Grazing Treatments Research Articles

Linking shifts in species composition induced by grazing with root traits for phosphorus acquisition in a typical steppe in Inner Mongolia

Long-term overgrazing tends to cause soil phosphorus (P) deficiency in grasslands. The relationships between grazing-induced shifts in species composition and root traits associated with P acquisition involved in these shifts remain unknown. Species vary in their P-acquisition strategies, and we hypothesize that species that acquire P more efficiently are better adapted to overgrazing. We measured relative biomass, root physiological activities (e.g., rhizosheath acid phosphatase activity (Apase), and leaf manganese concentration ([Mn]) as a proxy for carboxylate concentrations in rhizosheath) and morphological traits (e.g., specific root length) of six common species in a field experiment conducted in a typical steppe of Inner Mongolia. There were two exclosure demonstration plots, i.e. exclosed since 1983 and 1996, and long-term free grazing without exclosure of sheep. Long-term overgrazing caused a reduction in bulk soil Olsen P concentration and increased community-weighted leaf nitrogen: P ratio by 27% and 37%, respectively, indicating more severe P limitation for steppe vegetation. Carex duriuscula exhibited an inherently greater specific root length, proportion of fine roots and rhizosheath Apase than other species did in both exclosure and grazing treatments. Cleistogenes squarrosa showed a greater leaf [Mn] induced by overgrazing. The increased dominance of C. duriuscula and C. squarrosa was positively correlated with finer roots, greater rhizosheath Apase or carboxylate release under long-term overgrazing. Species that had inefficient root traits for P acquisition (e.g., low specific root length and low leaf [Mn]), i.e. Stipa grandis, exhibited a decreased dominance in response to overgrazing. Dominance of species did not change under grazing which may be related to either relatively inefficient inherent morphological (i.e. in Artemisia frigida) or physiological traits (i.e. in Leymus chinensis and Agropyron michnoi) for P acquisition. Our study highlights the importance of acknowledging root traits involved in efficient P acquisition for theories on community succession induced by overgrazing.

Integrated crop‐livestock effects on soil carbon and nitrogen in a semiarid region

AbstractIntegrated crop−livestock (ICL) system effects on soil organic carbon (SOC) and total nitrogen (TN) are highly variable due to differences in ecoregion‐specific management practices, historical land use, and inherent climatic/edaphic attributes. Few studies have evaluated ICL system effects on SOC and TN in semiarid regions, where soil attributes change slowly. This study quantified ICL system effects on SOC and TN in a long‐term experiment near Mandan, ND. Effects of three residue management treatments (Grazed, Removed, Control) on SOC and TN were determined at five depths (0−0.08, 0.08−0.15, 0.15−0.31, 0.31−0.61, and 0.61−0.91 m) in 1999 and 2014. No‐till practices were employed throughout the study following conversion of perennial grass pastures. A significance criterion of P ≤ .10 was used to assess treatment effects as the experimental design was constrained to two replications. Residue management affected SOC and TN in near‐surface depths only, with greater concentration of SOC and TN at 0−0.08 m under Grazed compared to Removed in 2014 (P = .0844 and .0576). When expressed on an equivalent mass basis, SOC stocks were greater under Grazed and Control compared to Removed. Soil organic C and TN stocks increased over time in the Control by 11.2 Mg C ha−1 and 1.2 Mg N ha−1, respectively (P = .0728 and .0868). Soil organic C stocks also increased over time under the Grazed treatment by 10 Mg C ha−1 (P = .0630). Study results highlighted the importance of residue retention and livestock grazing for increasing SOC and TN in ICL systems under semiarid conditions.

