关键词: 阔叶红松林, 叶面积指数, Voronoi图, 垂直分布倾向度, 空间自相关

Abstract:

【Objective】This study aims to investigate the vertical and short-range horizontal spatial distribution patterns of leaf area index (LAI) in broadleaved-Korean pine forests and explore the application value of the stratified Voronoi diagram method in simulating the spatial distribution of LAI in multi-storey forest ecosystems.【Method】The study focused on the virgin broadleaved-Korean pine forest located on the downhill side of the core zone of Liangshui National Nature Reserve. The trees within the forest stand that reached the minimum diameter at breast height (5 cm) were divided into five height classes (Class Ⅰ, H < 10 m; Class Ⅱ, 10 m ≤ H < 15 m; Class Ⅲ, 15 m ≤ H < 20 m; Class Ⅳ, 20 m ≤ H < 25 m; Class Ⅴ, H ≥ 25 m).The Voronoi diagram method was used to simulate the spatial distribution of LAI in different height classes within the forest. The results were combined to form an overall spatial distribution of LAI for the forest stand. Furthermore, the overall characteristics of LAI at the forest stand scale were analyzed, including the vertical distribution patterns of LAI for different tree species and the entire forest stand. The short-range horizontal spatial autocorrelation patterns of LAI at different height classes and the overall forest stand were analyzed using the spatial semivariance function and incremental spatial autocorrelation method. 【Result】Three results were obtained. First, the overall LAI of the study plot was 10.807, with Pinus koraiensis, Acer momo, Betula platyphylla, Tilia amurensis and Fraxinus mandshurica making the top five contributions to the stand LAI. The local LAI in the understorey varied within the range of 0-75, with 48.7% of the understorey having a LAI of 0. The probability density histogram of the LAI in the area with canopy cover had a single-peak distribution, with the peak between 15-25. Second, the LAI of broadleaved-Korean pine forest was 0.420, 2.420, 2.210, 2.707 and 3.050 from height class I to height class V respectively, with vertical distribution tendency degree of total LAI in the stand being 1.171 and the coefficient of variation of total LAI in different height classes being 47.3%. From height class Ⅰ to Ⅴ, the number of canopy patches was 53, 39, 12, 11, and 8 respectively. The LAI under the canopy patches of each species showed an increasing trend as the height level increased. Third, the Nugget value, Sill value, range and Nugget/Sill ratio of the spatial semi-variance function of LAI in broadleaved Korean pine forest were 4.770, 164.010, 5.108 m and 0.029, respectively. The LAI was similarly clustered at lag distances less than 27.0 m and greater than 38.5 m, and spatially random at lag distances between 27 m and 38.5 m (P<0.05). As the lag distance gradually increased, the Z-score of the LAI showed two peaks at 14 and 24 m.【Conclusion】The LAI of broadleaved-Korean pine forests in gentle slope positions exhibits distinct vertical stratification. The leaf area of different tree species tends to be distributed at different heights. For instance, Pinus koraiensis, Picea asperata, and Fraxinus mandshurica, as tall arbor species, have their leaf area concentrated in the upper canopy. On the other hand, Acer opalus and Ulmus, representing middle-sized and small-sized arbor species, have their leaf area concentrated in the lower canopy. The LAI of broadleaved-Korean pine forests in lower gentle slope positions exhibits strong short-range spatial autocorrelation in the horizontal direction. The horizontal spatial distribution of LAI within the forest stand was similarly clustered at most research scales, which is strongly influenced by the spatial distribution of trees.

Key words: broadleaved-Korean pine forest, leaf area index, Voronoi diagram, vertical distribution tendency degree, spatial autocorrelation