Leaf injury symptoms of Tilia sp. as an indicator of urban habitat quality

Urban habitat quality and its effects on humans and the environment are of great concern in regard to human and vegetation health security, urban planning and habitat management. Different methods have been used to monitor habitat quality. Certain of these methods are expensive, labor-intensive, time-consuming and problematic to extrapolate to a larger spatial region of interest. s paper, we evaluate a non-destructive and low-cost method to assess urban habitat quality. The method is based on quantifying leaf injury symptoms using imagery obtained with a digital camera. The leaves of lime trees (Tilia sp.), split up into two different groups of with and without trichomes, were sampled in Ghent (Belgium) during the summer of 2009. Leaf sampling was conducted in four different urban habitats, corresponding to four land use classes that are characterized by different degrees of environmental pollution. Leaf necrotic spots, as well as chlorotic patches, were selected as indicators of leaf injury. Our results reveal that the density of necrotic spots, as well as chlorotic patch areas, significantly increase in industrial land use zones compared with other land use classes for both Tilia sp. groups. The injured leaf area reflectance significantly increased for the camera RGB bands of industrial zones compared with the three other types of habitats. These results indicate that injured leaf area reflectance is a sensitive indicator that can be quickly determined. Thus, this technique enables fast, site-based bio-monitoring of urban habitats compared with the determination of leaf parameters, such as leaf density, area or the number of (necrotic and chlorotic) leaf spots as other indicators of leaf injury. ustrated that the injured leaf area reflectance, as determined using leaf surface reflectance, and extracting symptoms is a novel, as well as practical, approach to assessing urban habitat quality.