Types and species diversity of Cupressus communities in Southeast Tibet, China

Cupressus communities are the important parts of natural forests in Southeast Tibet, with significance on plateau biodiversity conservation and ecological security. To clarify their types and plant species diversity, we analyzed species composition and diversity indices, diameter class pattern of constructive species in different communities in Milin County, Lang County and Bomi County, Southeast Tibet. The results showed that Cupressus communities could be classified into four types: C. torulosa-Lonicera lanceolate + Philadelphus tomentosus-Pteris cretica var. nervosa + Digitaria violascens community (Community1), C. gigantea-Desmodium elegans + Sophora moorcroftia-na-Tripogon filiformis + Cymbopogon distans + Orinus thoroldii community (Community2), C. gigantea-Leptodermis purdomii-Chenopodium hybridum + O. thoroldii community (Community 3), and C. gigantea-Ceratostigma minus-A. desertorum + O. thoroldii + Tribulus terrester community (Community 4). Across those four community types, Margalef index, Shannon index, Pielou index and interspecies encounter probability index all ranked with the decreasing order of Community1, Community2, Community 3 and Community 4. Diameter class pattern of the constructive species showed that many young and few middle/old individuals were within the four communities. High mortality rate occurred during the interim period from young to middle age classes. In general, populations of Cupressus plants showed a declining trend.