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Abstract:
Old growth forests are a substantial part of the global forested area, but differ in age, structure and composition from younger or managed forests. In this chapter we review how these characteristics lead to differences in the biosphere–atmosphere exchange of carbon, water, and energy of old-growth forests compared to younger and managed forests. A global compilation of net ecosystem exchange data from eddy covariance measurements reveals that – in contrast to classical theory – most of the old-growth forests being studied remain net carbon sinks, and suggests that, rather than age, other factors such as tree structure and resource competition limits growth in forests. Water fluxes exhibit an ambiguous response to age with some old forests showing reduced water fluxes due to hydraulic limitation, while others show higher water fluxes due to better groundwater access and lower surface reflectance (albedo) in old and tall forests.
