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Forest biomass has become a viable alternative energy source for replacing fossil fuels, particularly after the European Union acknowledged its sustainability status. To reach zero net greenhouse gas emissions by 2045 in Sweden, new efficient methods of biomass extraction, such as geometrical biomass thinnings, are being explored and tested. These machine-based methods involve the extraction of above-ground biomass in narrow, 1–2 m-wide strips between extraction racks. While evidence-based optimization of biomass extraction mostly focuses on time- and cost-efficiency and on stand growth, criteria such as tree diversity are often overlooked. However, with ongoing climate change, tree diversity is crucial to strengthening the resilience and productivity of future forests, which also enhance the provision of ecosystem services and overall biological diversity. Therefore, we studied the effects of different biomass thinning strategies on spatial tree diversity in southern Sweden using nearest-neighbour summary statistics. We found scientific evidence that different geometrical designs of biomass thinning, especially in 1 or 2 m-wide strips, resulted in higher spatial tree diversity compared to conventional biomass thinning. Hence, in mixed conifer-broadleaved forests, biomass thinning in 1 or 2 m-wide strips is recommended for maintaining spatial tree diversity. [ABSTRACT FROM AUTHOR]

Structural indices are oftenproposedas guidingmeasures for increasing structuralheterogeneity. However, few studies have examined the association between such indices and conventional stand attributes. The primary objectives of this studywere to evaluate changes in structural heterogeneity and tree species diversity at different plot sizes and to quantify the relationships between conventional stand attributes (mean tree diameter, absolute tree density, basal area, species proportion) and structural indices in a mixed old-growth forest in Southeast Europe. Paired tests were used to identify significant changes in structural heterogeneity with increased plot area, while the relationships between stand attributes and analyzed indices (Gini, diameter differentiation, species mingling, and Shannon’s index) were evaluated with Pearson’s correlations. The index values of Gini, diameter differentiation, and tree speciesminglingwere rather stablewith the increase of plot size, whereas tree species diversity increased significantlywith the increase of plot area from200m² to 1500m². Themeasures of tree speciesmingling and tree species diversity were strongly associated with each other, while their association with diameter variability was weak to moderately strong. Tree species mingling index was strongly associated with the changes in tree species proportions. However, conventional stand attributes were generally not strongly correlated with the examined indices. For restoring and maintaining old-growth characteristics, forest managers may use structural indices to increase small-scale structural heterogeneity, tree species mingling, and diversity, but only as an additional set of measures, not as surrogates for conventional stand attributes. [ABSTRACT FROM AUTHOR]

Forest structure analysis is important for understanding the properties and development of a forest community, and its outcomes can be influenced by how trees are measured in sampled plots. Although there is a general consensus on the height at which tree diameter should be measured [1.3 m: diameter at breast height (DBH)], the minimum measured diameter (MMD) often varies in different studies. In this study, we assumed that the outcomes of forest structure analysis can be influenced by MMD and, to this end, we applied g(r) function and stand spatial structural parameters (SSSPs) to investigate how different MMDs affect forest spatial structure analysis in two pine-oak mixed forests (30 and 57 years old) in southwest China and one old-growth oak forest (>120 years old) from northwest China. Our results showed that 1) MMD was closely related to the distribution patterns of forest trees. Tree distribution patterns at each observational scale (r = 0–20 m) tended to become random as the MMD increased. The older the community, the earlier this random distribution pattern appeared. 2) As the MMD increased, neighboring trees became more regularly distributed around a reference tree. In most cases, however, nearest neighbors of a reference tree were randomly distributed. 3) Tree species mingling decreased with increasing diameter, but it decreased slowly in older forests. 4) No correlations can be found between individual tree size differentiation and MMD. We recommend that comparisons of spatial structures between communities would be more effective if using a unified MMD criterion. [ABSTRACT FROM AUTHOR]