Low vegetation recovery after short-term cattle exclusion on Robinson Crusoe Island

Livestock browsing and grazing are considered serious threats to the conservation of the Juan Fernández Islands’ flora, Chile. Nowadays the elimination of grazing by cattle is very difficult. In order to prevent the␣entrance of cattle into the native forests, an 8.3 km-long fence was established on the main island (Robinson Crusoe). The response of the vegetation was evaluated during 27 months of exclusion. The changes in abundances and composition of species were monitored in 12 permanent plots, each of 25 m², located in ungrazed and grazed areas. We expected an increase in plant height and total ground cover in the ungrazed area, and also a directional compositional change towards forest species. We found five different patterns of variation or non-variation for the 22 species observed: (i) one species (Acaena argentea) diminished in abundance in the ungrazed area; (ii) another one (Conium maculatum) increased in the ungrazed area; (iii) one species (Vulpia bromoides) increased in the grazing area; and some species displayed no net variation, but they showed (iv) a nearly constant occurrence, or (v) they appeared and disappeared sporadically. Contrary to our hypothesis, the vegetation showed no net differences in cover on both sides of the fence. As expected, plant height increased in the ungrazed area. In this area, we detected no noteworthy changes in floristic composition towards forest species. On the contrary, four new pastureland species appeared outside of the exclusion area during the last year of evaluation. Other ungrazed sectors of the island showed qualitative differences from grazed sectors, such as major height and density of plants, and lower intensity of browsing, grazing, and trampling, attributable to a reduction of herbivorous pressure. The modest responses reported in this study could be related to the short lapse of time since the exclusion, soil compaction, overgrowth by a single species (A. argentea), great seasonal variations in different species’ abundances, the reduction in the number of cattle grazing the area previous to the fence’s installation, and persistent herbivory by rabbits (Oryctolagus cuniculus L.). We conclude that the effect of grazing by cattle is␣less than expected, and that there are other factors that delay the recovery of the Juan Fernández pasturelands.     

Impact of reindeer grazing on ground-dwelling Carabidae and Curculionidae assemblages in Lapland

Reindeer Rangifer tarandus L. grazing shapes forest vegetation, microclimate, and soil respiration in Lapland, especially due to grazing on lichens (Cladina). We studied how these changes and their magnitude affect ground‐dwelling species of beetle families Carabidae (predators) and Curculionidae (herbivores), by using pitfall traps to collect invertebrates from pairs of grazed and ungrazed study plots over a wide range of site types. Changes in abundance, composition, richness and diversity of beetle assemblage were tested in relation to magnitude of the impacts on vegetation. The species compositions of Carabidae and Curculionidae differed between grazed and ungrazed plots in all sites. The relative difference between grazed and ungrazed plots in the number of individuals increased linearly with the impact of reindeer on vegetation cover. Carabid beetles, as a family, were more common in grazed plots in all sites. Curculionid beetles were more common in ungrazed plots in the birch dominated sites. This difference was mainly due to the species that feeds on deciduous leaves. In the pine dominated sites with high Cladina cover and more changes in ground vegetation, the number of curculionids feeding on conifers was higher in grazed plots. Species richness and diversity (H’) of both families were higher in grazed plots. Of the total 27 species, 11 were found only in grazed plots, while not a single species was found only in ungrazed plots. The relative difference between plots in diversity and evennes (H’/H'max) had humped response to the difference in Cladina cover. The diversity values were greater in grazed plots at the intermediate levels of grazing impact, and only in sites with very low or extremely high Cladina cover difference was the diversity higher in ungrazed plots. The response of beetle diversity resembled the hypotheses suggested for the relationship between grazing and vegetation diversity: greatest positive effect at intermediate grazing intensity and negative effects at unproductive sites.     

