Species-specific drought effects on flower and fruit production in a Mediterranean holm oak forest

A holm oak forest was exposed to an experimental drought (reductionof 15 per cent soil moisture as predicted for this area forthe next decades by General Circulation Models and ecophysiologicalmodels) during 7 years to elucidate the reproductive responsesof the dominant species Quercus ilex L., Arbutus unedo L. andPhillyrea latifolia L. Soil moisture was partially reduced byplastic strips intercepting rainfall and by ditch exclusionof water runoff. During the period studied, meteorological conditionsand soil moisture were continuously monitored, together withflower and fruit production in the three dominant species. InQ. ilex and A. unedo, flower and specially fruit productionwere strongly correlated with annual rainfall, but not in P.latifolia. The experimental drought reduced flower and fruitproduction in Q. ilex by 30 per cent and 45 per cent, respectively.Reductions in flower and fruit production were not significantin A. unedo and were not observed in P. latifolia. A decreasein production of reproductive structures and the different responseof the species studied to a decrease in water availability couldinduce important changes in the competitive ability of the differentspecies and in the long term in the community species compositionand future distribution of these Mediterranean species.     

Determinants of drought effects on crown condition and their relationship with depletion of carbon reserves in a Mediterranean holm oak forest

Severe droughts may increase physiological stress on long-lived woody vegetation, occasionally leading to rapid defoliation and progressive increase in mortality of overstorey trees. Over the last few years, episodes of drought-induced tree dieback have been documented in a variety of woodlands and forests around the world. However, the factors determining tree survival and subsequent recovery are still poorly understood, especially in resprouter species. We have studied the effects of a single drought episode on crown condition in a holm oak (Quercus ilex L.) forest located in NE Spain 7 years after the drought event. Generalized linear models were used to study the environmental correlates of forest crown condition 7 years after the drought event. Additionally, we evaluated the association between crown condition and the carbon and nutrient reserves stored in lignotubers 7 years after the drought. Our study reveals the multifactor nature of a drought-driven forest dieback in which soil depth and the characteristics of individual trees, particularly their number of stems, determined a complex spatial pattern of tree-level responses. This dieback was associated with a depletion of the carbon reserves in lignotubers 7 years after the episode, representing a reduction of up to 60% in highly drought-damaged trees. Interestingly, in the absence of new acute droughts, successive surveys in 2007-11 showed a direct association between carbon reserves depletion and further deterioration of crown condition. More frequent droughts, as predicted by climate change projections, may lead to a progressive depletion of carbon reserves and to a loss of resilience in Mediterranean resprouter species.     

Decreased mushroom production in a holm oak forest in response to an experimental drought

A holm oak forest located in the Prades mountains (north-eastSpain) was subjected to an experimental drought, reducing soilwater moisture by 15 per cent by the use of plastic strips andfunnels that partially excluded rain throughfall and by ditchexclusion of water runoff. We monitored mushroom productionper plot once a week during 1999 and 2000. Drought treatmentdid not delay mushroom appearance, but reduced mushroom productionby 62 per cent on average. This suggests that in a drier environment– as predicted for Mediterranean areas in the near future– there is likely to be a decrease in mushroom production,and as a result, changes in some ecological parameters suchas soil organic matter decomposition, and also a reduction inthe economic and recreational value of these Mediterranean forests.     

Stomatal patchiness in the Mediterranean holm oak (Quercus ilex L.) under water stress in the nursery and in the forest

