藏东南色季拉两种树线交错带及其不同生境的小气候特征

Microclimate characteristics of two treeline ecotones and their different habitats in Segera,southeast Tibet

明确色季拉高山树线交错带的小气候特征,为深入开展高山树线维持机制研究提供基础数据。基于2018—2020年色季拉山树线交错带(急尖长苞冷杉树线交错带和方枝柏树线交错带)自动气象站及不同生境空气-土壤温湿度的连续观测,分析了两种树线交错带的总体小气候特征及3个生境(林下、灌木、林隙)温度、水分条件的变化特征。结果表明:两种树线交错带最热月均温8.71~9.32℃,最冷月均温-7.23~-9.08℃,年均温0.55~0.88℃,气温年较差15.95~18.40℃,年生物温度2.79~3.33℃,温暖指数与寒冷指数分别为9.15~12.94℃·月-1、-60.22~-64.98℃·月-1,以空气温度定义的生长季均温和生长季长度分别为7.45~8.31℃、106~136 d,以10 cm土壤温度定义的生长季均温和生长季长度则分别为6.06~7.01℃、120~141 d;两种树线交错带不同生境的地上温度和水分条件均较为相似,而地下层面温度和水分条件最优的均是林隙,但其土壤温度日振幅大,同时林下的土壤温度均小于其他生境,出现了“凉脚”效应;以土壤温度定义的生长季要比以空气温度定义的滞后约1个月,林隙的空气均温、土壤均温、土壤含水量较大,林隙与灌木的冻害事件频率多、强度大、持续时间长。色季拉山树线交错带内不同生境的小气候特征的差异主要表现在土壤温度、生长季温度以及生长季内冻害事件的发生。

This work described the microclimate characteristics of Sygera alpine treeline ecotones,and provided basic data for further study of alpine treeline maintenance mechanisms.Based on the data of automatic weather stations in two treeline ecotones(Abies georgei var.smithii treeline and Juniperus saltuaria treeline)and the observations of temperature and humidity of air and soil in different habitats of both ecotones in the Sygera Mountain during 2018-2020,we analyzed the microclimatic characteristics of treeline ecotones and the variation characteristics of hydrothermal conditions of the three habitats(under forest,shrub,and forest gap).In both ecotones,mean temperature of the warmest month was 8.71-9.32℃.The mean temperature for the coldest month ranged from-7.23 to-9.08℃.The annual mean temperature was 0.55-0.88℃.The annual temperature difference was 15.95-18.40℃.The annual biological temperature was 2.79-3.33℃.The warm index was 9.15-12.94℃·month-1 and the cold index ranged from-60.22 to-64.98℃·month-1.The mean temperature and length of the growing season defined by air temperature were 7.45-8.31℃and 106-136 days,while those defined by 10 cm soil temperature were 6.06-7.01℃and 120-141 days,respectively.Air temperature and humidity in the different habitats of the two ecotones were similar,whereas soil temperature and moisture were highest in the forest gap,with large daily amplitude of soil temperature.Soil temperature in the forest was lower than that of the other habitats,with a“cool foot”effect.The growing season defined by soil temperature lagged behind that defined by air temperature by about one month.The average air temperature,average soil temperature,and soil water content of the forest gaps were higher.The freezing injury events in the forest gaps and shrubs were frequent,strong,and lasting.The differences in microclimate characteristics among different habitats in the treeline ecotones of Sygera Mountain were mainly reflected in soil temperature,growing season temperature,and occurrence of freezing injury events in the growing season.