Cork Oak Woodlands Research Articles

Using Landsat 8 imagery in detecting cork oak (Quercus suber L.) woodlands: a case study in Calabria (Italy)

In the Mediterranean basin, cork oak (Quercus suber L.) woodlands are characteristic and widespread forestry ecosystems. Though presenting significant economic potential as a renewable resource, they are not adequately valorised, in spite of a growing market demand for cork and cork-based products, which are appreciated, today, for their use in sustainable building. In this respect, cork meets the needs of the building industry in responding to the growing demand for quality products, which are eco- and energy-friendly and hygienically safe. Moreover, European cultural and biodiversity value has been attributed to cork oak woodlands and their most significant examples have been included in the Natura 2000 framework. So far, in some countries like Italy, the territorial distribution and characterisation of cork oak woodlands have not been adequately investigated. This study provides a method for mapping the actual presence of cork oak woodlands and for assessing their potential distribution. Special attention was given to the characterisation of cork oak spectral signature. To this end, Landsat 8 satellite images, digital photointerpretation and in situ surveys were implemented. The work carried out allows assessing the effectiveness of GIS and remote sensing techniques coupled with ancillary data and tools, and their applicability for the development of a comprehensive mapping and monitoring system of cork oak woodlands in Mediterranean ecosystems. Such techniques are vital to develop a detailed management strategy and to assist restoration activities and the economic assessment of semi-natural habitats. A case study, carried out in two different locations in Calabria (Italy), is provided.

Impacts of protected colonial birds on soil microbial communities: When protection leads to degradation

Colonial nesting and roosting birds can degrade their habitat by soil salinization, eutrophication, and acidification associated with excessive deposition of avian excreta. We studied the impact of a protected wading bird colony on soil microbial communities from cork oak woodlands in Doñana National Park (SW Spain). Over one year we analyzed soil properties (pH, salinity, soluble N and P forms, extractable organic carbon - EOC -), microbial activity (basal respiration, community-level physiological profile, extracellular enzyme activities) and community structure (fungal, bacterial and archaeal terminal restriction fragments -TRFs-) along a gradient of bird nesting intensity. Bird nesting largely impacted soil chemical environment, with increases from 25 to 500 μS cm−1 in soil salinity, from 6 to 725 mg kg−1 in soil P, from 5 to 22 mg kg−1 in N-NH4, and from 5.4 to 245 mg kg−1 in N-NO3 between the extremes of the nesting intensity gradient in the wet season. Most of these chemical changes were enhanced in the dry season. We observed positive linear or log-linear relationships between the bird nesting footprint on soils (indicated by an integrated soil chemistry index) and microbial biomass, basal respiration and most of the studied enzyme activities. This was likely due to the concurrent increases in EOC along the avian intensity gradient, which counteracted the negative impacts of salinity. Soil P and EOC were the main drivers for fungal, bacterial and archaeal TRFs diversity. Bacterial TRFs richness and diversity index decreased along the avian intensity gradient in the dry season, while archaeal TRFs diversity increased in those soils highly salinized by excess of avian excreta deposition. Our study clearly shows that this oversized bird colony has profound effects on soil chemistry and biological activity, and highlights the need for a re-evaluation of management strategies in this protected area, towards a greater consideration of soil processes in conservation priorities.

A Latent Class Nested Logit Model for Rank-Ordered Data with Application to Cork Oak Reforestation

We analyze stated ranking data collected from recreational visitors to the Alcornocales Natural Park (ANP) in Spain. The ANP is a large protected area which comprises mainly cork oak woodlands. The visitors ranked cork oak reforestation programs delivering different sets of environmental (reforestation technique, biodiversity, forest surface) and social (jobs and recreation sites created) outcomes. We specify a novel latent class nested logit model for rank-ordered data to estimate the distribution of willingness-to-pay for each outcome. Our modeling approach jointly exploits recent advances in discrete choice methods. The results suggest that prioritizing biodiversity would increase certainty over public support for a reforestation program. In addition, a substantial fraction of the visitor population are willing to pay more for the social outcomes than the environmental outcomes, whereas the existing reforestation subsidies are often justified by the environmental outcomes alone.

