Search

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]

The epidemiology and severity of ash dieback (ADB), the disease caused by the ascomycete fungus Hymenoscyphus fraxineus, has been linked to a variety of site conditions; however, there has been a lack of analysis at an individual tree scale.Symptoms of ADB were scored on ca. 400 trees of Fraxinus excelsior (ash) in permanent sample plots during two successive years in a UK natural woodland reserve. Using comprehensive plot records maintained since 1945, and detailed spatial records updated since 1977, we assembled an array of potential explanatory variables, including site environment factors, ash tree density, previous and present tree condition and near neighbourhood summary statistics (NNSS), such as species mingling and size dominance. Their impact on the severity of ADB of focal ash trees was tested with generalised linear mixed effects models (GLMM).The severity of ADB was much greater in the lower slope parts of the site with moister soils and least in a managed area subject to tree thinning in the previous 35 years. Severity of ADB had a negative association with focal ash tree prior relative growth rate over a period of a decade immediately before the disease was detected at the site. Greater ADB severity was also significantly associated with smaller diameter at breast height of ash trees. Additionally, ADB was significantly positively associated with a greater proportion of heterospecific trees amongst the six nearest neighbours of the focal tree.Synthesis. The relationship of the severity of ADB disease with site environment, tree condition and neighbourhood is complex but nevertheless important in the progression of the disease. The findings suggest some silvicultural interventions, such as thinning to increase the vigour of retained ash trees, might reduce the impact of ADB. [ABSTRACT FROM AUTHOR]

In this study, the nearest neighbor indices and diameter distribution in Pistacia atlantica Desf. and Prunus arabica (Olivier) Meikle stands in Iran were studied. To conduct this study, a 100 m × 100 m inventory was used in two 1-hectare plots in November and December 2021. The study area was Kare-Bass habitat, which is located between the west and the center of Iran. According to the conditions of species in this habitat, Root Collar Diameter (RCD) was used for measurements. The collected data on RCD and nearest neighbor indices were analyzed using Crancod software. The results showed that the structure of the forest is noticeably disturbed. Human intervention, livestock grazing and fires are the main reasons for this disturbance. The results show that the mingling index is 0.45 in Plot 1 and 0.65 in Plot 2. The Structural Diversity Index (SI) is 0.48 in the first Plot and 0.59 in the second Plot. Although the SI status of all stands in both Plots is weak or moderate, the SI of stands in the second Plot is better. It seems that more species diversity in the second Plot is the main reason for this increase in SI. The conclusion of this article is that the structure of the stands depends on socio-economic aspects and human interventions as well as species diversity. [ABSTRACT FROM AUTHOR]

• Key message: We identified the significant spatial relationships between tree species mingling and size inequality in various species-rich natural forests in South China. Forest communities with low species mingling, or segregation of heterospecific trees, exhibited increased segregation of trees with dissimilar sizes. Large trees were more likely to be associated with high species mingling, and variation in neighboring tree sizes would also increase neighborhood species diversity. • Context: Numerous hypotheses such as Janzen–Connell and herd immunity effects have been proposed to explain the coexistence of diverse species in plant communities. However, these mechanisms for maintaining diversity have been studied primarily through the lens of species diversity, whereas tree size diversity or relationships between size and species diversity resulting from local interactions have rarely been investigated. • Aims: We aimed to identify relationships between spatial species mingling and tree size inequality using extensive plot data from species-rich forest ecosystems. • Methods: We applied neighborhood-based methods and explored relationships between spatial species mingling and size inequality indices in 22 large forest plots (30 ha in total) in subtropical and tropical China. • Results: Forest communities with low species mingling, or segregation of heterospecific trees, exhibited increased segregation of trees with dissimilar sizes. In most plots, large trees (e.g., dbh > 30 cm) were extensively associated with high species mingling, and individual-tree neighborhood species and size diversity were closely correlated. • Conclusion: Our findings suggest that both the spatial patterns of conspecific dispersal and neighborhood interactions play an important role in determining the spatial patterns of tree size and species diversity and eventually in shaping the structure of forest communities. [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]

• Spatial species mingling was extended to better describe species-rich forest ecosystems. • We demonstrated the value of the new species segregation function through cluster analysis. • Evidence of improvement was obtained from applying the innovative spatial reconstruction method. • The new characteristic is robust and effective in monitoring species-rich plant communities. Species rich woodland communities play an important role in ecosystem functioning at local, regional and global scale. With ongoing climate change and an ever-increasing human world population we certainly cannot take high species diversity for granted. In fact species diversity is a precious and threatened commodity that requires monitoring and conservation. China has a wealth of natural woodlands with high species diversity that stretch over several climate zones and even in the temperate zone tree diversity is considerable in this country. For monitoring species diversity it is crucial to rely on meaningful summary characteristics that offer sufficient information to make correct decisions in conservation. We analysed large, fully mapped plots from ten species-rich temperate forest sites with the new species segregation function as a significantly more meaningful extension of the traditional spatial species mingling index. The new characteristic is a function of distance and we defined a number of auxiliary measures describing its shape for a more effective analysis of spatial species diversity. We could show that these auxiliary characteristics helped to classify species-rich forests as part of a cluster analysis, which supports the view that the species segregation function provides high quality information. We also successfully applied non-parametric modelling through spatial reconstruction for testing the contribution of the species segregation function to a synthesis of observed spatial species diversity patterns. The results demonstrated that the new characteristic described the complex diversity patterns well and has the potential of being a robust and effective characteristic in monitoring species-rich woodland communities. [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]

