Browsing by Author "Esler, K. J."
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- ItemThe distribution of invasive Pennisetum setaceum along roadsides in western South Africa: the role of corridor interchanges(European Weed Research Society, 2010) Rahlao, S. J.; Milton, S. J.; Esler, K. J.; Barnard, P.Roads and rivers may be dispersal corridors for invasive alien grass seeds that fly and float. These two systems interact at bridge interchanges that are also disturbed artificial habitats. The invasive grass Pennisetum setaceum (perennial fountain grass) establishes on roadsides and river banks and benefits from habitat conditions prevailing at these interchanges. The distribution of the grass across biomes and vegetation types and the influence of environmental variables were assessed. A road survey method was used to record and map the distribution of P. setaceum along 1 km roadside transects at 10 km intervals and at every road-river corridor interchange for 5112 km of South African national roads in the arid and semi-arid parts of the country. Pennisetum setaceum populations occurred in 10% of the total length sampled, including the interchanges. Fynbos Swartland Shale Renosterveld was the most significantly invaded amongst the vegetation types surveyed. Our results indicate that, although P. setaceum performs better on the interchanges, it does not preferentially colonise them over other parts of the landscape. The presence of P. setaceum was, however, closely associated with the presence of water bodies and disturbances away from the roads. Corridor interchanges should be considered important targets of both local and regional efforts to prevent and control P. setaceum invasions.
- ItemEffects of alien plant management, fire and soil chemistry on selected soil microbial populations in the Table Mountain National Park, South Africa(NISC Pty Ltd., 2005-06) Cilliers, C. D.; Botha, A.; Esler, K. J.; Boucher, C.This pilot study examined changes in soil chemistry and microbial population sizes following the extensive wildfires in 2000 on the Cape Peninsula. The effects of standing alien plants and stacks of mechanically-cleared alien plant material on selected post-fire microbial populations and their recovery were investigated. These were compared to burnt fynbos and the burnt cleared areas surrounding wildfire burnt stacks. Microbial population sizes and chemical changes were also monitored in unburnt fynbos and dense unburnt stands of invasive alien plants. Differences in soil chemistry and microbial population sizes occurred in the samples taken from the various post-fire environments while marked seasonal changes were also apparent. Microbial population sizes were linked to pre-fire vegetation characteristics, fire intensity, the management of alien plants, soil chemical changes and seasonal influences. High volumes of woody alien plant biomass impacted on post wildfire microbial population sizes during summer. During winter, however, microbial population sizes were primarily influenced by soil texture and nutrient composition. Copyright © NISC Pty Ltd.
- ItemMeasuring the effectiveness of regional conservation assessments at representing biodiversity surrogates at a local scale: A case study in Réunion Island (Indian Ocean)(Ecological Society of Australia, 2010) Payet, K.; Rouget, M.; LaGabrielle, E.; Esler, K. J.In a context of scarce financial and human resources, the allocation of conservation efforts needs to be optimized. Our analysis attempts to draw conclusions on the integration of regional and local conservation assessments, specifically, with regard to the acquisition of fine-scale data to complement the regional assessment. This study undertaken in Réunion Island (Indian Ocean) assessed how biodiversity surrogates targeted at a regional scale represented other biodiversity surrogates at a local scale. Biodiversity surrogates at both scales consisted of species, habitats and processes. Habitats and processes at regional scale were defined using a coarser scale of thematic resolution than at local scale.The surrogacy was tested in terms of incidental representation of local-scale features in the regional assessments, and correlation of irreplaceability values between scales. Near-minimum sets and irreplaceability values were generated using MARXAN software. Our results revealed that conservation targets for processes at local scale were never met incidentally, while threatened species and fragmented habitats were also usually under-represented. More specifically, requiring only 12% of the local planning domain, the application of species as surrogates at regional scale was the least effective option at representing biodiversity features at local scale. In contrast, habitats at a coarse scale of thematic resolution achieved a significant proportion of conservation targets incidentally (67%) and their irreplaceability values were well correlated with the irreplaceability values of surrogates at local scale. The results highlighted that all three types of biodiversity surrogates are complementary for assessing overall biodiversity. Because of the cost of data acquisition, we recommended that the most efficient strategy to develop nested regional/local conservation plans is to apply habitats and processes at a coarse scale of thematic resolution at regional scale, and threatened species and degraded habitats at local scale, with their fine-scale mapping limited to highly transformed areas.
