Effects of forest gaps on spatial distribution and growth of Phellodendron amurense saplings

Objective Forest gaps have an important impact on the regeneration of understory saplings by increasing the complexity of stand spatial structure and the heterogeneity of understory habitat. Phellodendron amurense is a national key protected wild plant in China. Analysing the correlation between growth status as well as spatial distribution of understory Ph. amurense saplings and the spatial structure of forest gaps is helpful to explore adaptability of Ph. amurense to understory habitat, which is of great significance to promote the regeneration of Ph. amurense population.

Method Ph. amurense sapling data were collected in 2021, which were planted under the natural forest of Baihuashan Nature Reserve in 2014, and we also obtained the point cloud data of forest gaps by backpack LiDAR. We assessed the effects of spatial structure of forest gaps on the spatial distribution patterns and the growth status of Ph. amurense saplings using spatial point pattern analysis, habitat association analysis and ANOVA.

Result (1) Under natural conditions, the survival rate of Ph. amurense saplings after 7 years was 19.25%. All of the saplings showed an aggregated distribution under the condition of completely excluding the dispersal limitation. (2) The heterogeneity of understory habitat caused by the forest gaps was main reason for the formation of spatial distribution patterns of Ph. amurense saplings. The distribution of Ph. amurense saplings had a significant positive association with the distribution area of the canopy edge, while it had a significant negative association with the canopy area. (3) The basal diameter of Ph. amurense saplings was significantly higher at the edge of forest gap than in the canopy area and the center of gap (P<0.01), and there was no significant difference between the canopy area and the center of gap. The crown width and height of Ph. amurense saplings showed a significant gradient change (P<0.05), with the edge of forest gap> crown area> the center of forest gap.

Conclusion The results show that the spatial distribution pattern and growth status of Ph. amurense saplings are significantly affected by forest gaps. Ph. amurense saplings prefer the habitat conditions under the canopy edge, and may be inhibited by the forest gaps and forest canopy.