Changes in woody community structure and composition under constrasting landuse systems in a semi-arid savanna, South Africa

We aimed to explore the farm scale effects of three landuse types, communal grazing, wildlife management and commercial cattle farming, on the woody vegetation of a semiarid savanna. Location The study farms were located within a single bioclimatic zone in semiarid savanna, South Africa. Methods The species composition and structure of woody vegetation on three farms of each of three landuse types were sampled. Results We found that communal grazing land sites were classified outside the topland-bottomland vegetation dichotomy characteristic of this region. Comparisons of size class distributions showed the communal grazing lands had fewer small and large individuals; suggesting both lower levels of regeneration and regenerative capacity in the communal grazing lands. The species richness and biomass of woody plants was lower on communal grazing lands than on private game reserves and commercial cattle farms. The longevity of tree species explains the observed lag between changes in abundance and species loss; we consequently predict that there will be future losses of species in the communal grazing lands. By classifying species into a range of use-categories we showed that utilization and species loss was not limited to certain plant use categories. Higher levels of wood harvesting measured in the communal grazing lands are likely to be responsible for the observed differences. Main conclusions It is concluded that communal grazing management at this study site has substantially changed the composition and structure of woody plant communities, and that these changes have reduced the current availability of natural resources and will reduce resource production in the future.     

Can heavy grazing on communal land elevate plant species richness levels in the Grassland Biome of South Africa?

A common perception, particularly in South Africa, is that heavily and continuously grazed communal land leads to degradation and loss of plant diversity when compared to commercial rangeland farming or conservation areas. We focus on whether this applies to the Grassland Biome of South Africa and whether the opposite can occur, namely, an increase in plant species richness under heavy grazing. A study of a contrast between a communal area of the former Ciskei and a neighbouring nature reserve showed that intense utilization under communal use led to a significant increase in plant species richness. However, this increase was scale-dependent with the greatest significant difference occurring at sample plot scale (50 m²) but converging at the broader scale of the whole study site. Species that increased with heavy grazing included those from arid Karroid areas as well as some from more mesic grassland and savanna areas. The contribution of beta diversity to gamma diversity across the grazing contrast was relatively low which reflects the relatively high proportion of species shared between treatments. Total plant canopy cover declined sharply with heavy grazing. In terms of plant canopy cover, grazing favoured annual over perennial plants, prostrate over erect plants, and stoloniferous over tussock plant architecture. This pattern was not supported when expressed in terms of number of species belonging to these grazing response groups or traits.     

A fence-line contrast reveals effects of heavy grazing on plant diversity and community composition in Namaqualand,South Africa

Changes in plant species richness and community composition were investigated across a fence separating heavily grazed communal and lightly grazed commercial farming systems in Namaqualand, South Africa. No significant differences in plant species richness between communal and commercial farming systems were detected either locally within individual plots or overall across all plots. Within-plot, richness of species tolerant of grazing, such as annuals and geophytes, has increased, while the richness of large palatable shrub species has decreased on the communal rangeland. In terms of plant cover, species' responses to grazing were strongly associated with growth form. Annuals and geophytes formed the majority of grazing increasers, while large, presumably palatable, shrubs and leaf succulents were characteristic grazing decreasers. An investigation into population processes of five shrub species revealed that heavy grazing on the communal rangeland has resulted in: reduced size of palatable shrub species; reduced flower production and seedling recruitment of palatable species; increased density and recruitment of the unpalatable shrub, Galenia africana. Reductions in shrub volume, reproductive output and seedling recruitment were most marked in the palatable shrub Osteospermum sinuatum and were in the order of 90%. The results are further discussed in terms of their relevance to rangeland dynamics and the current land use practices of the region.     

