Effects of differences in aboveground dead organic matter types on the stand‐scale necromass and CO2 efflux estimates in a subtropical forest in Okinawa Island, Japan

Abstract

AbstractDead organic matter (DOM), which consists of leaf litter, fine woody debris (FWD; <3 cm diameter), downed coarse woody debris (CWDlog), and standing or suspended coarse woody debris (CWDsnag), contributes to forest carbon cycling; however, few studies have considered effects of differences in DOM types on the stand‐scale estimates of carbon stocks of necromass and CO2 efflux (Rstand). This study investigated characteristics of necromass and Rstand in a subtropical forest in Okinawa Island, Japan, to quantify the effect of DOM type on total necromass, total Rstand, and estimate error of total necromass and Rstand. The CWDsnag accounted for the highest proportion (54%) of total necromass (1499.7 g C m−2), followed by CWDlog (24%), FWD (11%), and leaf litter (11%). Leaf litter accounted for the highest proportion (37%) of total Rstand (340.6 g C m−2 year−1), followed by CWDsnag (25%), CWDlog (20%), and FWD (17%). The CWDsnag was distributed locally with 173% coefficient of variation for necromass, which was twofold higher than those of leaf litter and FWD (72%–73%). The potential error in CWD accounted for 99% and 79% estimate error for total necromass and Rstand, respectively. For the estimates of CWDsnag and CWDlog necromass with the estimates error of <10% in this study area, sampling areas of ≥28,750 m2 and ≥2058–42,875 m2, respectively, were required. Our results showed that CWD considerably contributed to stand‐scale carbon stocks and efflux among aboveground DOM in this forest, resulting in a major source of errors in the stand‐scale estimates.