Mediterranean Basin Ecosystems Research Articles

Some like it burnt: species differences in small mammal assemblage in a Mediterranean basin nearly 3 years after a major fire

The habitat accommodation model (HAM) is a theoretical framework that predicts wildlife community recovery based on their habitat requirements. While post-fire habitat-related research is well documented in the Mediterranean basin, studies specifically focusing on HAM are scarce. Here, we described the small mammal assemblage in a Mediterranean area ~3 years after a fire, specifically examining three functional small mammalian categories: ground-foraging insectivorous, ground-foraging herbivorous/granivorous, and arboreal-foraging species. The study was conducted in Monte Pisano (Italy), where fire burnt ~12 km2 in September 2018. A stratified random sampling was adopted, basing on burnt status and forest type. In each of the 50 sites, during late spring-summer 2021, 12 hair-tubes were deployed, and collected hairs were taxa-attributed based on morphology. A presence/absence dataset was built, and db-RDA was used to explore assemblage composition, and single-species occupancy models to test specific hypotheses. The relative abundance of ground-foraging herbivorous/granivorous was higher in the burnt area, characterised by a dense undergrowth, which could be related to anti-predatory strategies and food opportunities. Insectivorous could be in a recolonisation phase, masking their earlier absence, which could explain why their abundance was not associated with any factor tested. Arboreal-foraging species were associated with forest type, indicating a primary role for tree cover and other factors such as rocky cover and likely in situ survival. The HAM was overall confirmed also in Mediterranean basin ecosystems. This may facilitate predictions about post-fire animal successions, which in turn may provide valuable insights into post-fire management practices and biodiversity conservation strategies.

Nitrogen Deposition Effects on Soil Properties, Microbial Abundance, and Litter Decomposition Across Three Shrublands Ecosystems From the Mediterranean Basin

Atmospheric nitrogen (N) inputs in the Mediterranean Basin are projected to increase due to fossil fuel combustion, fertilizer use, and the exacerbation of agricultural production processes. Although increasing N deposition is recognized as a major threat to ecosystem functioning, little is known about how local environmental conditions modulate ecosystem function response to N addition, particularly in the context of Mediterranean-Basin ecosystems. Here, we assess how N addition affects important ecosystem properties associated with litter decomposition, soil physical-chemical properties, soil extracellular enzymatic activity and microbial abundance across three long-term N addition experimental sites in the Mediterranean Basin. Sites were located in El Regajal (Madrid, Spain), Capo Caccia (Alghero, Italy), and Arrábida (Lisbon, Portugal) and are all representative of Mediterranean shrublands. No common pattern for litter decomposition process or other studied variables emerged among the control plots of the studied sites. Nitrogen supply only affected soil pH, a major driver of decomposition, in two out of three experimental sites. Moreover, when we explored the role of N addition and soil pH in controlling litter decay, we found that the effects of these factors were site-dependent. Our results point out to local ecosystem features modulating N addition effects in controlling litter decomposition rates in Mediterranean ecosystems, suggesting that the responses of soil functioning to N deposition are site-dependent. These findings provide further knowledge to understand contrasting ecosystem responses to N additions based on a single field experiments.

Soil microbiome drives the recovery of ecosystem functions after fire

Fire is an ecological disturbance that alters soil microbiomes and the functions they mediate in terrestrial ecosystems. Soil microbial diversity in Mediterranean Basin ecosystems shows resilience to fire following the restoration of plant-soil feedbacks. We hypothesised that microbial functions related to organic matter decomposition and nutrient cycling might show similar patterns of recovery. We quantified the rates of microbial respiration and enzymatic activities related to C, N and P cycling in three 20-year fire chronosequences including 150 transects in 50 burned and unburned plots (no historical fire registers) in a paired experimental design. Microbial functions, except for the hydrolysis of N compounds, were sensitive to fire but recovered the levels of unburned plots in approximately 20–24 years. The recovery of microbial functions responded to abiotic and biotic drivers. Total soil nitrogen concentration was overall strong predictor of microbial functions. In addition, fungal phylogenetic diversity significantly explained the post-fire trajectories of potentially mineralizable C, while bacterial diversity was involved in the restoration of organic C and P hydrolysis. Our results suggest that the long-term recovery of soil biodiversity in Mediterranean Basin ecosystems creates resilience to restore essential ecosystem functions after fire.

