中国亚热带山地植被垂直带分布对气候季节性的响应

Variations in the vertical vegetation zonation of subtropical Chinese mountains:the importance of climatic seasonality

根据植被研究的文献,收集了中国亚热带地区(23°-34°N)具有亚热带常绿阔叶林基带的49个山地的地理位置、气候因子、植被垂直带分布等数据;计算了不同山地基带的温度和降水季节性(分别以月平均温度和降水量的变异系数表示),以及气候季节性强度指数(以月平均温度和降水量的变异系数的乘积表示);最后分析了季节性强度与植被垂直带分布的关系。结果显示,中国亚热带地区北纬25°以南的所有山体缺少落叶阔叶林带,而北纬32°以北的则一定具有落叶林带;在中间地带,具有落叶阔叶林带的山体比例随纬度上升而上升。温度的季节性强度和气候季节性强度随纬度上升而增加,但降水的季节性强度与纬度没有显著关系。非参数相关分析表明,中国亚热带山地植被垂直带落叶阔叶林缺失与否与气候要素的季节性强度显著相关,即随山体的温度季节性强度和气候季节性强度的增加,山体拥有落叶阔叶林带的可能性增加。这种纬度梯度上的山体植被垂直分布格局(落叶阔叶林带存在与否)的变化与叶片水平上碳平衡模型的预测一致。

One of the most significant research themes in plant ecology is the vegetation-climate relationship. Mean annual temperature and precipitation are frequently used to characterize stand qualities and predict vegetation distributions,while seasonalities of climate have seldom been employed to study the climate-vegetation relationship despite their long-recognized importance to the vegetation distributions. Mountain vertical vegetation zonations are often assumed to be the reduction of vegetation distribution patterns along gradient pattern. However,the seasonality of climatic conditions for a specific mountain doesn＇t vary with altitude as it does with latitude. According to cost-benefit analyses of leaf longevity,short leaf life spans are largely favored in habitats with intensive seasonalities. We therefore predict that deciduous broad-leaved forests are more likely to appear in high latitudinal mountains of subtropical China.We collected data on geographic locations,climatic conditions,and vertical vegetation distribution patterns for 49 subtropical Chinese mountains （23—34°N） from published literature. The coefficients of variations of monthly mean temperature and precipitation were calculated for each mountain to quantify the temperature and rainfall seasonality,respectively,and the production of the two coefficients was used to characterize climate seasonality as a whole. Then,we determined the relationship between the vertical patterns of vegetation distribution （existence or non-existence of deciduous broad-leaved forest zones） and the seasonality intensities across the mountains. The deciduous broad-leaved forest zone is not conspicuous when the mountains are located farther south than 25° N,whereas it is distinct when the location is farther north than 32° N. Within the latitudes ranging between 25° N and 32° N,the mountains are more likely to have the deciduous broadleaved forest in the low latitudinal areas than the high latitudinal areas. Both temperature and climate seasonalities increase with increasing latitude,whereas rainfall seasonality is insignificantly correlated with altitudes. Non-parametric correlation analyses indicate that the vertical vegetation zonations are closely correlated with the temperature and climatic seasonalities but not the rainfall seasonality. The possibility of the mountains having the deciduous forest increases with the seasonalities of temperature and climate but not rainfall. These suggest that the temperature seasonality is more important to influence the climate seasonality and the vertical vegetation zonations relative to the rainfall seasonality. However,the rainfall seasonality modifies the vegetation distribution pattern for several mountains and hence it may explain some exceptional mountains （e.g. that have apparent the deciduous forest in low latitudinal areas）. The relationships among mountain latitudes,vertical forest distributions,and climatic seasonalities are consistent with the prediction of current theoretical models on cost-benefit analysis of leaf lifespan. The revealed relationship between mountain vertical vegetation patterns and climatic seasonalities indicates the importance of studying the seasonality on vegetation structure,productivity and ecosystem functioning. It also suggests that ecological restoration practices should be site-specific,particularly on mountains. The physiological mechanisms underlying the relationship deserve to be an avenue of further researches.