Disturbance, Diversity, and Invasion: Implications for Conservation

Disturbance is an important component o f many ecosystemg and variations in disturbance regime can affect ecosystem and communi ty structure and functioning. The "'intermediate disturbance hypothesis" suggests that species diversity should be highest at moderate levels o f disturbance. However, disturbance is also known to increase the invasibility o f communities. Disturbance therefore poses an im. portant problem for conservation managemen£ Her~ we review the effects o f disturbances such as firg grazing soil disturbanc6 and nutrient addition on p lant species diversity and invasion, with particular emphasis on grassland vegetatiorL Individual components o f the disturbance regime can have marked effects on species diversity, but it is often mod. ifications o f the existing regime that have the largest influence. Similarly, disturbance can enhance invasion o f 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 area~ since fragmentation and human intervention have usually modified physical and biotic conditionx Active management decisions must now be made on what disturbance regime is requirea~ and this requires decisions on what species are to be encouraged or discouraged