Climate, and not fire, drives the phylogenetic clustering of species with hard-coated seeds in Mediterranean Basin communities

Hardseededness is a common trait in Mediterranean plant communities, although the origin of its selection is controversial. It may be a mechanism of persistence to fire temperatures, but could also form part of a gap-detecting mechanism to provide germination cues under arid conditions. To disentangle this, we studied the phylogenetic structure of plant communities against fire frequency and aridity gradients. The phylogenetic structure in Mediterranean Basin ecosystems was analysed for the hardseededness trait as a whole and was separated by the families composing this trait (Fabaceae and Cistaceae). This study focused on woody perennial species. The phylogenetic structure was also contrasted against soil classes. Hardseededness on the whole, and for the Fabaceae family alone, showed phylogenetic clustering as aridity increased. Cistaceae displayed the opposite pattern with phylogenetic clustering in most humid areas, together with a significant soil effect. Surprisingly, fire frequency had no influence in any case. This climate-driven phylogenetic clustering indicates that the hardseededness trait could confer some fitness advantage under dry conditions. For this reason, coexisting species were more closely related in the community with increasing aridity. This effect was especially evident for the Fabaceae family. These results shed some light on the evolutionary selection of this adaptive trait under Mediterranean conditions. Our results question the role of fire in the selection of the hardseededness trait in Mediterranean Basin ecosystems and indicates that climate is the most important factor. Therefore, we should be cautious in assigning to fire a preponderant role in the selection of some plant traits.

Post-fire nitrogen uptake and allocation by two resprouting herbaceous species with contrasting belowground traits

Immediately after fire, soil nitrogen availability increases due to ash deposition and the stimulation of mineralization by increased temperature. The coexistence of plant resprouters with contrasting root traits that grow soon after fire suggests different strategies operating for the re-acquisition of space, capturing resources and resisting additional stresses. Brachypodium retusum and Dactylis glomerata are two perennial grass species that co-occur in fire-prone Mediterranean basin ecosystems. B. retusum (Br) is a slow-growing grass with a developed rhizome, whereas D. glomerata (Dg) is a fast-growing grass that resprouts from rootstock buds. We hypothesized that the fast-growing grass would take advantage of the flush in available N after fire, whereas the aboveground growth of the slow-growing grass would rely on rhizome N reserves. The objective of this study was to ascertain the role of the root system characteristics and plant growth traits in relation to soil N uptake and plant N assimilation soon after fire followed by grazing. Therefore, in a pot experiment with plants and soil transplanted from the field, we applied 15N-NH4+ to the surface of the soil, immediately after cutting the aboveground plant biomass to simulate post-fire disturbance. Grazing defoliation was simulated using four successive cuttings. Both species resprouted quickly after the fire-simulation cutting, with the recovery of approximately 15% of the initial aboveground biomass only 5 days afterwards; 20 days later, the biomass reached 50% for Dg and 28% for Br. This regrowth was parallel to a reduction in belowground biomass. Later, the aboveground biomass remained approximately constant after four cuts over 75 days, maintaining the same total N content (close to 2.0 g N m−2 for Dg and 1.0–1.5 g N m−2 for Br). Both species showed high 15N atom % in their leaves after 20 days of 15N application, which slowly decreased over the successive cuts. After 55 days and two cuts, only Br showed a decline in the total plant 15N content. Plant growth and soil N uptake were higher in the non-rhizomatous species (Dg) showing greater root development and higher belowground/aboveground ratio. The rhizome of Br supported early resprouting but this species did not take much advantage of the initial N mineralization after fire. In Dg pots, the 15N-NO3- that leached out was lower than in Br pots. Dg showed higher nitrate reductase activity, in comparison to Br. In agreement with our hypothesis, the results suggest that the fast-growing strategy of Dg takes advantage of increased N availability after fire, whereas the slow growing Br relies on N rhizome reserves, which were slowly replenishing from available soil N. Both species showed high regeneration capacity after fire and high resilience to intensive post-fire grazing pressure.

