Objective In view of the problems existing in the study of in-forest landscape quality assessment of urban forest, such as many theoretical studies, poor unification in assessment index systems, a regional universal in-forest landscape quality evaluation index system of urban forest was constructed, and the classification standard of in-forest landscape was proposed, which could provide technical support for the optimization of urban forest structure, management and production practice.
Method Four types of urban forests, including scenic-recreational forest both in urban park and country park, urban forest of residential areas and scenic forest of suburban mountainous areas, were taken as the research objects. The evaluation indicators were selected on the scale of forest stand, the comprehensive quality index of forest structure quality was constructed by factor analysis, and the in-forest landscape quality grade of urban forest was classified by TOPSIS method and cluster analysis.
Result (1) Fifteen evaluation indices were selected based on four types of urban forest and were used for evaluation of in-forest landscape of urban forest. The in-forest landscape of urban forest was divided into four grades: excellent, high, medium and low. (2) The in-forest landscape quality evaluation index system of urban forest was established, the core indicators including tree species richness (TSR), species richness under canopy (SRC), the forest type (FT), cleanliness of the forest stand (CFS), dispersion of DBH (DDBH), canopy coverage (CC), ornamental organ diversity (OOD), seasonal abundance (SA), breast height basal area per hectare (BAH), ratio of crown width to diameter (RCWD), etc. (3) The index characteristics of the optimal landscape of different types of urban forests were not exactly the same. Scenic-recreational forest of urban park: relative under branch height (RBH) was the smallest, ratio of diameter-height (RDH) was smaller, RCWD was larger, CFS was high. Urban forest of residential areas: BAH was the largest, RBH was the smallest, RCWD was smaller, SA was high. Scenic-recreational forest of country park: BAH, dispersion of tree height (DTH) and RDH were the largest, tree species were the most, with diverse ornamental organs, mostly mixed forest. Scenic forest of suburban mountainous areas: CC was moderate, relative shrub height (RSH) was the lowest, stand vertical stratum (SS) and species under the canopy were richer, CFS was high.
Conclusion Seen as a whole, forests or landscapes which are of abundant tree species, mixed moderately, neat in-forest condition, both dispersion of DBH and canopy coverage are suitable, and with abundant ornamental organs and seasonal changes are more popular. The optimal range of stand density and RCWD is different for varied types of urban forest. In the management of urban forests, it is suggested to enrich the tree species appropriately, pay attention to the configuration of colored plants and multi-seasonal tree species, adjust the density of the forest properly, timely pruning, cutting and irrigation, remove litter and domestic garbage under the forest, keep the forest tidy, and give different managerial measures timely according to different urban forest types to improve its landscape quality.