Estimating the carbon loss under the influence of typhoons at a subtropical mountain forest

Disturbances play a critical role to alter the structures and functions of ecosystems. In East Asia, typhoons are among the most important and frequent natural disturbances to ecosystems. For forest ecosystems, therefore, typhoons may affect the carbon cycling within ecosystems, including gross primary production (GPP), soil respiration, and exchange between atmosphere and ecosystem via gaseous state. Nowadays, the eddy covariance (EC) method is widely applied to directly measure the carbon exchange between atmosphere and ecosystem. However, there were few studies focused on the carbon loss via gaseous state after storm disturbance, and particularly in East Asia. Each year, 3.8 typhoons on average hit Taiwan since the 1950’s. For the forests in Taiwan with frequent typhoon disturbance, the impact on forests is defoliation. That is different from the infrequent cyclones areas. The defoliation may directly induce the carbon loss of the forest ecosystem through the increasing of the soil respiration and reduction of the photosynthesis capacity. In this study, (1) we estimated the carbon loss from EC data and the empirical models of litter decomposition after a typhoon event in 2009 at Chi-Lan Mountain (CLM) site (24o35’N, 121o25’E), a subtropical mountain site in northeast Taiwan; (2) we estimated the GPP of CLM in 2008 and 2009 to access the impact of different typhoon attack time on the GPP of CLM. The results showed that the potential carbon loss of the forest ecosystem after a typhoon in 2009 was about 483.5 kg ha-1 that included 465 kg-ha-1 and 18.5 kg-ha-1 through GPP reduction and litterfall decomposition, respectively. The quantity of carbon loss was as more as 22% (483.5 kg-ha-1/2200 kg-ha-1) of the carbon sink in CLM. The comparison of the GPP in 2008 and 2009 showed that the GPP could quickly recover when the typhoons hit the forest during the growing seasons (Apr. ~ Sep.), but the photosynthetic capacity of the forest didn’t regain as the typhoon attacked in other periods. Several studies indicated that the ecosystems under more frequent disturbances may recover faster because of the natural collection. However, CLM may decrease more than 20 percent of the assimilation capacity under extending typhoon seasons (after growing seasons) or enhancing typhoon strength due to global climate change.