Effects of long-term cattle market conditions on continuous season-long and rotational grazing system revenues

In this study we evaluated the combination of long-term market conditions and the price slide in the cattle market on revenues associated with continuous and rotational grazing systems. A price slide is a market phenomenon in which lighter cattle sell at a higher price per unit of liveweight compared with their heavier counterparts. We used actual herd average starting and ending weights in this market analysis, and analysed the outcome using five years’ data from a continuous and rotational comparative grazing study. Despite consistently lower weight gains with rotational grazing, differences in gross revenues per steer between grazing treatments ranged from US$43.46 to minus $5.72 across the study years. We observed annual differences in the net returns across years between the two grazing systems; net returns were greater for steers in the continuous grazing treatment in three of the five years, one year with net returns that did not differ between systems, and one year in which net returns were lower with continuous grazing. These variable results showcase the complexity in having both differences in end of grazing season weight classes between the grazing systems and the differential effects of price slide among weight classes. Therefore, we argue that it may be a better management strategy for land managers to determine the optimal ending weights and the time of year to market livestock to meet the goals of an operation, rather than trying to determine which grazing system is ‘best’.

Grazing offsets the stimulating effects of nitrogen addition on soil CH4 emissions in a meadow steppe in Northeast China.

Grazing is the most common land use type for grasslands, and grazing may alter the impacts of the predicted enhancement of nitrogen deposition on soil CH4 flux. To understand the effects of nitrogen addition, grazing, and their interactions on soil CH4 flux, we conducted a field study on CH4 flux in a meadow steppe in Northeast China from 2017 to 2018. We measured the soil CH4 flux and soil physiochemical and vegetation parameters. The studied meadow steppe soil acted as a CH4 source due to the legacy effects of an extreme rainfall event. During the experimental period, the average CH4 fluxes were 7.8 ± 1.0, 5.8 ± 0.5, 9.3 ± 0.9 and 7.6 ± 0.6 μg m-2 h-1 for the CK (control), G (grazing), N (nitrogen addition) and NG (grazing and nitrogen addition) treatments, respectively. The cumulative CH4 fluxes were 24.9 ± 2.6, 11.5 ± 4.9, 28.8 ± 4.2 and 17.8 ± 3.5 μg m-2 yr-1 for the CK, G, N and NG treatments, respectively. The N addition increased the average CH4 flux by 19%, and the grazing treatment reduced it by 25%. The soil CH4 flux was positively correlated with the 0–10 cm soil water filled pore space (P < 0.01), soil NH4+-N (P < 0.01) and soil NO3--N (P < 0.01), but negatively correlated with the 0–10 cm soil temperature (P < 0.01), except for the sampling dates that were strongly influenced by the extreme rainfall event. The average CH4 flux was significantly (P < 0.05) affected by the grazing and N addition treatments with the N addition treatment significantly (P < 0.05) increased the CH4 flux, whereas grazing significantly (P < 0.05) decreased the CH4 flux. Grazing offset the stimulating effects of N addition on CH4 flux, and there was no difference (P = 0.79) in the CH4 flux between the CK and NG plots. In summary, moderate grazing has the potential to reduce the negative impacts of N addition on CH4 flux and can increase the capacity of the soil CH4 sink in the studied meadow steppe.

Integrating cover crops with chicken grazing to improve soil nitrogen in rice fields and increase economic output

Winter fallow is important for renewing and improving soil fertility under double-cropping rice systems, such as those in southern China. Using a regenerative farming technology of integrating grass-chicken farming in a winter fallow field, we investigated soil nitrogen conversion and assessed the agricultural economic benefits of the whole farmland ecosystem. To test the effects of chicken grazing on the fallow system, we established field treatments involving adding chickens to a field planted with the cover crops, including cover milk vetch (Astragalus sinicus) with chicken grazing treatment (MC) and cover ryegrass (Lolium spp.) with chicken grazing (RC); cover crops only, including cover milk vetch (Astragalus sinicus) treatment (M) and cover ryegrass (Lolium spp.) (R); and a bare fallow field treatment (CK). We found that both cover crops (M and R) and cover crops with chicken grazing (MC and RC) increased nitrate, ammonium, dissolved organic nitrogen, and total nitrogen contents, and the increase was higher in MC and RC treatments. We also observed increased straw biomass and grain yield in the all four treatments, with more increases with chicken treatments as compared with CK. On the economic profits, MC increased by 101.72% and RC increased by 104.12% as compared with CK, while R increased by 5.19% and M reduced by 1.86% as compared with CK. The nitrogen transfer rate (the output/input ratio) of MC, RC, M, and R increased by 66.71%, 71.50%, 65.97%, and 59.97%, respectively, while the nitrogen accumulation rate (input–output) of MC, RC, M, and R increased by 480.56%, 612.98%, 356.74%, and 267.65%, respectively. Our study demonstrates that retaining nitrogen and gaining economic profit by integrating cover crops with chicken grazing is potentially more sustainable than adding cover crops alone. We further suggest that using the integrated grass-livestock farming technology can reduce environmental damage caused by commercial fertilizers.

