Livestock Exclusion Research Articles

Effects of livestock exclusion in forests of Uruguay: Soil condition and tree regeneration

Livestock intervention, depending on the regime of grazing and the sensitivity of species, could alter the structure, composition and dynamics of forest ecosystems, with negative long-term impacts on plant communities, soil and water quality, and thus on the provision of ecosystem services. We studied here the effects of livestock on forest ecosystems of Uruguay where livestock ranching is the most extensive and traditional production activity. The aim of the present study was to investigate the effects of livestock exclusion on forest dynamics, particularly on tree regeneration and soil properties. We analyzed six grazed–ungrazed (4–17years of exclusion by fences) paired sites, in hillside forests of Uruguay. Our results indicate that exclusion contributes to improve soil conditions by increasing leaf litter cover and tending to reduce erosion. Regeneration was also improved under exclusions, with increased density of tree seedling (+20%) and saplings (+60%). Species composition of regenerating trees was in general not affected by exclusion, but one (i.e., Styrax leprosus) of the 11 sapling species sampled was almost absent in grazed sites. Despite the short-term experiment, our findings indicate that livestock exclusion is a useful tool to protect hillside forests of Uruguay by improving soil conditions and providing opportunities for the regeneration of shade-tolerant and grazing-susceptible species. Light-demanding species, such as canopy-dominant trees Scutia buxiflora and Lithraea brasiliensis presented very low densities of saplings and seedlings, in either grazed or un-grazed sites, suggesting that our enclosure treatment failed to generate adequate microsites for such species. Forest gaps and grassland–forest transitions should be incorporated in future enclosures to benefit light-demanding trees.

Herbivory and Competition of Tibetan Steppe Vegetation in Winter Pasture: Effects of Livestock Exclosure and Plateau Pika Reduction.

Rangeland degradation has been identified as a serious concern in alpine regions of western China on the Qinghai-Tibetan plateau (QTP). Numerous government-sponsored programs have been initiated, including many that feature long-term grazing prohibitions and some that call for eliminating pastoralism altogether. As well, government programs have long favored eliminating plateau pikas (Ochotona curzoniae), assumed to contribute to degraded conditions. However, vegetation on the QTP evolved in the presence of herbivory, suggesting that deleterious effects from grazing are, to some extent, compensated for by reduced plant-plant competition. We examined the dynamics of common steppe ecosystem species as well as physical indicators of rangeland stress by excluding livestock and reducing pika abundance on experimental plots, and following responses for 4 years. We established 12 fenced livestock exclosures within pastures grazed during winter by local pastoralists, and removed pikas on half of these. We established paired, permanent vegetation plots within and outside exclosures and measured indices of erosion and biomass of common plant species. We observed modest restoration of physical site conditions (reduced bare soil, erosion, greater vegetation cover) with both livestock exclusion and pika reduction. As expected in areas protected from grazing, we observed a reduction in annual productivity of plant species avoided by livestock and assumed to compete poorly when protected from grazing. Contrary to expectation, we observed similar reductions in annual productivity among palatable, perennial graminoids under livestock exclusion. The dominant grass, Stipa purpurea, displayed evidence of density-dependent growth, suggesting that intra-specific competition exerted a regulatory effect on annual production in the absence of grazing. Complete grazing bans on winter pastures in steppe habitats on the QTP may assist in the recovery of highly eroded pastures, but may not increase annual vegetative production.

Long-term impacts of grazing intensity on soil carbon sequestration and selected soil properties in the arid Eastern Cape, South Africa.

