Print PagePopulations of Sansevieria volkensii, a succulent plant endemic to the drylands of north central Kenya, have grown dramatically in recent decades. Such a shift in plant community structure, as in the cases of exotic species invasion and woody encroachment, can alter the ecological functioning and productivity of rangelands and thereby threaten the livelihood of pastoralists. Indeed, the dense stands that S. volkensii forms impede livestock and human movement, and the plant itself is poor fodder and undesirable to local pastoralists. Little is known of the dynamics of S. volkensii proliferation; our research, done at the request of affected communities, endeavors to identify environmental conditions associated with population expansion, the effect of this species’ expansion on ecosystem and hydrologic function, and potential management strategies. Here we present the findings of an observational study that examined the early stages of S. volkensii proliferation. In July of 2009 and 2010, we surveyed four plots (covering approx. 10 ha and containing 150 patches in total), in a region where the succulent occurred in comparatively small patches, and where populations were anecdotally reported to be newly expanding. We recorded a number of environmental variables associated with the status of these ‘nascent’ patches, including most notably associated tree canopy cover.
Results/Conclusions
In 2009, a drought year, we found that S. volkensii patches under tree canopies were significantly larger and healthier than those in the open inter-canopy areas, but the likelihood of a patch containing tree canopy was neither greater nor less than expected due to random association. These findings indicated that patches are not obligately establishing under the canopies of trees, but larger under-canopy patches suggest either earlier establishment or a higher growth rate under trees. Revisiting the patches in 2010, after a season of heavy rains, we found an average of 30% more ramets and leaves than 2009. While patches under trees were still larger, the proportion of new leaves was greater in patches not associated with trees, suggesting that inter-canopy conditions allowed greater utilization of the resource pulse. These findings are in agreement with other recent experimental and modeling studies of this system that argue that S. volkensii patches proliferate under conditions of degraded surrounding soils and preferential capture of intense resource pulses. We conclude that the nascent patches observed in this study are likely to continue proliferating, with particularly rapid expansion into inter-canopy areas after heavy rains.
