grazing lands. The results show that the inconsistences are essentially due to (1) effects of spatiotemporal scales on both economic and ecological outcomes, and (2) simplistic representations of multi-faceted grazing systems and sustainability. The development of multi-faceted monitoring systems needs to be further parametrized and standardized to make consistent for meaningful and comparable assessment of grazing management impacts on SOC and GHGs.

Boreal forests are increasingly exposed to industrial well site development. Little information exists on the optimal construction and reclamation strategies needed for vegetation recovery, including methods of well site preparation, soil storage, woody debris management, and revegetation. In this study we examined intermediate-term (10 yr) recovery of vegetation on 33 well sites distributed across NE Alberta, Canada, constructed and reclaimed using different site preparation methods, including high (HD), intermediate (ID), and low intensity (LD) disturbance of surface soils. Comparisons also included soil piling methods on HD sites, debris management on ID and LD sites, and tree planting on all sites. Comparisons were made to adjacent uncut forest to assess similarity, and at a subset of locations to harvested clear cuts. Ten years into recovery, vegetation was most similar between uncut forest and well sites developed using LD construction methods in species richness, diversity, and cover of vegetation growth forms and ground cover components (bare soil, litter, moss and lichen). Well sites using HD and ID had vegetation more dissimilar to uncut forest. Clear cuts harvested at the same time as the well sites also differed in composition from the forested controls, but remained more similar to the LD well sites than the HD and ID well sites. Effects of reforestation (tree planting), the technique of soil piling, and different forms of woody debris management (spreading vs windrowing) had little impact on vegetation recovery. Overall results highlight the importance of using LD well site preparation techniques where possible to keep mineral soil and embedded plant propagules intact to maximize boreal forest recovery following disturbance.

Extracellular enzymes are the proximate drivers of biogeochemical cycling in ecosystems. In terrestrial environments, studies of extracellular enzyme activities (EEAs) in soils far outpace studies in substrates such as leaf litter. Despite recent methodological advances that have made EEA assays feasible for researchers conducting large-scale studies, there are still a number of methodological uncertainties that exist, particularly when working with less studied substrates (i.e. grassland leaf litter). These uncertainties are of particular importance when considering the logistics of sample processing after collecting samples in large numbers and/or from distant field sites. Studies of soil handling suggest that while assaying biochemical and molecular markers in fresh samples is ideal, that freezing samples is often a viable solution if the former is not feasible. Due to the inherent differences of litter and soil materials and associated microenvironments, we can draw only limited conclusions from the results of studies on sample handling using soil. As a result, we investigated the effect of two typical freezing temperatures (−20° and −80 °C) on subsequent EEAs in decomposing leaf litter material. We incubated litter material from six grassland plant communities for 12 weeks at 25 °C, then measured the EEA of five hydrolytic and two oxidative enzymes in fresh litter, and in litter that was frozen for four weeks at either −20° or −80 °C. Results indicate that freezing only affected the activity of N-acetyl-β glucosaminidase (NAG), an enzyme that was affected by freezing in prior soil studies. We observed an approximate 35% increase in NAG activity with freezing. The remaining six EEAs measured were not observed to be affected by freezing, and the level of freezing (i.e. temperature) did not influence any of the seven EEAs measured, suggesting that freezing is a suitable alternative when laboratory analyses on fresh litter samples are not logistically possible.

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 89 kg CO2 ha− 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 (76 kg CO2 ha− 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.

Grassland composition is affected by livestock grazing and moisture availability, yet little is known about how defoliation and soil moisture interact to affect belowground processes. In particular, microbial activity, the proximate driver of decomposition, may be affected by plant responses and environmental variability. We hypothesize that grassland soils with different defoliation and moisture treatments will differ in soil biogeochemical cycling in response to both physical environment (i.e. soil moisture) and biotic (i.e. plant community) shifts. To understand how microbial function is affected by defoliation and moisture, we measured extracellular enzyme activity (EEA) at two mixed grass prairie ecosites (mesic lowland and xeric upland) in Alberta, Canada using a fully factorial experiment that manipulated growing season defoliation and water addition over 4 years. The defoliation treatments were: high intensity – high frequency (HIHF), high intensity − low frequency (HILF), or low intensity – high frequency (LIHF) from May through August each year, and a treatment where defoliation was deferred until the end of each summer. The watering treatments were: ambient and water addition (150 mm month−1 above ambient), which was intended to eliminate moisture limitations. In the fourth year of treatment, we measured the activities of 5 hydrolytic extracellular enzymes responsible for carbon (C), nitrogen (N) and phosphorous (P) release. We observed that water addition reduced activity of most EEAs across both sites, although these effects were distinctly mitigated by defoliation at the lowland site. Within the lowland, water addition reduced C cycling enzyme activities under deferred and HILF defoliation, with a similar pattern in the activity of the P cycling enzyme in response to HILF and LIHF defoliation. Defoliation effects on EEA in the lowland were limited largely to ambient moisture conditions, where severe (HIHF) defoliation reduced C cycling EEA, with a similar pattern in the upland, though only for β- d -cellobiosidase activity. Independent of moisture treatment, deferred defoliation reduced activity of phosphatase in the lowland, as well as the activity of one enzyme responsible for C cycling in the upland site. There was no effect of defoliation or water addition on N-acetyl-β glucosaminidase activity at either site. Overall, we demonstrate that while EEAs are strongly affected by environmental conditions, defoliation during the growing season may interact with the physical environment and regulate biogeochemical cycling.