How dependent are cork oak (Quercus suber L.) woodlands on groundwater? A case study in southwestern Portugal

Cork oak (Quercus suber L.) woodlands in the Mediterranean basin may cope with drought continuing to grow during the dry summer period. This growth pattern relies on the presence of extensive and deep root systems and on their access to groundwater. When the water table level is not within the reach of roots or decreases below a certain level following periods of drought, tree growth and survival might be affected. So far, little is known about the sensitivity and resilience of cork oak to both the rising and lowering of the water table over a long-term period, e.g., during one cork production cycle (9–10years). In this study, we determined whether changes in groundwater levels influence cork growth in two cork oak woodlands located at the Tagus alluvium aquifer in southwestern Portugal. The selected areas have contrasting groundwater levels and an integrated framework was developed combining: (a) a standardized annual cork growth index series for tree (cork) growth assessment; (b) a monthly Standardized Precipitation Evapotranspiration Index (SPEI) for drought periods assessment and; (c) a Geographical Information System (GIS)-based model for mapping the mean water table depth in the dry period. Results showed a decrease of cork growth index (up to 40%) immediately following a severe drought, which lowered the water table in the dry period. Moreover, in the site with deeper groundwater levels the reduction of cork growth index was higher. The mean water table depth (in dry period) of −2.5m was found to be a trigger value for cork growth. Our findings suggest that, under shallow water table conditions groundwater mitigates the seasonal fluctuations of precipitation and trees may use groundwater to decouple cork growth from the annual precipitation regime. We conclude that, under changing Mediterranean environments, with expected increase in drought events, the decrease of groundwater levels may severely affect cork (and tree) growth and ultimately tree survival. The management and conservation of cork oak woodlands should therefore rely on adequate policies for the sustainability of groundwater resources.

Severe dry winter affects plant phenology and carbon balance of a cork oak woodland understorey

Mediterranean climates are prone to a great variation in yearly precipitation. The effects on ecosystem will depend on the severity and timing of droughts. In this study we questioned how an extreme dry winter affects the carbon flux in the understorey of a cork oak woodland? What is the seasonal contribution of understorey vegetation to ecosystem productivity?We used closed-system portable chambers to measure CO2 exchange of the dominant shrub species (Cistus salviifolius, Cistus crispus and Ulex airensis), of the herbaceous layer and on bare soil in a cork oak woodland in central Portugal during the dry winter year of 2012. Shoot growth, leaf shedding, flower and fruit setting, above and belowground plant biomass were measured as well as seasonal leaf water potential. Eddy-covariance and micrometeorological data together with CO2 exchange measurements were used to access the understorey species contribution to ecosystem gross primary productivity (GPP).The herbaceous layer productivity was severely affected by the dry winter, with half of the yearly maximum aboveground biomass in comparison with the 6 years site average. The semi-deciduous and evergreen shrubs showed desynchronized phenophases and lagged carbon uptake maxima. Whereas shallow-root shrubs exhibited opportunistic characteristics in exploiting the understorey light and water resources, deep rooted shrubs showed better water status but considerably lower assimilation rates. The contribution of understorey vegetation to ecosystem GPP was lower during summer with 14% and maximum during late spring, concomitantly with the lowest tree productivity due to tree canopy renewal. The herbaceous vegetation contribution to ecosystem GPP never exceeded 6% during this dry year stressing its sensitivity to winter and spring precipitation.Although shrubs are more resilient to precipitation variability when compared with the herbaceous vegetation, the contribution of the understorey vegetation to ecosystem GPP can be quite variable and will ultimately depend of tree density and canopy cover.