Ants drive invertebrate community response to cattle grazing

Livestock grazing acts as a disturbance that alters ground-level habitat structure and can shape faunal communities. Invertebrate fauna have complex responses to grazing, driven by grazing-induced changes to vegetation structure, and may also be influenced by changes to predation pressure and prey availability. However, there is a dearth of knowledge about the effects of grazing on invertebrates, and research is rarely conducted across multiple orders, or at multiple trophic levels. We examined the ordinal-level response of a tropical savanna invertebrate assemblage to four replicated grazing treatments in two vegetation types at a long-term grazing trial in northern Australia. We used overall measures of abundance, order richness, and the assemblage composition (using the 17 orders we observed) to compare invertebrate communities among grazing treatments and between vegetation types. Responses of individual orders were modelled in relation to microhabitat variables. At the end of the dry season in October 2014 and 2015, we sampled 25,785 invertebrates from 17 orders. Ants accounted for over 80% of all individuals captured. We found that, overall, invertebrate abundance was higher in the most heavily grazed treatments, driven by the response of ants, but assemblage composition was not significantly different among grazing treatments. Araneae, Orthoptera, Scolopendromorpha and Scorpiones responded to vegetation type and were associated with % cover of Carissa ovata, bare ground, and grass. Ants, while responsive to grazing treatment, was not associated with any of the microhabitat variables, suggesting habitat structure in combination with other factors may be driving this response. Our results confirm the importance of ants as a sensitive biological indicator of disturbance. Considering their role in ecosystem function, invertebrates, and their responses to livestock grazing, need to be considered when making land management decisions on rangelands, and maintaining invertebrate diversity should be a priority for land managers.

Community assembly mechanisms and succession processes significantly differ among treatments during the restoration of Stipa grandis \u2013 Leymus chinensis communities

Understanding community assembly mechanisms is helpful to predict community dynamics. To explore which community assembly mechanism(s) drive(s) the grassland restoration in semi-arid region, we investigated the relationships between plant trait and species relative abundance (SRA), and estimated community functional diversity indices for each community under different treatments (enclosure, grazing and mowing treatment) in a restoration region of Stipa grandis – Leymus chinensis communities in the northern China from 2010 to 2012. There was a high fraction of significant relationships between trait value and SRA, suggesting that niche theory structured the grassland restoration in this region. The functional richness was higher and the functional divergence was lower in the enclosure community than that in the grazing or mowing community, and significantly positive plant height - SRA relationship was found in the enclosure community. These findings demonstrated that limiting similarity based on niche theory was more important in structuring the enclosure community and that environmental filtering based on niche theory played a more important role in driving the grazing or mowing community. Only the factor of year significantly affected the functional evenness (FEve), and the lowest FEve in 2011 implied that the relatively lower precipitation could enhance the effect of limiting similarity on community assembly in the semi-arid grassland.

