Distribution of Cenozoic plant relicts in China explained by drought in dry season

Abstract

Cenozoic plant relicts are those groups that were once widespread in the Northern Hemisphere but are now restricted to some small isolated areas as a result of drastic climatic changes. They are good proxies to study how plants respond to climatic changes since their modern climatic requirements are known. Herein we look at the modern distribution of 65 palaeoendemic genera in China and compare it with the Chinese climatic pattern, in order to find a link between the plant distribution and climate. Central China and Taiwan Island are shown to be diversity centres of Cenozoic relict genera, consistent with the fact that these two regions have a shorter dry season with comparatively humid autumn and spring in China. Species distribution models indicate that the precipitation parameters are the most important variables to explain the distribution of relict genera. The Cenozoic wide-scale distribution of relict plants in the Northern Hemisphere is therefore considered to be linked to the widespread humid climate at that time, and the subsequent contraction of their distributional ranges was probably caused by the drying trend along with global cooling.

Figure 1. Selected representatives of Cenozoic relict genera in China:

(a) Keteleeria, (b) Metasequoia, (c) Dipelta, (d) Euptelea, (e) Hemiptelea, (f) Idesia, (g) Toricellia, (h) Tripterygium, (i) Euscaphis. Image (b) was provided by Dr. Li Wang from Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, and images (c–i) were provided by Dr. Zhuo Zhou from Kunming Institute of Botany, Chinese Academy of Sciences.

Figure 2. Modern climate of China, with the green line representing regions where both autumn and spring precipitations are over 300 mm:

(a) cold month mean temperature, (b) warm month mean temperature, (c) autumn precipitation, regions with autumn precipitation over 300 mm are in blue, (d) spring precipitation, regions with spring precipitation over 300 mm are in blue. (1) Tibet, (2) Sichuan, (3) Yunnan, (4) Chongqing, (5) Guizhou, (6) Guangxi, (7) Hubei, (8) Hunan, (9) Guangdong, (10) Fujian, (11) Zhejiang, (12) Taiwan. Maps were generated using the software ArcGIS 9.3.

Figure 3. Distribution of relict genera in China, with the green line representing regions where both autumn and spring precipitations are over 300 mm:

(a) number of relict genera per county, (b) results of the hotspot analysis, with red colours indicating hotspot regions and blue colours indicating cold-spot regions. Maps were generated using the software ArcGIS 9.3.