Responses of canopy three-dimensional structural and spectral characteristics to anthropogenic disturbance in the Qianjiangyuan section of the Qianjiangyuan- Baishanzu National Park candidate area

doi:10.17520/biods.2024174

Abstract

Abstract:

Aim: National parks prioritize the conservation of their unique and representative vegetation ecosystems. Monitoring these ecosystems is crucial for evaluating conservation effectiveness and formulating sustainable management strategies. This study utilized remote sensing data to characterize canopy characteristics in Qianjiangyuan section of the Qianjiangyuan-Baishanzu National Park candidate area (Qianjiangyuan section). By establishing direct links between canopy features and disturbance regimes, we aimed to evaluate the effectiveness of forest biodiversity protection.

Method:We analyzed airborne LiDAR (light detection and ranging) and hyperspectral data for 21,820 100 m × 100 m pixels and naturalness survey data for 6,977 subcompartments within Qianjiangyuan section. The three-dimensional canopy structural characteristics were derived from airborne LiDAR data, while vegetation indices were calculated from hyperspectral data. These canopy characteristics were then correlated with the naturalness of forest subcompartments to assessed differences across various naturalness levels.

Results: (1) Canopy characteristics within Qianjiangyuan section exhibited a wide range of variability, with considerable differences across regions of the park. (2) Canopy structural and spectral characteristics varied significantly between areas with varying degrees of anthropogenic disturbance, reflecting the success of conservation efforts. Specifically, heavily disturbed secondary and plantation forests exhibited the lowest canopy height, leaf area index, vertical complexity, and light resource utilization efficiency, with a higher proportion of shorter and sparser vegetation, increased stress levels, and higher leaf senescence. In contrast, moderately disturbed secondary deciduous broad-leaved forests and lightly or undisturbed old-growth evergreen broad-leaved forests demonstrated elevated canopy heights, leaf area index, and vertical complexity. However, old-growth forests experienced lower stress levels, higher light use efficiency, and reduced leaf senescence compared to moderately disturbed forests.

Conclusion:The canopy characteristics in Qianjiangyuan section vary widely depending on the level of anthropogenic disturbance, with such disturbances negatively impacting canopy attributes. Our findings indicate that airborne LiDAR and hyperspectral imaging are effective in quantifying the three-dimensional structure and spectral attributes of the canopy, offering valuable insights into conservation effectiveness. Our study serves as a scientific foundation for the protection and management of subtropical forests within Qianjiangyuan section. Furthermore, it highlights the potential of airborne remote sensing technologies in monitoring changes in canopy characteristics to evaluate conservation efficacy, thereby supporting the development of informed conservation strategies and sustainable management practices.

Key words: Qianjiangyuan-Baishanzu National Park candidate area, subtropical forest, LiDAR, canopy structure, hyperspectral, vegetation indices, anthropogenic disturbance

Liu Yonghua, Tong Guangrong, Yu Hangyuan, Wang Ningning, Ren Haibao, Chen Lei, Ma Keping, Mi Xiangcheng. Responses of canopy three-dimensional structural and spectral characteristics to anthropogenic disturbance in the Qianjiangyuan section of the Qianjiangyuan- Baishanzu National Park candidate area[J]. Biodiv Sci, 2025, 33(4): 24174.

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URL: https://www.biodiversity-science.net/EN/10.17520/biods.2024174

https://www.biodiversity-science.net/EN/Y2025/V33/I4/24174

Figures/Tables 8

Table 1 Technical parameters of airborne LiDAR system

参数 Parameters	值 Values
飞行速度 Flight speed (km/h)	250
飞行高度 Flight height (m)	1,960
相对航高 Relative flight height (m)	1,660
脉冲频率 Pulse repetition rate (kHz)	700
视场角 Field angle of view	58.52°
扫描速率 Scanning rate (lps)	246
扫描幅宽 Scanning width (m)	1,860
点密度 Point density (points/m²)	> 4
旁向重叠度 Side overlap (%)	20

Table 2 Technical parameters of airborne hyperspectral system

参数 Parameters	值 Values
光谱范围 Spectral range (nm)	400-1,000
光谱分辨率 Spectral resolution (nm)	8.8-9.7
视场角 Field angle of view	37.7°
瞬时视场角 Momentary field angle of view (mrad)	0.646
焦距 Focal length (mm)	18.5
空间分辨率 Spatial resolution (m)	1
波段数 Number of bands	64
空间像元数Number of spatial pixels	1,024
光谱采样间隔 Spectral sampling interval (nm)	9.2
数字分辨率 Digital number (bit)	16
相对航高 Relative airspeed (m)	1,000
旁向重叠度 Side overlap (%)	20

Table 3 Hyperspectral vegetation indices

植被指数 Vegetation indices	计算公式 Formulas	参考文献 Reference
归一化植被指数 Normalized difference vegetation index (NDVI)	$ N D V I=\frac{R_{800.88}-R_{675.78}}{R_{800.88}+R_{675.78}}$	Rouse et al, 1973
红边归一化植被指数 Red-edge normalized difference vegetation index (NDVI₇₀₅)	$ N D V_{705}=\frac{R_{752.58}-R_{704.50}}{R_{752.58}+R_{704.50}}$	Elvidge & Chen, 1995
光化学反射指数 Photochemical reflectance index (PRI)	$ P R I=\frac{R_{534.44}-R_{571.70}}{R_{534.44}+R_{571.70}}$	Gamon et al, 1997
植被衰减指数 Plant senescence reflectance index (PSRI)	$ \text { PSRI }=\left(R_{675.78}-R_{497.58}\right) / R_{752.58}$	Merzlyak et al, 1999

Fig. 1 Functional divisions and their main subareas (the yellow area is the core protection area, and the blue area is the general control area) in Qianjiangyuan section of the Qianjiangyuan-Baishanzu National Park candidate area, and naturalness of the 2018 subcompartment survey of the section. Meanings of different naturalness: 1, Zonal climax forests in pristine condition or with slight anthropogenic disturbances (broad-leaved evergreen forests); 2, Anthropogenically disturbed natural forests or secondary forests in the middle or late successional stages with obvious anthropogenic disturbances (deciduous broad-leaved forests, shrub forests, etc.); 3, Heavily disturbed or degraded coniferous forests in a highly fragmented secondary forests or plantation forests).

Fig. 2 Spatial patterns of canopy three-dimensional structural characteristics in Qianjiangyuan section of the Qianjiangyuan-Baishanzu National Park candidate area. (A) Leaf area index; (B) Mean height of canopy; (C) Normalized Shannon vertical complexity index; (D) First principal component.

Fig. 3 Spatial patterns of canopy spectral characteristics in Qianjiangyuan section of the Qianjiangyuan-Baishanzu National Park candidate area. (A) Normalized difference vegetation index; (B) Red-edge normalized difference vegetation index; (C) Photochemical reflectance index; (D) Plant senescence reflectance index.

Fig. 4 Differences in canopy three-dimensional structural characteristics among different degrees of naturalness in Qianjiangyuan section of the Qianjiangyuan-Baishanzu National Park candidate area. (A) Leaf area index; (B) Mean height of canopy; (C) Normalized Shannon vertical complexity index; (D) First principal component. Different letters indicate significant differences at P < 0.001.

Fig. 5 Differences in canopy spectral characteristics among different degrees of naturalness in Qianjiangyuan section of the Qianjiangyuan-Baishanzu National Park candidate area. (A) Normalized difference vegetation index; (B) Red-edge normalized difference vegetation index; (C) Photochemical reflectance index; (D) Plant senescence reflectance index. Different letters indicate significant differences at least at P < 0.01.

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