The effect of simulated sheep grazing on male and female reproductive performance in Caragana microphylla Lam. (Leguminosae)

Understanding the reproductive response of host plants to herbivores is important in grazing ecology and grassland management. Simulated grazing experiments were conducted to determine the influence of different grazing intensities on reproductive performance of a shrub, Caragana microphylla Lam. The total leaf mass, total flower mass, total flower mass allocation, and single flower mass allocation decreased with increased grazing intensity. The total spine mass, single flower mass and total spine mass allocation increased with increased grazing intensity. The stem mass, stem mass allocation and total leaf mass allocation had not significant change with the increasing grazing intensity. Under heavy grazing treatments, the host plants significantly decreased their investment in reproduction and increased investment in physical defense organs. Although there were no significant differences in the number of ovules among different grazing intensities, herbivory negatively affected reproductive performance, including the number of flowers, the number of pollen grains per flower, the number of ripe seeds and the rate of pod-set in host plants. These results indicate that there are trade-offs among vegetative and reproductive and defensive organs. Compared with male reproduction, female reproductive performance was less sensitive to herbivory and grazing intensity. Moreover, pollen grains from heavily browsed plants seemed to be less likely to sire pods and ripe seeds than those from unbrowsed plants, indicating that herbivory not only decreased pollen production, but also adversely affected pollen performance.

Response of early-successional Bahamian dry forest habitat to goat grazing and implications for Kirtland's warbler (Setophaga kirtlandii) wintering ground management

Limited financial resources coupled with competing social demands may require novel approaches for biodiversity conservation. Within the Bahamas archipelago, subtropical dry forest (“coppice”) provides habitat for many resident and migratory bird species including the U.S. federally endangered Kirtland's warbler (Setophaga kirtlandii). On the islands, this migratory bird relies heavily on fruits of shrubs in early-successional coppice. Evidence indicates shrub species of particular importance in the bird's diet may not be generally widespread, while attempts to actively manage for these plant species could be cost-prohibitive or counterproductive to other conservation concerns. Because these shrubs and Kirtland's warblers have been frequently found on goat farms we investigated whether periodic goat grazing might be a practical tool for maintaining suitable coppice habitat in other semi-natural areas where late-successional coppice is unsupportable (e.g. utility rights-of-way) and whether it promotes increased abundance of important fruiting shrubs. In experiments conducted in young coppice within a pipeline corridor, we found little evidence that grazing would increase abundance of these shrubs, but our grazed coppice plots returned quickly to their pre-grazing state and exhibited few subsequent structural or compositional differences from ungrazed coppice plots. Thus, if appropriately applied and managed, goat grazing may serve as an economically viable tool for biodiversity preservation because (1) suitability as habitat for Kirtland's warblers and many other birds returns quickly after a short-term grazing treatment and (2) periodic, short-term grazing will forestall succession toward a vegetation type less appropriate for these birds or for certain types of human land use.

Grazing Affects the Ecological Stoichiometry of the Plant–Soil–Microbe System on the Hulunber Steppe, China

Grazing affects nutrient cycling processes in grasslands, but little is known by researchers about effects on the nutrient stoichiometry of plant–soil–microbe systems. In this study, the influence of grazing intensity (0, 0.23, 0.34, 0.46, 0.69, and 0.92 AU ha−1) on carbon (C), nitrogen (N) and phosphorus (P) and their stoichiometric ratios in plants, soil, and microbes was investigated in a Hulunber meadow steppe, Northeastern China. The C:N and C:P ratios of shoots decreased with grazing increased. Leaf N:P ratios &lt;10 suggested that the plant communities under grazing were N-limited. Heavy grazing intensities increased the C:N and C:P ratios of microbial biomass, but grazing intensity had no significant effects on the stoichiometry of soil nutrients. The coupling relationship of C:N ratio in plant–soil–microbial systems was tightly significant compared to C:P ratio and N:P ratio according to the correlation results. The finding suggested grazing exacerbated the competition between plants and microorganisms for N and P nutrition by the stoichiometric changes (%) in each grazing level relative to the no grazing treatment. Therefore, for the sustainability of grasslands in Inner Mongolia, N inputs need to be increased and high grazing intensities reduced in meadow steppe ecosystems, and the grazing load should be controlled within G0.46.

