Ecology of grazing lawns in Africa Hempson, Gareth P.; Archibald, Sally; Bond, William J. ...
Biological reviews of the Cambridge Philosophical Society,
08/2015, Letnik:
90, Številka:
3
Journal Article
Recenzirano
ABSTRACT
Grazing lawns are a distinct grassland community type, characterised by short‐stature and with their persistence and spread promoted by grazing. In Africa, they reveal a long co‐evolutionary ...history of grasses and large mammal grazers. The attractiveness to grazers of a low‐biomass sward lies in the relatively high quality of forage, largely due to the low proportion of stem material in the sward; this encourages repeat grazing that concomitantly suppresses tall‐grass growth forms that would otherwise outcompete lawn species for light. Regular grazing that prevents shading and maintains sward quality is thus the cornerstone of grazing lawn dynamics. The strong interplay between abiotic conditions and disturbance factors, which are central to grazing lawn existence, can also cause these systems to be highly dynamic. Here we identify differences in growth form among grazing lawn grass species, and assess how compositional differences among lawn types, as well as environmental variables, influence their maintenance requirements (i.e. grazing frequency) and vulnerability to degradation. We also make a clear distinction between the processes of lawn establishment and lawn maintenance. Rainfall, soil nutrient status, grazer community composition and fire regime have strong and interactive influences on both processes. However, factors that concentrate grazing pressure (e.g. nutrient hotspots and sodic sites) have more bearing on where lawns establish. Similarly, we discuss the relevance of enhanced rates of nitrogen cycling and of sodium levels to lawn maintenance. Grazer community composition and density has considerable significance to grazing lawn dynamics; not all grazers are adapted to foraging on short‐grass swards, and differences in body size and relative mouth dimensions determine which species are able to convert tall‐grass swards into grazing lawns under different conditions. Hence, we evaluate the roles of different grazers in lawn dynamics, as well as the benefits that grazer populations derive from having access to grazing lawns. The effects of grazing lawns can extend well beyond their borders, due to their influence on grazer densities, behaviour and movements as well as fire spread, intensity and frequency. Variation in the area and proportion of a landscape that is grazing lawn can thus have a profound impact on system dynamics. We provide a conceptual model that summarises grazing lawn dynamics, and identify a rainfall range where we predict grazing lawns to be most prevalent. We also examine the biodiversity associated with grazing lawn systems, and consider their functional contribution to the conservation of this biodiversity. Finally, we assess the utility of grazing lawns as a resource in a rangeland context.
This innovative interdisciplinary study focuses on the history, science, and policy of tree planting and water conservation in South Africa. South Africa’s forestry sector has sat—often ...controversially—at the crossroads of policy and scientific debates regarding water conservation, economic development, and biodiversity protection. Bennett and Kruger show how debates about the hydrological impact of exotic tree planting in South Africa shaped the development of modern scientific ideas and state policies relating to timber plantations, water conservation, invasive species control, and biodiversity management within South Africa as well as elsewhere in the world. Forestry and Water Conservation in South Africa shows how scientific research on the impact of exotic and native vegetation led to the development of a comprehensive national policy for conserving water, producing timber, and protecting indigenous species from invasive alien plants. Policies and laws relating to forests and water began to change in the late 1980s and early 1990s as a result of political and administrative changes within South Africa. This book suggests that the country’s contemporary policies towards timber plantations, guided by the National Water Act of 1998, need to be reconsidered in light of the authors’ findings. Bennett and Kruger also call for more interdisciplinary research and greater emphasis on integrated policies and management plans for forestry, invasive alien plants, water conservation, and biodiversity preservation.
This paper describes the first step in developing an approach to fire risk assessment aimed at balancing the reduction of risks to lives and livelihoods and maintaining fire regimes which protect ...ecosystem biodiversity and function in fire‐prone ecosystems. Wildfires pose a major hazard to people's lives, livelihoods and ecosystems in South Africa with poor communities generally being highly exposed and vulnerable. Although general information exists, an adequate understanding of the fire regimes, how they vary spatially, and the related vegetation management requirements is lacking. This study resolves the environmental variation in fire regimes across South Africa into a systematic framework for wildfire risk assessment and ecologically sound ecosystem management. The available descriptions of fire regimes, vegetation classifications, and fire occurrence data from remote sensing are synthesized to derive a set of 13 distinct fire‐ecology types, that is, sets of vegetation units which experience distinct fire regimes. Fuel dynamics, fire‐dependence, ecologically acceptable fire regimes, and guidelines for fire management are described for each of these fire‐ecology types and they are grouped into three categories: fire dependent, fire independent and fire sensitive. Fire‐dependent ecosystems comprise more than 60% of South Africa and fire‐independent ones 32%, the latter mainly in the arid west and northwest, while the remainder are fire sensitive. Fire‐dependent systems require fires and generally coincide with the greatest rural population densities. The outputs from this framework can be used to analyse wildfire risk and translate the risk into practical management measures which are responsive to local ecological, social and institutional settings.
