102 research outputs found
Bird community structure and convergence in Afromontane forest patches of the Karkloof/Balgowan range, KwaZulu-Natal.
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.Forest fragmentation is caused by the clearing of patches of indigenous vegetation for
agriculture, urban development, and other human land uses. Such action results in
patches of remnant natural vegetation being surrounded by altered vegetation. I
investigate the effects of forest fragmentation and matrix type on avian diversity and
assemblage structure in forest patches of the historically fragmented Karkloof / Balgowan
forest range, KwaZulu-Natal, South Africa. This study compares the bird assemblage
diversity and composition of indigenous forest patches surrounded by commercial
forestry (Gilboa complex) with that surrounded by natural grassland matrix (Balgowan complex). Insularisation of Afromontane Mistbelt forest in KwaZulu-Natal has led to loss of
species where forest fragments support fewer bird species than comparably sized patches
of mainland forest. Small fragments within natural grassland have fewer bird species per
unit area than larger fragments. Forest patch area-dependent density compensation is
evident and bird assemblages appear saturated. Bird assemblages are characterised by a
non-random species distribution pattern where area-dependent processes are dominant,
and the loss of species from fragments follows a deterministic sequence. In forests in the
plantation-dominated matrix no island-effect is detectable and it appears that forest
patches are converging on the same bird species richness, regardless of forest size. No
density compensation is evident and bird assemblages are not saturated. The sequence of
species loss from forest patches is not as predictable, where a random yet prominent
colonisation process exists. As commercial plantations provide suitable habitat cover for
movement of forest birds, colonisation of both distant and small indigenous forest
patches has been possible, reducing the effects of area-dependent extinction in the forest
patches but also resulting in lower species richness in larger patches.
Bird species of the Karkloof / Balgowan forest range appear to be fragmentation
adapted, and most species are resilient to further landscape change. Certain species are
however more prone to local extinction than others. The major predictors of extinction
risk are body size, abundance status, and feeding guild. Patch area is the dominant force
governing traits in the natural Balgowan complex where larger species with low natural
abundance and an insectivorous diet are most prone to local extinction. In the Gilboa
complex the nature of the plantation matrix appears to be masking the species natural
responses to fragmentation making it difficult to predict which species are most at risk.
In order to preserve maximum bird diversity, including high-risk species, the largest
intact forest units (≥302ha) must be conserved. Evidently, the nature of the matrix affects
avifaunal diversity and distribution in forest patches, and plantations have the capacity to
significantly alter bird assemblage structure and composition in indigenous forest
patches. Forest fragments must be considered as integrated parts of a complex landscape
mosaic, and this study emphasises the importance of understanding landscape-scale
processes. Knowledge of ecological and life history traits proves valuable for predicting community level response to landscape change
Combined effects of landscape composition and heterogeneity on farmland avian diversity
Conserving biodiversity on farmland is an essential element of worldwide efforts for
reversing the global biodiversity decline. Common approaches involve improving the
natural component of the landscape by increasing the amount of natural and
seminatural habitats (e.g., hedgerows, woodlots, and ponds) or improving the
production component of the landscape by increasing the amount of biodiversity-friendly
crops. Because these approaches may negatively impact on economic output,
it was suggested that an alternative might be to enhance the diversity (compositional
heterogeneity) or the spatial complexity (configurational heterogeneity) of land cover
types, without necessarily changing composition. Here, we develop a case study to
evaluate these ideas, examining whether managing landscape composition or
heterogeneity, or both, would be required to achieve conservation benefits on avian
diversity in open Mediterranean farmland. We surveyed birds in farmland landscapes
of southern Portugal, before (1995–1997) and after (2010–2012) the European
Union’s Common Agricultural Policy (CAP) reform of 2003, and related spatial and
temporal variation in bird species richness to variables describing the composition, and
the compositional and configurational heterogeneity, of the natural and production
components of the landscape. We found that the composition of the production
component had the strongest effects on avian diversity, with a particularly marked
effect on the richness of farmland and steppe bird species. Composition of the natural
component was also influential, mainly affecting the richness of woodland/shrubland
species. Although there were some effects of compositional and configurational
heterogeneity, these were much weaker and inconsistent than those of landscape
composition. Overall, we suggest that conservation efforts in our area should focus
primarily on the composition of the production component, by striving to maximize
the prevalence of biodiversity-friendly
crops. This recommendation probably applies
to other areas such as ours, where a range of species of conservation concern is
strongly associated with crop habitatsinfo:eu-repo/semantics/publishedVersio
A review of source tracking techniques for fine sediment within a catchment
