Effects of typhoon damage on the carbon dynamics of a larch forest

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A plantation (42°44'N, 141°31'E) of Japanese larch (Larix kaempferi Sarg.) in Tomakomai, Hokkaido, Japan was destroyed by Typhoon Songda in September 2004. About 90% trees were blown down by strong wind. In this study, we compared vegetation properties, biomass and net ecosystem CO_2 uptake (NEP) before and after the typhoon damage. Before the typhoon damage, this forest was a 45-year-old plantation of Japanese larch with some broad-leaved trees. The canopy height was 15 m and the maximum leaf area index (LAI) was 5.6m^2 m^<-2>. After the typhoon, all stems of larch trees were removed from the forest floor for commercial use, whereas stumps and branches were left. NEP was continuously measured using the eddy covariance technique and a multichannel automated chamber system for the growing season of 5 months from June through November in 2006 and 2007. Ecosystem respiration (RE) in the daytime was estimated from soil temperature at 0.01m depth using an empirical model derived from nighttime NEE. Gross primary production (GPP) was calculated as the difference between RE and NEE (GPP=RE-NEE). Cumulative values of RE, GPP and NEP for the 5 months were 1125, 1370 and 245 gC m^<-2>, respectively, on average between 2001 and 2003, whereas they were 711, 607 and -104gC m^<-2>, respectively, in 2006, and 664, 622 and -42 gC m^<-2>, respectively, in 2007. This clear change of NEP indicates that the forest ecosystem changed from carbon sink to source by the typhoon damage, and the strength of carbon source was gradually decreasing because of vegetation recovery.