森林放牧对东北虎豹国家公园东部有蹄类动物灌草层食物资源的影响

森林放牧是中国东北虎豹国家公园内影响最广泛且强度最大的人类干扰之一。研究放牧对有蹄类动物食物资源的影响,是估算当前状态下东北虎和东北豹主要猎物承载力的关键,可以为国家公园的管理提供有效的科学依据。本研究于2016年在中国东北虎豹国家公园东部的牧场和非牧场区域分层抽取50个林下样地设置围栏对照实验,于2017年生长季进行灌草层植被调查 (每个样地的围栏与对照各随机调查3个1m×1m的样方,共调查300个植物样方) ,并应用红外相机技术获取对照样地内有蹄类动物丰富度和活动情况,研究放牧对研究区灌草层植物及动物的影响。研究结果显示：在生长季内,森林放牧显著降低林下灌草层植物生物量 (减少约24%),牧场样地的嫩枝叶显著降低。除禾草外,牧场样地中其他类别植物的氮含量均显著高于非牧场样地 (平均超出非牧场样地25 %)。非牧场样地梅花鹿的相 对丰富度指数 (RAI) 显著高于牧场样地,而狍与野猪的相对丰富度指数 (RAI) 在这两类样地之间没有显著差别。研究结果表明,东北虎豹国家公园东部森林放牧,减少了有蹄类动物灌草层食物资源,降低了有蹄类动物的多度。建议停止森林放牧,恢复有蹄类动物栖息地。     

Influence of grazing and soil conditions on secondary savanna vegetation in India

Abstract. Savanna vegetation and pertinent soil features were studied on 43 sites in a dry tropical forest region of India. Grazing intensity ranged from 0.68 to 0.98. Soil moisture was positively related to the proportion of fine soil particles (< 0.1 mm), and the latter decreased while the proportion of coarse particles (2.0-0.5 mm) increased with increasing grazing intensity. Canopy biomass ranged from 28 to 104 g/m² in grazed communities and from 230 to 337 g /m² in ungrazed communities and was positively related to vegetation cover which ranged between 30–72 % in grazed and 68 - 91 % in ungrazed communities. Vegetation cover was negatively related to grazing intensity. Species richness and diversity were highest at low grazing intensity. Using community coefficients and Detrended Correspondence Analysis, the grazed stands were clustered into six and the ungrazed ones into three communities. The grazed communities were recognised as degradation stages and the ungrazed ones as recovery stages. Only five grass species, in various combinations were able to dominate in one of the different stages. Evidently the harsh climatic conditions (high temperatures, high variability in rainfall and a long dry period) in the region permit only a few species already adapted to these conditions to participate in the succession.     

Influence of cattle grazing practices on forest understorey structure in north‐eastern New South Wales

Abstract In eastern Australia the practice of grazing cattle in eucalypt forests and woodlands, as a supplementary activity to farmland grazing, is widespread. It is typically accompanied by burning at frequent intervals by graziers to promote more nutritious and digestible growth of the ground cover for their livestock. Collectively, these forest grazing practices affect understorey structure, which in turn affects other biotic and abiotic components of these ecosystems. In order to test how significant the effects of forest grazing practices are relative to the effects of other management practices and environmental variables and the degree to which grazing practices determine understorey vegetation structure, we surveyed 58 sites on the northern tablelands of New South Wales, Australia. All sites were located in eucalypt forest and were stratified by grazing status (presence or absence): time since logging, time since wildfire, geology, aspect, slope and topographic position. At each site an index of vegetation complexity and the most abundant plant species were recorded. The data were analysed by a backwards stepwise multiple regression. Grazing practices had the greatest influence on understorey vegetation complexity of any of the measured attributes. The grazed sites were characterized by a significantly lower vegetation complexity score, different dominant understorey species, reduced or absent shrub layers, and an open, simplified and more grassy understorey structure compared with ungrazed sites. Time since logging and time since wildfire also significantly affected understorey structure. Our results indicate that cattle grazing practices (i.e. grazing and the associated frequent fire regimes) can have major effects on forest structure and composition at a regional level.     