Grazing or Not Grazing: Implications for Ecosystem Services Provided by Biocrusts in Mediterranean Cork Oak Woodlands

AbstractLivestock grazing is one of the most common practices in managed woodlands affecting the abundance and diversity of plant and soil communities. While grazing effects have been studied thoroughly in vascular plants, little is known about grazing consequences for soil lichens and mosses (“biocrusts”) in managed woodlands. However, these complex communities have critical contributions to soil functioning in drylands. We evaluated grazing effects on biocrust abundance and functional composition in Mediterranean cork‐oak woodlands under long‐term grazing and after 7 and 17 years of grazing exclusion. We found four main groups in the region regarding the functional trait ‘growth form’: fruticose and foliose lichens, and short and tall mosses. Each group presented different water absorption and retention capacity, and showed group‐specific effects on soil water and temperature. Fruticose lichens were the most sensitive group to grazing, decreasing dramatically in cover with grazing (~7 times). Also, this group presented higher water retention capacity (~19 h), together with a consistent reducing effect on soil temperature along the grazing gradient (up to 0·9 °C). The shift in biocrust abundance and functional composition under grazing pressure has direct consequences in microclimate regulation, and is likely to influence other ecosystem processes such as CO2 fixation, soil surface protection and habitat provision. In particular, microclimate regulation may affect cork‐oak regeneration processes, which is one of the main concerns in managed woodlands. Copyright © 2016 John Wiley & Sons, Ltd.

Drivers of Productivity Trends in Cork Oak Woodlands over the Last 15 Years

Higher biodiversity leads to more productive ecosystems which, in turn, supports more biodiversity. Ongoing global changes affect ecosystem productivity and, therefore, are expected to affect productivity-biodiversity relationships. However, the magnitude of these relationships may be affected by baseline biodiversity and its lifeforms. Cork oak (Quercus suber) woodlands are a highly biodiverse Mediterranean ecosystem managed for cork extraction; as a result of this management cork oak woodlands may have both tree and shrub canopies, just tree and just shrub canopies, and just grasslands. Trees, shrubs, and grasses may respond differently to climatic variables and their combination may, therefore, affect measurements of productivity and the resulting productivity-biodiversity relationships. Here, we asked whether the relationship between productivity and climate is affected by the responses of trees, shrubs, and grasses in cork oak woodlands in Southern Portugal. To answer this question, we linked a 15-year time series of Enhanced Vegetation Index (EVI) derived from Landsat satellites to micrometeorological data to assess the relationship between trends in EVI and climate. Between 2000 and 2013 we observed an overall decrease in EVI. However, EVI increased over cork oaks and decreased over shrublands. EVI trends were strongly positively related to changes in relative humidity and negatively related to temperature. The intra-annual EVI cycle of grasslands and sparse cork oak woodland without understorey (savannah-like ecosystem) had higher variation than the other land-cover types. These results suggest that oaks and shrubs have different responses to changes in water availability, which can be either related to oak physiology, to oaks being either more resilient or having lagged responses to changes in climate, or to the fact that shrublands start senesce earlier than oaks. Our results also suggest that in the future EVI could improve because the rate of increase in minimum EVI is greater than the rate of decrease in maximum EVI, and that this is contingent on management of the shrub understorey as it affects the rate of decrease in maximum EVI. This will be the challenge for the persistence of cork oak woodlands, their associated biodiversity and social-ecological system.

Climate response of cork growth in the Mediterranean oak (Quercus suber L.) woodlands of southwestern Portugal

In the Mediterranean climate regions, drought events are expected to affect the growth of forests ecosystems by changing trees growth rates and eventually inducing shifts in their growth patterns. Cork oak (Quercus suber L.) is a strictly western Mediterranean tree species periodically harvested for its bark, the cork. So far, cork oak has received limited attention for dendroclimatological studies due to its typical faint and erratic tree wood rings. Moreover, its distinct cork rings chronologies have been completely neglected. In this study we introduce an approach using cork ring chronologies dated back 9–10 years for climate response. Despite enhancing interannual variability and increasing statistical response to short-term climatic variability, still poorly understood, this study will possibly allow infer long-term climate response. We analyzed the cork ring chronologies of 55 cork samples collected in mature (under exploitation) trees in three distinct locations in southwestern Portugal. Cork growth recorded a high climate signal, with highly significant and coherent responses to the yearly climate-related sources of variation. We successfully assessed trends of cork growth via correlation analysis including selected climate variables among mean monthly temperature, monthly precipitation and, on an annual basis, eight precipitation indices. The high mean sensitivities and inter-series correlations found for cork ring chronologies combined with the significant variance explained by climate variables suggest that climate is likely one dominant signal that affects cork growth, but local environmental stresses can decisively affect this (climate) signal. Assuming cork growth as a proxy for cork oak growth, it seems conceivable that despite the trees being highly resistant to drought stress, cork oak woodlands in southwestern Portugal would have to face lesser growth in a global warming scenario.

