Mediterranean Oak Woodlands Research Articles

Ungulates Mitigate the Effects of Drought and Shrub Encroachment on the Fire Hazard of Mediterranean Oak Woodlands

Ungulates Mitigate the Effects of Drought and Shrub Encroachment on the Fire Hazard of Mediterranean Oak Woodlands

Ungulates mitigate the effects of drought and shrub encroachment on the fire hazard of Mediterranean oak woodlands.

Climate change is increasing the frequency of droughts and the risk of severe wildfires, which can interact with shrub encroachment and browsing by wild ungulates. Wild ungulate populations are expanding due, among other factors, to favorable habitat changes resulting from land abandonment or land-use changes. Understanding how ungulate browsing interacts with drought to affect woody plant mortality, plant flammability, and fire hazard is especially relevant in the context of climate change and increasing frequency of wildfires. The aim of this study is to explore the combined effects of cumulative drought, shrub encroachment, and ungulate browsing on the fire hazard of Mediterranean oak woodlands in Portugal. In a long-term (18 years) ungulate fencing exclusion experiment that simulated land abandonment and management neglect, we investigated the population dynamics of the native shrub Cistus ladanifer, which naturally dominates the understory of woodlands and is browsed by ungulates, comparing areas with (no fencing) and without (fencing) wild ungulate browsing. We also modeled fire behavior in browsed and unbrowsed plots considering drought and nondrought scenarios. Specifically, we estimated C. ladanifer population density, biomass, and fuel load characteristics, which were used to model fire behavior in drought and nondrought scenarios. Overall, drought increased the proportion of dead C. ladanifer shrub individuals, which was higher in the browsed plots. Drought decreased the ratio of live to dead shrub plant material, increased total fuel loading, shrub stand flammability, and the modeled fire parameters, that is, rate of surface fire spread, fireline intensity, and flame length. However, total fuel load and fire hazard were lower in browsed than unbrowsed plots, both in drought and nondrought scenarios. Browsing also decreased the population density of living shrubs, halting shrub encroachment. Our study provides long-term experimental evidence showing the role of wild ungulates in mitigating drought effects on fire hazard in shrub-encroached Mediterranean oak woodlands. Our results also emphasize that the long-term effects of land abandonment can interact with climate change drivers, affecting wildfire hazard. This is particularly relevant given the increasing incidence of land abandonment.

Fragmentation and Connectivity in dehesa Ecosystems Associated with Cerambyx spp. Dispersion and Control: A Graph-Theory Approach

Xylophagous insects play a crucial role in forest ecosystems, contributing to population dynamics. The “Cerambyx complex” (CC) constitutes an emerging pest in Mediterranean oak woodlands. We studied the fragmentation and connectivity of holm and cork oak stands in Andalusia (Spain), and the relationships with the current dispersion of CC, as well as the effect on the connectivity and dispersion patterns with the implementation of nests of a predator bird (Garrulus glandarius) to reduce insect populations in highly connected areas. The Kernel Density Estimation (KDE) was used to assess the spatial distribution of CC. Connectivity was assessed using graphs theory (Graphab 2.6) to characterize the importance of patches and linkages for contributing to dispersal. We selected the Eurasian jay (G. glandarius) as a reference bird species to generate “barriers” to the dispersion of the CC. We used the probability of connectivity (PC) and the flux (F) to compare the effect of the introduction of Eurasian jay nets. Results showed an increasing trend in the distribution and incidence of CC during the period 2001–2016, resulting in 7.3% and 13.1% mortality rates for Q. ilex and Q. suber, respectively. The connectivity model using only Q. ilex and Q. suber forests as reference habitats was not enough to explain the distribution of CC. The value of PC and F metrics decreased by 38.09% and 20.59% by introducing 300 nests of Eurasian jay. Our methodology provides a pest management tool using connectivity metrics, which can be integrated with other variables to control pest outbreaks and pest dispersion.

