Grassland Plant Communities Research Articles

Measuring the effect of freezing on hydrolytic and oxidative extracellular enzyme activities associated with plant litter decomposition

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.

Plant species richness negatively affects root decomposition in grasslands

Summary Plant diversity enhances many ecosystem functions, including root biomass production, which drives soil carbon input. Although root decomposition accounts for a large proportion of carbon input for soil, little is known about plant diversity effect on this process. Plant diversity may affect root decomposition in two non‐exclusive ways: by providing roots of different substrate quality (e.g. root chemistry) and/or by altering the soil environment (e.g. microclimate). To disentangle these two pathways, we conducted three decomposition experiments using a litter‐bag approach in a grassland biodiversity experiment. We hypothesized that: (i) plant species richness negatively affects substrate quality (indicated by increased C:N ratios), which we tested by decomposing roots collected from each experimental plot in one common plot; (ii) plant species richness positively affects soil environment (indicated by increased soil water content), which we tested by decomposing standardized roots in all experimental plots; (iii) the overall effect of plant species richness on root decomposition, due to the contrast between quality and environmental effects, is neutral, which we tested by decomposing community roots in their ‘home’ plots. Plant species richness negatively affected root decomposition in all three experiments. The negative effect of plant species richness on substrate quality was largely explained by increased root C:N ratios along the diversity gradient. Functional group presence explained more variance in substrate quality than species richness. Here, the presence of grasses negatively affected substrate quality and root C:N ratios, while the presence of legumes and small herbs had positive effects. Plant species richness had a negative effect on soil environment despite its positive effect on soil water content which is known to stimulate decomposition. We argue that – instead of soil water content – a combined effect of soil temperature and seasonality might drive environmental effect of plant diversity on decomposition in our plant communities, but this remains to be tested. Synthesis. Our results demonstrate that both substrate quality and soil environment contribute to the net negative effect of plant diversity on root decomposition. This study promotes our mechanistic understanding of increased soil carbon accumulation in more diverse grassland plant communities.

Soil Aggregate Dynamics and Plant Community Response after Biosolids Application in a Semiarid Grassland.

Biosolids may improve the ecological function of degraded semiarid grasslands, but an understanding of the plant community is essential. An experiment was established in 2001 to determine the effects of a single surface application of biosolids on soil aggregate stability and the composition of the plant community in a semiarid grassland in British Columbia, Canada. Four treatments were evaluated: (i) surface biosolids application at 20 (Bio-20) and (ii) 60 Mg ha (Bio-60), (iii) mineral fertilizer, and (iv) a control. All treatments were replicated in four blocks. Soil was sampled during the spring (May), summer (June-July), and fall (October) in 2005, 2006, and 2009; the plant community was assessed in 2009. The greatest increases in size of stable aggregates relative to the control were in the spring and summer, which coincided with a 1.6- to 2.1-fold increase in the spring concentration of N within stable aggregates when biosolids were applied at 20 and 60 Mg ha , respectively. Nitrogen concentrations from the Bio-60 treatment were not different from the control, but the Bio-20 treatment had 42% greater N than all other treatments during summer. Biosolids application in this ecosystem did not increase perennial forage grass species relative to the control, and when biosolids were applied at a rate of 60 Mg ha there was a 75% reduction in the perennial forage plant species. The application of biosolids to native grasslands in semiarid environments should be done cautiously, especially when winter annual plant species (e.g., cheatgrass [ L.]) are present before application.

