Land use change of transhumant drove roads leads to soil quality degradation: a case study in Central Spain

Abstract

Grassland soils, beyond their role as biodiversity reservoirs, actively contribute to the provision of numerous ecosystem services. In the Iberian Peninsula, drove roads, the traditional routes used for seasonal livestock movements in search of the most productive pastures, play a key role in the preservation of semi-natural grasslands and in the protection of the upper soil horizon. However, the absence of transhumant pastoralism has led to the degradation of these natural corridors, with unexplored consequences in terms of soil quality and functioning. To investigate the relationship between the conservation state of these livestock routes and soil characteristics, which had not been researched to date, we selected thirty sites within the Madrid drove road network in central Spain. We established three categories: (i) reference well-preserved drove roads and two degraded states: (ii) overgrown abandoned and (iii) eroded drove roads and collected soil samples at each state. We determined soil physicochemical variables like the percentage of C, total N and P, available K, pH and electrical conductivity. We also measured soil enzyme activity using fluorometric methods and assessed litter decomposition through the Tea Bag Index experiment. Our findings demonstrated that the preservation state of drove roads had a significant impact on soil fertility. The mean carbon percentage was up to ten times lower in eroded drove roads compared to reference sites, while nitrogen content was four times higher in reference sites, and phosphorus and potassium content were twice as high in reference drove roads compared to eroded sites. Litter decomposition rate was also half in eroded soils compared to reference sites. Although the nutrient content and litter decomposition of overgrown abandoned drove roads did not differ from reference sites, enzyme activity was significantly higher in reference soils compared to both degraded states. Arylsulfatase activity was six times higher in reference plots, which also showed twice as much phosphatase activity and up to four times as much β-xylosidase activity. Our results confirmed our hypothesis that drove roads suffering from erosion have the most degraded soils. Additionally, we found that both the excessive accumulation of biomass due to grazing abandonment and the loss of vegetation cover through erosion contribute to the loss of soil functionality within the Madrid drove road network. The lack of use and subsequent degradation of drove roads compromise both the stability of the soil ecosystem and the availability of nutrients for plants. Given the vast surface area covered by this network of corridors, the reintroduction of transhumant and local extensive grazing can be an important tool to improve soil characteristics.