The evergreen holm oak Quercus ilex L. is the most representative tree in Mediterranean forests. Accurate estimation of the limiting factors of photosynthesis for Q. ilex and the prediction of ecosystem water-use efficiency by mechanistic models can be achieved only by establishing whether this species shows heterogenic stomatal aperture, and, if so, the circumstances in which this occurs. Here, we collected gas-exchange and chlorophyll fluorescence data in Q. ilex leaves from a nursery to measure the effects of stomatal oscillations on PSII quantum yield (Φ(PSII)) under water stress. Stomatal conductance (g(s)) was used as an integrative indicator of the degree of water stress. Images of chlorophyll fluorescence showed heterogeneous Φ(PSII) when g(s) was <50 mmol H(2)O m(-2) s(-1), representative of severe drought and corresponding to a container capacity <45%. Stomatal patchiness was related to a coefficient of variation (CV) of Φ(PSII) values >2.5%. A parallel study in the forest confirmed heterogeneous Φ(PSII) values in leaves in response to declining water availability. Three kinds of Q. ilex individuals were distinguished: those resprouting after a clear-cut (resprouts, R); intact individuals growing in the same clear-cut area as resprouts (controls, C); and intact individuals in a nearby, undisturbed area (forest controls, CF). Patchiness increased in C and CF in response to increasing drought from early May to late July, whereas in R, Φ(PSII) values were maintained as a result of their improved water relations since the pre-existing roots were associated with a smaller aerial biomass. Patchiness was related to a % CV of Φ(PSII) values >4 and associated in the summer with mean g(s) values of 30 mmol H(2)O m(-2) s(-1). Under milder drought in spring, Φ(PSII) patchiness was less strictly related to g(s) variations, pointing to biochemical limitants of photosynthesis. The occurrence of heterogenic photosynthesis caused by patchy stomatal closure in Q. ilex during severe drought should be taken into account in ecosystem modelling in which harsher water stress conditions associated with climate change are predicted.     

Assessing forest fragmentation in north-western Himalaya: a case study from Ranikhet forest range,Uttarakhand, India

The northwestern Himalaya harbors high levels of biodiversity due to its unique topography, climatic conditions and heterogeneity. Forest fragmentation is one of the major threats causing a decline in biodiversity in the Himalayan region. We assesses forest fragmentation and changes in land use land cover(LULC) patterns using multi-temporal satellite data over a time span of four decades(1976–2013). Fragmentation analysis using the Landscape Fragmentation Tool(LFT) reveals a decrease in core and edge areas by 14 and 2.3 %, respectively; while an increase in non-forest, patch area and perforation area by 2.1, 0.4, and 14 %, respectively. The LULC dynamics show that the areas under dense forest and scrub forest have decreased by 2.8 % and 1.9 %, respectively; and there is an increase in open forest, crop land and fallow land area by 2.6, 1.7 and 2.1 %, respectively. The quantification of landscape heterogeneity is undertaken with the help of landscape metrics computed using FRAGSTATS at class and landscape level, showing signs of increased fragmentation. Our study provides baseline database that can support the future biodiversity conservation and sustainable forest management initiatives.     

Light spectral composition in a tropical forest: measurements and model

I present a simple model that simulates vertical variations in the light spectrum within a forest canopy. The model considers only the vertical, downward transmission of light. The light in each canopy level was assumed to consist of non-intercepted radiation and radiation intercepted within the level and transmitted. The spectrum of non-intercepted light in each canopy level is the same as that of incident light above the canopy (input parameter), whereas the spectrum of transmitted light depends on leaf area index (LAI) and the mean transmission spectrum of leaves. The model was tested in a forest and provided adequate predictions of measured values. Stronger deviations were produced in the near infrared (NIR) waveband in lower canopy levels. Multiple regression between LAI, as the dependent variable, and spectral characteristics (Blue, Green, Red and NIR intensities) had an r(2) of 0.926. As a complement to other methods, I suggest light spectrum analysis as a non-destructive technique for estimating LAI in forest canopies.     

An approach to cork oak forest management planning: a case study in southwestern Portugal

This paper presents results of research aiming at the development of tools that may enhance cork oak (Quercus suber L.) forest management planning. Specifically, it proposes an hierarchical approach that encompasses the spatial classification of a cork oak forest and the temporal scheduling of cork harvests. The use of both geographical information systems and operations research techniques is addressed. Emphasis is on the achievement of cork even flow objectives. Results from an application to a case study in the Charneca Pliocénica of Ribatejo in southern Portugal encompassing a cork oak forest extending over 4.8 thousand ha are discussed. They suggest that the proposed approach is capable of effective spatial classification of cork oak management units. They further suggest that it may be used to select optimal cork even flow scheduling strategies. Results also show that the proposed approach may lead to a substantial increase in net present value when compared to traditional approaches to cork oak forest management planning.     