Little is known about how defoliation intensity and frequency alter plant community composition and diversity in northern Great Plains mixedgrass communities. We evaluated defoliation effects in combination with watering on vascular plant composition and diversity in two contrasting ecological sites, a drier upland and more mesic lowland, in the Dry Mixedgrass natural subregion of Alberta, Canada. Treatments were applied for three growing seasons (2010 through 2012, inclusive) and included defoliation regimes of high intensity at high frequency, high intensity at low frequency, low intensity at high frequency, and defoliation deferred until the end of the growing season. Moisture regimes were ambient and elevated. Defoliation rather than moisture was the primary determinant of plant composition after 3 yr, particularly in the lowland site. Watering effects on composition were more apparent in the drier upland. All growing season defoliation regimes markedly altered composition relative to the deferred control, with relatively minor differences in composition among growing season defoliation treatments, particularly in the mesic lowland site. We conclude that growing season defoliation alters mixedgrass composition by reducing canopy dominant grasses (Pascopyrum smithii and Hesperostipa comata) and releasing shorter-statured grasses and forbs, which can either increase or decrease diversity depending on site (edaphic) conditions and the relative dominance of midgrasses and shortgrasses (Koeleria macrantha and Bouteloua gracilis). Finally, increased moisture did not ameliorate defoliation effects during the growing season, suggesting compositional responses were predictable and independent of growing season defoliation regime.

Hybrid poplar plantations have the potential to produce a large amount of biomass for the forest industry; however, competition for resources by neighbouring vegetation can severely reduce that potential. Intensive vegetation control of all neighbouring vegetation is potentially costly and an inefficient use of limited resources, thus identifying the characteristics of competing vegetation most detrimental to tree growth is essential for optimizing plantation inputs and yields. Our objectives were to model tree growth losses as a function of neighbouring vegetation composition, abundance, and spatial proximity. We then tested different vegetation control treatments for their effectiveness with different neighbouring vegetation. Field work took place on four operational plantation sites in northeastern Alberta over the course of three years, and commenced at the beginning of the second growing season after plantation establishment. Regression tree and Nonmetric Multidimensional Scaling (NMDS) analyses indicated that perennial grasses in general, and Elytrigia repens in particular, were detrimental to hybrid poplar growth – especially for younger trees. Planting site also played a large role in determining tree productivity, although it is difficult to quantify its influence relative to competition because site and vegetation community differed among sites. Increasing intensity of vegetation control treatments did not increase tree survival rates in any of the sites, but did result in commensurate increases in tree growth on most sites. Intensive vegetation control with herbicides dramatically increased tree growth on sites containing populations of perennial grasses. Using only cultivation as a form of vegetation control was the least effective option, and was ineffective for control of perennial grasses compared to other treatments. These results suggest that control of perennial grasses by means of herbicides over the other forms of competition control tested will have the greatest impact on reducing losses in tree growth due to competition.

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.

Relationships among vegetation components in perennial pastures are complex, particularly those including grasses, weeds, legumes, and other forbs. Where herbicides are used for broadleaf weed control, a trade-off may exist between the benefits of weed removal and legume loss. Few studies have separated the contribution of different vegetation components to total forage yield, either prior to or after spraying. Herein we use Structural Equation Modelling (SEM) to quantify relationships among grasses, legumes (Medicago sativa L. or Trifolium spp.), a common noxious weed (Cirsium arvense (L.) Scop), and other forbs, at two locations within the Parkland region of central Alberta, Canada. After removal of broadleaf vegetation with herbicide, we quantified changes in forage relative yield ratio (RYR) for two years. The SEM approach revealed marked differences in the relationships among sward components between sites. At the more mesic site, abundant thistle biomass had little influence on other sward components and no benefit was observed post-spraying from weed removal. In contrast, even low levels of thistle biomass suppressed grass and legume biomass at the more xeric location, and post-spraying responses revealed benefits from weed removal. Unexpectedly, legumes were found to suppress grass biomass at both sites, suggesting strong interspecific competition between forage types. Subsequent removal of legumes appeared to release grass biomass from competition within sprayed plots, as exemplified by increased forage yields two years after spraying. These results highlight the complexity within temperate perennial pastures, and add clarification to the potential short-term impacts of weeds and legumes to overall sward dynamics and forage production.

