Abstract
Strong wind events frequently result in creating large areas of windthrow, which causes abrupt environmental changes. Bare soil surfaces within pits and root plates potentially expose soil to erosion. Absence of forest may alter the dynamics of water circulation. In this study we attempt to answer the question of whether extensive windthrows influence the magnitude of geomorphic processes in 6 small second- to third-order catchments with area ranging from 0.09 km2 to 0.8 km2. Three of the catchments were significantly affected by a windthrow which occurred in December 2013 in the Polish part of the Tatra Mountains, and the other three catchments were mostly forested and served as control catchments. We mapped the pits created by the windthrow and the linear scars created by salvage logging operations in search of any signs of erosion within them. We also mapped all post-windthrow landslides created in the windthrow-affected catchments. The impact of the windthrow on the fluvial system was investigated by measuring a set of channel characteristics and determining bedload transport intensity using painted tracers in all the windthrow-affected and control catchments. Both pits and linear scars created by harvesting tend to become overgrown by vegetation in the first several years after the windthrow. The only signs of erosion were observed in 10% of the pits located on convergent slopes. During the period from the windthrow event in 2013 until 2019, 5 very small (total area <100 m2) shallow landslides were created. The mean distance of bedload transport was similar (t-test, p=0.05) in most of the windthrow-affected and control catchments. The mapping of channels revealed many cases of root plates fallen into a channel and pits created near a channel. A significant amount of woody debris delivered into the channels influenced the activity of fluvial processes by creating alternating zones of erosion and accumulation.
Highlights
Strong wind events may result in extensive damage in forest stands and thereby the creation of large areas of uprooted trees
The creation of a windthrow entails many environmental changes which potentially may impact the type and intensity of slope and fluvial processes acting within a catchment
It may be expected that the lack of forest cover and presence of bare soil surfaces may alter the hydrosedimentary dynamics within a catchment and increase the intensity of fluvial processes
Summary
Strong wind events may result in extensive damage in forest stands and thereby the creation of large areas of uprooted trees. Such phenomena are frequent in mountain landscapes and have many geomorphic consequences. Bare soil surfaces within windthrow pits which, after the uprooting of all the trees in a forest, may cover several percent of a windthrow area (Phillips et al 2008; Strzyżowski et al 2016), may be supposed to increase the delivery of sediment from slopes into channels by intensified slope wash. Lack of roots strengthening the soil mantle may lead to an increase in the landsliding rate (Ziemer 1981) All those changes may cause an increased delivery of sediment into channels. It may be expected that the lack of forest cover and presence of bare soil surfaces may alter the hydrosedimentary dynamics within a catchment and increase the intensity of fluvial processes
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