Results/Conclusions
Neither nematode densities (320-1380 individuals 100 g^-1 soil) nor family richness (15-19 families 100 g^-1 soil) were altered by woody encroachment.  However, family evenness decreased dramatically in woody stands >20 yrs old.  The trophic structure of nematode communities was strongly modified following grassland to woodland conversion.  Although root biomass was 2-5X greater in wooded areas, plant parasites decreased from 40% of all nematodes in grasslands to <10% in the older wooded areas, suggesting the quality of woody plant root tissue could be limiting plant feeders.  In contrast, bacterivores increased from 30% of nematodes in grasslands to 70-80% in older woody patches.  This large increase in bacterivores may be a response to the 1.5-2.5X increase in soil microbial biomass following woody encroachment.  Therefore, while energy flow through grassland nematode communities appears to be based nearly equally on herbivory and bacterivory, energy flow through nematode communities in wooded areas appears to be based primarily on bacterivory.  We speculate that these shifts in nematode community composition and trophic structure could have important implications for ecosystem patterns and processes.  First, the low abundance of root parasites (and presumably root herbivory) under woody plants may be one mechanism by which woody plants are able to establish and compete effectively with grasses during succession from grassland to woodland.  Second, the large increase in bacterivores following woody encroachment likely accelerates microbial turnover and the mineralization of N, thereby providing a feedback that enables the persistence of N-rich woody plant communities.