Agroforestry systems are common land uses across Canada and could play a substantial role in sequestering carbon (C) as part of efforts to combat climate change. We studied the impact of component land cover types (forested vs. adjacent herbland) in three agroforestry systems (hedgerow, shelterbelt and silvopasture) on organic C and nitrogen (N) distribution in three density fractions of soils at the 0–10 and 10–30 cm layers. The study evaluated 36 sites (12 hedgerows, 12 shelterbelts and 12 silvopastures) in central Alberta, Canada, distributed along a soil/climate gradient of increasing moisture availability. At the 0–10 cm layer, soil organic C (SOC) stock in the bulk soil was significantly greater in the silvopasture system (101) than in either the hedgerow (77) or shelterbelt system (67 Mg C ha−1). Soil organic C stock in both soil layers (0–10 and 10–30 cm) was also significantly greater in the forested land cover (89 and 119 Mg C ha−1, respectively) than in adjacent herblands (76 and 77 Mg C ha−1). Across all sites, 31.5, 29.1, and 35.5% of SOC was found in the light fraction ( 1.6 g cm−3) of soils, respectively. The largest pool of SOC in the more labile light fraction of the 0–10 cm layer was in the silvopasture system (50 Mg C ha−1), whereas the smallest labile light fraction component of SOC was in the shelterbelt system (17 Mg C ha−1). The largest pool of SOC in the more stable heavy fraction of both the 0–10 and 10–30 cm depth classes was in the shelterbelt (33 and 35 Mg C ha−1, respectively), while the least SOC was in the silvopasture system (26 and 20 Mg C ha−1, respectively). We conclude that the presence of Populus based silvopasture system can increase C storage in surface mineral soils, and that the establishment of Picea based shelterbelts in an otherwise annually cropped agricultural landscape enhances the size of the stable SOC pool.

On the Ground Variability in spatial and temporal patterns of herbage production is common in grasslands and can affect land uses, such as grazing. Total herbage biomass in northern mixed grass prairie was similar on loamy and sand dune ecologic sites but varied in composition. Cool-season grasses were uniformly produced throughout the grazing season, whereas warm-season grasses grew rapidly during August. Litter conservation was important for increasing cool-season grass biomass, whereas warm-season grasses remained independent of litter. Biomass and composition of herbage in the northern mixed grass varies spatially and intra-annually, affecting seasonal grazing opportunities for livestock.

Grasslands cover more than 25% of the terrestrial surface of the Earth and hold 30% of the world’s terrestrial carbon (C) pool. While nearly all native grassland ecosystems are used for livestock production, sustainably managed grasslands also provide many ecosystem goods and services such as C storage. Despite the importance of grasslands to the global C cycle, little is known about how long-term management practices, including the presence or absence of grazing, directly and indirectly affect the soil microbial processes that regulate C and nutrient cycling. We measured the effect of long-term cattle grazing on microbial extra cellular enzyme activity (EEA) at 12 locations stratified among three distinct grassland types (foothills fescue, aspen parkland, and mixed grass prairie) across Alberta, Canada. Each location included paired grazed and non-grazed plant communities managed this way for at least 30 years. Specifically, we quantified EEA of enzymes responsible for C (β-1,4-glucosidase, β- d -cellobiosidase, β-xylosidase), C and nitrogen ( N -actyl-glucosaminidase), and phosphorous (phosphatase) cycling in soil from 0 to 15 and 15–30 cm depths. Although grazing effects on EEA remained weak (0.05 ≤ p ≤ 0.10) they were relatively consistent among enzymes ( n = 3/5), with β- d -cellobiosidase, N -actyl-glucosaminidase, and phosphatase EEAs all greater in non-grazed plant communities than in grazed communities. All EEAs were greater in the foothills fescue and mixed grass regions than in the parkland with the exception of β-1,4-glucosidase, which was relatively high at all locations. Multivariate analyses suggested the soil properties that best describe EEA are soil pH, organic matter and moisture content, together with total nitrogen (N). Additionally, EEAs were correlated with the cover of several dominant plant species. Four of five EEAs were positively correlated with the grass Festuca campestris , while N and C degrading enzymes were negatively correlated with the grasses Bouteloua gracilis and Koeleria macrantha , respectively. Net C cycling appears to be strongly controlled by β-1,4-glucosidase. In conclusion, grazing and associated changes in plant communities appear to decrease the EEAs of some enzymes, suggesting that microbes in non-grazed communities are actively decomposing a relatively greater amount of organic matter. However, when working across broad spatial ranges, our marginally significant results and post-hoc power analysis suggest the need for larger sample sizes (>23 replicates) to further elucidate relationships between EEAs and low intensity disturbances such as cattle grazing.

