Abstract
Abstract. Erosion is a relevant soil degradation factor in mountain agrosilvopastoral ecosystems that can be enhanced by the abandonment of agricultural land and pastures left to natural evolution. The on-site and off-site consequences of soil erosion at the catchment and landscape scale are particularly relevant and may affect settlements at the interface with mountain ecosystems. RUSLE (Revised Universal Soil Loss Equation) estimates of soil erosion consider, among others, the soil erodibility factor (K), which depends on properties involved in structure and aggregation. A relationship between soil erodibility and aggregation should therefore be expected. However, erosion may limit the development of soil structure; hence aggregates should not only be related to erodibility but also partially mirror soil erosion rates. The aim of the research was to evaluate the agreement between aggregate stability and erosion-related variables and to discuss the possible reasons for discrepancies in the two kinds of land use considered (forest and pasture). Topsoil horizons were sampled in a mountain catchment under two vegetation covers (pasture vs. forest) and analyzed for total organic carbon, total extractable carbon, pH, and texture. Soil erodibility was computed, RUSLE erosion rate was estimated, and aggregate stability was determined by wet sieving. Aggregation and RUSLE-related parameters for the two vegetation covers were investigated through statistical tests such as ANOVA, correlation, and regression. Soil erodibility was in agreement with the aggregate stability parameters; i.e., the most erodible soils in terms of K values also displayed weaker aggregation. Despite this general observation, when estimating K from aggregate losses the ANOVA conducted on the regression residuals showed land-use-dependent trends (negative average residuals for forest soils, positive for pastures). Therefore, soil aggregation seemed to mirror the actual topsoil conditions better than soil erodibility. Several hypotheses for this behavior were discussed. A relevant effect of the physical protection of the organic matter by the aggregates that cannot be considered in $K$ computation was finally hypothesized in the case of pastures, while in forests soil erodibility seemed to keep trace of past erosion and depletion of finer particles. A good relationship between RUSLE soil erosion rates and aggregate stability occurred in pastures, while no relationship was visible in forests. Therefore, soil aggregation seemed to capture aspects of actual vulnerability that are not visible through the erodibility estimate. Considering the relevance and extension of agrosilvopastoral ecosystems partly left to natural colonization, further studies on litter and humus protective action might improve the understanding of the relationship among erosion, erodibility, and structure.
Highlights
Soil erosion is a key issue in mountain regions worldwide (Leh et al, 2013; Mandal and Sharda, 2013; Haregeweyn et al, 2013; Wang and Shao, 2013)
We studied the relationships between soil aggregate stability and both erodibility (RUSLE K factor) and erosion rates (RUSLE estimate) in a mountain catchment with two different vegetation covers
In this work we wanted to assess the relationships between aggregate loss and both soil erodibility and erosion rates in a mountain agrosilvopastoral ecosystem characterized by two land cover types
Summary
Soil erosion is a key issue in mountain regions worldwide (Leh et al, 2013; Mandal and Sharda, 2013; Haregeweyn et al, 2013; Wang and Shao, 2013). Mountain soils develop in very sensitive environments subject to natural and anthropic disturbances (e.g., Cerdà and Lasanta, 2005; Vanwalleghem et al, 2011; Van der Waal et al, 2012; García Orenes et al, 2012), and they are often located at the interface with. Considering that mountain soils are generally shallow and their fertility is often concentrated in the uppermost layers, soil erosion represents a crucial problem affecting the landscape at different scales and is a serious challenge for land management and soil conservation (García-Ruiz and LanaRenault, 2011; Angassa et al, 2014; Bravo Espinosa et al, 2014). RUSLE (Revised Universal Soil Loss Equation), derived from USLE (Wischmeier and Smith, 1978; Renard et al, 1997), is one of the most widely accepted empirical methods and, despite originally being applied at plot scale, is being applied on catchments in a wide set of environments, including semi-natural ecosystems. Examples of mountain applications are widespread and reported by Meusburger et al (2010) for the Swiss Alps, Haile and Fetene (2012) for Ethiopia, Ligonja and Shrestha (2013) in Tanzania, and Taguas et al (2013) in Spain
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