Mediterranean Evergreen Forests Research Articles

Across and Within-Forest Effects on Breeding Success in Mediterranean Great TitsParus major

Forest type and habitat structure can have profound effects on different aspects of avian life histories. These effects may, however, strongly differ across and within forests that vary in vegetation composition and structure, especially when an ancient forest has been replaced by a new forest. To test for these differences in effect, we studied Great Tit Parus major life-history traits (280 first clutches) in two Mediterranean evergreen forests during 2005–07: an ancient Holm Oak Quercus ilex and a reforested pine forest. A comparison between forests revealed that females breeding in the Holm Oak forest started laying one week later, and produced larger clutches and broods both at hatching and at fledging. Chicks raised in the Holm Oak forest also fledged in better condition. Within forests, however, the reproductive success was not higher for pairs breeding in nestboxes surrounded by oaks within the pine forest, and also reproductive success was not lower in nestboxes surrounded by pines within oak forest. Instead, vegetation maturity around nestboxes, rather than tree species composition, affected hatching success. Surprisingly, hatching success was higher in nestboxes surrounded by immature vegetation. We suggest that this may be due to a lower nest predation rate in nestboxes surrounded by immature vegetation, compared to nestboxes surrounded by mature vegetation. We suggest that different factors appear to affect variation in breeding success in Mediterranean Great Tits comparing across forests (e.g. food availability) vs. within a forest (e.g. nest predation).

Ya'ar Bar'am—An old <i>Quercus calliprinos</i> forest of high nature conservation valuein the Mediterranean region of Israel

Sclerophyllous oak forests are an important ecosystem type of the natural vegetation in the Mediterranean region. As a part of the mosaic-like landscape, old-growth oak forests, in particular, provide a wide range of ecosystem functions and services. However, due to the general scarcity of older forests in the Mediterranean region, studies on structure and dynamics of oak forests are mostly restricted to younger stands. The aim of this study was to analyze stand structure, dead wood, and natural regeneration of an old Quercus calliprinos forest in northern Israel (nature reserve Ya'ar Bar'am) and to compare the results with those reported from other evergreen Mediterranean oak forests. The mean density of trees was 735 ha-1, and the mean basal area amounted to 25.0 m2 ha-1. The mean tree height was 6.6 m, and the maximum tree height was 13.2 m. The mean dead wood volume was 11 m3 ha-1. The sapling density ranged from 1,050 to 6,250 ha-1. We conclude that Bar'am Forest is of great value for conservation bi...

Exceptional carbon uptake in European forests during the warm spring of 2007: a data–model analysis

AbstractTemperate and boreal forests undergo drastic functional changes in the springtime, shifting within a few weeks from net carbon (C) sources to net C sinks. Most of these changes are mediated by temperature. The autumn 2006–winter 2007 record warm period was followed by an exceptionally warm spring in Europe, making spring 2007 a good candidate for advances in the onset of the photosynthetically active period. An analysis of a decade of eddy covariance data from six European forests stands, which encompass a wide range of functional types (broadleaf evergreen, broadleaf deciduous, needleleaf evergreen) and a wide latitudinal band (from 44° to 62°N), revealed exceptional fluxes during spring 2007. Gross primary productivity (GPP) of spring 2007 was the maximum recorded in the decade examined for all sites but a Mediterranean evergreen forest (with a +40 to +130 gC m−2 anomaly compared with the decadal mean over the January–May period). Total ecosystem respiration (TER) was also promoted during spring 2007, though less anomalous than GPP (with a +17 to +93 gC m−2 anomaly over 5 months), leading to higher net uptake than the long‐term mean at all sites (+12 to +79 gC m−2 anomaly over 5 months). A correlative analysis relating springtime C fluxes to simple phenological indices suggested spring C uptake and temperatures to be related. The CASTANEA process‐based model was used to disentangle the seasonality of climatic drivers (incoming radiation, air and soil temperatures) and biological drivers (canopy dynamics, thermal acclimation of photosynthesis to low temperatures) on spring C fluxes along the latitudinal gradient. A sensitivity analysis of model simulations evidenced the roles of (i) an exceptional early budburst combined with elevated air temperature in deciduous sites, and (ii) an early relief of winter thermal acclimation in coniferous sites for the promotion of 2007 spring assimilation.