Modelling future scenarios to improve woodland landscapes for birds in the Mediterranean

Agro-silvo-pastoral systems occupy much of the Mediterranean region. Promoting landscape heterogeneity in these systems is a potentially valuable management strategy to enhance woodland biodiversity. We evaluated the effects on birds of managing patches of olive groves and riparian galleries to promote heterogeneity of these systems in Portugal.For a large cork oak woodland we (i) used nesting season bird density estimates and habitat descriptors to generate suitability models for each studied species; (ii) identified areas suitable to establish new patches of riparian galleries and olive groves, and used this information to (iii) generate scenarios maps with different levels of cover of both habitats. Finally, (iv) the model of each bird species was applied over the future scenarios to estimate potential changes in its distribution and abundance.Future scenarios with greater availability of riparian vegetation resulted in major increases in projected populations of seven of the 21 studied species, but gains with increases of olive groves were predicted in just three species. Bird species predicted to increase the most with the recovery of riparian vegetation are presently among the least abundant in the region. Restoring riparian galleries would be highly beneficial for birds, whereas promoting traditional olive groves would have lower conservation implications.The methodology used proved helpful to select areas particularly appropriate for habitat management, generate simulated landscapes incorporating this management, and predict the population and spatial responses of species to these simulated scenarios, thus having a good potential to guide conservation management. Moreover, our results indicate that simple management measures should have substantial positive effects on the bird community of oak woodlands, without compromising the essential economic return of the system.

Conservation zones promote oak regeneration and shrub diversity in certified Mediterranean oak woodlands

Mediterranean oak woodlands are ecosystems of high conservation and socio-economic value that occur in Southwestern Europe, North Africa and California. Oak regeneration failure is occurring in these ecosystems and may be endangering their long-term conservation. Most studies suggest that inadequate management practices may be contributing to oak regeneration failure. Forest certification is a voluntary type of certification, based on third-party auditing of compliance with performance-based sustainable management standards that has been expanding in forest ecosystems worldwide, including in Mediterranean oak woodlands. The Forest Stewardship Council (FSC) certification is the dominant certification scheme in Mediterranean oak woodlands and requires landowners to establish conservation zones in their estates. Conservation zones usually correspond to a tenth of the estate and are primarily managed for biodiversity conservation. In spite of recent studies reporting positive effects of FSC certification and conservation zones on biodiversity and forest structure in tropical regions, its effects on tree regeneration in Mediterranean oak woodlands are unknown. In this study, conducted in Southwestern Europe, we compared the abundance of cork oak (Quercus suber) regeneration and the cover, richness and diversity of Mediterranean shrublands between conservation and non-conservation zones in FSC certified cork oak woodlands. We found that in conservation zones oak regeneration was more abundant and that species richness and diversity of shrubs were significantly higher. Our results suggest that the creation of set-aside areas in cork oak woodlands, such as conservation zones, may help avert the tree regeneration crisis this ecosystem is facing.

Modelling spectral reflectance of open cork oak woodland: a simulation analysis of the effects of vegetation structure and background

ABSTRACTThis study analyses the influence of vegetation structure (i.e. leaf area index and canopy cover) and seasonal background changes on moderate-resolution imaging spectrometer (MODIS)-simulated reflectance data in open woodland. Approximately monthly spectral reflectance and transmittance field measurements (May 2011 to October 2013) of cork oak tree leaves (Quercus suber) and of the herbaceous understorey were recorded in the region of Ribatejo, Portugal. The geometric-optical and radiative transfer (GORT) model was used to simulate MODIS response (red, near-infrared) and to calculate vegetation indices, investigating their response to changes in the structure of the overstorey vegetation and to seasonal changes in the understorey using scenarios corresponding to contrasting phenological status (dry season vs. wet season). The performance of normalized difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI), and enhanced vegetation index (EVI) is discussed. Results showed that SAVI and EVI were very sensitive to the emergence of background vegetation in the wet season compared to NDVI and that shading effects lead to an opposing trend in the vegetation indices. The information provided by this research can be useful to improve our understanding of the temporal dynamic of vegetation, monitored by vegetation indices.

