云南地区种子植物区系过渡性地理分布格局的群落尺度分析

Geographical patterns of flora transition of seed plants at community scale in Yunnan,China

探索植物区系过渡性的地理分布格局,对于理解植物区系的起源、迁移和分布具有重要意义。本研究利用620个植物群落样方,探讨了云南地区植物区系过渡性的地理分布格局及其生物地理意义。研究结果表明,随着纬度、海拔的升高,温带区系成分所占比重呈显著递增趋势,但在经度梯度上呈递减趋势;热带区系成分所占的比重在地理梯度上则表现为相反的变化趋势。地形格局较好地反映了区系成分的地理分布格局;热带区系成分所占比重与温带区系成分所占比重的比值从南到北呈递减趋势。区系过渡性的低值主要出现在滇西北地区和包括滇西南、滇东南与滇南在内的云南南部地区,而高值主要出现在云南中部地区和中海拔地区,这可能与区系迁移过程和海拔梯度有关。热带区系成分在云南地区基带植被中占主导地位;热带区系成分占优势地位的区域主要集中在低海拔地区,占云南土地面积的60%左右,而温带区系成分占优势地位的区域主要集中在高海拔的北部地区,占土地总面积的40%左右。本研究从基带植被的区系性质和温、热带植物区系成分占优势地位的土地面积的构成证实了云南地区可能是一个"热带山原"的假说。区系过渡性随着年平均温度的升高,呈先增强后减弱的单峰格局。当年均温在13.1℃左右时,出现区系平衡点。相对水平分布而言,云南地区植被的垂直分布可能更值得注意。

The investigation of flora transition may enhance our understanding on the mysteries of origin, migration and distribution of flora. In this study, we investigated the geographical patterns of flora transition of seed plants and their biogeographical implications using 620 plots of plant communities in Yunnan, Southwest China. The results showed that an increasing trend of proportions of temperate elements was observed on latitudinal gradients, and a decreasing trend was observed on longitudinal gradients. The trends of proportions of tropical elements were on the contrary to those of temperate elements. The ratios between proportions of between tropical elements and those of temperate elements decreased with the increase of latitude. Weak flora transition was mostly observed in northwest part and southern part of the studied area, while strong flora transition was observed in central part of Yurman province or mid-altitude regions, which may be associated with flora migration in the past and spatial patterns of energy gradients. The southern part of the studied area was mostly dominated by tropical elements, consisting 59.6% of the area, while the northern part of the studied area was mostly predominated by temperate elements, covering 40.4% of the area, which supported the theory that the studied area was a tropical mountain area. The flora transition increased, then decreased with the increase of mean annual temperature, and floristic equilibrium point can be observed around 13.1℃. Compared with distribution patterns in the dimensions of latitude and longitude, altitudinal patterns of vegetation should be paid much more attention.