Excessive transport of fine sediment, and its associated pollutants, can cause detrimental impacts in aquatic environments. It is therefore important to perform accurate sediment source apportionment to identify hot spots of soil erosion. Various tracers have been adopted, often in combination, to identify sediment source type and its spatial origin; these include fallout radionuclides, geochemical tracers, mineral magnetic properties and bulk and compound-specific stable isotopes. In this review, the applicability of these techniques to particular settings and their advantages and limitations are reviewed. By synthesizing existing approaches, that make use of multiple tracers in combination with measured changes of channel geomorphological attributes, an integrated analysis of tracer profiles in deposited sediments in lakes and reservoirs can be made. Through a multi-scale approach for fine sediment tracking, temporal changes in soil erosion and sediment load can be reconstructed and the consequences of changing catchment practices evaluated. We recommend that long-term, as well as short-term, monitoring of riverine fine sediment and corresponding surface and subsurface sources at nested sites within a catchment are essential. Such monitoring will inform the development and validation of models for predicting dynamics of fine sediment transport as a function of hydro-climatic and geomorphological controls. We highlight that the need for monitoring is particularly important for hilly catchments with complex and changing land use. We recommend that research should be prioritized for sloping farmland-dominated catchments
A review of source tracking techniques for fine sediment within a catchment
Excessive transport of fine sediment, and its associated pollutants, can cause detrimental impacts in aquatic environments. It is therefore important to perform accurate sediment source apportionment to identify hot spots of soil erosion. Various tracers have been adopted, often in combination, to identify sediment source type and its spatial origin; these include fallout radionuclides, geochemical tracers, mineral magnetic properties and bulk and compound-specific stable isotopes. In this review, the applicability of these techniques to particular settings and their advantages and limitations are reviewed. By synthesizing existing approaches, that make use of multiple tracers in combination with measured changes of channel geomorphological attributes, an integrated analysis of tracer profiles in deposited sediments in lakes and reservoirs can be made. Through a multi-scale approach for fine sediment tracking, temporal changes in soil erosion and sediment load can be reconstructed and the consequences of changing catchment practices evaluated. We recommend that long-term, as well as short-term, monitoring of riverine fine sediment and corresponding surface and subsurface sources at nested sites within a catchment are essential. Such monitoring will inform the development and validation of models for predicting dynamics of fine sediment transport as a function of hydro-climatic and geomorphological controls. We highlight that the need for monitoring is particularly important for hilly catchments with complex and changing land use. We recommend that research should be prioritized for sloping farmland-dominated catchments
Using source-specific models to test the impact of sediment source classification on sediment fingerprinting
Sediment fingerprinting estimates sediment source contributions directly from river sediment. Despite being fundamental to the interpretation of sediment fingerprinting results, the classification of sediment sources and its impact on the accuracy of source apportionment remain underinvestigated. This study assessed the impact of source classification on sediment fingerprinting based on diffuse reflectance infrared Fourier transform spectrometry (DRIFTS), using individual, source-specific partial least-squares regression (PLSR) models. The objectives were to (a) perform a model sensitivity analysis through systematically omitting sediment sources and (b) investigate how sediment source-group discrimination and the importance of the groups as actual sources relate to variations in results. Within the Aire catchment (United Kingdom), five sediment sources were classified and sampled (n = 117): grassland topsoil in three lithological areas (limestone, millstone grit, and coal measures); riverbanks; and street dust. Experimental mixtures (n = 54) of the sources were used to develop PLSR models between known quantities of a single source and DRIFTS spectra of the mixtures, which were applied to estimate source contributions from DRIFTS spectra of suspended (n = 200) and bed (n = 5) sediment samples. Dominant sediment sources were limestone topsoil (45 ± 12%) and street dust (43 ± 10%). Millstone and coals topsoil contributed on average 19 ± 13% and 14 ± 10%, and riverbanks 16 ± 18%. Due to the use of individual PLSR models, the sum of all contributions can deviate from 100%; thus, a model sensitivity analysis assessed the impact and accuracy of source classification. Omitting less important sources (e.g., coals topsoil) did not change the contributions of other sources, whereas omitting important, poorly-discriminated sources (e.g., riverbank) increased the contributions of all sources. In other words, variation in source classification substantially alters source apportionment depending on source discrimination and source importance. These results will guide development of procedures for evaluating the appropriate type and number of sediment sources in DRIFTS-PLSR sediment fingerprinting
The Development of the Doctrine of Evolution and Its Influence in England During the 19th Century Upon Religious Thought
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