Spatial patterning and demography in Strandveld succulent Karoo : implications for biodiversity management

[摘要] ENGLISH ABSTRACT:This thesis focuses on the effects of vegetation resting on biodiversity and communitydynamics at Rocherpan Nature Reserve (320 36'S, 180 18'E) in the semi-arid coastal strip ofthe Succulent Karoo known as Strandveld. As a whole, the Succulent Karoo has anextraordinary high level of phyto diversity with high levels of endemism. This is particularlytrue for succulent shrubs belonging to the groups Mesembryanthemaceae, Crassulaceae andAsteraceae.The thesis begins with an investigation into effects that vegetation resting has on plantdiversity. The aim was to determine if resting affected biodiversity levels and if so, whichplant groups are affected and why. Through a numerical approach, it was determined thatwith resting overall species richness remained the same. However, different plant life formsresponded to resting differently. With increased resting, abundance of succulent shrubsdecreased, while richness of annuals increased.The second aspect under investigation was to determine how resting the vegetation affectedcommunity dynamics. The aim was to understand how vegetation structure and interspecificassociations changed with resting and to apply these findings to known community models.Through an autocorrelation approach, it was found that horizontal patterning of long-livedwoody species, that formed distinctive vegetation clumps, did not change with resting, whiledifferences were found in woody matrix species and succulent species. These changes instructure were investigated further through a study on the demography of specific species.Demography of woody species associated with vegetation clumps did not change withvegetation resting, while significant changes were observed for woody matrix species andsucculent species. In longer rested vegetation, woody matrix species showed a greater range insize class distribution (i.e. had both very large and smaller plants) with the tendency towardslarger plant sizes. Succulents on the other hand, had a smaller range in size class distributionwith a tendency towards larger plants. For all species investigated there were low seedlingscounts. It was concluded that succulent shrub populations were 'mature' and continued restingcould result in local extinction of some species due to the lack of regeneration. The overalllack of seedlings was attributed to a saturated establishment environment. Implications forconservation management were discussed.

[发布机构] Stellenbosch University