Long‐term effects of exclusion of grazing stock on degraded herbaceous plant communities in a riparian Eucalyptus camaldulensis forest in south‐eastern Australia

Abstract Stock grazing has degraded many riparian ecosystems around the world. However, the potential for ecosystem recovery following the removal of grazing stock is poorly known. We developed a conceptual model to predict the responses of native and exotic herbaceous plants to grazing exclusion, based on site productivity and the degree of initial vegetation degradation. The effects of excluding grazing stock on richness, cover and composition of herbaceous plants were examined over 12 years in the degraded understorey of a riparian forest in Gulpa Island State Forest in south‐eastern Australia. We predicted that grazing exclusion would lead to limited changes in vegetation cover, richness and composition, owing to presumed low site productivity and the high degree of understorey degradation. Results showed that the cover, richness and composition of native and exotic species varied significantly among years. Over all plots, regions and years, total cover was slightly but significantly lower in grazed than in ungrazed plots (43.4% vs. 50.8%). While the cover of native plants increased over time in both treatments, the rate of increase was slightly greater in ungrazed plots. Grazing exclusion had no effect on the richness of native or exotic species, but had a significant but minor impact on plant composition, with different common species (mostly exotics) being promoted or diminished in ungrazed plots. The composition of grazed and ungrazed areas did not become more different over time. Overall, the effects that could be attributed to grazing exclusion were relatively minor and transient. Results are consistent with predictions based on site productivity and initial degradation, and should not be extrapolated to other more productive, or less degraded, riparian systems.     

Correlation of burning and grazing indicators with composition of woody understorey flora of dells in a temperate eucalypt forest

Abstract Areas of warm temperate eucalypt forests of northern NSW escarpment, previously managed for cattle production, have recently been transferred into the conservation reserve system. The forests were seasonally grazed by cattle and were burnt frequently to promote green pick for stock feed. The hypothesis that disturbances associated with previous management had led to a simplification of the forest understorey, particularly a depletion in the density and species richness of shrubs was investigated. A disturbance history of the study area was constructed by compiling fire history records and using surrogate measures for recent and historical grazing. Shrub species composition was sampled in randomly located quadrats in dells within the forest, with a set of environmental and spatial covariables. Variation in shrub composition was partitioned among three sources (disturbance, environment and space) using a stepwise canonical correspondence analysis. Grazing and burning disturbance explained substantially more variation in vegetation than the environmental and spatial variables combined. Between 15 and 45% of total variation in adult shrub composition was attributable to the disturbance indicators. Similar results were obtained for composition of juvenile shrubs. Species richness and population densities of woody species were lower where disturbance was more intensive. It is concluded that historical grazing and burning practices had a substantial impact on the woody understoreys of the north‐east escarpment forests. The species that were adversely affected spanned a range of life‐history functional types. Estimates of the magnitude of grazing and burning impacts were limited by the lack of spatially explicit disturbance history data over the full period of pastoral exploitation and the unavailability of suitable ungrazed‘controls’for sampling.     

Impact of grazing on the species richness of plant communities in Mediterranean temporary pools (western Morocco)

The impact of grazing on the vegetation of Moroccan temporary pools has been studied at 2 scales: regional (inter-pools) and local (intra-pools). Half of the 16 forest pools studied is located in a reserve and ungrazed. The other half, located within public forest, is grazed. Vegetation relevés coupled to water-depths measurements were carried out in each pool. The results showed a significant effect of grazing on both scales of analysis. This effect was found in the species composition of the vegetation, which differed between the 2 types of pools, and in the lower species richness and abundance of plant species in the grazed pools. These differences are interpreted as resulting from the selection by herbivores and the differential tolerance of species to disturbance. These impacts are likely to expose certain species to local extinction by reducing their populations.     

