云南常绿阔叶林的植被地理研究

云南具有极其丰富的生物多样性和以常绿阔叶林为优势的植被类型。该研究利用6个基于样方层面的1 hm²样地资料, 以及通过对整个植被类型的植物区系的调查, 对云南常绿阔叶林植被型的3个植被亚型(季风常绿阔叶林、半湿润常绿阔叶林和中山湿性常绿阔叶林)的生态外貌特征、植物区系组成及其生物地理演化进行了研究。在样方层面, 尽管这3个常绿阔叶林在树种组成上优势种均为壳斗科、樟科和山茶科植物, 但它们在种类组成、多样性、生态外貌和生物地理特征上呈现多样化。分布在南部及西南部的季风常绿阔叶林物种组成极其丰富, 具有热带森林的生态外貌, 并以热带亚洲分布种为优势种。主要分布在云南高原的半湿润常绿阔叶林和云南中部和北部山地的中山湿性常绿阔叶林具有亚热带常绿阔叶林的生态外貌特征和以中国-喜马拉雅及中国特有种占优势, 是中国西南独特的植被类型。在植被亚型层面, 这3个常绿阔叶林的植物区系(包括所有生活型的种子植物)中种数最多的科, 按地理成分均为世界分布型的科, 含种数较少的科则为其他各种分布型的科。半湿润常绿阔叶林和中山湿性常绿阔叶林的植物区系, 热带分布属分别占总属数的44.91%和44.04%, 温带分布属占46.29%和48.19%, 其中北温带分布属比例最高, 分别为18.36%和19.95%。季风常绿阔叶林植物区系则显示了不同的地理成分格局: 热带分布属占总属数的78.05%, 并以热带亚洲分布属占最高比例。通过对这3个常绿阔叶林的比较发现, 半湿润常绿阔叶林和中山湿性常绿阔叶林除生态外貌特征有一定区别外, 在植物区系组成和地理成分上很接近, 它们在种的组成上, 与季风常绿阔叶林的类似性仅为17.1%和15.4%。季风常绿阔叶林因其在植物区系和生态外貌上与后二者区别明显, 建议在云南植被分类上划分一个独立的植被型, 它是东南亚低山常绿阔叶林分布在中国西南部热带北缘山地的一个植被类型。结合云南的地质历史和古植物学资料, 认为云南的常绿阔叶林及其植物区系受晚中新世以来的地质历史事件深刻影响。半湿润常绿阔叶林是中国西南独特而特有种丰富的植被类型, 由于严重的人为干扰破坏, 现已片段化或成为萌生灌丛状, 应给予优先保护。

Vegetation geography of evergreen broad-leaved forests in Yunnan,southwestern China

Aims Yunnan in southwestern China supports an extremely rich biodiversity and various vegetation types dominated by evergreen broad-leaved forest. Of these, three major types—monsoon evergreen broad-leaved forest (MEB), semi-wet evergreen broad-leaved forest (SWEB) and middle-montane wet evergreen broad-leaved forest (MMEB)—have not had a detailed scientific comparison. This article compares their floristic composition, species diversity, physiognomy, biogeography, and possible historical evolution, and gives suggestions for their conservation priorities.Methods Six 1 hm² sampling plots, representing the three evergreen broad-leaved forests in Yunnan, were set up based on the present distribution of primary forest. All trees in each plot were identified and their diameter at breast height (DBH)(minimum 5 cm) and height measured. In four plots, all plants, including understory shrubs, herbs, lianas, and epiphytes, were surveyed for life forms and biogeographical element analyses at plot level. Importance value indices (IVI) of tree species were calculated for each plot. At the vegetation level, all seed plants for the three major vegetation types were inventoried to compare their floristic composition and biogeography.Important findings At plot level, the three forest types differ considerably in species composition, diversity, physiognomy, and biogeography, although they are commonly dominated by species of the families Fagaceae, Lauraceae and Theaceae. The MEB in southern Yunnan is extremely rich in species and is characterized by a tropical physiognomy. It is dominated by tropical Asian species, which is similar to the tropical lower montane evergreen forest in southeast Asia. The SWEB on plateaus and the MMEB in central and northern Yunnan are characterized by a subtropical physiognomy and are dominated by Sino-Himalayan and Chinese endemic species, which are unique in southwestern China. At the vegetation sub-type level, the three forest types commonly have species-rich families, which tend to have cosmopolitan distributions, but the families with fewer species exhibit other distribution types. The SWEB and the MMEB showed similar biogeographical patterns in the proportions of tropical (44.91% and 44.04%, respectively) and temperate (46.29% and 48.19%) elements, with northern temperate distributions comprising the highest percentage (18.36% in the SWEB and 19.95% in the MMEB) of total genera. In MEB, tropical elements comprised 78.05% of the total genera, with elements with tropical Asian distributions contributing the highest percentage (29.02%). Similarity between SWEB and MMEB was high at species level, but lower similarities were shown between MEB and both of the SWEB and MMEB with 17.1% and 15.4% respectively at species levels. These results indicate divergence of the three forest floras, possibly from events in the geological history of Yunnan. The SWEB and the MMEB should be given high conservation values due to their uniqueness and abundant Chinese endemic species. Especially, the SWEB should be given the highest protection.