Effects of thinning intensity on spatial structure of multi-species temperate forest at Jiaohe in Jilin Province, northeastern China

Studying on the differences of spatial structure among different thinning intensity conditions has guiding significance for forest management. Four permanent plots were established in the secondary coniferous and broadleaved mixed forest in Jiaohe, Jilin Province of northeastern China, representing 4 different thinning intensity plots of 0% (control, CK), 14.3% (light treatment, LT), 29.4% (moderate treatment, MT) and 50.4% (high treatment, HT), with 1 ha area of each plot. Three years after thinning, we analyzed the neighborhood pattern, neighborhood comparison, mingling degree and crowding degree of forest, as well as the spatial structure of 5 main tree species, Ulmus davidiana var. japonica, Pinus koraiensis, Acer mono, Fraxinus mandshurica and Tilia amurensis. Our results showed that the horizontal distribution pattern of the whole stand after LT treatment was more reasonable, with higher mingling degree and more stable stand structure than the CK. The thinning has less impact on neighborhood comparison. The crowding degree decreased gradually with the increase of cutting intensity and sparse individual has an opposite result. In terms of the main tree species, the response to logging disturbance was different among species. Although logging had a significant effect on the horizontal distribution pattern of all the five species, the conclusion cannot be used to determine the intensity of logging. In addition, for the neighborhood comparison and mingling degree of these species, LT treatment was more beneficial to Ulmus davidiana var. japonica, Fraxins mandshurica and Tilia amurensis, while ML treatment was better for Pinus koraiensis and Acer mono. Furthermore, the crowding degree of all species decreased with the increase of logging intensity. In conclusion, we find that forest logging has a significant effect on the spatial structure of stands as well as the principal tree species in a short time, and 15% logging intensity is best for formatting a more reasonable stand space structure. We can also consider the forest management needs and increase logging intensity for individual species, but more than 20% logging intensity should not be advocated.