Modelling tree size diversity from airborne laser scanning using canopy height models with image texture measures Ibrahim Ozdemir a,⇑ , Daniel N.M. Donoghue b a Department of Wildlife Ecology and Management, Suleyman Demirel University, Faculty of Forestry, 32260 Isparta, Turkey b Department of Geography, Durham University, Science Laboratories, DH1 3LE Durham, UK article info Article history: Received 18 October 2012 Received in revised form 22 December 2012 Accepted 29 December 2012 Available online 19 February 2013 Keywords: LiDAR Vertical structure Stand complexity Airborne laser scanning abstract The aim of this study is to investigate the relationships between the plot-level tree size diversity and vari- ables derived from airborne laser scanning (ALS) data, which is a type of LiDAR measurement. We con- ducted a study using forest stands with a range of managed and near-natural stands with a broad range of species. 33 Plots that represent the forest stand variety in the study area were sampled; within each plot four biophysical variables were measured by ground-based methods, these were height (TH), diameter at breast height (DBH), crown length (CL), and crown width (CW). The resultant tree size diver- sity was parameterised as Lmoments (t) statistics and compared with both point-based and grid-based laser scanning diversity variables. Point-based measures included the ratios of the Percentile means (P99/P25, P99/P50, P99/75, and P99/P90), Coefficient of variation, Skewness, Kurtosis, and Lmoments (t). The grid-based texture measures derived from the ALS Canopy Height Models (CHMs) included first- order texture, Standard Deviation of Grey Levels (SDGL), and three second-order texture measures, includ- ing Contrast, Entropy and Correlation. Furthermore, we tested the influence of scale by analysing the effect of grid cell sizes when generating CHMs from the raw point cloud ALS data. Using linear regression anal- ysis, we show that the grid-based texture measures are superior predictors of tree height diversity than the point-based metrics. Sixty percent of the variance in the tree height diversity and 51% of the variance in the DBH Diversity were explained by the SDGL and Correlation texture measures, respectively (p < 0.01). The associations between the texture features and the CL Diversity and CW Diversity were weaker com- pared to the TH Diversity and DBH Diversity (The highest R 2 was 0.46 and 0.45, respectively, p < 0.01). While the CHM calculated from a 3 Â 3 m grid cell had the strongest correlation with TH Diversity (0.60, p < 0.01), the CHMs calculated from 1 Â 1 m and 2 Â 2 m cell size had the strongest association with DBH Diversity (0.51, p < 0.01). Combining selected point- and grid-based variables accounted for up to 85% of the variance of tree height diversity, 68% of the variance of DBH Diversity and 52% of the var- iance of CL Diversity. Our study shows that the combination of laser-based height percentile ratios and texture measures derived from the ALS–CHM can be used to estimate tree size diversity across forest landscapes. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Forests ecosystems contain critically important habitats in terms of biological diversity (Franklin, 1993). Assessment of forest biodiversity is an important task to help understand the negative impacts of natural and human-induced disturbance factors and to take necessary measures for sustainable management of forest resources (Roberts and Gilliam, 1995). The United Kingdom (UK) Government, like many others, produced a national Biodiversity Action Plan (BAP) representing its response to the Convention on Biological Diversity (CBD), which is an international agreement adopted at the 1992 Earth Summit, in Rio de Janeiro. Woodland Ac- tion Plans in the UK, and similar initiatives in many other coun- tries, are the policy instruments designed to maintain and enhance the biodiversity potential of forests and woodlands. Thus, assessment of biodiversity at stand-level is critical to assessing the outcome of silvicultural treatments at this basic unit of forest management. Structural diversity is the most straightforward measurement that indicates the potential biodiversity and habitat suitability of a forest stand. Structurally diverse forest stands with vertical foli- age layering provide important habitats (for example foraging, nesting, hiding and roosting) for different forest-dwelling organ- isms (Magurran, 1988; Clawges et al., 2008; Hinsley et al., 2009; Wood et al., 2012a). Therefore, numerous biodiversity guidelines promote silvicultural practices that develop structural diversity 0378-1127/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.foreco.2012.12.044 ⇑ Corresponding author. Tel.: +90 506 5817237; fax: +90 246 2371810. E-mail addresses: ibrahimozdemir@sdu.edu.tr (I. Ozdemir), danny.donoghue@ durham.ac.uk (D.N.M. Donoghue). Forest Ecology and Management 295 (2013) 28–37 Contents lists available at SciVerse ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco