Large wood in two catchments from the Coastal Mountain range with different land use history

Abstract

Previous researches indicated that in-stream large wood (LW) depended on the characteristics of the riparian vegetation. This is the first study about LW abundance, longitudinal distribution and sediment trapped by large wood structures comparing two stream segments in catchments with contrasting land use, located in the Coastal Mountain Range, Southern Chile. One such catchment (Vuelta de Zorra) is covered mainly by native forests and the other (Pichún) runs under productive plantations. In a stream segment of each catchment the riparian vegetation was characterized, each LW piece was measured and geo-referenced and the channel morphology was defined. Vegetation along the Vuelta de Zorra channel corresponded to an adult second growth forest ca. 200 years old with a basal area of 69 m² ha^-1; while in Pichún, it was a much degraded remnant of old native forests with a basal area of 24 m² ha^-1. Considering channel bankfull area as reference, LW volume at Vuelta de Zorra and Pichún was 109 and 56 m³ ha^-1, respectively. Trapped sediment values in the stream segments were 82 and 30 m³ km^-1 for Vuelta de Zorra and Pichún, respectively; in both channels the accumulations of LW played a key role in the amount of trapped sediment. LW volume was associated with the characteristics of the riparian vegetation which is a consequence of the history of forest interventions and land uses in each catchment.