Coping Strategies in Livestock-dependent Households in East and Southern Africa: A Synthesis of Four Case Studies

Integrated assessment seeks to combine models of the ecological as well as the social system to allow different scenarios to be tested in terms of their likely impacts on ecological functioning and household well-being. We outline such work undertaken in four case studies in East and southern Africa: pastoralist communities in northern Tanzania, agro-pastoralists in southern Kenya, communal and commercial ranchers in South Africa, and mixed crop-livestock farmers in western Kenya. Results from these case studies are synthesised to test the hypothesis that households’ capacity to adapt in the face of increasing external stresses is governed by flexibility in livelihood options. The results support this hypothesis. There is considerable variation in how households in these places cope with external stresses. Options include intensification, diversification, and increasing off-farm economic activities, and these depend on household objectives and attitudes as well as on access to natural resources, inputs and output markets. The results also indicate that generally it is the poorer households that can gain the most from implementing such options for coping and managing risk. Quantifying likely household and ecosystem impacts of different options is a crucial step in targeting appropriate technology, policy and adaptation interventions in the face of considerable system changes. We conclude with some research needs to improve integrated assessment tools that may allow us to represent more realistically the highly complex decision-making milieu of householders in sub-Saharan Africa who are dependent on ecosystem goods and services for a large part of their livelihoods.     

Bush encroachment under three contrasting land-use practices in a mesic South African savanna

This study determined the effects of land-use practice had on the rate and extent of bush encroachment in a mesic savanna in KwaZulu-Natal, South Africa. Changes in woody cover were measured for 1 km² sites in areas under communal, commercial and conservation land-use systems for the period between 1937 and 2000. Land users from each area were interviewed to gain the histories of each area and to determine how the changes in woody cover had impacted them and whether anything was being done to counteract the spread of trees and shrubs on their land. Bush encroachment occurred across all three of the land-use types in the 67-year period between 1937 and 2000. The results showed that land-use practice had enormous impacts on the process of bush encroachment. The communal site showed a decrease in grass (21%) and tree (5%) cover and an increase in shrub cover (13%). At the commercial site, there was a considerable decrease in grass cover (46%) and moderate increase in shrub cover (10%) and a massive increase in tree cover (36%). The area under conservation showed a substantial decrease in grass cover (47%), a slight decrease in shrub cover (19%) and a massive increase in tree cover (66%). The perceived causes of these changes were fairly similar amongst the different land users. The changes were mostly not perceived to be a problem for the communal land users. The main advantages mentioned were increased woody resources for building and firewood and increased browse availability. The commercial and conservation land users perceived the changes to have significant negative connotations including the loss of grazing land and biodiversity and secondary invasion of encroached areas by alien plant species. Despite these perceptions, very little has been done to combat bush encroachment in the commercial and conservation land use systems.     

Fisheries tenure in an African floodplain village and the implications for management

Floodplain fisheries make an important contribution to the total freshwater catch of Africa. Rules and institutions controlling access to these fisheries have received little attention in the literature. This paper explores property regimes operating in the Hadejia-Jama'are floodplain fishery, Nigeria, with a focus on a case-study village. Private, communal property, and open-access tenure regimes exist. The physical characteristics of the resources under each of these categories are differentiated. The economic cost of making resources more exclusive appears to be a key factor affecting tenure. However, the social benefits of communal access are also extremely important. In a risky environment that is characterized by spatial and temporal variation in the distribution of resources, maintaining rights of access to a wide geographical portfolio of resources is an important consideration. This is especially true considering recent environmental changes in the floodplain caused by dams and drought. This suggests that recommendations to improve productivity of the fishery by making access more exclusive may not maximize overall benefits from the fishery, since gains in productivity may be outweighed by losses in social benefits.     

Ecological gradients as a framework for analysis of land-use change in East Africa

This paper discusses the ecological gradient as an organizing framework to assist understanding the complex interactions between societal and ecological processes underlying land-use change in East Africa. Detailed case studies on the gradients of the slopes of Mt Kilimanjaro, Kenya show how land-use change is responsive to the dynamics of both local and external driving forces. The study has shown that the distinct ecological conditions at the extremities of gradients are associated with specific land uses which may be different within livelihood systems such as for wet and dry season grazing. Access to water for cultivation, domestic use, livestock and wildlife is critical in determining the nature and distribution of livelihood systems. Land-use systems interact across the different ecological zones of the gradients characterized by vigorous spatial, cultural and economic interactions. Sometime conflicts occur between or within land-use/livelihood systems. There is strong evidence that the areas of higher economic potential remain advantaged compared with areas lower on the gradient. The ecological characteristics have been found to influence human activities and distribution. Interactions between societies are important in terms of trade, social relations and access to resources.     

