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Abstract

As trees become older and grow taller, they increase their relative fitness to competing trees or to other life forms, but also face constraints that differ drastically from those experienced by smaller species or early ontogenetic stages, including the maintenance costs and disadvantages of transporting water to a greater height and increased risk of breakage. No wonder that trees do not grow infinitely high. In general, absolute and relative growth rates tend to decrease with age and height. This decline in productivity – observed at both the tree and stand level – has been attributed to a range of processes, e.g. increasing respiratory demand and limitation of photosynthesis on the tree level, and, on the stand level, increasing sequestration of nutrients in slow-decomposing litter and ecophysiological differences between early-, mid- and late-successional canopies. This chapter will review these current hypotheses, first on the tree level, then on the stand level, as well as in the context of successional changes of community composition.