灌木年轮学研究进展

灌木往往分布在树线以上或以北的高海拔和高纬度地区以及干旱、半干旱区,是把传统上以乔木为主的树轮研究扩展至森林分布界限以外的唯一选择.尽管灌木具有以上研究潜力,迄今用于树木年代学研究的灌木种类仅有30种左右.介绍了灌木年轮研究方法,综述了过去几十年来环北极高纬度地区,干旱、半干旱区以及高海拔地区的灌木年轮研究的主要进展.主要研究进展如下:(1)发掘一些灌木的树木年代学潜力；(2)揭示限制灌木生长的主要环境因子,并尝试利用灌木年轮宽度等指标重建过去区域气候变化历史；(3)探讨全球变暖的背景下,灌木的生长或分布范围的变化；(4)通过人为控制增温来揭示变暖对灌木生理特征和生长的影响.这些研究展示了灌木在扩展传统乔木树轮研究网络方面的潜力,也是树木年代学研究中最有前景的研究方向之一.目前的灌木年轮学研究多集中于环北极苔原带.作为地球的第三极,青藏高原具有广泛的高山灌木分布,具有把青藏高原边缘区以乔木为主的树木年轮网络扩展至更高海拔和高原内部的潜力.青藏高原高山灌木的年轮学研究并没有引起足够的重视.青藏高原高山灌木的生长是如何适应极端环境条件的,全球变暖的背景下,青藏高原高山灌木的分布和生长正在发生哪些变化等,都有待深入研究.

Progresses in dendrochronology of shrubs

In general, shrubs can grow above or beyond the alpine and high-latitude tree lines, arid and semi-arid areas. They provide a unique opportunity to extend the traditional tree-ring network into high-elevation, high-latitude, as well as arid and semi-arid environments. Despite of their great potentials, around 30 shrub species, to date, have been applied in dendrochronological studies. This paper briefly summarized the major progresses of shrub dendrochronology in high latitudes, semi-arid and arid areas and high altitudes in the past decades. They can be included the following four parts: (1) to detect dendrochronological potentials of shrub species; (2) to identify major environmental factors in controlling their growth, and to reconstruct the past climate change by the annual ring width and isotope of shrub species; (3) to investigate their growth and expansion in response to global warming; (4) to investigate the effects of the warming on the growth and physiology of the shrub species by controlling temperature variations. These studies demonstrated the high dendrochronological potential of shrub species in extending the present tree-ring network, being the most promising research direction in dendrochronology. In addition, most shrub dendrochronology studies focused on the northern circumpolar areas. As the third pole of the world, the Tibetan Plateau has a widespread distribution of alpine shrub species, being an excellent platform in investigating the responses of alpine shrub growth to extreme environments. Meanwhile, shrub species on the Tibetan Plateau provide a unique chance to extend the present tree-ring network beyond the survival limit of forests which are confined to the surrounding areas of the Tibetan plateau. However, dendrochronology of alpine shrub species on the Tibetan Plateau did not get enough attention in the last decades. How can the alpine shrubs adapt to extreme environments? What will happen for their growth and spatial distribution in response to global warming on the Tibetan plateau? These questions deserve further studies in the future.