Mediterranean Evergreen Forests Research Articles

Decline of soil volatile organic compounds from a Mediterranean deciduous forest under a future drier climate

Biogenic volatile organic compounds (BVOCs) are crucial for ecosystem functioning, atmospheric chemistry and climate. While modulation of BVOC emissions from living vegetation with biotic and abiotic factors is well documented, how these factors drive soil BVOC emissions remain less understood, particularly in Mediterranean forests. To fill this gap, this pioneer study investigates whether BVOC fluxes from natural soil covered by litter (referred to as forest soil) vary under natural and amplified long-term water stress (35% annual rain exclusion over the past 10 years) in a deciduous oak Mediterranean forest (Quercus pubescens Willd.) compared to natural climate conditions. This aim has only been tackled in a single evergreen Mediterranean forest so far. Using proton transfer reaction time of flight mass spectrometer (PTR-ToF-MS) we also provide, for the first time, a detailed diurnal cycle of soil BVOCs in relation to air temperature, air humidity, and biotic factors including soil respiration and litter content in lignin, cellulose and hemicellulose. The main results revealed that forest soil represents a source of most BVOCs (e.g., acetaldehyde, acetone, acrolein, hexanol, monoterpenes) with maximum values at mid-day (45 μgC.m-2.h-1) in response to higher temperatures while it acts as a clear sink of isoprene. Total soil BVOC emission rates, together with soil respiration, decreased by 43% after a decade of partial rain restriction. These results will contribute to enhance further modeling of soil BVOC emissions under various climate scenarios both at regional and global scales.

Foliar nitrogen uptake in broadleaf evergreen Mediterranean forests: Fertilisation experiment with labelled nitrogen

Atmospheric nitrogen (N) deposition in Mediterranean sclerophyllous forests of Holm oak (Quercus rotundifolia, Q. ilex) in Spain often exceeds empirical critical loads established for ecosystem conservation. There are still uncertainties on the capacity of canopy retention and uptake of the atmospheric N deposited of these forests. Studying and analysing all the forest nitrogen-cycle processes is essential to understand the potential effect of N deposition in these ecosystems. This study conducted a year-long short-term fertilisation experiment with labelled ammonium (15N-NH4) and nitrate (15N-NO3) to estimate foliar N absorption rates and assess the influence of leaf phenology and meteorological seasonal variations. Fertilising solutions were prepared to simulate low and high wet N deposition concentration, based on data reported from previous studies. Additionally, ecophysiological and meteorological measurements were collected to explore potential relationships between absorption rates, plant activity, and weather conditions. The results showed that Holm oak leaves were able to absorb both oxidised and reduced N compounds, with higher rates of NH4+ absorption. N recovery of both NH4+ and NO3− was higher in the low concentration treatments, suggesting reduced effectiveness of absorption as concentration increases. Foliar absorption rates were leaf-age dependent, with the highest values observed in young developing leaves. Foliar uptake showed seasonal changes with a clear reduction during the summer, linked to drought and dry weather conditions, and showing also smaller leaf net assimilation and stomatal conductance. During the rest of the year, foliar N absorption was not clearly associated to plant physiological activity but with environmental conditions. Our findings suggest that Holm oak canopies could absorb an important part of the incoming N deposition, but this process is compound, season and leaf phenology dependent. Further research is therefore needed to better understand and model this part of the N cycle.

First palynological results from Spila nad Procjepom cave, Mljet island (Croatia)

This paper presents the first results of palynological research from the Spila nad Procjepom cave, situated in the Mljet National Park, Croatia. The palynological data obtained, enables a partial insight into the local vegetation cover, temporal changes in the vegetation during the accumulation of studied deposits (at ca. 3500 cal years BP), and post-depositional processes that influenced the palynomorph assemblage. Results of palynofacies analysis indicate changes from fluvial (channel deposits), through palustrine to terrestrial environments. Although the interpretation of changes in plant cover, due to the lack of statistical significance, should be taken with caution, preserved pollen types confirm the dominance of the Mediterranean evergreen forest vegetation on Mljet island. Moreover, a high proportion of non-arboreal pollen (NAP) indicates some level of forest degradation, ranging from Mediterranean open forest to degraded maquis. Abundant charcoal additionaly confirms that the cave was inhabited by humans.