Response to grazing after nine years of cattle exlusion in a Flooding Pampa grassland,Argentina

This paper reports on changes induced by the introduction of cattle in a grassland that had remained ungrazed for 9 yr, in comparison with two adjacent grasslands: one that remained enclosed and one that has been continuously subject to grazing. Basal cover was measured on 25 interception lines, each 1 m long, three times during one year. The variables studied were: total cover, cover of grasses and dicots, cover of creeping grasses, floristic composition, and dissimilarity among sites. At the first sampling, 2 yr after cattle re-introduction, the newly grazed site was more similar to the ungrazed than to the grazed site. The newly grazed site had very low cover of dicots; the species of dicots present were different from those found in the continuously grazed area. Creeping grasses had higher cover in the newly grazed site than in the other sites, and continued to increase. At the last sampling, one year later, the newly grazed site had become more similar to the contiuously grazed site. Only after 5 yr of cattle grazing the exotic dicots that were dominant in the continuously grazed site, were recorded in the re-opened site. The absence of propagules of these species or the absence of safe sites may account for this delayed invasion.     

Grazing‐induced changes in plant–soil feedback alter plant biomass allocation

Large vertebrate herbivores, as well as plant–soil feedback interactions are important drivers of plant performance, plant community composition and vegetation dynamics in terrestrial ecosystems. However, it is poorly understood whether and how large vertebrate herbivores and plant–soil feedback effects interact. Here, we study the response of grassland plant species to grazing‐induced legacy effects in the soil and we explore whether these plant responses can help us to understand long‐term vegetation dynamics in the field. In a greenhouse experiment we tested the response of four grassland plant species, Agrostis capillaris, Festuca rubra, Holcus lanatus and Rumex acetosa, to field‐conditioned soils from grazed and ungrazed grassland. We relate these responses to long‐term vegetation data from a grassland exclosure experiment in the field. In the greenhouse experiment, we found that total biomass production and biomass allocation to roots was higher in soils from grazed than from ungrazed plots. There were only few relationships between plant production in the greenhouse and the abundance of conspecifics in the field. Spatiotemporal patterns in plant community composition were more stable in grazed than ungrazed grassland plots, but were not related to plant–soil feedbacks effects and biomass allocation patterns. We conclude that grazing‐induced soil legacy effects mainly influenced plant biomass allocation patterns, but could not explain altered vegetation dynamics in grazed grasslands. Consequently, the direct effects of grazing on plant community composition (e.g. through modifying light competition or differences in grazing tolerance) appear to overrule indirect effects through changes in plant–soil feedback.     

Recovery of understorey vegetation after release from a long history of sheep grazing in a herb‐rich woodland

The effects of stock grazing on native grassy ecosystems in temperate southern Australia are well documented. However, less is known about the potential of ecosystems to recover after a long history of stock grazing and, in particular, whether the removal of stock will have positive, negative or neutral impacts on biodiversity. We examined the response of understorey vegetation to the removal of sheep grazing in a herb‐rich Eucalyptus camaldulensis (red gum) woodland in western Victoria. Using a space‐for‐time chronosequence, woodlands were stratified into groups based on their time‐since‐grazing removal; these were long‐ungrazed (>20 years), intermediate‐time‐since‐grazing (9–14 years), recently ungrazed (5 years) and continuously grazed. We found significantly higher species density in long‐ungrazed sites relative to sites with a more recent grazing history. No differences were found in species density between continuously grazed sites and those ungrazed in the previous 14 years. Species composition differed with time‐since‐grazing removal and indicator species analysis detected several native species (including tall native geophytes and herbs) associated with long‐ungrazed sites that were absent or in low abundance in the more recently grazed sites. Seven of the eight species significantly associated with continuously grazed sites were exotic. Removal of sheep grazing in red gum woodlands can have positive benefits for understorey diversity but it is likely that recovery of key indicators such as native species will be slow.     

Grazing effects upon plant community structure in subhumid grasslands of Argentina

Changes in plant community structure are identified as a result of grazing in grasslands of the flooding pampa which evolved under supposedly light grazing conditions. The effect of excluding grazing upon total leaf area index was an increase of 30%. The largest response was observed in the distribution of leaves in the canopy. In the grazed areas, most of the green material was concentrated in the 0–5 cm layer while in the ungrazed treatments the largest portion of the leaf area was in the 10–30 cm layer. Grazing exclusion resulted in a small change in total basal area but a larger change in its distribution, from many small tussocks to less numerous large ones. The effect of grazing upon leaf area and basal area was accounted for by changes in vigor as well as by changes in species composition. The major effect of excluding grazing upon species composition was the disappearance of some native planophile species and most of the exotics. The species composition of grazed areas of both communities was very similar while there were large differences between the ungrazed areas and between the grazed and ungrazed areas of the same community. It is suggested that there is a group of species which responds to the coarse-grained ‘signal’ of grazing and its presence can cause dissimilar communities to converge under grazing conditions. The other group of species responded to the fine-grained ‘signal’ of the environmental conditions associated with topography.     

