Patterns and causes of forest gap disturbance in a semi-humid evergreen broadleaved forest in the Jizu Mountains, Yunnan

doi:10.17520/biods.2023219

Abstract

Abstract:

Aims: Forest gaps are a common form of forest disturbance and play an important role in forest regeneration and species coexistence. The forest gaps serve as the basis for the forest landscape’s shifting mosaic structure. We aim to provide the scientific basis for better conservation and management of the semi-humid evergreen broad-leaved forests in the Jizu Mountains.

Methods: This study analyzed the species composition and DBH class structure of all woody plants (including all standing living trees and coarse woody debris (CWD) based on a survey of the forest dynamics plot in a semi-humid evergreen broad-leaved forest in the Jizu Mountains starting in 2022. The spatial patterns of the basal area of all woody plants and the number of forest gap makers (FGM) in the plot were mapped using ArcGIS. An environmental interpretation using a generalized linear model combined with variance partitioning analysis was performed.

Results (1) The number and the basal area of CWD were about 13.6% and 15.8% for all standing living trees, respectively. A total of 57 woody species contributed to CWD formation, with a total of 12,317 individual trees; among which 12 species acted as FGMs, with a total of 2,280 individual trees. (2) The DBH class structure of standing living trees and CWD was like an inverted “J” type: with more individual trees having smaller DBH classes and fewer larger classes, indicating the main source of tree mortality was the self-thinning process during the early stage of community succession. (3) The number and average density of the FGM decreased as follows: trunk snapping (TS), dead fallen tree (DFT), standing dead tree (SDT), and leaning live tree (LLT); The sum of basal area for the standing living trees, CWD, and FGM differed significantly within the plot, with the hillsides on both sides of the gully being higher and at the gully bottom being lower; the number of all four types of FGM were abundant on the hillsides on both sides of the shallow gully, while it was lowest in the bottom of the shallow gully, all three types of FGM were distributed in the bottom and the hillsides on both sides of the deep gully except for LLT. (4) The variance of environmental factors increased as follows: 16.7% for SDT, 25.6% for DFT, 37.2% for TS, and 76.0% for LLT. Biological competition and a self-thinning process caused the formation of SDT and DFT. Soil nutrient contributed the most to the number of LLT, while topographic factors and biological factors drive the formation of TS.

Conclusion: The semi-humid evergreen broad-leaved forest in the Jizu Mountains has small-scale disturbances, the number of SDT and DFT is closely associated with the tree density within the forest community. For LLT, soil nutrient influences the rate of tree survival more than topographic factors. Areas in the forest where TS occurres are driven by topographic factors and biological factors.

Key words: semi-humid evergreen broad-leaved forest, coarse woody debris, forest gap maker, sum of basal area, spatial pattern, environmental interpretation

Xi Tian, Wencong Liu, Jiesheng Rao, Xiaofeng Wang, Tao Yang, Xi Chen, Qiuyu Zhang, Qiming Liu, Yanxiao Xu, Xu Zhang, Zehao Shen. Patterns and causes of forest gap disturbance in a semi-humid evergreen broadleaved forest in the Jizu Mountains, Yunnan[J]. Biodiv Sci, 2023, 31(11): 23219.

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URL: https://www.biodiversity-science.net/EN/10.17520/biods.2023219

https://www.biodiversity-science.net/EN/Y2023/V31/I11/23219

Figures/Tables 8

Fig. 1 DBH classes distribution of individual numbers of standing living trees (a) and coarse woody debris (b) by growth-form in the forest dynamics plot in a semi-humid evergreen broad-leaved forest in the Jizu Mountains

Fig. 2 Spatial distribution patterns of the sum of basal area (SBA) of all living and dead trees of the forest dynamics plot in a semi-humid evergreen broad-leaved forest in the Jizu Mountains. (a) Standing living tree (SLT); (b) Coarse woody debris (CWD); (c) CWD/SLT; (d) Forest gap maker.

Fig. 3 Point distribution of forest gap maker. (a) Standing dead tree; (b) Dead fallen tree; (c) Trunk snapping; (d) Leaning live tree. Red ovals represent the concentrated areas.

Table 1 The number, sum of basal area (SBA) and their ratio in four types of forest gap maker

林隙形成木 Forest gap maker	数量 No.	数量占比 Ratio (%)	胸高断面积之和 SBA (m²)	胸高断面积之和占比 Ratio of SBA (%)	样方数量 No. of the quadrats	平均密度 Average density (%)
枯立木 Standing dead tree	339	14.9	20.6	14.9	176	34.9
枯倒木 Dead fallen tree	818	35.9	57.4	41.7	329	65.3
折干木 Trunk snapping	1,082	47.5	55.9	40.6	385	76.4
活倒木 Leaning live tree	41	1.7	3.9	2.8	26	5.2
总计 Total	2,280	100	137.8	100	504	181.8

Fig. 4 The bar chart of the number (a) and stacked percentage of DBH classes (b) for forest gap maker by species

Fig. 5 DBH classes distribution of forest gap maker

Table 2 Proportion of number of four types of forest gap maker (FGM) in the total number of all coarse woody debris (CWD) and FGM

类型 Type	枯立木 Standing dead tree		枯倒木 Dead fallen tree		折干木 Trunk snapping		活倒木 Leaning live tree		总计 Total
类型 Type	数量 No.	%	数量 No.	%	数量 No.	%	数量 No.	%	总计 Total
粗木质残体 CWD	8,759	71.1	2,035	16.5	1,094	8.9	429	3.5	12,317
林隙形成木 FGM	339	14.9	818	35.9	1,082	47.5	41	1.7	2,280

Fig. 6 Relative effects of environment factors of forest gap maker. (a) Standing dead tree; (b) Dead fallen tree; (c) Trunk snapping; (d) Leaning live tree. Left of the figure show the relative importance of each predictor (expressed as a percentage of explained variance; and the right of the figure show mean parameter estimates (standardized regression coefficients) of the model predictors and their 95% confidence intervals. Bio, Biotic factor, including number of species (Nus), sum of basal area of standing living tree (Sbaslt), quadrat age (Age); Topo, Topographic factor, including relative altitude (Alti), slope (Slop), aspect (Aspe), curvature (Curv), roughness (Roug), topographic wetness index (Twi); Soil_C, Soil chemical factor, including organic carbon (OrgC), total nitrogen (TotN), available phosphorus (AvaP), pH; Soil_P, Soil physical factor, including clay content (Clay), silt content (Silt), sand content (Sand). * P < 0.05; ** P < 0.01; *** P < 0.001.

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