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 Niño. 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.

Figure 1

Interannual variation in tree growth in old-growth lowland rain forest at La Selva, Costa Rica. Bars show the annual mean growth deviations of adult trees of six canopy species (left to right in each year: Mg, La, Dp, Ha, Be, and Hm; see Table 1 for species names and sample sizes); growth deviations are calculated as the percent departure of the species' mean annual diameter increment, from that species' 16-yr mean annual increment. x axis: yr 2 of measurement years.

Figure 2

The relation between the annual mean tree growth deviation (±1 SE) at La Selva, Costa Rica, averaged over the six species, and the net CO₂ flux from the terrestrial tropics (note inverted y axis), as inferred from an inverse model calculation [ref. ; annual means centered on January 1 and June 1 each year; positive values (lower part of the y axis) indicate net flux to the atmosphere]. Pearson's r = −0.77, n = 15 yr, P < 0.001 for the correlation between annual fluxes (centered on January 1) and annual mean growth deviations for the six tree species (centered on October 1, previous year). x axis: yr 2 of tree measurement years.

Figure 3

The relation between the annual diameter growth of six canopy tree species (mean of the six species' growth deviations in each year ± 1 SE) and annual means of daily minimum temperatures at La Selva, Costa Rica. Data labels: yr 2 of tree measurement years (nonunderlined, La Selva automated temperature data; underlined, data calculated by regression from a nearby surface station; ref. 21).