Responses of Shrub Midstory and Herbaceous Layers to Managed Grazing and Fire in a North American Savanna (Oak Woodland) and Prairie Landscape

Worldwide, savanna remnants are losing acreage due to species replacement with shade-tolerant midstory forest species as a response to decades of fire suppression. Because canopy closes grasses and other easily ignitable fuels decline, therefore, fire, when reintroduced after years of absence, is not always effective at restoring the open structure original to these communities. Our study sought to determine if managed grazing is an alternative tool for reducing shrub densities and restoring savanna structure without the impacts on soils and native vegetation observed with unmanaged grazing. We compared effects of fire and managed grazing on shrub and herb composition within degraded oak savanna and tallgrass prairie of the U.S. Upper Midwest using a randomized complete block design. The vegetation response to treatments differed by species and by vegetation type. Total shrub stem densities declined 44% in grazed and 68% in burned paddocks within savanna and by 33% for both treatments within prairie. Within savanna, cattle reduced stem densities of Rubus spp. 97%, whereas fire reduced Ribes missouriense stems 96%. Both fire and grazing were effective at reducing stem numbers for several other shrub species but not to the same degree. Native forbs were suppressed in grazed savanna paddocks, as were native grasses in grazed prairie paddocks along with a minor increase of exotic forbs. We did not observe changes in soil bulk density. We conclude that managed grazing can serve as a valuable supplement but not as a replacement to fire for controlling shrubs in these systems.     

Differential Indirect Effects of Excluding Livestock and Rabbits from Chalk Heath on the Associated Leafhopper (Hemiptera: Auchenorrhyncha) Fauna

Preliminary results are presented of sampling the leafhopper assemblages on a field experiment designed to examine the differential effects of rabbits and livestock (mainly sheep) on the vegetation of chalk heath in southern England. Experimental plots that excluded livestock either allowed entry by rabbits or excluded them. Results were compared with those from plots grazed by both livestock and rabbits. After 7 years, exclusion of grazing herbivores had resulted in predictable increases in vegetation height, but no major changes were detected in the species composition of the vegetation. As expected, ungrazed plots had higher species richness and greater abundances of several individual leafhopper species. However, plots grazed only by rabbits had a leafhopper assemblage that was distinct from either ungrazed or mixed grazing plots. It is suggested that rabbit grazing may have subtle effects on grassland invertebrate assemblages that are not necessarily predictable from an examination of the species composition of the vegetation. Chalk heath vegetation contains an unusual mixture of calcicole and calcifuge plant species, but the leafhopper assemblage included a restricted number of calcareous grassland specialist species and only one species strongly associated with acidic grasslands; most leafhoppers recorded were generalist grassland species.     

Managing open habitats by wild ungulate browsing and grazing: A case‐study in North‐Eastern Germany

Question: Can wild ungulates efficiently maintain and restore open habitats? Location: Brandenburg, NE Germany. Methods: The effect of wild ungulate grazing and browsing was studied in three successional stages: (1) Corynephorus canescens‐dominated grassland; (2) ruderal tall forb vegetation dominated by Tanacetum vulgare; and (3) Pinus sylvestris‐pioneer forest. The study was conducted over 3 yr. In each successional stage, six paired 4 m²‐monitoring plots of permanently grazed versus ungrazed plots were arranged in three random blocks. Removal of grazing was introduced de novo for the study. In each plot, percentage cover of each plant and lichen species and total cover of woody plants was recorded. Results: Wild ungulates considerably affected successional pathways and species composition in open habitats but this influence became evident in alteration of abundances of only a few species. Grazing effects differed considerably between successional stages: species richness was higher in grazed versus ungrazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Herbivory affected woody plant cover only in the Pioneer forest sites. Although the study period was too short to observe drastic changes in species richness and woody plant cover, notable changes in species composition were still detected in all successional stages. Conclusion: Wild ungulate browsing is a useful tool to inhibit encroachment of woody vegetation and to conserve a species‐rich, open landscape.     

