Spruce forest litter structure, distribution, and water retention along hiking trails in the Ukrainian Carpathians

Almost 24% of the Ukrainian Carpathian ecosystems are assigned to the conservation fund due to their ecological values and attraction to numerous tourists. The forest litter in mountain forest stands plays an important role in terms of its ability to mitigate the impact of tourist activities, and erosion processes along with its contribution to the soil mineralization. Water interception, infiltration, and retention ability of forest litter have an impact on hydrological processes of forest ecosystems. At the same time, the accumulation and spatial distribution of litter can be affected not only by environmental conditions, but also by tourism. In this study, 13 Norway spruce (Picea abies L.) stands distinguished by average distance to the trail were chosen to investigate whether there are any differences in litter structure, water retention, and infiltration abilities as well as litter accumulation in areas along popular hiking trails in the Ukrainian Carpathians. Results showed that the litter thickness has increased with altitude and slope steepness. Moreover, results of one-way ANOVA demonstrate a significant difference (P < 0.05) in litter stock between two groups of sample plots: established directly to adjoin hiking trails and at a distance. Therefore, the forest litter stock nearby hiking trails may indicate that trampling caused by tourists has a negative impact on litter accumulation. However, no statistical difference was found (P > 0.05) in the accumulation of litter along three trails and altitudes across all surveyed forest stands. Results of the immersion test showed that the litter infiltration rate has a significant negative correlation with the maximum mass of absorbed water (r = –0.62, P < 0.05), litter stock (r = –0.69, P < 0.01), and retained precipitation (r = –0.62, P < 0.05). Despite our assumption, the infiltration rate was lower for sites distanced from the hiking trail in comparison with adjoining ones. According to our measurements, the water holding capacity of the litter varies from 42.3 t·ha^–1 to 187.3 t·ha^–1 regardless of the stand composition. Further, the precipitation amount retained by litter varies between 4.2 mm and 18.7 mm. Insignificant differences in litter fractional structure and accumulation were observed in pure spruce stands and mixed spruce-beech with an admixture of beech up to 20%. Further observational and modelling studies are necessary to clarify the role of the beech share in stand composition in relation to fractional structure and water interception and retention ability.