Effects of ungulates on oak regeneration in Mediterranean woodlands: A meta-analysis

Mediterranean-climate oak woodlands, including those in North America and in the Mediterranean basin, are human-shaped ecosystems with high biodiversity value, which generate different ecosystem services, including grazing resources for livestock production. Low oak recruitment rates, however, are affecting the ecological sustainability of these ecosystems. Understanding the factors affecting recruitment dynamics in Mediterranean oak woodlands is crucial for adequately managing these ecosystems.We used a meta-analysis approach to evaluate the direct effects of ungulates on Mediterranean oak woodlands at various stages of recruitment, analysing publications based on ungulate exclusion experiments. The relationship between ungulates and recruitment is complex, involving multiple interacting factors, but, with very few exceptions, studies reported substantial negative direct impacts. Our meta-analyses show that the odds of an acorn surviving are much lower when ungulates are present and that the impact of wild ungulates on acorn survival was more marked than that of domestic animals. Ungulates also reduce the recruitment rates of oak seedlings and saplings as well as their growth rates.Ungulate management is crucial to achieve adequate oak recruitment in Mediterranean oak woodlands. We suggest management practices that may contribute to reduce the effects of ungulates in oak recruitment and to ecologically sustainable Mediterranean oak woodlands.

Conservation zones increase habitat heterogeneity of certified Mediterranean oak woodlands

Forest certification is a conservation tool, which aims to promote the sustainable management and conservation of forest ecosystems. Establishing set-aside or lower intervention conservation zones to promote biodiversity conservation is a requisite of forest certification. We tested the effects of conservation zones on the tree biometrics and regeneration, as well as on the taxonomic, functional, and structural diversity of the shrub and herb understory, in Mediterranean oak woodlands. We also assessed how oak biometrics, regeneration and understory diversity varied among conservation zones established 10, 14, and 20 years before our sampling dates. Oak regeneration tended to be higher in conservation zones than in controls, but results varied with the age of conservation zones. For example, the abundance of oak seedlings and saplings was higher in 10-year-old conservation zones than in those established 20 years ago. Abundance of young oak trees was higher in 14-year-old conservation zones than in 10- and 20-year-old conservation zones. The understory vertical diversity was significantly higher in 14- and 20-year-old conservation zones than in controls. Functional diversity differed significantly between conservation zones and controls, with a higher abundance of late-successional shrubs, namely fleshy-fruited species in 20-year-old conservation zones. The plant species composition of the shrub and the herb understory was most dissimilar between older conservation zones and controls. Additionally, the cover and diversity of the understory herb species decreased with the age of conservation zones. Conservation zones implemented under forest certification increase habitat structural complexity of oak woodlands, which may benefit wildlife species, but there will be trade-offs with the cover and diversity of the herb understory. Forest managers must evaluate such trade-offs when establishing conservation zones in cork oak woodlands under forest certification schemes.

Ant functional structure and diversity changes along a post-grazing succession in Mediterranean oak woodlands

Grazing exclusion may be used to promote the recovery of disturbed ecosystems. A promising way for the evaluation of its effectiveness is through the monitoring of key biological groups, particularly those more responsive to disturbance and playing key roles in ecosystem functioning. Ants have been used as ecological indicators as they are abundant, diverse and sensitive to environmental changes. Here, we aimed to evaluate changes in ant taxonomic and functional structure and diversity, using functional groups, along a post-grazing succession in a Mediterranean oak woodland and to understand which environmental variables drive them. The post-grazing succession comprised a chronosequence of grazing excluded sites for 8, 12 and 18 years and a grazed control site. We found that ant species richness, functional structure and diversity increased with years since grazing exclusion: Generalist/Opportunist and the Hot Climate specialists increased in the 18 years grazing excluded site, while the Cryptic Species group increased in the 12 years grazing excluded site. Yet, their responses were not linear over time. Time since grazing exclusion and vegetation structure explained differences in ant taxonomic and functional structure and diversity. The Invasive/Exotic group dominated in all sites, except in the longest excluded site, where it occurred in the lowest proportion. The invasive Argentine ant dominated the grazed site, where it may have led to ant taxonomic and functional homogenization. Our results suggest that the time and changes in habitat structure may favour the recovery of ant biodiversity, although the presence of the invasive Argentine ant species may have slowed it down.