In all areas of academic or practical work related to disaster risk, climate change and development more generally, community and its adjunct community-based have become the default terminology when ...referring to the local level or working ‘with the people’. The terms are applied extensively to highlight what is believed to be a people-centred, participatory, or grassroot-level approach. Today, despite, or because of, its inherent ambiguity, ‘community’ tends to be used almost inflationarily. This paper aims to analyse the way the concept of ‘community’ has come into fashion, and to critically reflect on the problems that come with it. We are raising significant doubts about the usefulness of ‘community’ in development- and disaster-related work. Our approach is to first consider how ‘community’ has become popular in research and with humanitarian agencies and other organisations based on what can be considered a ‘moral licence’ that supposedly guarantees that the actions being taken are genuinely people-centred and ethically justified. We then explore several theoretical approaches to ‘community’, highlight the vast scope of different (and contested) views on what ‘community’ entails, and explain how ‘community’ is framing practical attempts to mitigate vulnerability and inequity. We demonstrate how these attempts are usually futile, and sometimes harmful, due to the blurriness of ‘community’ concepts and their inherent failure to address the root causes of vulnerability. From two antagonistic positions, we finally advocate more meaningful ways to acknowledge vulnerable people’s views and needs appropriately.
The 2nd African Water Symposium, in conjunction with the 6th Orange River Basin Symposium, was held on the campus of the University of the Free State, Bloemfontein, on Oct 7, 2015 and Oct 8, 2015. ...The theme of the symposium was 'systems thinking in environmental water resources management', with the aim of evaluating and debating a holistic approach to water management in southern Africa. The symposium included a panel discussion that was originally intended to define a roadmap towards effective water resources management, but it soon took on a life of its own and evolved into a discussion on how to develop and train the next generation of managers and scientists to tackle the current challenges being faced by the wider water sector. The 2-hour long discussion session consisted of opening statements from a panel of scientists and practitioners specifically selected for their experience in different parts of the water sector.
This paper focuses on the work of Louis Scott and co-workers on the palynology of present-day and past savanna fossil-pollen sites in southern Africa. Evidence for the persistent though fluctuating ...presence of the pollen of extant species of trees indicates species survival under marked variations in climate over the past 200 ka, but variable assemblage of communities over time, at any one site. This, with contemporary information on the genetics and demographics of savanna tree species, requires that ecologists today must see the savanna as an individualistic, ecogenetic or eco-evolutionary community. Further, present-day savanna communities are the outcome of recent and older history, requiring that ecology must encompass the methods of historical science.
This paper focuses on the work of Louis Scott and co-workers on the palynology of present-day and past savanna fossil-pollen sites in southern Africa. Evidence for the persistent though fluctuating ...presence of the pollen of extant species of trees indicates species survival under marked variations in climate over the past 200 ka, but variable assemblage of communities over time, at any one site. This, with contemporary information on the genetics and demographics of savanna tree species, requires that ecologists today must see the savanna as an individualistic, ecogenetic or eco-evolutionary community. Further, present-day savanna communities are the outcome of recent and older history, requiring that ecology must encompass the methods of historical science.
This innovative interdisciplinary study focuses on the history, science, and policy of tree planting and water conservation in South Africa. South Africa’s forestry sector has sat—often ...controversially—at the crossroads of policy and scientific debates regarding water conservation, economic development, and biodiversity protection. Bennett and Kruger show how debates about the hydrological impact of exotic tree planting in South Africa shaped the development of modern scientific ideas and state policies relating to timber plantations, water conservation, invasive species control, and biodiversity management within South Africa as well as elsewhere in the world. Forestry and Water Conservation in South Africa shows how scientific research on the impact of exotic and native vegetation led to the development of a comprehensive national policy for conserving water, producing timber, and protecting indigenous species from invasive alien plants. Policies and laws relating to forests and water began to change in the late 1980s and early 1990s as a result of political and administrative changes within South Africa. This book suggests that the country’s contemporary policies towards timber plantations, guided by the National Water Act of 1998, need to be reconsidered in light of the authors’ findings. Bennett and Kruger also call for more interdisciplinary research and greater emphasis on integrated policies and management plans for forestry, invasive alien plants, water conservation, and biodiversity preservation.
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