Flora and vegetation of dry grasslands of Northeastern Ukraine, and problems of diversity conservation

Abstract The aim of this study was to describe the flora and vegetation of the grasslands of Northeastern Ukraine and to analyse how the steppe vegetation responds to grazing or its abandonment. We studied two gully systems in the east of the Kharkiv Region: the Regional Landscape Park “The Velykyi Burluk-Steppe” (steppe grasslands on chernozem soils; 10 sites) and the National Nature Park “Dvorichanskyi” (steppe grasslands on chalky outcrops; 5 sites). Long-term monitoring data exist for both these sites starting in 1991, shortly after grazing intensity reduced. We recorded the major grassland plant communities (reflecting their successional status) as well as their dominant species. Tree and scrub encroachment increased after management ceased. We conclude that (i) heterogeneous grazing (including ungrazed patches) in space and time is necessary in order to preserve grassland biodiversity in our study system; (ii) erosion of chalky outcrops (natural erosion as well as driven by cattle grazing) is a key factor promoting the richness of cretaceous species in steppe grassland.

Roles of Arbuscular Mycorrhizal Fungi and Soil Abiotic Conditions in the Establishment of a Dry Grassland Community.

BackgroundThe importance of soil biota in the composition of mature plant communities is commonly acknowledged. In contrast, the role of soil biota in the early establishment of new plant communities and their relative importance for soil abiotic conditions are still poorly understood.Aims and MethodsThe aim of this study was to understand the effects of soil origin and soil fungal communities on the composition of a newly established dry grassland plant community. We used soil from two different origins (dry grassland and abandoned field) with different pH and nutrient and mineral content. Grassland microcosms were established by sowing seeds of 54 species of dry grassland plants into the studied soils. To suppress soil fungi, half of the pots were regularly treated with fungicide. In this way, we studied the independent and combined effects of soil origin and soil community on the establishment of dry grassland communities.Key ResultsThe effect of suppressing the soil fungal community on the richness and composition of the plant communities was much stronger than the effect of soil origin. Contrary to our expectations, the effects of these two factors were largely additive, indicating the same degree of importance of soil fungal communities in the establishment of species-rich plant communities in the soils from both origins. The negative effect of suppressing soil fungi on species richness, however, occurred later in the soil from the abandoned field than in the soil from the grassland. This result likely occurred because the negative effects of the suppression of fungi in the field soil were caused mainly by changes in plant community composition and increased competition. In contrast, in the grassland soil, the absence of soil fungi was limiting for plants already at the early stages of their establishment, i.e., in the phases of germination and early recruitment. While fungicide affects not only arbuscular mycorrhizal fungi but also other biota, our data indicate that changes in the AMF communities are the most likely drivers of the observed changes. The effects of other soil biota, however, cannot be fully excluded.ConclusionsThese results suggest that the availability of soil fungi may not be the most important limiting factor for the establishment of grassland species in abandoned fields if we manage to reduce the intensity of competition at these sites e.g., by mowing or grazing.

Grazing and solar irradiance drive patterns of change in two grassland plant communities in southern British Columbia

We compared the recovery of two plant communities over 14 years following a switch from spring to fall grazing (G), and in ungrazed exclosures (UG), at six sites in Lac du Bois Grasslands Provincial Park, British Columbia. Both communities showed similar large increases in cover of their respective dominant grasses – rough fescue (Festuca campestris), and bluebunch wheatgrass (Pseudoroegneria spicata) – in both G and UG treatments. As expected, the more productive rough fescue community had higher amounts of soil polysaccharides, and total soil C and N. Repeated measures ANOVA indicated significant declines in species richness and Shannon diversity over time, especially in the ungrazed rough fescue community. Non-metric multidimensional scaling of species cover data showed continued divergence between communities, largely due to an increase in abundance of the two dominant grasses. Community differences were mainly determined by aspect and its impact on soil temperature and water content. We concluded that, from a management perspective, switching to light fall grazing was as effective as removing grazing to assist in recovery from previous overgrazing, and that the relationship of grazing combined with the fine-scale pattern of variable solar irradiance was responsible for the closely interspersed mosaic of the two grassland communities.

Direct effects dominate responses to climate perturbations in grassland plant communities.