Hemixerophilic forests in the caucasus

Hemixerophilic vegetation of the lower mountain belt belongs to the class Quercetea pubescenti-petraeae Jakucs (1960) 1961, order Orno-Cotinetalia Jakucs (1960) 1961. Hemixerophilic forests in the Caucasus are represented by two types: Oak hemixerophylic forests from Quercus pubescens Wiild. and forest from Carpinus orientalis Mill. The forests of Quercus pubescens are confined to the Sub-Mediterranean, where they are known under the name “shiblyak.” The northern boundary of the species spreads across Northern France, southern Belgium and Germany, where it grows in the forests of the Atlantic Europe on carbonate soils. Further, the border goes along the southern Carpathians (Romania) and Podillia to the Crimea and the Caucasus in the east. Fluffy forests are a link between evergreen Mediterranean forests and Central European deciduous deciduous forests. Quercus pubescens is a derivative of the tertiary flora that developed in the drier and warmer climate of low mountains in the Mediterranean region bordering on Central Europe..

Long‐term hydrological and biogeochemical datasets from a Mediterranean forest site (Montseny, NE Spain)

AbstractWe present here, and make freely available, two long‐term datasets on the hydrology and hydrochemistry of two small catchments totally or partially covered by holm oak (Quercus ilex) forests. Data have been collected over four decades of research on the ecology of Mediterranean evergreen forests. The datasets contain data on water fluxes in precipitation and runoff, and on the ion concentrations and fluxes in precipitation, throughfall and streamwater. Among other applications, these data have been used to obtain catchment budgets of water and elements, to document decadal changes in atmospheric deposition and streamwater chemistry, to assess the role of Saharo‐Sahelian dust on forest nutrient cycling, and to model habitat suitability for an endangered amphibian under future climates. To encourage their further use by the scientific community, in this paper we summarize the data context and methods, and give a nutshell of obtained results. We provide the links to these datasets on the Zenodo platform.

Lower COVID-19 mortality in Italian forested areas suggests immunoprotection by Mediterranean plants.

The COVID-19 pandemic has induced dramatic effects on the population of the industrialized north of Italy, whereas it has not heavily affected inhabitants of the southern regions. This might be explained in part by human exposure to high levels of fine particulate matter (PM) in the air of northern Italy, thus exacerbating the mortality. Since trees mitigate air pollution by intercepting PM onto plant surfaces and bolster the human immune system by emitting bioactive volatile organic compounds (VOCs), we hypothesize a protective role of evergreen forested areas in southern Italy. We compared the mortality rate due to COVID-19, the death number, the positivity rate and the forest coverage per capita in various Italian regions. Hectares of forest per capita and prevalence of deciduous versus evergreen forestal species were also estimated. In silico docking studies of potentially protective compounds found in Laurus nobilis L., a typical Mediterranean plant, were performed to search for potential antivirals. We found that the pandemic’s severity was generally lower in southern regions, especially those with more than 0.3 hectares of forest per capita. The lowest mortality rates were found in southern Italy, mainly in regions like Molise (0.007%) and Basilicata (0.005%) where the forest per capita ratio is higher than 0.5 Ha/person. Our findings suggest that evergreen Mediterranean forests and shrubland plants could have protected the southern population by emission of immuno-modulating VOCs and provision of dietary sources of bioactive compounds. Moreover, in silico studies revealed a potential anti-COVID-19 activity in laurusides, which are unexplored glycosides from bay laurel. Overall, our results highlight the importance of nature conservation and applications to the search for natural antivirals.Electronic supplementary materialThe online version of this article (10.1007/s10311-020-01063-0) contains supplementary material, which is available to authorized users.

