High-intensity and fast-spreading wildfires are natural in the Mediterranean basin. However, since 1960, wildfire occurrence has increased because of changes in land use, which resulted in extensive ...land abandonment, increases in the fuel load and continuity in the landscape. The level of soil degradation related to wildfire occurrence depends on fire recurrence, topography of the site, intensity of the soil erosion processes and plant cover post-fire regeneration rate. Therefore assessing fire impacts on soil properties is critical to quantify land degradation processes and to assess post-fire restoration plans. This article reviews the changes in soil nutrient status of Mediterranean ecosystems affected by wildfires by focusing on the interactions between the different drivers and factors, and the underlying processes of these changes. Articles dealing with wildfires in areas belonging to the Mediterranean basin and characterized by an annual average rainfall of 300–900mm and a mean annual temperature around 14–19°C, have been reviewed. The data show that the soil nutrient content in Mediterranean drylands affected by wildfires depends on the vegetation type, fire recurrence and fire intensity. Immediately after a fire, the nutrient content in both the O and A horizons often increases because of ash deposition, nutrient release from the burnt vegetation and formation of stable nutrient forms. Ash deposition persistence on the soil surface is one of the most important factors in determining the soil nutrient content both immediately after a fire and for the long-term. For the restoration of burned habitats it is important to know the content and the spatial distribution of nutrients in the soil because this can act as a limiting factor to vegetation recovery. Carbon and nitrogen pools in the soil have been recognized as fundamental to vegetation recuperation after a fire. To promote the accumulation and retention of nutrients in soil after a fire, it is important to stabilize the burnt site by applying post-fire measures that limit soil erosion, surface runoff and wind loss of the ash. Depending on the plant species and the time elapsing between consecutive wildfires, fire is responsible for the transition from mature ecosystems (i.e. conifer forests) to shrublands, which are poorer in soil nutrient status. Wildfire occurrence can be reduced by planting fire-resilient plants in fire-prone areas. To define the best post-fire and restoration treatments, the impacts of fire on both the O and the A horizon as well as the impacts of different post-fire treatments on the soil nutrient content require further study.
In dryland ecosystems, post-transplant water stress produces high seedling mortality after the first summer following outplanting. Our aim was to assess the effects of clay and hydrogel, both on the ...water holding capacity of the growing media and on various morphological and physiological characteristics of Quercus suber seedlings in the nursery and, subsequently, during the first 2 years in the field. Quercus suber L. seedlings were grown in four types of growing media: CS (Control growing media, standard mixture of limed peat and coconut peat, 1:1 v/v ratio), SC-10 (CS mixed with sepiolite clay at 10% v/v) and HS (CS mixed with hydrogel Stockosorb® K-400 at two doses, 0.7 and 1.5% w/w). HS-1.5 showed the best results, increasing the water holding capacity of the root plug, improving seedling water status and increasing seedling survival in the field. SC-10 showed an intermediate effect on seedling response in the field. Mixing hydrogel with a peat-based growing medium to form root plugs is a suitable technique for cultivating species to be planted in areas with a strong water deficit. This technique reduces post-transplant water stress in seedlings during their first months in the field and contributes to improve forestrestoration methods in dryland ecosystems.
Fire is a major agent involved in landscape transformation and an indirect cause of changes in species composition. Responses to fire may vary greatly depending on life histories and functional ...traits of species. We have examined the taxonomic and functional responses to fire of eight taxonomic animal groups displaying a gradient of dietary and mobility patterns: Gastropoda, Heteroptera, Formicidae, Coleoptera, Araneae, Orthoptera, Reptilia and Aves. The fieldwork was conducted in a Mediterranean protected area on 3 sites (one unburnt and two burnt with different postfire management practices) with five replicates per site. We collected information from 4606 specimens from 274 animal species. Similarity in species composition and abundance between areas was measured by the Bray-Curtis index and ANOSIM, and comparisons between animal and plant responses by Mantel tests. We analyze whether groups with the highest percentage of omnivorous species, these species being more generalist in their dietary habits, show weak responses to fire (i.e. more similarity between burnt and unburnt areas), and independent responses to changes in vegetation. We also explore how mobility, i.e. dispersal ability, influences responses to fire. Our results demonstrate that differences in species composition and abundance between burnt and unburnt areas differed among groups. We found a tendency towards presenting lower differences between areas for groups with higher percentages of omnivorous species. Moreover, taxa with a higher percentage of omnivorous species had significantly more independent responses of changes in vegetation. High- (e.g. Aves) and low-mobility (e.g. Gastropoda) groups had the strongest responses to fire (higher R scores of the ANOSIM); however, we failed to find a significant general pattern with all the groups according to their mobility. Our results partially support the idea that functional traits underlie the response of organisms to environmental changes caused by fire.
