我国西南地区喀斯特森林树木年轮对气候变化的响应

利用贵州省2个典型喀斯特地区与1个非喀斯特地区的6个优势树种(化香树Platycarya strobilacea为重复树种)的树轮宽度资料,建立了6个树轮宽度年表,研究了不同地区不同树种的树木年轮对近50年来气候变化的响应异同,探讨了影响6个优势树种生长的气候限制因素。结果表明,季风期前的水热条件是喀斯特地区针叶树和阔叶树径向生长的最主要的气候限制因素。季风期前降水减少、月均温升高,导致土壤水分蒸发加快,加强了水分胁迫,不利于喀斯特地区针叶树和阔叶树的生长。帕尔默干旱指数虽表明喀斯特地区未达到干旱胁迫程度,但实际上水分渗漏加剧了喀斯特地区针叶树和阔叶树生长的水分胁迫。非喀斯特地区采样点的高海拔导致的低温,减少了春冬季节土壤水分蒸发。并且非喀斯特地区土壤和地形有利于水分涵养,同时,较高海拔的地形改变了季风期前的降水格局,消除了季风到来前树木生长的降水限制,因此,降水并不是喀斯特地区树木生长的限制因子;但其针叶树的径向生长受到上一年12月的温度控制,产生正响应信号,阔叶树径向生长仅受到生长季温度、降水增加带来的较小促进。

Tree-rings of Dominant Species in Karst Forests in Southwestern China and Their Responses to Climate Change

Tree-ring data of six dominant tree species (Platycarya strobilacea isthe repeated tree species) of two typical karst areas and a non-karst area in Guizhou Province, China were used to develop six tree-ring chronologies. The different and similar responses of radial growth to climate change during the past five decades of different tree species of different areas were investigated, and the effects of climate factors to the six tree species were also discussed. Results show that the water-heat condition before the monsoon season is the main climate limitation for the radial growth of both coniferous and broad-leaved trees in karst forests. The reduction of monthly mean precipitation and the rise of monthly mean temperature before the monsoon season lead to faster evaporation of soil moisture before the monsoon, thus, water stress is enhanced, resulting in drought stress on the radial growth of both coniferous and broad-leaved trees in karst forests. The Palmer drought severity index (PDSI) indicates weak restrictions on most of the tree growth, but in fact, water leakage aggravates the water stress for the growth of coniferous and broad-leaved trees in the karst areas. Precipitation is not the limitation for trees growing in the non-karst area, because lower temperature at higher elevation of sampling point in the non-karst area reduces the evaporation of soil moisture from last winter to next spring. The soil and land form in non-karst area is crucial for water reservation, meanwhile, high elevation also changes the precipitation patterns before the monsoon, which eliminates the water restriction of soil moisture for the growth of trees before the monsoon. The low temperature in previous December is the main limitation for the radial growth of coniferous trees with a positive response signal, and broad-leaved trees are slightly promoted by temperature and precipitation in growing season.