The application of gap dynamics theory appears to be a promising option for tropical forest management and conservation. In the present study of a tree species-rich and old-growth Ecuadorian Neotropical forest, we assessed the spatial distribution of gaps and gap size in relation to: i) tree number at the gap edge, ii) number of tree species at the gap edge, iii) number of tree species per stem at the gap edge, iv) species similarity, v) species evenness at the gap edge, vi) size differentiation at the gap edge, vii) gap isolation and viii) species mingling at the gap edge. Our results demonstrated that the spatial distribution of gaps was random. Various gap attributes were strongly associated with gap size. The number of tree species per stem at the gap edge was negatively correlated to the gap size. Gap sizes up to 50 m2 were mostly sufficient to generate tree species-rich forest stands. Assuming that our results were representative for an old-growth neotropical rainforest in Ecuador, our study remarks the following management recommendations: 1) Rainforests have a very complex spatial and diversity structure and logging activities should preferably be omitted because of adverse effects. 2) If logging is inevitable, this should mimic a random choice of trees and tree species, to prevent special selection of tree dimension and species; and a random distribution of trees to be logged, to produce gaps smaller than 50 m2 and never larger than 400 m2. Additionally, we suggest cutting not more than 5 % of the tree biomass per 10-20 years period, to preclude stronger alterations of ecosystem processes, and the reduction of existing dead wood from the ecosystem. Rev. Biol. Trop. 66(1): 149-163. Epub 2018 March 01. [ABSTRACT FROM AUTHOR]

Neighborhood-based indices such as mingling index and diameter differentiation are a set of diversity measures that are based on the relationship between a reference tree and a certain number of nearest neighbors (i.e., trees to which it has the lowest horizontal distance). Using stem-mapped data from eight headwater sites, we compared the relative bias and relative root mean square error (relative to the true mean of each site) of several different methods of choosing reference trees for calculation of diameter differentiation () and species mingling () index. Indices were defined using two, three, and four neighbors and methods for selection of the reference tree were random selection of a tree in a fixed-radius plot (FI), random selection of a tree in a variable-radius plot (VA), azimuth selection method (AZ), and nearest tree selection (NT). In general, the relative bias was lower than ±2.5% for and lower than ±10% for regardless of the method. The FI method consistently had the lowest relative bias and relative root mean squared error. The NT and AZ methods were second in terms of relative root mean squared error for and , respectively. Simplicity of these two methods might outweigh their slightly worse performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thinning treatments were applied to adjust stand structural. • A tree-level tool for optimizing stand spatial structure was developed. • The optimal thinning intensities varied from 22.2% to 26.1% of standing volume. • Mingling and crowdedness have the highest priority in structure-based forest management. Over the past fifty years, societies have placed increasing demands on forests, and their use has shifted gradually from wood production to the diversified benefits and functions of ecosystem services. The effects of neighborhood-based structural characteristics on regulating growth and promoting sustainability have therefore drawn much attention. However, direction for managing natural mixed forests using neighborhood-based indexes are still not clear. Thus, a tree-level harvest planning tool that considers four neighborhood-based structural indexes (species mingling, diametric differentiation, horizontal spatial pattern and crowdedness of trees) while concurrently recognizing other operational constraints, was developed using simulated annealing algorithm. The approach was applied to four 1-ha mapped stands in northeast China, namely a natural larch forest (NLF), a natural birch forest (NBF), a natural secondary forest (SEF), and a Korean pine broad-leaved forest (KBF). The results indicated that the tree-level harvest optimization tool improved the objective function values by approximately 78.33% of NLF, and 134.96% of NBF, and 156.70% of SEF and 252.95%, respectively. The optimal harvest intensities for partial cutting activities varied from 22.16% (SEF) to 26.07% (NBF) of the standing volume. In evaluating the four neighborhood-based structural indexes, both species mingling and crowdedness have the highest priority to be adjusted in structure-based forest management. Our results demonstrated that that the commonly used neighborhood-based structural indexes could be employed to control the spatial layout of potential harvest trees, in turn may be conducive to regulate the growth and stability of forests. [ABSTRACT FROM AUTHOR]

The data paper refers to the research article "Assessment of spatial stand structure of hemiboreal conifer dominated forests according to different levels of naturalness" [1]. Forest ecosystem structure was quantified by using structural indices based on the nearest-neighborhood approach for individual trees. Species mingling, deadwood mingling, deadwood distribution, diameter differentiation and the uniform angle indices characterize the patterns of the complexity and diversity of forest ecosystems, including the arrangement of tree dimensions, species and deadwood as well as tree positioning regularities. The data is collected all over Estonia from the Estonian Network of Forest Research Plots; altogether 212 sample plots were used in this study. The plots of the Estonian Network of Forest Research Plots are re-measured in nature with an interval of five years. Forests were classified by their naturalness level as managed forests, recovering forests and natural forests. The information in this paper can be used by forest inventories for developing the methods of ecosystem naturalness assessment as well as for analysing naturalness, stand structures and tree patterns in hemiboreal forest ecosystems., (© 2020 The Author(s).)