Does forest age affect soil biodiversity? Case study of land snails in Mediterranean secondary forests

Based on a sampling design used for vascular plants, the effect of forest age (i.e. the time in years since a land patch became a real forest patch as a measure of temporal continuity of forest characteristics) on land snail richness, abundance and composition was assessed in 18 plots in Mediterranean evergreen and deciduous oak forests, belonging to four Sites of Community Importance in Italy. Most examined plots belong to young forests; in particular, three age classes were considered (class 1, <22 years; class 3, 38–56 years; class 5, >77 years). Twenty-seven species and 2433 individuals were recorded. Box plots showed that forest age did not seem to be a key factor for land snail species richness and abundance at least in the time range of examined forests. However, this may not be true, if real old-growth forests are considered. No differences between evergreen and deciduous forest were found too. With regard to species composition, Non-metric multidimensional scaling demonstrated an assemblage of species widespread in all forest age classes, while Indicator Species Analysis failed to identify any species as indicator for any age category. This shows that a process is underway but has had insufficient time to differentiate assemblages and to accumulate the majority of rare species, due to the young nature of examined forests. Habitat structure may affect communities more than forest age: suitable microhabitats (a few old/very old trees for shelter) are a sufficient prerequisite for land snail diversity, ensuring community survival and protection, irrespective of forest age class. These findings highlight the importance of habitat structural complexity at local scale for preserving invertebrate diversity in Mediterranean secondary forests.

Quantitative study on nitrogen deposition and canopy retention in Mediterranean evergreen forests.

To assess the impact of nitrogen (N) pollutants on forest ecosystems, the role of the interactions in the canopy needs to be understood. A great number of studies have addressed this issue in heavily N-polluted regions in north and central Europe. Much less information is available for the Iberian Peninsula, and yet this region is home to mountain forests and alpine grasslands that may be at risk due to excessive N deposition. To establish the basis for ecology-based policies, there is a need to better understand the forest response to this atmospheric impact. To fill this gap, in this study, we measured N deposition (as bulk, wet, and throughfall fluxes of dissolved inorganic nitrogen) and air N gas concentrations from 2011 to 2013 at four Spanish holm oak (Quercus ilex) forests located in different pollution environments. One site was in an area of intensive agriculture, two sites were influenced by big cities (Madrid and Barcelona, respectively), and one site was in a rural mountain environment 40km north of Barcelona. Wet deposition ranged between 0.54 and 3.8kgNha-1year-1 for ammonium (NH4+)-N and between 0.65 and 2.1kgNha-1year-1 for nitrate (NO3-)-N, with the lowest deposition at the Madrid site for both components. Dry deposition was evaluated with three different approaches: (1) a canopy budget model based in throughfall measurements, (2) a branch washing method, and (3) inferential calculations. Taking the average dry deposition from these methods, dry deposition represented 51-67% (reduced N) and 72-75% (oxidized N) of total N deposition. Canopies retained both NH4+-N and NO3-N, with a higher retention at the agricultural and rural sites (50-60%) than at sites located close to big cities (20-35%, though more uncertainty was found for the site near Madrid), thereby highlighting the role of the forest canopy in processing N pollutant emissions.

Stomatal conductance models for ozone risk assessment at canopy level in two Mediterranean evergreen forests

Forests in Mediterranean Europe are located in a hot spot for tropospheric ozone formation. We applied two canopy-level stomatal conductance models (Jarvis-type and Ball-Woodrow-Berry models) to two Mediterranean evergreen forests (Umbrella pine at San Rossore, and Holm oak at Castelporziano, in central Italy), which is essential for assessing ozone impact on forests via the stomatal flux-based approach. Parameterizations of the models was carried out by the Eddy Covariance technique. Both Jarvis-type and Ball-Woodrow-Berry models well explained the observed stomatal conductance and stomatal ozone flux in both forests. Maximum stomatal conductance was 72% higher in Umbrella pine than in Holm oak, leading to higher stomatal ozone flux. Inclusion of a soil water function improved the performance of the Jarvis-type model for the estimation of stomatal ozone flux. We found contrasting results concerning the coefficient m (the slope of the photosynthesis-stomatal conductance relationship) in the Ball-Woodrow-Berry model between the two forests: while m was constant for varying soil water status in the Holm oak forest, it declined with soil drying in the Umbrella pine forest. This may result from higher stomatal sensitivity to drought in Umbrella pine as a response to avoid drought stress. Overall, these results advance our understanding of ozone risk assessment in Mediterranean forests.