Ecological, biophysical and production effects of incorporating rest into grazing regimes: A global meta‐analysis

Abstract Grazing can have considerable ecological impacts when managed inappropriately, however livestock production is a significant contributor to global food security and the removal of land from production is not always a viable option. Grazing management practices that incorporate periods of planned rest (i.e. strategic‐rest grazing) may be an alternative to grazing exclusion or continuous grazing that could achieve ecological and animal production outcomes simultaneously. We conducted a meta‐analysis of global literature to investigate how strategic‐rest grazing mediates ecological (i.e., plant richness and diversity), biophysical (plant biomass and ground cover) and production response variables (animal weight gain and animal production per hectare) compared to continuously grazed or ungrazed areas. Overall, total ground cover and animal production per hectare were significantly greater under strategic‐rest grazing than continuous grazing management, but biomass, plant richness, plant diversity and animal weight gain did not differ between grazing treatments. Increasing the length of rest relative to graze time under strategic‐rest grazing was associated with an increase in plant biomass, ground cover, animal weight gain and animal production per hectare when compared to continuous grazing. Synthesis and applications. Understanding both the ecological and animal production trade‐offs associated with different grazing management strategies is essential to make informed decisions about best‐management practices for the world's grazing lands. We show that incorporating periods of rest into grazing regimes improves ground cover and animal production per hectare and that these benefits are more pronounced with increases in the length of time land is rested for. This extended rest also improves biomass production and weight gain compared to continuous grazing systems. Based on these meta‐analyses, we recommend that future research considers the duration of rest compared to graze time in comparisons of grazing systems.

Modelling aboveground net primary production (ANPP) of an Atlantic mountain grassland based on time series approach

Because primary productivity is related both with the energy that sustains food webs and with species diversity, it is usually considered a key ecosystem property and a reliable indicator of available forage. In this work the aboveground net primary production (ANPP) of an Atlantic mountain grassland system was modelled in order to attempt producing short-term forecasts. Since grazing influences productivity, two treatment levels (grazing and exclusion) were experimentally applied in each of three field sites. Monthly ANPP data were then collected over three consecutive vegetative periods (2006-2008), thereby obtaining six time series (one per plot). Since no significant differences among sites (within treatments) were found, these six series were later reduced through averaging to only two series (one per treatment level). Two kinds of statistical models were then used to attempt monthly ANPP forecasting: exponential smoothing methods and ARIMA models. Both methodologies turned out to produce inadequate forecasts due to the presence of marked local features (innovative outliers) in our relatively short time-series data. Nonetheless, useful information for a more innovative shepherding management was revealed (e.g. the presence of within-year variation in ANPP, and differences between the grazing and exclusion treatments). Longer data series, which would require a more demanding effort in sampling investment, are likely necessary in order to obtain adequate forecasts using these time series methodologies.

Effects of grazing intensity on spatial heterogeneity of the constructive species Stipa breviflora in desert steppe.

This study evaluated the changes of spatial distribution of the constructive species Stipa breviflora in the desert steppe under different grazing intensities (control, light, moderate, and heavy grazing) in Siziwang, Inner Mongolia. The small-scale spatial distribution of S. breviflora was measured. Results showed that population density of S. breviflora was following the order: heavy grazing (27.81 individuals·m-2) > moderate grazing (22.17 individuals·m-2) > control (11.31 individuals·m-2) > light grazing (10.76 individuals·m-2). The moderate and heavy grazing significantly increased population density of S. breviflora. According to the model fitting by semi-variance function, the population density of S. breviflora under the control, light, moderate and heavy gra-zing treatments were consistent with the exponential model, spherical model, exponential model and spherical model, respectively. Results from spatial distribution pattern analysis showed that structural ratio of S. breviflora population was control (99.7%) > heavy grazing (94.7%) > light grazing (92.7%) > moderate grazing (87.9%). Such a result indicated that the spatial autocorrelation of the four treatments was high, which were mainly affected by structural factors. In comparison, S. breviflora population structure ratio under moderate grazing treatment was the smallest, and partly affected by random factors. Based on fractal dimension analysis, spatial structure of the four treatments was good with simple spatial distribution. With the increases of grazing intensity, the spatial distribution was simpler and more homogeneous. Combined with 2D and 3D views, both light and heavy grazing changed spatial distribution of S. breviflora population from gradient distribution to patch distribution and resulted in the reduction of spatial heterogeneity.

