Monitoring the Health Status of Trees in Maksimir Forest Park Using Remote Sensing Methods

Background and Purpose: In Zagreb, the forests have assumed the characteristics of forest parks, of which the most famous and the most visited is Maksimir Park. The health condition of many trees has deteriorated due to environmental changes and the forest’s age. The tree health status can be monitored by direct observation in the field using the terrestrial method, or by remote sensing methods. Recent advances in technology have made it possible to use high-resolution satellite imagery to monitor the damage. Materials and Methods: In order to estimate the health status of trees, the research area - Maksimir Forest Park - was visually interpreted by means of the WorldView 2 (WV2) satellite image, color composite (8, 5, 3). Such color composite was also used to delineate the strata. After delineation, a systematic sample of 25x25 m was laid over the stratum to help interpret the tree health status. Differences in tree damage were observed by comparing the WV2 images and other satellite images (Google Earth images from 2014 and 2016) recorded at different points in time. Field research was then conducted in order to inventory the current situation. Results: The main results of the research in Maksimir Forest Park include the calculation of damage indicators by tree species, as well as thematic maps with the spatial distribution of the mean damage (SO) and damage index (IO) for those tree species which are most represented in a particular stratum. Mean and significant damage of the most represented tree species and overall is also presented spatially in the form of thematic maps. A comparison of the results of WV2 satellite imagery and satellite images taken from Google Earth denoted a change in the tree health status, which confirms that satellite imagery can serve to inventory and track the condition in an area over a number of years. Field investigations and the assessment of tree health status confirmed the results obtained by satellite imagery interpretation. Conclusions: Since quality forest monitoring is based on systematic collection of forest data in any area or at any point in time, the obtained results not only represent the current health status, but also provide a basis for monitoring and predicting the future conditions