Linking naturalness and quality improvement of monoculture plantations in urban area: A case study in Wuhan city, China

Abstract

Forest naturalness is an important indicator of forest ecosystem resilience. It demonstrates the response status of forests to disturbances in comparison to native communities. Understanding the response of forest naturalness to human-induced disturbances is critical for revealing the maintenance mechanisms of forest ecosystem resilience, particularly in urbanized environments. However, the responses of forest naturalness to anthropogenic disturbances in urban regions are still unclear. Here, we assessed the responses of forest naturalness to management practices via a case study of monoculture plantations in Wuhan, China. We developed a framework of forest naturalness assessment based on the forest characteristics of multi-storied, uneven-aged, and mixed-species forests and compared the differences in forest naturalness under various management practices based on field sampling surveys. Ten indicators were screened from species composition, stand structure, forest succession and disturbance degree to establish the naturalness assessment model of urban forests at the stand scale. Naturalness variations in Pinus massoniana plantations transformed by close-to-nature measures from 2008 to 2015 were evaluated in eight forest scenery districts of Wuhan city. The results showed that the overall naturalness of P. massoniana plantations increased from degree IV to degree III. The average of the integrated naturalness index (NI) increased from 0.271 (control stands) to 0.545 (transformed stands), and the index values of species composition, stand structure, forest succession, and disturbance degree increased by 90.91 %, 20.62 %, 495.00 % and 108.54 % compared to the control stands, respectively. The close-to-nature management increased the species richness and proportion of indigenous plants, reduced human interference and natural disturbance of urban forests, and promoted regeneration of climax and subclimax species and forest succession. However, only the Mulan scenery district attained the highest naturalness degree (I), and two forest scenery districts (Jiufeng Mountain and Songyang Mountain) attained degree II. The classification model of the forest naturalness degree can be used as a supportive decision-making tool when adopting close-to-nature measures aimed at upgrading the naturalness of P. massoniana plantations in Wuhan city.