Theory predicts that strong indirect effects of environmental change will impact communities when niche differences between competitors are small and variation in the direct effects experienced by competitors is large, but empirical tests are lacking. Here we estimate negative frequency dependence, a proxy for niche differences, and quantify the direct and indirect effects of climate change on each species. Consistent with theory, in four of five communities indirect effects are strongest for species showing weak negative frequency dependence. Indirect effects are also stronger in communities where there is greater variation in direct effects. Overall responses to climate perturbations are driven primarily by direct effects, suggesting that single species models may be adequate for forecasting the impacts of climate change in these communities.

Different‐sized grazers have distinctive effects on plant functional composition of an African savannah

Summary Grazing ungulates play a key role in many ecosystems worldwide and can form diverse assemblages, such as in African savannahs. In many of these ecosystems, present‐day ungulate communities are impoverished subsets of once diverse assemblages. While we know that excluding all ungulates from grasslands can exert major effects on both the structure and composition of the vegetation, how different individual ungulate species may have contrasting effects on grassland communities remains poorly understood. Here, we performed a long‐term ‘Russian doll’ grazing exclosure experiment in an African savannah to test for the effects of different size classes of grazers on grassland structure and composition. At five sites, grazer species of decreasing size class (ranging from white rhino to scrub hare) were excluded using four fence types, to experimentally create different realized grazer assemblages. The vegetation structure and the grass functional community composition were characterized in 6 different years over a 10‐year period. Additionally, animal footprints were counted to quantify the abundance of different ungulate species in each treatment. We found that while vegetation height was mostly driven by total grazing pressure of all species together, ungulate community composition best explained the functional community composition of grasses. In the short term, smaller ungulate species (‘mesoherbivores’) had strongest effects on vegetation composition, by shifting communities towards dominance by species with low specific leaf area and low nutritional value. In the long term, large grazers had stronger but similar effects on the functional composition of the system. Surprisingly, the largest ‘mega‐herbivore’, the white rhinoceros, did not have strong effects on the vegetation structure or composition. Synthesis. Our results support the idea that different size classes of grazers have varying effects on the functional composition of grassland plant communities. Therefore, the worldwide decline in the diversity of ungulate species is expected to have (had) major impacts on community composition and functioning of grassland ecosystems, even if total grazing pressure has remained constant, for example, due to replacement by livestock.

Cape ground squirrels as ecosystem engineers: modifying habitat for plants, small mammals and beetles in Namib Desert grasslands

AbstractBurrowing and foraging of semi‐fossorial rodents can affect species distribution and composition. Ground squirrels dig large burrow systems for refuge from predators and temperature extremes. Burrowing and foraging around burrows by squirrels may affect habitat and resource distributions for other organisms. We examined the impact of Cape ground squirrels (Xerus inauris) on vegetation, small mammals and beetles during winter and summer in grasslands on the edge of the Namib Desert. At each burrow system and paired control site without burrows, we estimated plant cover and height using quadrats (N = 8 paired sites), small mammal abundance and species richness using mark‐recapture techniques (N = 8 paired sites) and beetle abundance and species richness using pitfall traps (N = 6 paired sites, winter only). Squirrel burrowing and foraging activities resulted in lower plant cover and height, higher small mammal abundance and lower beetle abundance and species richness. Squirrels also reduced more plant cover in winter compared to summer, but had no effect on small mammal species richness. Furthermore, plant cover and height were higher in summer, whereas small mammal abundance and species richness were higher in winter. Our results suggest that Cape ground squirrels are important ecosystem engineers that influence plant and animal communities in the Namib Desert grasslands.

