The effects of fire (Control burned soil) and two emergency stabilisation techniques (grass Seeding and straw Mulching) on 20 chemical characteristics were evaluated on 0-5 cm top-soils sampled 1, 90, 180 and 365 days after an experimental fire in a steep shrubland of a temperate-humid region (NW Spain). Most part of pH (in H 2 0 and KC1) variance was explained by the sampling date. No clear temporal trends were identifiable for total soil C and N content, likely due to the large SOM pool in these soils; however, changes on soil 8 13 C were explained by the deposition of 13 C-depleted ashes, followed by its progressive erosion, while those on soil S 15 N were a consequence of fire induced N outputs. After the fire, NH^-N, P, Na, K, Mg, Ca, Mn, Cu, Zn and B concentrations increased, while those of NO^ -N, Al, Fe and Co did not vary significantly. Despite a significant decline with time, concentrations of Mg, Ca and Mn at the end of the study were still higher than in unburned soil, while those of K, Cu, Zn and B were similar to the pre-fire levels and those of Nftf-N, P and Na were below pre-fire values. Mulching and Seeding treatments for burned soil emergency stabilisation had significant effects on soil 8 15 N and extractable K, Mg and Ca, while data were inconclusive for their possible effects on the extractable Al, Fe and Co.

Abstract.After an experimental fire in steep shrubland in a temperate-humid region (north-west Spain), the effects of two post-fire stabilisation treatments (grass seeding and straw mulching) on the chemical properties of eroded sediments, and the amount of nutrients lost with them, were evaluated relative to control burnt soil, over a period of 13 months. Total C and N concentrations, and 8 13 C, indicated that sediments were mainly contributed by charred plant and litter material. The highest concentrations of extractable base cations in the sediments occurred during the first 3 months following fire, especially for Na and K. As treatments had little or no effect on nutrient concentration in sediments, differences in nutrient losses were due to the 10-fold lower sediment production in mulching compared with other treatments. In control and seeding treatments, the accumulated amounts of nutrients lost with sediments were 989-1028 kg ha" 1 (C), 77 kg ha" 1 (N), 1.9-2.4 kg ha" 1 (Ca), 0.9-1.1 kg ha" 1 (Mg), 0.48-0.55 kg ha" 1 (NH|-N), 0.39-0.56 kg ha" 1 (K), 0.19-0.34kgha" 1 (Na) and <0.1 kg ha" 1 (P and NOF-N). These values accounted for 22-25% (total C and N) and 5-12% (NH|-N, Ca, P and Mg) of available nutrients in ash, and 1.0-2.4% of those in ash+topsoil. As nutrient and sediment losses were strongly correlated, the reduction of the latter by mulching application leads to an effective decrease of post-fire nutrient losses.

Long‐term effects of improved pasture establishment (with high proportion of legumes) on soil organic‐C status and N availability in Mediterranean cork oak (Quercus suber L.) woodlands were assessed. Soils were sampled beneath scattered crowns and in open areas, considering two systems: unmanaged and managed woodlands where improved pastures were installed 26 and 32 years ago. Total and labile C and N pools were measured and C and N mineralization were determined over 24 weeks laboratory incubation. Soils under improved pastures showed higher organic‐C, total‐N and net N mineralization than those under unmanaged pasture, mainly when established beneath trees. Potentially mineralizable C, C mineralization rate and microbial C were not statistically different between the unmanaged and improved pasture sites, but were higher closer to the tree than in the open area (1.8, 1.2 and 1.2 times, respectively). The qCO2 was higher in improved pastures (1.7 times). Labile pool of C and N extracted with hot water increased under improved pasture (3.4 and 1.7 times, respectively). Results indicate that soil quality amelioration by improved pastures is stronger in the presence of oak trees. Management systems that favour oak tree maintenance and regeneration should be taken into account to reverse soil degradation.

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Background and aimsIntensive land use has led to degradation and abandonment of Portuguese oak woodlands, and subsequent shrub encroachment may have altered the spatial heterogeneity of soil C and N pools. The aim of this study was to evaluate the effects of shrub invasion on soil C and N dynamics in an oak woodland in Southern Portugal. MethodsSoil was sampled beneath and outside scattered Quercus suber L. canopies, considering non encroached areas and areas encroached by shrubs (Cistus ladanifer L. or Cistus salviifolius L.). ResultsThe spatial heterogeneity of soil C and N contents was mainly associated with tree presence. Outside tree canopies, the labile C pools were larger (mainly beneath C. ladanifer) and C cycling was faster in encroached areas than in non encroached areas. Net and gross N mineralization and urease and protease activities were also higher in encroached than in non encroached areas; however, the metabolic quotient and the Cmicrobial/Corganic ratio were not significantly affected. Beneath the tree canopy, significant effects of encroachment included a small increase in soil labile C and the enzymatic activity beneath C. ladanifer. ConclusionsThe results indicate the potential capacity of shrub encroachment to accumulate soil organic C in the long term. The rate of soil C and N turnover promoted by shrub encroachment may depend on the Cistus species present.