Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan 666303, China.
Int J Biometeorol. 2013 May;57(3):487-92. doi: 10.1007/s00484-012-0570-6. Epub 2012 Jun 30.
Our current understanding is that plant species distribution in the subtropical mountain forests of Southwest China is controlled mainly by inadequate warmth. Due to abundant annual precipitation, aridity has been less considered in this context, yet rainfall here is highly seasonal, and the magnitude of drought severity at different elevations has not been examined due to limited access to higher elevations in this area.In this study, short-term micrometeorological variables were measured at 2,480 m and 2,680 m, where different forest types occur. Drought stress was evaluated by combining measurements of water evaporation demand (E p) and soil volumetric water content (VWC). The results showed that: (1) mean temperature decreased 1 °C from 2,480 m to 2,680 m and the minimum temperature at 2,680 m was above freezing. (2) Elevation had a significant influence on E p; however, the difference in daily E p between 2,480 m and 2,680 m was not significant, which was possibly due to the small difference in elevation between these two sites. (3) VWC had larger range of annual variation at 2,680 m than at 2,480 m, especially for the surface soil layer.We conclude that the decrease in temperature does not effectively explain the sharp transition between these forest types. During the dry season, plants growing at 2,680 m are likely to experience more drought stress. In seeking to understand the mountain forest distribution, further studies should consider the effects of drought stress alongside those of altitude.
目前我们的理解是，中国西南亚热带山地森林中植物物种的分布主要受热量不足的控制。由于丰富的年降水量，在这种情况下干旱的影响较小，但这里的降雨具有很强的季节性，而且由于该地区通往高海拔地区的通道有限，尚未对不同海拔高度的干旱严重程度的幅度进行研究。在这项研究中，在海拔 2480 米和 2680 米处（不同森林类型发生的地方）测量了短期微气象变量。通过结合测量水分蒸发需求（E p）和土壤体积含水量（VWC）来评估干旱胁迫。结果表明：（1）从 2480 米到 2680 米，平均温度下降了 1°C，而 2680 米处的最低温度高于冰点。（2）海拔对 E p 有显著影响；然而，2480 米和 2680 米之间的日 E p 差异并不显著，这可能是由于这两个地点之间的海拔差异较小。（3）VWC 在 2680 米处的年变化幅度大于 2480 米处，特别是在表层土壤中。我们得出的结论是，温度的下降并不能有效地解释这些森林类型之间的急剧转变。在旱季，生长在 2680 米处的植物可能会经历更大的干旱胁迫。在寻求理解山地森林分布时，进一步的研究应考虑干旱胁迫与海拔的影响。
