143 research outputs found
Ecological resilience at semi-arid and temperate boundaries of the Mediterranean-type Fynbos Biome, South Africa, during the Holocene
Mediterranean-type ecosystems are amongst the most vulnerable to global change. Threats from desertification are projected due to rapid expansion of adjacent semiarid systems. Changes in fire frequency and intensity can alter ecosystem composition and structure, and potentially facilitate transitions between alternative stable states. Given the outstanding biodiversity of the Mediterranean-type fynbos biome in the Greater Cape Floristic Region (GCFR) of South Africa, understanding of the longterm impacts of global change are particularly important. In this study, palaeoecological data are used to assess the effects of changes in climate, fire and land use on vegetation at the semi-arid and temperate margins of the fynbos biome. Previous palaeoecological studies have shown stable fynbos during the recent geologic past, which restricts interpretation of the long-term ecological processes that determine biome resilience. This study sourced sediment cores directly from presentday fynbos-succulent karoo (semi-arid) and fynbos-afrotemperate forest biome boundaries to emphasise ecological dynamics. Fossil pollen, spores and charcoal were extracted from radiocarbon dated sediment cores to provide proxies for vegetation, hydrology, large herbivore abundance and fire. Constrained hierarchical clustering (CONISS), optimal sequence splitting by least-squares, and Non-metric Multidimensional Scaling (NMDS) was applied to the fossil data to identify distinct assemblages in the record, and to further elucidate ecosystem trajectories through time. At the semi-arid boundary at Groenkloof (5,500 cal yrs BP - near present), decreased moisture and fire from 4,000-735 cal yrs BP allowed colonisation of fynbos by a possible 'no-analogue' community dominated by Asteraceae and Poaceae. From 735 cal yrs BP however, climatic amelioration allowed fynbos to re-establish. The system can therefore be viewed as resilient through a capacity for 'recovery' and persistence through turnover in internal composition of fynbos taxa. This sensitive response to climatic forcing reflects the dominant influence of physiological stress at the semiarid limits of Mediterranean-type ecosystems, as well as a Gleasonian type community composition with loose species associations. In contrast, ecosyste
Piospheres in semi-arid rangeland: Consequences of spatially constrained plant-herbivore interactions
This thesis explains two aspects of animal spatial foraging behaviour arising as a direct consequence
of animals' need to drink water: the concentration of animal impacts, and the response of animals to
those impacts.
In semi-arid rangelands, the foraging range of free-ranging large mammalian herbivores is constrained
by the distribution of drinking water during the dry season. Animal impacts become concentrated
around these watering sites according to the geometrical relationship between the available foraging
area and the distance from water, and the spatial distribution of animal impacts becomes organised
along a utilisation gradient termed a "piosphere". During the dry season the temporal distribution of
the impacts is determined by the day-to-day foraging behaviour of the animals. The specific
conditions under which these spatial foraging processes determine the piosphere pattern have been
identified in this thesis.
At the core of this investigation are questions about the response of animals to the heterogeneity of
their resources. Aspects of spatial foraging are widely commented on whilst explaining the
consequences of piosphere phenomena for individual animal intake, population dynamics, feeding
strategies and management. Implicated are our notions of optimal foraging, scale in animal response,
and resource matching. This thesis addressed each of these. In the specific context of piospheres, the
role of energy balance in optimal foraging was also tested.
Field experiments for this thesis showed a relationship between goat browsing activity and measures
of spatial impact. As a preliminary step to investigating animal response to resource heterogeneity, the
spatial pattern of foraging behaviour/impacts was described using spatial statistics. Browsing activity
varied daily revealing animal assessment of the spatial heterogeneity of their resources and an
energetic basis for foraging decisions. This foraging behaviour was shown to be determined by
individual plants rather than at larger scales of plant aggregation. A further experiment investigated
the claim that defoliation has limited impact on browser intake rate, suggesting that piospheres may
have few consequences for browser intake. This experiment identified a constraining influence of
browse characteristics at the small scale on goat foraging by relating animal intake rate to plant bite
size and distribution.
Computer simulation experiments for this thesis supported these empirical findings by showing that
the distribution of spatial impacts was sensitive to the marginal value of forage resources, and
identified plant bite size and distribution as the causal factors in limiting animal intake rate in the
presence of a piosphere. As a further description of spatial pattern, piospheres were characterised by
applying a contemporary ecological theory that ranks resource patches into a spatial hierarchy.
Ecosystem dynamics emerge from the interactions between these patches, with piospheres being an
emergent property of a natural plant-herbivore system under specific conditions of constrained
foraging. The generation of a piosphere was shown to be a function of intake constraints and available
foraging area, whilst piosphere extent was shown to be independent of daily energy balance including
expenditure on travel costs. A threshold distance for animal foraging range arising from a
hypothesised conflict between daily energy intake and expenditure was shown not to exist, whereas
evidence for an intermediate distance from water as a focus for accumulated foraging activity was
identified.
