Overgrazing

Desertification is the process that turns productive deserts into non-productive deserts as a result of poor land-management. Desertification reduces the ability of land to support life, affecting wild species, domestic animals, agricultural crops and humans. The reduction in plant cover that accompanies desertification leads to accelerated soil erosion by wind and water. South Africa is losing approximately 300–400 million tons of topsoil every year. As vegetation cover and soil layer are reduced, rain fall impact and run-off increases. This paper discusses the extent of desertification, its potential threat to sustained irrigated agriculture and possible measures adopted to control ongoing desertification processes to minimize the loss of agricultural productivity in an arid country such as the Kingdom of Saudi Arabia.

This study uses Landsat data and Tasseled Cap Transformation green vegetation index (GVI) technique to assess the condition of rangeland resources in the Sahel region of West Africa. Three representative zones in the sahelian region of Mali, Burkina Faso and Niger were selected for this study. Satellite data covering fifteen years period was used to assess the extent to which rangeland resources have degraded on a country by country basis between 1984 and 1999. The study results show all three countries in the study area experienced vegetation decline. However, loss of vegetation cover was most pronounced in the northern part of the study area than in the south. This decline could be attributed to changing temperature and rainfall gradients.

Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small-scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta-analysis of the outcomes of plant–herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between-taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore–plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed-nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed-nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore–plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant–herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top-down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats that contain aquatic plants.

Though wetlands are vital for the proper functioning of terrestrial ecosystems and provisioning of a wide range of goods and services, their sustainability is being threatened by inappropriate human resource use practices due to our limited understanding of how these systems operate and lack of appropriately informed interventions. We attempt to address these limitations by using historical CORONA photographs of 1967, Landsat imagery of 1989, 1994 and 2001 and information from the literature to investigate the role of natural and human factors in influencing the direction of environmental change in the proximal reaches of Botswana's Okavango Delta. Results of this investigation point to fragmentation of natural habitats, localised degradation of areas close to perennial water supplies, significant increase in woody cover, significant decrease in open grassland, increase in scrub and shrubs, deterioration in the quality of grazing and depletion of specific woody species. With the direction of change pointing to persistent decrease in the environment's supporting potentials, there is urgent need to adopt intervention strategies potentially capable of enhancing sustainable utilisation of natural resources in this sub-region.

In this study, we attempted to map the degradation of Mongolian grasslands using MODIS imagery and statistical data which is number and composition of livestock from 2000 to 2006. Firstly we generated the distribution map by MODIS LAI using a biomass estimation equation which was derived from in-situ measurement of biomass with a geo-located match up database. Secondly the amount of biomass which is the quantity required for feeding the livestock in each county was calculated using data on numbers of livestock over the same time period. Thirdly, degradation intensity was determined in overgrazed areas in which the number of livestock exceeds grazing capacity and use of many goats creates high grazing intensity. As result,19 counties were identified as at high risk for degradation of the grasslands. These areas are located in southern region of Mongolia.

Climatic changes have affected populations of caribou and reindeer (Rangifer tarandus) at scales ranging from a single winter to tens of thousands of years, and from micro-habitats to entire continents. Individuals, populations and the species have adapted to these climatic changes, however, producing complex evolutionary and ecological issues requiring multi-scale, interdisciplinary research. Caribou populations wintering on arctic tundra may be most susceptible to the impacts of anthropogenic climatic change, given the low productivity of their forage, the severity and duration of the winters, and the physical barriers that limit dispersal.

Sub-speciation of Rangifer tarandus hypotheticaly occurred during the Wisconsin glaciation. Recent genetic analyses support the current classification of subspecies, except that Baffin Island caribou may be distinct from barren-ground caribou, R. t. groenlandicus, on mainland Northwest Territories. Baffin caribou may have originated from a small ancestral population in a refugium on Baffin Island during the Wisconsin glaciation; or, they may have originated from immigrants after the Wisconsin glaciation, later experiencing a severe population bottleneck.

