Vegetation influences climate at the macro and micro levels. Growing evidence suggests that undisturbed forest helps to maintain the rainfall in its immediate vicinity by recycling water vapour at a steady rate back into the atmosphere and through the canopy's effect in promoting atmospheric turbulence. At smaller scales, vegetation has a moderating influence on local climates and may create quite specific micro-climates.
The species composition of forests and other terrestrial ecosystems is likely to change - entire forest types may disappear. Although forest productivity could increase, the standing biomass of forests may not increase because of more frequent outbreaks and extended ranges of pests and pathogens, and increasing frequency and intensity of fires.
Agenda 21 recommends assessing the potential impact on forests of climatic change, as well as effects of forests on climate, and initiating in-depth studies on the carbon cycle relating to different forest types to provide scientific advice and technical support.