Effects of grazing on geophytes in Mediterranean vegetation

Abstract. The response of geophyte species diversity and frequency of individual geophyte species to cattle grazing was measured at 68 site pairs along fences separating ungrazed from grazed grassland and woodland on different geological formations in northern Israel. Over all site pairs, geophyte species density per 4 m² was significantly greater in grazed (2.37) than in protected (1.96) sites of the same site pair. There was considerable variation between site pairs in the magnitude and in the direction of the grazing effect. Part of this variation could be explained by differences in site altitude and in geological formation. The positive effect of grazing on geophyte diversity was lower in sites with low productivity. Of 22 geophyte taxa for which sufficient data were available, nine indicated greater frequency in grazed sites compared to only two in ungrazed sites. In 11 other taxa the response was not consistent. A positive response to grazing was most common in geophytes with narrow leaves of the Iridaceae, Liliaceae and allied families. Conservation of the entire geophyte flora in Mediterranean vegetation requires livestock grazing at moderate to high intensities in parts of the area of each community, and light or no grazing in other parts.     

Impact of cervid browsing and grazing on the terrestrial gastropod fauna in the boreal forests of Fennoscandia

Selective foraging by cervids can affect vegetation, and that in turn can have far-reaching effects on various components of the boreal forest ecosystem. Since terrestrial gastropods are sensitive to habitat alterations, they can be expected to respond to changes caused by grazing. This study is based on gastropod specimens from two data sets that were collected with pitfall traps in order to study the effects of moose and reindeer on ground-layer invertebrates. Invertebrates were trapped from 23 pairs of plots, where one plot was open to all animals while the other one was fenced to exclude large mammals. Half of the sites were in Finnish Lapland, where reindeer grazing was the main cause of differences between the plots; the rest were located in central Sweden and southern Finland, where moose was the most important cervid grazer. The composition of the gastropod fauna differed between grazed and ungrazed plots in both areas, and the abundance of gastropods in general and that of many species was higher in ungrazed plots (the number of gastropods caught was 17% lower in grazed than in ungrazed plots in moose sites, and 24% smaller in reindeer sites). Species richness differed significantly between grazed and ungrazed plots in the combined data of both site types, and was 15% higher in ungrazed plots. In moose sites the relative diversity (H′/H′_max) of gastropods was 17% higher in grazed plots. In reindeer sites, the means of richness and diversity (H′) were considerably higher in ungrazed plots (35% and 40% respectively) but the differences were only marginally significant. By indirectly modifying the microclimate within the forest, cervids fulfil the criteria for a ‘physical ecosystem engineer’. Since the population density and distribution of terrestrial gastropods depend largely on the physical conditions of the microhabitat, the engineering effects of cervids are the most likely cause of the changes observed in the density and composition of the gastropod fauna in the boreal forest.     

Long-term vegetation dynamics mediated by herbivores,weather and fire in a Juniperus-Quercus savanna

