Grass competition and the savanna-grassland ‘treeline’: A question of root gaps?

Upland grasslands in South Africa occur in climates warm enough and wet enough for forests yet, unlike savannas, trees are absent. We hypothesize that the lack of trees in grasslands is due to the scarcity of gaps suitable for tree seedling establishment in the grass root layer. We assessed which demographic bottlenecks, seedling recruitment or sapling release, were limiting large tree populations of Acacia species in 229 sites on a gradient...