Unravelling the mechanisms of spatial correlation between species and size diversity in forest ecosystems

With ongoing climate change at global scale we are currently losing biodiversity at an unprecedented rate. The insurance hypothesis and associated research, however, suggest that biodiversity has a major stabilising effect in ecosystems. In this situation, it is crucial to develop a better understanding of natural processes of maintaining biodiversity for employing them in conservation practice. In forest ecosystems, spatial species and size diversity are important aspects of α-diversity at woodland community and species population level. Both aspects of spatial diversity stem from complex relationships between tree interaction, disturbances and subsequent waves of colonisation by tree seedlings of various species. Using point process statistics, particularly the mark mingling function and the mark variogram, we studied the processes causing spatial correlations of species and size diversity. We found that spatial species dispersal and conspecific size distributions are key drivers of spatial species-size correlations and that a combination of simple random size-labelling techniques applied to mark variograms is instrumental in efficiently diagnosing them. If size ranges differ between species, spatial size diversity is largely a function of spatial species mingling. The existence of these correlations is crucial to conservation because they imply that conservation efforts can be rationalised: It is possible to focus on only one of the two tree diversity aspects. Interestingly, in multi-species forest ecosystems, although general species diversity is high, spatial species-size correlations can be diluted, because some of the many species populations may have similar size distributions

Diversity and production in an Afromontane Forest

Background This contribution evaluates the effect of forest structure and tree species diversity on plot productivity and individual tree growth in the unique Knysna forests in Southern Africa using mapped tree data from an observational study that has been re-measured over a period of 40 years. Methods The effects of tree species diversity and forest structure on tree growth and forest production are evaluated on three levels of resolution: a) the forest community (canopy, sub-canopy species), b) the subplots (number of trees per ha, skewness of the diameter distribution, diameter coefficient of variation) and c) the immediate neighborhood of selected reference trees (“Mingling”, “Dominance”, Aggregation” and “Size Variation”). Results An analysis of the community level identified two distinct clusters, one including dominant/canopy species with the highest growth rates and a greater variation of growth, and another cluster which includes the remaining subcanopy species which have a smaller maximum size and lower rates of growth. The area-based structure variables on plot level have a highly significant effect on total basal area growth. However, the effects of forest density and species richness on productivity were not straight forward. Maximum basal area production of about 0.75 m2/ha/year is achieved at medium levels of richness (around 20 species per ha) and medium levels of density (around 30 m2/ha basal area) using percentile regression estimates. The relative “Dominance” of a selected reference tree had a highly significant effect on individual tree growth on all investigated species. Other neighbourhood structure variables were only occasionally significant or not significant at all. Conclusion This contribution presents a new theoretical framework for analysing natural forests that includes community, plot and neighborhood variables of forest structure and diversity, and a first specific analysis of the structure and dynamics of the Knysna Afromontane Forest, based on a unique set of longterm observations. The species-area (SAR) model developed in this study, represents a new general approach that can be used to derive a common standard of tree species diversity for different plot sizes, the species richness per hectare

Thecal cell sensitivity to luteinizing hormone and insulin in polycystic ovarian syndrome

This study examined whether a defect of steroid synthesis in ovarian theca cells may lead to the development of PCOS, through contributions to excess androgen secretion. Polycystic ovarian syndrome (PCOS) is one of the leading causes of infertility worldwide affecting around 1 in 10 of women of a reproductive age. One of the fundamental abnormalities in this syndrome is the presence of hormonal irregularities, including hyperandrogenemia, hyperinsulinemia and hypersecretion of luteinizing hormone (LH). Studies suggest that insulin treatment increases progesterone and androstenedione secretion in PCOS theca cells when compared to insulin treated normal theca cells. Furthermore the augmented effects of LH and insulin have been seen to increase ovarian androgen synthesis in non-PCOS theca cultures whilst also increasing the expression of steroidogenic enzymes specific to the PI3-K pathway. Our examination of primary thecal cultures showed an increase in both the expression of the steroidogenic enzyme CYP17 and androgen secretion in PCOS theca cells under basal conditions, when compared to non-PCOS cells. This was increased significantly under treatments of LH and insulin combined. Our results support the previous reported hypothesis that a dysfunction may exist within the PI3-K pathway. Specifically, that sensitivity exists to physiological symptoms including hyperinsulinemia and hyper secretion of LH found in PCOS through co-stimulation. The impact of these findings may allow the development of a therapeutic target in PCOS

A new nearest-neighbour index for monitoring spatial size diversity: The hyperbolic tangent index

