Trade-offs between tree growth and survival rates along elevation gradients in forests of New Zealand

Trade-offs between fundamental demographic rates emerge from constraints within individuals related to morphology, physiology, and resource allocation with respect to the environment.  For example, a well-established demographic trade-off among trees, that species that grow fast in high light usually have high mortality in shade, contributes to tree species coexistence and distribution along light gradients.  Constraints on demographic rates may, however, arise along other environmental gradients along which forest community composition varies.  In New Zealand, composition varies substantially along striking elevation gradients.  We parameterized a hierarchical model to quantify the interspecific and intraspecific trade-offs between growth and survival rates and whether they varied with elevation using data collected over 36 years on 56 woody species throughout New Zealand.  We found that a species’ position along the interspecific trade-off axis was related to the shape of its intraspecific trade-off curve and that both trade-offs varied with elevation.  Fast-growing tree species had lower survival at higher elevations than did slower-growing species, although within species, the faster-growing individuals always survived better, regardless of elevation.  We conclude by relating variation in the growth-survival trade-off to forest community composition in New Zealand.