岷江上游植被覆被对水热条件的响应

The Response of Vegetation Cover to the Variation of Heat and Water Conditions in Upper Minjiang Watershed,China

利用2000—2011年间的水文气象和植被遥感等资料,分析了该地区植被覆盖对水热条件响应的季节规律及年际变化。研究表明,岷江上游以2 000～3 000 m高程带水热组合条件最好,分布了川滇高山栎等阔叶林;3 000m以上逐渐受热量制约,植被依次为针叶林、灌木、草甸和高山植被;2 000 m以下受干热河谷效应及人类活动影响,植被以灌木类为主。植被的实际"基带"位于河谷灌木带之上,植被垂直带谱呈部分折叠对称。在植被的水分响应方面,4 000 m以下植被水分指数的季相规律呈夏高冬低,同降水基本一致;而4 000 m以上寒旱特征明显,夏季由于强辐射导致水分指数年内最低。此外,过去40年来岷江上游气候暖干化明显,径流系数则呈缓慢减小趋势。因此,未来水热条件变化可能会导致岷江上游森林覆盖萎缩,其生态和水资源供给等问题应予以重视。

The upper Minjiang Watershed of China locates in the transfer zone from Tibetan Plateau to Sichuan Ba- sin, where the local ecosystem is sensitive to the variation of heat and water conditions. Understanding the response mechanism of vegetation to heat and water is beneficial to conserve the water source of upper Yangtze River and to alleviate the soil erosion. The hydrological and meteorological observation and remote images were used to explore the intra - and inter-annual variations in the response of vegetation covers to heat and water conditions in upper Minjiang watershed. Results of this study suggested the preferable combination of heat and water in upper Minjiang is at the altitude belt between 2 000 - 3 000 m, where the dominant tree species is Sichuan - Yunnan Quercus semecarpifolia Smith. The region above 3 000 m in altitude is limited by heat condition, and the vegetation types are coniferous forest, shrub, meadow and alpine plant with the increase in altitude. The water plays the limiting factor in the region be- low 2 000 m because of the arid valley effect, and the dominant vegetation type is shrub. Therefore, the ACTUAL base vegetation spectrum （i. e. coniferous forest） is above the valley shrub belt, which causes the partial folding of the vertical vegetation spectrum in upper Minjiang valley. and drought during The climate of this area has been in the trend of warming past 40 years, which resulted in the gradual decrease in upper Minjiang discharge. The chan- ging conditions of heat and water may shrink the distribution of forest in upper Minjiang watershed, which calls for necessary attentions to the increasing needs in water resources for the urban lower Minjiang watershed.