Sacred sites in north‐western Morocco – naturalness of their vegetation and conservation value for vulnerable plant species

The vegetation and flora of 86 sacred sites (surroundings of tombs of local saints, cemeteries) in NW Morocco was studied to assess their conservation value for undisturbed Mediterranean evergreen forests and vulnerable plants. Habitats were mapped, based on life form, maximum height and cover value, and classified according to naturalness. Vascular plants were classified according to pre‐defined risk factors like stenochory or grazing sensitivity. Naturalness index and refugial value were calculated for each site. Only 20% of the mapped site area was closed forest. On many places, human impact had created a vegetation mosaic. Most of the vulnerable plants were mesophilous forest species or grazing sensitive taxa. Endemic species occurred only rarely. The occurrence of vulnerable plants and the naturalness of the vegetation were positively correlated. Sacred site extension had no significant effect on the number of vulnerable species. Results indicate a limited relevance of sacred sites in northern Morocco for the protection of intact forests and vulnerable plants. However, these localities can play an important role as stepping stones in agricultural landscapes. They protect plants, sensitive to opening of the tree layer, to deforestation and to intense grazing. Certain formerly widespread forest communities survived exclusively on sacred sites.

Environmental and biological controls on CH4 exchange over an evergreen Mediterranean forest

Methane (CH4) fluxes in a Mediterranean holm oak (Quercus ilex L.) forest were measured over 19 months, using eddy covariance technique and soil chambers measurements, complemented by microbiological characterization of CH4-cycling microorganisms along a vertical soil profile.CH4 budget at the site was close to the neutrality, although periodical switching of the ecosystem from sink to source was observed at daily and seasonal scale. Forest soil represented a net sink for atmospheric CH4 throughout the whole study period (mean uptake rate of 1.64×10−3μmolm−2s−1).Different environmental parameters influenced CH4 fluxes at different time scales.At half-hour timescale, CH4 fluxes followed a half-sinusoid curve with high emission recorded during the central hour of day (mean emission rate of 1.05×10−2μmolm−2s−1). Stomatal conductance, solar radiation (global and UV) and latent heat flux were the main drivers controlling ecosystem CH4 emissions, suggesting the occurrence of a plant-mediated transport through xylem as a way of CH4 emissions from canopy and supporting the hypothesis of UV-induced production of CH4 from leaves at the site.At daily scale, CH4 fluxes were strongly connected to temperature and precipitation which promote CH4-oxidizing microorganisms activity during the cold season and methanogens activity during the dry season.This study is the first long-term CH4 eddy covariance measurement above a Mediterranean forest and demonstrates that, at present, the ecosystem is a small sink of CH4 when considering both the soil and vegetation processes together, and this sink capacity is strictly connected to the water availability. Future changes in temperature and precipitation patterns may increase CH4 emissions, turning the ecosystem to a source of CH4.

Modelling the climatic drivers determining photosynthesis and carbon allocation in evergreen Mediterranean forests using multiproxy long time series