Assessing foraging strategies of herbivores in Mediterranean oak woodlands: a review of key issues and selected methodologies

Montados are agro-silvo-pastoral ecosystems, typical of the Southwest Iberian Peninsula, of high socio-economic and conservation importance, where grazing is a dominant activity. Montados are characterized by an open tree canopy of Quercus sp. and a diverse undercover of shrubs and grasslands that constitute the plant food resources for grazing animals. Plant food resources of Montados are highly variable, both spatially and seasonally, in quantity and quality. Reliable and easy to use methods to monitor grazing are necessary to allow proper understanding of foraging strategies of grazing animals and to set sustainable grazing management. We describe the main characteristics of the plant food resources available for grazing animals, striking its variability, and revise the potential of using N-alkanes and saliva proteome methods to assess foraging strategies in Montados. In a scenario of dynamic multiple choices, we discuss the use of n-alkane methodology for the simultaneous estimation of diet composition and voluntary intake and saliva proteome as a mean of increasing the knowledge on diet adjustments.     

Biotic interactions in a Mediterranean oak forest: role of allelopathy along phenological development of woody species

Plant–plant chemical interactions in forests can have a strong impact on the biodiversity and dynamics of these ecosystems, particularly in Mediterranean forests where plants exhibit a high secondary metabolite diversity. Allelopathic interactions in Mediterranean ecosystems have been mostly studied in the first stages of ecosystem dynamics, shrublands and pine forests, but little is known about these interactions in mature oak forests. In this study, the allelopathic effect of three main woody species of downy oak forests (Quercus pubescens, Acer monspessulanum and Cotinus coggygria) on germination and growth of two herbaceous species (Festuca ovina and Linum perenne) was tested through aqueous extracts obtained from different leaf phenological stages (green, senescent and litter). The germination velocity of the two target species was inhibited by the aqueous extracts of senescent leaves from all the woody species. The growth of F. ovina seedlings was affected by aqueous extracts of green leaves of all the woody species, while the growth of L. perenne was only affected by aqueous extracts of green leaves of A. monspessulanum. This shows that (i) allelochemicals released by leaf leachates of the dominant woody species could control the dynamic of the herbaceous species, and then their potential competition with trees and (ii) allelopathic effects of woody species are related to their phenological stage and seem consistent with the development stage of target species.

     

A tree species range in the face of climate change: cork oak as a study case for the Mediterranean biome

Species distribution models are feasible methods for projecting theoretical responses of living organisms’ occurrence under several future climate change scenarios. The major interest is focused on trees, which regulate the equilibrium within ecosystems and guarantee the survival of many life forms on the Earth. The repercussions of climatic drivers are expected to pose the strongest threats for the Mediterranean biome, an acknowledged hotspot of biodiversity. Here, we focused on cork oak (Quercus suber L.), a keystone species of many landscapes, sustaining a rich biodiversity, ecological processes and economic incomes. Results of 8 combined ecological modelling techniques and two Global Circulation Models highlight a broad contraction of the species potential range over the twenty-first century, both under intermediate and high emissions scenarios. Coupled northward and upward shifts are predicted, mostly pertaining Iberia and North Africa. The potential areas detected at Levantine will likely undergo disappearance. To exacerbate the impacts of climate change, the future of the ecosystems linked to cork oak remains uncertain, because of the expected implications on the phenotypic plasticity or evolutionary responses. A synergy among niche-based, physiological and eco-genetic investigations is strongly needed in the field of applied research, to improve the assessment of conservation and reforestation actions.     