On a shorter time scale, recent research has suggested that density-independent climatic events occurring over a single winter have caused at least one major population decline among Peary caribou on the Queen Elizabeth Islands. Dramatic fluctuations of Greenland populations over the past 200 years have been attributed to climatic changes. However, the onset of some population changes on western Greenland have been inconsistent with the timing of climatic changes. Inuit knowledge of Baffin caribou and studies of tundra caribou on Svalbard, Coats and Southampton islands, South Georgia, and Norway suggest that caribou populations are affected primarily by density-dependent grazing impacts on forage that can last several decades. The discrepancy between these views may be caused by differences in the temporal and spatial scales over which scientific investigations have been conducted, and the measurement of only some ecological factors. Arctic ecological studies require extensive spatial and temporal data before impacts of anthropogenic climate change can be assessed. This will require a long-term interdisciplinary study integrating scientific data from several disciplines, as well as Inuit knowledge.

This study analyzed land use/cover dynamics in the mountain landscape of Tara Gedam and adjacent agro-ecosystem of northwest Ethiopia over a period of 46 years (1957–2003). The changes were measured through interpretation of aerial photographs taken in ...

Botanical and particle size compositions of the feces of sympatric Mongolian gazelles, sheep/goats, and horses collected in southern Mongolia in autumn 2002 were analyzed. The botanical composition of Mongolian gazelles was similar to that of sheep/goats where dicotyledonous plants (64.6% for Mongolian gazelles, 65.6% for sheep/goats), particularly woody fibers were important (39.5% for Mongolian gazelles, 19.5% for sheep/goats). In contrast, horse feces were exclusively composed of graminoids (93.2%). Consequently, food overlap was great between Mongolian gazelles and sheep/goats (Pianka’s index: 0.977) but was small between Mongolian gazelles and horses (0.437) and sheep/goats and horses (0.421). Particle size distributions were also similar between Mongolian gazelles and sheep/goats, whereas they were different between horses and Mongolian gazelles and horses and sheep/goats. These results support our expectation based on the Jarman-Bell principle. Although interspecific competition cannot be inferred from a mere food overlap, our analyses suggest that sheep and goats are potential competitors for Mongolian gazelles. Therefore, the increase in the numbers of domestic sheep/goats might pose a risk for Mongolian gazelle populations.

This study uses Landsat data and Tasseled Cap Transformation green vegetation index (GVI) technique to assess the condition of rangeland resources in the Sahel region of West Africa. Three representative zones in the sahelian region of Mali, Burkina Faso and Niger were selected for this study. Satellite data covering fifteen years period was used to assess the extent to which rangeland resources have degraded on a country by country basis between 1984 and 1999. The study results show all three countries in the study area experienced vegetation decline. However, loss of vegetation cover was most pronounced in the northern part of the study area than in the south. This decline could be attributed to changing temperature and rainfall gradients.

The paper is concerned with degradation narratives in Mkomazi Game Reserve, Tanzania, the role of received wisdom in scientific literature in creating and endorsing these narratives, and with the potential role of science in challenging that wisdom. Traditional wisdom holds ...

