生态地理区域系统的热带北界中段界线的新认识

New Recognition on Boundary between Tropical and Subtropical Zone in the Middle Section of Ecogeographic System

从我国热带北界中段界线的划分 ,探讨生态地理区域的认识和界线的划分 ,着重生态地理区域之间界线的逐渐过渡特征。分析前人的研究成果及其对热带北界中段划分的差异 ,指出他们在概念、资料和方法上的差异。在热带与亚热带的过渡区域中提出热带、年热带、真热带和热带波动带的概念 ,从新的角度认识热带区域。在确定和建立热带北界划分指标体系的基础上 ,划分了热带北界中段的界线。探讨了本次热带北界中段的界线划分与前人研究的差异 ,热带波动带的意义 。

This paper discusses division on tropical and subtropical boundary in middle portion of South China. This discussion results in new understanding on eco geographic regions and their boundaries, especially on gradual changes of natural conditions between eco geographic regions. It also analyzes results of the same area by other researchers, clarifies differences and causes of the differences of the results. Boundaries of eco geographic region cannot be drawn as a line as changes from tropical to subtropical zone are gradual. Therefore, for an eco geographic region like tropical zone, definite boundaries must be drawn while considering gradual changes. Temperature, vegetation and soil are relevant indexes to divide tropical and subtropical zones. After indexes of the tropical zone are confirmed, data of annual average index reflect general state of the tropical zone. Line from such data is called “tropical boundary”. On the other hand, affected by the monsoon climate, some years are hotter and some are cooler. In hotter year, temperature of north area of tropical boundary reaches tropical state while in cooler year, such area moves southward. Boundary of the hottest year is called annual tropical line and that of the coolest year is called real tropical line. Temperatures in areas of south to annual tropical line can probably reach that of tropical zone in some years. Temperatures in areas of south to real tropical line can reach that of tropical every year. Area from true tropical to annual tropical is called tropical fluctuating zone. Therefore, new concepts of tropical, annual tropical, true tropical and tropical fluctuating zone are formed to understand tropical area in a new point of view in the paper. Based on the index of climate, vegetation and soil, boundaries of tropical, annual tropical, true tropical and tropical fluctuating zone of the study area are established. The tropical fluctuating zone explains different locating of different researchers. The paper also puts forward a new method to displaies boundary for eco geographic regions.