This study focuses on the synthesis of merlinoite from Chinese coal fly ashes by KOH direct conversion method, with special emphasis on the application of synthetic merlinoite as fertilizer. These ...fly ashes were collected from two pulverized-coal combustion (PCC) power plants in Xinjiang, Northwest China. The synthesis results are influenced by fly ash characteristics and different synthesis conditions (KOH solution concentrations, activation temperature, time, and KOH/fly ash ratios). A high quality merlinoite-rich product was synthesized under optimal activation conditions (KOH concentration of 5M, activation temperature of 150°C, activation time of 8h and KOH/fly ash ratio of 2l/kg), with a cation exchange capacity (CEC) of 160cmolkg(-1). The synthetic merlinoite is proved to be an efficient slow release K-fertilizer for plant growth, indicating that it can be widely used for high-nutrient demanding crops growing in nutrient-limited soils and for large-area poor soil amendment in opencast coal mine areas around the power plants that will substantially grow with the increasing coal combustion in Xinjiang in the near future.
Reforestation efforts in dryland ecosystems frequently encounter drought and limited soil productivity, although both factors usually interact synergistically to worsen water stress for outplanted ...seedlings. Land degradation in drylands (e.g. desertification) usually reduces soil productivity and, especially, soil water availability. In dry sub-humid regions, forest fires constitute a major disturbance affecting ecosystem dynamics and reforestation planning. Climate change projections indicate an increase of drought and more severe fire regime in many dryland regions of the world. In this context, the main target of plantation technology development is to overcome transplant shock and likely adverse periods, and in drylands this is mostly related to water limitations. In this paper, we discuss some selected steps that we consider critical for improving success in outplanting woody plants, both under current and projected climate change conditions including: (1) Plant species selection, (2) Improved nursery techniques, and (3) Improved planting techniques. The number of plant species used in reforestation is increasing rapidly, moving from a reduced set of well-known, easy-to-grow, widely used species, to a large variety of promising native species. Available technologies allow for reintroducing native plants and recovering critical ecosystem functions for many degraded drylands. However, climate change projections introduce large uncertainties about the sustainability of current reforestation practices. To cope with these uncertainties, adaptive restoration approaches are suggested, on the basis of improved plant quality, improved techniques for optimizing rain use efficiency in plantations, and exploring native plant species, including provenances and genotypes, for their resilience to fire and water use efficiency.
The biochemical quality of soil organic matter (SOM) was studied in various profiles under
Quercus rotundifolia Lam. stands on calcareous parent material. Special attention was paid to the question ...of how biochemical quality is affected by position within the soil profile (upper versus lower horizons). The following global SOM characteristics were investigated: (a) overall recalcitrance, using hydrolysis with either hydrochloric or sulphuric acid; (b) hydrolyzable carbohydrates and polyphenolics; (c) extractability by hot water and quality of the extract; and (d) abundance of inert forms of SOM: charcoal and soot-graphite. The recalcitrance of soil organic carbon (OC) decreases with depth, following the order: H horizons>A horizons>B horizons. In contrast, the recalcitrance of nitrogen is roughly maintained with depth. The ratio carbohydrate C to total OC increases from H to B horizons, due to the increasing importance of cellulosic polysaccharides in B horizons, whereas other carbohydrates are maintained throughout the soil profile at a relatively constant level, 12–15% of the total OC in the horizon. Whereas the quality of the hydrolyzable carbon (measured by the carbohydrate to polyphenolic C ratio) decreases with depth from H to B horizons, the quality of the hot-water extractable organic matter is much higher in B horizons than in A or H horizons. The relative importance of both charcoal and soot-graphitic C and N tends to increase with depth. The ratio black/total is usually higher for N than for C, a result that suggests that inert SOM may represent a relevant compartment in the nitrogen cycle. Overall, our data suggest that in Mediterranean forest soils the organic matter in B horizons could be less stable than often thought.
• Recent observations suggest that repeated fires could drive Mediterranean forests to shrublands, hosting flammable vegetation that regrows quickly after fire. This feedback supposedly favours ...shrubland persistence and may be strengthened in the future by predicted increased aridity. An assessment was made of how fires and aridity in combination modulated the dynamics of Mediterranean ecosystems and whether the feedback could be strong enough to maintain shrubland as an alternative stable state to forest.