Little is known about how basic soil properties respond to contrasting grazing intensities in the Karoo biome, South Africa. The aim of this study was to investigate impacts of long-term (>75 years) grazing at 1.18 heads ha(-1) (heavy; CGH), 0.78 heads ha(-1) (light; CGL), and exclosure on selected soil properties. Soil samples were collected to a depth of 60 cm from the long-term experimental site of Grootfontein Agricultural Development Institute, Eastern Cape. The samples were analyzed for C, N, bulk density and infiltration rate, among others. Generally, heavy and light grazing reduced soil N storage by 27.5% and 22.6%, respectively, compared with the exclosure. Animal exclusion improved water infiltration rate and C stocks significantly (P < 0.05), which was 0.128, 0.097, and 0.093 Mg ha(-1) yr(-1) for exclosure, CGL and CGH, respectively. Soil penetration resistance was higher for grazing treatments in the top 3-7 cm soil layer but for exclosure at the top 1 cm soil surface. Although livestock exclusion has the potential to improve C sequestration, a sufficient resting period for 1-2 years followed by three consecutive grazing years at light stocking rate would be ideal for sustainable livestock production in this arid region of South Africa.

Long-term livestock exclusion facilitates native woody plant encroachment in a sandy semiarid rangeland.

The role of livestock grazing in regulating woody cover and biomass in grass-dominant systems is well recognized. However, the way in which woody plant populations in respond when livestock are removed from grazing in the absence of other disturbances, such as fire, remains unclear.We conducted a 10-year, replicated fencing experiment in a sandy semiarid rangeland in northern China (which has a mean annual rainfall of 365 mm), where fires have been actively suppressed for decades.Fencing dramatically influenced the growth and age structure of the native tree species, Ulmus pumila, which is the sole dominant tree in the area. After a decade, the density of the U. pumila tree population in the fencing plots increased doubly and canopy cover increased triply. The proportion of both saplings (U2) and young trees (U3) increased in fencing plots but decreased in grazing plots after the 10-year treatment period. The effects of fencing on U. pumila trees varied by age class, with potential implications for the future structure of the U. pumila tree community. Decadal fencing led to approximately 80-fold increase in recruitment and a nearly 2.5-fold decrease in the mortality of both U2 and U3. Further, livestock grazing generated a “browsing trap” to the recruitment of both U2 and U3, and had a small impact on the mortality of old trees. A long-term, fencing-driven shift in woody species composition was mediated via its effects on both recruitment and mortality rates.Synthesis and applications. Our results demonstrate that in the long-term absence of both fire and livestock, native woody plant encroachment tends to occur in sandy rangelands, transforming the woody plant demography in the process. The feasibility of full livestock exclusion in sandy rangelands requires further discussion. A balanced amount of livestock grazing may provide critical ecosystem services by regulating woody cover and mediating woody plant encroachment.

Effects of open grazing and livestock exclusion on floristic composition and diversity in natural ecosystem of Western Saudi Arabia

Livestock grazing is one of the main causes of rangeland degradation in Saudi Arabia. Fencing to exclude grazers is one of the main management practices used to restore vegetation and conserve biodiversity. The main objectives of this study were to investigate the changes in plant diversity and abundance, floristic composition and plant groups of the major life forms in response to thirty-five years of grazing exclosure in western Saudi Arabia. These vegetation attributes and palatability were compared in 30 sampling stands located in the excluded and grazed sites. Our results showed that livestock exclusion significantly increased covers, density and species richness of annuals, grasses, perennial forbs, shrubs and trees. Exclosure enhanced the abundance and richness of palatable species and depressed the development of weedy species. About 66.7% of the recorded species at the excluded site were highly palatable compared to 34.5% at the grazed site. In contrary, about 55.2% unpalatable species were found in the grazed site compared to 25.8% in the protected site. Jaccard’s similarity index between the excluded and grazed sites showed lower values of 0.39%, 0.40% and 0.31% at levels of families, genus and species, respectively. The results suggest that establishing livestock exclusion may be a useful sustainable management tool for vegetation restoration and conservation of plant diversity in degraded rangelands of arid regions.

