The fractal dimensional structure of a shelterbelt: Definition and model of fractal geometry porosity
Tree shelterbelts are linearly planted barriers that improve the environmental conditions or microclimate in agro-ecosystems primarily by reducing and redirecting wind. They not only have considerable height and length, but also significant width, forming a three-dimensional vegetative body with a complicated internal structure and diverse external characteristics. Optical porosity is a commonly used structural descriptor of a shelterbelt. By projecting a shelterbelt side on a two-dimensional plain, porosity is defined as the ratio of open space to the solid portion on the side view of a barrier. This definition can well represent the aerodynamic structure of a slate fence without a significant width dimension. A visual representation of a tree shelterbelt structure, however, misses some details. Numerous researchers have been aware of its weakness, trying to define better structural descriptor(s) as an altemative. A shelterbelt canopy is composed of individual trees with leaves. branches. seeds, and a trunk. while a tree has a typical fractal dimensional structure. Therefore. we assert that the structure of a shelterbelt should be best described using the fractal geometry approach. Populus xiaozuanica is the main tree species in the southeastern part of the Kerqin sand land. As an example, the structure of shelterbelts composed of trees of this species is described in two scales, those of the tree and the shelterbelt, using the theory and method of plant morphology, fractal geometry, and fractal graphics. The relationship of crown volume to leaf mass or branch mass shows the self-similarity of tree architecture. Thus, the fractal dimension inside a crown can be estimated using the fractal geometry approach. Using the shelterbelt volume function in terms of crown width and crown height, as well as the shelterbelt constant volume (as defined by the designed width and height of a shelterbelt, the model for the fractal dimension of vegetative materials inside a shelterbelt canopy (fractal geometry density, Df ) is developed. The fractal dimension of the open portion through which air flows is defined as the fractal dimension of the void spaces in the shelterbelt canopy (fractal geometry porosity,βf) The sum of fractal geometry density and fractal geometry porosity is equal to three (fractal dimension of a solid body, as 3). Fractal geometry porosity represents shelterbelt structural characteristics more precisely than transitional structural descriptors optical porosity. Defining the optimum structure of a shelterbelt is important, as the definition can guide its management.
fractal geometry density fractal geometry porosity Populus iaozuanica tree architecture windbreak.
Chunping Li Xinhua Zhou Fanxing Su Bin Wu Wenbin Guan
Beijing Forestry University, Key Laboratory of Soil and Water Conservation & Desertification Combati University of Nebraska, School of Natural Resources, USA Qingdao Istitute of Bioenergy and Bioprocess Technology,Chinese Academy of Sciences,Qingdao 2661O1,P
国际会议
西安
英文
673-678
2010-10-11（万方平台首次上网日期，不代表论文的发表时间）