Seedling and sapling spatial patterns are important in community regeneration, and understanding the natural regeneration mechanisms of tree species in relation to spatial patterns will help improve forest management and community restoration efficiency. Based on data from three fixed plots established in birch forests (BF), coniferous and broadleaved mixed forests (CBMF) and coniferous mixed forests (CMF) in the central Greater Khingan Mountains in Heilongjiang Province, China, in 2017, we used the univariate and bivariate O-ring functions of the point pattern analysis method to evaluate the spatial patterns and associations of the main tree species in these three forest types at different development stages and identified the community successional stages according to the interspecific associations between dominant tree species and other tree species. The results showed that Betula platyphylla and Larix gmelinii in BF exhibited identical spatial distribution patterns and had a tendency to transition from an aggregated to a random distribution from saplings to adult trees, whereas every tree type in CBMF generally showed a random distribution. Adult trees of the main tree species in CMF, i.e., L. gmelinii and Picea koraiensis, mainly showed a random distribution, but P. koraiensis at other size classes generally showed an aggregated distribution. The intraspecific associations of the main tree species in BF and CMF at different development stages were constrained by the spatial scale within a given scope, while those in CBMF at different development stages were not significantly constrained by spatial scale. The results also show that the density of the three forest types was affected by the distance between the individuals of the various tree classes and adult trees, with different levels of influence. We analyzed the interspecific associations between dominant tree species and other tree species and then assessed community succession progress and found that the BF and CMF exhibited medium-term community succession, while the CBMF was in the primary stage. Our results further show that the spatial distribution patterns of the tree species in the small-diameter classes were jointly affected by adjacent habitats and diffusional limitations and that scale dependence existed in the intraspecific and interspecific associations. The analysis of the natural regeneration of spatial distribution and interspecific associations represents an efficient way to explore the stability of forest communities and dynamic changes in interspecific relationships during succession. The study results thus provide a theoretical basis for developing rational forest management measures.

Forest carbon sequestration has become an important ecological service for human society. Given the widespread attention paid to global climate change over the last few decades, a potential need has arisen to develop forest management plans that integrate carbon management and other spatial and non-spatial goals. The objective of this research was to develop a spatial forest planning process by which one could assess either a carbon stocks objective, a timber production objective, or a spatial objective related to the arrangement of forest management activities. This process was used to evaluate the maximization of (1) volume scheduled for harvest; (2) carbon stocks; and (3) spatial aggregation of the management activities through a utility function where all are equally weighted objectives. The process was employed for the development of 30-year plans for a forested landscape in northeast China that was approximately 120,000 ha in size. In addition, the sensitivity of the results with respect to four initial forest age structures was tested. Constraints mainly included those related to the need for an even flow of scheduled harvest volume and to the need to adhere to a maximum harvest opening size. The proposed scheduling process employed a simulated annealing algorithm to schedule harvests in an attempt to produce a high value of the utility function. Results showed that carbon stocks in the case study forests could significantly increase in the next 30 years under the proposed harvesting plans. Of the case study forest landscapes, the values of both the utility function and the computing time required were significantly different between different initial forest age structures (p < 0.05), i.e., the older forest landscape obtained the highest average solution value (0.6594 ± 0.0013) with the fastest processing speed (2.45 min per solution). For a fixed harvest level, the average carbon density (tons per hectare) at the end of planning horizon also increased by 4.48 ± 9.61 t/ha, 8.73 ± 10.85 t/ha, 2.99 ± 9.19 t/ha and 1.03 ± 9.77 t/ha when maximizing the total utility functions for the actual, young, normal and older forests, respectively, when compared those at their initial conditions. This heuristic spatial forest planning process can allow forest managers to examine a number of different management activities, for both timber production and carbon stocks, prior to selecting a preferred alternative.

The fine-scale spatial patterns of trees and their interactions are of paramount importance for controlling the structure and function of forest ecosystems; however, few management techniques can be employed to adjust the structural characteristics of uneven-aged mixed forests. This research provides an accurate, efficient, and impersonal comprehensive thinning index (P-index) for selecting candidate harvesting trees; the index was proposed by weighting the commonly used quantitative indices with respect to stand fine-scale structures, competition status, tree vigor, and tree stability. The applications of the proposed P-index in evaluating and simulating the process of thinning operations were examined using four 1-ha mapped plots with different forest types, namely, natural secondary forest, natural pine-broadleaved mixed forest, natural larch-birch mixed forest, and natural oak forest, which were widely distributed across the Heilongjiang Province in Northeast China. The results indicated that the proposed P-index could effectively affect the structural differentiations between different forest types and alternative thinning intensities. The marginal benefits of alternative thinning intensities on the integrated forest structure indicated that removing 10% of the trees from the plots might be the optimal thinning intensity from the perspective of optimizing stand structure, in which the P-index values could be increased by approximately 5%–11% for the four tested plots. The main conclusion from this paper was that the proposed P-index could be used as a quantitative tool to manage uneven-aged mixed forests.

Introduction: The stability of forest productivity is an important management goal in order to sustain ecosystem services for an expanding human population and in the face of global climate change. Evidence from theoretical, observational, and experimental studies has demonstrated that higher biodiversity promotes stability of forest productivity. However, the majority of these studies have focused solely on tree diversity and have neglected the potentially important role of understory plant and soil biodiversity.Methods: In this study, we explain the effect of tree, understory woody and herbaceous plant, and soil biota (fauna, fungi, and bacteria) species diversity on forest productivity and its stability over time (2000–2020) across an area of Northeast China covering 145 million hectares. We explore the eight stand structure variables for stability of forest productivity and the relationship between productivity stability and tree, understory plant, and soil biota species diversity.Results: Our results show no significant, direct impact of understory plant, soil fungi, and bacteria species diversity on the stability of the forest ecosystem. Tree species diversity indirectly affects productivity stability by directly influencing stand structure, whereas soil fauna species diversity indirectly influences stability through its relationship with tree species diversity. Stand structure is more important than tree and soil fauna species diversity for forest productivity stability. Specifically, increasing crown height (CH) from its minimum to maximum value leads to a substantial gain of 20.394 in forest productivity stability. In contrast, raising tree species diversity (α-Tree) and soil fauna species diversity (α-Fauna) from their minimum to maximum values results in a modest reduction of only 0.399 and 0.231 in forest productivity stability, respectively.Discussion: To increase the stability of forest productivity in response to climate change, we should adjust the stand structure more in the process of management rather than just considering biodiversity. Overall, this study highlights the ecological risks associated with large-scale biotic homogenization under future climate change and management practices.