Regional assessment of forest effect on watershed hydrology: Slovakia as a case study

Recently, the importance of forest effect on watershed hydrology has been increasingly recognized due to an elevated threat of floods and expected alterations of water regime in watersheds induced by climate change. We assessed the trade-off between natural conditions of 61 basic watersheds in Slovakia and expected water-regulatory capacity of forest in these watersheds. A multi-criteria decision-making scheme was proposed to calculate a coefficient for each watershed indicating the need to regulate its water regime as given by natural conditions, and another coefficient indicating the magnitude of forest water-regulatory capacity given by forest structure and distribution. Factors indicating the forest water-regulatory capacity were extent of forest cover, forest fragmentation and distribution in watersheds relative to the spring area, forest stand density and vertical structure, and tree species composition. The results indicate that the present structure and distribution of forests in Slovakia has potential to moderately regulate the water regime at the scale of basic watersheds. We identified critical watersheds where natural conditions imply the unfavourable water regime and/or the forest water-regulatory capacity is weak. Limits of forest effect on watershed hydrology and caveats for interpreting the presented findings are discussed.