Nutritional Quality of Herbaceous Vegetation in a Phryganic Mediterranean Ecosystem During the Grazing Period

Grazing is an economically and environmentally valuable activity in phryganic Mediterranean ecosystems. The herbaceous vegetation of these ecosystems provides an essential feed source for grazing ruminants. Despite the extension and economic importance of phryganic ecosystems in Mediterranean Basin there has been relatively little scientific focus on nutritional quality of their herbaceous vegetation. The nutritional quality of herbaceous vegetation in a phryganic ecosystem was assessed for two consecutive years during the grazing period (March to July). Herbage samples were analysed for chemical composition, metabolizable energy, in vitro dry matter digestibility, in vitro neutral detergent fiber digestibility and mineral content (Ca, P, K, Mg) at monthly basis. According to the results time of harvest significantly affected crude protein, neutral detergent fiber, acid detergent fiber, lignin and the content of minerals (i.e. Ca, P, Mg, K). Mean monthly temperature found to have a great negative impact on nutritional quality. During the grazing period, the nutritional quality of herbage vegetation was strongly correlated with growing degree days. Over a threshold of about 700 growing degree days the nutritional quality of herbage dramatically decreased. Overall the current study provides crucial information for the nutritional dynamics of the herbage vegetation of the phryganic Mediterranean ecosystems that can be towards developing an efficient grazing strategy.

Climate change: The 2015 Paris Agreement thresholds and Mediterranean basin ecosystems.

The United Nations Framework Convention on Climate Change Paris Agreement of December 2015 aims to maintain the global average warming well below 2°C above the preindustrial level. In the Mediterranean basin, recent pollen-based reconstructions of climate and ecosystem variability over the past 10,000 years provide insights regarding the implications of warming thresholds for biodiversity and land-use potential. We compare scenarios of climate-driven future change in land ecosystems with reconstructed ecosystem dynamics during the past 10,000 years. Only a 1.5°C warming scenario permits ecosystems to remain within the Holocene variability. At or above 2°C of warming, climatic change will generate Mediterranean land ecosystem changes that are unmatched in the Holocene, a period characterized by recurring precipitation deficits rather than temperature anomalies.

Mulch application as post-fire rehabilitation treatment does not affect vegetation recovery in ecosystems dominated by obligate seeders

Mulching treatments have been successfully tested for reducing soil erosion in the first years after fire. However, little is known about their possible negative effect on vegetation regeneration. The aim of this work is to assess the effect of mulch application (woody chips) on the regeneration of Mediterranean Basin ecosystems dominated by obligate seeders. For this purpose, two different mulch ratios (1 and 2kgm−2) were applied immediately after fire as a post-fire rehabilitation treatment. Soil micro-environmental modifications were tested by monitoring soil temperature and moisture. Vegetation regeneration was assessed by monitoring seedling emergence, seedling establishment, species richness and plant cover during the following three years. Mulch application modified micro-environmental conditions as soil temperature lowered and soil moisture increased. However, no significant effects were found in the final establishment of individuals, plant cover and species richness. In addition, application ratios of 2kgm−2 increased the seedling survival of obligate seeders species. Mulch application reduced only seedling emergence in one species (Cistus albidus) in the 2kgm−2 treatment, but did not affect final establishment. The lack of negative effects on vegetation regeneration is of paramount importance in the ecosystems studied as all plant individuals die and the root system protecting the soil must be completely restored by new individuals. Rapid vegetation establishment and growth will help reduce the “window of disturbance” for soil erosion, which occurs until vegetation is recovered. In conclusion, woody chip applications may be a suitable post-fire rehabilitation treatment as they have no negative effects on vegetation regeneration.

Ammonium as a Driving Force of Plant Diversity and Ecosystem Functioning: Observations Based on 5 Years' Manipulation of N Dose and Form in a Mediterranean Ecosystem

