Forest stand spatial structure measurement method using handheld tree measurement smart station

Abstract: Spatial structure is an important characteristic of forest and spatial distribution pattern is one part of researches on population spatial behavior．Based on the relationship of neighborhood trees, three kinds of stand spatial structure parameters including uniform angle index，mingling and dominance was proposed by Professor Gangying Hui. In the past decade, stand spatial structure parameters are widely used to analyze stand spatial structure, calculate trees dominance, judge competition among trees, measure species diversity and recover or reconstruct stand structure at domestic and international study.. Measurement accuracy of spatial structural parameters (uniform angle index, mingling degree, and dominance) has a significant role in studying stand spatial structure. In the traditional direct interpretation method(DIM), it is difficult to measure the angle between reference tree and 4 nearest neighbor trees. For this method, the error derived from tree diameters at breast height is not considered in the process of measurement, so uniform angle index value is inaccurate. Moreover, based on DIM, other two parameters of mingle degree and dominance measurement required at least two operators, one person completed measurement and the other recorded field data, thus it is impossible to calculate the observing results immediately In this paper, a new measuring method named as HSSM was proposed using handheld smart station to measure stand spatial structure parameters in order to enhance measurement precision and accuracy, decrease field investigation workload. For measuring uniform angle index , the angle between reference tree and four nearest neighbor trees is not measured directly. Firstly, X-Y coordinates of reference tree and four nearest neighbor trees are measured using handheld smart station. Secondly, the diameters at breast height of five trees are measured corresponding with each tree, specifically, diameters at breast height measurement is to obtain center coordinates of five selected trees so as to increase angle calculation accuracy. Finally, reference tree as central point, intersection angles between four nearest neighbor trees are resolved according to the law of cosines. According to the above-mentioned measurement method, experiment was carried out in one stand forest plot (100 m×100 m) which located at Beijing Olympic Forest Park by three operators. The relative error of uniform angle index average value of HSSM was 2% less than that of DIM, average time-consuming (single person) of HSSM was 90.1s more than that of DIM (double person, 40.7 s), and measurement efficiency of HSSM was 8% lower than that of DIM. The mingle measurement result of HSSM were as the same as that of DIM, but the average time-consuming (single person) of HSSM was 21.5s less than that of DIM (double person, 32.2 s), measurement efficiency of HSSM was about 3 times that of DIM. The results of dominance relative error was 4% between HSSM and DIM, but the average time-consuming (single person) of HSSM was 74.8s more than that of DIM (31.05 s for double person), measurement efficiency of HSSM was 20% lower that of DIM. HSSM had the advantages of single person operation, display and storage directly by the equipment. Moreover, compared with the DIM, HSSM resolved the problem that DIM could not measure the tree center coordinate at breast height of reference tree and nearest neighbor tree , and for HSSM, the distribution of reference tree and nearest neighbor tree could draw conveniently and visually display according to measuring data in the process of interior work . This research can provide references for measuring forest spatial structure measurement accurately and efficiently.