Distribution patterns of the Cupressus gigantea populations in the Yarlung Tsangpo River and their responses to environmental changes

Plant population distribution pattern is one of the basic quantitative characteristics of plant population, and is of great significance to understand adaptation of plants to the environment by comprehensive influence of plant biological characteristics and environmental factors． In this paper, the spatial distribution pattern of the Cupressus gigantea population was studied by point pattern analysis, correlation analysis and stepwise regression methods, differences and influencing factors of C. gigantea population distribution patterns at different scales were analyzed． The spatial distribution pattern of C. gigantea population was found to be of mainly random distribution or cluster distribution, which changed with altitude, soil nutrients, texture and other conditions． The distribution pattern of low-altitude populations on semi-shady slopes was randomly distributed on the scale of 0.9-10.0 m (P < 0.05), and clustered or randomly distributed on other scales． Medium-altitude populations are clustered on the 2.8-10.0 m scale (P < 0.05) and randomly distributed on other scales． Low-altitude populations on sunny slope were clustered on the scale of 0.6-10.0 m (P < 0.05) and randomly distributed on other scales． The low-altitude populations on slope with poor light were randomly distributed on the scale of 0-10.0 m (P < 0.05)． The medium-altitude population of slope with moderate light was randomly distributed on the scale of 0-10.0 m (P < 0.05)． On a scale of < 5.0 m, the clustered degree of C. gigantea population gradually weakened with increased altitude, and when the scale was > 5.0 m, the influence of altitude on the population distribution of C. gigantea gradually decreased, and influence of soil nutrients, soil texture and other factors gradually dominated． The distribution pattern of C. gigantea population at different scales is affected by a variety of environmental factors, and small environmental changes caused by altitude and topography changes will significantly affect the distribution pattern． In future protection of C. gigantea, influence of environmental factors should be comprehensively considered．