Understanding natural mechanisms of maintaining diversity is a crucial pre-requisite for successfully mitigating adverse effects of climate change such as the loss of diversity. To make such an understanding possible, both experiments and an effective, continued monitoring of diversity are required. Recently spatial measures of plant diversity have greatly contributed to the quality of diversity monitoring. In this article, we first reviewed existing principles of nearest-neighbour index construction and on this basis introduced a new spatially explicit size diversity index that is based on trigonometry, i.e. the hyberbolic tangent index. We discussed the index' mathematical reasoning by explaining its relationship to individual-based modelling and to other size diversity construction principles. Then we demonstrated the usefulness of the hyperbolic tangent index in indicating important interspecific relationships in mixed-species forest ecosystems. As part of studying the behaviour of the new size diversity construction principle we additionally found that there is a high correlation between the hyberbolic tangent index and absolute growth rates, i.e. the index is suitable both as a diversity and a competition index. Finally a detailed correlation analysis in a Norway spruce forest ecosystem with tree densities between 590 and 3800 trees per hectare made us understand that in most cases 7-10 neighbours are sufficient to consider when calculating the hyperbolic tangent index for explaining absolute growth rates. When using the index as an indicator of plant diversity only, smaller numbers of nearest neighbours may suffice. The index is straightforward to apply even, if the monitoring system used involves small circular sample plots

Random Trees Are the Cornerstones of Natural Forests

Natural forests serve as the main component of the forest ecosystem. An in-depth interpretation of tree composition and structure of forest community is of great significance for natural forest conservation, monitoring, management, and near-natural silviculture of plantation forest. In this study, we explored the importance of key tree groups—random trees—in natural communities, compared the similarity between the random trees and the communities. This research studies six stem-mapped permanent plots (100 × 100 m2) of the typical natural forests in three different geographic regions of China. Several variables and their distributions were applied to study community characteristics comprehensively, including species abundance, diameter distribution, spatial pattern, mingling, crowding, and competition. The genetic absolute distance method is used to analyze the similarity between the random trees and the communities. Our results show that the features of random trees are highly consistent with the communities. The study proposes that random trees are the cornerstones of natural forests. Its quantitative advantage explains the key role that random trees play in natural forests. The study could provide a scientific insight into the protection, monitoring, and management of forests

A simple and effective approach to quantitatively characterize structural complexity

Abstract This study brings insight into interpreting forest structural diversity and explore the classification of individuals according to the distribution of the neighbours in natural forests. Natural forest communities with different latitudes and distribution patterns in China were used. Each tree and its nearest neighbours form a structural unit. Random structural units (or random trees) in natural forests were divided into different sub-types based on the uniform angle index (W). The proportions of different random structural units were analysed. (1) There are only two types of random structural units: type R1 looks similar to a dumbbell, and type R2 looks similar to a torch. These two random structural units coexist in natural forests simultaneously. (2) The proportion of type R1 is far less than that of R2, is only approximately 1/3 of all random structural units or random trees; R2 accounts for approximately 2/3. Furthermore, the proportion of basal area presents the same trend for both random structural units and random trees. R2 has approximately twice the basal area of R1. Random trees (structural units) occupy the largest part of natural forest communities in terms of quantity and basal area. Meanwhile, type R2 is the largest part of random trees (structural units). This study finds that the spatial formation mechanism of natural forest communities which is of great significance to the cultivation of planted forests

A Novel Comprehensive Evaluation Method of Forest State Based on Unit Circle

Comprehensive evaluation of forest state is the precondition and critical step for forest management. To solve the problem that the radar plot and unit circle only focus on the value of each the evaluation index, this paper proposes a novel method for comprehensively and simultaneously evaluating the functionality and inhomogeneity of forest state based on the modified unit circle method. We evaluated the forest state of the Quercus aliena BL. var. acuteserrata Maxim. ex Wenz. broad-leaved mixed forest in the Xiaolong Mountains Forest Area of Gansu Province and the Pinus koraiensis Sieb. et Zucc. broad-leaved mixed forest in Jilin Province in China. According to the principle of comprehensive, scientific and operability, 10 evaluation indices on forest structure and vitality were selected to construct the evaluation indicator system. Each index was normalized based on the assignment method and ensured to be strictly positive based on reciprocal transformation method. The areas and arc length of the closed graph, formed by connecting every two adjacent indicators, in the radar plot and unit circle were extracted. Based on the isoperimetric theorem (isoperimetric inequality), a comprehensive evaluation model was constructed. Compared with radar chart and unit circle method, each index in the newly proposed unit circle method is represented by an independent sector region, reflecting the contribution of the index to the overall evaluation result. Each index has the same relative importance weight, contributing to the estimation the relative sizes of each aspect of forest state. The unique area and arc length of the closed graph help summarize the overall performance with a global score. The expression effect of improved unit circle has been enhanced, and as an English proverb put it, “A picture is worth a thousand words.„ The new proposed method simultaneously evaluates the functionality and inhomogeneity of the forest state and it is a powerful tool for the diagnosis of forest state problems and the decision-making of forest management

