川西亚高山森林木质残体及其附生苔藓持水特性

Water-holding characteristics of woody debris and epiphytic moss in the subalpine forest of western Sichuan

木质残体及其附生苔藓是森林生态系统的基本结构,在水源涵养、水土保持、生物多样性保育、碳和养分循环等方面具有重要作用。然而,有关亚高山森林木质残体及其附生苔藓的水源涵养功能研究尚未见报道。因此,以川西亚高山针叶林区紫果云杉原始林、岷江冷杉原始林、方枝柏原始林等8种典型森林类型为研究对象,调查研究了木质残体及其附生苔藓持水能力随林型、腐烂等级和径级的变化特征。结果表明:(1)亚高山针叶林木质残体饱和储水量在林型之间变化显著。其中,紫果云杉原始林具有最大的饱和储水量(22.06 mm),柳树次生林木质残体饱和储水量最小(4.55 mm),但林型之间木质残体饱和持水率的差异不显著。(2)不同林型的附生苔藓持水能力具有显著差异。其中,紫果云杉原始林木质残体附生苔藓饱和储水量最高(7.01 mm),方枝柏原始林最低(0.21 mm)。(3)腐烂等级显著影响木质残体饱和储水量,Ⅳ腐烂等级的饱和储水量较高(3.77 mm),Ⅱ腐烂等级较低(0.75 mm);木质残体饱和持水率和附生苔藓饱和储水量与腐解程度显著正相关,均符合Q(Q′)=ex^(2)+fx+g的函数关系式。(4)木质残体和附生苔藓的饱和储水量均随径级增大而升高,大径级(D5)的饱和储水量占比分别超过60%和40%。可见,林型和木质残体腐解程度及径级大小是决定亚高山针叶林区木质残体及其附生苔藓持水性能的关键因子,特别是附生苔藓对于提高亚高山针叶林水源涵养具有重要作用。

Woody debris(WD) is the basically structural component in most of forest ecosystems worldwide, and plays crucial roles in holding water, conserving soil, promoting forest regeneration, nursing biodiversity, and modulating the cycles of carbon and nutrients in the forest ecosystem. Generally, WD consists of coarse woody debris(CWD) and fine woody debris(FWD). Among these, CWD provides better substrate for the growth of epiphytic moss. Further, the epiphytic moss on the CWD also plays important roles in holding water, regulating the bioelement cycles, and nursing biodiversity. Together, both WD and its associated epiphytic mosses might exert paramount roles in regulating the hydrological process, in particular holding water in the the forest ecosystem. Although the water-holding characteristics of CWD and moss have been widely investigated in different forest ecosystems, the simultaneous investigation on the water-holding capacity in both WD and its associated epiphytic moss has not been reported. Furthermore, the changes in water-holding capacity of epiphytic moss on CWD with decay classes and diameter sizes are not investigated. The changes in water-holding capacity of WD and its epiphytic moss with forest types, decay classes and diameter classes were therefore investigated in eight typical subalpine forests in western Sichuan. The saturated water-holding capacity of WD varied greatly with forest types, decay classes and diameter sizes. The highest and lowest saturated water-holding capacity of WD were observed in Picea purpurea primary forest(22.06 mm) and willow secondary forest(4.55 mm), respectively, but the ratio of water-holding varied slightly with forest types. Meanwhile, the saturated water-holding capacity of epiphytic mosses on the WD also varied greatly with forest types, and the highest and lowest values of saturated water-holding capacity were found in Picea purpurea primary forest(7.01 mm) and Sabina saltuaria primary forest(0.21 mm), respectively. Moreover, decay classes gave stronger effects on the saturated water-holding capacity of WD, higher and lower values of saturated water-holding capacity of WD were respectively measured on decay class Ⅳ(3.77 mm) and decay class Ⅱ(0.75 mm). Particularly, the saturated water-holding rate of WD and saturated water-holding capacity of epiphytic moss correlated significantly(P<0.05) and positively with WD decay class, which fitted the quadratic term function as Q(Q′)=ex^(2)+fx+g. The saturated water-holding capacity of WD and its associated epiphytic mosses on the WD increased with diameter classes, and the saturated water-holding capacities of WD with diameter size>50 cm(D5) and its epiphytic mosses on the D5 WD accounted for 60% and 40% of the total saturated water-holding capacity in the subalpine forest ecosystems in Wanglang National Nature Reserve. In conclusion, these results suggested that forest types, decay degree and diameter sizes of WD were the key factors that determine the water-holding capacity of WD and its epiphytic mosses in the subalpine forest region. Particularly, CWD epiphytic moss plays an important role in improving the water-holding capacity in the subalpine coniferous forest region.