Planted saltbush (Atriplex nummularia) and its value for birds in farming landscapes of the South Australian Murray Mallee

Summary In the fragmented agricultural landscapes of temperate southern Australia, broad‐scale revegetation is underway to address multiple natural resource management issues. In particular, commercially‐driven fodder shrub plantings are increasingly being established on non‐saline land to fill the summer‐autumn feed gap in grazing systems. Little is known of the contribution that these and other planted woody perennial systems make to biodiversity conservation in multifunctional landscapes. In order to address this knowledge gap, a study was conducted in the southern Murray Mallee region of South Australia. Selected ecological indicators, including plant and bird communities, were sampled in spring 2008 and autumn 2009 in five planted saltbush sites and nearby areas of remnant vegetation and improved pasture. In general, remnant vegetation sites had higher biodiversity values than saltbush and pasture sites. Saltbush sites contained a diverse range of plants and birds, including a number of threatened bird species not found in adjacent pasture sites. Plant and bird communities showed significant variation across saltbush, pasture and remnant treatments and significant differences between seasons. This study demonstrates that saltbush plantings can provide at least partial habitat for some native biota within a highly modified agricultural landscape. Further research is being conducted on the way in which biota, such as birds, use available resources in these dynamic ecosystems. An examination of the effects of grazing on biodiversity in saltbush would improve the ability of landholders and regional natural resource management agencies in making informed land management decisions.     

Cultural theory and management of common property resources

Cultural theory utilizes concepts drawn from social anthropology, sociology, and organization theory to explain the social and cultural biases of policy actors and interest groups. Certain ideas of nature are associated with each cultural bias; these ideas of nature are in turn associated with types of resource management institutions. By identifying an actor or group's culture bias, analysts can explain the success or failure of different management activities. This paper explains the evolution of cultural theory from its anthropological roots to its applications in ecological management. It then applies cultural theory to a typology of common property resources and illustrates its usefulness by examining grazing subsidies in the American southwest.     

Shrub‐based plantings of woody perennial vegetation in temperate Australian agricultural landscapes: What benefits for native biodiversity?

Summary  In the highly fragmented agricultural landscapes of temperate southern Australia, fodder shrubs are being established as part of commercial grazing enterprises to fill the summer-autumn livestock feed gap. These woody perennial plantings have greater structural complexity than conventional grazing systems and may supplement resources for native fauna. However, to date the resources provided by these systems are poorly defined or documented. In this paper, we identify the potential environmental values of fodder shrub plantings by considering natural and planted shrub-based systems, with a particular focus on planted saltbush in non-saline lands. In marginal agricultural areas, shrub-based perennial fodder crops can not only provide economic benefits through improved livestock productivity, but also contribute to reducing soil erosion and offer potential carbon sequestration opportunities. We contend that these systems may also provide resources for a range of native fauna. More information is needed on the biodiversity value of grazing systems based on perennial shrubs so that their potential to contribute to conservation in multifunctional landscapes can be fully realised and appropriate management recommendations provided.     

The Evolution of Conservation Management Philosophy: Science, Environmental Change and Social Adjustments in Kruger National Park

In this ‘perspectives’ article, we share experiences gained from the century-old Kruger National Park (KNP) in South Africa to illustrate the dynamic complexity of biophysical and socio-political systems, the interactions that occur between them, and the consequences for ecosystem-scale functions and resources and for their management. As in KNP, the social-ecological milieu surrounding many national parks and protected areas is changing rapidly. There will be significant managerial adjustments as human populations grow and the needs for resources accelerate. The changes, driven largely by global-scale environmental shifts as well as by new knowledge, are intimately intertwined with evolving societal perceptions, values, and expectations. Many KNP resource-related issues of the past century originated more internally and were largely environmental, whereas the emerging issues are more external and largely social. Here, we illustrate how interrelated scientific and managerial advances in integrating biophysical and social systems are acting to conserve and rehabilitate resources within KNP, and to aid in their conservation. Where appropriate, we relate these advances to similar examples in the region or other protected areas in the world. Strategies to address emerging issues are identified and discussed—and their combined effects on resource conservation and management are evaluated. In our experience the approach to conservation within KNP has been successful, despite well-intended but damaging management actions in the past. We believe that the perceived success stems from a willingness to continually incorporate new knowledge into management, to foster close working and personal associations among scientists, managers, and rangers, to acquire an intimate knowledge and understanding of the social-ecological system by the administrators as well as by the staff, and to be actively ‘forward’ thinking in an increasingly complex and uncertain world. We accept that many decisions taken today will be challenged by future managers and scientists, and we expect that some will be found wanting as emerging knowledge and continued learning shape future decisions. Further, evolving political, social, and environmental contexts may mean that protected areas will need to be managed in different ways. Therefore, we emphasize the importance of minimizing the permanency and impact of decisions so that today’s actions do not compromise future decisions when meaningful changes need to be made.

