高山森林林窗和粗木质残体对木生苔藓生物量和多样性的影响

Effects of forest gap and coarse woody debris on biomass and diversity of epixylous moss in an alpine forest

木生苔藓植物是原始森林的基本组成部分,其生长和分布对林窗和粗木质残体(CWD)等环境因子的响应可能非常敏感,但林窗和CWD对木生苔藓植物群落的影响研究未见报道。因此,我们研究了高山森林不同林窗位置(林窗、林缘和林下)和不同粗木质残体类型(倒木、大枯枝、枯立木和根桩)木生苔藓生物量(储量、单位面积生物量和生物积累量)和多样性(Shannon 多样性指数、Simpson 优势度指数和 Pielou 均匀度指数)特征。结果表明:川西高山粗木质残体木生苔藓植物生物量储量为141.14kg/hm^2,倒木生苔藓生物量储量最大为78.80kg/hm^2,枯立木生苔藓生物量储量最小为3.11kg/hm^2。其中,第Ⅲ、Ⅳ腐解等级粗木质残体木生苔藓生物量储量较高,在Ⅰ腐解等级时为最低。整体来看不同粗木质残体类型木生苔藓单位面积生物量均在林缘最高,但不同粗木质残体类型单位面积木生苔藓生物量积累量差异显著。木生苔藓生物多样性受林窗位置和粗木质残体类型显著影响。倒木、大枯枝和根桩的苔藓 Simpson 优势度指数从林窗至林下均为下降趋势。倒木的苔藓 Shannon 多样性指数和 Pielou 均匀度指数在林下最高,在林缘最低。林窗大枯枝木生苔藓三种多样性指标均大于倒木。枯立木和根桩木生苔藓多样性指标随林窗变化表现各异。研究也发现,曲尾藓(Dicranum)和平藓(Neckera)在川西高山苔藓生物量中比重较大。我们的研究结果表明在高山森林生态系统中,林缘效应对木生苔藓生物量具有促进作用,但对木生苔藓生物多样性的影响作用不明显。这也意味着,森林更新导致林窗形成和 CWD 产生对木生苔藓生长具有显著影响。

Both epixylous moss plant and coarse woody debris (CWD) are two essential components in most primary forest ecosystems, and their interaction exerts critical roles in carbon and nutrient cycles, soil and water conservation, and maintain biodiversity. Meanwhile, epixylous moss growing on the woody substrate is very sensitive to substrate quality change and microclimate as affected by canopy and CWD properties. However, the effects of gap position and CWD on epixylous moss plant communities in the forest ecosystem remains unknown. The study aimed to understand the effects of gaps and CWD type and decay class on epixylous moss communities. The biomass, Shannon, Simpson, and Pielou diversity indices for epixylous moss communities on fallen logs, large dead branches, snags, and stumps in the gap center, gap edge, and closed canopy were investigated in an alpine Minjiang fir (Abies faxoniana Rehd.) forest ecosystem in the upper reaches of the Yangtze River. The results showed that the biomass stock of epixylous moss on CWD totaled 141.14 kg/hm^2 in the studied alpine forest, and varied greatly with CWD type, decay class and gap position. The largest and smallest biomass stocks of epixylous moss were respectively observed on fallen logs (78.80 kg/hm^2) and snags (3.11 kg/hm^2). Meanwhile, higher stocks of epixylous moss were found on CWD with decay classes of Ⅲ and IV, and lower stock on CWD with decay class Ⅰ. In addition, the highest epixylous moss biomass per unit area on fallen logs, large dead branches, and snags were observed in the gap edge. The biomass accumulation of epixylous moss on CWD varied greatly with gap position and CWD type. The diversity of epixylous moss communities was also affected by forest gap position and CWD type. First, the Simpson index of epixylous moss communities grown on fallen logs, large dead branches, and stumps decreased from the gap center to closed canopy. Second, the highest and lowest Shannon and Pielou diversity indices for epixylous moss on fallen logs were observed in the closed canopy and gap edge, respectively. Third, the Shannon, Simpson, and Pielou diversity indices of epixylous moss communities on large dead branches in the gap center were higher than those on fallen logs. In addition, the diversity indices of epixylous moss on snags and stumps varied with gap position, and Dicranum and Neckera dominated the epixylic moss communities. The "edge effect" well explained the higher expixylous moss biomass in the gap edge but gave no good interpretation of the epixylous moss community diversity. In conclusion, forest regeneration can have strong effects on the growth and species diversity of epixylous moss communities by affecting CWD type, CWD decay process, and microclimate.