Quantifying vertical forest stand structure using small-footprint LIDAR to assess potential stand dynamics

The vertical distribution of plant elements (e.g., foliage and wood) within a forest can yield important information on stand structure, dynamics and growth stage but such information is often difficult to acquire across landscapes using traditional methods of field survey and aerial photograph interpretation. Recent advances in airborne laser scanning (ALS), however, have facilitated rapid assessment of stand height and cover to levels of accuracy considered acceptable for forest inventory and management. A few studies have extended this analysis to the descriptions of growth stage and retrieval of biomass, particularly in complex forest environments. However, current research has raised issues as to how well the vertical profile can be represented and whether the relative amounts of over and understorey can be quantified accurately. Focusing on subtropical open forests and woodlands, in central Queensland, Australia, this paper provides a better insight into how small footprint Light Detection and Ranging (LiDAR) sensor data can be used to create apparent vertical profiles to describe aspects of vertical stand structure (e.g., overstorey/understorey) and also infer broad successional or growth stages. Such profiles were integrated with field measurements within a common reference matrix (based on 1 m cubes), thereby providing spatially explicit tree/crown maps in three dimensions and allowing validation of those generated from LiDAR. Such interpretations, as well as enhancing forest information retrieval, were considered important in the interpretation of other forms of remote sensing data, including radar and optical data. The conceptual basis for this integration method is outlined with an example utilising one field plot, and the role this method might play in quantifying stand dynamics and carbon sequestration is discussed