Significant areas of the mixedgrass prairie (MGP) in Alberta have experienced heavy equipment traffic due to industrial infrastructure development, which may change edaphic conditions that influence soil microbial communities. Direct wheeled traffic effects may be alleviated by using access mats that spread traffic impacts over a larger area; however, no scientific assessments of access mat efficacy have been conducted on soil microbial responses. Our objectives were to assess soil properties and the diversity, community structure, and size of soil microbial communities, as impacted by wheeled traffic occurring with and without access mat use on grassland. Two representative sites with differing soil texture (sandy versus loamy) were selected from a set of MGP sites established at the University of Alberta Mattheis Research Ranch in SE Alberta, Canada. Treatments at each site included non-disturbed vegetation controls, areas affected by direct traffic, and grassland with access mats placed for 12 weeks with traffic applied. Soil was sampled in July 2015 (immediately after access mat/traffic treatments ended) and in 2016 (12 months after access mat/traffic treatments) from both sites. Soil DNA was extracted and used to target N-cycling genes via qPCR and for next-generation sequencing (Illumina Miseq) of bacterial, archaeal, and fungal communities. Direct wheeled traffic without access matting increased the size of the N2O-reducing community in the sandy soil and conversely deceased the size of this community in the loamy soil. Non-metric multidimensional scaling, perMANOVA, and indicator species analyses indicated a large effect of traffic without access mat use on fungal community structure, as well as distinct bacterial and fungal indicator OTUs associated with disturbed soils compared to control soils. Fungal community structure remained affected by traffic impacts 12 months later, highlighting the extended impacts of traffic on fungal communities. Access matting mitigated some of the impacts direct traffic had on fungal community structure, but in the loamy site increased soil N and decreased the size of the N2O-reducing bacterial community. The latter indicates that ecosystem functioning of these grasslands may not only be impacted by direct wheeled traffic but also by using matting as a mitigation technique.

Agroforestry land-use systems have significant potential for increasing soil carbon (C) storage and mitigating increases in atmospheric greenhouse gas (GHG) concentrations. We studied the impact of three agroforestry systems (hedgerow, shelterbelt, and silvopasture) on soil organic C (SOC) and nitrogen (N) in the 0–10 cm mineral layer, by comparing SOC and N distributions in whole soils and three particle-size fractions (

Logging of aspen (Populus tremuloides Michx.) forests on public grazing land in west central Alberta creates a mosaic of habitat types that may alter cattle (Bos taurus) use of these landscapes. We used an extensive network of field plots and global positioning system (GPS) collars deployed on cattle within four experimental pastures, each containing a mix of uncut forest, clear cut forest, partially harvested areas, and in-block haul roads, to examine habitat preferences during mid-summer grazing in 2008 and 2009. We also examined the effect of two cattle stocking rates the first year. Although cattle removed similar amounts of forage in all habitats, GPS data indicated cattle spent more time in uncut forests, and avoided clear cuts and in-block haul roads during both years, patterns that remained consistent under either livestock stocking rate tested. Observed patterns of habitat use were attributed to conservative cattle stocking rates consistent with or greater than those allocated on publicly grazed forest land in Alberta, combined with specific habitat attributes. Preferred use of uncut forest was attributed in part to favorable forage quality, which was positively associated with cattle utilization (standardized β = +0.13) among plots. Although forage use by cattle of plots also increased with forage biomass (β = +0.33), sharp increases in biomass following clear cut logging appeared to be offset by reductions in forage use associated with increased slash cover (β = −0.12) and sapling density (β = −0.11), both of which may have impeded cattle access. As a result, forage removal remained similar among habitats. Finally, cattle use of forage decreased with increasing distance from water (β = −0.22), highlighting the importance of ensuring reliable access to water across forested pastures to prevent localized overuse. Overall, the reduced time cattle spent in clear cut habitats coupled with similar forage removal suggests that under low cattle stocking rates, grazing can be compatible with deciduous forest management in the region.

Little is known about habitat selection by free-ranging feral horses in Montane environments, including how horse use may vary seasonally throughout the year. We tracked four global positioning system collared horses in four separate harems between November 2008 and October 2010 for a portion of the Rocky Mountain Forest Reserve in southwest Alberta, Canada. We assessed seasonal habitat selection for the study period by combining locational data with landscape data (including vegetation types) in an information theoretic framework. Home ranges for horses varied from 12.4 to 90 km2 and were confined to local watersheds. Horses selected most for lowland grasslands across all seasons, with shrublands increasingly selected in spring and summer. Harvested conifer forests were only selected by horses during winter. Resource selection functions indicated that in addition to vegetation type, horses were selecting for a variety of habitat characteristics (i.e., distance to forest and solar radiation), while water availability, topographic accessibility, and disturbance features (e.g., distance to roads, recreational trails, and seismic lines associated with energy exploration) had little or no influence on horse selection. Overall, horses demonstrated selection for habitats covering 14% of the study area while avoiding 42% of habitats: remaining areas were used in proportion to their availability. Concentration of horse use within sparse vegetation types (grassland and shrubland), particularly during one or more times of the year, help identify critical horse habitat including areas where multiple, overlapping land uses interact on public land.

