Global distribution of hydrologic controls on forest growth

Vegetation provides key ecosystem services and is an important component in the hydrological cycle. Traditionally, the global distribution of vegetation is explained through climatic water availability. Locally, however, groundwater can aid growth by providing an extra water source (e.g. oases) or hinder growth by presenting a barrier to root expansion (e.g. swamps). In this study we analyse the global correlation between humidity (expressing climate-driven water and energy availability), groundwater and forest growth, approximated by the fraction of absorbed photosynthetically active radiation, and link this to climate and landscape position. The results show that at the continental scale, climate is the main driver of forest productivity; climates with higher water availability support higher energy absorption and consequentially more growth. Within all climate zones, however, landscape position substantially alters the growth patterns, both positively and negatively. The influence of the landscape on vegetation growth varies over climate, displaying the importance of analysing vegetation growth in a climate–landscape continuum.