树木年代学在山地自然灾害研究中的应用

Potential Applications of Dendrochronology in the Research of Mountain Natural Disasters

中国山地自然灾害频发但灾害发生历史研究少。识别过去发生的滑坡、泥石流、落石、山洪等山地灾害发生的时间,确定灾害的大小及影响范围,对于研究区域山地灾害发生频率,预测未来灾害发生风险,制订科学可行的防灾减灾措施十分重要,树木年代学在研究灾害发生历史和影响范围等方面可发挥重要作用。树木的生长发育受光照、温度、水分、土壤、养分和生物等环境条件制约,任何环境因素的变化都会影响其生长,并常在年轮上表现出来。树木年轮能记载树木的生长状况和影响树木生长的环境条件变化,其宽度变化与环境因素之间的相关性高,能揭示环境条件变化发生时间。在气候变化影响不断增加和人类活动对自然环境影响强度日益加大的综合影响下,自然灾害发生频率及损失呈明显增加趋势,成为影响社会可持续发展的一个重要因素。山地自然灾害对树木的直接损伤包括树木顶端和枝条折断、根系受损、淹没主干下部、撕裂树干或根系、擦伤或撞伤树干,灾害会使树木倾斜和弯曲,也会改变树木生长的环境条件,这些影响和变化都能够显著影响树木的生长,树木出现年轮变窄或变宽、形成反应木和偏心年轮、停止生长等响应方式,这种自然灾害发生与树木生长响应之间形成的"事件-响应"关系,是利用树木年代学重建灾害发生历史的理论基础,受影响的树木的这些年轮系列为确定自然灾害发生的时间提供了可靠的信息。当树冠、树干或根系受损时,为确保生存,树木会将其合成或获得的物质优先用于新组织的生长,以替换受损的根系和树冠,减少用于径生长的物质资源,年轮变窄;而当灾害导致一些树木死亡或冲毁一些树木后,会改变未受损伤树木的生长条件,树木生长加快,年轮变宽。本文综述了地震、滑坡、泥石流、落石和山洪等不同自然灾害对树木生长影响的特点及树木的响应表现,介绍了利用树木年代学重建山区常见自然灾害的历史、影响范围的研究;针对新的科技发展,将来的研究应该关注不同年龄或大小的树木对同一灾害的响应差异、树木高生长对灾害的响应以及根系对灾害的响应等方面。

Disaster reduction and proper pre-disaster preparedness are an important issue in sustainable development and in achieving the sustain- able development goals.Despite frequent natural disasters and huge losses in China,few studies are available on the frequency and affected areas of past disasters.Information of dating,magnitude and scope of past landslides,debris/mud flows,rockfalls,rush floods and earthquakes is critical to understand disaster frequency and to predict future risk of disasters,and is essential to make practical planning of pre-disaster preparedness and disaster reduction.But such information is usually not readily available.Dendrochronology has unique advantages in providing needed informa- tion.Growth of trees depends on environmental factors of light,temperature,moisture,soil nutrients and other plants.Changes in a factor can affect tree growth that can usually be easily observed in tree rings.Tree rings record changes in both tree growth rate and environmental conditions.There is a high correlation between tree growth rate changes and environmental changes.With increasing climate change impacts and ever intensifying human activities on the nature,there has been an increase trend in frequency,magnitude,severity and losses of natural disasters.Disasters can dir- ectly damage,wound or even kill trees.Disasters can also cause trees to tilt and bend,or affect tree growth rate through eliminating trees or damageto trees.Trees respond to these impacts by changes in tree ring width,or formation of reaction wood,as trees use the available resources to main- tain its survival and to make new tissues to replace the damaged ones.In the study of response process and mechanism of trees to natural disasters,a series of research methods/methodologies have been developed in dendrochronology.The study of tree rings can reveal the history and characteristics of past natural disasters.It has great advantages in studying the time and influence of such disasters as earthquake,debris flow,land- slides,rush floods,rockfalls in mountains.Recent studies of application of dendrochronology in these disasters are reviewed.New areas of future re- search interests are proposed.