Exploratory quantification of 3D spatial competition in ecotone of trees and bamboos using terrestrial laser scanner

Abstract

With the intrinsic advantages of fast growth, high fecundity, diversity of forms, and group synergy, bamboos have been rapidly spreading in China and abroad. The spatial invasion of bamboo is actually the outcome of unbalanced competition between trees and bamboos. However, there is currently no competition index (CI) specially designed to quantitatively analyze the 3D spatial competition occurring between trees and bamboos. In this study, the point cloud data of the sample plot at the ecotone of trees and bamboos was scanned using a terrestrial laser scanner (TLS). The structure parameters of individual trees and bamboos were first extracted after point clustering and segmentation. Then, the survival intersection angle index (SAI) was constructed to incorporate the height difference and diameter at breast height (DBH) ratio of trees and bamboos. The crown distance index (CDI) was used to measure the serious mechanical damages made by bamboo culms to tree crowns. The final survival index (SI) was the output of direction-weighted sub SIs in four directions around objective trees. As a result, the final SIs of Masson pines in study site ranged from 0.48 to 1.0, indicating most tree crowns had been seriously intruded by Moso bamboo culms. The minimum final SI was caused by group-synergetic pressure exerted by competitive bamboos around. Therefore, the final SI calculated using the snapshot point cloud was applicable for evaluating the tentative survival statuses of objective trees in the ecotone, and helpful for analyzing the potential of bamboo spatial invasion.