• 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.
•Modified Gaussian models were applied to fit peaks of enantiomeric compounds•Restrictions were applied to control the baseline out of the peak region•Peak models allowed excellent fitting of ...isolated symmetric and asymmetric peaks•Deconvolution of peaks with moderate overlapping was also satisfactory•Approaches were applied to eight drugs analysed with several chiral columns
The description of the profiles of chromatographic peaks has been studied extensively, with a large number of proposed mathematical functions. Among them, the accuracy achieved with modified Gaussian models that describe the deviation of an ideal Gaussian peak as a change in the peak variance or standard deviation over time, has been highlighted. These models are, in fact, a family of functions of different complexity with great flexibility to adjust chromatographic peaks over a wide range of asymmetries and shapes. However, an uncontrolled behaviour of the signal may occur outside the region being fitted, forcing the use of different strategies to overcome this problem. In this work, the performance of the LMG (Linear Modified Gaussian), PVMG (Parabolic Variance Modified Gaussian), and PLMG (Parabolic-Lorentzian Modified Gaussian) models is compared with variants obtained by combination of the modified Gaussian models with an equation that adds an exponential tail and with other functions that limit the growth of the independent variable. The behaviour of the approaches is checked through the simultaneous fitting of enantiomeric peaks showing a wide range of characteristics, obtained in the separation of drugs with chiral activity by liquid chromatography using enantioselective columns. The study is also carried out with the purpose of performing the deconvolution of the peaks of the enantiomers, when these are not completely resolved, in order to evaluate the enantiomeric fraction.
Post-fire regeneration in Pinus halepensis' forests, one of the most abundant vegetation types in the Mediterranean basin, often generates overstocked and vulnerable stands. They accumulate a high ...fuel load, increasing the risk of further fires, and present high levels of vulnerability due to their reduced seed production. In addition, these dense stands substantially reduce the availability of light and nutrients, which may hinder the recruitment of other species, often generating mono-specific and homogeneous stands, which potentially supply fewer ecosystem services than mixed forests with more heterogeneous structures. In these dense pine stands, management is of high priority to reduce fire hazards and promote their functionality. In overstocked pine stands (>75,000 trees·ha−1), we assessed the long-term effects (10 years) of two thinning levels (600 and 1200 trees·ha−1), in combination with the plantation of Quercus faginea (a resprouter species typical of advanced successional stages in our study area) on 28 above and belowground ecosystem attributes, including fire hazard. After ten years, thinning and plantation interacted to enhance ecosystem attributes associated with disturbance regulation and biodiversity conservation (up to 200%) and food production (up to 90%), while no effects were observed on those attributes related to carbon sequestration and supporting services. These effects were mainly driven by aboveground attributes, as they responded more strongly to our treatments than those belowground. Our results are relevant for the restoration of Mediterranean degraded ecosystems, and show that tree thinning in overstocked pine stands, combined with the plantation of resprouter species, may not only reduce fire risks and accelerate post-fire succession but also enhance the supply of multiple ecosystem services in the long run.
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•The combination of thinning and resprouter plantation improved ecosystem functions.•Moderate thinning suffices to enhance individual aboveground attributes.•Plantation of resprouter species helps to maximize ecosystem services.•Ecosystem responses to management are driven by aboveground but not belowground attributes.
The ecological stability of Mediterranean ecosystems is being threatened by climate change. One of the impacts that is expected to be aggravated is the effect of summer drought prolongation toward ...previous or subsequent seasons by becoming more frequent. This, along with wildfires, could trigger synergistic negative effects on ecosystem regeneration capacity. Here we assessed how extending summer drought in two different ways (to autumn, AutExcl treatment, or bringing it forward to the following spring, SprExcl treatment) would affect plant recovery after an experimental fire carried out in summer in a Mediterranean seeder community. By installing rainout shelters, we assessed differences in seedling emergence, survival and establishment in the main families (Cistaceae, Labiatae, Leguminosae), and the effect on species richness and community composition. We observed that these post-fire dry season extensions reduced the total number of established seedlings and species richness. The most impacting drought treatment was AutExcl. However, the regeneration response was variable depending on the studied family. SprExcl was also determinant for Labiate survival rates. These results suggest that drought events which prolong the usual summer season may have a permanent drought legacy effect on seeder communities as practically all the seeder species populations were established in the first post-fire year. This fact is relevant for Mediterranean ecosystems dominated by seeder species as severer and longer droughts are increasingly recorded and are expected to become more frequent in forthcoming decades.
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•Climate change alters the recurrence, prolongation or temporality of summer droughts.•Prolonged summer-droughts events in critical periods negatively impacts the post-fire regeneration.•Seedling emergence, survival and establishment are affected differently depending on the plant family.•Extended summer drought after a fire may have a permanent drought legacy.