Environmental and microbial factors influencing methane and nitrous oxide fluxes in Mediterranean cork oak woodlands: trees make a difference.

Cork oak woodlands (montado) are agroforestry systems distributed all over the Mediterranean basin with a very important social, economic and ecological value. A generalized cork oak decline has been occurring in the last decades jeopardizing its future sustainability. It is unknown how loss of tree cover affects microbial processes that are consuming greenhouse gases in the montado ecosystem. The study was conducted under two different conditions in the natural understory of a cork oak woodland in center Portugal: under tree canopy (UC) and open areas without trees (OA). Fluxes of methane and nitrous oxide were measured with a static chamber technique. In order to quantify methanotrophs and bacteria capable of nitrous oxide consumption, we used quantitative real-time PCR targeting the pmoA and nosZ genes encoding the subunit of particulate methane mono-oxygenase and catalytic subunit of the nitrous oxide reductase, respectively. A significant seasonal effect was found on CH4 and N2O fluxes and pmoA and nosZ gene abundance. Tree cover had no effect on methane fluxes; conversely, whereas the UC plots were net emitters of nitrous oxide, the loss of tree cover resulted in a shift in the emission pattern such that the OA plots were a net sink for nitrous oxide. In a seasonal time scale, the UC had higher gene abundance of Type I methanotrophs. Methane flux correlated negatively with abundance of Type I methanotrophs in the UC plots. Nitrous oxide flux correlated negatively with nosZ gene abundance at the OA plots in contrast to that at the UC plots. In the UC soil, soil organic matter had a positive effect on soil extracellular enzyme activities, which correlated positively with the N2O flux. Our results demonstrated that tree cover affects soil properties, key enzyme activities and abundance of microorganisms and, consequently net CH4 and N2O exchange.

Temporal dynamics of spectral bioindicators evidence biological and ecological differences among functional types in a cork oak open woodland.

The application of spectral vegetation indices for the purpose of vegetation monitoring and modeling increased largely in recent years. Nonetheless, the interpretation of biophysical properties of vegetation through their spectral signature is still a challenging task. This is particularly true in Mediterranean oak forest characterized by a high spatial and temporal heterogeneity. In this study, the temporal dynamics of vegetation indices expected to be related with green biomass and photosynthetic efficiency were compared for the canopy of trees, the herbaceous layer, and two shrub species: cistus (Cistus salviifolius) and ulex (Ulex airensis). coexisting in a cork oak woodland. All indices were calculated from in situ measurements with a FieldSpec3 spectroradiometer (ASD Inc., Boulder, USA). Large differences emerged in the temporal trends and in the correlation between climate and vegetation indices. The relationship between spectral indices and temperature, radiation, and vapor pressure deficit for cork oak was opposite to that observed for the herbaceous layer and cistus. No correlation was observed between rainfall and vegetation indices in cork oak and ulex, but in the herbaceous layer and in the cistus, significant correlations were found. The analysis of spectral vegetation indices with fraction of absorbed PAR (fPAR) and quantum yield of chlorophyll fluorescence (ΔF/Fm') evidenced strongest relationships with the indices Normalized Difference Water Index (NDWI) and Photochemical Reflectance Index (PRI)512, respectively. Our results, while confirms the ability of spectral vegetation indices to represent temporal dynamics of biophysical properties of vegetation, evidence the importance to consider ecosystem composition for a correct ecological interpretation of results when the spatial resolution of observations includes different plant functional types.