Effects of Livestock Exclusion on Soil Physical and Biochemical Properties of a Desert Rangeland

Livestock grazing is recognized as one of the main causes of vegetation and soil degradation and desertification in the arid and semiarid parts of northern China. The effects of grazing on soil enzyme activities, soil properties, and plant characteristics in a typical degraded area of desert steppe in the Alxa region were studied. We set sampling transects for vegetation property evaluation and soil sampling, and compared soil enzyme activities, soil properties, and plant characteristics under continuous year-long livestock grazing (FU), grazing excluded for six years (2002EX), and grazing excluded for 10 years (1998EX). Soil enzyme activities increased significantly with the duration of livestock exclusion. Compared with FG, activities in 1998EX of urease (URE), alkaline phosphatase (AKP), catalase (CAT), and saccharase (SAC) were 214%, 121%, 17%, and 76% higher, respectively. Exclusions also enhanced organic carbon (SOC), total nitrogen (TN) and phosphorus (TP), and inorganic nitrogen (IN) and phosphorus (2) accumulation, but reduced soil pH and bulk density. Microbial biomass carbon (MBC) and nitrogen (MBN) were ranked 1998EX > 2002EX > PG. Soil enzyme activities were significantly positively correlated with SOC (p<0.01), MBC, and MBN (p<0.01), but negatively correlated with soil bulk density. While continuous overgrazing in the erosion-prone desert steppe is detrimental to soil and vegetation, this can be reversed and significant increases in soil fertility, cover, and biomass can be achieved by grazing exclusion. Our results also indicate that soil microbial biomass and enzyme activities are sensitive to exclusion, and thus may be important indicators of the soil changes associated with management history.

Bird responses to riparian management of degraded lowland streams in southeastern Australia

We assessed the degree to which fencing, livestock exclusion, and replanting of riparian zones affected avian assemblages in massively cleared landscapes. Measurements were made at three creeks in the southern Murray–Darling Basin in southeastern Australia, each of which had circa 1‐km long treated sections and paired “untreated” circa 1‐km sections, where no fencing, planting, or stock exclusion was done. We measured the change in vegetation characteristics and abundances of native birds for up to 8 years after works were completed. Prior to data collection, we developed expected responses of bird species based on the anticipated time‐courses of change in vegetation structure. We used hierarchical Bayesian models to explore the effects of the management actions, and to account for within‐site variation in vegetation characteristics. There were major changes in vegetation structure (reductions in bare ground and increases in shrubs and tree recruitment) but avian responses generally were small and not as expected. There are at least four possible reasons for the limited avian responses: (1) there has been a long‐term decline in woodland birds across the region; (2) the study was conducted during the longest drought in the instrumental record in the study region; (3) the total amount of replanted vegetation was small in a massively denuded region; and (4) monitoring may have been over too short a term to detect responses to longer‐term changes in structural vegetation.

Experimental evidence that even minor livestock trampling has severe effects on land snail communities in forest remnants

Summary Land‐use intensification is increasing dramatically in production systems world‐wide. Livestock production is an important component of production land use, and increases in livestock densities have had a wide range of negative consequences. The off‐site effects of livestock grazing and trampling on native vegetation adjacent to pastoral land have received less attention than on‐farm effects. Moreover, where significant ecological effects of livestock spillover have been identified, the mechanistic determinants of these effects have not typically been investigated. Here, we tested the mechanistic drivers of livestock trampling effects on land snail communities in forest remnants using simulated trampling under field conditions. We used a factorial combination of leaf‐litter manipulation and trampling treatments to partition different causal drivers of livestock impacts on land snail communities and related them to five environmental variables that are altered by livestock. We show that even very low frequency trampling caused severe changes to land snail communities. Land snail density, even under the lowest trampling frequency, declined by an average of 42 individuals m−2 and land snail species richness decreased by an average of 10 species per plot compared with control plots. The underlying drivers of changes in land snail communities varied, but were primarily linked to leaf‐litter mass, rather than soil compaction. Synthesis and applications. Overall, these results suggest that even minimal disturbance by livestock has large effects on land snail communities, but the underlying drivers of these effects require further investigation in longer duration and more intensive studies. Our results provide strong support for livestock exclusion as an important management tool for native forest remnants embedded within production landscapes.

