Study on Forest Ecosystem Health Evaluation of Secondary Forest in Greater Hinggan Mountains

The community structure, soil status, stand spatial structure, resistance index and water conservation status of the Genhe forest area in the Greater Khingan Mountains and the secondary forest area in the Mohe forest area of Heilongjiang Province were investigated and analyzed in 30 plots. The evaluation index system was established by selecting 16 evaluation indexes, such as mean diameter at breast height, storage volume per unit area, total nitrogen, angular scale, fire hazard grade, pest grade and litter water capacity. The forest ecosystem health status of secondary forests in the Greater Hinggan Mountains was evaluated by using the comprehensive index of forest health evaluation, and the weight of each index was determined by using the analytic hierarchy process. The forest health index of the study area was divided into five levels, namely, high quality, healthy, sub-healthy, medium healthy and unhealthy, combined with the survey data of the ground plots. The results showed that 13. 33% of the plots in the study area were in the "sub-health" state, and the 26 plots of "healthy" grade accounted for 86.67% of the total, and there were no healthy, medium healthy and high-quality forests. From the perspective of forest type, the forest health status of broad-leaved secondary forest is better and should be maintained to promote its transformation to "high quality" state. The health status of mixed forest is low, and proper afforestation, thinning, pruning and fertilization need to strengthen forest fire prevention to ensure the safety of forest resources. In different age groups, the young forest has the highest health status, and the mature forest has the highest sub-health status. Among them, 91.18% were healthy and 8 82% were sub-healthy. The proportion of healthy and sub-healthy forests was 87.30% and 12.70% respectively. Nearly mature forest health accounted for 74.96%, sub-health accounted for 25.04%; 33.33% of mature forests were healthy, 66.67% were sub-healthy, 66.67% were over-mature forests were healthy.