The hydrological and geomorphological effects of an exceptional 14 rainstorm event that occurred in the central Spanish Pyrenees during 19-21 October 15 2012 were studied in five experimental catchments under various land covers: (i) 16 subhumid badlands; (ii) dense forest; (iii) an abandoned farmland area recolonized by 17 shrubs and forest patches; and (iv) subalpine grasslands. Hydrographs and sedigraphs 18 demonstrated that vegetation cover is a major factor affecting the control of floods even 19 during exceptional rainstorms, at least at the spatial scale at which the phenomenon was 20 studied (catchment sizes: 0.3-2.8 km 2 ) and under dry catchment conditions. The 21 combined precipitation over the two days (ca. 250 mm) was the greatest for any two-22 day event recorded since 1950 in the central-western Pyrenees for all but one of the 23 stations in the study. Five pulses of most intense rainfall were recorded. The forested 24 catchment did not react to the two most intense rainfall pulses, because of the very low 25 antecedent level of the water table. The main peak flow occurred only when at least a 26 part of the catchment was saturated. The abandoned farmland catchment had two small 27 peak discharges at the beginning of the event, which were produced by infiltration 28 excess overland flow from eroded areas close to the main stream. During the third most 29 intense rainfall period a large part of this catchment contributed to runoff and a 30 relatively high peak discharge was produced. The badland catchment reacted 31immediately from the beginning of the rainstorm, yielding very high discharges 32 accompanied by high suspended sediment concentrations. The subalpine catchment 33 showed a hydrograph mirroring the hyetograph, with brief but intense hydrological 34 responses to increased precipitation, because of the marked gradients and the presence 35 of bare rock in the headwaters. A high volume of bedload was carried during the peak 36 discharge. Mediterranean region, particularly in coastal areas where rainfall of more than 200 mm 44 in 24 hr is commonly recorded, generally in autumn (López Bermúdez and Romero 45 Díaz, 1993; Poesen and Hooke, 1997; González Hidalgo et al., 2003). These rainstorms 46 are usually caused by warming of the Mediterranean Sea at the end of summer and the 47 occurrence of cold advection at high atmospheric levels, which results in 48 thermodynamically unstable cut-off systems (Nieto et al., 2005) having a duration of 49 two or three days. As a consequence, the most extreme flash floods within Europe tend 50 to occur in the Mediterranean region (Gaume et al., 2009), with some studies reporting 51 a change in flow from zero to hundreds of cubic meters per second in minutes 52 (Camarasa Belmonte and Segura Beltrán, 2001). 53Very large and intense rainstorms also occur in the interior of the Iberian 54Peninsula. These are typically localized and affect relatively small areas. This was the 55 case for the Rivillas ravine in the Guadiana River basin, where a flash ...

Woody encroachment has been an ongoing process in the subalpine belt of Mediterranean mountains, after land abandonment, the disappearance of the transhumant system and the decrease of the livestock number. The main objectives of this study were: (i) to identify land use/land cover (LULC) changes from 1956 to 2015, and (ii) to investigate the effects of LULC changes in physical and chemical soil properties and soil organic carbon (SOC) and nitrogen (N) stocks. It is hypothesized that woody encroachment in the subalpine belt may lead to significant changes in soil properties, and will generate an increase in the SOC stocks. A land use gradient was identified in the subalpine belt of the Central Spanish Pyrenees: (i) subalpine grasslands, (ii) shrublands, (iii) young forests, and (iv) old forests. Mineral soil samples were collected every 10 cm, down to 40 cm, at three points per each LULC and a total of 48 samples were analyzed. The results showed that (i) woody encroachment has occurred from 1956 to 2015 due to the expansion of coniferous forests and shrublands (at the expense of grasslands), (ii) land cover and soil depth had significant effects on soil properties (except for pH), being larger in the uppermost 0-10 cm depth, (iii) SOC and N contents and stocks were higher in the grassland sites, and (iv) the woody encroachment process initially produced a decrease in the SOC stocks (shrublands), but no differences were observed considering the complete soil profile between grasslands and young and old forests. Further studies, describing SOC stabilization and quantifying above-ground carbon (shrub and tree biomass) are required.

Many studies have reported the phytotoxicity of allelopathic compounds under controlled conditions. However, more field studies are required to provide realistic evidences for the significance of allelopathic interference in natural communities. We conducted a 2-years field experiment in a semiarid plant community (NE Spain). Specifically, we planted juvenile individuals and sowed seeds of Salsola vermiculata L., Lygeum spartum L. and Artemisia herba-alba Asso. (three co-dominant species in the community) beneath adult individuals of the allelopathic shrub A. herba-alba, and assessed the growth, vitality, seed germination and seedling survival of those target species with and without the presence of chemical interference by the incorporation of activated carbon (AC) to the soil. In addition, juveniles and seeds of the same three target species were planted and sown beneath the canopy of adults of S. vermiculata (a shrub similar to A. herba-alba, but non-allelopathic) and in open bare soil to evaluate whether the allelopathic activity of A. herba-alba modulates the net outcome of its interactions with neighboring plants under contrasting abiotic stress conditions. We found that vitality of A. herba-alba juveniles was enhanced beneath A. herba-alba individuals when AC was present. Furthermore, we found that the interaction outcome in A. herba-alba microsite was neutral, whereas a positive outcome was found for S. vermiculata microsite, suggesting that allelopathy may limit the potential facilitative effects of the enhanced microclimatic conditions in A. herba-alba microsite. Yet, L. spartum juveniles were facilitated in A. herba-alba microsite. The interaction outcome in A. herba-alba microsite was positive under conditions of very high abiotic stress, indicating that facilitative interactions predominated over the interference of allelopathic plants under those conditions. These results highlight that laboratory studies can overestimate the significance of allelopathy in nature, and consequently, results obtained under controlled conditions should be interpreted carefully.

Land abandonment followed by natural revegetation constitutes the main land-use change in the Mediterranean mountains, affecting soil quality and soil organic carbon (SOC) stocks; however, there are few studies analysing the effects of cropland abandonment on soils in mid-mountains. In the Leza Valley (Spain), 43.2% of the area was cultivated but abandoned during the 20th-century. Natural revegetation gave rise to five land uses (LULCs): pastures (5 years), shrubs (Cistus laurifolius, 20-35 years), bushes (Juniperus communis, 35-50 years), young forests (Quercus pyrenaica) and old forests (>70 years). The aim of this research was to study the effects of natural revegetation of abandoned fields on physico-chemical soil quality and SOC in various LULCs. In each of the LULCs, soil samples were collected every 10 cm, down to 40 cm depth, at three points, with a total of 60 samples being analysed (12 per LULC). In addition, plant species inventories were carried out. The results indicated (a) significant differences in physico-chemical soil quality between the first years of abandonment and forests; (b) the SOC content increased with revegetation duration and decreased with increase in soil depth; (c) the highest SOC and TN stocks were found in the first 10 cm; (d) the results of the principal component analysis with all the data differentiate forests from shrubs and pastures. This study confirms the need to be aware of the effects of land abandonment and natural revegetation processes on the soil, in order to promote management strategies to preserve ecosystem services that agricultural marginal lands can provide.