Airborne Hyperspectral Data Predict Fine-Scale Plant Species Diversity in Grazed Dry Grasslands

Semi-natural grasslands with grazing management are characterized by high fine-scale species richness and have a high conservation value. The fact that fine-scale surveys of grassland plant communities are time-consuming may limit the spatial extent of ground-based diversity surveys. Remote sensing tools have the potential to support field-based sampling and, if remote sensing data are able to identify grassland sites that are likely to support relatively higher or lower levels of species diversity, then field sampling efforts could be directed towards sites that are of potential conservation interest. In the present study, we examined whether aerial hyperspectral (414–2501 nm) remote sensing can be used to predict fine-scale plant species diversity (characterized as species richness and Simpson’s diversity) in dry grazed grasslands. Vascular plant species were recorded within 104 (4 m × 4 m) plots on the island of Öland (Sweden) and each plot was characterized by a 245-waveband hyperspectral data set. We used two different modeling approaches to evaluate the ability of the airborne spectral measurements to predict within-plot species diversity: (1) a spectral response approach, based on reflectance information from (i) all wavebands, and (ii) a subset of wavebands, analyzed with a partial least squares regression model, and (2) a spectral heterogeneity approach, based on the mean distance to the spectral centroid in an ordinary least squares regression model. Species diversity was successfully predicted by the spectral response approach (with an error of ca. 20%) but not by the spectral heterogeneity approach. When using the spectral response approach, iterative selection of important wavebands for the prediction of the diversity measures simplified the model but did not improve its predictive quality (prediction error). Wavebands sensitive to plant pigment content (400–700 nm) and to vegetation structural properties, such as above-ground biomass (700–1300 nm), were identified as being the most important predictors of plant species diversity. We conclude that hyperspectral remote sensing technology is able to identify fine-scale variation in grassland diversity and has a potential use as a tool in surveys of grassland plant diversity.

Plant community controls on short-term ecosystem nitrogen retention.

Summary Retention of nitrogen (N) is a critical ecosystem function, especially in the face of widespread anthropogenic N enrichment; however, our understanding of the mechanisms involved is limited. Here, we tested under glasshouse conditions how plant community attributes, including variations in the dominance, diversity and range of plant functional traits, influence N uptake and retention in temperate grassland.We added a pulse of 15N to grassland plant communities assembled to represent a range of community‐weighted mean plant traits, trait functional diversity and divergence, and species richness, and measured plant and microbial uptake of 15N, and leaching losses of 15N, as a short‐term test of N retention in the plant–soil system.Root biomass, herb abundance and dominant plant traits were the main determinants of N retention in the plant–soil system: greater root biomass and herb abundance, and lower root tissue density, increased plant 15N uptake, while higher specific leaf area and root tissue density increased microbial 15N uptake.Our results provide novel, mechanistic insight into the short‐term fate of N in the plant–soil system, and show that dominant plant traits, rather than trait functional diversity, control the fate of added N in the plant–soil system.

Shifting grassland plant community structure drives positive interactive effects of warming and diversity on aboveground net primary productivity.

Ecosystems worldwide are increasingly impacted by multiple drivers of environmental change, including climate warming and loss of biodiversity. We show, using a long-term factorial experiment, that plant diversity loss alters the effects of warming on productivity. Aboveground primary productivity was increased by both high plant diversity and warming, and, in concert, warming (≈1.5 °C average above and belowground warming over the growing season) and diversity caused a greater than additive increase in aboveground productivity. The aboveground warming effects increased over time, particularly at higher levels of diversity, perhaps because of warming-induced increases in legume and C4 bunch grass abundances, and facilitative feedbacks of these species on productivity. Moreover, higher plant diversity was associated with the amelioration of warming-induced environmental conditions. This led to cooler temperatures, decreased vapor pressure deficit, and increased surface soil moisture in higher diversity communities. Root biomass (0-30 cm) was likewise consistently greater at higher plant diversity and was greater with warming in monocultures and at intermediate diversity, but at high diversity warming had no detectable effect. This may be because warming increased the abundance of legumes, which have lower root : shoot ratios than the other types of plants. In addition, legumes increase soil nitrogen (N) supply, which could make N less limiting to other species and potentially decrease their investment in roots. The negative warming × diversity interaction on root mass led to an overall negative interactive effect of these two global change factors on the sum of above and belowground biomass, and thus likely on total plant carbon stores. In total, plant diversity increased the effect of warming on aboveground net productivity and moderated the effect on root mass. These divergent effects suggest that warming and changes in plant diversity are likely to have both interactive and divergent impacts on various aspects of ecosystem functioning.

