Assessment of trampling impact in Icelandic natural areas in experimental plots with focus on image analysis of digital photographs

Sammanfattning: Increasing tourism in the spectacular but sensitive ecosystems in Iceland arises concern to the country’s authorities how to best manage tourism in these natural areas within a level of acceptable change. Research is thus required regarding what affect tourism has on different environments. Deterioration of natural areas in Iceland from trampling by numerous hikers are causing visible vegetation loss, widening and deepening of existing hiking trails with subsequent soil erosion. In this study, the primary goal was to assess impact to three typical Icelandic vegetation types (grassland, mossheath and moss) due to recreational short-duration trampling pressure. Measurements in experimental plots of soil compaction, soil moisture, soil surface depth, and vegetation cover were analysed for different hiking pressures. The study areas include the two most popular areas of nature-based tourism in Iceland; Þingvellir [ˈθiŋkˌvɛtlɪr̥] National Park and Fjallabak Nature Reserve. One of the main issues in field measurement techniques is how to achieve a cost- and time effective method to estimate vegetation cover with adequate accuracy. The second goal of this study was to assess the performance of digital photography and subsequent image analysis as a tool for estimating vegetation cover, a method not previously used in the field of recreational trampling research. Three different methods are evaluated; supervised classification of the images, segmentation of the images using the ExGR (Excess Green minus Excess Red) index and extraction of greenness information from the images through application of the Green Chromatic Coordinate (GCC). The results, together with previous research show that image analysis of digital photography is a valuable tool for detecting changes in vegetation. All three methods applied show ability to assess vegetation cover, the supervised classification method being the most accurate method for quantitative measurements. The Icelandic vegetation types consist greatly of moss species of various colors not enhanced when greenness indices are applied to the RGB images. Nevertheless, the greenness index methods resulted in the same conclusion as the supervised classification method as regards the relationship between vegetation cover and trampling pressure, and in the evaluation of the resistance of each vegetation type. All vegetation types show being significantly altered with added trampling pressure in terms of change of the physical properties of soil and of vegetation cover. The mossheath vegetation type, and especially the type in the highland (Fjallabak Nature Reserve) is verified as being the least resistant to trampling pressure. Relationships of soil compaction, surface depth and vegetation cover with trampling were curvilinear, suggesting higher rates of damage at initial stages of trampling.