Viability of holm and cork oak seedlings from acorns sown in soils naturally infected with Phytophthora cinnamomi

The emergence and survival of pregerminated holm oak (Quercus ilex) and cork oak (Quercus suber) acorns from two ecologically different dehesas (Mediterranean open woodlands) were studied in two soils from these stands naturally infected with Phytophthora cinnamomi, and in the same soils previously sterilized in the autoclave. Phytophthora cinnamomi was consistently isolated from the radicles of all unemerged and all emerged but dead seedlings from the unsterilized substrates. Seedlings of holm oak were more susceptible to P. cinnamomi than those of cork oak. Mortality of holm oak seedlings was significantly different depending only on soil treatment (sterilized or unsterilized), and it was 100% in unsterilized soils, independent of acorn provenance and soil origin. Mortality of cork oak seedlings was significantly different depending on the acorn origin and soil treatment, and on the interactions acorn origin × soil origin and soil origin × soil treatment. The demonstrated high susceptibility of holm and cork oak young seedlings to P. cinnamomi could be a limiting factor in Mediterranean open woodlands (dehesas) not only in natural regeneration processes but also when reforestation by direct sowing is implemented.     

Seedling quality and field performance of commercial stocklots of containerized holm oak (Quercus ilex) in Mediterranean Spain: an approach for establishing a quality standard

Holm oak is the hardwood most used for reforestation in Mediterranean Spain, which makes the development of stock quality standards in order to improve establishment success, a priority. However, its nursery culture is characterized by a wide range of practices resulting in stock heterogeneity and a potentially varied outplanting performance. Previous research has focused on specific seedling quality attributes, obviating the integral effect of nursery culture on overall quality. We studied growing regime, seedling quality, and field performance in nine holm oak stocklots produced in commercial nurseries during two consecutive growing years. Results proved variations in field performance were related to stocklot quality and, hence, to the growing regime practised. This dependence on stock quality may vary with planting site weather: in the drier year, survival was related to attributes like height, water status and K concentration, while, in the second, milder year, only growth performance was related to nutrient concentrations, plant size and water status. Results indicated the following quality standards for height: 12–17 cm, diameter: 3.5–4.8 mm, shoot and root weights: 1.3–1.6 and 2.8–4.7 g, respectively, N–P–K foliar concentrations: over 10–0.9–3.7 mg g⁻¹, respectively and in water status parameters: E_MX < 5 MPa and SWD_TL > 15%. These attributes can be adjusted using nursery cultural practices in order to meet seedling quality standards for holm oak for planting across similar sites.     

Seasonal and spatial mortality patterns of holm oak seedlings in a reforested soil infected with Phytophthora cinnamomi

The viability of 1-year-old holm oak (Quercus ilex) seedlings in a soil naturally infected with Phytophthora cinnamomi was studied during 2 consecutive years in a plot located in south-western Spain. In both years, total mortality during autumn and winter was not noticeable (<2.1%). In spring, mortality levels were higher (8.3–4.6%), especially the first year. A steep increase in total mortality occurred in summer, both in the first (11.4%) and second (24.2%) year, but mortality attributable to P. cinnamomi was 1.9 and 7.6%, respectively. Thus, 2 years after planting, total cumulative mortality was 43.4%, and that attributable to P. cinnamomi 9.6% (i.e. 22.1% of total mortality). Fungus-derived mortality followed a spatially aggregated pattern in the reforestation plot, suggesting a clustered distribution of the inoculum in the soil. Furthermore, mortality by P. cinnamomi was also associated with nearness of infected adult trees in the plot. Results obtained are discussed in the framework of seasonal water deficit, P. cinnamomi damage, weed competition and sanitation techniques to be used in declined holm oak stands in Spain.     