Topography and aridity influence oak woodland bird assemblages in southern Europe

The increasing frequency and severity of drought spells in southern Europe has been associated with reduced growth and increased defoliation and mortality of several tree species, consequently affecting woodland productivity, structure and associated biodiversity. However, topographic variation and associated microclimatic features may buffer against the negative effects of drought at a local level. Here, we aimed to evaluate the influence of topographic variation on oak woodland communities along an aridity gradient. For this, we quantified cork oak woodland structure, bird species richness, abundance, and caterpillar biomass on north- and south-facing slopes along an aridity gradient across the south-western Iberian Peninsula. Drier microclimates on south-facing slopes had lower tree cover and bird richness and abundance than north-facing slopes, and the magnitude of these differences increased markedly from wetter (tree cover and woodland bird abundance ∼5–15% lower on south facing slopes) to drier regions (∼50–60% lower). This reduction in woodland bird richness and abundance is mainly driven by tree foraging species and likely a response to lower tree cover and resource availability, as caterpillar abundance was also ∼50% lower on south-facing slopes. The topographic complexity of the Mediterranean Basin seems to be shaping woodland community-level and trophic chain responses to increasing aridity in Southern Europe. Our results suggest that topographic and microclimatic conditions on north-facing slopes can potentially act as refugia for the high biodiversity characteristic of cork oak woodlands and other Mediterranean landscapes. We discuss cork oak woodland management measures needed to help maximize the resiliency of these Mediterranean socio-ecological systems in the face of climate change.

Role of the Mediterranean Sea in differentiating European and North African woodland bird assemblages

The Mediterranean Sea has separated the sclerophyllous forests of southern Europe and northern Africa for millions of years, but its role structuring forest bird assemblages remains unclear. To address this issue we sampled bird assemblages in cork oak woodlands located north and south of the Strait of Gibraltar and compared abundance, diversity, and species and guild assemblage structure between regions. Abundance and diversity patterns were remarkably similar, but dissimilarity analyses of species and guild composition revealed differences in bird assemblage structure between regions. Differences are partly attributable to the effect of the Mediterranean as barrier to the dispersal of forest birds; a few species were unable to colonize North Africa, and many that colonized it remained in sufficient isolation to evolve into distinct taxa. In addition to this divergence of biogeographic genesis, assemblages also differ because in North African cork oak woodlands forest and insectivorous specialist species are less abundant. This dissimilarity could be due to the effect of different exploitation levels present in each region. Managed cork oak woodlands are widespread in the Western Mediterranean, and are valuable because they conciliate economic exploitation with high biodiversity. In North Africa these woodlands are of greater conservation concern because they harbour endemic bird species that give its assemblage a distinct character, cover a smaller area, and are currently under greater pressure from overexploitation. These results highlight the importance to implement management practices that increase resilience and maintain biodiversity value throughout the range of cork oak woodlands.

Tree patch distribution drives spatial heterogeneity of soil traits in cork oak woodlands

Spatial heterogeneity of soil resources is linked to tree patch distribution in Mediterranean cork oak woodlands. Tree patch distribution modifies soil traits by varying litterfall inputs due to different tree covers. The spatial heterogeneity of soil resources affects the structure and functioning of the different plant communities on ecosystems. In Mediterranean oak woodlands, the scattered trees play a key role in this spatial heterogeneity and might strongly influence ecosystem functioning and its productivity. To assess the influence of the spatial pattern of trees and litter nutrient content on the spatial heterogeneity of soil properties. We used a combination of geostatistical techniques and a linear mixed model to evaluate the spatial heterogeneity of soil and the seasonal and spatial variability of litter nutrient content, respectively. Soil parameters showed a high spatial heterogeneity. Tree cover was positively related with soil pH, and the organic matter, N, K, and Ca soil content. The return of nutrients to the soil via leaf fall had a marked seasonality and a high spatial variability, but this spatial variability had no effect on the spatial pattern of soil resources. The spatial heterogeneity of soil in cork oak woodlands is mainly driven by tree patches distribution. The importance of the spatial heterogeneity of soil resources and the spatial pattern of trees on the functioning of the dehesa ecosystem makes it necessary to include them in plant nutrition studies and modeling approaches in these ecosystems.