Long-term effect of different management regimes on the survival and population structure of Gladiolus imbricatus in Estonian coastal meadows

QuestionsHow does the population structure of the threatened plant species Gladiolus imbricatus differ in the early and late stages of habitat restoration under different management regimes? What is the best management regime for the species? LocationLuitemaa Nature Reserve in Southwest Estonia. MethodsA long-term field experiment (2002–2004 and 2014–2016) studied the effect of four management regimes: (1) mowing in late July, (2) grazing by cattle, (3) grazing by sheep and (4) continuous lack of management (i.e. the control). ResultsIn contrast to the highly positive short-term response to habitat restoration, in the long term, late-season mowing was the most favourable management type for G. imbricatus. The universal increase in juveniles across treatments during the early phase of the restoration project remained high only in mown plots. For the other treatments, after 10 years, the number of juveniles declined to the starting level or lower. Additionally, in contrast to the uniformly high number of premature and generative plants across treatments during the first two years of restoration, the number of premature plants in grazed sites declined. In particular, the frequency of premature and generative plants differed between the mowing and sheep grazing treatments in the long term. The success of generative reproduction was poor in the sheep-managed pasture, as all the shoots were grazed and none had any fruits or flowers. ConclusionsWhile grazing is the most commonly subsidised restoration measure applied to coastal meadows, we recommend diversification of management types by promoting late-season mowing and reducing grazing intensity. In particular, sheep grazing must be avoided. The results of short-term evaluation of restoration methods can be misleading, and long-term monitoring must be a default evaluation task in biodiversity management support schemes.

Dung fungi as an indicator of large herbivore dynamics in peatlands

Coprophilous fungal spores (CFS) have gained prominence in paleoecology as a proxy for large herbivore dynamics. Dung availability is one of several factors that influences spore abundance so it is unclear how closely CFS levels track herbivore biomass. This uncertainty is particularly relevant in peat- and moorland, where grazing impacts are a recurring topic in paleoecology and source of tension in environmental management, and where the method has yet to be tested. The current study used three ecological and conservation grazing experiments in UK peat- and moorland to study modern and recent historic relationships between grazing treatment and the abundance of three key CFS types and three pollen disturbance indicators. A total of 78 surface samples and 2 short peat cores were analyzed. Dispersal distances are estimated to range from <10 m to tens of meters, based on significantly lower CFS abundance in exclosed than grazed plots at two sites, and similar CFS trends over the last century in short peats cores located 80 m apart at the third site. The CFS signal thus represents activity in the surrounding landscape, despite predominantly local dispersal. CFS abundance does not correspond with animal biomass when compared across the three sites, however, and pollen disturbance indicators in the peat cores matched recent historic grazing records more consistently than CFS abundance. Potential reasons for these mismatches are discussed. Quantitative inferences about large herbivore abundance from CFS in peatlands should therefore be made with caution and recommendations are made for further testing of the method.

Pasture allowance, duration, and stage of lactation—Effects on early and total lactation animal performance

