Table_1_Elevation gradients alter vegetation attributes in mountain ecosystems of eastern Himalaya, India.DOCX

The present study describes how vegetation (the tree layer) is shaped along the elevation gradients in the eastern part of the Indian Himalayan Region. Various vegetation attributes, distribution, population structure, and regeneration patterns of 75 tree species belonging to 31 families were studied. Tree species richness shows a low plateau (peaked between 1,300–1,500 m) with a linearly decreasing pattern above 1,500 m asl. Ericaceae was found as the dominant family, followed by Lauraceae and Rosaceae. The distributional pattern of species-to-genera ratio (S/G) did not follow any particular trends, while β-diversity increased along the elevation gradient. The Margalef index of species richness, the Menheink index of species richness, and the Fisher alpha were found to be highest at lower altitudes (1,000–1,500 m), while the Simpson index was highest at middle altitudes (2,600–3,000 m). Random distribution was shown by maximum tree species (47.3%), followed by a contagious distribution (42.9%), and regular distribution (10.8%). The regeneration of tree species was found to be good with a healthier number of seedlings (10.2%), fair (43.5%), poor (30.3%), while 16% were observed not regenerating. Acer laevigatum (1,500 m), Prunus nepalensis (3,300 m), Viburnum sympodiale (3,400 m) were among the new regenerating species at the respective altitudes. The population structure of tree species in terms of proportion of individuals in seedlings, saplings, and the adult class varied in all the elevation transects. Species with better regeneration on upper distribution limits have been recognized as probable for upward movement.

本研究阐述了印度喜马拉雅山区东部沿海拔梯度的乔木层植被分布格局及其形成机制，并针对隶属于31个科的75个树种的多项植被特征、分布格局、种群结构以及更新模式开展了系统调查。树种丰富度呈现低平台特征，在海拔1300–1500米处达到峰值，而在海拔1500米以上则呈线性下降趋势。研究发现杜鹃花科（Ericaceae）为该区域的优势科，其次为樟科（Lauraceae）与蔷薇科（Rosaceae）。物种属比（S/G）的分布格局未呈现显著规律性，而β多样性（β-diversity）则随海拔梯度呈递增趋势。玛格列夫物种丰富度指数（Margalef index）、梅尼尼克物种丰富度指数（Menheink index）以及费希尔α指数（Fisher alpha）均在低海拔区域（1000–1500米）达到最高值，而辛普森指数（Simpson index）则在中海拔区域（2600–3000米）取得最高值。多数乔木树种呈随机分布（占比47.3%），其次为集群分布（42.9%），均匀分布占比为10.8%。乔木树种的更新整体状况可分为四类：健康更新的幼苗占比10.2%，更新状况一般占比43.5%，更新较差占比30.3%，另有16%的树种未出现更新现象。在对应海拔区域，光叶槭（Acer laevigatum，1500米）、尼泊尔樱（Prunus nepalensis，3300米）、合轴荚蒾（Viburnum sympodiale，3400米）均为该海拔带的新记录更新树种。各海拔样带内，乔木种群在幼苗、幼树以及成树个体的占比结构均存在显著差异。在分布上限区域更新状况更佳的树种，被认为具备向上迁移的潜在可能性。