The integration of multiple uses on public rangeland requires reliable information on patterns of livestock use. We used GPS data and field plot utilization indices to examine cattle selection at the landscape and patch levels, respectively, within a heterogeneous Montane environment of SW Alberta, Canada. We also evaluated factors associated with patterns of summer cattle use, including topographic features, distance to water and roads, as well as forage quantity and quality. Cattle preferred lowland and upland grasslands, while avoiding conifer forests and clear cuts. Selection patterns differed markedly between the landscape and plot scales. At the landscape scale, forage use was related to abiotic factors, primarily slope ( β = −0.70) but also distance to water (−0.34) and distance from roads (+0.21). The negative impact of slope was greater than that observed in previous studies, and has implications for identifying primary ranges and deriving sustainable carrying capacities in Montane landscapes. At the plot (feeding patch) scale, forage use was additionally related to biomass availability ( β = +0.58), and to a lesser extent crude protein concentration (+0.16), highlighting the importance of forage characteristics in regulating cattle use. Lowland grasslands had the highest biomass and received the greatest forage use (43% utilization). Low visitation (44% of plots) and associated forage use (3% herbage utilization) by cattle within cut blocks, combined with conservative forage use across all habitats (3–43%), indicate grazing by cattle is consistent with maintaining other uses within this area, including riparian function, native grassland conservation and forest management.

Grazing by large herbivores has been shown to condition vegetation in a manner that improves grassland quality for subsequent herbivory. Fescue grasslands evolved with disturbance from fire and winter grazing by bison but are now grazed primarily by cattle during summer. We examined the effect of long-term summer grazing on the seasonal forage production and quality of fescue grasslands in an examination of the hypothesis that long-term grazing had conditioned fescue grasslands to benefit livestock. This hypothesis was examined by comparing, between grazed and ungrazed plots, the biomass and composition of herbage components, concentrations of nitrogen (N) and acid detergent fiber (ADF) therein, and the ability of major plant types to maintain their biomass and quality throughout the growing season. The study was conducted in southern Alberta at five sites that had long-term exclosures (20+ yr) on grasslands that had been moderately grazed. Grazing had no effect on the N concentration of associated grasses, but grasses had lower N concentration than forbs. Concentrations of ADF followed a reciprocal trend to N. Grazing increased the mass of forbs from about 10% to 20% as a proportion of total biomass, which in turn, was not affected by grazing history. However, this grazing-induced shift to a higher quality vegetation type was not sufficient to affect total mass of N or total digestible nutrients at the community level. Rather than changes in current growth and quality, the predominant effect of summer grazing was in reducing litter mass, which also had the potential for affecting forage production and selection by herbivores. Finally, grazing reduced the relative contribution of rough fescue to total biomass by about 30%, and despite no significant effect on the potential to support summer grazing, this change could reduce the quality of these grasslands for winter grazing.

Interest in native species is growing across the tropics as reforestation of degraded lands becomes more widespread. In this study four tree species native to Panama – Cedrela odorata , Pachira quinata , Samanea saman , and Tabebuia rosea – were grown on rural farms at two dry tropical sites in Panama for up to five years. Survivorship and growth data at these “on-farm” trials are compared to data recorded from nearby experimental or “species selection” trial sites and evaluated in terms of soil fertility and management. Participant farmers were also asked about their interest in planting trees in general as well as their interest in 61 species grown in the species selection trial. Although, on-farm survivorship was variable and generally lower than that found on the species selection trial, one species ( S. saman ) experienced high and consistent survivorship. High survivorship combined with growth data from farms at both sites for this species suggests it would be a good candidate for extension projects working with rural farmers. Survivorship of other species appears more sensitive to farmer management and/or local site conditions. Generally lower growth on the Los Santos farms as compared to the species-selection trial is attributed to the lower soil fertility (plant available P) at the on-farm sites compared to the species selection trial. In contrast, only one species – P. quinata – had a growth variable found to be significantly lower between the on-farm and species selection trial sites in Rio Hato. C. odorata , P. quinata T. rosea can all be used in on-farm conditions with consideration to specific site and management conditions. By 2009, approximately 80% of the farmers planting trees still wished to participate in tree planting activities. All of the farmers no longer wishing to continue with the project expressed slow growth rates of trees as a principal reason. All but one of these farmers had growth rates for his/her trees markedly below those of the species selection trial nearby. Some farmers wishing to continue had very high mortality rates (>70% for all species), suggesting non-tangible benefits for participating in project activities. Other species that were not tested on-farm but grew well in the species-selection trials and were of interest to local farmers are discussed. As long as specific site and management conditions are carefully considered, data from species selection trials can be useful in informing tree planting projects with rural farmers; however, care should be taken to manage expectations.

Little is known of the effect of selective plant defoliation at different intensities and frequencies in altering weed-forage dynamics in pasture. We conducted a field experiment to quantify Cirsium arvense responses to varying defoliation regimes of neighboring forage implemented for 2 years under high or low fertility conditions. Defoliation regimes were based on common grazing systems, and included: (1) high intensity–high frequency (HIHF) defoliation simulating continuous grazing, (2) high intensity–low frequency (HILF), (3) low intensity–high frequency (LIHF), and (4) deferred (DEF) defoliation to peak growth in late summer. All vegetation except C. arvense was defoliated during the growing season to examine weed responses to changes in neighboring forage abundance. Year-end C. arvense biomass at the end of the study was greatest in the HIHF treatment and lowest in the DEF, with the LIHF and HILF treatments intermediate in response. The HILF treatment also provided improved suppression of C. arvense biomass relative to the LIHF, although this response was inconsistent among sites. Trends in C. arvense shoot densities among defoliation treatments were similar to those for biomass. While weed abundance was lower in the absence of fertilization, rankings among defoliation treatments remained the same. Notably, trends in forage biomass among defoliation regimes followed a pattern opposite that of C. arvense , and are implicated in observed weed decreases. Our results indicate that defoliation regimes enhancing forage growth and biomass, particularly a DEF or HILF regime, reduce C. arvense the most. Grazing systems that employ these defoliation regimes are therefore likely to optimize the interspecific competitive suppression of C. arvense .