Response of broadleaved evergreen Mediterranean forest vegetation to fire disturbance during the Holocene: insights from the peri‐Adriatic region

AbstractAim To test whether fire contributed to the expansion and compositional change of evergreen forests in the Mediterranean region during the Holocene.Location The peri‐Adriatic region, encompassing the Italian peninsula, Sicily and the western and southern Balkans between latitudes 46° and 37° N.Methods New high‐resolution pollen and microscopic charcoal data from Lago dell’Accesa (Tuscany, Italy) were used to estimate the response of the evergreen oak, Quercus ilex L., to fire during its expansion phase at 8500 cal. yr bp. The data were compared with the pollen and charcoal series from other Mediterranean sites (Lago di Massaciuccoli in Tuscany, Malo Jezero in Croatia, Biviere di Gela in Sicily) and analysed using numerical techniques (redundancy analysis, detrended canonical correspondence analysis) to identify long‐term fire–vegetation linkages and the degree of compositional change.Results Microscopic charcoal and pollen of evergreen oaks were negatively correlated during the period of quasi‐natural fire regime (Mesolithic, 10,000–8000 cal. yr bp). In addition, there was no such positive correlation during periods when the fire regime was potentially more influenced by people (Neolithic–Bronze Age, 8000–3000 cal. yr bp). Compared with inland sites, coastal sites that are currently located at a distinct ecotone showed more compositional change.Main conclusions The analyses suggest that climatic change, without an additional effect of fire regimes, favoured the expansion and compositional change of evergreen forests across the peri‐Adriatic region. Strikingly different patterns occurred along a north–south gradient. In the north (Tuscany and Croatia, meso‐Mediterranean belt), Q. ilex replaced deciduous forests when conditions became drier; in the south (Sicily, thermo‐Mediterranean belt) the species replaced maquis or steppe vegetation when climatic conditions became moister. We conclude that the projected increase in fire activity may lead to the loss of most of the remaining relict forests of Q. ilex in southern Europe.

Seasonal and annual variation of carbon exchange in an evergreen Mediterranean forest in southern France

AbstractWe present 9 years of eddy covariance measurements made over an evergreen Mediterranean forest in southern France. The goal of this study was to quantify the different components of the carbon (C) cycle, gross primary production (GPP) and ecosystem respiration (Reco), and to assess the effects of climatic variables on these fluxes and on the net ecosystem exchange of carbon dioxide. The Puéchabon forest acted as a net C sink of −254 g C m−2 yr−1, with a GPP of 1275 g C m−2 yr−1 and a Reco of 1021 g C m−2 yr−1. On average, 83% of the net annual C sink occurred between March and June. The effects of exceptional events such the insect‐induced partial canopy defoliation that occurred in spring 2005, and the spring droughts of 2005 and 2006 are discussed. A high interannual variability of ecosystem C fluxes during summer and autumn was observed but the resulting effect on the annual net C budget was moderate. Increased severity and/or duration of summer drought under climate change do not appear to have the potential to negatively impact the average C budget of this ecosystem. On the contrary, factors affecting ecosystem functioning (drought and/or defoliation) during March–June period may reduce dramatically the annual C balance of evergreen Mediterranean forests.

