群落演替对夏蜡梅种群分布和数量的影响

对夏蜡梅(Sinocalycanthus chinensis(Cheng et S.Y.Chang)Cheng et S.Y.Chang)所有分布地(浙江临安、天台和安徽绩溪)进行了详细调查,分析夏蜡梅种群面积、密度、结构和群落特征等,并与前人调查结果对比,阐明群落演替对夏蜡梅种群的影响。10余年来,由于国家相关政策的实施(退耕还林、天然林保护以及自然保护区的建立等)以及夏蜡梅分布地林地经营模式的改变,不同夏蜡梅群落呈现发展演替的不同状态,从而对夏蜡梅种群产生了显著影响。从群落类型来看,较为稳定的种群为大明山、西坑、白水坞、捣臼孔种群,种群结构为增长型或稳定型,群落处于乔木或顶级乔木阶段,原生植被保存较好,生境相对稳定,各物种在长期竞争中趋于稳定;直源种群为严重衰退的种群,群落经历了从灌丛阶段向灌乔阶段演化,原来同层次的常绿乔木逐渐形成密集的乔木层,郁闭度高,造成夏蜡梅生长不良甚至死亡,幼苗缺少或数量少,更新困难,此区域的夏蜡梅呈逐渐退化消亡趋势;而溪古坪、龙塘山种群所处群落正是属于这种群落演替的早期阶段,处于衰退过程中种群,不加人工干预也会逐渐退化;而双石边、经过坪等种群虽目前数量多,分布集中,更新良好,但变数最大,一旦人工干扰加剧或消除,则种群结构将快速发生变化,走向消亡的几率极大。该研究结果可为夏蜡梅保护提供科学依据。

Effects of community succession on population distribution and size of Sinocalycanthus chinensis(Cheng et S.Y. Chang) Cheng et S.Y. Chang

We aimed to evaluate the effects changes in national forest policy and woodland management regulations on community succession, and population size, density and structure of Sinocalycanthus chinensis (Cheng et S.Y. Chang) Cheng et S.Y. Chang. Population structure and community characteristics were recorded over the whole distribution of the species and compared with previous studies. Due to the implementation of new national forestry policies (Grain for Green, Natural Forest Conservation, the establishment of nature reserves, etc.), as well as changes in woodland management in the past two decades, S. chinensis communities vary in their state of succession. These differences among communities have significant effects on the maintenance and development of natural populations of S. chinensis. Populations DMS (Daming Shan), XK (Xikeng), BSW (Baishui Wu), and DJK (Daojiu Kou) are relatively stable in terms of age composition and habitat. These communities have been at the tree stage or climax stage for a long time and are relatively stable, having achieved a balance in interspecific competition. Population ZY (Ziyuan) appears to be in serious decline. This community has undergone succession from shrub stage to shrub-tree stage and growth of evergreen trees, which previously belonged to the same shrub layer as S. chinensis, gradually resulted in formation of a canopy that limits growth and reproduction of S. chinensis, even causing death of some individuals. In this region, S. chinensis populations will gradually decline and eventually become locally extinct. LTS (Longtang Shan) and XGP (Xigu Ping) populations are located in communities at the early tree stage of community succession, and these populations are at risk of extinction due to the gradual disappearance of suitable habitat. Although SSB (Shuangshibian) and JGP (Jingguo Ping) populations are compose of abundant, densely distributed individuals and are reproducing well, they are most sensitive to human disturbance. If human disturbances increase, the structure of these populations will change dramatically and they face significant risk of extinction. As is the case with many other species with the specialized habitat requirements, community succession has a large influence on the fate of populations.