Characteristics of geographic distribution of four critically endangered species of Abies in subtropical China and its relationship with climate

Aims Our objectives were to analyze the geographic distribution characteristics of four critically endangered species of Abies in China's subtropical regions, clarify their relationship with climatic conditions and determine the climatic factors that restrict the geographic distributions. Methods Geographic distribution information was collected from field survey and literature materials. Climate information was collected from China's meteorological stations and used to build a climate database of the distri- bution area. Commonly used climatic indexes and research methods were applied to analyze the relationship be- tween geographic distribution and climate. Restrictive climatic factors were determined based on factor analysis. Important findings Abies beshanzuensis, A. fanjingshanensis, A. yuanbaoshanensis and A. beshanzuensis var. ziyuanensis are scattered in the subtropical region of China. The horizontal range of distribution is narrow: 25°25'-27°55' N, 108°42'-119°12' E. The populations are distributed vertically in the upper part of mountains, with altitude ranging from 1 363 to 2 390 m. The uppermost altitude rises with decreasing longitude. Temperature of the entire distribution area is low, with mean annual temperature 7.4-11.2 °C. Precipitation is abundant, with a mean annual precipitation of 1 265-1 946 mm, of which 75% falls in the growing season. Humidity is high, and annual relative humidity reaches 77%-86%. The ranges of climatic indexes are narrow, indicating specific re- quirements for water and heat. The coldness index of the distribution area is low, limiting vertical diffusion to- wards low altitude. Therefore, the populations are confined in the upper part of mountains. The distribution areas of different species share similar climatic conditions. The temperature is relatively lower in the distribution area of A. fanjingshanensis. The humidity is slightly higher in the distribution area of A. yuanbaoshanensis. Three