The paradox of great longevity in a short-lived tree species

Thuja occidentalis is a tree species that was once thought to be relatively short-lived (80 years). Up until 10 years ago maximum ages were considered to be near 400 years, but such trees were thought to be rare. Research alo ng the cliffs of the Niagara Escarpment has altered this view. Exceptionall y slow-growing trees of this species have been found with ring counts to 16 53 years and estimated ages to 1890 years. Senescence is slow or absent. In jury and death is due to rockfall and sporadic severe drought that kills sm all sectors of the trees by exposing and killing the roots. Experiments in which colored dyes are infused into roots show that each tree is composed o f hydraulically independent units that allow mortality in one part of the ' individual' with little negative effect on the remaining parts of the tree. The trees are small, so environmental loadings of ice, snow, and wind are low. Slow growth of the trees results in a much greater mechanical strength in the wood. Together these properties increase the ability of the cedars to persist on cliffs for long periods of time. The paradox of great longevi ty in this 'short-lived' tree species is explained by slow growth that mini mizes maintenance and repair costs while maximizing durability and strength , combined with an internal architecture that creates functionally independ ent units within each tree. (C) 2001 Elsevier Science Inc. All rights reser ved.