Plantaciones forestales vs. regeneración natural in situ : El caso de los pinos y la rehabilitación en el Parque Nacional Cofre de Perote

El conocimiento de la estructura y dinámica de la vegetación como estimadores del desempeño de las plantaciones forestales y de la regeneración natural en la rehabilitación es escaso, y tampoco se conoce el efecto de la ganadería extensiva sobre ambas. El objetivo de este estudio fue comparar el número de individuos por hectárea y la tasa anual de crecimiento entre las comunidades de pinos ( Pinus patula , P. montezumae y P. teocote ) procedentes de las plantaciones forestales y de la regeneración natural en sitios con dos diferentes condiciones (con y sin exclusión de ganado). Se encontraron diferencias significativas (P &lt; 0.0001) en la tasa anual de crecimiento de la altura, en el diámetro basal del tallo y en el diámetro promedio de cobertura entre las plantaciones vs . la regeneración natural y entre las dos condiciones de exclusión de ganado. El número de individuos establecidos por hectárea fue significativamente mayor en la regeneración natural con exclusión de ganado (1,380 ± 120 y 1,130 ± 130) que en aquella sin exclusión (430 ± 250), y en las plantaciones forestales con o sin exclusión de ganado (995 ± 90 y 455 ± 125, respectivamente; P &lt; 0.0001). Se concluye que la regeneración natural de pinos es una opción adecuada para la rehabilitación ecológica en terrenos degradados, especialmente si están protegidos del ganado, en comparación con las plantaciones forestales.

Biological soil crusts across disturbance–recovery scenarios: effect of grazing regime on community dynamics.

Grazing represents one of the most common disturbances in drylands worldwide, affecting both ecosystem structure and functioning. Despite the efforts to understand the nature and magnitude of grazing effects on ecosystem components and processes, contrasting results continue to arise. This is particularly remarkable for the biological soil crust (BSC) communities (i.e., cyanobacteria, lichens, and bryophytes), which play an important role in soil dynamics. Here we evaluated simultaneously the effect of grazing impact on BSC communities (resistance) and recovery after livestock exclusion (resilience) in a semiarid grassland of Central Mexico. In particular, we examined BSC species distribution, species richness, taxonomical group cover (i.e., cyanobacteria, lichen, bryophyte), and composition along a disturbance gradient with different grazing regimes (low, medium, high impact) and along a recovery gradient with differently aged livestock exclosures (short-, medium-, long-term exclusion). Differences in grazing impact and time of recovery from grazing both resulted in slight changes in species richness; however, there were pronounced shifts in species composition and group cover. We found we could distinguish four highly diverse and dynamic BSC species groups: (1) species with high resistance and resilience to grazing, (2) species with high resistance but low resilience, (3) species with low resistance but high resilience, and (4) species with low resistance and resilience. While disturbance resulted in a novel diversity configuration, which may profoundly affect ecosystem functioning, we observed that 10 years of disturbance removal did not lead to the ecosystem structure found after 27 years of recovery. These findings are an important contribution to our understanding of BCS dynamics from a species and community perspective placed in a land use change context.

