Evolution of life history in balsam fir (Abies balsamea) in subalpine forests

Subalpine forests in North America and Japan dominated Abies spp. show an u nusual pattern of regeneration in which recruitment is confined to a narrow window in time and space that just precedes the death of the largest trees . Previously, Silvertown suggested that selection in such forests should fa vour delayed reproduction A graphical model supporting this prediction also suggests that trees in 'normal' forests should benefit from precocious rep roduction when they are taller than their neighbours, while trees in wave p opulations should not. Here, we present a field test of the two hypotheses based upon a comparison of the life history of trees in adjacent wave and n on-wave populations at Whiteface Mountain, New York. The results show that reproduction commences at a similar age in both kinds of forest, and that t rees in the subalpine zone reproduce later and die earlier than conspecific s in lowland forests. The failure of the first hypothesis can be explained by modifying our original assumptions about how reproductive costs and bene fits vary with age in the model. In our test of the second hypothesis, we f ind that the reproductive behaviour of individual trees in the two kinds of forest is different and consistent with our prediction. Phenotypic plastic ity for age at first reproduction appears to be present only in the populat ion where it is adaptive.