Mapping Spatial Variations of Structure and Function Parameters for Forest Condition Assessment of the Changbai Mountain National Nature Reserve

Lin Chen,Chunying Ren,Bai Zhang,Yeqiao Wang,Zongming Wang

doi:10.3390/rs11243004

Abstract

Forest condition is the baseline information for ecological evaluation and management. The National Forest Inventory of China contains structural parameters, such as canopy closure, stand density and forest age, and functional parameters, such as stand volume and soil fertility. Conventionally forest conditions are assessed through parameters collected from field observations, which could be costly and spatially limited. It is crucial to develop modeling approaches in mapping forest assessment parameters from satellite remote sensing. This study mapped structure and function parameters for forest condition assessment in the Changbai Mountain National Nature Reserve (CMNNR). The mapping algorithms, including statistical regression, random forests, and random forest kriging, were employed with predictors from Advanced Land Observing Satellite (ALOS)-2, Sentinel-1, Sentinel-2 satellite sensors, digital surface model of ALOS, and 1803 field sampled forest plots. Combined predicted parameters and weights from principal component analysis, forest conditions were assessed. The models explained spatial dynamics and characteristics of forest parameters based on an independent validation with all r values above 0.75. The root mean square error (RMSE) values of canopy closure, stand density, stand volume, forest age and soil fertility were 4.6%, 33.8%, 29.4%, 20.5%, and 14.3%, respectively. The mean assessment score suggested that forest conditions in the CMNNR are mainly resulted from spatial variations of function parameters such as stand volume and soil fertility. This study provides a methodology on forest condition assessment at regional scales, as well as the up-to-date information for the forest ecosystem in the CMNNR.

Highlights

Forests occupy almost one third of the Earth’s land area [1], playing a major role in sustaining global material and energy cycles [2]
To evaluate forest conditions in a comprehensive and comparable manner, this study developed a methodology on forest condition assessment based on explicit modeling and mapping of forest parameters from satellite images
Topographic and spectral indices from L band interferometric SAR (InSAR) and multispectral instrument (MSI) contributed more than L and C band synthetic aperture radar (SAR) in random forests (RF) modeling of complex forest parameters such as forest age and soil fertility

Summary

Introduction

Forests occupy almost one third of the Earth’s land area [1], playing a major role in sustaining global material and energy cycles [2]. Forest condition is an essential component of both forest management and ecological evaluations. It reflects the stability, resilience, and capability of carbon sequestration, timber production, as well as other services [5,6]. It is essential to assess forest condition based on modeling structural and functional parameters. The condition assessment based on remote sensing usually contains indicators of community structure and productivity [6,7,8]. The sub-compartment measurements of the National Forest Inventory in China contain the information about structure, including canopy closure, stand density and forest age, and function, including stand volume and soil condition [9,10]

Methods

Results

Discussion

Conclusion