• A model was developed for vegetation dynamics, including stochastic fires and different plant fire-responses. Parameters were calibrated using observational data from a period up to 100 yr ago, from 77 sites with and without fires in Southeast Spain and Southern France.
• The forest state was resilient to the separate impact of fires and increased aridity. However, water stress could convert forests into open shrublands by hampering post-fire recovery, with a possible tipping point at intermediate aridity.
• Projected increases in aridity may reduce the resilience of Mediterranean forests against fires and drive post-fire ecosystem dynamics toward open shrubland. The main effect of increased aridity is the limitation of post-fire recovery. Including plant fire-responses is thus fundamental when modelling the fate of Mediterranean-type vegetation under climate-change scenarios.
Fire-prone Mediterranean shrublands may be seriously threatened by land degradation due to progressive opening of the vegetation cover driven by increasing drought and fire recurrence. However, ...information about the consequences of this opening process for critical ecosystem functions is scant. In this work, we studied the influence of vegetation amount, type, and spatial pattern in the variation of extracellular soil enzyme activity (acid phosphatase, β-glucosidase, and urease) in fire-prone shrublands in eastern Spain. Soil was sampled in vegetation-patch and open-interpatch microsites in 15 shrubland sites affected by large wildfires in 1991. On average, the activities of the three enzymes were 1.5 (β-glucosidase and urease) to 1.7 (acid phosphatase) times higher in soils under vegetation patches than in adjacent interpatches. In addition, phosphatase activity for both microsites significantly decreased with the fragmentation of the vegetation. This result was attributed to a lower influence of roots -the main source of acid phosphatase- in the bigger interpatches of the sites with lower patch cover, and to feedbacks between vegetation pattern, redistribution of resources, and soil quality during post-fire vegetation dynamics. Phosphatase activity was also 1.2 times higher in patches of resprouter plants than in patches of non-resprouters, probably due to the faster post-fire recovery and older age of resprouter patches in these fire-prone ecosystems. The influence on the studied enzymes of topographic and climatic factors acting at the landscape scale was insignificant. According to our results, variations in the cover, pattern, and composition of vegetation patches may have profound impacts on soil enzyme activity and associated nutrient cycling processes in fire-prone Mediterranean shrublands, particularly in those related to phosphorus.
•Increasing fire recurrence and drought are changing fire-prone Mediterranean shrublands•Changes in vegetation amount, type and spatial structure alter soil enzyme activities•The opening of the vegetation cover may lead to non-linear decreases in mineralization•Soil acid phosphatase activity is a potential early warning for shrubland
In the Mediterranean Basin, most cultivated areas were abandoned in the last century and are now in various stages of old-field succession. The aim of this work was to analyse the successional ...trajectories of these ecosystems, and to assess possible deviations in these pathways due to fire occurrence at high or low recurrence levels. Old-fields abandoned either about 50 or about 100 years ago were selected in SE Spain. Within the 50-year-old abandoned fields, plots were established which had been burned by 1, 2 and 3 fires in the last 25 years. Cover values of vascular species were sampled and then analysed by means of multivariate analysis. Euclidean distances between resulting communities were used as an indicator of the possible deviation from the unburned successional pathway. Our results pointed to the possibility that different successional pathways may exist depending on fire occurrence and recurrence. In the absence of fire, the vegetation is dominated by pioneer species, mainly Pinus. With the passage of time this vegetation will become dominated by later successional tree species (Quercus). However, when early-successional communities are affected by fire, the succession can be diverted. A single fire is enough to change Pinus forests into alternative stable states dominated by Rosmarinus officinalis shrub communities, where the colonisation of species in later successional stages is arrested. This deviation increases in high fire recurrence regimes where the vegetation changes to dwarf shrubs and herbs.
During the last decades, climate and land use changes led to an increased prevalence of megafires in Mediterranean-type climate regions (MCRs). Here, we argue that current wildfire management ...policies in MCRs are destined to fail. Focused on fire suppression, these policies largely ignore ongoing climate warming and landscape-scale buildup of fuels. The result is a 'firefighting trap' that contributes to ongoing fuel accumulation precluding suppression under extreme fire weather, and resulting in more severe and larger fires. We believe that a 'business as usual' approach to wildfire in MCRs will not solve the fire problem, and recommend that policy and expenditures be rebalanced between suppression and mitigation of the negative impacts of fire. This requires a paradigm shift: policy effectiveness should not be primarily measured as a function of area burned (as it usually is), but rather as a function of avoided socio-ecological damage and loss.
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