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.

The impact of three fire fighting chemicals (FFC) on 11 chemical soil properties and on soil recovery (0-2 cm depth) was evaluated 1, 30, 90 and 365 d after a prescribed fire. Five treatments were considered: unburnt soil (US) and burnt soil with 2 l m -2 of water alone (BS) or mixed with the foaming agent Auxquímica RFC-88 at 1% (BS+Fo), Firesorb at 1.5% (BS+Fi) and FR Cross ammonium polyphosphate at 20% (BS+Ap). At t=1 d, soil pH increases in the order US < BS . BS+Fo, BS+Fi < BS+Ap, which was most likely due to the accumulation of ashes, the reduction of organic acids and the cations supplied by FFC. In all burnt treatments, soil pH remained significantly higher than in US up until t=90 d. SOM richness remained similar and constant until t=90 d in all plots, but, probably due to fire-triggered erosion, at t=365 d it was significantly lower in BS+Ap (C, N), BS and BS+Fo (C) than in US. Immediately after the fire, soil * + -N levels in BS+Ap (200x that of US; 9-18x those of BS, BS+Fo and BS+Fi), and its persistence can delay the post-fire vegetation recovery due to the toxicity of NH 4 + to seeds and seedlings. NO 3 -N levels changed significantly only in BS+Ap between t=30 and t=90 d due to the nitrification of its large NH 4 + -N pool. Except in BS+Ap, whose soil P levels were 70-140x (t=1 d) and 10-20x (t=365 d) higher than in the other treatments, available P content in BS and BS+FFC was not significatively higher than in US. The concentrations of available cations in BS and BS+FFC were higher (not always significatively, except for K) than in US until t=90 d, likely due to ashes-and FFC-derived cations. Contrarily to divalent cations, monovalent cations (more soluble and easily leached) decreased slowly until t=90 d.

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.

No abstract

The impacts of fire and fire-fighting chemicals (FFC) on soil properties and the soil-plant system were evaluated five years after treatment application. Unburnt soils (US) were compared with burnt soils treated with water alone (BS) or with foaming agent (BS+Fo), Firesorb polymer (BS+Fi), or ammonium polyphosphate (BS+Ap). Soils (0-2 cm depth) and foliar material (Ulex micranthus, Pterospartum tridentatum, Erica umbellata and Pinus pinaster) were analysed for total-C, total-N, δ BS+Ap than in other treatments, while the opposite was observed for Erica; shrubs were always taller in BS+Ap. After 3 years of growth, the size of pine seedlings followed the order BS+Ap > US > other treatments.Foliar N and P, scrub regeneration and growth of pines showed the long-term fertilizing effect of ammonium polyphosphate, although the second highest pine mortality was found in the BS+Ap treatment. The foaming agent did not affect vegetation cover, and Firesorb had no noticeable effect on shrubs but the highest pine mortality.