Effects of an extremely dry winter on net ecosystem carbon exchange and tree phenology at a cork oak woodland

In seasonally dry climates, such as the Mediterranean, lack of rainfall in the usually wet winter may originate severe droughts which are a main cause of inter-annual variation in carbon sequestration. Leaf phenology variability may alter the seasonal pattern of photosynthetic uptake, which in turn is determined by leaf gas exchange limitations. The current study is based on the monitoring of an extremely dry winter in an evergreen cork oak woodland under the Mediterranean climate of central Portugal. Results are focused on net ecosystem CO2 exchange (NEE), phenology and tree growth measurements during two contrasting years: 2011, a wet year with a typical summer drought pattern and 2012, with an extremely unusual dry winter (only 10mm of total rainfall) that exacerbated the following summer drought effects. Main aims of this study were to assess the effects of an extreme dry winter in (1) annual and seasonal net ecosystem CO2 exchange, and in (2) cork oak phenology. The dry year 2012 was marked by a 45% lower carbon sequestration (−214 vs. −388gCm−2year−1) and a 63% lower annual tree diameter growth but only a 9% lower leaf area index compared to the wet year 2011. A significant reduction of 15% in yearly carbon sequestration was associated with leaf phenological events of canopy renewal in the early spring. In contrast to male flower production, fruit setting was severely depressed by water stress with a 54% decrease during the dry year. Our results suggest that leaf growth and leaf area maintenance are resilient ecophysiological processes under winter drought and are a priority carbon sink for photoassimilates in contrast to tree diameter growth. Thus, carbon sequestration reductions under low water availabilities in cork oak woodland should be ascribed to stomatal regulation or photosynthetic limitations and to a lesser extent to leaf area reductions.

Drought impact on carbon and water cycling in a Mediterranean <i>Quercus suber</i> L. woodland during the extreme drought event in 2012

Abstract. Savannah-type ecosystems account for 26–30% of global gross primary productivity GPP, with water being one of the major driving factors. In Europe, savannah-type woodlands cover an area of about 1.5 million ha. Here, the recent past has shown a significant decrease in precipitation P in winter and spring as well as a decrease in total annual precipitation. Strong effects on local water balance and carbon sink strength have thus been reported due to changes in precipitation regime. The objective of this study is to quantify the impact of the extreme drought event in 2012 on the water balance, gross primary productivity and carbon sink strength of a typical Portuguese cork-oak woodland (montado) compared to the wet year of 2011. Physiological responses of the dominant tree species Quercus suber (L.) are disentangled employing combined photosynthesis and stomatal conductance modelling. Precipitation effectiveness ET/P increased from 86% in 2011 to 122% in the 2012 dry year due to deep soil or groundwater access of the Q. suber trees leaving no water for groundwater replenishment. Understorey and overstorey GPP were strongly reduced, by 53 and 28%, respectively, in 2012 compared to 2011, due to the late onset of the autumn rains in 2011 and an additional severe winter/spring drought. However, the ecosystem was still a carbon sink in both years, but with a 38% reduced sink strength under extreme drought in 2012 compared to 2011. The combined photosynthesis–stomatal conductance model yielded the best results if it was allowed to adjust photosynthetic and stomatal parameters simultaneously. If stomatal response was modelled with the Leuning approach, which allows for a different sensitivity to vapour pressure deficit, the stomatal model parameters were highly coupled. A change in either of the parameters needed to be compensated by the other to guarantee a stable sensitivity of stomatal conductance to assimilation, independent of variations in vapour pressure deficit. The Q. suber trees showed a 37% reduced stomatal conductance during the drought period of 2012 compared to 2011, due to water supply limitations. In response to reduced leaf-internal CO2 availability, the trees strongly reduced the apparent maximum carboxylation rate by 43% in 2012 compared to 2011. Unexpectedly, the optimum temperature Topt of the maximum electron transport rate decreased during the drought period, enhancing the susceptibility of the trees to high temperature stress during the summer. Our results suggest that, if the trend of decreasing annual precipitation and changed precipitation patterns on the Iberian Peninsula continues, sustained effects on local groundwater reservoirs, understorey species composition and tree mortality have to be expected in the long term. To model the effect of drought on the montado ecosystem successfully, variable apparent maximum carboxylation rate Vc,max, stomatal conductance parameter m and vapour pressure deficit sensitivity parameter D0 need to be incorporated into photosynthesis–stomatal conductance modelling.

