Pathogens and the structure of plant communities.

There is increasing interest in the direct and indirect effects of pathogens and parasites on the structure of plant communities. The direct influence of pathogens is seen in cases where pathogens reduce the populations of adult and seedling plants or prevent the recruitment of seeds. Indirect effects occur when epidemic outbreaks or endemic parasites of herbivores lead to reductions in grazing pressure, which temporarily allow plants to escape from the detrimental effects of their herbivores. In both cases, the presence of pathogens can lead to changes in the relative abundance of the species in a plant community, which are discernible for many years after the initial disease outbreak has passed.