Coupling relationship between stand growth and impacting factors based on structural equation model

In order to find out the relationship between stand growth and impacting factors, the structural equation model of the site condition-stand structure-tree diversity-stand growth was built taking secondary multiple species forest beside Ashi River , Heilongjiang of northeastern China as example. The results showed that among three factors of site condition, stand structure and tree diversity, site condition was the most important factor affecting three hardwood ( Fraxinus mandshurica, Phellodendron amurense and Juglans mandshurica) volume, total path coefficient was 0.541 and direct path coefficient was 0.597. Structure was the second important factor, total path coefficient was 0.402 and direct path coefficient was 0.451. Tree diversity had negative impact on three hardwood volume, direct path coefficient was -0.190. Among three factors of site condition, stand structure and tree diversity, stand structure was the most important factor affecting stand volume, total path coefficient was 0.776 and direct path coefficient was 0.720. Site condition was the second important factor, total path coefficient was 0.394 and direct path coefficient was 0.153. Total path coefficients and indirect path coefficients of tree diversity and three hardwood volume to stand volume was 0.111, 0.060 and -0.011, 0, respectively. Site condition and stand structure had a positive impact on three hardwood volume, but their positive impact on tree diversity could produce a negative impact on three hardwood volume. Site condition had a positive impact on stand growth, most parts of which was formed indirectly by improving forest structure and tree diversity. Stand structure had a positive impact on stand growth. Tree diversity had a negative impact on three hardwood volume, which had a small indirect impact on stand growth.