Abstract. Long-term (45-yr) basal area dynamics of dominant graminoid species were analyzed across three grazing intensity treatments (heavily grazed, moderately grazed and ungrazed) at the Texas A&M University Agricultural Research Station on the Edwards Plateau, Texas. Grazing intensity was identified as the primary influence on long-term variations in species composition. Periodic weather events, including a severe drought (1951–1956), had little direct influence on composition dynamics. However, the drought interacted with grazing intensity in the heavily grazed treatment to exacerbate directional changes caused by grazing intensity. Species response to grazing was individualistic and noisy. Three response groups were identified. Taller, more productive mid-grasses were most abundant under moderate or no grazing. Short grasses were most abundant under heavy grazing. Intermediate species were most abundant under moderate grazing and opportunistic to weather patterns. Graminoid diversity increased with the removal or reduction of grazing intensity. The moderately and ungrazed treatments appeared most resistant to short-term weather fluctuations, while the heavily grazed treatment demonstrated significant resilience when grazing intensity was reduced after over 110 yr of overgrazing. Identification of a ‘climax’ state is difficult. Significant directional change, which took nearly 20 yr, appears to continue in the ungrazed treatment after 45 yr of succession. The observed, relatively linear patterns of perennial grass composition within the herbaceous patches of this savanna were generally explained by traditional Clementsian succession. However, when dynamics of the herbaceous community are combined with the woody component of this savanna, the frequency and intensity of fire becomes more important. Across the landscape, successional changes follow several pathways. When vegetation change is influenced by several factors, a multi-scale model is necessary to demonstrate interactions and feedbacks and accurately describe successional patterns. Absence of fires, with or without grazing, leads ultimately to a Juniperus/Quercus woodland with grazing intensity primarily influencing the fuel load and hence fire intensity.     

Mediating Water Temperature Increases Due to Livestock and Global Change in High Elevation Meadow Streams of the Golden Trout Wilderness

Rising temperatures due to climate change are pushing the thermal limits of many species, but how climate warming interacts with other anthropogenic disturbances such as land use remains poorly understood. To understand the interactive effects of climate warming and livestock grazing on water temperature in three high elevation meadow streams in the Golden Trout Wilderness, California, we measured riparian vegetation and monitored water temperature in three meadow streams between 2008 and 2013, including two “resting” meadows and one meadow that is partially grazed. All three meadows have been subject to grazing by cattle and sheep since the 1800s and their streams are home to the imperiled California golden trout (Oncorhynchus mykiss aguabonita). In 1991, a livestock exclosure was constructed in one of the meadows (Mulkey), leaving a portion of stream ungrazed to minimize the negative effects of cattle. In 2001, cattle were removed completely from two other meadows (Big Whitney and Ramshaw), which have been in a “resting” state since that time. Inside the livestock exclosure in Mulkey, we found that riverbank vegetation was both larger and denser than outside the exclosure where cattle were present, resulting in more shaded waters and cooler maximal temperatures inside the exclosure. In addition, between meadows comparisons showed that water temperatures were cooler in the ungrazed meadows compared to the grazed area in the partially grazed meadow. Finally, we found that predicted temperatures under different global warming scenarios were likely to be higher in presence of livestock grazing. Our results highlight that land use can interact with climate change to worsen the local thermal conditions for taxa on the edge and that protecting riparian vegetation is likely to increase the resiliency of these ecosystems to climate change.     

Removal of cattle accelerates tropical dry forest succession in Northwestern Mexico

Domestic livestock influence patterns of secondary succession across forest ecosystems. However, the effects of cattle on the regeneration of tropical dry forests (TDF) in Mexico are poorly understood, largely because it is difficult to locate forests that are not grazed by cattle or other livestock. We describe changes in forest composition and structure along a successional chronosequence of TDF stands with and without cattle (chronic grazing or exclusion from grazing for ~ 8 year). Forest stands were grouped into five successional stages, ranging from recently abandoned to mature forest, for a total of 2.7 ha of the sampled area. The absence of cattle increased woody plant (tree and shrub) density and species richness, particularly in mid-successional and mature forest stands. Species diversity and evenness were generally greater in sites where cattle were removed and cattle grazing in early successional stands reduced establishment and/or recruitment of new individuals and species. Removal of cattle from forest stands undergoing succession appears to facilitate a progressive and non-linear change of forest structure and compositional attributes associated with rapid recovery, while cattle browsing acts as a chronic disturbance factor that compromises the resilience and structural and functional integrity of the TDF in northwestern Mexico. These results are important for the conservation, management, and restoration of Neotropical dry forests.