WOODY PLANT RICHNESS AND NDVI RESPONSE TO DROUGHT EVENTS IN CATALONIAN (NORTHEASTERN SPAIN) FORESTS

The role of species diversity on ecosystem resistance in the face of strong environmental fluctuations has been addressed from both theoretical and experimental viewpoints to reveal a variety of positive and negative relationships. Here we explore empirically the relationship between the richness of forest woody species and canopy resistance to extreme drought episodes. We compare richness data from an extensive forest inventory to a temporal series of satellite imagery that estimated drought impact on forest canopy as NDVI (normalized difference vegetation index) anomalies of the dry summer in 2003 in relation to records of previous years. We considered five different types of forests that are representative of the main climatic and altitudinal gradients of the region, ranging from lowland Mediterranean to mountain boreal-temperate climates. The observed relationship differed among forest types and interacted with the climate, summarised by the Thorntwaite index. In Mediterranean Pinus halepensis forests, NDVI decreased during the drought. This decrease was stronger in forests with lower richness. In Mediterranean evergreen forests of Quercus ilex, drought did not result in an overall NDVI loss, but lower NDVI values were observed in drier localities with lower richness, and in more moist localities with higher number of species. In mountain Pinus sylvestris forests NDVI decreased, mostly due to the drought impact on drier localities, while no relation to species richness was observed. In moist Fagus sylvatica forests, NDVI only decreased in plots with high richness. No effect of drought was observed in the high mountain Pinus uncinata forests. Our results show that a shift on the diversity-stability relationship appears across the regional, climatic gradient. A positive relationship appears in drier localities, supporting a null model where the probability of finding a species able to cope with drier conditions increases with the number of species. However, in more moist localities we hypothesize that the proportion of drought-sensitive species would increase in richer localities, due to a higher likelihood of co-occurrence of species that share moist climatic requirements. The study points to the convenience of considering the causes of disturbance in relation to current environmental gradients and historical environmental constraints on the community.

Drought changes phosphorus and potassium accumulation patterns in an evergreen Mediterranean forest

Summary Climate models predict more extreme weather in Mediterranean ecosystems, with more frequent drought periods and torrential rainfall. These expected changes may affect major process in ecosystems such as mineral cycling. However, there is a lack of experimental data regarding the effects of prolonged drought on nutrient cycling and content in Mediterranean ecosystems. A 6‐year drought manipulation experiment was conducted in a Quercus ilex Mediterranean forest. The aim was to investigate the effects of drought conditions expected to occur over the coming decades, on the contents and concentrations of phosphorus (P) and potassium (K) in stand biomass, and P and K content and availability in soils. Drought (an average reduction of 15% in soil moisture) increased P leaf concentration by 18·2% and reduced P wood and root concentrations (30·9% and 39·8%, respectively) in the dominant tree species Quercus ilex, suggesting a process of mobilization of P from wood towards leaves. The decrease in P wood concentrations in Quercus ilex, together with a decrease in forest biomass growth, led to an overall decrease (by approximately one‐third) of the total P content in above‐ground biomass. In control plots, the total P content in the above‐ground biomass increased 54 kg ha−1 from 1999 to 2005, whereas in drought plots there was no increase in P levels in above‐ground biomass. Drought had no effects on either K above‐ground contents or concentrations. Drought increased total soil soluble P by increasing soil soluble organic P, which is the soil soluble P not directly available to plant capture. Drought reduced the ratio of soil soluble inorganic P : soil soluble organic P by 50% showing a decrease of inorganic P release from P bound to organic matter. Drought increased by 10% the total K content in the soil, but reduced the soil soluble K by 20·4%. Drought led to diminished plant uptake of mineral nutrients and to greater recalcitrance of minerals in soil. This will lead to a reduction in P and K in the ecosystem, due to losses in P and K through leaching and erosion, if the heavy rainfalls predicted by IPCC (Intergovernmental Panel on Climate Change) models occur. As P is currently a limiting factor in many Mediterranean terrestrial ecosystems, and given that P and K are necessary for high water‐use efficiency and stomata control, the negative effects of drought on P and K content in the ecosystem may well have additional indirect negative effects on plant fitness.

Litter production in aQuercus suberforest of Montseny (NE Spain) and its relationship to meteorological conditions

From 1996 to 2002 the monthly litterfall in a Quercus suber forest ecosystem of Montseny (NE Spain) was recorded and its relationship to meteorological variables was statistically analysed. The average annual production (477 g m −2 yr −1 ) was similar to those found in other Mediterranean evergreen forests with relatively high rainfall. The main components were the leaves (55% of the total biomass), followed by acorns (22%) and twigs (16%). Litter production was highest during May and June, when the majority of the old leaves fell. When the meteorological conditions were favourable, a second leaf fall collection was observed. Acorn production in 2001 was about nine times that of the previous years, indicating a mast year. In general, the different litterfall components were highly correlated in time except for the acorns. Interannual covariation was significant for leaves/twigs and leaves/catkins. Catkins were the most variable component with also strong seasonality, acorns were also very variable with low seasonality, while leaves were less variable and with the strongest seasonality. After accounting for seasonal covariation, there were significant effects of rainfall on twig litterfall and of temperature on leaf litterfall, the years with highest leaf litterfall being the hottest. litterfall / Iberian Peninsula / coark oak / Mediterranean climate / weather