Abstract. Climatic drivers limit several important physiological processes involved in ecosystem carbon dynamics including gross primary productivity (GPP) and carbon allocation in vegetation. Climatic variability limits these two processes differently. We developed an existing mechanistic model to analyse photosynthesis and variability in carbon allocation in two evergreen species at two Mediterranean forests. The model was calibrated using a combination of eddy covariance CO2 flux data, dendrochronological time series of secondary growth and forest inventory data. The model was modified to be climate explicit in the key processes addressing the acclimation of photosynthesis and the pattern of C allocation, particularly to water stress. It succeeded in fitting both the high- and the low-frequency response of stand GPP and carbon allocation to stem growth. This would support its capability to address both C-source and C-sink limitations. Simulations suggest a decrease in mean stomatal conductance in response to a recent enhancement in water stress and an increase in mean annual intrinsic water use efficiency (iWUE) in both species during the last 50 years. However, this was not translated into a parallel increase in ecosystem water use efficiency (WUE). The interannual variability in WUE closely followed that in iWUE at both sites. Nevertheless, long-term decadal variability in WUE followed the long-term decrease in annual GPP matching the local trend in annual precipitation observed since the late 1970s at one site. In contrast, at the site where long-term precipitation remained stable, GPP and WUE did not show a negative trend and the trees buffered the climatic variability. In our simulations these temporal changes were related to acclimation processes at the canopy level, including modifications in LAI and stomatal conductance, but also partly related to increasing [CO2] because the model includes biochemical equations where photosynthesis is directly linked to [CO2]. Long-term trends in GPP did not match those in growth, in agreement with the C-sink hypothesis. The model has great potential for use with abundant dendrochronological data and analyse forest performance under climate change. This would help to understand how different interfering environmental factors produce instability in the pattern of carbon allocation and, hence, the climatic signal expressed in tree rings.

Particulate matter and meteorological conditions in Castelporziano forest: a brief commentary

In industrialized areas, the highest contribution to the fine and ultrafine particles comes from anthropogenic activities, namely from emissions of industrial combustion processes and traffic-related emissions. Peri-urban forests can act as a sink of these compounds through different mechanisms, helping to ameliorate air quality. Here, we present the preliminary results of a study to investigate the patterns of the aerosol particle distribution and their correlations with meteorological parameters. Concentration of particles with size down 2.5 nm in diameter was continuously measured above an evergreen Mediterranean forest from January to June 2014 inside the presidential estate of Castelporziano. Results indicate a strong effect of the boundary layer height on particle dispersion that determines higher particle concentration level at night and then diffusion in cleaner air during the day when turbulence enhances the vertical mixing. We found a pronounced reduction of particle concentration during the rain events, supporting the conclusion that rain events represent the major mechanism of particle deposition. By correlating wind direction and particle concentration, we hypothesize large marine aerosol contribution overlapping the anthropogenic sources, although we cannot discriminate yet between biogenic and anthropogenic origins of particulate.

Breeding ecology of the Atlas Pied Flycatcher Ficedula speculigera in an old oak Quercus suber forest in northeastern Algeria

Capsule Low clutch size (CS) in the Atlas Pied Flycatcher breeding in evergreen Mediterranean forest was compensated for by relatively high overall reproductive success.Aims To describe the breeding ecology of the Atlas Pied Flycatcher Ficedula speculigera in detail for the first time, in an old oak Quercus suber forest.Methods A total of 102 nests were monitored during 2010–2012. Breeding phenology, population density, clutch and brood sizes, egg biometrics, breeding losses and breeding success were accurately determined.Results The species arrived in the breeding area in late April. Population density was very high with 4.87 (±1.02) pairs/ha. Mean egg laying date (LD) was 19 May and CS averaged 4.92 eggs. Hatching and fledging success were 88.7% and 83.5%, respectively. The number of fledged young averaged 3.8 (±1.66) and decreased with LD (4.2 ± 1.45 chicks fledged per nest at the start of the season versus 2.8 ± 1.56 at the end).Conclusion Lower CS compared to Ficedula hypoleuca populations was compensated by relatively high fledging success, thereby ensuring overall reproductive success of this species. Moreover, the Atlas Pied Flycatchers seem to benefit from the lower seasonality in their food in the evergreen habitat.

