Cessation effects of grazing and burning on species composition in humid temperate semi-natural grasslands through environmental modifications

To elucidate the cessation impacts of agricultural management on a semi-natural grassland ecosystem, effects of grazing and burning on species composition of vascular plants were investigated in Mt. Aso, Japan. Species richness was significantly increased by both grazing and burning at the plot scale (1m(2)), and a negative interaction between grazing and burning was recognized by two-way analysis of variance. No significant effect existed at the transect (10m(2)) or the site (20m(2)) scales. Most of the environmental factors measured in this study (e.g. soil physical properties) were significantly, although differently, modified by grazing and/or burning. According to logistic regression analyses, 32 of 77 species recorded at the study sites were significantly correlated with the environmental variables, yet each species appeared to respond to the environmental factors in different ways. Canonical correspondence analysis showed that both grazing and burning are important factors in determining species composition; that cessation of grazing changes shortgrass communities to tallgrass ones; and that cessation of burning changes communities composed of colorful-flowering species to shrubby communities. This study concludes that within several years of the cessation of grazing and burning, species richness could be lowered in semi-natural grasslands at such small scales as 1-m(2) plots. Grazing and burning would modify some environmental factors, especially hydraulic conditions, in semi-natural grasslands, and would create various habitat types for plants, thus allowing species diversity to be maintained over time.