Genetic survey of two endangered grasshopper subspecies, Prionotropis hystrix rhodanica and Prionotropis hystrix azami (Orthoptera, Pamphagidae): within- and between-population dynamics at the regional scale

The fragmentation and destruction of natural habitats is one of the major causes of extinction of wild flora and fauna due to human activities. The area around the Mediterranean Basin is particularly affected: this region is one of the world’s richest in terms of biodiversity and is undergoing substantial modification due to extensive changes in land use. We investigated the demographic state (through a genetic survey) of an endangered grasshopper, the geographical distribution of which is restricted to arid open land or glades in south-eastern France. We compared two subspecies: one is severely threatened by the fragmentation of its specific and restricted habitat (Prionotropis hystrix rhodanica in the ‘Crau’ steppe) whereas the other, P.␣h.␣azami, occurs more widely in glades or clearings in the evergreen Mediterranean forest. Genetic diversity at eight microsatellite loci was highly structured, indicating substantial isolation of populations. Within-population diversity was high at all but one site. Genetic drift was the major force involved in this genetic structure, with very little gene flow at the regional scale of observation, consistent with both the limited dispersal of this flightless species and the patchy configuration of its habitat. No significant differences in the extent of genetic diversity or population dynamics were observed between the two subspecies. The observed genetic pattern calls into question the validity of the subspecies status, and shows no strong impact of recent anthropogenic modification of the Crau steppe. The evolution of the Mediterranean xeric and open habitats under both natural and anthropogenic processes is discussed.

Ozone uptake by an evergreen mediterranean forest ( L.) in Italy—Part II: flux modelling. Upscaling leaf to canopy ozone uptake by a process-based model

Ozone (O 3 ) induces deleterious effects on plants by its oxidising capacity. Efforts have aimed at defining O 3 critical loads which are based on O 3 penetrating into the plant through the stomata, being an important mechanism of O 3 removal. Recently, papers have proposed the use of process-based models for estimating the O 3 dose at the community level. These models should define the stomatal O 3 flux ( F st ) on vegetation, correlating it to O 3 -induced injury and hence to improve the data-base available for decision makers. A process-based model has been utilised for the quantification of O 3 flux ( F ) toward a Holm oak forest and its repartition in F st and non-stomatal flux ( F nost ) during daylight. The model outputs have been compared with eddy covariance measurements. Simulation of O 3 fluxes under the climatic limitations of summer 2003 showed that the mean values of F st represented only 28.9% of F , which was similar to eddy covariance (31.5%). The use of LAI effective to link the leaf F st to the canopy scale O 3 stomatal flux ( F effectjve ; on ground unit) is shown to be useful not only for the model validation but also for upscaling purposes from leaf to canopy. Forest acts as a LAI = 1 , i.e. a “real” big leaf for canopy O 3 uptake. Changes in O 3 fluxes were more closely related to the factors that control O 3 deposition than to the factors controlling O 3 concentration. Simulations showed that Holm oak forest was most effective at taking up O 3 under moderate to high irradiance and high physiological activity, but not in limiting environmental conditions. The model used here does not require a great number of input variables and it is based on simple assumptions with respect to other more recognised models. So, the use of this model can have useful applications for the risk assessment of level II for the forests.

Ozone uptake by an evergreen Mediterranean Forest () in Italy. Part I: Micrometeorological flux measurements and flux partitioning

Ozone, water and energy fluxes have been measured over a Mediterranean evergreen forest in Central Italy from August to October 2003 with the eddy-correlation technique in order to evaluate the amount of ozone taken up by plants in dry summer and in mild autumn conditions. The stomatal ozone fluxes have been calculated using the analogy with water vapor fluxes inside the stomata, which are easily measurable. The total ozone dose was obtained by integrating the stomatal fluxes over time. Stomatal flux resulted a minor part (31.5%) of the total ozone flux over the forest ecosystem. The main part of ozone deposition follows non-stomatal pathways. Chemical sink seems to play a relevant role in the morning non-stomatal deposition. Stomatal uptake is enhanced by water availability but, on the average, it does not exceed the 34.4% of the total ozone flux. A comparison between the cumulated stomatal ozone fluxes and the currently used AOT40 exposure index highlighted important distortions introduced by this index. AOT40, which do not take into account plant physiology, lead to substantial overestimation of ozone risk, particularly when water supply is limited, as occurs frequently in Southern European and Mediterranean areas.