Effects of different restoration measures and sand dune topography on short- and long-term vegetation restoration in northeast China

Our study investigated the effects of different restoration measures and sand dune topography on vegetation restoration in the Horqin Sandy Land, China. We conducted a vegetation survey at different topographic positions on sand dunes at four different types of restoration sites (i.e., grazing-exclusion, shrub-planting, pine-planting, and poplar-planting sites) with restoration periods of ≤35 years and two control sites (i.e., shifting sand dunes and fixed sand dunes). We found a restoration trajectory, starting from shifting sand dunes and aligning all the sites in chronological order. Five restoration phases were identified by distinct species composition in the trajectory. The planting of trees progressed vegetation restoration faster than livestock exclusion and the planting of shrubs. The planting of trees restored shifting sand dunes to the same level of fixed sand dunes after 25 years. Thirty-five years may restore shifting sand dunes to a near-stable state characterized by Cleistogenes squarrosa. We found sequential turnover in species composition along the upward topographic gradient throughout the restoration trajectory, indicating that vegetation restoration on sand dunes is promoted by a process where diaspores establish and spread upward from interdune lowland. Our study provides ecological foundations and suggestions for developing and implementing practical restoration programs in the sand dune area.

Effects of grazing exclusion on soil carbon and nitrogen storage in semi-arid grassland in Inner Mongolia, China

The semi-arid grasslands in Inner Mongolia, China have been degraded by long-term grazing. A series of ecological restoration strategies have been implemented to improve grassland service. However, little is known about the effect of these ecological restoration practices on soil carbon and nitrogen storage. In this study, characteristics of vegetation and soil properties under continued grazing and exclusion of livestock for six years due to a nationwide conservation program—‘Returning Grazing Lands to Grasslands (RGLG)’ were examined in semi-arid Hulun Buir grassland in Inner Mongolia, China. The results show that removal of grazing for six years resulted in a significant recovery in vegetation with higher above and below-ground biomass, but a lower soil bulk density and pH value. After six years of grazing exclusion, soil organic C and total N storage increased by 13.9% and 17.1%, respectively, which could be partly explained by decreased loss and increased input of C and N to soil. The effects of grazing exclusion on soil C and N concentration and storage primarily occurred in the upper soil depths. The results indicate that removal of grazing pressure within the RGLG program was an effective restoration approach to control grassland degradation in this region. However, more comprehensive studies are needed to evaluate the effectiveness of the RGLG program and to improve the management strategies for grassland restoration in this area.

Can livestock grazing maintain landscape diversity and stability in an ecosystem that evolved with wild herbivores?

The livestock industry is converting mountain ecosystems in central Argentina into rocky deserts. However, it helps to conserve plant biodiversity, presumably because the ecosystem has evolved under wild herbivores now locally extinct. We hypothesized that low or moderate livestock stocking rates, instead of the high stocking rates currently used for commercial production, might mimic pre-hispanic herbivore pressures. Thus, the mosaic of physiognomies necessary to maintain landscape diversity and soil integrity could be preserved. To test this hypothesis we tracked physiognomic changes in 200 plots (16 m2 each) under different stocking rates, including livestock exclusion, for five years. Contrary to our expectations, we found that both low and moderate stocking rates failed to maintain landscape diversity. As observed for livestock exclusion, low to moderate stocking rates promote retraction and, finally, elimination of short grazing lawns and their replacement by tall tussock grasslands, or possibly by woody vegetation. In turn, heavy grazing pressure maintains the desired short lawn patches in the landscape, but also promotes a concomitant loss and eventual elimination of woodlands, together with an expansion of bare rock as a consequence of soil erosion. These results indicate that the present mosaic of physiognomic types is difficult to maintain and raise questions about the past stability of the ecosystem. We suggest that during the last 400 years of livestock production in the ecosystem, short lawns have been maintained by means of heavy stocking rates and anthropogenic fires ignited to eliminate tussocks. However, this relative stability of lawns has been attained concomitantly with a progressive loss of soils and woodland area. We also discuss some possible explanations for the maintenance of short lawns before the introduction of livestock, based on main climatic and floristic shifts during the late Holocene.

