秦岭天然次生油松林冠层降雨再分配特征及延滞效应

Time lag effects and rainfall redistribution traits of the canopy of natural secondary Pinus tabulaeformis on precipitation in the Qinling Mountains,China

为了研究秦岭典型地带性植物油松林冠层降雨再分配特征及延滞效应,选择陕西宁陕县秦岭森林生态系统国家野外科学观测研究站55龄天然次生油松林,从2006—2008年(5—10月份)对林外降水、穿透降雨和树干茎流进行定位观测。利用其中100次实测数据进行分析研究,结果表明:总降雨量为1576.4 mm,穿透降雨量为982.9 mm,树干茎流量为69.5 mm,冠层截留量为524.0mm,分别占总降雨量的62.4%、4.4%和33.2%。降雨分配与降雨量级密切相关,降雨量级增大,穿透降雨率和茎流率呈增大趋势,截留率呈降低趋势,变化幅度分别为46.6%—68.9%、0.8%—9.2%、53.4%—22.0%。穿透降雨量、树干茎流量和林冠截留量与林外降雨量之间的关系分别为:TF=0.6548P-0.4937,R2=0.9596;SF=-0.2796+0.0452P+0.0005P2,R2=0.8179;I=0.5958P0.8175,R2=0.8064。降雨事件发生后,穿透降雨和树干茎流出现的时间与降雨发生的时间并不同步,均表现出一定的延滞性,随着降雨量级增大,滞后时间表现出逐渐缩短的趋势((78.5±8.8)—(16.0±0.0)min,(111.0±33.0)—(41.2±0.0)min)。降雨终止时,特别是当降雨量>10.0 mm,穿透降雨终止时间也存在一定的延滞性((3.2±2.6)—(12.0±0.0)min)。但树干茎流终止时间先于降雨终止时间,降雨量级越小,树干茎流终止时间愈早((-58.3±21.5)—(-9.8±0.0)min)。

The interception of precipitation by vegetation and subsequent evaporation during and after rain events is an important component of the hydrological budget of forest ecosystems,particularly for forests in ecologically and hydrologically sensitive regions such as Qinling National Forest.This forest was incorporated into the State Natural Forest Protection Project and is managed solely for soil and water conservation.The Qinling Mountains are a major mountain range in China and are the major headwater source for one of the three routes of the South-to-North Water Transfer Project.The evergreen Pinus tabulaeformis is the dominant canopy species at elevations from 1400 to 1700 m.Extensive studies have been conducted to examine the canopy interception,throughfall and stemflow in P.tabulaeformis forest ecosystems across China,mostly in juvenile（≤30 years） or middle-aged（31—50 years） plantations.However,information on rainfall partitioning in natural forests,especially near-mature stands（51—60 years）,is lacking,which impedes our understanding of the hydrological ecosystem services in this region.The objective of this study was to understand rainfall partitioning characteristics and lag effects in the Qinling natural secondary P.tabulaeformis forest.Fifty-five-year-old stands of P.tabulaeformis in Ningshan,Shaanxi,were chosen and the precipitation,canopy interception,throughfall and stemflow were measured from 2006 to 2008（recorded in 5—10 months of each year）.One-hundred times complete measurement data were analyzed.Total precipitation was 1576.4 mm.Rainfall was partitioned as follows： 62.4% throughfall,4.4% stemflow and 33.2% interception by the tree canopy.The redistribution of precipitation by the canopy was more closely related to the rainfall classes.In a single rainfall event,the higher the rainfall class,the greater the stemflow and throughfall rate and the lower the interception rate.The relationships between throughfall（TF）,stemflow（SF）,crown interception（I） and total rainfall（P） were described significantly by linear,quadratic and power functions,respectively（TF = 0.6548P-0.4937,R2 = 0.9596;SF=-0.2796 ＋ 0.0452P ＋ 0.0005P2,R2 = 0.8179;I = 0.5958P0.8175,R2 = 0.8064）.Under similar rainfall conditions,the higher the rainfall intensity,the shorter the time to saturate the canopy.The timing of throughfall,stemflow and rainfall events after precipitation were not synchronous,and lag periods ranged from（78.5±8.8） min to（16.0±0.0） min and from（111.0 ± 33.0） min to（41.2 ± 0.0） min following precipitation for throughfall and stemflow,respectively.The time lag shortened gradually as rainfall class increased.After precipitation had ceased,especially,when the rainfall is greater than 10.0 mm,the termination of throughfall also lagged from（3.2±2.6） min to（12.0±0.0） min.However,with regard to stemflow prior to termination of rainfall,the smaller the rainfall class,the earlier termination occurred from（-58.3±21.5） min to（-9.8±0.0） min.