Some researchers have suggested that over periods of several decades, Arctic tundra caribou (Rangifer tarandus) may be regulated by density-dependent forage depletion. Winter range shifts could potentially delay such regulation when a population is at or near long-term maximum abundance. In the 1980s, Inuit correctly predicted the mass emigration of caribou from a traditional winter range on Foxe Peninsula (FP) on southern Baffin Island, Nunavut, Canada. Most FP caribou subsequently emigrated to a new winter range on Meta Incognita Peninsula (MIP). To determine if MIP provided emigrating caribou with better foraging habitats, we compared winter forage resources and snow cover at caribou foraging sites, and food selection by caribou on FP and MIP in April 1992. Caribou that remained on FP dug feeding craters in shallower, softer snow than those on MIP did. Biomass of most fruticose lichens was greater within foraging sites on MIP than on FP. Biomass of shrubs, other than Cassiope tetragona and Dryas integrifolia, was also greater on MIP than on FP. Dryas integrifolia was the only plant class that had higher biomass on FP than on MIP. Cladina spp. Cladonia spp., Sphaerophorus fragilis, and Cetraria nivalis occurred less frequently in the rumens of FP caribou. Proportions of fruticose lichens in rumens of caribou on both peninsulas were similar to those on other overgrazed and High Arctic tundra winter ranges. Caribou on FP showed a higher preference for the shrub C. tetragona. Biomasses of plants sensitive to long-term feeding or trampling by caribou (i.e., the five most common fruticose lichens, other shrubs, and plant debris) were consistently lower on FP, which is congruous with Inuit reports that long-term cumulative overgrazing had reduced the supply of important forage plants on FP sites that were accessible to caribou in winter. FP caribou that emigrated to MIP gained access to more abundant, higher quality forage resources than those that remained on FP. Because most FP caribou had emigrated, this South Baffin subpopulation escaped, at least temporarily, the regulating effects of historical cumulative overgrazing.

Major declines of populations of caribou and reindeer (Rangifer tarandus) that permanently reside on Arctic tundra have been attributed to short-term inaccessibility of forage through restrictive snow cover. Such density-independent phenomena would produce unpredictable changes in populations of Arctic tundra caribou. In 1985, Inuit correctly predicted mass emigration from the winter range of a caribou subpopulation on Foxe Peninsula (FP), southern Baffin Island, Canada. During 1982-94, we conducted aerial surveys, satellite telemetry, and physical condition studies to examine features of the predicted range shift. Between 1984 and 1992, caribou density on upland terrain on FP dropped (P < 0.001) from 6.2 to 0.3 caribou/km2. Cows began to emigrate en masse during winter 1988-89 (P = 0.10) toward Meta Incognita Peninsula (MIP), where caribou showed greater fidelity to that wintering area during 1988-94 (P = 0.005). Density of caribou on upland terrain on MIP increased (P = 0.001) from 0.2 to 5.0 caribou/km2 between 1982 and 1992. In April 1992, body size did not differ (P - 0.47) between FP and MIP. Cows on MIP had greater (P - 0.04) fat and muscle reserves than cows on FP, while only fat reserves of MIP bulls were greater than (P - 0.03) those of FP bulls. Our results support Inuit observations of declining physical condition of FP caribou in the early 1980's, and their view that the range shift was caused by cumulative annual overgrazing of the winter range during the previous 10 to 30 yr. Fewer cows on FP were pregnant (2 of 8) than on MIP (10 of 10; P = 0.002). Calf:cow ratios were higher (P = 0.05) on MIP than on FP in 1992. Although few caribou had occupied MIP for 50 yr before 1988-89, MIP caribou were in relatively poor condition by April 1992 compared to those on overgrazed Coats Island during mild winters. Winter range shifts and population declines by Arctic tundra caribou may be predictable. Ecological indicators may enable managers to mitigate the effects of overgrazing on caribou populations through intensive harvesting at critical stages during long-term population increases.

Over the last decades agroforestry parklands in Burkina Faso have come under increasing demographic as well as climatic pressures, which are threatening indigenous tree species that contribute substantially to income generation and nutrition in rural households. Analyzing the threats as well as the species vulnerability to them is fundamental for priority setting in conservation planning. Guided by literature and local experts we selected 16 important food tree species (Acacia macrostachya, Acacia senegal, Adansonia digitata, Annona senegalensis, Balanites aegyptiaca, Bombax costatum, Boscia senegalensis, Detarium microcarpum, Lannea microcarpa, Parkia biglobosa, Sclerocarya birrea, Strych-nos spinosa, Tamarindus indica, Vitellaria paradoxa, Ximenia americana, Ziziphus maur-itiana) and six key threats to them (overexploitation, overgrazing, fire, cotton production, mining and climate change). We developed a species-specific and spatially explicit approach combining freely accessible datasets, species distribution models (SDMs), climate models and expert survey results to predict, at fine scale, where these threats are likely to have the greatest impact. We find that all species face serious threats throughout much of their distribution in Burkina Faso and that climate change is predicted to be the most prevalent threat in the long term, whereas overexploitation and cotton production are the most important short-term threats. Tree populations growing in areas designated as 'highly threatened' due to climate change should be used as seed sources for ex situ

Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the Canadian High Arctic. Because of severe population declines following years of unfavorable winter weather with ice coating on the ground or thicker snow cover, it is believed that density-independent disturbance events are the primary driver for Peary caribou population dynamics. However, it is unclear to what extent density dependence may affect population dynamics of this species. Here, we test for different levels of density dependence in a stochastic, single-stage population model, based on available empirical information for the Bathurst Island complex (BIC) population in the Canadian High Arctic. We compare predicted densities with observed densities during 1961–2001 under various assumptions of the strength of density dependence. On the basis of our model, we found that scenarios with no or very low density dependence led to population densities far above observed densities. For average observed disturbance regimes, a carrying capacity of 0.1 caribou km−2 generated an average caribou density similar to that estimated for the BIC population over the past four decades. With our model we also tested the potential effects of climate change-related increases in the probability and severity of disturbance years, that is unusually poor winter conditions. On the basis of our simulation results, we found that, in particular, potential increases in disturbance severity (as opposed to disturbance frequency) may pose a considerable threat to the persistence of this species.

Guadalupe Island, an oceanic island in the northwest of Mexico, is an outlier of the California Floristic Province that has been disturbed by introduced goats for more than a century, with dramatic effects of goats on plant communities and local species extinctions. In 2004 the island went through a successful eradication program. Since then, six previously unrecorded species have been discovered and four supposed extinct species have been found again. Quantifying the true species richness of the island at the time of eradication, to set a benchmark for the future monitoring of this large-scale natural experiment, is both a challenge and a necessity. For this purpose, we estimated (a) current and (b) accumulated historical plant species richness of the island through accumulation functions. Estimation of current species richness was based on the geographical accumulation process of species richness (80 species) obtained from sampling 110 (50 m × 2 m) transects distributed along the island in year 2004. Historical species richness was estimated through the temporal accumulation of species richness (119 species) from botanical records (1,960 specimens reviewed) between 1875 and 2000. The predicted value of historical richness (213 species) is similar to known historical records (218 species), but estimation of current richness (203 species) is significantly higher than accepted extant plant richness (187 species). Our results suggest that currently there may be more plant species living in the island than estimated through recent botanical exploration. Future monitoring of the island as it recovers will clarify this hypothesis.

Indigenous peoples possess knowledge about wildlife that dates back many generations. Inuit observations of historical changes in a caribou population on southern Baffin Island, collected from 43 elders and active hunters during 1983–95, indicate that caribou were abundant and their distributions extensive in most coastal areas of southern Baffin Island from c.1900–25. Subsequently, caribou distributions contracted and abundance declined, probably reaching an overall low in the 1940s. Beginning in the mid-1950s, distributions and abundance increased gradually, at least until the mid-1980s. Changes in distribution occurred mainly during autumn, as caribou migrated to their wintering areas. Within most wintering areas, increases in caribou abundance followed a process of range expansion, range drift (i.e., expanding on one front while contracting on another), and finally range shift (i.e., mass emigration to a new winter range). During the population decline and low, the caribou often exhibited winter range volatility (i.e., frequent, unpredictable interannual range shifts). On the basis of Inuit descriptions of caribou abundance, we estimated that the population as a whole decreased an average of 9% annually from 1910 to 1940, and then increased about 8% annually from 1940 to 1980. This pattern was largely consistent across southern Baffin Island. As Inuit elders had predicted in 1985, the population essentially abandoned its highest-density wintering area on Foxe Peninsula during the late 1980s, apparently emigrating en masse to a new wintering area on Meta Incognita Peninsula, about 375 km to the southeast. Inuit knowledge suggested that caribou population fluctuations are cyclic, with each full cycle occurring over the lifetime of an elder. Both this study and historical records dating from 1860 support a periodicity of 60–80 years for fluctuations of the South Baffin caribou population. Inuit elders suggested that the abundance of caribou on wintering areas decreases several years after caribou occupy small coastal islands, a phenomenon currently occurring throughout southern Baffin Island, except on Cumberland Peninsula. The Inuit recognize two ecotypes of caribou: migratory upland-lowland caribou and resident mountain-plateau caribou. After migratory caribou from Foxe Peninsula shifted their winter range around 1990, Meta Incognita Peninsula was occupied by both ecotypes. The migratory caribou apparently occupy low elevations, while the resident caribou remain in the mountains, producing two seasonal migratory patterns. Inuit knowledge proved to be temporally and spatially more complete than the written record.