A Novel Method for Calculating Stand Structural Diversity Based on the Relationship of Adjacent Trees

Understanding the diversity and complexity of stand structure is important for managing the biodiversity of forest ecosystem, and stand structural diversity is essential for evaluating forest management activities. Based on the relationship of adjacent trees, a quantitative method of stand structure diversity is proposed to express the heterogeneity of stand structure in tree species, distribution pattern, species separation and size differentiation. In this study, we defined the diversity of structural unit types and derived a new index of forest structural diversity (SD′) employing the additivity principle of the Shannon–Weiner index. The efficiency of the index was verified by applying the new measure to sixteen field survey samples at different locations. The mountain rainforest in Hainan had the highest forest structural diversity, followed by broad-leaved Korean pine forests in Jiaohe (2), Jiaohe (1) and an oak-broadleaved mixed natural forest at Xiaolongshan (2). The SD′ values of plantations and pure natural forest were lower. The simulated data of different thinning methods and the intensity of broad-leaved Korean pine forests show that the new measure can reflect forest management changes on stand structure diversity. The value of SD′ compared with no treatments and the differences were greater as thinning intensity increased. The SD′ index provides minimum and maximum values for different structural unit types in forests to achieve a unified comparative basis for calculating forest structure diversity. It has the characteristics of the general diversity index and can well express the diversity of tree species, distribution pattern and size differentiation simultaneously. The SD′ index can not only calculate the structural diversity of mixed species forests but can also be used to calculate the structural diversity of pure forests. It can also be used to evaluate the change in stand structure diversity after management interventions

Prevalence of Inter-Tree Competition and Its Role in Shaping the Community Structure of a Natural Mongolian Scots Pine (Pinus sylvestris var. mongolica) Forest

Inter-tree competition is considered one of the most important ecological processes of forest development. However, its importance in structuring the spatial patterns of plant communities remains controversial. We collected observational data from two plots in a natural Mongolian Scots pine forest to study the contribution of competition to tree growth, mortality, and size inequality. We used the nearest neighbour method to determine the presence of competition, and unmarked and marked spatial point pattern analyses to test the density-dependent mortality effects and the spatial autocorrelation of tree size. We identified significant positive correlations between tree canopy diameter and nearest neighbour distance in both plots, which were more evident in the denser plot. The pair correlation functions of both plots indicated regular distribution patterns of living trees, and trees living in more crowded environments were more likely to die. However, the mark differentiation characteristics showed weak evidence of a negative spatial autocorrelation in tree size, particularly in the high-density plot. The high mortality rate of suppressed trees and weak asymmetric competition may have accounted for the lack of dissimilarity in tree size. This study showed that inter-tree competition is an important determinant of the development of Mongolian Scots pine forests

Designing near-natural planting patterns for plantation forests in China

Abstract Background China has a long tradition of managing planted forests. Different species of Populus, Eucalyptus, Larix, Cunninghamia and Pinus are planted to satisfy the local demand for wood products and provide ecological services at the same time. Evidence of the greater resilience of natural forests provides the motivation to develop asymmetric planting patterns, which is the focus of this study. We present a new method for designing plantation patterns that follow those observed in natural ecosystems and to maintain some regularity for operational convenience. Methods Based on the uniform angle index, we analyzed the spatial structure of six natural forests in different regions of China. The uniform angle index describes the degree of spatial uniformity of the n nearest neighbors of a given reference tree. Accordingly, we identified all possible patterns of a neighborhood group within a regular planting pattern and developed a method to optimize planting point arrangements that contain some randomness as well as a minimum degree of regularity. Results (1) There are 13 types of structural units in a regular planting, including seven random units, five even units and one cluster unit; (2) Five near-natural arrangements are presented with a minimum proportion of 50% of random units. These five arrangements represent a combination of regularity for operational convenience and asymmetry. Conclusions The new planting patterns developed in this study are expected to increase the asymmetric competition and resilience of these important ecosystems. Some experimental plantings, based on our findings, have already been established, e.g., in Pinus tabulaeformis plantations in Tianshui, Gansu Province, and in a Populus deltoides plantation in Fangshan near Beijing