Increasing drought decreases phosphorus availability in an evergreen Mediterranean forest

Mediterranean ecosystems are water-limited and frequently also nutrient-limited. We aimed to investigate the effects of increasing drought, as predicted by GCM and eco-physiological models for the next decades, on the P cycle and P plant availability in a Mediterranean forest. We conducted a field experiment in a mature evergreen oak forest, establishing four drought-treatment plots and four control plots (150 m 2 each). After three years, the runoff and rainfall exclusion reduced an overall 22% the soil moisture, and the runoff exclusion alone reduced it 10%. The reduction of 22% in soil moisture produced a decrease of 40% of the accumulated aboveground plant P content, above all because there was a smaller increase in aerial biomass. The plant leaf P content increased by 100 ± 40 mg m −2 in the control plots, whereas it decreased by 40 ± 40 mg m −2 in the drought plots. The soil Po-NaHCO3 (organic labile-P fraction) increased by 25% in consonance with the increase in litterfall, while the inorganic labile-P fraction decreased in relation to the organic labile-P fraction up to 48%, indicating a decrease in microbial activity. Thus, after just three years of slight drought, a clear trend towards an accumulation of P in the soil and towards a decrease of P in the stand biomass was observed. The P accumulation in the soil in the drought plots was mainly in forms that were not directly available to plants. These indirect effects of drought including the decrease in plant P availability, may become a serious constraint for plant growth and therefore may have a serious effect on ecosystem performance.

Seasonal variation in the contribution of different behavioural mechanisms to lizard thermoregulation

Summary We studied seasonal changes in the thermoregulatory behaviour of the lacertid lizard Psammodroums algirus in a Mediterranean evergreen forest. Body temperatures (Tb), environmental operative temperatures (Te) and upper and lower limits of the selected thermal range (Tsel) were lower in May than in July. On average, mean deviations of Tb from Tsel (0·7 °C in both seasons) were much smaller than those of Te (8·3 °C in both seasons). Thus both the accuracy (average difference between Tb and Tsel) and effectiveness (the extent to which Tb are closer than Te to Tsel) of thermoregulation were high, and similar in both seasons. However the thermoregulatory contribution of two distinct behavioural mechanisms varied markedly between seasons. Daily activity contributed significantly to the regulation of Tb in May (when a population of Te thermometers matching lizard activity patterns would be, on average, 1·0 °C closer to Tsel than were randomly available Te), but not in July (when such a population would be only 0·2 °C closer to Tsel than were randomly available Te). The selection of sun–shade patches, the contribution of which was larger than that of daily activity in both seasons, was more important in July (when it produced a distribution of Te that would be, on average, 3·1 °C closer to Tsel than were randomly distributed Te) than in May (when a population of thermometers matching the lizards’ pattern of exposure to sunlight would be 1·3 °C closer to Tsel than were randomly available Te). These changes are discussed in the light of seasonal differences in the daily patterns of among‐patch variation in Te. In spring, lizard activity was low in the early morning because even the selection of sunlit patches was of limited utility to attain Tb within Tsel; in summer, lizards could remain active at midday, despite low overall thermal suitability, by selecting shaded patches. Thus the contribution of patch selection to thermoregulation was important in the early basking period of both seasons, and at summer midday hours. Our data suggest that shuttling between sun and shade, rather than selecting sun or shade, may be an additional mechanism of behavioural thermoregulation, the importance of which would be greatest at times of day when lizards use patches at random (e.g. spring midday hours), and that their mean Tb is closer to the grand mean of full sun and full shade Te than to the mean equilibrium Te within any type of patch.

