Analyzing the reciprocity among many factors in an urban ecosystem requires an effective methodology to collect information regarding both the amount as well as the vertical structure of urban vegetation community. It is the precondition to defining a suitable descriptor to depict the plant’s detail vertical structure and to be used in a broad-scale detection with such fast detecting technique as remote sensing. The descriptor, living vegetation volume (hereafter refer to as LVV) was designed for both requirements.
LVV, a 3D descriptor of urban vegetation community, refers to the volume of the space occupied by the crown of a plant. The generally used items are the sum of LVV with the unit of m3, the summation of LVV all around a certain area, and the relative LVV with the unit of m3 /m2, the ratio of LVV to the land area in the same plot. The main reason to take the LVV as a descriptor of urban vegetation community is that the crown plays an important role in ecology and is responsible for the majority of material and energy exchanges with the atmosphere.
This study suggests two methods of getting LVV, one is the basic the other fast. The basic one is semiautomatic based on computer-aided interpretation and simulating calculation. The principal are the plant canopy diameter-height equations (refer to as D-H Eqs) and the mean error of algebra sum is only 1.31% when calculating canopy height by D-H Eqs. Then a fast method for renewing LVV data was developed in the consideration that a renewal can be taken by a simpler and quicker way after the accurate database was established. The principal are the general D-H Eqs (refer to as G-D-H Eqs) and the correlating equation between the ratio of perimeter to area (P/A) and the canopy diameter (refer to as P/A-D Eq). With the use of the fast method, every step for getting LVV can be processed by computer automatically. The trees, shrubs, lawns can be classified without intervention; the species of trees will be either provided by the existing database for the stable green lands or treated as the general species whose height will be simulated by one of the G-D-H Eqs for those green land with no record in the database. And by some classifying and tracing algorithms as well as the P/A-D Eq, the canopy diameter, another indispensable parametere for getting LVV, could be obtained with a veracity as high as near 90%.
The main objective of this study is to develop effective methods for getting LVV for a broad urban area especially to develop a fast method to meet the requirement of renewing the LVV database periodically.