Site quality evaluation of broadleaved mixed forest in Xiaoxing’an Mountains of northeastern China based on volume potential productivity

Objective Site quality evaluation is an important foundation for forest management planning and decision-making. This article introduces the potential productivity of stand volume by establishing a stand volume growth model to evaluate the site quality of broadleaved mixed forest in the Xiaoxing’an Mountains of northeastern China, providing a scientific basis for predicting forest growth and harvest, forest management planning, and sustainable management in the region.

Method Using data from the two consecutive inventory periods of the Xiaoxing’an Mountains broadleaved mixed forest in Heilongjiang Province from 2010 to 2015, a model for average tree height and volume growth of the forest stand was established. The site levels were classified, and the potential productivity of each site level for broadleaved mixed forest stands was calculated. We evaluated the actual condition and potential improvement space of the current aged forest stand based on the difference between actual productivity of the forest stand and its potential productivity for accumulation.

Result (1) The fitting effect of volume growth model of broadleaved mixed forest in the Xiaoxing’an Mountains was good, and the range of potential productivity at the baseline age of forest was between 3.87−6.10 m³/（ha·year）. The average improvement space of broadleaved mixed forest stands ranged from 50.78% to 62.97%, and gradually increased with decrease of site level. (2) The potential productivity of broadleaved mixed forest in Xiaoxing’an Mountains gradually decreased with the increase of stand age, and eventually tended to flatten out. The difference between the realized productivity and the potential productivity gradually decreased with the increase of stand age; (3) The potential productivity and realized productivity of each age group showed a decreasing trend with the decrease of site grade. Forests with moderate site quality accounted for 77.24% of the total sample size, and the potential productivity of each site grade was always greater than the realized productivity.

Conclusion The potential productivity of stand volume can serve as an indicator for site quality evaluation of broadleaved mixed forest in the Xiaoxing’an Mountains. For the broadleaved mixed forest in Xiaoxing’an Mountains, stands at the initial stage of development within various site classes exhibit greater potential productivity of stand volume compared with those nearing maturity, and the potential for improvement in stand productivity is also larger. As site quality decreases, the scope for stand improvement gradually expands. Therefore, differentiated management measures should be adopted based on the stand development stage and site conditions, with emphasis on stands of medium site quality. Priority should be given to the tending of middle-aged and young forests to enhance the overall productivity of the stands.