Journal Article

Remote Sensing of Woody Plant Encroachment: A Global Systematic Review of Drivers, Ecological Impacts, Methods, and Emerging Innovations

Toqeer, Abdullah, Hall, Andrew, Horta, Ana, Wassens, Skye

2026

Overview

Globally, grasslands, savannas, and wetlands are degrading rapidly and increasingly being replaced by woody vegetation. Woody Plant Encroachment (WPE) disrupts natural landscapes and has significant consequences for biodiversity, ecosystem functioning, and key ecosystem services. This review synthesizes findings from 159 peer-reviewed studies identified through a PRISMA-guided systematic literature review to evaluate the drivers of WPE, its ecological impacts, and the remote sensing (RS) approaches used to monitor it. The drivers of WPE are multifaceted, involving interactions among climate variability, topographic and edaphic conditions, hydrological change, land use transitions, and altered fire and grazing regimes, while its impacts are similarly diverse, influencing land cover structure, water and nutrient cycles, carbon and nitrogen dynamics, and broader implications for ecosystem resilience. Over the past two decades, RS has become central to WPE monitoring, with studies employing classification techniques, spectral mixture analysis, object-based image analysis, change detection, thresholding, landscape pattern and fragmentation metrics, and increasingly, machine learning and deep learning methods. Looking forward, emerging advances such as multi-sensor fusion (optical– synthetic aperture radar (SAR), Light Detection and Ranging (LiDAR)–hyperspectral), cloud-based platforms including Google Earth Engine, Microsoft Planetary Computer, and Digital Earth, and geospatial foundation models offer new opportunities for scalable, automated, and long-term monitoring. Despite these innovations, challenges remain in detecting early-stage encroachment, subcanopy woody growth, and species-specific patterns across heterogeneous landscapes. Key knowledge gaps highlighted in this review include the need for long-term monitoring frameworks, improved socio-ecological integration, species- and ecosystem-specific RS approaches, better utilization of SAR, and broader adoption of analysis-ready data and open-source platforms. Addressing these gaps will enable more effective, context-specific strategies to monitor, manage, and mitigate WPE in rapidly changing environments.

• Publisher: MDPI AG
• Subject: Analysis / Aquatic ecosystems / Artificial satellites in remote sensing / Automation / Biodiversity / Boolean / Carbon cycle / Change detection / Changing environments / Climate change / Climate variability / Cloud computing / Deep learning / Dissertations & theses / Earth resources technology satellites / ecological drivers / Ecological function / Ecosystem resilience / Ecosystem services / Ecosystems / Encroachment / Environmental changes / Environmental economics / Grasslands / Grey literature / Human influences / Hydrology / Image analysis / Image processing / Innovations / Keywords / Land cover / Land use / land use and land cover change / Landsat / Landscape / Learning algorithms / Lidar / Literature reviews / Machine learning / multi-sensor fusion / Multisensor fusion / Nutrient cycles / Nutrient dynamics / Optical radar / Radar detection / Remote monitoring / Remote sensing / Resilience / Sensors / Synthetic aperture radar / Systematic review / Unmanned aerial vehicles / Vegetation / Wetlands / woody plant encroachment / Woody plants