Decline and dieback of cork oak(Quercus suber L.) forests in the Mediterranean basin: a case study of Kroumirie,Northwest Tunisia

Assessing the vulnerability of forest ecosystems in the climate change context is a challenging task as the mechanisms that determine this vulnerability cannot be directly observed. Based on the ecological interrelationships between forests and climate, the present review focused on providing current information about vulnerability assessments of cork oak(Quercus suber L.) forests in the Mediterranean basin, especially, in the Kroumirie region(northwest Tunisia), currently under historic extreme drought conditions. From comparing recent findings in this region, we synthesized data on cork oak decline and mortality collected during the historic drought years 1988–1995 period. Climate change impacts cork forest decline, with special interest shown in elevated temperatures and drought; cork oak forest regeneration, and the adaptation of the Kroumirie forest to climate change, are reviewed herein. The studied region has been influenced largely by frequent prolonged drought periods, especially from 1988 to 1995. Droughts were found to consistently have a more detrimental impact on the growth and mortality rates of cork oak populations. Cork oak mortality was recorded for up to 63,622 trees. In the future, more research studies and observational data will be needed, which could represent an important key to understand ecosystem processes, and to facilitate the development of better models that project climate change impacts and vulnerability. The study is useful for researchers and forestry decision makers to develop the appropriate strategies to restore and protect ecosystems, and to help anticipate potential future droughts and climate change.     

Volatile organic compound emission from holm oak infested by gypsy moth larvae: evidence for distinct responses in damaged and undamaged leaves

Foliage of Quercus ilex L. (holm oak), a widespread Mediterranean species, constitutively emits large quantities of a complex genotype-dependent mixture of volatile organic compounds (VOCs). During a mass outbreak of gypsy moth (Lymantria dispar L.) in southern France, we examined the effects of gypsy moth feeding on VOC production from whole apices and single leaves of Q. ilex. Feeding induced the emission of new VOCs at rates up to 240 ng m(-2) s(-1) (16% of the total VOC release), which mainly consisted of sesquiterpenes, a homoterpene and a monoterpene alcohol. The new compounds were emitted after a delay of several hours following infestation and their production declined rapidly when caterpillars were removed. Undamaged leaves of infested trees emitted new VOCs, but with a different composition to those of damaged leaves and at lower rates. Neither caterpillars nor caterpillar excrement released VOCs. Emission of constitutive VOCs by undamaged leaves of infested trees temporary increased by up to 30%, whereas, in damaged leaves, they remained stable and decreased after some days when necrotic spots occurred around the feeding sites. In continuous light and at constant temperature, emissions of new VOCs showed a marked diurnal cycle, whereas those of constitutive VOCs did not. The results suggest that induced VOCs make a significant contribution to the atmospheric VOC load and may mediate trophic interactions. The observed differential local and systemic responses in composition, quantity and time courses of emissions mirror the existence of several regulation processes triggered by different signaling compounds and elicitors.     

Assessing vulnerability of a forest ecosystem to climate change and variability in the western Mediterranean sub-region of Turkey

Climate change is a real, pressing and significant global problem. The concept of ‘climate change vulnerability’ helps us to better comprehend the cause/effect relationships behind climate change and its impact on human societies, socioeconomic sectors, and physiographical and ecological systems. In this study, multifactorial spatial modelling evaluated the vulnerability of a Mediterranean forest ecosystem to climate change and variability with regard to land degradation. This produced data and developed tools to support better decision-making and management. As a result, the geographical distribution of Environmental Vulnerability Areas(EVAs) of the forest ecosystem is the estimated Environmental Vulnerability Index(EVI) values. These revealed that, at current levels of environmental degradation, physical, geographical, policy enforcement, and socioeconomic conditions, the area with a ‘‘very low’’ degree of vulnerability covered mainly the town, its surrounding settlements and agricultural lands found principally over the low, flat travertine plateau and the plains to the east and southeast of the district. The spatial magnitude of the EVAs of the forest ecosystem under current environmental degradation was also determined. This revealed that the EVAs classed as ‘‘very low’’accounted for 21% of the area of the forest ecosystem,those classed as ‘‘low’’ for 36%, those classed as ‘‘medium’’ for 20%, and those classed as ‘‘high’’ for 24%.     