Effects of livestock exclusion and climate change on aboveground biomass accumulation in alpine pastures across the Northern Tibetan Plateau

To better understand the ecological and economic benefits of short-term grazing exclusion on the aboveground net primary productivity (ANPP) of alpine pastures, we conducted annual multi-site transect surveys in the summers from 2009 to 2011 and calculated the aboveground biomass discrepancy (ABD) between grazed and ungrazed pastures at plant community and economic group levels for three zonal alpine grassland types—meadow, steppe, and desert-steppe—across the northern Tibetan Plateau. Our results indicated that aboveground biomass (AGB) significantly differed among grassland types and declined northwesterly from 64.07 to 11.44 g m−2 with decreasing precipitation and increasing temperature. The mean ABD exhibited considerable community dependency, with meadow (12.47 g m−2) > steppe (6.91 g m−2) > desert steppe (2.54 g m−2), and it declined from 25.42 to 1.29 g m−2 with decreasing precipitation and increasing temperature. ‘Good forage’, i.e. grasses and sedges, benefited most from grazing exclusion, followed by edible forbs. With longer grazing exclusion durations (GEDs), the aboveground biomass of poisonous locoweeds initially decreased and then increased compared with the adjacent grazed sites. In the nested analysis of co-variances with a general linear model, growing season precipitation (GSP; from May to September) accounted for 52.67% of the observed variation in AGB, followed by AGT (9.77 %) and pasture management systems (PMSs; grazing or grazing-excluded, 5.31 %). The variation in ABD was explained primarily by AGT (16.52 %), GED (20.25 %), and the interaction of AGT × GED (19.58 %). Our results confirm that precipitation is the primary factor controlling the ANPP of alpine grasslands on the Northern Tibetan Plateau and that the ecological benefits arising from grazing exclusion are also partly dependent on grassland type and exclusion duration. Therefore, spatial and temporal variations in growing season precipitation and plant functional traits or economic group composition should be jointly considered when developing policies concerning the management and spatial layouts of grazing exclosures in this region.

Effectiveness of exclosures for restoring soils and vegetation degraded by overgrazing in the Junggar Basin, China

AbstractThe desert steppe exclosure system was constructed in 2003 to implement the Chinese policy that banned livestock grazing to permit recovery of overgrazed rangeland. Empirical data on the effectiveness of excluding livestock grazing on restoring degraded desert soils and vegetation in western China is limited. Additional data are necessary for making alternative grassland management decisions and implementing effective subsidy policy. In this paper, desert vegetation in an extremely dry area, which was fenced to exclude winter sheep grazing in 2003, was compared to adjacent sites where winter grazing has been continued. Vegetation was sampled to determine plant species richness, vegetation composition and herb‐shrub layer cover. Soil properties were also measured. Results showed that excluding sheep grazing from desert steppe for 8 years increased plant cover and approximately tripled the biomass of standing vegetation, especially the shrub component. Livestock exclusion was more favorable for the growth of perennial grasses. Annual forbs were more abundant in the grazed area than in the ungrazed area. Species richness, evenness and diversity as measured by Simpson or Shannon‐Wiener indices did not differ between the grazed and ungrazed areas (P &gt; 0.05), which indicated that species composition of the desert vegetation is difficult to restore. Excluding livestock grazing increased soil organic carbon in the 0–10 cm (by 66%) and 10–20 cm (26%) soil depths, total nitrogen in the 0–10 cm (110%) and 10–20 cm (60%) soil depths and total phosphorus in the 0–10 cm (114%) and 10–20 cm (64%) soil depths (P &lt; 0.05). Our results demonstrated that vegetation biomass and soil properties can be improved by removal of sheep grazing, but had less impact on the species richness and diversity in this extremely dry region. It also affirms the current central government's policy of banning grazing to benefit the recovery of ecological services.