ABSTRACT The effects of land management and disturbance on ecosystem performance (i.e. biomass production) are often confounded by those of weather and site potential. The current study overcomes this issue by calculating the difference between actual and expected ecosystem performance (EEP) to generate ecosystem performance anomalies (EPA). This study aims to delineate and quantify average EPA from 2000–2009 within the Greater Platte and Upper Colorado River Basins, USA. Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) images averaged over the growing season (GSN) served as a proxy of actual ecosystem performance. Yearly EEP was determined with rule-based piecewise regression tree models of abiotic data (climate, soils, elevation, etc.), independently created for each land cover. EPA were calculated as the residuals of the EEP to GSN relationship, and characterized as normal performing, underperforming, and overperforming at the 90% confidence level. Validation revealed that EPA values were related to biomass production (R2 = 0.56, P = 0.02) and likely to the proportion of biomass removed by livestock in the Nebraska Sandhills. Overall, 60.6% of the study area was (normal) performing near its EEP, 3.0% was severely underperforming, 5.0% was highly overperforming, and the remainder was slightly underperforming or overperforming. Generally, disturbances such as fires, floods, and insect damage, in addition to high grazing intensity, result in a negative EPA. Conversely, mature stands and appropriate management often result in positive EPA values. This method provides information critical to land managers to evaluate the appropriateness of previous management practices and restoration efforts and quantify disturbance impacts. Results are at a scale sufficient for many of the large management units of the region and for locating areas needing further investigation. Applications of EPA data to monitoring invasive species, grazing impacts, and vulnerability

Rangeland degradation is a serious problem in semiarid Africa. Extensive areas of bare, compacted, nutrient-poor soils limit the productivity and biodiversity of many areas. We conducted a set of restoration experiments in which all eight combinations of soil tilling, fertilization, and seeding with native perennial grasses were carried out in replicated plots. After 6 months, little aboveground biomass was produced in plots without tilling, regardless of seeding or fertilization. Tilling alone tripled plant biomass, mostly of herbaceous forbs and annual grasses. Perennial grasses were essentially limited to plots that were both tilled and seeded. The addition of fertilizer had no significant additional effects. After 7 years, vegetation had declined, but there were still large differences among treatments. After 10 years, one tilled (and seeded) plot had reverted to bare ground, but the other tilled plots still had substantial vegetation. Only one seeded grass (Cenchrus ciliaris) was still a contributor to total cover after 10 years. We suggest that restoration efforts on these soils be directed first to breaking up the surface crust, and second to the addition of desirable seed. A simple ripping trial inspired by this experiment showed considerable promise as a low-cost restoration technique.

This study uses Landsat data and Tasseled Cap Transformation green vegetation index (GVI) technique to assess the condition of rangeland resources in the Sahel region of West Africa. Three representative zones in the sahelian region of Mali, Burkina Faso and Niger were selected for this study. Satellite data covering fifteen years period was used to assess the extent to which rangeland resources have degraded on a country by country basis between 1984 and 1999. The study results show all three countries in the study area experienced vegetation decline. However, loss of vegetation cover was most pronounced in the northern part of the study area than in the south. This decline could be attributed to changing temperature and rainfall gradients.