Effects of prescribed burning for pasture reclamation on soil chemical properties in subalpine shrublands of the Central Pyrenees (NE-Spain)

Highlights: • Prescribed burning is used to remove shrubs and recover subalpine pastures. • We studied its effect on soil chemical properties immediately and one year after. • Fire had few direct effects on nutrient content but it decreased one year later. • New SOM inputs induced changes in cation exchange capacity and exchangeable cations. • Research further in time is needed to assess the sustainability of this practice. The abandonment of the traditional pastoral activities in the subalpine grasslands of the Central Pyrenees (NE-Spain) has resulted in shrub encroachment processes that are dominated by species such as the Echinospartum horridum. Therefore, prescribed burning has been recently readopted in this region as a management tool to stop the spread of shrubs and recover grasslands. We aimed to assess the effect that this practice may have on soil chemical properties such as SOC, N, pH, EC, water-extractable and exchangeable cations (Ca²⁺, Mg²⁺ and K⁺), cation exchange capacity, inorganic N forms (N-NH₄⁺ and N-NO₃⁻) and available P. We studied two prescribed burnings conducted at the subalpine level of the Central Pyrenees in the municipalities of Tella-Sin (April 2015) and Buisán (November 2015). At each site, the topsoil was sampled in triplicate at soil depths of 0–1, 1–2 and 2–3 cm immediately before (U), immediately after (B0) and one year after (B12) burning, and litter and/or ashes were removed prior to sampling. The results indicate that in the B0 samples, burning significantly reduced the SOC and N contents as well as the exchangeable Ca²⁺ and Mg²⁺ at 0–1 cm, whereas the rest of the studied properties remained virtually unchanged. However, in the B12 samples we detected a decrease of nutrient content that was probably related to leaching and/or erosion processes.