Towards Automated Characterization of Canopy Layering in Mixed Temperate Forests Using Airborne Laser Scanning

Reik Leiterer,Reinhard Furrer,Felix Morsdorf,Michael Schaepman,Hossein Torabzadeh

doi:10.3390/f6114146

Abstract

Canopy layers form essential structural components, affecting stand productivity and wildlife habitats. Airborne laser scanning (ALS) provides horizontal and vertical information on canopy structure simultaneously. Existing approaches to assess canopy layering often require prior information about stand characteristics or rely on pre-defined height thresholds. We developed a multi-scale method using ALS data with point densities >10 pts/m2 to determine the number and vertical extent of canopy layers (canopylayer, canopylength), seasonal variations in the topmost canopy layer (canopytype), as well as small-scale heterogeneities in the canopy (canopyheterogeneity). We first tested and developed the method on a small forest patch (800 ha) and afterwards tested transferability and robustness of the method on a larger patch (180,000 ha). We validated the approach using an extensive set of ground data, achieving overall accuracies >77% for canopytype and canopyheterogeneity, and >62% for canopylayer and canopylength. We conclude that our method provides a robust characterization of canopy layering supporting automated canopy structure monitoring.

Highlights

Forests provide a wide range of valuable ecosystem goods and services [1]
We propose using an automated and transferable area-based approaches (ABA) to provide quantitative assessments of canopy layering at different scales
As we showed in a previous study [34], the point density was not a limiting factor: Even for the small grid-cell size of 1 m ×1 m, the available point cloud has almost the maximum achievable information on the canopy structure that current Airborne laser scanning (ALS) systems can provide

Summary

Introduction

Forests provide a wide range of valuable ecosystem goods and services [1]. Understanding forest ecosystems and their underlying processes help with forecasts using scenarios under global change conditions and supports the establishment of sustainable management strategies [2,3,4,5]. Canopy structure itself is not a measurable quantity, but the properties of canopy structure can be described by means of a wide variety of structural variables, such as tree height, tree diameter distribution, or canopy layering [14]. Canopy layers provide essential structural components of wildlife habitat [15], affect stand productivity [16], and are used to manage forest stands and to identify forest structural stages [17]. From the various existing definitions of canopy layer (cf. [18]), we follow Franklin and Spies [19] and understand canopy layer as continuous vertical distribution of foliage within the canopy

Objectives

Methods

Results

Discussion

Conclusion