Global woodland structure from local interactions: new nearest-neighbour functions for understanding the ontogenesis of global forest structure

Abstract

Background: A number of hypotheses and theories, such as the Janzen-Connell hypothesis, have been proposed to explain the natural maintenance of biodiversity in tropical and temperate forest ecosystems. However, to date the details of the processes behind this natural maintenance are still unclear. Recently two new nearest-neighbour characteristics were proposed and in this paper we demonstrate how they can contribute to a better understanding of the ontogenesis of global forest structure from localised neighbourhoods. Methods: We applied the new species and size segregation functions together with appropriate test procedures to four example woodland data sets from China at Daqingshan, Jiaohe, Jiulongshan and Xiaolongshan forest regions. In addition we quantified the morphology of the new characteristics and modelled a neighbourhood allometric coefficient linking the two functions. Results: The results revealed quite different species segregation patterns with both conspecific and heterospecific attraction. We found these to be generally matched by equivalent size segregation patterns of attraction of similar and different sizes. It was straightforward to model the size segregation function from the knowledge of the species segregation function by estimating a neighbourhood allometric coefficient. Conclusions: The new characteristics have helped to quantify the extent and rate of decline of neighbourhood interactions in terms of spatial species and size diversity. Through the allometric neighbourhood coefficient the analysis highlighted once more how closely related species and size segregation are, thus supporting the minglingsize hypothesis. Using both a traditional and a restricted random-labelling test has provided a valuable tool for understanding the exact nature of species-mingling and size-inequality relationships.

Analyzing the Biological and Structural Diversity of Hyrcanian Forests Dominated by Taxus baccata L.

“…We used indices of mingling, dominance, and size differentiation to describe the specific neighborhood constellations of each individual species. These three measures of species-specific structural diversity are defined in Table 1 [13,49].…”

“…Dominance measures the size dominance of the reference tree in relation to its four nearest neighbors [51]. Size differentiation measures the difference in tree size between the reference tree and its four nearest neighbors [13,49].…”

Observations on the Biology and Structure of Three Dry Tropical Forests in South India

“…Dominance measures the size dominance of the reference tree in relation to its immediate surrounding (Hui et al, 1998). Size Differentiation measures the variation of tree sizes between the reference tree and its nearest neighbors (Pommerening et al, 2020). Instead of selecting a particular reference species (as was done in this study), we may wish to select all trees that belong to a particular family, or all dominant trees of a given species, as reference trees with the aim to study their particular neighborhoods.…”

Localized neighborhood species mingling is correlated with individual tree size inequality in natural forests in South China

“…Extensive studies have shown that both JC and herd protection effects are well-documented driving factors that maintain local species diversity in plant communities (Wright 2002;Zhu et al 2010;Bagchi et al 2011;Shuai et al 2014). To date, however, the processes involved in maintaining tree diversity have been studied primarily through the lens of species diversity, whereas tree size diversity (also referred to as size inequality or size hierarchy) or relationships between tree size and species diversity resulting from these local interactions have rarely been investigated (Pommerening et al 2020;Wang et al 2020).…”

“…Spatial clustering of conspecific trees has been documented in various natural forest types (Condit et al 2000;Perry et al 2008), and the causes have generally been attributed to dispersal limitations and environmental filtering (Seidler and Plotkin 2006;Shen et al 2013). Spatial aggregation of conspecifics results in low species mingling of individuals in their immediate neighborhood, and due to tree size distribution of the same species is often limited within a range in natural forests (Pommerening et al 2020;Wang et al 2020) conspecific clustering would also lead to neighborhood size equality or spatial aggregation of similar tree sizes. According to the JC and herd protection effects, the emergence of conspecific cohorts increases the significance of intraspecific interactions, leading to the selective exclusion of neighboring conspecifics and hence increasing distances between conspecifics as trees move from early-to late-growth stages (Sterner et al 1986;Zhu et al 2010;Yao et al 2016).…”