Rangeland Mismanagement in South Africa: Failure to Apply Ecological Knowledge

Chronic, heavy livestock grazing and concomitant fire suppression have caused the gradual replacement of palatable grass species by less palatable trees and woody shrubs in a rangeland degradation process termed bush encroachment in South Africa. G razing policymakers and cattle farmers alike have not appreciated the ecological role fire and native browsers play in preventing bush encroachment. Unpredictable droughts are common in South Africa but have deflected too much blame for bush encroachment away from grazing mismanagement. Bush encroachment is widespread on both black and white farms, although the contributing socioeconomic, cultural, and political forces differ. Managers at Madikwe Game Reserve have reintroduced fire and native game animals into a formerly overgrazed system in an attempt to remediate bush encroachment, with encouraging preliminary results. A bush control program is needed that educates cattle farmers about the ecological causes of bush encroachment and encourages the use of fire and native browsers as tools for sustainable grazing management.     

Restoration of native vegetation following exclosure establishment on communal grazing lands in Tigray,Ethiopia

Questions: Is plant species richness, diversity and above‐ground standing biomass enhanced after establishing exclosures on communal grazing lands? What factors influence the effectiveness of exclosures to restore degraded native vegetation in Tigray, Ethiopia? Location: Northern Ethiopia. Methods: We used a space‐for‐time substitution approach to detect changes in plant species richness, diversity and above‐ground standing biomass after conversion of communal grazing lands to exclosures. We selected replicated (n=3) 5‐, 10‐, 15‐ and 20‐year‐old exclosures and paired each exclosure with an adjacent communal grazing land to ensure that soil and terrain conditions were as similar as possible among each pair. Results: All exclosures displayed higher plant species richness, diversity and biomass than the communal grazing lands. Differences in plant species richness and biomass between an exclosure age and adjacent communal grazing land were higher in oldest than in youngest exclosures. In exclosures, much of the variability in plant species composition and biomass was explained by a combination of edaphic (total nitrogen, phosphorus, texture and soil pH) and site (precipitation and altitude) variables (R²=0.72–0.82). Edaphic and site variables also explained much of the variability in plant species composition in communal grazing lands (R²=0.76–0.82). Our study shows that all exclosures are at an early stage of succession. The increase in economically important indigenous shrub and tree species with exclosure age suggests that, with time, a valuable afromontane forest may develop. Conclusions: Establishment of exclosures on communal grazing lands is a viable option to restore degraded native vegetation. However, before expanding exclosures, the ecological consequences of additional exclosures should be investigated as further expansion of exclosures could increase grazing pressure on remaining grazing areas. Furthermore, consideration of edaphic and site variables will help optimize selection of areas for establishment of exclosures and enhance natural regeneration in exclosures in the future.     

全球主要生态退化区和研究热点区的空间分布与演变

掌握生态退化区和研究热点区的空间分布、退化区生态系统的演变态势是认识生态问题、开展生态治理的基础,但目前缺乏全球主要生态退化区空间分布图等基础数据和相关知识。应用多源数据集成融合、长时序卫星遥感分析、互联网文献大数据建模分析等方法,对以荒漠化、水土流失、石漠化为代表的全球主要生态退化类型区的空间分布、演变态势、研究关注热度等进行了研究。结果表明：（1）全球荒漠化区面积约15.4×10⁶ km²,水土流失区面积约14.3×10⁶ km²,石漠化区面积约1.1×10⁶ km²;这些生态退化区主要分布在非洲撒哈拉沙漠南北边缘,欧洲西部、地中海沿岸、东欧平原南部,南亚印度河流域,中国西北地区、云贵高原,北美洲落基山脉以及南美洲阿根廷等地区。（2）2000年以来,上述退化区中约有3.9%的面积处于退化加重态势,73.3%的面积处于脆弱平衡状态,22.8%的区域出现好转趋势。（3）全球生态退化研究热点区的分布与全球生态退化区的分布总体呈现一致性。但在沙特阿拉伯中部、哈萨克斯坦北部,巴西大部,安哥拉、南非等生态退化区,存在生态系统继续恶化、缺乏研究界足够关注的情况。研究成果深化了对全球主要生态退化区分布格局的认识,对于防范全球发展和建设中出现加重的生态退化等具有参考价值。     

