Abstract ID: 3.10004 | Not reviewed | Requested as: Talk | TBA | TBA

Coarse woody debris (CWD) consists of standing and suspended dead trees (snag) and fallen trees and branches in contact with the soil. The contribution of CWD to carbon stocks and fluxes varies with temperature and moisture conditions, with temperature limitation increasing in importance with elevation and latitude. Climate change and forest fragmentation will change the rate of decomposition of CWD and the release of CO₂. To project such changes in the contribution of CWD to carbon stocks and CO₂ emissions in tropical montane forests, we quantified CWD (> 2 cm in diameter) on the forest floor in five permanent plots between 1600 and 1950 m a.s.l. in the Atlantic Forest domain (22.5 S).

We measured CO₂ fluxes in the field and in the laboratory at temperatures that span the range of winter and summer soil surface temperatures (5-15°C) experienced by CWD, and at 25°C, simulating a substantial warming. The estimated mean CWD mass on the forest floor ranged from 8.6 to 21.0 Mg ha^-1. Mean CO₂ emission showed relatively low temperature sensitivity between 15 °C (1.1 – 3.0 Mg CO₂ ha^-1 year^-1) and 25 °C (1.4 – 3.6 Mg CO₂ ha^-1 year^-1); the quantity of emitted CO₂ was halved at 5 °C (0.7 – 1.8 Mg CO₂ ha^-1 year^-1). Our results suggest that most temperature related changes in CO₂ emission from CWD decomposition will likely to be caused by increasing minimum temperatures. While a general warming trend has been detected at our study site since the 1970s, caused by an increase in daily maxima, minimum temperatures have not increased, thus there does not appear to be an indication of an immediate increase in CO₂ emission from CWD.