Soil moisture can limit plant production in cool-temperate grasslands, particularly under recent increases in drought severity and predictions of future climate change. This necessitates research that examines moisture mitigation strategies under the dominant land use of grazing. We examined the effectiveness of plant litter in regulating soil moisture dynamics and associated plant production in a native grassland and tame pasture in the Aspen Parkland of Alberta, Canada during 2007/2008, specifically testing (1) how litter and defoliation (as a surrogate for grazing) alter the micro-environment at the soil surface, (2) whether litter, in combination with defoliation, alters forage production, and (3) whether production changes can be linked to observed micro-environmental changes created by litter modification. The full factorial randomized complete block design consisted of three litter treatments (litter removal, in situ control, and double litter) and three defoliation treatments (undefoliated control, light defoliation to 6.5 cm stubble height, and heavy defoliation to 2.5 cm). Soil moisture levels were assessed over four periods after summer precipitation to examine soil moisture depletion. Plant phenological development and canopy cover were also assessed throughout 2007, and biomass was measured in August 2007 and 2008. Abundant litter (up to 14,000 kg ha−1) improved soil moisture levels in both native and tame grasslands by either maintaining higher absolute moisture levels or reducing total moisture loss after rainfall. Both litter removal and double litter reduced total growing season production compared to in situ levels at the Native Site, despite highest vegetation cover in litter removal plots. High litter levels also improved growth of individual grass tillers at this site, but negatively impacted sexual production. Conversely litter removal improved overall production at the Tame Site, although litter did enhance grass tiller recovery following mid-season defoliation at both sites, in part due to positive influences on soil moisture. Treatment effects on plant production were less pronounced in 2008 than in 2007. Overall, high litter levels improve soil moisture retention and can improve or stabilize plant production particularly in native prairie sites, and can provide an important drought management strategy in the Aspen Parkland.

This study evaluated the impact of shrub encroachment within cool-season floodplain meadows in a portion of the Rocky Mountain Forest Reserve in southwestern Alberta, where nearly half of open grasslands have been lost since 1958. Sample transects situated in meadows, known formerly to be in open grassland, were assessed in 2001 ( n = 21) and 2002 ( n = 33) in areas ranging from 0% to 92% shrub cover. Shrub cover, density, and height were correlated to understory parameters, including herbaceous production, bunchgrass cover and density, and species richness and diversity. Additional data on soil horizon depths were obtained. Analysis was conducted using regression to assess empirical relationships between understory or soil characteristics and the overstory. Stronger empirical relationships (i.e., greater R 2 ) were found in 2002, coincident with larger sample sizes and greater rainfall. Among independent overstory variables, aggregate shrub cover for all species accounted for the greatest variation in understory characteristics. Significant ( P –1 in meadows containing less than 12% shrub cover, to 2 797 kg · ha –1 in areas where shrub cover exceeded 35%. Negative linear trends were found ( P

This study compared the suitability of LIDAR (LIght Detection And Ranging) data, three-band multispectral data, and LIDAR data integrated with multispectral information, for classifying spatially complex vegetation in the Aspen Parkland of western Canada. Classifications were performed for both a) general vegetation classes limited to three major formations of deciduous forest, shrubland and grassland, and b) eight detailed vegetation classes including upland mixed prairie and fescue grasslands, closed and semi-open aspen forests, western snowberry and silverberry shrublands, and fresh and saline riparian (lowland) meadows. A Digital Elevation Model (DEM) and Surface Elevation Model (SEM) developed from LIDAR data incorporated both topographic and biological biases in community positioning across the landscape. Using multispectral data, the original digital image mosaic, its hybrid color composite, and an intensity–hue–saturation (IHS) image were each tested. Final vegetation classification was done through integration of information from both digital images and LIDAR data to evaluate the improvement in classification accuracy. Among the land cover schedules with three and eight classes of vegetation, classification from the multispectral imagery, specifically the hybrid color composite image, had the highest accuracy, peaking at 74.6% and 59.4%, respectively. In contrast, the LIDAR classification schedules led to an average classification accuracy of 64.8% and 52.3%, respectively, for the general and detailed vegetation data. Subsequent integration of the LIDAR and digital image classification schedules resulted in accuracy improvements of 16 to 20%, resulting in a superior final accuracy of 91% and 80.3%, respectively, for the three and eight classes of vegetation. A final land cover map including 8 classes of vegetation, fresh and saline water, as well as bare ground, was created for the study area with an overall accuracy of 83.9%, highlighting the benefit of integrating LIDAR and multispectral imagery for enhanced vegetation classification in heterogenous rangeland environments.