Fire exclusion and soil texture interact to influence temperate grassland flora in south-eastern Australia

Fire has a major influence on the structure and composition of temperate grasslands and woodlands. We investigated whether the impacts of fire exclusion on a temperate grassland plant community varied according to the scale of investigation and soil texture. Ten sites with known fire histories were selected along a soil texture gradient in south-eastern Australia. Floristics and ground layer attributes were investigated at small (0.25 m2) and large (100 m2) spatial scales in regularly burnt and unburnt grasslands. Fire exclusion over a 10 year period led to declines in native species diversity, richness and cover at both spatial scales and in most cases effects were consistent regardless of soil texture. However, the richness of native plant species at small scales and the cover of native plants at large scales were most negatively influenced by fire exclusion on fine textured soils. Conversely, at large scales, exotic plant richness and cover were only weakly increased by fire exclusion. Responses of eight common species were modelled and in seven of these, fire exclusion was a strong predictor of occurrence, although both positive and negative responses were observed. These results reiterate the importance of frequent fire as a management tool in temperate grasslands, but also shed light on how sites may require specific fire management regimes depending on the underlying soil texture.

Comparing grazing and resting electivity of beef cattle for BC bunchgrass communities using GPS collars

Thompson, D., Wheatley, B. J., Church, J. S., Newman, R. and Walker, J. 2015. Comparing grazing and resting electivity of beef cattle for BC bunchgrass communities using GPS collars. Can. J. Anim. Sci. 95: 499–507. Grasslands in the interior of British Columbia often contain a mosaic of plant communities that provide variable habitat for free-ranging cattle. Global positioning system (GPS) collars have been used to study natural habitat use by cattle on a coarse scale (such as riparian, grassland and forested habitats), but not on a fine scale (such as choice among grassland plant communities). Cows equipped with GPS collars were tracked during the spring grazing period for 4 yr. Six grassland pastures were used as replicates. The activity (grazing or resting) of cattle at GPS locations was classified using a distance travelled algorithm. A detailed plant community map of five plant community types was constructed, and cow relative use within the plant communities was determined. Electivity, which scales for differences in community area, was used to compare the use of plant communities. While grazing, electivity for the Kentucky bluegrass community (mean +0.3) was greater than for the bluebunch wheatgrass community (mean −0.2). While resting, these differences were more pronounced. GPS collars can be used to estimate fine-scale choices among grassland communities.

Invasive species cover, soil type, and grazing interact to predict long‐term grassland restoration success

Grasslands are undergoing tremendous degradation as a result of climate change, land use, and invasion by non‐native plants. However, understanding of the factors responsible for driving reestablishment of grassland plant communities is largely derived from short‐term studies. In order to develop an understanding of the factors responsible for longer term restoration outcomes in California annual grasslands, we surveyed 12 fields in Davis, CA, U.S.A., in 2015 that were seeded with native species mixtures starting in 2004. Using field surveys, we investigated how invasive plant richness and cover, native plant richness and cover, aboveground biomass, grazing, soil type, and restoration species identity might provide utility for explaining patterns of restoration success. We found a negative relationship between invasive cover and restoration cover, which was attributed to the slow establishment of seeded species and subsequent dominance by weeds. The relationship between invasive cover and restoration cover was modified by grazing, likely due to a change in the dominance of exotic forbs, which have a more similar growing season to restoration species, and therefore compete more strongly for late season moisture. Finally, we found that soil type was responsible for differences in the identity and abundance of invasive plants, subsequently affecting restoration cover. This work highlights the value of focusing resources on reducing invasive species cover, limiting grazing to periods of adequate moisture, and considering soil type for successful long‐term restoration in California annual grasslands. Moreover, observations of long‐term restoration outcomes can provide insight into the way mechanisms driving restoration outcomes might differ through time.

