Tree seedling recruitment dynamics in forest-savanna transitions : Trait responses to vegetation controls mediate differential seedling establishment success of tree functional types

Abstract

In the transition between tropical forests and savannas, forest may be lost to savanna-like vegetation or may occasionally encroach on savannas affecting climate and other benefits to humans. Vegetation in the forest savanna-transition of Ghana often appears stable, except in forests with significant human-induced deforestation where forests are being replaced by savanna-like vegetation. This phenomenon is still poorly understood, but may be explained by how changes in vegetation controls (e.g. fire and precipitation) affect recruitment of forest and savanna-transition tree seedlings differently. Savanna-transition species occur both in forest and humid savanna. I showed that high grass biomass in savanna both directly (via competition) and indirectly (via dry season fire) select for species which invest higher in belowground resource capture and carbohydrate storage. Lower precipitation decreases chances of tree seedling recovery from defoliation disturbance, but allocation trait differences between forest and savanna-transition tree species may explain relative stability of transition forests and the lack of success of true forest species in the forest-savanna transition.