Pasture availability in early spring can be limited due to climatic effects on grass production, increasing the likelihood of feed deficits in early lactation of spring-calving pasture-based systems. We hypothesized that restricting pasture allowance (PA) when animals are at peak milk production will have more negative implications on milk production compared with restricting animals before this period. A total of 105 cows were assigned to 1 of 7 grazing treatments from March 14 to October 31, 2016 (33 wk). The control treatment was offered a PA to achieve a postgrazing sward height > 3.5 cm and mean pasture allowance of 15.5 kg of dry matter per cow. The remaining treatments were offered a PA representing 60% of that offered to the control for a duration of 2 or 6 wk from March 14 (mid-March; MMx2 and MMx6), March 28 (end of March; EMx2 and EMx6), or April 11 (mid-April; MAx2 and MAx6). Within grazing treatment, animals were also assigned to 1 of 2 calving dates (early and late) based on days in milk (DIM) on March 14. Early calved (EC) cows were ≥36 DIM, while late calved (LC) were ≤35 DIM. Restricting PA for 2 and 6 wk reduced daily milk yield (-1.6 and -2.2 kg/cow, respectively), cumulative milk protein yield (-4.0 and -6.3 kg/cow, respectively), and cumulative milk solids yield (-5.8 and -9.5 kg/cow, respectively) in the first 10 wk of the experiment. Daily milk yield was similar across the treatments at the end of the 33-wk period (16.8 kg/cow, average of all treatments), as was daily milk solids yield (1.40 kg/cow). Cows in the EC group produced less milk over the first 10 wk of the experiment (20.0 kg/cow per day) compared with the LC animals (22.1 kg/cow per day). However, body weight was greater (+15 kg/cow) in the EC animals compared with the LC, while body condition score was similar (2.85). This outcome indicates that animals that are restricted later in early lactation (circa onset of peak milk production) partition a greater proportion of available energy to maintenance, resulting in greater losses in milk production. These data indicate that despite the immediate reduction in milk production, restricting intake of grazing cows to 80% of that required to achieve spring grazing targets for postgrazing sward height for up to 6 wk may be used as a method of managing short-term pasture deficits on farm with minimal effects on total lactation performance.

Effects of reindeer grazing and recovery after cessation of grazing on the ground-dwelling spider assemblage in Finnish Lapland.

The effect of reindeer Rangifer tarandus L. grazing on the ground-dwelling spider assemblage in Northern Finland was studied. Changes in species richness, abundance and evenness of spider assemblages were analyzed in relation to changes in vegetation and environmental factors in long term grazed and ungrazed sites as well as sites that had recently switched from grazed to ungrazed and vice versa. Grazing was found to have a significant impact on height and biomass of lichens and other ground vegetation. However, it seemed not to have an impact on the total abundance of spiders. This is likely caused by opposing family and species level responses of spiders to the grazing regime. Lycosid numbers were highest in grazed and linyphiid numbers in ungrazed areas. Lycosidae species richness was highest in ungrazed areas whereas Linyphiidae richness showed no response to grazing. Four Linyphiidae, one Thomisidae and one Lycosidae species showed strong preference for specific treatments. Sites that had recovered from grazing for nine years and the sites that were grazed for the last nine years but were previously ungrazed resembled the long term grazed sites. The results emphasize the importance of reindeer as a modifier of boreal forest ecosystems but the impact of reindeer grazing on spiders seems to be family and species specific. The sites with reversed grazing treatment demonstrate that recovery from strong grazing pressure at these high latitudes is a slow process whereas reindeer can rapidly change the conditions in previously ungrazed sites similar to long term heavily grazed conditions.

Milk production per cow and per hectare of spring-calving dairy cows grazing swards differing in Lolium perenne L. ploidy and Trifolium repens L. composition

Grazed grass is the cheapest feed available for dairy cows in temperate regions; thus, to maximize profits, dairy farmers must optimize the use of this high-quality feed. Previous research has defined the benefits of including white clover (Trifolium repens L.) in grass swards for milk production, usually at reduced nitrogen usage and stocking rate. The aim of this study was to quantify the responses in milk production of dairy cows grazing tetraploid or diploid perennial ryegrass (Lolium perenne L.; PRG) sown with and without white clover but without reducing stocking rate or nitrogen usage. We compared 4 grazing treatments in this study: tetraploid PRG-only swards, diploid PRG-only swards, tetraploid with white clover swards, and diploid with white clover swards. Thirty cows were assigned to each treatment, and swards were rotationally grazed at a farm-level stocking rate of 2.75 cows/ha and a nitrogen fertilizer rate of 250 kg/ha annually. Sward white clover content was 23.6 and 22.6% for tetraploid with white clover swards and diploid with white clover swards, respectively. Milk production did not differ between the 2 ploidies during this 4-yr study, but cows grazing the PRG-white clover treatments had significantly greater milk yields (+596 kg/cow per year) and milk solid yields (+48 kg/cow per year) compared with cows grazing the PRG-only treatments. The PRG-white clover swards also produced 1,205 kg of DM/ha per year more herbage, which was available for conserving and buffer feeding in spring when these swards were less productive than PRG-only swards. Although white clover is generally combined with reduced nitrogen fertilizer use, this study provides evidence that including white clover in either tetraploid or diploid PRG swards, combined with high levels of nitrogen fertilizer, can effectively increase milk production per cow and per hectare.