Enhanced nitrogen (N) availability is one of the main drivers of biodiversity loss and degradation of ecosystem functions. However, in very nutrient-poor ecosystems, enhanced N input can, in the short-term, promote diversity. Mediterranean Basin ecosystems are nutrient-limited biodiversity hotspots, but no information is available on their medium- or long-term responses to enhanced N input. Since 2007, we have been manipulating the form and dose of available N in a Mediterranean Basin maquis in south-western Europe that has low ambient N deposition (<4 kg N ha−1 yr−1) and low soil N content (0.1%). N availability was modified by the addition of 40 kg N ha−1 yr−1 as a 1∶1 NH4Cl to (NH4)2SO4 mixture, and 40 and 80 kg N ha−1 yr−1 as NH4NO3. Over the following 5 years, the impacts on plant composition and diversity (richness and evenness) and some ecosystem characteristics (soil extractable N and organic matter, aboveground biomass and % of bare soil) were assessed. Plant species richness increased with enhanced N input and was more related to ammonium than to nitrate. Exposure to 40 kg NH4 +-N ha−1 yr−1 (alone and with nitrate) enhanced plant richness, but did not increase aboveground biomass; soil extractable N even increased under 80 kg NH4NO3-N ha−1 yr−1 and the % of bare soil increased under 40 kg NH4 +-N ha−1 yr−1. The treatment containing less ammonium, 40 kg NH4NO3-N ha−1 yr−1, did not enhance plant diversity but promoted aboveground biomass and reduced the % of bare soil. Data suggest that enhanced NHy availability affects the structure of the maquis, which may promote soil erosion and N leakage, whereas enhanced NOx availability leads to biomass accumulation which may increase the fire risk. These observations are relevant for land use management in biodiverse and fragmented ecosystems such as the maquis, especially in conservation areas.

Effects of fire regime shift in Mediterranean Basin ecosystems: changes in soil seed bank composition among functional types

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.

Long-term post-fire dynamics of co-occurring woody species in Pinus brutia forests: the role of regeneration mode

Regeneration mode is one of the key attributes determining population structure and dynamics of plant species. We investigated long-term patterns after fire in the cover of plant species in a 100-year chronosequence of burned Pinus brutia forests in a humid Mediterranean climate region in Turkey. Significant trends were present in the change of cover in major species through post-fire chronosequence, and species with similar trends were clustered in relation to their regeneration modes. Obligate resprouters increased their cover from the early post-fire years to the later stages, while cover of obligate seeders with a soil seed bank increased in the early years, but then decreased through time. Facultative resprouters were at an intermediate position, with an increase in cover until mid-successional stages and then a decrease through time. The cover of the only obligate seeder with a canopy seed bank (P. brutia) followed a linear increasing trend during the succession. When species with the same regeneration mode were grouped, the same trends were observed with more explained variances. A few life-history traits were enough to explain the observed trends. Our study shows that regeneration mode is an explanatory functional grouping system for describing long-term post-fire dynamics of Mediterranean Basin woody species. We suggest that regeneration mode must be a major component of any vegetation or forest stand dynamics model in the Mediterranean Basin. This result has important implications for the management of Mediterranean Basin ecosystems, and can potentially be extrapolated to other Mediterranean-type fire-prone ecosystems.

Physiological differences explain the co‐existence of different regeneration strategies in Mediterranean ecosystems

• Fire and drought are selective driving forces in Mediterranean plants, and thus their ability to resprout or recruit after these disturbances is of paramount importance. The contrast in regeneration niche between resprouters and seeders, and each group's different root characteristics, suggest that they are subjected to different degrees of environmental stress and, consequently, to different evolutionary forces. • We compared leaf traits, xylem traits related to hydraulic efficiency and vulnerability to cavitation, and the physiological response to an imposed drought between seedlings of resprouters and seedlings of seeders. We used 12 species co-existing in Mediterranean basin ecosystems. • Major differences were found in the xylem architecture and leaf traits, and in the response to drought conditions. Seeders were more efficient at transporting water to leaves but formed, in turn, a safer xylem network. They also presented higher photosynthesis and transpiration rates, and earlier stomatal closure with drought, but good leaf dehydration tolerance. • Seeders and resprouters can be considered two syndromes whose different functional characteristics are related to water availability and drought responses. These characteristics, together with their differences in rooting habits, account for their distinct regeneration niches and, thus, their co-existence.

The Effect of Fire on Biotic Interactions in Mediterranean Basin Ecosystems: Pollination and Seed Dispersal

Mediterranean type ecosystems are among the world's most fire-prone regions. Focusing on the Mediterranean basin, we review the literature and propose conceptual models to explain the direct and indirect effects of fire on plant-pollinator interactions, seed dispersers, and predators, as well as the temporal changes in these systems along post-fire succession and ecosystem recovery processes. Post-fire plant communities change in their composition, structure, floral resources, as well as seed and fruit resources. Fire directly affects communities of pollinators, seed dispersers, and seed predators mainly by mortality, and indirectly through changes in the quality and quantity of food and nesting resources. Pollinators, seed-dispersers, and seed predators depend on plant community composition and on the flower, seed, and fruit resources they produce. As a consequence, their community composition, structure, and function are expected to vary in response to post-fire temporal and spatial changes in plant com...

