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Recreational trails are a vital element of protected natural areas (PNAs) infrastructure, which enables visitors to travel through and engage in various activities such as hiking, biking, horse riding. Degradation of trails adversely affects the natural environment as well as the safety and comfort of visitors. As the role of many PNAs is to protect the natural environment and to provide recreational opportunities, the need to obtain accurate information about the condition of the trails and the direction of their transformation is evident. Spatial characteristics of trails can be very heterogenic even within a single park, and this heterogeneity hinders our understanding of different types of direct human impacts across the landscape. Therefore, there is a need for a tool allowing for mapping large portions of trail networks within a reasonable time to get a full picture of trail conditions in space and their change through time. In this paper, we present a protocol for high-resolution mapping and monitoring of recreational trail conditions using UAV surveys, Structure-from-Motion (SfM) data processing and geographic information systems (GIS) analysis to derive spatially coherent information about indicators of trail degradation and associated trail characteristics, e.g., by detailed mapping of trail width, and incision. We tested the approach in three dramatically different settings: (1) Two trails studied in Orange County (California, USA) were characterized by mean width of 0.6 m and 2.8 m and mean incision of 0.05 m and 0.3 m, respectively – in this case study we demonstrated a strong correlation between ground-based and UAV-based surveys of trail width and incision; (2) Valle de Cocora (Colombia) hiking and horse-riding trails were characterized by mean width of 0.5 m and 1.2 m respectively, and incision which occurred on 28% of hiking and 87% horse-riding trail – this case study indicated good agreement between object-based classification and manual delineation of the trail tread; (3) in Rainbow Mountain (Peru) mean width was 1.8 m for hiking, 15.6 m for horse-riding trail and 23.6 m for the multi-use trail. Presented case studies enabled us to verify the broad applicability of the proposed workflow. |
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