Experimental Rehabilitation of Degraded Spawning Habitat of a Diadromous Fish, Galaxias maculatus (Jenyns, 1842) in Rural and Urban Streams

AbstractRiparian vegetation has been compromised worldwide by anthropogenic stressors, including urbanization and livestock grazing. In New Zealand, one consequence has been a reduction in the obligate riparian spawning habitat of Galaxias maculatus. This diadromous species forms the basis of an important fishery where juveniles are caught as they migrate into freshwater. Spawning success of G. maculatus is closely associated with the nature of available riparian habitat. We used a field experiment in a rural stream to test whether livestock grazing limits egg production and whether there is a lag in increased egg production after protection from grazing because of the recovery time of riparian vegetation. In a separate experiment in an urban stream we tested whether improved riparian management can increase egg production. Livestock exclusion produced an immediate and long‐lasting increase in the height and density of riparian vegetation with reduced fluctuations in the ground‐level physical environment, and positive changes to the density and survival of eggs. After 4 years, egg densities in exclosures were 400 times greater than in grazed controls and egg survival had doubled. Mowing riparian vegetation 2 months prior to spawning reduced egg densities by 75% and survival by 25%. Our experiments showed that altering grazing and mowing in spawning sites produced dense riparian vegetation, that this improved the microsite environment and resulted in greatly increased egg deposition and survival over several years. This clearly indicates that the single most effective step in rehabilitating G. maculatus spawning habitat is a simple reduction in grazing/mowing pressure.

Divergent responses to long-term grazing exclusion among three plant communities in a flood pulsing wetland in eastern Australia.

We examined the effects of grazing exclusion over a period of 14 years on the species richness and community composition of three plant communities with different dominant species and water regimes in the Gwydir Wetlands in eastern Australia. Responses to grazing exclusion varied among the three plant communities, and were most likely to be evident during dry periods rather than during periods of inundation. In frequently flooded plant communities, there was an increase in phytomass following exclusion of domestic livestock, but changes in plant community composition and species richness due to livestock exclusion varied depending on the morphological attributes of the dominant plant species. In a plant community where tall sedge species were dominant, livestock exclusion further increased their dominance and overall species richness declined. In contrast, where a prostrate grass species such as Paspalum distichum was dominant, species richness increased following livestock exclusion, due to an increase in the abundance of taller dicotyledon species. However, livestock exclusion in a community where flooding was less frequent and native grass species have been largely replaced with the introduced species Phyla canescens, resulted in no significant changes to phytomass, species richness or community composition among the grazing exclusion treatments over time. Our results indicate responses to exclusion of domestic livestock are dependent upon the dominant species within the plant community and will likely vary over time with the extent of wetland inundation. Grazing exclusion alone, without increased flooding, is unlikely to restore floristically degraded floodplain plant communities.

Protection Benefits Desert Tortoise (Gopherus agassizii) Abundance: The Influence of Three Management Strategies on a Threatened Species

We surveyed an area of ∼260 km2 in the western Mojave Desert to evaluate relationships between condition of Agassiz's Desert Tortoise populations (Gopherus agassizii) and habitat on lands that have experienced three different levels of management and protection. We established 240 1-ha plots using random sampling, with 80 plots on each of the three types of managed lands. We conducted surveys in spring 2011 and collected data on live tortoises, shell-skeletal remains, other signs of tortoises, perennial vegetation, predators, and evidence of human use. Throughout the study area and regardless of management area, tortoise abundance was positively associated with one of the more diverse associations of perennial vegetation. The management area with the longest history of protection, a fence, and legal exclusion of livestock and vehicles had significantly more live tortoises and lower death rates than the other two areas. Tortoise presence and abundance in this protected area had no significant positive or negative associations with predators or human-related impacts. In contrast, the management area with a more recent exclusion of livestock, limited vehicular traffic, and with a recent, partial fence had lower tortoise densities and high death rates. Tortoise abundance here was negatively associated with vehicle tracks and positively associated with mammalian predators and debris from firearms. The management area with the least protection—unfenced, with uncontrolled vehicle use, sheep grazing, and high trash counts—also had low tortoise densities and high death rates. Tortoise abundance was negatively associated with sheep grazing and positively associated with trash and mammalian predator scat.