Individual animal foraging efficiency in the computer model was shown to be sensitive to the
piosphere, while animal population dynamics were found to be determined in the longer term by dry
season key resources near watering points. Time lags were found to operate in the maintenance of the
gradient, and the density dependent moderation of the animal population. The latter was a direct result
of the inability of animal populations to match the distribution of their resources with the distribution
of their foraging behaviour, because of their daily drinking requirements. The result is that animal
forage intake was compromised by the low density of dry season forage in the vicinity of a water
point.
This thesis also proposes that piospheres exert selection pressures on traits to maximise energy gain
from the spatial heterogeneity of dry season resources, and that these have played a role in the
evolution of large mammalian herbivores
Tipping points in natural systems. An inventory of types, early warnings, and consequences
Hoe creatief om te gaan met de toenemende druk door de menselijke populatie en de mogelijke belangenverstrengelingen van verschillende belangenhouders die dat met zich meebrengt, bv. door systemen meerdere functies tegelijk te laten vervullen. Het KB IV-programma âgroenblauwe ruimteâ beoogt te onderzoeken hoe, door goed gebruik te maken van de half-natuurlijke terrestrische (âgroeneâ) en aquatische (âblauweâ) ruimte, hier oplossingen kunnen worden geboden. Onderzoek heeft uitgewezen dat er in meerdere natuurlijke en menselijke systemen mogelijke âkantelpuntenâ (Eng. âtipping pointsâ) bestaan: Kleine veranderingen in factoren die van belang voor het systeem zijn, kunnen onverwacht leiden tot plotselinge grote veranderingen
Desertification in Europe: mitigation strategies, land use planning: Proceedings of the advanced study course held in Alghero, Sardinia, Italy from 31 May to 10 June 1999
The present volume is based on lectures given at the course held in Alghero, Sardinia, Italy, from 31 May to 10 June 1999 on âDesertification in Europe: Mitigation Strategies, Land Use Planningâ. It also contains presentations, given by the participating students, on their own research activities and interests.
With the adoption of the International Convention to Combat Desertification, which represents a follow up of the Rio recommendations, this publication is timely. It highlights the specific situation of the Southern European regions and provides a comprehensive and state-of-the-art review of this complex issue
Land-related global habitability science issues
The scientific investigation of the viewpoint of the biosphere that living organisms and their physical and chemical environment are bound, inseparable parts of one set of closely coupled global processes of the global biogeochemical system, life and life support cycles, is discussed as one of the major scientific challenges of the next decade by building from understanding land processes to interdisciplinary, holistic studies of biospheric dynamics including human impacts
Risk-Informed Sustainable Development in the Rural Tropics
Many people live in rural areas in tropical regions. Rural development is not merely a contribution to the growth of individual countries. It can be a way to reduce poverty and to increase access to water, health care, and education. Sustainable rural development can also help stop deforestation and reduce live-stock, which generate most of the greenhouse gas emissions. However, eorts to achieve a sustainable rural development are often thwarted by oods, drought, heat waves, and hurricanes, which local communities are not very prepared to tackle. Agricultural practices and local planning are still not very risk-informed.
These deciencies are particularly acute in tropical regions, where many Least Developed Countries are located and where there is, however, great potential for rural development. This Special Issue contains 22 studies on best practices for risk awareness; on local risk reduction; on several cases of soil depletion, water pollution, and sustainable access to safe water; and on agronomy, earth sciences, ecology, economy, environmental engineering, geomatics, materials science, and spatial and regional planning in 12 tropical countries
Forest and Rangeland Soils of the United States Under Changing Conditions
This open access book synthesizes leading-edge science and management information about forest and rangeland soils of the United States. It offers ways to better understand changing conditions and their impacts on soils, and explores directions that positively affect the future of forest and rangeland soil health. This book outlines soil processes and identifies the research needed to manage forest and rangeland soils in the United States. Chapters give an overview of the state of forest and rangeland soils research in the Nation, including multi-decadal programs (chapter 1), then summarizes various human-caused and natural impacts and their effects on soil carbon, hydrology, biogeochemistry, and biological diversity (chapters 2â5). Other chapters look at the effects of changing conditions on forest soils in wetland and urban settings (chapters 6â7). Impacts include: climate change, severe wildfires, invasive species, pests and diseases, pollution, and land use change. Chapter 8 considers approaches to maintaining or regaining forest and rangeland soil health in the face of these varied impacts. Mapping, monitoring, and data sharing are discussed in chapter 9 as ways to leverage scientific and human resources to address soil health at scales from the landscape to the individual parcel (monitoring networks, data sharing Web sites, and educational soils-centered programs are tabulated in appendix B). Chapter 10 highlights opportunities for deepening our understanding of soils and for sustaining long-term ecosystem health and appendix C summarizes research needs. Nine regional summaries (appendix A) offer a more detailed look at forest and rangeland soils in the United States and its Affiliates
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