Spatial structure of the vertical layers in a subtropical secondary forest 57 years after clear-cutting

Abstract

Stratification is an important phenomenon in natural forests. The mixed pineoak forests along the Nanpan River in southwest China was clearly formed by two layers in the vertical direction. These forests developed in an area where the virgin forests suffered clear-cutting. After excluding habitat heterogeneity, we divided two plots into upper and lower layers according to the tree height, and then analyzed the spatial pattern, species distribution, and size differentiation using the pair correlation function g(r) and the mark correlation function (MCF) kmm (r), respectively. The following key results were obtained: (1) the upstory was slightly clustered, whereas the understory had an intensively clumped pattern. An uneven pattern of germplasm resources in the early stages of succession and seed dispersion limitation may have contributed to the aggregation of tree species. (2) The spatial correlation among the main populations in each layer, and between both layers, had a largely random association, suggesting that differences in tree growth and physiological characteristics play an important role in species association. (3) Species aggregation decreased as the observation scale increased; however, the aggregation intensity of the understory was significantly higher than that of the upstory, which may be related to negative density dependence and niche complementarity. (4) Size differentiation in the upstory was significant, with small trees gathered together. There were no obvious differences in tree size in the lower layer, indicating a higher competitive pressure among trees in the upper layer. In conclusion, the spatial structure of trees in terms of vertical stratification differs, which is of great significance for investigating the mechanisms by which species coexist.

Species diversity patterns differ by life stages in a pine-oak mixed forest

“…Results from natural forests in tropical and subtropical regions support our findings, in that R and N tend to decrease in the upper canopy (Feroz et al, 2016;Shankar, 2019). The progression from S3 to S5 is associated with increased competition and mortality, which can reduce both R and N (Li et al, 2019). Other factors, such as stand origin, floral and faunal communities, geography and climate, and disturbance may also influence the pattern and quantitative relationships of R and N among life stages (D'Amato et al, 2009;Ostertag et al, 2014;Jin et al, 2019;Ray et al, 2021).…”

Effects of Tree Diversity, Functional Composition, and Large Trees on the Aboveground Biomass of an Old-Growth Subtropical Forest in Southern China

“…The average annual relative humidity is 82%. Soils are dominated by brown laterites in the Hongshui River valley below altitudes of 500 m, whereas mountain red soils occur at altitudes of 500-1000 m, and mountain yellow soils are common above 1000 m. The vegetation is characterized by the typical evergreen broad-leaved forests of the southern subtropical zone [33]. The sample plot was established in the Jiulong Forest Farm of Yachang National Natural Reserve.…”

Distribution attributes of natural canopy gaps in the Hyrcanian mixed-oriental beech forests

“…The K f (r) function can flexibly measure the spatial correlation of the mark of the i th and j th neighbours at a distance r (Li et al 2019). The size classes of CGs can be interpreted as so called marks of the considered point process characterizing the points or CGs in some way.…”

“…This test function attributes the correlation between the marks m i and m j at different points on the basis of distance r (Wälder, Wälder 2007). In Equation 1, E ij is the conditional expected value of the i th and j th gaps at distance r in the point process X, and M i and M j are the marks attached to the i th and j th gaps (Li et al 2019). In the denominator, M and Mʹ are random markers independently drawn from the edge distribution of the mark, and E is the common expected value (Li et al 2019).…”

“…In Equation 1, E ij is the conditional expected value of the i th and j th gaps at distance r in the point process X, and M i and M j are the marks attached to the i th and j th gaps (Li et al 2019). In the denominator, M and Mʹ are random markers independently drawn from the edge distribution of the mark, and E is the common expected value (Li et al 2019). For gap sizes, k mm (r) = 1 indicates that the gap sizes at the scale r are independent of each other, and k mm (r) > 1 indicates that the gaps sizes are positively correlated, i.e., similar gap sizes are observed in the specified spatial distribution.…”