Effects of rain, nitrogen, fire and grazing on tree recruitment and early survival in bush-encroached savanna, South Africa

摘要: Moisture, nutrients, fire and herbivory are the principal factors governing tree–grass cover ratios of savannas. We investigated tree (Acacia mellifera) recruitment after under conditions maximum-recorded rainfall, nitrogen addition grazing in a completely-crossed field experiment. employed similar garden experiment with exception treatment. Tree germination was extremely low, probably due to below-average natural rainfall plots that only received rain, insufficient watering frequency irrigated plots. Due low experiment, no treatment significantly affected recruitment. In frequent watering, nutrient control (i.e. addition) enhanced significant interactions between grazing. infer above-average years events required for mass Grass defoliation makes space resources available seedlings. Nitrogen enrichment increases competitive ability fast-growing grasses more than N2-fixing component. contrast conventional wisdom alone causes encroachment, we suggest there complex above-mentioned ‘triggering’ such as unusually high rainfall.