Download B51C-‐0569 -‐ Clima`c controls on aboveground net primary produc

B51C-­‐0569 -­‐ Clima&c controls on aboveground net primary produc&vity & par&&oning of canopy and wood produc&on in tropical rainforests Florian Ho2ansl, Sigrid Drage, Eva-­‐Maria Pölz, Andreas Richter, Wolfgang Wanek Background Aboveground net primary producMon (ANPP) of tropical forests is driven by soil ferMlity and climate. Recent projecMons of global circulaMon models predict large tracts of tropics to become drier and warmer. Therefore interannual climate variaMons such as El Niño Southern OscillaMon (ENSO) have been used to assess potenMal responses of tropical ANPP to projected climate change. The focus of this study was to (1) invesMgate how seasonal and interannual climate varia&on affects ANPP and the parMMoning between canopy (liWerfall) and wood producMon (stem increment) on three forest sites differing in soil ferMlity and disturbance regime in SW Costa Rica, and (2) iden&fy major drivers of ANPP by integraMng our results into a dataset of 101 tropical old-­‐growth forests. 1. Local controls 2. Global controls We demonstrate that tropical ANPP is sensiMve to seasonal and interannual climate variaMon at three forest sites studied, but that climaMc controls differ for canopy and wood producMon. Globally mean annual temperature (MAT) was the strongest predictor of tropical ANPP (0.31 Mg C ha-­‐1 yr-­‐1 per °C). However, we found differences in the response of ANPP along the elevaMon gradient from lowland to montane forests. While MAT promoted the producMvity of montane forests, wood producMon of lowland forests was reduced. While drought (DD) promoted liWerfall (LF), stem increment (ABI) was posiMvely related to monthly precipitaMon (BP) but negaMvely related to maximum temperature (Tmax). Thus, both processes peaked during different seasons, liWerfall during dry season and stem increment during the dry-­‐wet transiMon. Across the tropical biome, carbon allocaMon shi]ed from canopy (LF) to wood producMon (ABI) from low producMve montane (Δ) to high producMve lowland (Ο) rainforests. Conclusions We conclude that the balance between canopy and wood producMon is climate sensiMve, in a local and a global context. We idenMfy a shi] in ecosystem funcMons from nutrient cycling (i.e. producMon of canopy biomass) towards greater nutrient conservaMon (i.e. producMon of wood biomass) across the producMvity gradient from montane to lowland rainforests. O u r r e s u l t s i n d i c a t e t h a t i n c r e a s i n g temperatures will likely enhance the producMvity of montane forests but negaMvely affect the carbon sequestraMon potenMal of highly producMve lowland forests. Climate change thus may shiO the balance between nutrient cycling and carbon sequestra&on and adversely affect tropical ecosystem funcMons. Affilia&on University of Vienna, Department of Terrestrial Ecosystem Research, Althanstrasse 14, 1090 Vienna, Austria Biodiversity and Ecosystem Func&ons (BDEF) – hTp://www.univie.ac.at/bdef/ – fl[email protected] Reference Ho2ansl F, Drage S, Pölz EM, Richter A, Wanek W (2012) ClimaMc controls on aboveground net primary producMvity and the parMMoning between canopy and wood producMon in tropical rainforests. Global Change Biology -­‐ submiWed