Abstract
Abstract. The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm yr−1 (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall < 2000 mm yr−1.
Highlights
Tropical forests have a primary role in the terrestrial carbon (C) cycle
We have found a remarkably strong climate signal in the seasonal carbon cycle components studied across tropical forests
While wood and litterfall production appear to be dependent on a single major climate driver across the tropics, the control of photosynthetic capacity varies according to the increase in annual water availability, shifting from water-only to light-only drivers
Summary
Tropical forests have a primary role in the terrestrial carbon (C) cycle. They constitute 54 % of the total aboveground biomass carbon of Earth’s forests (Liu et al, 2015) and account for half (1.19 ± 0.41 PgC yr−1) of the global carbon sink of established forests (Pan et al, 2011; Baccini et al, www.biogeosciences.net/13/2537/2016/2012). Tropical forests have a primary role in the terrestrial carbon (C) cycle. They constitute 54 % of the total aboveground biomass carbon of Earth’s forests (Liu et al, 2015) and account for half (1.19 ± 0.41 PgC yr−1) of the global carbon sink of established forests Based on annual or multi-annual measurements of forest wood productivity, changes in carbon dynamics and functioning of the tropical trees have already been observed. Increasing evidence shows that the tropical forests present a seasonality in the assimilation and storage of carbon, associated with climate seasonality (Wu et al, 2016; Doughty et al, 2014; Rowland et al, 2014b, a, 2015; Wagner et al, 2014). Understanding the seasonal drivers of the carbon cycle in a pan-tropical context by using the maximum information available on carbon storage and assimilation is needed to assess the mechanisms driving changes in forest carbon use and predict tropical forest behaviour under future climate changes
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