Unbalanced forest displacement across the coastal urban groups of eastern China in recent decades.

The Jing-Jin-Ji urban group (JJJug), the Yangtze River Delta urban group (YRDug) and the Pearl River Delta urban group (PRDug) are major urban groups of eastern China that play crucial roles in the economy and ecology. With rapid urbanization, demand for land for urban construction has significantly increased, causing direct and indirect losses of forests. At the same time, forest protection and restoration are being promoted in the construction of forested urban groups in response to the 13th Five-Year Plan for forestry development of China in the abovementioned regions. These inevitable contradictory demands for land may inhibit regional sustainable development. However, how forest coverage changed and its ecological impacts in recent decades have rarely been systematically evaluated. To address this issue, this paper quantitatively investigated the spatial and temporal variations in forest coverage and the evolution of landscape patterns using remote sensing data across the JJJug, the YRDug and the PRDug from 1992 to 2015. The results show that forest coverage in the JJJug first increased and then decreased, while that in the YRDug and the PRDug showed a sustained decline during the study period. In the case of land displacement, on the one hand, the three urban groups exhibited a transition from forest to farmland in the forest-farm ecotone at medium and high altitudes. On the other hand, grassland and shrubland were changed into forest mainly in the outer suburbs. Furthermore, in general, the landscape fragmentation in the urban groups significantly increased because of urban expansion. Besides, that of the JJJug exhibited an obvious spatial heterogeneity with a decline in the north while an increase in the south. Overall, unbalanced forest displacement, which could lead to a negative effect on both forest-coverage quantity and landscape quality, should be given more attention in the future development of forested urban groups.