Semiarid Rangeland Is Resilient to Summer Fire and Postfire Grazing Utilization

Most wildfires occur during summer in the northern hemisphere, the area burned annually is increasing, and fire effects during this season are least understood. Understanding plant response to grazing following summer fire is required to reduce ecological and financial risks associated with wildfire. Forty 0.75-ha plots were assigned to summer fire then 0, 17, 34 or 50% biomass removal by grazing the following growing season, or no fire and no grazing. Root, litter, and aboveground biomass were measured before fire, immediately after grazing, and 1 yr after grazing with the experiment repeated during 2 yr to evaluate weather effects. Fire years were followed by the second driest and fifth wettest springs in 70 yr. Biomass was more responsive to weather than fire and grazing, with a 452% increase from a dry to wet year and 31% reduction from a wet to average spring. Fire reduced litter 53% and had no first-year effect on productivity for any biomass component. Grazing after fire reduced postgrazing grass biomass along the prescribed utilization gradient. Fire and grazing had no effect on total aboveground productivity the year after grazing compared to nonburned, nongrazed sites (1 327 vs. 1 249 ± 65 kg · ha-1). Fire and grazing increased grass productivity 16%, particularly for Pascopyrum smithii. The combined disturbances reduced forbs (51%), annual grasses (49%), and litter (46%). Results indicate grazing with up to 50% biomass removal the first growing season after summer fire was not detrimental to productivity of semiarid rangeland plant communities. Livestock exclusion the year after summer fire did not increase productivity or shift species composition compared to grazed sites. Reduction of previous years' standing dead material was the only indication that fire may temporarily reduce forage availability. The consistent responses among dry, wet, and near-average years suggest plant response is species-specific rather than climatically controlled.

Effects of Cultivation and Grazing Exclusion on the Soil Macro-faunal Community of Semiarid Sandy Grasslands in Northern China

Cultivation and overgrazing can cause desertification of sandy grasslands in arid and semiarid regions. However, little was known about their effects on soil macro-fauna. In this study, we described the soil macro-faunal community structure at cultivated, grazed, and ungrazed sites in the semiarid Horqin steppe, northern China. Soil bulk density was 1.61 g cm−3 at grazed sites, similar to that at cultivated sites. Cultivation reduced soil organic carbon and total nitrogen by 36 and 46%, respectively, compared with grazed grassland. Grazing exclusion decreased soil bulk density and pH by 16 and 3%, respectively, and increased soil moisture, soil organic carbon and total nitrogen by 75, 22, and 4%, respectively, compared with grazed grassland. Cultivated and grazed sites had similar group richness (9 and 10 groups, respectively) and Shannon's index (1.98 and 1.93, respectively); both were significantly lower there than at ungrazed sites. Simpson's index at grazed sites was 0.18, markedly higher than at ungrazed (0.12) and cultivated (0.16) sites. There were no significant differences in soil macro-faunal density among the three treatments, although the density at grazed sites was 24% higher than at cultivated sites and 30% lower than at ungrazed sites. Soil bulk density, electrical conductivity, pH, and the C/N ratio significantly affected the community structure. Specific macro-faunal groups responded to the different living conditions by adaptation to or selection of specific habitats. For example, the Thomisidae, Reduviidae, Staphilinidae, and Curculionidae responded negatively to increasing soil bulk density and all of these except the Curculionidae responded negatively to increasing soil temperature. These groups have important implications for the soil food web, and thus for the soil ecosystems. Our results suggested that cultivation and continuous grazing negatively affected soil properties and macro-faunal diversity, whereas livestock exclusion enhanced soil macro-faunal assemblies and improved their biodiversity. Changes in these assemblies might be potential indicators of ecosystem recovery and management impacts. Supplementary materials are available for this article. Go to the publisher's online edition of Arid Land Research and Management to view the supplemental file.