Deciphering the history of forest disturbance and its effects on landforms and soils – lessons from a pit-and-mound locality at Rogowa Kopa, Sudetes, SW Poland

Abstract

The historical dimension of pit-and-mound topography has been studied at the Mt Rogowa Kopa locality, Stołowe Mountains, SW Poland. This site represents one of the best developed regional examples of hummocky forest floor relief due to widespread tree uprooting and subsequent degradation of root plates. Through map analysis and dendrochronology the disturbance history was traced to at least the 1930s and, most likely, a strong wind episode from 1933 was the reason for the forest calamity that resulted in the nearly total destruction of the original stand. However, the affected forest was a planted Norway spruce monoculture, introduced and managed until at least the beginning of the 20 th century, and not a natural forest. The windthrow niche was then used by beech, whose individuals preferentially chose mounds to grow, conserving the hummocky microtopography. Changes in soil evolutionary pathways brought about by wind-driven disturbance include both haploidisation (rejuvenation) and horizonation (differentiation). Evidence of soil rejuvenation includes a decrease in organic carbon content and an increase in pH in the upper parts of soils developed on mounds relative to the pH of undisturbed references soils. Soil texture was relatively homogenised in pits and mounds. Dating of the pit-and-mound microrelief by means of soil properties (organic carbon content, iron forms) was only partly successful. Although the young age of pits and mounds is evident, the actual age inferred from soil properties was underestimated by a few tens of years. Evaluation of factors potentially controlling the propensity to widespread treethrow suggests that the type of forest is a far more important variable than local abiotic factors of bedrock geology, regolith characteristics, and slope inclination.