广东省森林死木碳库特征

基于广东省第8次国家森林资源清查的固定样地调查数据和2016年典型抽样的死木调查数据,利用分树种、分腐朽程度的各个组分相兼容的生物量模型以及相对应的地上、地下部分含碳系数,对广东省森林死木碳库动态进行估算,分析死木种类、林分类型和龄组对死木碳库的影响,量化林分生长特性和自然灾害对死木碳库的贡献。结果表明:2007—2012年间广东省乔木林死木碳库新增碳储量5811.86 Pg,占同期乔木林活立木碳库的2.94%,其中枯倒木多于枯立木;阔叶混交林和马尾松林贡献了近70%的死木碳储量;马尾松、其他软阔、湿地松、阔叶混交林和其他硬阔的死木碳储量占同类森林总活立木碳储量的比例较大,均超过4.00%,桉树和杉木比例最小,均不足1.00%;从龄组看,发生在中龄林的死木碳储量占总死木碳储量比例最大,过熟林最小。与同龄组林分的现存碳储量相比,从幼龄林(2.03%)到过熟林(4.56%)基本呈上升趋势。全省新增死木库碳密度为(0.7612±3.3988)Mg/hm~2。竞争和衰老引起的枯死在林分中普遍存在,占发生死木林分面积的60%以上,但增加到死木碳库的储量不足总量的四分之一,而自然灾害只占发生死木林分面积的10%,对死木碳库的贡献却超过40%。到2016年,2007—2012年间增加到死木库的碳储量下降到785.57 Pg,减少约85%,枯倒木的腐朽程度重于枯立木,不同树种间腐朽程度不一,杉木腐朽程度最低。清林等人为经营活动和死木的腐朽是存量减少的主要原因。

Characteristics of the forest deadwood carbon pool in Guangdong Province

We used compatible tree biomass equations for each component grouped by species and decay classes, and carbon fractions of above-ground and below-ground parts, based on the 8^th Chinese National Forest Inventory (CNFI) data in Guangdong Province and the deadwood investigation data from typical sampling in 2016, to estimate the dynamics of the forest deadwood carbon pool in Guangdong Province, including the effects of deadwood type, stand type, and age groups. Furthermore, the contribution of stand growth characteristics and natural disasters to the deadwood carbon pool were quantified. The results showed that the carbon storage of the deadwood pool of arbor forests in Guangdong Province increased 5811.86 Pg from 2007 to 2012, which accounted for 2.94% of biomass carbon in arbor forests during the same period. Logs contributed more carbon to deadwood pool than snags. Broad-leaved mixed forests and Pinus massoniana contributed approximately 70% to the deadwood carbon pool. Within the same forest type, the deadwood carbon storage of Pinus massoniana, light hardwoods, Pinus elliottii, broad-leaved mixed forests, and hardwoods accounted for a larger proportion (>4%) of standing carbon stock, whereas Eucalyptus and Cunninghamia lanceolata accounted for a lower proportion (<1%). With respect to age groups, middle-aged stands accounted for the largest proportion of the increased carbon, whereas over-mature stands accounted for the smallest. Comparing the existing biomass carbon storage within the same age group revealed an upward trend from 2.03% for the young-aged to 4.56% for the over-mature stands. The increased carbon density was (0.7612 ±3.3988) Mg/hm² in the province. Death owing to competition or old age was very common in the stand, and was observed in approximately 60% of the stands with deadwoods, but contributed to less than 1/4 of the increased deadwood carbon. Rather, natural disasters, which only happened in approximately 10% of the stand, contributed more than 40% to the increased deadwood carbon. The increased deadwood carbon from 2007 to 2012 declined until 2016 by approximately 85% to 785.57 Pg. The degree of decay of logs was greater than for snags. The degree of decay varied among different species and was lowest for Cunninghamia lanceolata. Human disturbance, such as over-cleaning, and decay of trees could be the main reasons for the reduced carbon storage.