Browsing by Author "Swart, Rudi Crispin"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    The effect of commercial forestry plantations and roads on southern Afrotemperate forest arthropod diversity
    (Stellenbosch : Stellenbosch University, 2016-03) Swart, Rudi Crispin; Roets, Francois; Pryke, James S.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: With only about 12% of the Earth’s surface under some form of official protection and the human population on the rise exponentially, production landscapes can and should contribute significantly towards biodiversity conservation in the future. Globally, management practices that balance production and conservation are important for creating sustainable agriculture and timber production landscape. This study aims to determine how a heterogeneous, unfenced national park in South Africa, containing a mosaic of commercial plantations, natural forests and fynbos is affected by land transformation. This was achieved by focussing on artificially created and natural edges found in this landscape, through analysing and comparing the composition and species richness of arthropods across linear transects. Specifically I determined if natural edges next to southern Cape Afrotemperate forests are altered by anthropogenic influences such as forestry plantations, and their felling, as measured by epigaeic arthropod diversity. The effects of different road types, and directions that these roads dissect the forest, were also assessed. I found that pine plantations provide little suitable habitat for either forest or fynbos arthropods. The natural fynbos-forest ecotone harbours a unique composition of arthropod assemblages, with the smallest edge effect into the forest. Once this is replaced by commercial pine plantations, an edge effect up to 30 m into the forests from the plantation edge is detected. When plantations bordering natural forests are felled, the edge effect increases to 50 m into natural forests. Research on edge effects created by roads showed that both wider, arterial roads as well as secondary roads affected the diversity of forest arthropods up to 50 m into the natural forest. These effects are therefore similar to that observed after clear felling of plantations except that, in contrast to possible regeneration of natural edge habitat after clear felling, these edges are now permanent fragmentary features in the forest with little chance of recovery. Even hiking trails affected overall arthropod assemblages in the adjacent forests up to 10 m. Although this likely does not lead to forest fragmentation due to an in-tact forest canopy, these areas alter natural assemblages with unknown population dynamic consequences. I also show that east-west directed roads have stronger fragmentary effects as determined by arthropod diversity, along their southern edge than north-south directed roads, with east and west facing edges. Increased sunlight penetration, with its accompanying changes in microclimatic conditions is put forward to explain these differences. Habitat loss due to the establishment of commercial plantation forestry in the region not only leads to a decrease in suitable fynbos habitat, but also impacts adjacent natural forest arthropod diversity. The remaining southern Cape Afrotemperate forests are greatly fragmented by a network of roads. Due to the uniqueness of these forests, special management is needed to ensure that the biodiversity in the region is optimally conserved without adversely affecting production yields. Some possible mitigation actions are put forward. However, these should be assessed for their effectiveness in future research studies before they are implemented.
  • Thumbnail Image
    Item
    Interactions between indigenous southern Afrotemperate forest trees and arthropod diversity
    (Stellenbosch : Stellenbosch University, 2020-04) Swart, Rudi Crispin; Samways, Michael J.; Roets, Francois; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Although small compared to other temperate rainforests in the southern Hemisphere, the southern Cape Afrotemperate forest complex is the largest in South Africa. While it occurs at temperate latitudes, it has strong tropical elements resulting from its paleo-history. Of the numerous species occupying forest ecosystems, insects comprise a major part of the total biodiversity, most of which occur in tree canopies. Prior to this study, little work had been done on insects in southern Afrotemperate forests in general, and no work at all has been done on the diversity and distribution of their canopy-inhabiting arthropods. Therefore, the aim here is to determine the extent to which various environmental factors affect the interaction between indigenous tree species and associated arthropod diversity in South African Afrotemperate forests. I first determine whether the context and contrast in which an individual tree grows (i.e. where it grows and what surrounds it) will impact its physiology and associated canopy arthropod diversity. I found that the contrast of vegetation surrounding an individual tree can affect leaf morphology, and, in turn, its ability to host particular arthropods, with trees with low contrast (i.e. surrounded by denser vegetation) revealing larger leaves and increased arthropod diversity. Furthermore, plant physiological features fluctuated according to the context in which a tree grows (natural, semi-natural, or planted vegetation), which affected associated canopy arthropods. Therefore, to optimally conserve local arthropod diversity using indigenous tree plantings in transformed landscapes, it is imperative to mimic natural tree context and natural variations in contrast. Forest arthropods maintain ecosystem health by driving ecosystem processes such as litter decomposition. I designed an experiment to compare the litter decomposition performed by arthropods vs. fungi, and determined which local factors influence variations in decomposition rates. In addition, I tested the home-field advantage (HFA) hypothesis at the tree-level. The HFA states that leaf litter decomposes more rapidly beneath plant species from which the leaves originate (home environment), than under other plant species. I demonstrated that arthropods perform the bulk of the decomposition function in these forests, and that their ability to do so varies significantly between different tree species, although the role of bacteria may also be substantial. Contrary to expectations, and despite selective arthropod responses toward different source leaves, HFA is not prevalent in this mixed forest system. Given the responses of arthropods to tree identity, tree context- and-contrast, and accompanying changes in plant physiological features, it was reasonable to assume that these factors may influence arthropods associated with the canopies of southern Afrotemperate forests. I therefore established the relative effects of tree species identity, plot characteristics, and plant physiology on the diversity and distribution of canopy arthropods. Tree species identity and differences in plant physiological features explained differences in arthropod diversity between individual trees. Individual trees surrounded by denser vegetation also had less diverse arthropod assemblages compared to trees in more open areas. I argue that in diverse mixed forests, tree crown heterogeneity is of significant importance in conserving arthropod diversity, driven not only by architectural variation, but also by fluctuating levels of light exposure. Differences in plant physiological features at the tree species level was accompanied by many effects on canopy arthropods, which would make generalisations of forest arthropod responses to anthropogenic changes difficult. As this study represents a first attempt to describe the diversity of arthropods in the canopies of southern Afrotemperate forests, I conclude by providing a synthesis of this diversity, placing it in a global context. I provide evidence that arthropod diversity in these forests is more similar to those of temperate forests than to arthropods associated with tree canopies in tropical forests. However, these forest canopies are ten-fold richer in species than the forest floors in this region. Combined with the high numbers of species sampled, many of which are undescribed, special conservation efforts is justified to protect southern Afrotemperate forest canopies across a wide biogeographical gradient.