Recolonization of methyl-bromide sterilized soils by plant and soil nematodes over 52 months

Recolonization of soils by organisms is dependent not only on biological factors but also on site factors including soil and vegetation. The total nematode populations in soil sterilized 52 months earlier with methyl bromide ranged from 77 to 123% of those in untreated soil; both vegetation and rainfall appear to have been important factors in the recolonization. In a high-rainfall pasture the dominant plant-feeding nematode Helicotylenchus did not recolonize and was replaced by Paratylenchus. Under high rainfall, Iotonchus failed to recolonize either pasture or forest, but Clarkus recolonized well. While indices such as the maturity index, the summed maturity index, PPI, the ratio of fungal: bacterial feeding nematodes, species richness, the Shannon-Weaver index, and indices of evenness, dominance, and diversity showed various effects, none gave consistent trends; rainfall and vegetation probably exerted too much influence. In the light of trends in our data, in data for other ecosystems, and the reality of r-K strategies in animals, it may not be reasonable to expect a global nematode index of soil health or ecosystem condition. While a nematode index may be useful in local or regional studies, research efforts may be better directed towards elucidating key populations of nematodes for investigating the impact of particular land management practices on ecosystem sustainability.