Creating vegetation density profiles for a diverse range ofecological habitats using terrestrial laser scanning

摘要

1. Vegetation structure is an important determinant of species habitats and diversity. It is often represented bysimple metrics, such as canopy cover, height and leaf area index, which do not fully capture three-dimensionalvariations in density. Terrestrial laser scanning (TLS) is a technology that can better capture vegetation structure,but methods developed to process scans have been biased towards forestry applications. The aim of this studywas to develop a methodology for processing TLS data to produce vegetation density profiles across a broaderrange of habitats.2. We performed low-resolution and medium-resolution TLS scans using a Leica C5 Scanstation at four locationswithin eight sites near Wollongong, NSW, Australia (3438–3441°S, 15084–15091°E). The raw pointclouds were converted to density profiles using a method that corrected for uneven ground surfaces, varyingpoint density due to beam divergence and occlusion, the non-vertical nature of most beams and for beams thatpassed through gaps in the vegetation without generating a point. Density profiles were evaluated against visualestimates from three independent observers using coarse height classes (e.g. 5–10 m).3. TLS produced density profiles that captured the three-dimensional vegetation structure. Although sites wereselected to differ in structure, each was relatively homogeneous, yet we still found a high spatial variation in densityprofiles. There was also large variation between observers, with the RMS error of the three observers relativeto the TLS varying from 162% to 321%. Part of this error appeared to be due tomisjudging the height of vegetation,which caused an overestimation in one height class and anunderestimationinanother.4. Ourmethod for generating density profiles using TLS can capture three-dimensional vegetation structure in amanner that is more detailed and less subjective than traditionalmethods. The method can be applied to a broadrange of habitats – not just forests with open understoreys. However, it cannot accurately estimate near-surfacevegetation density when there are uneven surfaces or dense vegetation prevents sufficient ground returns. Nonetheless,TLS density profiles will be an important input for research on species habitats, microclimates andnutrient cycles.