Multiyear impacts of partial throughfall exclusion on Buxus sempervirens in a Mediterranean forest

Aim of study: We examined the impact of sustained partial throughfall exclusion on the functional performance of Buxus sempervirens L. in the understory of a Mediterranean evergreen forest. We further considered whether any impacts of throughfall exclusion were affected by light availability.Area of study: The study was conducted in the south of France.Material and methods: Several leaf physiological and branch structural traits were measured along a light gradient after seven years from the onset of a throughfall exclusion experiment (TEE). The results were analysed along with annual growth and survival data.Main results: Plant mortality was nil in both the throughfall exclusion and control treatments. Stem diameter growth was reduced by 39% in plants subjected to throughfall exclusion, but this difference was only significant at the p = 0.10 significance level. Leaf physiology remained unaffected by the TEE, but small changes were evident in branch structural traits in high light microsites following throughfall exclusion; branches had lower wood density in the TEE plot, and more biomass was partitioned to leaves relative to stems.Research highlights: These changes do not seem to reflect an acclimatory response that would enhance drought tolerance. Instead, we suggest that these drought effects might exacerbate vulnerability to xylem cavitation in the more open microsites. Reduced growth and increased vulnerability to drought may indicate an incipient decline in plant vitality following TEE. The extension of observations to the whole-plant level and longer periods will elucidate the consequences of these observations for plant fitness, and permit verification of the positive effect of shade on Buxus sempervirens under increased drought.Key words: common box; drought susceptibility; shade; rainfall manipulation; abiotic stress; long-term study.

Vegetation dynamics during the early to mid-Holocene transition in NW Malta, human impact versus climatic forcing

A pollen diagram was constructed for the early- to mid-Holocene transition (ca. 7350–5600 cal. b.p./5400–3650 b.c.) from the Burmarrad ria located in NW Malta. The vegetation at ca. 7350–6960 cal. b.p./5400–5010 b.c. was characterized by an almost tree-less steppe-like open landscape. Early Holocene dry climatic conditions were most probably due to intensification of the subtropical monsoon circulation that strengthened the subtropical anticyclonic descent over the central Mediterranean and blocked the penetration of humid air masses from the North Atlantic Ocean. At ca. 6950 cal. b.p./5000 b.c., the steppe-like vegetation was suddenly replaced by a Mediterranean evergreen forest or dense scrub dominated by Pistacia cf. lentiscus trees. This event, which has simultaneously been recorded in southern Sicily, was most probably caused by the southward shift of the ITCZ permitting the eastward movement of the North Atlantic cyclonic systems. Traces of human activities are evident in the pollen diagram since the beginning of the record but become more pronounced from the onset of the Temple Cultural Phase at ca. 6050 cal. b.p./4100 b.c. with a gradual decline of tree pollen. We suggest that the early- to mid-Holocene vegetation transformation was mainly controlled by a regional climatic change that occurred in a landscape only slightly impacted by human activities.

EVSItalia Database of Evergreen Mediterranean Forests

A database of the Evergreen Mediterranean Forests of peninsular Italy is presented (EVSItalia Database of Evergreen Mediterranean Forests, GIVD ID EU-IT-014). The database stores 1,266 releves from published certified phytosociological sources, belonging to the syntaxa of Quercion ilicis. Specifically, Quercus ilex forest of Viburno-Quercetum ilicis and the cork oak forest in the syntaxa of Viburno-Quercetum ilicis suberetosum (according to a centralMediterranean classical interpretation). Q. suber stands are a variant of the Q. ilex forests, although the continued exploitation of cork and grazing activities in the cork forests, do not allow a precise analysis of the true spatial limits of the two biocoenoses. All the releves are uploaded to TURBOVEG; a related ArcGIS Database stores information about localization: Operational Geographic Units (OGU), corresponding to the quadrates of the Italian floristic grid, precise GPS or toponym information as well as descriptive records of locations extracted from geographical information systems are stored. The data-set aims to support reviews based on large data-sets for the classification of Italian vegetation types, classification of communities and their parameterization over larger areas by geostatistical analysis, the exploration geographic changes in community distribution along topographical gradients and to test changes along geographical gradients. A different insight in the patterns of synonymy and reassessment among syntaxa on the basis of a geographical approach is expected.