Responses of plant diversity and primary productivity to nutrient addition in a Stipa baicalensis grassland, China

Nutrient addition can affect the structure and diversity of grassland plant communities, thus alter the grassland productivity. Studies on grassland plant community composition, structure and diversity in response to nutrient addition have an important theoretical and practical significance for the scientific management of grassland, protection of plant diversity and the recovery of degraded grassland. A randomized block design experiment was conducted with six blocks of eight treatments each: control (no nutrient addition) and K, P, N, PK, NK, NP, and NPK addition. We evaluated plant composition, height, coverage, density, and aboveground biomass to estimate primary productivity and plant diversity. Results showed that all treatments increased primary productivity significantly (P<0.05) with the exception of the K and the NPK treatments had the greatest effect, increasing aboveground biomass 2.46 times compared with the control (P<0.05). One-way ANOVA and factorial analysis were used for the species richness, Shannon-Wiener index, Pielou index and aboveground biomass, and the relationships between the diversity indices and aboveground biomass were determined through linear regression. We found that fertilization altered the community structure; N (but not P or K) addition increased the proportion of perennial rhizome grasses and significantly reduced that of perennial forbs (P<0.05), thus it presented a trend of decrease in species richness, Shannon-Wiener and Pielou indexex, respectively. Only the main effects of N had significant impacts on both the diversity indices and the aboveground biomass (P<0.05), and the interactions between N-P, N-K, P-K and N-P-K could be neglected. With fertilization, plant diversity (correlation coefficient, −0.61), species richness (−0.49), and species evenness (–0.51) were all negatively linearly correlated with primary productivity. The correlations were all significant (P<0.01). Scientific nutrient management is an effective way to improve grassland productivity, protect the plant diversity as well as recover the degraded grassland.

Biodiversity increases the resistance of ecosystem productivity to climate extremes.

It remains unclear whether biodiversity buffers ecosystems against climate extremes, which are becoming increasingly frequent worldwide. Early results suggested that the ecosystem productivity of diverse grassland plant communities was more resistant, changing less during drought, and more resilient, recovering more quickly after drought, than that of depauperate communities. However, subsequent experimental tests produced mixed results. Here we use data from 46 experiments that manipulated grassland plant diversity to test whether biodiversity provides resistance during and resilience after climate events. We show that biodiversity increased ecosystem resistance for a broad range of climate events, including wet or dry, moderate or extreme, and brief or prolonged events. Across all studies and climate events, the productivity of low-diversity communities with one or two species changed by approximately 50% during climate events, whereas that of high-diversity communities with 16-32 species was more resistant, changing by only approximately 25%. By a year after each climate event, ecosystem productivity had often fully recovered, or overshot, normal levels of productivity in both high- and low-diversity communities, leading to no detectable dependence of ecosystem resilience on biodiversity. Our results suggest that biodiversity mainly stabilizes ecosystem productivity, and productivity-dependent ecosystem services, by increasing resistance to climate events. Anthropogenic environmental changes that drive biodiversity loss thus seem likely to decrease ecosystem stability, and restoration of biodiversity to increase it, mainly by changing the resistance of ecosystem productivity to climate events.

Scale‐specific processes shape plant community patterns in subtropical coastal grasslands

