Increased early growth rates decrease longevities of conifers in subalpine forests

Abstract

For trees, fast growth rates and large size seem to be a fitness benefit because of increased competitiveness, attainment of reproductive size earlier, reduction of generation times, and increased short‐term survival chances. However, fast growth rates and large size entail reduced investment in defenses, lower wood density and mechanical strength, increased hydraulic resistance as well as problems with down‐regulation of growth during periods of stress, all of which may decrease tree longevity. In this study, we investigated the relationship between longevity and growth rates of trees and quantified effects of spatial environmental variation (elevation, slope steepness, aspect, soil depth) on tree longevity. Radial growth rates and longevities were determined from tree‐ring samples of 161 dead trees from three conifer species in subalpine forests of the Colorado Rocky Mountains (Abies lasiocarpa, Picea engelmannii) and the Swiss Alps (Picea abies). For all three species, we found an apparent tradeoff between growth rate to the age of 50 years and longevity (i.e. fast early growth is associated with decreased longevity). This association was particularly pronounced for larger P. engelmannii and P. abies, which attained canopy size, however, there were also significant effects for smaller P. engelmannii and P. abies. For the more shade‐tolerant A. lasiocarpa, tree size did not have any effect. Among the abiotic variables tested only northerly aspect significantly favored longevity of A. lasiocarpa and P. engelmannii. Trees growing on south‐facing aspects probably experience greater water deficits leading to premature tree death, and/or shorter life spans may reflect shorter fire intervals on these more xeric aspects. Empirical evidence from other studies has shown that global warming affects growth rates of trees over large spatial and temporal scales. For moist‐cool subalpine forests, we hypothesize that the higher growth rates associated with global warming may in turn result in reduced tree longevity and more rapid turnover rates.

The effects of thinning intensity and tree size on the growth response to annual climate in Cedrus atlantica: a linear mixed modeling approach

“…In another view, the lower growth sensitivity of suppressed trees is due to a loss of plastic capacity in those trees strongly constrained by competition (Linares et al 2010). A third plausible explanation of the greater sensitivity of large trees to climatic stress is their higher water needs and the higher risk of cavitation that they face due to their longer xylem path (Bigler and Veblen 2009). We reported a significant increase in sensitivity between the co-dominant and the dominant classes, regardless of the thinning treatment.…”

“…Indeed, previous studies produced seemingly contradictory results, reporting higher mortality rates for trees showing highly variable growth (Suarez and Ghermandi 2004) or a weaker correlation between the growth of the dying trees and the climate variables (Linares et al 2010). As recent reports suggest a lower capacity of large trees to overcome severe drought (Bigler and Veblen 2009), the long-term effect on thinning on the ability of mature cedar stands to survive extreme water stress events need further investigations.…”

Land-use and climate change risks in the Amazon and the need of a novel sustainable development paradigm

“…Although the tree growth data confirmed the Earth's surface as a strong carbon sink, the same data show a decline in the growth rate of carbon accumulation and a one-third decline in net increase in aboveground biomass in the 2000s compared with the 1990s. Factors explaining this behavior are still not clear, but the main hypothesis is that the increase in forest productivity in recent years due to CO 2 fertilization effect could have accelerated the life cycle of trees, anticipating their death when still young (131,(139)(140)(141)(142). To reduce the uncertainties about the effect of increasing atmospheric CO 2 concentrations on tropical ecosystems, a group of international scientists are proposing to carry out a Forest Free-Air CO 2 Enrichment-type experiment in the Amazon (143).…”

Insect outbreak shifts the direction of selection from fast to slow growth rates in the long-lived conifer Pinus ponderosa

“…Our results provide insight into the mechanisms contributing to the maintenance of genetic diversity in a long-lived organism, and show that strong and fluctuating selection can contribute to the evolutionary potential of trees under climate change. with shorter lifespan (29), with long-term consequences on lifetime reproductive output. Thus, selection pressures for fast growth at early life stages may conflict with fitness costs at later stages (29,30).…”

“…with shorter lifespan (29), with long-term consequences on lifetime reproductive output. Thus, selection pressures for fast growth at early life stages may conflict with fitness costs at later stages (29,30). These conflicts may explain the substantial intraspecific genetic variation in growth rates observed both within and among natural populations of organisms (23).…”