Functional changes in the control of carbon fluxes after 3 years of increased drought in a Mediterranean evergreen forest?

AbstractOur objective was to test how a long‐term increased water limitation affects structural and functional properties of a Mediterranean ecosystem, and how these changes modify the response of the main carbon fluxes to climatic controls. In 2003, a 27% throughfall exclusion experiment was installed in a Quercus ilex L. forest in France. Gross primary production (GPP), ecosystem respiration (RECO) and net ecosystem exchange (NEE) were estimated in a control and a dry treatment. Decreasing throughfall decreased GPP by 14% and had a smaller effect on RECO (−12%), especially soil respiration RS (−11%). Interannual variability of GPP (29%) was higher than for RECO (12%). Error propagation was used to estimates uncertainties in the NEE fluxes, which ranged from 3% to 10% in the control treatment but up to 167% for NEE in the dry treatment because more steps and data types were involved in the scaling. After 3 years of throughfall exclusion, we found no acclimation of RS to climatic drivers. Functional properties of the response of RS to soil water, temperature and rain pulse remained similar in the control and the dry treatments. A diurnal clockwise hysteresis in RS was probably controlled by canopy photosynthesis with a 3 h lag. The proportion of diurnal variation of respiration due to photosynthesis was similar in all treatments (4–5%). Because of the characteristic of rain in Mediterranean climates, a continuous decrease of water input in these environments have an effect on topsoil water and consequently on RS only during short periods when rainfall is characterized by infrequent and small events that does not allow the topsoil to reach field capacity and does not allow to dry completely. However, in the longer term, we expect a stronger decrease in RS in the dry treatment driven by the decrease in GPP.

Self-shading in cork oak seedlings: Functional implications in heterogeneous light environments

The high self-shading found in Quercus suber seedlings has been interpreted as a feature common for plants growing in high light environments. But many studies reveal that Q. suber has high survival rates under low-light conditions, so a high degree of self-shading could be the consequence of a foliage composed of many small leaves, with no drawbacks for coping with low light. A characterization of the light environment in a Q. suber stand together with a study of photosynthetic parameters of full sunlight-exposed (FSLE) and self-shaded (SS) leaves were carried out to tackle this apparent contradiction. Although the number of sunflecks longer than 120 min during the 3 months of measurements was low, the occurrence of at least one sunfleck longer than 120 min per day in the understory of the forest studied was very common. Sunflecks shorter than 30 min promoted an increase in net photosynthesis ( A) in FSLE leaves, but not in SS leaves. However, sunflecks longer than 60 min led to a very strong decrease in A and in actual photosystem II efficiency (Φ PSII) in FSLE leaves, when compared to sunflecks shorter than 30 min. In SS leaves, changes were, again, negligible. The multi-layered foliage of Q. suber seedlings allowed i) FSLE leaves to obtain the maximum photosynthetic yield for short sunflecks, and ii) SS leaves to increase their contribution to the photosynthesis of the whole plant for long sunflecks, thus, optimizing the use of light by FSLE and SS leaves during short and long sunflecks respectively. Therefore, shoot architecture of Q. suber seedlings involving high levels of self-shading allows to adequately cope with the low but highly heterogeneous light conditions of the understory, particularly when sunflecks of contrasting durations take place as it is frequently the case for evergreen Mediterranean forests.

Xeromphalina setulipes (hygrophoroid clade, Agaricales), a new Mediterranean species

A new Xeromphalina species from Mediterranean evergreen forests of the southern part of the Iberian Peninsula is described. It is characterized by its habitat on soil, arcuate-decurrent lamellae, trama hyphae which turn distinctly orange-brown to red-brown in KOH solution, thick-walled caulocystidia with an attenuate apex reminding setulae, and versiform to irregularly cylindrical cheilocystidia, which are conspicuously branched forming coralloid excrescences. LM microphotographs illustrate its diagnostic features. Additionally, two nuclear ribosomal DNA regions from this new taxon were sequenced and compared with homologue sequences from existing species in the genus Xeromphalina, supporting its recognition as a new species.