DISTURBANCE, DIVERSITY, AND INVASION - IMPLICATIONS FOR CONSERVATIONS

Disturbance is an important component of many ecosystems and variations in disturbance regime can affect ecosystem and community structure and functioning. The "intermediate disturbance hypothesis" suggests that species diversity should be highest at moderate levels of disturbance However, disturbance is also known to increase the invasibility of communities. Disturbance therefore poses an important problem for conservation management Here, we review the effects of disturbances such as fire, grazing soil disturbance, and nutrient addition on plant species diversity and invasion, with particular emphasis on grassland vegetation. Individual components of the disturbance regime can have marked effects on species diversity, but it is often modifications of the existing regime that have the largest influence. Similarly, disturbance can enhance invasion of natural communities, but frequently it is the interaction between different disturbances that has the largest effect The natural disturbance regime is now unlikely to persist within conservation areas, since fragmentation and human intervention have usually modified physical and biotic conditions. Active management decisions must now be made on what disturbance regime is required, and this requires decisions on what species are to be encouraged or discouraged.