Variations in the vertical vegetation zonation of subtropical Chinese mountains:the importance of climatic seasonality
Variations in the vertical vegetation zonation of subtropical Chinese mountains:the importance of climatic seasonality
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作者：
Sun Shu-cun
植物生态学最重要的研究主题之一是植被与气候的关系。年平均气温和降水量经常被用来表征林分质量和预测植被分布，而气候季节性尽管长期以来对植被分布的重要性已被认识到，但很少被用来研究气候与植被的关系。山地垂直植被带通常被认为是植被分布模式沿梯度模式的减少。然而，特定山脉的气候条件的季节性并不像纬度那样随海拔而变化。根据叶片寿命的成本效益分析，在季节性强烈的栖息地中，较短的叶片寿命在很大程度上受到青睐。因此，我们预测落叶阔叶林更有可能出现在中国亚热带高纬度山区。我们从已发表的文献中收集了中国49座亚热带山区（23—34°N）的地理位置、气候条件和植被垂直分布格局的数据。计算各山地的月平均气温和降水量的变异系数，分别量化气温和降水的季节性，并利用这两个系数的产生来表征整体的气候季节性。然后，我们确定了植被分布的垂直格局（是否存在落叶阔叶林带）与山脉季节性强度之间的关系。山地在北纬25°以南时落叶阔叶林带不明显，在北纬32°以北则明显。在25°N～32°N范围内，山地低纬度地区比高纬度地区更容易出现落叶阔叶林。气温和气候季节性随纬度增加而增加，而降雨季节性与海拔高度相关性不显着。非参数相关分析表明，植被垂直带与气温和气候季节性密切相关，但与降雨季节无关。山区存在落叶林的可能性随温度和气候的季节性而增加，但不随降雨量的增加而增加。这表明，相对于降雨季节，温度季节对气候季节和垂直植被带的影响更为重要。然而，降雨季节性改变了一些山脉的植被分布格局，因此它可以解释一些特殊的山脉（例如，在低纬度地区有明显的落叶林）。山地纬度、森林垂直分布和气候季节之间的关系与现有叶片寿命成本效益分析理论模型的预测一致。山地垂直植被格局与气候季节性之间所揭示的关系表明了研究季节性对植被结构、生产力和生态系统功能的重要性。它还建议生态恢复实践应该针对具体地点，特别是在山区。这种关系背后的生理机制值得进一步研究。
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.