A model analysis of the influence of root and foliage allocation on forest production and competition between trees

A general model was constructed relating forest growth to nitrogen uptake and the partitioning of biomass among leaves, fine roots and woody tissues. The model was used to assess the influence of the allocation pattern on stand wood production, individual tree growth and nutrient cycling for even-aged conifer stands with adequate water, but suboptimal nitrogen. Stand wood production was maximized by quite low allocation to roots for specified amounts of plant-available nitrogen. However, the wood production of the individual was maximized by higher allocation to roots, because large root systems enhanced the ability of individuals to compete for nutrients. The optimal fine root allocation for a competing individual was less than 5% of total production for adequate nitrogen, but rose to 30% as nitrogen became more limiting, in general agreement with observed allocation patterns for fertilized versus non-fertilized forests. The high allocation to roots predicted for competitors may also enhance long-term productivity by decreasing nutrient losses from the ecosystem. Although collective, short-term stand wood production could be increased by shifting growth from roots to stems, this strategy may increase nutrient losses, ultimately decreasing productivity.