In order to ensure the effective analysis and reconstruction of forests, it is key to ensure the quantitative description of their spatial structure. In this paper, a distance model for the optimal stand spatial structure based on weighted Voronoi diagrams is proposed. In particular, we provide a novel methodological model for the comprehensive evaluation of the spatial structure of forest stands in natural mixed conifer-broadleaved forests and the formulation of management decision plans. The applicability of the rank evaluation and the optimal solution distance model are compared and assessed for different standard sample plots of natural mixed conifer-broadleaved forests. The effect of crown width on the spatial structure unit of the trees is observed to be higher than that of the diameter at breast height. Moreover, the influence of crown length is greater than that of tree height. There are nine possible spatial structure units determined by the weighted Voronoi diagram for the number of neighboring trees in the central tree, with an average intersection of neighboring crowns reaching 80%. The rank rating of natural forest sample plots is correlated with the optimal solution distance model, and their results are generally consistent for natural forests. However, the rank rating is not able to provide a quantitative assessment. The optimal solution distance model is observed to be more comprehensive than traditional methods for the evaluation of the spatial structure of forest stands. It can effectively reflect the trends in realistic stand spatial structure factors close to or far from the ideal structure point, and accurately assesses the forest spatial structure. The proposed optimal solution distance model improves the integrated evaluation of the spatial structure of forest stands and provides solid theoretical and technical support for sustainable forest management.

Thinning is an important way to adjust and optimize the spatial structure of forests. The study of its impacts support a better understanding of the succession process of secondary forests after interference. To study the changes in forest spatial structure under different thinning intensities and stand densities, we considered five thinning intensities including unthinned (0%), low (3.4%, 6.2%, 12.5%), medium (16.8%, 20.9%, 25.5%), high (34.4%, 40.0%, 47.9%), and extra-high (50.6%, 59.9%, 67.3%) intensity. In addition, three different stand densities for each degree of thinning intensity. The results showed that the most horizontal distribution patterns after thinning were uniform distribution and near-uniform random distribution. Most of the trees were not mixed while several were mixed to an above medium degree. The effect on dominance of thinning was not significant and the overall plots were in the middle level. The tree density was in the sparse status. Competitive pressure on the reference tree was reduced. Thinning intensity and stand density affected stand spatial structure to different degrees. There were no obvious pattern under different thinning intensities and it was optimal at approximately 1600 trees/ha. As thinning intensity increased, the impact tended to decrease first and then increase under certain stand density. The improvement was greatest when thinning intensity was low. By analyzing the stand’s spatial structure after thinning, the unreasonableness of the stand’s spatial structure can be found, which provides the basis for optimizing management measures. We used the AHP-entropy to weigh the importance of each spatial structure parameter and we proposed a comprehensive distance evaluation index based on the optimal value obtained in order to perform a comprehensive evaluation of a forest’s spatial structure.

Long-term predictions of forest dynamics, including forecasts of tree growth and mortality, are central to sustainable forest-management planning. Although often difficult to evaluate, tree mortality rates under different abiotic and biotic conditions are vital in defining the long-term dynamics of forest ecosystems. In this study, we have modeled tree mortality rates using conditional inference trees (CTREE) and multi-year permanent sample plot data sourced from an inventory with coverage of New Brunswick (NB), Canada. The final CTREE mortality model was based on four tree- and three stand-level terms together with two climatic terms. The correlation coefficient (R²) between observed and predicted mortality rates was 0.67. High cumulative annual growing degree-days (GDD) was found to lead to increased mortality in 18 tree species, including Betula papyrifera, Picea mariana, Acer saccharum, and Larix laricina. In another ten species, including Abies balsamea, Tsuga canadensis, Fraxinus americana, and Fagus grandifolia, mortality rates tended to be higher in areas with high incident solar radiation. High amounts of precipitation in NB’s humid maritime climate were also found to contribute to heightened tree mortality. The relationship between high GDD, solar radiation, and high mortality rates was particularly strong when precipitation was also low. This would suggest that although excessive soil water can contribute to heightened tree mortality by reducing the supply of air to the roots, occasional drought in NB can also contribute to increased mortality events. These results would have significant implications when considered alongside regional climate projections which generally entail both components of warming and increased precipitation.

Forest degradation, driven by human and natural factors, diminishes ecological functions and carbon storage. Understanding the complex dynamics of soil carbon pools is crucial for the global carbon cycle, although these dynamics are poorly understood. This study examines how different thinning intensities influence seasonal soil carbon cycling in degraded forests. ANOVA revealed significant differences in soil properties across treatments (p < 0.05). Redundancy analysis and random forest analyses were used to explore relationships among thinning intensities, soil properties, and carbon sequestration. Thinning significantly altered soil attributes, as revealed by field experiments and data analysis. Moderate thinning (20% intensity) significantly enhanced litter retention and soil nutrient levels year-round (p < 0.05). Seasonal variations affected soil carbon dynamics and lower thinning intensities improved carbon sequestration in spring and summer. Conversely, higher thinning intensities led to carbon loss in autumn and winter. Litter carbon, fine root carbon, and correction factor significantly respond to thinning intensities year-round as examined through redundancy analysis and random forest analyses. Findings indicate moderate thinning effectively enhances soil carbon sequestration in degraded forests. Strategically planned thinning could aid climate change mitigation by boosting forest soil carbon storage, influencing forest management and conservation.

To explore how to respond to seasonal freeze–thaw cycles on forest ecosystems in the context of climate change through thinning, we assessed the potential impact of thinning intensity on carbon cycle dynamics. By varying the number of temperature cycles, the effects of various thinning intensities in four seasons. The rate of mass, litter organic carbon, and soil organic carbon (SOC) loss in response to temperature variations was examined in two degrees of decomposition. The unfrozen season had the highest decomposition rate of litter, followed by the frozen season. Semi-decomposed litter had a higher decomposition rate than undecomposed litter. The decomposition rate of litter was the highest when the thinning intensity was 10%, while the litter and SOC were low. Forest litter had a good carbon sequestration impact in the unfrozen and freeze–thaw seasons, while the converse was confirmed in the frozen and thaw seasons. The best carbon sequestration impact was identified in litter, and soil layers under a 20–25% thinning intensity, and the influence of undecomposed litter on SOC was more noticeable than that of semi-decomposed litter. Both litter and soil can store carbon: however, carbon is transported from undecomposed litter to semi-decomposed litter and to the soil over time. In summary, the best thinning intensity being 20–25%.