Patterns of nitrate reductase activity vary according to the plant functional group in a Mediterranean maquis

Since little is known about how the Mediterranean Basin ecosystems are affected by nitrogen deposition, we aimed to understand the use of nitrogen by distinct plant functional groups (PFG: summer semi-deciduous and evergreen sclerophylls) present in the Mediterranean maquis in order to assess which may be more affected by changes in nitrogen availability. The availability of soil inorganic nitrogen, leaf nitrate concentrations and nitrate reductase activity (in vivo and in vitro) were measured during the year in three plant species from each PFG. The patterns of in vitro NRA along the shoot and through the day were also determined. Although summer semi deciduous species occupied soil patches richer in nitrate, their leaf NRA were significantly lower than that of evergreen sclerophylls species. The pattern of nitrate and ammonium availabilities along the year also distinguished the PFG. Results show that each PFG is composed of a number of physiologically similar species. Patterns of NRA varied according to the PFG, which may represent distinct specializations of co-occurring species to access nitrogen. Therefore, the NRA can be used as an indicator of the nitrate availability taking into consideration the time of the year, the plant species and its PFG.

Vulnerability of Mediterranean Basin ecosystems to climate change and invasion by exotic plant species

AbstractAim To assess at a broad scale the vulnerability of Mediterranean vegetation to alien plant invasion under different climatic and disturbance scenarios.Location We simulated the vegetation biogeography and dynamics on five of the main islands of the Mediterranean Basin: Mallorca, Corsica, Sardinia, Crete and Lesvos.Methods We used LPJ‐GUESS, a generalized ecosystem model based on dynamic processes describing establishment, competition, mortality and ecosystem biogeochemistry. We simulated the vegetation distribution and dynamics using a set of plant functional types (PFTs) based on bioclimatic and physiological parameters, which included tree and shrub PFTs defined especially for the Mediterranean. Additionally, two invasive PFTs, an invasive tree type and an invasive herb type, were defined and used to estimate the vulnerability to invasion of a range of different ecosystems. The model was used to simulate climate changes and associated changes in atmospheric [CO2] to 2050 according to two SpecialReport on Emissions Scenarios climate scenarios (A1Fi and B1) combined with mean disturbance intervals of 3 and 40 years.Results The simulations and scenarios showed that the effect of climate change alone is likely to be negligible in many of the simulated ecosystems, although not all. The simulated progression of an invasion was highly dependent on the initial ecosystem composition and local environmental conditions, with a particular contrast between drier and wetter parts of the Mediterranean, and between mountain and coastal areas. The rate of ecosystem disturbance was the main factor controlling susceptibility to invasion, strongly influencing vegetation development on the shorter time scale.Main conclusions Further invasion into Mediterranean island ecosystems is likely to be an increasing problem: our simulations predict that, in the longer term, almost all the ecosystems will be dominated by exotic plants irrespective of disturbance rates.

Vegetation dynamics of Mediterranean shrublands in former cultural landscape at Grazalema Mountains, South Spain

Plant community dynamics in Mediterranean basin ecosystems are mainly driven by an alternation of episodes of human intervention and land abandonment. As a result, a mosaic of plant communities has evolved following different stages of degradation and regeneration. Some authors has relate secondary succession to abandoned culture lands and regeneration to natural systems with abandonment of livestock or forestry exploitation. In this paper, the dynamics of shrublands in mid-mountain areas in the South of Spain after disturbance and land abandonment has been studied. The plant cover and 13 environmental variables of 137 selected sites on the Grazalema mountains was analysed to determine the vegetation pattern in relation to environmental factors and the succession types, either regenerative or secondary succession. The results show that today the Grazalema mountains have a heterogeneous vegetation pattern. Besides physical factors such as altitude or soil , human disturbance has modulated current vegetation patterns and dynamics. Two main types of vegetation dynamics can be distinguished in the study area. In areas affected by cutting, regeneration results in rich and dense shrub land, with resprouters as dominant species. In areas affected by recurrent wildfires or agriculture, secondary succession became dominant, resulting in less diverse shrubland, due to the dominance of seeders and decrease in resprouter species richness and cover.