Determining the structure and fuel load is key to know the flammability of vegetation in the Mediterranean Basin where forest fires are frequent. Determine which plant structural variable is best ...related to living and dead fuel to develop allometric equations in nine species in the Western Mediterranean Basin. In the east of the Iberian Peninsula (Valencia Province), we measured four structural variables (basal stem diameter, height, maximum diameter and perpendicular diameter) that were related, by means of allometric equations, to the living and dead fuel separated into different size classes. We also analyze fuel changes across developmental states of the studied species, and the vertical distribution of dead fuel. General equations that consider all development states can be used to determine living fuel. However to obtain dead fuel, we recommend using specific equations for each development state and fuel fraction for better accuracy. The basal stem diameter was the best structural variable in almost all cases for estimating fuel in the studied species. Dead fuel load throughout species’ ontological development is a key factor to manage Mediterranean plant communities.
We studied the soil seed bank in a possible scenario of fire regime shift and asked: (1) Does high fire frequency impact the density of seeds stored, species richness and evenness? (2) Overall, does ...high fire frequency produce changes in the presence–absence and abundance of species? The study was implemented in a Mediterranean Basin ecosystem in plots with increasing fire frequency (unburned, burned once and burned twice in the last 66 years). The number of seeds increased with fire frequency for all life forms (shrub, scrub, perennial forb, annual forb and perennial graminoid). Species richness of annual forbs also increased. Evenness of shrubs diminished because the number of seeds in all the species decreased, except C. albidus, which increased. Overall, differences in the abundance of species were found, mainly by depleting shrubs and increasing forbs. There were no differences in the presence–absence data. In conclusion, high fire frequencies act as a filtering factor for species of a larger size and advanced maturity age. In contrast, life forms of small size and rapid onset of reproductive maturity can be enhanced. This community conversion from woody to herbaceous soil seed banks is fundamental to identify vegetation changes in future regimes of high fire frequency.
The extensive abandonment of agricultural lands in the Mediterranean basin has led to large landscapes being dominated by early-successional species, characterized by high flammability and an ...increasing fire risk. This fact promotes fire occurrence and places ecosystems in a state of arrested succession. In this work, we assessed the effectiveness of several restoration actions in redirecting these ecosystems toward more resilient communities dominated by resprouting species. These actions included the mechanical clearing of early-successional species, the plantation of resprouting species, and the combination of both treatments. For 13 years, we assessed shifts in the successional trajectory and ecosystem flammability by changes in: species composition, species richness, ecosystem evenness, the natural colonization of resprouting species, total biomass and proportion of dead biomass. We observed that the plantation and clearing combination was a suitable strategy to promote resilience. Species richness increased as well as the presence of the resprouting species introduced by planting. The natural colonization of the resprouting species was also enhanced. These changes in the successional trajectory were accompanied by a possible reduction of fire risk by reducing dead fuel proportion. These findings are relevant for the management of Mediterranean basin areas, but also suggest new tools for redirecting systems in fire-prone areas worldwide.
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•Large landscapes are dominated by highly flammable species with high fire risk.•Clearing and planting key species can be suitable management strategies.•Restoration actions displace the system towards a more resilient community.•The introduction of resprouters to the detriment of seeder species is a key step.
Recurrent fires can impede the spontaneous recruitment capacity of pine forests. Empirical studies have suggested that this can lead to a prolonged replacement of pine forest by shrubland, especially ...if shrub species are pyrophytic. Model-based studies, however, have suggested that post-fire succession of pine forest under current climatic conditions will eventually tend towards the dominance of oaks under high fire severity and recurrence. These previous modelling studies did not address the role of the various post-fire regeneration traits of the understory shrub species. Considering the dichotomy of obligate seeder vs. resprouter species, either obligate or facultative resprouter, we hypothesized that when the shrubs present are post-fire seeders, the oaks steadily occupy the forest, whereas resprouter shrub species might compete with oaks and delay or arrest post-fire succession. To test this hypothesis, we developed a dynamic, cellular automaton model for simulating post-fire successional transitions in pine forests, including shrubs, pines and oaks, and stochastic fires of regular frequency. Our results showed a strong tendency towards oak dominance as final model state and a very reduced role of fire recurrence in this final state, with low yearly acorn input delaying oak dominance. Most relevantly, and in line with our hypothesis, the trend towards oak dominance depended markedly on the two types of shrub species, being delayed by resprouter species, which extended the shrub-dominated succession stage for several centuries. Our simulation results supported the view that the type of understorey species should be a key consideration in post-fire restoration strategies aiming to enhance fire resilience.
In this preliminary work, carbon nanohorns (CNHs) have been dispersed for the first time in an inert polymeric matrix for the development of a new 0D CNH-based polymer nanocomposite carbon-paste ...electrode (pNC–CPE). As a first demonstration, the electrically conductive networks were optimized by tuning the filler/polymer composition ratio in order to achieve transducers with enhanced electroanalytical responses. Further, direct electrochemical comparison with additional pNC–CPEs employing conventional carbon nanoallotropes is provided, demonstrating that pNC–CPEs can be electrically modulated by customizing the filler/polymer composition ratio as well as the carbon nature. Consequently, this work wide the pNC–CPE family and paves the way for exploiting CNH-based polymer nanocomposites as novel sensitive and reproducible electrochemical (bio)sensing devices.
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