Righting the Wrongs: Contesting Water Property Rights in Southern Ethiopia

Resolution of disputes and investigation of institutions that have attempted to right the wrongs (some of which have persisted for centuries) regarding pastoralists’ property rights over indigenous water sources in East Africa have rarely been the subject of formal study. Using a framework of water property rights, hereafter konfi, we report on contestations over rights to the ancient tula wells in southern Ethiopia, some of which have been in operation for more than 500 years. Unlike grazing lands, which are communal resources, wells are private properties managed by corporate clan members. We reconstructed the history of contests over property rights to 64 wells and found that some contests over konfi have remained unresolved for many generations. Only a small percentage (20%) of the wells have no history of disputes over property rights. The resolution of disputes relies on the principal tenet of the non-transferability of konfi property rights, except in the case of the family of the ancestral konfi dying out. Contestants are expected to reconstruct how they lost the konfi in the first place. The Borana tend to discourage contests over wells through the long duration of investigations, as well as myths associated with false claims that appeared to result in deaths among the claimants.     

Searching for potential wintering and migration areas of a Danish Barn Swallow population in South Africa by correlating NDVI with survival estimates

On the basis of correlation analyses between annual Normalised Difference Vegetation Index (NDVI) values in Africa and the annual survival rate estimated for a breeding population of barn swallows Hirundo rustica from Denmark, we identified potential wintering and migration areas in South Africa during December–February and March–May, when barn swallows commonly occur in South Africa. During December–February we identified potential wintering areas only in the western part of South Africa, in the Karoo. Potential areas in the central and eastern parts of the country were only identified during March–May. NDVI values in the Karoo during March–May explained most of the variance in annual adult survival rate of the population. The high ratio of European ringed barn swallows among controlled individuals in the Karoo was similar to the ratio that would be expected based on the number of ringed barn swallows and the population sizes of barn swallows in north-western European breeding populations. The level of this ratio in the Karoo was higher than in any other locality in the central and eastern parts of South Africa and Botswana, indicating that ringed birds from the eastern flyway are absent to a much smaller extent than ringed birds from the western flyway. This approach shows that the NDVI and survival method can focus ringing efforts to regions and areas that are likely to harbour specific breeding populations, thereby helping to identify potential wintering and migration areas for breeding populations of migratory birds.     

Niche-based modelling as a tool for predicting the risk of alien plant invasions at a global scale

Predicting the probability of successful establishment of plant species by matching climatic variables has considerable potential for incorporation in early warning systems for the management of biological invasions. We select South Africa as a model source area of invasions worldwide because it is an important exporter of plant species to other parts of the world because of the huge international demand for indigenous flora from this biodiversity hotspot. We first mapped the five ecoregions that occur both in South Africa and other parts of the world, but the very coarse definition of the ecoregions led to unreliable results in terms of predicting invasible areas. We then determined the bioclimatic features of South Africa's major terrestrial biomes and projected the potential distribution of analogous areas throughout the world. This approach is much more powerful, but depends strongly on how particular biomes are defined in donor countries. Finally, we developed bioclimatic niche models for 96 plant taxa (species and subspecies) endemic to South Africa and invasive elsewhere, and projected these globally after successfully evaluating model projections specifically for three well‐known invasive species (Carpobrotus edulis, Senecio glastifolius, Vellereophyton dealbatum) in different target areas. Cumulative probabilities of climatic suitability show that high‐risk regions are spatially limited globally but that these closely match hotspots of plant biodiversity. These probabilities are significantly correlated with the number of recorded invasive species from South Africa in natural areas, emphasizing the pivotal role of climate in defining invasion potential. Accounting for potential transfer vectors (trade and tourism) significantly adds to the explanatory power of climate suitability as an index of invasibility. The close match that we found between the climatic component of the ecological habitat suitability and the current pattern of occurrence of South Africa alien species in other parts of the world is encouraging. If species' distribution data in the donor country are available, climatic niche modelling offers a powerful tool for efficient and unbiased first‐step screening. Given that eradication of an established invasive species is extremely difficult and expensive, areas identified as potential new sites should be monitored and quarantine measures should be adopted.     