- ItemMedium-term vegetation recovery after removal of invasive Eucalyptus camaldulensis stands along a South African river(Elsevier, 2018) Ruwanza, S.; Gaertner, M.; Esler, K. J.; Richardson, D. M.Effective ecological restoration requires detailed monitoring to determine the success achieved through different interventions in achieving objectives. In 2017, we resurveyed riparian sites along the Berg River in the Western Cape, South Africa, that have been cleared of invasive stands of Eucalyptus camaldulensis in 2010 using two clearing methods (fell-and-stackburn and fell-and-remove) and two restoration approaches: passive (where vegetation was allowed to recover without intervention) and active (assisted recovery). A significant increase in vegetation cover (P b .001) and diversity (P b .05) of native riparian species was recorded in passive restoration plots, but an increase in the cover of woody invasive alien plants was also observed. Only four of the nine native species that were planted to fast-track restoration were still present in the active restoration plots, but the abundance of these native species was significantly (P b .001) lower in 2017 than in 2011. We conclude that native vegetation recovery following E.camaldulensis removal seven years ago is following a positive recovery trajectory in both passive and active restoration sites, as shown by the increased occurrence of native trees and shrubs, e.g. Maytenus oleoides, Melianthus major and Searsia angustifolia which were not present before clearing. However, the reinvasion of cleared sites by woody invasive alien plants has the potential to slow down and potentially halt the recovery process. Further management interventions, e.g. removal of reinvading woody invasive alien plants, are required, emphasizing the sustained engagement to ensure restoration in these ecosystems.
- ItemMicrobial diversity and community structure in Fynbos soil(Blackwell Publishing Ltd, 2010) Slabbert, E.; Kongor, R. Y.; Esler, K. J.; Jacobs, K.The Fynbos biome in South Africa is renowned for its high plant diversity and the conservation of this area is particularly important for the region. This is especially true in the case of endangered vegetation types on the lowlands such as Sand Fynbos, of which only small fragments remain. The question is thus whether the diversity of the aboveground flora is mirrored in the below-ground microbial communities. In order to determine the relationship of the above- and below-ground communities, the soil community composition of both fungal and bacterial groups in Sand Fynbos was characterized over space and time. A molecular approach was used based on the isolation of total soil genomic DNA and automated ribosomal intergenic spacer analysis of bacterial and fungal communities. Soil from four different sites was compared to resolve the microbial diversity of eubacterial and fungal groups on a local (alpha diversity) scale as well as a landscape scale (beta diversity). The community structures from different sites were compared and found to exhibit strong spatial patterns which remained stable over time. The plant community data were compared with the fungal and the bacterial communities. We concluded that the microbial communities in the Sand Fynbos are highly diverse and closely linked to the above-ground floral communities.
- ItemNutrient addition and moisture promote the invasiveness of crimson fountaingrass (Pennisetum setaceum)(Weed Science Society of America, 2010) Rahlao, S. J.; Esler, K. J.; Milton, S. J.; Barnard, P.We conducted a greenhouse study to examine the effects of different habitat conditions and environmental resources on the growth rates of crimson fountaingrass, an invasive, alien, perennial grass in South Africa. To help understand the factors promoting the spread of this emergent alien grass, we investigated the effects of temperature regimes, nutrient and moisture addition, and soil type on seedling growth rates and biomass allocation. Our results suggest that crimson fountaingrass seedlings do not tolerate drought because they died within 1 mo without water. Additional nutrients and extra water increased seedling growth rates throughout the study period. Higher temperatures with extra moisture increased seedling growth rates and the development of belowground biomass throughout the study period. This study demonstrates the importance of available environmental resources and their interaction with some habitat conditions in promoting crimson fountaingrass growth. We suggest that soil moisture and nutrient availability are critical factors affecting successful establishment of crimson fountaingrass in arid environments. Managers should target seedlings for removal following precipitation and in areas of nutrient enrichment, such as near rivers and at road–river crossings.