The Natural Regeneration Count Model of Spruce-fir Mixed Stand Based on Generalized Mixed Effect Models

As the best method of forest restoration, natural regeneration has a profound impact on the structure and biodiversity of future forest. The model of natural regeneration can simulate reality and future situation of natural regeneration and provide accurate forest plan for forest managers. The 12 spruce-fir coniferous-broad-leaved mixed forest plots in Wangqing Forestry Bureau of Jilin Province were selected an example, the natural regeneration model was constructed. The Poisson and negative binomial distribution were selected, and the plot’s random effect was taken into account. The findings indicated that different stand factors lead to differences in various tree species. The regeneration number of Betula platyphylla was negatively correlated with stand basal area per hectare and stand mean square diameter; the regeneration number of Pinus koraiensis and Fraxinus mandschurica were not affected by stand factor, and the regeneration number was stochastic; the regeneration number of Abies nephrolepis was negatively correlated with stand basal area per hectare; the regeneration number of Acermono and Picea jezoensis var. micrisperma were negatively correlated with stand mean square diameter. After considering the plot’s random intercept effect, the simulation effect of the model is significantly improved. In construction of natural regeneration model, stand density is a very important factor. If we want to artificially promote natural regeneration, we should take scientific and reasonable management measures to ensure reasonable stand density. In addition, the difference among plots can’t be ignored, so it is necessary to use the mixed effect models method to reduce the prediction error.