Fire and grazing impacts on silica production and storage in grass dominated ecosystems

Grassland ecosystems are an important terrestrial component of the global biogeochemical silicon cycle. Although the structure and ecological functioning of grasslands are strongly influenced by fire and grazing, the role of these key ecological drivers in the production and storage of silicon represents a significant knowledge gap, particularly since they are being altered worldwide by human activities. We evaluated the effects of fire and grazing on the range and variability of plant derived biogenic silica stored in plant biomass and soils by sampling plants and soils from long-term experimental plots with known fire and grazing histories. Overall, plants and soils from grazed sites in the South African ecosystems had up to 76 and 54% greater biogenic silica totals (kg ha^?1), respectively, than grazed North American sites. In North American soils, the combination of grazing and annual fire resulted in the greatest abundance of biogenic silica, whereas South African soils had the highest biogenic silica content where grazed regardless of burn frequency. These results as well as those that show greater Si concentrations in grazed South African plants indicate that South African plants and soils responded somewhat differently to fire and grazing with respect to silicon cycling, which may be linked to differences in the evolutionary history and in the grazer diversity and grazing intensity of these ecosystems. We conclude that although fire and grazing (as interactive and/or independent factors) do not affect the concentration of Si taken up by plants, they do promote increased silicon storage in aboveground biomass and soil as a result of directly affecting other site factors such as aboveground net primary productivity. Therefore, as management practices, fire and grazing have important implications for assessing global change impacts on the terrestrial biogeochemical cycling of silicon.     

Predicting the Effects of Woody Encroachment on Mammal Communities,Grazing Biomass and Fire Frequency in African Savannas

With grasslands and savannas covering 20% of the world’s land surface, accounting for 30–35% of worldwide Net Primary Productivity and supporting hundreds of millions of people, predicting changes in tree/grass systems is priority. Inappropriate land management and rising atmospheric CO₂ levels result in increased woody cover in savannas. Although woody encroachment occurs world-wide, Africa’s tourism and livestock grazing industries may be particularly vulnerable. Forecasts of responses of African wildlife and available grazing biomass to increases in woody cover are thus urgently needed. These predictions are hard to make due to non-linear responses and poorly understood feedback mechanisms between woody cover and other ecological responders, problems further amplified by the lack of long-term and large-scale datasets. We propose that a space-for-time analysis along an existing woody cover gradient overcomes some of these forecasting problems. Here we show, using an existing woody cover gradient (0–65%) across the Kruger National Park, South Africa, that increased woody cover is associated with (i) changed herbivore assemblage composition, (ii) reduced grass biomass, and (iii) reduced fire frequency. Furthermore, although increased woody cover is associated with reduced livestock production, we found indigenous herbivore biomass (excluding elephants) remains unchanged between 20–65% woody cover. This is due to a significant reorganization in the herbivore assemblage composition, mostly as a result of meso-grazers being substituted by browsers at increasing woody cover. Our results suggest that woody encroachment will have cascading consequences for Africa’s grazing systems, fire regimes and iconic wildlife. These effects will pose challenges and require adaptation of livelihoods and industries dependent on conditions currently prevailing.     

Practical Environmentalism on the Pine Ridge Reservation: Confronting Structural Constraints to Indigenous Stewardship

Parallels exist between the academic theory of a dwelling approach to resilience and the Indigenous Stewardship Model developed on the Pine Ridge Indian Reservation in South Dakota. In both approaches, sustainable resource management depends on a practical environmentalism that creates linkages between local community members and their surrounding ecosystem. Research on the Pine Ridge Indian Reservation reveals that Lakota people possess a conservation ethic that stems from their physical connection to place. However, tribal, state, and federal land policies create structural barriers that reduce access of Lakota households to the land, which in turn reduces adaptability and resilience in their ecological practice. To overcome these barriers, Lakota households envision local stewardship of reservation lands and resources. Particular emphasis is placed on the intergenerational transfer of knowledge to Lakota youth, to transcend local and political conflict, and to reestablish social and cultural relationships with the reservation’s ecology.