Abstract:

By using the model and ANOVA analysis,the result proved that the varieties of forests damaged degree with planted ages were in accord with logistic model,after improvement of secondary forests on loess plateau.In woodland by using over-all felling,the forests damaged degree was most,using reforestation,the forests damaged degree was lowest.The ages of Chinese pine,Chinese arborvitae and Silver chain damaged by zokors were ordinal planted 11 years,9 years and 6 years.On Chinese pine by planted from 2th year to 6th year,Chinese arborvitae from first year to 4th year and Silver chain from first year to 2 year,the forests damaged degree was the most.The damaged degree,individual zokor did harm to Chinese pine and Silver chain,primarily depended on planted ages,not depended on improvement pattern and zokor density.The damaged degree of Chinese arborvitae not only depended on planted ages,but also depended on improvement pattern and zokor density.The planted ages and the harm degree of individual zokor were key factors to influence forest damaged mortality,the zokor density and the improvement pattern were main factors.

Key words: Loess plateau, improvement of secondary forests, zokor, regularity of outbreak, forests damaged degree