Effects of forest certification on the ecological condition of Mediterranean streams

SummaryForest certification, a proxy for sustainable forest management, covers more than 10% of the world's forests. Under forest certification, forest managers and landowners must comply with environmental, economic and social management standards aiming to promote forest conservation. Despite an increasing area of certified forests, there is a dearth of data on how forest certification is affecting the conservation of forest ecosystems and associated habitats.Here, we assess the effects of Forest Stewardship Council (FSC) certification, one of the largest certification schemes in the world, on the ecological condition of streams crossing Mediterranean evergreen oak woodlands.We used the Stream Visual Assessment Protocol (SVAP) to compare the ecological condition of streams located in areas with 3 and 5 years of certification, in non‐certified areas and in least disturbed streams.Forest certification positively affected the ecological condition of the surveyed streams, but its effects were only measurable after 5 years of certification. Streams with 5 years of certification had more continuous, dense and diverse riparian vegetation when compared to streams located in non‐certified areas. Moreover, the condition of streams located in areas with 5 years of forest certification was similar to the condition of least disturbed streams.Synthesis and applications. Forest certification promotes the ecological condition of streams occurring within Mediterranean evergreen oak woodlands. This mainly happens because in areas under forest certification, managers and landowners have to comply with management practices that require them to remove or reduce the main causes for stream degradation, allowing riparian habitats to recover. Within landscapes with large and increasing areas under forest certification, such as the Mediterranean cork oak woodlands, the positive effects of certification on the ecological condition of streams may spread across the hydrographic network in the medium to long term.

Analysis of raw cork production in Portugal and Catalonia using life cycle assessment

This study aims to (1) evaluate the environmental impacts associated with the three types of raw cork produced in Portuguese cork oak woodlands (in Alentejo region) considering two alternative practices for stand establishment (plantation and natural regeneration), (2) compare the environmental impacts of raw cork production in Portuguese cork oak woodlands and in Catalonian cork oak forests, and (3) assess the influence of different allocation criteria for partitioning the environmental impacts between the different types of raw cork produced. A cradle-to-gate approach was adopted starting with stand establishment up to cork storage in a field yard. The system boundaries include all management operations undertaken during the following stages: stand establishment, stand tending, cork stripping, and field recovery. The allocation of the environmental impacts to reproduction, second, and virgin cork was based on mass and market price criteria. An alternative allocation approach was simulated by allocating environmental impacts also to the wood produced in the cork oak stands. The impact assessment was performed using the characterization factors recommended by the International Reference Life Cycle Data System (ILCD). In Portugal, cork produced from naturally regenerated stands has a better environmental performance than cork produced from planted stands, but the differences are smaller than 10 %. Different management models of cork oak stands in Portugal and Catalonia (agro-silvopastoral system and forest system, respectively) originate different impact levels, which tend to be significantly lower in Catalonia. The environmental hot spots in the two regions are also distinct. In Catalonia, they are associated with cleaning, road maintenance, and worker and cork transport. In Portugal, they are fertilization, pruning, and cleaning. The two allocation criteria affect significantly the results obtained for virgin cork in Portugal and for virgin and second cork in Catalonia. Besides, when impacts are also allocated to wood, mass allocation should be avoided as it would not create incentives for a sustainable management of cork oak stands. The environmental impact from Catalonian cork may be reduced by decreasing mechanized shrub cleaning and road maintenance operations through the introduction of livestock in cork oak forests, and also by a better planning of management operations. For the Portuguese cork, improvements may be achieved by optimizing fertilizer dosage, planting nitrogen-fixing crops and pastures that improve soil quality, avoiding unnecessary operations, improving the efficiency of management operations, and increasing tree density.