How Does Forest Litter Extraction Commonly Used in the Past Affect the Runoff Reaction to Heavy Rainfalls?

ABSTRACT

Until the middle of the 20th century, organic material was removed from the forest floor in Central Europe and used as bedding in the stables. The mixture of excrements and organic material was finally spread as fertilizer on the fields. The presented study aims at quantifying the hydrological effect of this historical extraction practise, also called litter raking, at extreme rainfall events. We measured surface runoff before and after such an intervention at four experimental plots simulating a rainfall intensity of 100 mm/h. Additionally, soil moisture has been recorded continuously on the plots with litter extraction and nearby control plots. The results of the rainfall simulation campaigns were as follows: One of the four experimental plots, which already produced a high amount of surface runoff without litter extraction, reacted with an increase of the surface runoff coefficient from 0.49 to 0.63 following this intervention. Another plot showed a slight reaction after litter extraction, with an increase of the surface runoff coefficient from 0.01 to 0.16, and on two plots there was hardly any reaction. After almost a year, the surface runoff that occurred after the intervention had already decreased again. The removal of ground vegetation and reduction of organic layers' thickness by litter raking causes faster changes in soil moisture and a more pronounced short‐term response. Combining the different results of this study reveals a complex interplay of precipitation type, organic layers properties, its system status and the characteristics of the underlying mineral soil, which all together also controls the occurrence and intensity of surface runoff.