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

Dead 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.

Spatial and seasonal variations in soil respiration in a subtropical forest in Okinawa, Japan

“…Among the Archipelago, the northern forested sector in Okinawa Island is one of the largest forested areas and is known as “Yambaru” or “Yanbaru.” In Yambaru, much attention has been paid to biodiversity and rare/endemic species, but the characteristics of the carbon cycle are yet to be fully investigated. Net primary production (Kawanabe, 1977), the amount of litterfall (Alhamd & Hagihara, 2004), and the mass and CO 2 efflux of dead organic matter on the soil surface (Abe et al, 2022) have been examined. For R s , although several studies have been conducted (Ishizuka et al, 2006; Sakai et al, 2012), the number of spatial or temporal samples is relatively low.…”