千岛湖岛屿苦槠(Castanopsis sclerophylla)种群的维持和天然更新

Maintenance and natural regeneration of Castanopsis sclerophylla populations on islands of Qiandao Lake Region

千岛湖是1959年新安江水电站建设时形成的,这里有1078个面积大于2500m2的岛屿和许多更小的小岛。水电站建设清库时,植被基本上被砍伐殆尽,后来受到较好保护,现在植被主要以先锋树种———马尾松为优势种,然而该群落生态效益较低,同时易感病虫害(如松毛虫、松材线虫),因此亟需开展恢复为常绿阔叶林的工作。前期调查表明在一些岛屿上存在常绿阔叶树种,主要以苦槠为主。对岛屿上分布的苦槠进行调查,以揭示其种群结构和主要更新方式,为生态恢复提供建议。结果表明,苦槠可以分布在海拔105.4m以上的岛屿上,而最高水位为108.2m,说明苦槠能耐一定的水淹。岛屿上苦槠个体数与岛屿面积和高度呈极显著的正相关。从基株来看,大岛(>100hm2)和多数中岛(10~100hm2)上苦槠种群为稳定型或发展型,能够自我维持,而小岛和部分中岛上的苦槠为衰退型,难以维持下去;然而若从分株种群来看,几乎所有的种群都为稳定型或发展型。从苦槠的起源来看,大多数苦槠为无性繁殖(主要是萌条)的后代,有性繁殖的贡献小于20%。以上结果表明,无性繁殖在岛屿苦槠种群的形成和维持中起着十分重要的作用,使得种群在没有较大环境变化情况下,能够在一定时期内维持下去;但在中小岛上,基株种群也不容易扩大,表明存在一定的制约因素。结果也表明,尽管一些岛屿很小,但也满足苦槠生存和生长的条件,一些岛屿上不存在苦槠的主要原因可能是缺乏种源,因此,在中大岛上开展生态恢复时,只要提供合适的种子种苗,这些岛屿上是能够恢复为常绿阔叶林的。但在小岛和一些中岛上,存在制约种群扩大的因素,生态恢复可能存在一定的困难。

Qiandao Lake was formed in 1959 when the Xin＇hnjiang Hydroelectric Plant was built. There are 1078 islands with the area larger than 2500 m^2 and many smaller islands. Potential vegetation of this area was dominated by evergreen broadleaved species. When the Plant was built, the vegetation was clear-cut and now vegetation on islands was dominated by Pinus ma^soniana, a pioneer species. However, pure pine vegetation is low in ecosystem service and apt to disease, such as Dendrolimus punctatus and pine wood nematodes. Therefore there is a need to restore potential vegetation, i.e. evergreen broadleaved forest. Previous surveys indicated that on some islands, there are some evergreen broadleaved species remaining, and Castanopsis sclerophylla is the most common one. We investigated the population structure of C. sclerophylla to reveal whether it can sustain on islands and to provide suggestions on ecological restoration. C. sclerophylla can be found on islands higher than 105.4m, while the highest water level of Qiandao Lake was 108.2 m. Number of individuals on islands, with a range from 4 to more than 4000, were Population structure indicated that, at genet level, C. significantly related with the areas or altitudes of the islands. sclerophylla on large and most medium-size islands could be self- sustainable, while on small and some medium-size islands C. sclerophylla could not be self-sustainable and will be decline. However, at the ramet level, almost all the C. sclerophylla populations, no matter on large, medium or small islands, seem to be self-sustainable. Further analysis indicated that resprouting contributed more than 81.6% of the genets and 94.8% of the shoots reproduced after the creation of the Lake. Above results indicated that, although small population size on some islands, these populations might be sustain via vegetative reproduction, especially resprouting, for a long period under the present situation without human＇s disturbance and dramatic environmental changes. Conditions of most islands meet the surviving and growth of C. sclerophylla. Therefore, lack of seed or seedling is the main limit of the ecological restoration of evergreen broadleaved forests on islands of Qiandao Lake. However, no individual reproduced from sexual reproduction on some medium and small islands indicated that environmental condition might be another limiting factor of restoration.