Palace Michael, Keller Michael, Silva Hudson
Complex Systems Research Center, Morse Hall, University of New Hampshire, Durham, New Hampshire 03824, USA.
Ecol Appl. 2008 Jun;18(4):873-84. doi: 10.1890/06-2022.1.
Necromass stocks account for up to 20% of carbon stored in tropical forests and have been estimated to be 14-19% of the annual aboveground carbon flux. Both stocks and fluxes of necromass are infrequently measured. In this study, we directly measured the production of fallen coarse necromass (> or = 2 cm diameter) during 4.5 years using repeated surveys in undisturbed forest areas and in forests subjected to reduced-impact logging at the Tapajos National Forest, Belterra, Brazil (3.08 degrees S, 54.94 degrees W). We also measured fallen coarse necromass and standing dead stocks at two times during our study. The mean (SE) annual flux into the fallen coarse necromass pool in undisturbed forest of 6.7 (0.8) Mg x ha(-1) x yr(-1) was not significantly different from the flux under a reduced-impact logging of 8.5 (1.3) Mg x ha(-1) x yr(-1) With the assumption of steady state, the instantaneous decomposition constants for fallen necromass in undisturbed forests were 0.12 yr(-1) for large, 0.33 yr(-1) for medium, and 0.47 yr(-1) for small size classes. The mass weighted decomposition constant was 0.15 yr(-1) for all fallen coarse necromass. Standing dead wood had a residence time of 4.2 years, and approximately 0.9 Mg x ha(-1) x yr(-1) of this pool was respired annually to the atmosphere through decomposition. Coarse necromass decomposition at our study site accounted for 12% of total carbon remineralization, and total aboveground coarse necromass was 14% of the aboveground biomass. Use of mortality rates to calculate production of coarse necromass leads to an underestimation of coarse necromass production by 45%, suggesting that nonlethal disturbance such as branch fall contributes significantly to this flux. Coarse necromass production is an important component of the tropical forest carbon cycle that has been neglected in most previous studies or erroneously estimated.
死有机质储量占热带森林碳储量的比例高达20%，据估计占地上碳年通量的14 - 19%。死有机质的储量和通量都很少被测量。在本研究中，我们通过在巴西贝莱特拉塔帕若斯国家森林（南纬3.08度，西经54.94度）未受干扰的森林区域以及实施低影响伐木的森林中进行重复调查，直接测量了4.5年期间直径大于或等于2厘米的粗大死有机质的产生量。我们还在研究期间的两个时间点测量了粗大死有机质和立木死亡储量。未受干扰森林中进入粗大死有机质库的平均（标准误）年通量为6.7（0.8）Mg·ha⁻¹·yr⁻¹，与低影响伐木情况下的通量8.5（1.3）Mg·ha⁻¹·yr⁻¹无显著差异。在稳态假设下，未受干扰森林中粗大死有机质的瞬时分解常数，大尺寸类为0.12 yr⁻¹，中尺寸类为0.33 yr⁻¹，小尺寸类为0.47 yr⁻¹。所有粗大死有机质的质量加权分解常数为0.15 yr⁻¹。立木死亡的滞留时间为4.2年，该库每年约有0.9 Mg·ha⁻¹·yr⁻¹通过分解释放到大气中。我们研究地点的粗大死有机质分解占总碳再矿化的12%，地上粗大死有机质总量占地上生物量的14%。使用死亡率来计算粗大死有机质的产生量会导致对其产生量的低估达45%，这表明诸如树枝掉落等非致命干扰对该通量有显著贡献。粗大死有机质的产生是热带森林碳循环的一个重要组成部分，在大多数先前的研究中被忽视或估计有误。