Environmental and plant-based controls of water use in a Mediterranean oak stand

In this work, new information is reported on water relations of the Mediterranean oak species Quercus pyrenaica based on environmental and physiological measurements carried out during the growing seasons of 2006 and 2007. The interest in this species has increased due to its use in reforestation programs and its impacts on the water resources due to the extensive spontaneous afforestation after the abandonment of forest (firewood, charcoal, livestock, etc.) and agricultural activities, in general in some areas in the Mediterranean region and in particular, in the studied area (Sistema Central range, Spain). The objectives were to evaluate the long-term water use of this stand and its limit and to analyse the specific traits to cope with summer drought, especially the use of stem water storage and deep soil water reserves. Tree water stress associated with depletion of soil water reserves was not observed since the oak trees appeared to avoid a marked water stress using water reserves from deeper soil layers as summer drought progresses. The contribution of mean daily stem water storage to transpiration was low (4%), although it could be greater under dryer conditions. Only at the end of summer of 2006, the transpiration and canopy conductance were reduced due to soil drought. Despite the absence of marked water stress an upper limit was found in transpiration (slightly higher than 3 mm day⁻¹). The heavy use of soil water resources by this species (75% of available soil water in this study) should be considered when evaluating the impact of spontaneous afforestation and reforestation programs on water resources.     

Optimizing management of goats and oak trees for sustainability and community's welfare: a case study from Zagros,Iran

A deterministic dynamic bio-economic model was used to analyse different management options for goats and charcoal production in a forest in Zagros, Iran. The study sought optimal management options from a local community point of view considering net present value (NPV) of income from sale of goats and charcoal under different restrictions on forest harvest imposed by the state. The model was run under six model scenarios: (1) business as usual (BAU), (2) no state intervention, (3) no forest harvesting, (4) strict quota, (5) medium quota and (6) loose quota on charcoal production. The scenarios' results were compared based on four numeric criteria (NPV of income from goats and charcoal, development of standing volume and tree size diversity in forest, interaction between goat population and oak forests) and one subjective criterion (state budget for managing forest). The results indicated that two main challenges exist in forest management in Zagros; (1) to determine the balance between local communities' welfare and biological stability of the forest and (2) to choose between a cheap management regime prohibiting wood harvest but implicitly accepting some illegal charcoal production and a more expensive, but legal, harvest regulation through charcoal production quota. We conclude that the BAU scenario, where forest harvesting was prohibited de jure, but some illegal charcoal production was still undertaken, was the only viable management, which also is practically acceptable by both state and local communities.     

Impact of targeted sheep grazing on herbage and holm oak saplings in a silvopastoral wildfire prevention system in south-eastern Spain

Several wildfire prevention programs in southern Europe are currently using livestock grazing for the maintenance of fuelbreaks. This silvopastoral management is valued for being sustainable and effective in reducing fuel loads, but few studies have analyzed other impacts linked to fuelbreak grazing. This paper reports on an experiment performed within the wildfire prevention program in Andalusia (southern Spain) with the aim of clarifying and quantifying the effect of fuelbreak grazing on herbage biomass, ground cover, herbage species composition, and growth of holm oak saplings. The study site, located in a semiarid Mediterranean environment, was grazed by a shepherded sheep flock from February to June in three consecutive years at a similar stocking rate. Livestock consumed between 33 and 68 % of herbage production in the different years, and the greatest fuel reduction (remaining dry matter of 200?kg?ha^?1) was registered in Year 2, when rainfall and herbage production was lowest. Ground cover was significantly affected by grazing: on average, the percentage of bare soil increased three-fold, while herbage cover was reduced by a quarter. The botanical composition of herbage varied remarkably between years, but very little between Grazed and Non-Grazed areas within each year. Non-browsed holm oak saplings became progressively larger than browsed ones, differences only reaching clear statistical significance at the end of the three experimental years. At this time, the volume of browsed saplings was 47–56 % smaller than that of non-browsed holm oaks, even though the former had also grown significantly in the course of the experiment.