Combining two or more treatments within an integrated weed control strategy can provide benefits to crops. While several studies have examined Cirsium arvense L. Scop control in pastures, few have assessed corresponding aggregate forage responses. These responses include the tradeoff of improved grass yield due to weed reduction combined with the potential loss of desirable forbs. We evaluated the 3-year response in pasture forage yield and quality in central Alberta, Canada, to one-time mowing or herbicides (2,4-D ester, 2,4-D+mecoprop+dicamba, clopyralid, or picloram+2,4-D) applied at the early bud stage of C. arvense growth, both with and without annual spring fertilization, at 4 locations. Forage (grass and non-thistle forb) dry matter yield and quality (crude protein concentration and yield, phosphorus, and acid detergent fiber) were determined. Herbicide treatment increased grass yields during the second year in response to reduced weed competition, with these increases consistent in relative magnitude regardless of fertilization. In contrast, herbicides reduced non-thistle forbs, including legumes. Where herbicides were combined with fertilization, grass yield and quality increased, but was partly offset by a decline in forb yield and associated quality. When combined with fertilization, picloram+2,4-D at 0.24+0.89 kg a.i. ha−1 nearly eliminated legumes by the second year. While the loss of desirable forbs is likely to be offset by improved grass yields following weed control in forage swards containing only a minor forb component, this was less likely in swards containing abundant forbs. In this latter situation, alternative weed control strategies may be necessary to maintain forage yield and quality.

Integrated weed management combines treatments for improved weed control. Few studies have compared integrated approaches for longer-term control of Cirsium arvense in pasture. We evaluated the response of this weed in perennial pasture to one-time mowing or herbicide application (2,4- d ester, 2,4- d +mecoprop+dicamba, clopyralid, or picloram+2,4- d ) at the early bud stage of growth, both with and without annual spring fertilization over a 3-year period in central Alberta, Canada. Regardless of fertilization, all herbicide treatments suppressed Cirsium arvense in the year of treatment. Fertilization without control measures decreased Cirsium arvense density but increased biomass, while a one-time mowing treatment increased shoot densities. Although all herbicide treatments tended to reduce Cirsium arvense into the second and third year, picloram+2,4- d at 0.24+0.89 kg ai/ha and clopyralid at 0.22 kg ai/ha provided the greatest weed suppression, particularly when fertilized annually. Overall, longer-term control of Cirsium arvense by herbicides was enhanced with annual spring fertilization, underscoring the importance of an integrated approach to controlling Cirsium arvense in temperate pastures.

We developed a computer model (PASTURE) to simulate both condition of pastures grazed by farmed wildlife and animal performance as dual measures of system performance. For representative habitat types (e.g., aspen forest and open grasslands), the model simulates herbage growth, maturation and senescence, habitat and diet selection, and nutrient intake of several wild ruminant species. The model generated seasonal patterns of pasture productivity and animal behavior expected for Bromus-Poa pastures in aspen boreal ecosystems. Model calibration was conducted using data collected from studies conducted within the aspen boreal ecosystems at the Ministik Research Station in 1997 and 1998, and Elk Island National Park and the University of Alberta greenhouse in 1999 and parameters adjusted until the predicted and observed results were visibly close. Evaluation of the model was conducted using statistical criteria of calculating average error, root mean square, root mean square error, coefficient of residual mass and modeling efficiency and comparing these statistics against optimal values. Statistical tests indicated a good fit between predicted and observed values for cumulative phytomass, herbage use and animal performance.

Effects of aspen (Populus tremuloides Michx.) canopy removal and root trenching on understory vegetation were examined at Parkland and Boreal sites in Alberta, Canada to provide a better understanding of the ecological basis of agroforestry systems suitable for north temperate and boreal areas. The greatest changes in understory production (ANPP) were in response to canopy removal with less consistent changes from reduction of root effects. Root trenching did not influence ANPP at the parkland site, but did at the boreal site where it interacted with canopy removal. During severe drought, ANPP under a full canopy at the parkland site increased and may relate to paradoxical understory resource increases during drought. At the parkland site there was a shift away from forb and shrub production under a full canopy towards a greater proportion of graminoids with complete or partial canopy removal. At the boreal site, partial canopy removal resulted in more shrubs and greater production from graminoid species relative to complete overstory removal but only with root trenching using a barrier. Trends in the relative yields of understory species and the cover of plant groups generally followed the patterns observed in ANPP. Leaf litter decreased with the level of canopy removal and may have factored in greater moisture conservation under aspen. Understory production gains with a partial canopy may be attributed to favourable microclimatic conditions of a closed forest retained by the partial aspen cover, while simultaneously increasing PAR penetration. Soil resources were important to ANPP and cover, particularly among forbs, however, when root trenching was significant, it generally coincided with increases in PAR.