Effects of Fire and Large Herbivores on Canopy Nitrogen in a Tallgrass Prairie

This study analyzed the spatial heterogeneity of grassland canopy nitrogen in a tallgrass prairie with different treatments of fire and ungulate grazing (long-term bison grazing vs. recent cattle grazing). Variogram analysis was applied to continuous remotely sensed canopy nitrogen images to examine the spatial variability in grassland canopies. Heterogeneity metrics (e.g., the interspersion/juxtaposition index) were calculated from the categorical canopy nitrogen maps and compared among fire and grazing treatments. Results showed that watersheds burned within one year had higher canopy nitrogen content and lower interspersions of high-nitrogen content patches than watersheds with longer fire intervals, suggesting an immediate and transient fire effect on grassland vegetation. In watersheds burned within one year, high-intensity grazing reduced vegetation density, but promoted grassland heterogeneity, as indicated by lower canopy nitrogen concentrations and greater interspersions of high-nitrogen content patches at the grazed sites than at the ungrazed sites. Variogram analyses across watersheds with different grazing histories showed that long-term bison grazing created greater spatial variability of canopy nitrogen than recent grazing by cattle. This comparison between bison and cattle is novel, as few field experiments have evaluated the role of grazing history in driving grassland heterogeneity. Our analyses extend previous research of effects from pyric herbivory on grassland heterogeneity by highlighting the role of grazing history in modulating the spatial and temporal distribution of aboveground nitrogen content in tallgrass prairie vegetation using a remote sensing approach. The comparison of canopy nitrogen properties and the variogram analysis of canopy nitrogen distribution provided by our study are useful for further mapping grassland canopy features and modeling grassland dynamics involving interplays among fire, large grazers, and vegetation communities.

Evaluating the Impacts of Continuous and Rotational Grazing on Tallgrass Prairie Landscape Using High-Spatial-Resolution Imagery

This study evaluated the impacts of different grazing treatments (continuous (C) and rotational (R) grazing) on tallgrass prairie landscape, using high-spatial-resolution aerial imagery (1-m at RGB and near-infrared bands) of experimental C and R pastures within two replicates (Rep A and Rep B) in the southern Great Plains (SGP) of the United States. The imagery was acquired by the National Agriculture Imagery Program (NAIP) during the agricultural growing season of selected years (2010, 2013, 2015, and 2017) in the continental United States. Land cover maps were generated by combining visual interpolation, a support vector machine, and a decision tree classifier. Landscape metrics (class area, patch number, percentage of landscape, and fragmentation indices) were calculated from the FRAGSTATS (a computer software program designed to compute a wide variety of landscape metrics for categorical map patterns) based on land cover results. Both the metrics and land cover results were used to analyze landscape dynamics in the experiment pastures. Results showed that both grass and shrubs of different pastures differed largely in the same year and had significant annual dynamics controlled by climate. High stocking intensity delayed grass growth. A large proportion of bare soil occurred in sub-paddocks of rotational grazing that were just grazed or under grazing. Rep A experienced rapid shrub encroachment, with a large proportion of shrub at the beginning of the experiment. Shrub may occupy 41% of C and 15% of R in Rep A by 2030, as revealed by the linear regression analysis of shrub encroachment. In contrast, shrub encroachment was not significant in Rep B, which only had a small number of shrub patches at the beginning of the experiment. This result indicates that the shrub encroachment is mainly controlled by the initial status of the pastures instead of grazing management. However, the low temporal resolution of the NAIP imagery (one snapshot in two or three years) limits our comparison of the continuous and rotational grazing at the annual scale. Future studies need to combine NAIP imagery with other higher temporal resolution imagery (e.g., WorldView), in order to better evaluate the interannual variabilities of grass productivity and shrub encroachment.