Phase and amplitude of ecosystem carbon release and uptake potentials as derived from FLUXNET measurements

As length and timing of the growing season are major factors explaining differences in carbon exchange of ecosystems, we analyzed seasonal patterns of net ecosystem carbon exchange ( F NEE) using eddy covariance data of the FLUXNET data base ( http://www-eosdis.ornl.gov/FLUXNET). The study included boreal and temperate, deciduous and coniferous forests, Mediterranean evergreen systems, rainforest, native and managed temperate grasslands, tundra, and C 3 and C 4 crops. Generalization of seasonal patterns are useful for identifying functional vegetation types for global dynamic vegetation models, as well as for global inversion studies, and can help improve phenological modules in SVAT or biogeochemical models. The results of this study have important validation potential for global carbon cycle modeling. The phasing of respiratory and assimilatory capacity differed within forest types: for temperate coniferous forests seasonal uptake and release capacities are in phase, for temperate deciduous and boreal coniferous forests, release was delayed compared to uptake. According to seasonal pattern of maximum nighttime release (evaluated over 15-day periods, F max) the study sites can be grouped in four classes: (1) boreal and high altitude conifers and grasslands; (2) temperate deciduous and temperate conifers; (3) tundra and crops; (4) evergreen Mediterranean and tropical forests. Similar results are found for maximum daytime uptake ( F min) and the integral net carbon flux, but temperate deciduous forests fall into class 1. For forests, seasonal amplitudes of F max and F min increased in the order tropical<Mediterranean and temperate coniferous<temperate deciduous and boreal forests, and the pattern seems relatively stable for these groups. The seasonal amplitudes of F max and F min are largest for managed grasslands and crops. Largest observed values of F min varied between −48 and −2 μmol m −2 s −1, decreasing in the order C 4-crops>C 3-crops>temperate deciduous forests>temperate conifers>boreal conifers>tundra ecosystems. Due to data restrictions, our analysis centered mainly on Northern Hemisphere temperate and boreal forest ecosystems. Grasslands, crops, Mediterranean ecosystems, and rainforests are under-represented, as are savanna systems, wooded grassland, shrubland, or year-round measurements in tundra systems. For regional or global estimates of carbon sequestration potentials, future investigations of eddy covariance should expand in these systems.

Nestling diet variation in an insular Mediterranean population of blue tits Parus caeruleus: effects of years, territories and individuals.

Mediterranean evergreen forests of Corsica are characterized by relatively high species diversity of arthropods with low population densities. Food is never superabundant for Corsican blue tits Parus caeruleus. This study focused on the composition of the food of blue tit nestlings and especially on two main components, caterpillars and spiders. The nestling diet was studied for two years using 8-mm cameras that automatically took photographs of adult birds with food. The diet was composed of c. 50% caterpillars and c. 30% spiders. There were between-year and between-individual differences in these proportions. In both years of the study the proportion of caterpillars declined during the course of the breeding season. Individual and time effects on prey sizes were also observed. Pairs and individuals were fairly constant in the proportions of prey over the feeding period. Different food items were not brought in runs. These findings suggest that strong food limitation exists on Corsica, which can considerably influence life-history traits of the blue tit.

Temporal Patterns of Basking Behaviour in a Mediterranean Lacertid Lizard

Abstract1. I studied the thermoregulatory behaviour of the diurnal basker Psammodromus algirus (Reptilia, Lacertidae) in the mosaic of sunshade patches of a Mediterranean evergreen forest. 48 behavioural sequences associated with measurements of the thermal environment provided data on the percentages of time spent basking by focal animals, the duration of individual basking periods and the frequency of basking. 2. The percentage of time basking decreased linearly from the onset of the activity period until midday. The average duration of basking periods had a pronounced decrease after 0700 h and remained constant throughout the rest of the morning, whereas the basking rates, that were minimal before 0700 h, reached a peak between 0700 and 0800 h followed by a progressive fall that continued until noon. 3. In order to explain these behavioural patterns, I experimentally determined the effects of environmental variables (air and ground temperature and solar angle) on the heating and cooling rates of captive lizards. The resulting regression models were then used to predict the heat exchange rates of the observed free-ranging animals. 4. The moment at which heating rates should equal and then exceed cooling rates, appeared to set off the behavioural shift towards a larger frequency of shorter basking periods. Under these circumstances, the apparently random movement of a shuttling heliotherm with respect to sun and shade might still be of thermoregulatory significance.

Coenological research on macrofungi in evergreen oak woods in the hills near Siena (Italy)

For a mycocoenological study of macromycetes in Mediterranean evergreen forests in the Siencese province, five stands belonging to theQuercion ilicis have been observed during more than two years.