Tropical rain forest tree growth and atmospheric carbon dynamics linked to interannual temperature variation during 1984–2000

Abstract

During 1984 -2000, canopy tree growth in old-growth tropical rain forest at La Selva, Costa Rica, varied >2-fold among years. The trees' annual diameter increments in this 16-yr period were negatively correlated with annual means of daily minimum temperatures. The tree growth variations also negatively covaried with the net carbon exchange of the terrestrial tropics as a whole, as inferred from nearly pole-to-pole measurements of atmospheric carbon dioxide (CO 2) interpreted by an inverse tracer-transport model. Strong reductions in tree growth and large inferred tropical releases of CO 2 to the atmosphere occurred during the record-hot 1997-1998 El Niñ o. These and other recent findings are consistent with decreased net primary production in tropical forests in the warmer years of the last two decades. As has been projected by recent process model studies, such a sensitivity of tropical forest productivity to on-going climate change would accelerate the rate of atmospheric CO 2 accumulation. A lthough human activities are rapidly increasing atmospheric levels of the greenhouse gas CO 2 (1), understanding of the global carbon budget and how it is affected by climatic change remains approximate and evolving (2). Current knowledge of plant function, however, raises the likelihood that continued warming will alter the net carbon balance of global vegetation (3,4). Plant respiration increases exponentially with increasing temperature, whereas photosynthetic rates increase to a temperature optimum and then decline (5). At the ecosystem level, the balance between these two processes determines net primary production (NPP). Decreasing terrestrial NPP with rising temperatures would constitute a biotic positive feedback to the increase in atmospheric CO 2 (3, 4).Tropical rain forests, among the warmest terrestrial ecosystems, might be expected to be among the first to show negative temperature responses (6). Because these forests account for a third of global terrestrial NPP (7), any such responses could strongly affect atmospheric CO 2 levels. Studies at the leaf (8, 9) and stand level (10, 11) in this biome already suggest reduced carbon uptake with even small temperature increases. Measured respiration rates of tree boles in one tropical rain forest show an 8% increase with a 1°C temperature rise (12); compared with that of boles, the respiration of other plant parts tends to be even more sensitive to temperature changes (13). In addition, carbon losses by tropical trees in the form of volatile organic compounds increase exponentially over current temperature ranges (8,9). Quantifying responses of these processes at the ecosystem level, however, remains elusive because of limitations of both data and methods (14,15). Estimating forest carbon exchange with eddy covariance techniques has been found to be problematic for tropical forests, because of the prevalent still-air conditions at night (Ͼ80% of nights; ref. 11). In addition, short-term data may be poor indicators of longer-term trends, given the possibilities of c...

Fingerprinting the impacts of global change on tropical forests

“…However, as Clark et al (2003) track a single cohort of trees including only those that survive the whole monitoring period and not a dynamic population of trees, this result ought to be treated with caution. Ageing populations are to be expected to exhibit a long-term decline in net stem growth as increasing numbers of trees would reach the canopy and switch (at least some) allocation from stem growth to reproduction, and/or others would reduce growth as they senesce.…”

“…The effect may be large, as only ca. 25% of the originally marked trees were included in the Clark et al (2003) analysis. In addition, the temperature data used are from two different sites (the first spans 1984-1991, the second 1992-2000).…”

Pervasive alteration of tree communities in undisturbed Amazonian forests

“…1). At each six-month time step, animals survive and breed according to probabilities observed in the long-term lion studies in the Serengeti National Park and in Ngorongoro Crater 14,15 . Demographic parameters depend on the age, sex and social status of individual lions.…”

“…In addition, lianasclimbing woody vines that often thrive in disturbed forest-appear to be increasing in size and abundance 12 . A plausible cause of these changes is increasing plant fertilization caused by rising atmospheric CO 2 concentrations [2][3][4][5][6][7][8][9][10][11][12][13] , although other large-scale phenomena, such as alterations in regional temperature 14 , rainfall 15,16 , available solar radiation 17 , or nutrient deposition 18 , might also play a role. However, no studies have assessed the effects of such large-scale changes on the taxonomic composition of Amazonian tree communities, which greatly influences the architecture, dynamics and ecological functioning of these forests.…”

Vegetative responses to temperature and photoperiod in saplings of brazilwood (Caesalpinia echinata Lam., Leguminosae)

“…However, studies relating the effects of daylength and temperature on plant growth are still scarce for tropical species (Vaz et al, 2004), if one considers the plant diversity in these areas. Concerning tropical trees, a long term study of six species of an old-growth tropical rain forest relating productivity, atmospheric carbon dynamics and annual temperatures was conducted by Clark et al (2003), in Costa Rica. The authors concluded that the annual increments in tree diameter were negatively correlated with annual means of daily minimum temperatures and that net primary production covaried negatively with inferred annual net CO 2 exchange between the terrestrial tropics and the atmosphere.…”