A Planted Forest Mapping Method Based on Long-Term Change Trend Features Derived from Dense Landsat Time Series in an Ecological Restoration Region

Yuanyuan Meng,Caiyong Wei,Yanpei Guo,Zhiyao Tang

doi:10.3390/rs14040961

Abstract

Planted forests provide a variety of meaningful ecological functions and services, which is a major approach for ecological restoration, especially in arid areas. However, mapping planted forests with remote-sensed data remains challenging due to the similarities in canopy spectral and structure characteristics and associated phenology features between planted forests and other vegetation types. In this study, taking advantage of the Google Earth Engine (GEE) platform and taking the Ningxia Hui Autonomous Region in northwestern China as an example, we developed an approach to map planted forests in an arid region by applying long-term features of the NDVI derived from dense Landsat time series. Our land cover map achieved a satisfactory accuracy and relatively low uncertainty, with an overall accuracy of 93.65% and a kappa value of 0.92. Specifically, the producer (PA) and user accuracies (UA) were 92.48% and 91.79% for the planted forest class, and 93.88% and 95.83% for the natural forest class, respectively. The total planted forest area was estimated as 3608.72 km2 in 2020, accounting for 20.60% of the study area. The proposed mapping approach can facilitate assessment of the restoration effects of ecological engineering and research on ecosystem services and stability of planted forests.

Highlights

Afforestation and reforestation are widely applied to restore disturbed ecosystems, to combat desertification and soil erosion, and to mitigate carbon emissions [1,2]
The producer accuracy (PA) and user accuracies (UA) of the natural forest class improved from approximately 69% and 88% to 100%
Contrast analysis confirmed that trend features were crucial for planted forest identification, which improved the separability and guaranteed the classification accuracy across the different vegetation types (Table 2 and Figures 5a and A2)

Summary

Introduction

Afforestation and reforestation are widely applied to restore disturbed ecosystems, to combat desertification and soil erosion, and to mitigate carbon emissions [1,2]. To restore the disturbed ecosystems, China has implemented a series of ecological programs, such as the Three-North Shelterbelt Program (since 1978), the Grain for Green Program (since 1999), and the Natural Forest Conservation Program (since 2000) [3,4]. Natural and planted forests provide different aspects of ecosystem services [7]. A precise map of both forest types can explicitly locate the planted forest expansion and natural forest loss [8]. Forest assessments without distinguishing planted from natural forests may underestimate forest change [9,10]. Fine-resolution mapping of planted forests is essential to assess ecosystem service and stability, and evaluate the restoration effects of ecological programs [11]

Methods

Results

Discussion

Conclusion