AbstractProcesses responsible for shaping community patterns act at specific spatial scales. In this study, we aimed at disentangling the effects of climate, soil and space as drivers of variation in a coastal grassland plant community. We were specifically interested in evaluating the relative influence of those processes at broad and fine spatial scales as well as when considering species groups with good and poor long‐distance dispersal capacity. We sampled grassland vegetation at 16 sites distributed along a latitudinal gradient of more than 500 km in subtropical southern Brazil and used variation partitioning procedures to ascertain the relative influence of climatic, edaphic and spatial processes on variation in species composition at different spatial scales, considering the entire community and subsets with only species from the Asteraceae family (good long‐distance dispersal) and Poaceae (poor long‐distance dispersal). Climatic filters were the most responsible for shaping grassland community composition at the broad scale, while edaphic filters showed higher importance at the fine scale. When not considering the influence of spatial scale, we observed higher influence of climate structured in space. Composition patterns of species with poor long‐distance dispersal (Poaceae) were more closely related to spatial variables than those of species with effective dispersal (Asteraceae). Our results stressed the importance of addressing different spatial scales to rightly ascertain the magnitude that different drivers exert on plant community assembly. Dividing the community into groups with different dispersal abilities proved useful for a more detailed understanding of the community assembly processes.

Impact of grazing abandonment on plant and soil microbial communities in an Atlantic mountain grassland

Livestock grazing is a global land-use activity with multiple social, cultural, and environmental impacts. However, it is expected to decrease progressively in the Cantabrian Mountain areas as notable changes in livestock management systems have been observed, such as shorter stay in mountain, lower stocking rates, and less shepherd control. This study aimed to evaluate the effect of grazing abandonment on microbial function and diversity through changes promoted in aboveground vegetation and soil properties. In 2005, we erected permanent fences around two 50×50-m plots (excluded plots) in a temperate mountain grassland that has historically supported livestock managed by an extensive grazing system. A grazed plot was defined around each excluded plot. After 5 years, grazing abandonment induced shifts in floristic composition, decreased soil compaction at 0–10cm soil depth, and reduced soil temperature in the summer due to a thicker plant layer. Consequently, microorganisms reduced soil enzymatic activity and microbial biomass, and increased CO2 emissions and metabolic quotient, which indicated a lower metabolic efficiency of soil processes in excluded plots. These results suggest that soil microbial community function was very sensitive to the impacts of livestock grazing exclusion. The bacterial community was more diverse compared to the fungal community, but no significant difference in bacterial species richness was found between excluded and grazed plots. Microbial genetic diversity was not directly correlated with aboveground vegetation diversity and no clear pattern emerged as a response to grazing abandonment, probably because soil microbial diversity depends on site attributes that operate at a very fine spatial scale.

Resilience of a novel ecosystem after the loss of a keystone species: plague epizootics and urban prairie dog management

In a complex urban‐impacted landscape, native black‐tailed prairie dogs (Cynomys ludovicianus) amplify the trajectory at which grassland plant communities deviate from historical configurations. Prairie dog removal has been proposed as an intervention method based upon the premise that removing a major directional driver of change will initiate the recovery of historically common plant communities. However, in a heavily anthropogenically influenced landscape with a matrix containing only small fragmented areas of native vegetation, the recolonization speed and success of native plant species may not match those observed in less anthropogenically influenced landscapes. This study examined the effect of urban prairie dog removal by using remote sensing to observe the response of plant communities near Boulder, Colorado, USA to plague epizootics. We used Mann‐Whitney U tests to compare the soil adjusted vegetation index (SAVI) values from colonies recently extirpated by plague to both areas unoccupied by prairie dogs and to plague‐absent colonies. Analysis of 67 Landsat images in three growing season subsets suggested that prairie dog removal alone does not return colony plant communities to compositions representative of grassland areas unoccupied by prairie dogs. The absence of SAVI value changes in the mid‐ and late‐growing seasons suggested that novel vegetation communities on urban prairie dog colonies were highly resilient systems, and prairie dog removal alone was insufficient for restoration. Furthermore, increased early season SAVI values on extirpated colonies could indicate a proliferation of introduced winter active species and exotic forbs, not the desired reemergence of native species, but rather species expected given current climatic changes. Intensive management efforts appear necessary for overcoming the thresholds required to restore urban prairie dog colonies to their historical compositions, an effort made increasingly more difficult with the ongoing effects of other global change drivers.