祁连山青海云杉林树线温度特征

Treeline temperature of Picea crassifolia forest in Qilian Mountains

树线温度对于解释树线位置及树线形成机理、预测树线对于气候变化的响应具有重要意义。通过在祁连山北坡青海云杉林郁闭林内、树线地带、高山灌丛分布带设置土壤温度自动观测仪器,初步分析了青海云杉林树线温度特征。结果表明:(1)树线处青海云杉根际土壤温度(10cm深度)生长季平均值为4.9℃,低于全球树线生长季平均土壤温度(6.7℃)。(2)生长季长度方面,青海云杉树线(104天)与亚北极(Subarctic,103天)、北方林(Boreal,106天)树线相近。(3)高山灌丛分布带在海拔上高于树线地带,但灌丛地带根际土壤生长季节均温(6.4℃),生长季长度(122天)均高于树线地带,显示了树线之上灌丛相对于乔木生活型有更佳的保持根际土壤热量的优势,从而也成为在树线之上灌丛能够很好生长,并且取代乔木的重要因素。

Over the past one hundred years, treeline temperature has attracted great concerns. Most hypotheses on treeline formation were related to temperature. Since most of meteorological stations were far away from treelines, temperature extrapolated from data by meteorological stations would not reflect actual temperatures experienced by trees at treeline. Hence, a direct treeline temperature measurement was demanded. Recently, K？ rner and Pauls- en launched a worldwide treeline temperature investigation, suggesting that high altitude climatic treelines were as- sociated with a seasonal mean ground temperature （10era soil depth） of 6.7 ±0.8℃. Irrespective of latitudes or climate zones, the global treeline showed surprisingly narrow range of root - zone temperature. China has a great deal of high altitude mountains, which could form alpine treeline, however, information on treeline temperature was not available. In this study, automatic temperature recorders were set up at Picea crassifolia treeline （3 280m altitude）, al- pine shrub distribution belt （3 350m altitude）, as well as Picea crassifolia＇s optimal distribution zone （2 950m alti- tude）, respectively, in Qilian Mountains, and root- zone temperatures at 10cm soil depth were monitored simulta- neously. The objectives were as follows ： 1 ） to investigate the temperature threshold of treeline trees ; 2） to compare root- zone temperature of treeline trees and alpine shrubs, attempting to discuss why alpine shrubs, rather than trees could grow at higher altitudes. Results showed that the mean seasonal root zone temperature at treeline was 4.9℃, which was lower than the global mean treeline temperature （6.7 ℃ ）. With respect to the length of growing season, Picea crassifolia treeline （104d） was consistent with subarctic （103d） and boreal （106d） treeline. Additionally, despite the higher altitude of alpine shrub distribution, both the growing season length （122d） and mean seasonal root -zone temperature （6. 4℃） were much higher than those of Picea crassifolia treeline, which suggested that shrub life form may prevail in maintaining soil heat over tree life - form above treeline altitude. Consequently, alpine shrubs could substitute trees above treeline altitude.