Study on impact factors of large-diameter wood formation of Cunninghamia lanceolatain Nanling Mountains

Objective  To explore the dominant ecological environment factors and stand control factors for the formation of large-diameter wood of Cunninghamia lanceolata in Nanling Mountains, investigate their influence rule and provide a theoretical guidance for cultivation and management of large-diameter wood stands of C. lanceolata in Guangdong Province.

Method  Based on the investigation of the existing large-diameter wood stands of C. lanceolata in Nanling Mountains, the site index (SI), soil integrated fertility index (I), micro-topography index (M) and geographical index (G) were extracted and the index evaluation system was established. The relationships of large-diameter wood volume (V_l), output (O_l), proportion (N_D≥26), outturn percentage (Y_l) with each index were analyzed.

Result  There were significant positive correlations of each index of large-diameter wood with SI, M (P<0.01), the correlation coefficients were 0.37−0.44 and 0.22−0.33 respectively.V_l、O_l and N_D≥26 had significant positive correlations with I(P<0.05), the correlation coefficients were 0.24−0.39.V_l and O_l showed a gentle quadratic curve trend of slowly increasing first and then slowly decreasing with the increase of reserved density (D), the correlations were significant (P<0.05). There were no significant correlations ofG, stand age (A) with each index of large-diameter wood. The large-diameter wood output at the age of 20−30 was predicted by a quantitative model: O_l= \rme^\rm5\rm.781 + 0\rm.004\;\rmSI + 5\rm.004A^\rm - 1\rm + 0\rm.261\ln D\rm - 45\rm.151S\rmI^\rm - 1 (R=0.62, P<0.01).

Conclusion  SI, I, M and D are the dominant impact factors for growth of large-diameter wood in Nanling Mountains. It is benefitial for large-diameter wood formation when SI is above 18, the soil has higher porosity, moisture and nutrient contents, the micro-topography condition is a shady and concave slope below 35° in the lower part, and the reserved density is 1 100−1 300 plants·hm⁻².