Extensive research exists on the eVects of Canada thistle [Cirsium arvense (L.) Scop.] (CT) in annual cropland, but few studies have examined CT impacts on pasture and rangeland. While it is known that grazing impacts weed presence and abundance, little is understood about how speciWc grazing systems can be used as a prescriptive tool to alter weed populations, including CT. The purpose of this study was to experimentally test three cattle grazing systems, including (1) continuous or season-long grazing (SL), (2) short duration (SD) (or low intensity-high frequency) rotational grazing, and (3) high intensity-low frequency (HILF) rotational grazing, for their ability to reduce CT and release non-CT herbage within permanent pastures of central Alberta, Canada. A secondary objective was to evaluate season-long changes in the quality of CT shoots as potential forage throughout the growing season. Results showed that SL grazing maintained or increased severe CT infestations and reduced forage yield. In contrast, the HILF rotational system reduced CT shoot density and biomass, as well as Xowering, and resulted in greater weed suppression than the SD system. Two intense defoliations annually over 2–3 years nearly eliminated CT stems. Remaining CT shoots were also primarily vegetative and greater in forage quality under HILF grazing. As a weed biological control tool for CT, prescribed grazing with an HILF system may be particularly important in areas where other control options, including the use of herbicides, are not possible due to environmental restrictions or inaccessibility to equipment.

Fescue grasslands are well suited to dormant-season grazing, whereas spring defoliation is detrimental to rough fescue (Festuca campestris Rydb.). Dormant-season grazing may also condition fescue plants for subsequent selection in spring by removing standing litter (i.e., senesced biomass). This relationship must be understood in order to manage grazing and conserve rough fescue. This study determined the effects of standing litter on plant selection and utilization by cattle in spring. Forty dormant rough fescue plants were conditioned in fall by removing standing litter in a 4 (treatments) 3 10 (blocks) randomized complete block design. This design was repeated with the use of 2 separately grazed paddocks. Treatments were a control (no litter removal) and standing litter removed at 14-, 7-, and 2.5-cm stubble height. Nonparametric plant selection data were analyzed with the use of v 2 methods. Spring biomass utilization was estimated nondestructively through height–weight modeling techniques, and data were analyzed with the use of analysis-of-variance procedures. The stubble height of standing litter affected (P , 0.05) plant selection by cattle in the first 2 days of the trial when grazing pressure was light. By the end of the 6-d grazing period 96% of fescue plants were selected at least once. Additionally, 18% of plants were regrazed at least once after 3 days, and 48% after 6 days. Thus, the protective barrier effect of standing litter had limited effect on plant selection by cattle except when grazing pressure was light. However, the degree of spring biomass utilization increased with shorter stubble heights. After 6 days of grazing, the current growth of plants with standing litter removed at 2.5 cm was utilized at 64%, and control plants were utilized 9%. Therefore, at high grazing pressure the mass of standing litter influenced the degree of utilization, suggesting litter retention is important in limiting grazing impacts on rough fescue.

This study evaluated a non-destructive scientific method that is non-invasive to the animal, for quantifying foraging selectivity by cattle within heterogeneous pasture swards in order to test the utility of a new grazing system designed to aid conservation of native rough fescue (Festuca campestris Rydb.) rangeland in western Canada. Skim grazing is a recently developed strategy that involves a light, once-over-spring defoliation, followed by a late to dormant season grazing period. Thispractice isthoughtto conserve roughfescue ascattle areassumed toprefer invasivegrassspecies during spring when fescue is sensitive to defoliation. We examined the preferences of cattle for each of four major grass species, two native and two introduced, within rough fescue rangeland, grazing during spring, fall, or spring and fall of 2000 and 2001. We developed height‐biomass models for each grassspecies in eachgrazing period,determined biomass removalbyspecies, and despite underestimating actual herbage removal, successfully evaluated cattle preferences. Though the interpretation of established preferences are limited to the conditions of this study, rough fescue together with the introduced species, Kentucky bluegrass (Poa pratensisL.), were preferred during spring, contrary to our hypothesis. Kentucky bluegrass was also preferred within both fall and fall regrowth pastures. Smooth brome (Bromus inermis Leyss.) and Parry oat grass (Danthonia parryii Scribn.) were generally avoided. The failure of cattle to avoid rough fescue during spring indicates skim grazing

Partitions were used to separate above- and below-ground effects of alfalfa (Medicago sativa L.) and marsh reedgrass (Calamagrostis canadensis (Michx.) Beauv.) on aspen (Populus tremuloides Michx.) seedlings. Surrounding herbaceous vegetation reduced soil water, available soil nitrates and photosynthetically active radiation. Although aspen survival was not affected, net competition was expressed with competitor biomass correlated negatively with most aspects of aspen growth. Competitive differences between herbaceous species were primarily related to individual plant sizes. Herbaceous species increased soil moisture when shoots were intermixed and root barriers were in place, but did not enhance soil moisture when below-ground effects were also present. This suggests herbaceous canopies increase soil moisture by blocking evaporation, but concomitant root uptake negates this increase. Aspen made little use of the N pool outside the immediate zone around the seedling, suggesting retention of herbaceous vegetation between trees could minimize N-leakage from the system. Thus, there may be some benefit to agroforestry systems in balancing the short-term competitive effects from herbaceous species presence against longer-term negative effects on soil fertility.