High-mountain soils are rich in partially decomposed organic matter, which is highly sensitive to mineralization and fire. Prescribed burning is performed in the Pyrenees to keep subalpine grasslands open for grazing. The compositions of the ash, litter and duff layers, and the particulate organic matter (POM) of the topsoil in the 0–1, 1–2, 2–3, and 3–5 cm depths were analyzed in relation to the nutrient availability after the prescribed burning of a stand encroached by erizón (Echinospartum horridum). The concentrations of C, N, P, and S and organic components (nonstructural, hemicellulose, cellulose, and lignin-type) were determined before the prescribed burn and 0, 6, 12, 18, and 24 months after the prescribed burn. The fire consumed the aboveground biomass, the litter and part of the duff layer, and the most thermostable (i.e., lignin-type) components and the least volatile elements (P, S) were selectively preserved in the resulting ash. Prescribed burning caused significant losses of organic-C and N only in the 0–1 cm depth (–72% and –68%, respectively). The organic-C loss was mostly (82%) from the POM, whereas the N loss was from more similar proportions of the POM (57%) and the nonparticulate organic matter (NPOM) (43%). However, few changes were observed in the composition of the organic matter, which pointed to a largely uneven combustion that resulted in a substantial part of the organic matter remaining largely untouched by the fire. After 6 months, the duff layer was depleted in hemicellulose by 32% compared to immediately after the burn, and fragmentation of the POM into the NPOM was observed. During the second spring, N- and P-rich charred POM were incorporated into the top 1 cm, while C-rich charcoal particles underwent fragmentation and vertical transport into the deeper soil. The preburn ecosytem was limited by P, and likely also by S. The plant available N showed transient increases of 1.5–2.1 times the immediate postburn levels for nitrate-N at 12 months after burning, and of up to 10–20 times for ammonium-N at 18 months. In contrast, the concentrations of plant-available P and S gradually declined to 1.8–3.3 and 1.8–4.0 times, respectively, lower at 24 months after the burn. Results indicated that fire-induced increases in the nutrient availability can be short-lived in high-mountain habitats, but steadier and likely more persistent nutrient inputs can derive from the gradual breakdown of charred organic matter.

高山区的土壤富含部分分解的有机物，这些有机物对矿化和火灾高度敏感。在比利牛斯山脉进行规定的燃烧，以保持亚高山草原开阔地放牧。分析了土壤中0-1、1、2、2、3和3-5 cm深度的表层土壤的灰分，垫料和粉尘层组成以及颗粒有机物（POM）与养分的有效性在按照规定烧掉erizón（Echinospartum horridum）。C，N，P和S以及有机成分（非结构性，半纤维素，纤维素和木质素类型）的浓度在规定的灼伤之前和规定的灼伤后0、6、12、18和24个月内确定。火烧掉了地上的生物质，垃圾和部分粉扑层，并且最热稳定的（即，木质素类）成分和最不挥发的元素（P，S）被选择性地保存在生成​​的灰烬中。规定的燃烧仅在0-1 cm深度（分别为–72％和–68％）内引起有机碳和氮的大量损失。有机碳的损失主要来自POM（82％），而氮的损失来自POM（57％）和非颗粒有机物（NPOM）的相似比例。但是，有机物的组成几乎没有变化，这表明燃烧过程很不均匀，导致大部分有机物质基本上未被火所触及。6个月后，与灼伤后立即相比，duff层的半纤维素减少了32％，并且观察到POM碎裂成NPOM。在第二个春季，将富含N和P的烧焦的POM掺入顶部1 cm，而富含C的木炭颗粒进行破碎并垂直输送到更深的土壤中。燃前生态系统受到P的限制，也可能受S的限制。工厂可利用的氮在燃烧后的12个月内显示出瞬时的立即燃烧水平，硝态氮的瞬时增加水平是硝化氮的1.5-2.1倍，铵的瞬时增加水平是氨的高达10-20倍。 -N在18个月。相比之下，植物可利用的磷和硫的浓度逐渐下降至1.8-3.3和1.8-4.0倍，分别在烧伤后24个月降低。结果表明，火烧引起的养分利用率的增加在高山区栖息地中可能是短暂的，但是更稳定，更持久的养分输入可能源于炭化有机物的逐渐分解。