Detecting shrub encroachment in seminatural grasslands using UAS LiDAR

Area of Science:

• Ecology
• Remote Sensing
• Conservation Biology

Background:

• Shrub encroachment in seminatural grasslands poses a significant threat to local biodiversity.
• Dense vegetation, such as *Cytisus scoparius*, can homogenize landscapes and negatively impact plant diversity.
• Effective management strategies require accurate methods for detecting structural changes like biomass variations.

Purpose of the Study:

• To investigate the accuracy of mapping *Cytisus scoparius* in three dimensions (3D) using Unmanned Aircraft System (UAS) Light Detection and Ranging (LiDAR) data.
• To assess the capability of ultrahigh-density point cloud data in deriving structural change metrics, specifically biomass.
• To evaluate UAS LiDAR as a tool for monitoring shrub dynamics and assessing the effectiveness of management interventions in grasslands.

Main Methods:

• Combined traditional field measurements with novel UAS LiDAR observations over a 6.7 ha seminatural grassland.
• Collected ultrahigh-density point cloud data (over 1,000 pts/m²) in both leaf-on (October 2017) and leaf-off (April 2018) seasons.
• Utilized 3D point-based classification to distinguish shrub genera and related LiDAR-derived volume metrics to measured biomass.

Main Results:

• Achieved overall classification accuracies exceeding 86% for shrub mapping from point cloud data across both seasons.
• Found that maximum volume metrics explained up to 77.4% of the variation in *C. scoparius* biomass.
• Quantified landscape-scale variations in biomass change between autumn 2017 and spring 2018, indicating a decrease in certain areas.

Conclusions:

• UAS LiDAR is a highly promising tool for mapping and monitoring grassland shrub dynamics at the landscape scale.
• The developed workflow enables accurate, standardized, and non-biased evaluation of management activities aimed at controlling shrub encroachment.
• Further research is needed to determine the specific drivers (e.g., grazing, frost) of observed biomass changes.