Canopy Cover Loss of Mediterranean Oak Woodlands: Long-term Effects of Management and Climate

Although forest areas have been growing in Europe, some forest types have been declining regionally. Since the 1980 s, there have been reports of defoliation and mortality in evergreen oak woodlands of the Iberian Peninsula. However, long-term and large-scale trends of Iberian oak decline are still poorly understood. We quantified trends in canopy cover for cork oak (Quercus suber) and holm oak (Q. rotundifolia) woodlands in mainland Portugal for a 50 year period (1965 to 2015). We considered loss of canopy cover a proxy of forest degradation and asked how it changed over time, in association with human activity and climate. Between 1965 and 2015, both cork oak and holm oak canopy cover showed declining trends (57.9% and 71.1% of sampling points, respectively). Canopy cover dynamics, however, differed across time. Between 1965 and 1990, canopy cover gains (over 35% of sampling points) prevailed over losses (under 20%), with larger differences for cork oak than holm oak. Between 1990 and 2015, canopy cover losses (over 70% of sampling points) were much higher than gains (under 9%). Oak canopy cover decrease was associated with flatter areas (usually having more intensive land use) for both oak species, higher cattle numbers (holm oak only) and higher mean temperature (cork oak only). Contrastingly, loss of holm oak canopy cover seems to have occurred in less hot and dry regions that enable more intensive land uses. Active restoration is urgently needed to reverse the current decline in canopy cover in Mediterranean evergreen oak woodlands.

The environmental drivers influencing spatio-temporal dynamics of oak defoliation and mortality in dehesas of Southern Spain

Quercus ecosystems have been affected globally by decline episodes, involving extreme defoliation and mortality events, during recent decades. Both abiotic and biotic factors seem to trigger these processes, including the spread of non-native invasive pathogens (e.g., Phytophthora spp.). However, we have limited understanding of how these factors interact in a spatio-temporal context. Regional forest health monitoring networks are a relevant but rarely used tool that enables us to disentangle the patterns of tree defoliation and mortality over time in relation to environmental and silvicultural drivers. In this study, we used a combination of statistical approaches (i.e., Kaplan-Meier, Kernel Density Estimation and generalized mixed models) to analyse 3635 records of oak trees (152 plots) from the Regional Forest Health Network of Andalusia (Spain) (2001–2016, ICP Level I). In this way, we studied the spatio-temporal variation of defoliation and mortality in dehesas of Quercus spp. in relation to oomycetes occurrence and the average and annual values of environmental factors related to oak decline. The annual defoliation and mortality were correlated with the mean annual temperature, Standardised Precipitation-Evapotranspiration Index (SPEI 18 summer and 1 spring) and soil organic matter content. The effect of oomycetes on forest decline was mediated by environmental factors, having greater importance in rich soils and wet years. These results imply that variation in defoliation and mortality is clearly linked to relevant spatio-temporal changes in environmental factors. Regional forest health networks are a crucial part of adaptive forest management strategies to significantly narrow the uncertainty regarding climate change impacts on Mediterranean oak woodland ecosystems. The timely information provided here could lead to better silvicultural practices, preventive measures against the spread of the oomycete and the implementation of early warning tools, to deliver accurate assessments of the defoliation and mortality risk on a meaningful spatio-temporal scale.

Effects of declining oak vitality on ecosystem multifunctionality: Lessons from a Spanish oak woodland

Mediterranean oak woodlands are currently facing unprecedented degradation threats from oak decline. The Iberian oak decline “Seca”, related to Phytophthora infection, causes crown defoliation that may adversely affect ecosystem services (ESs). We aim to improve our understanding of how Seca-induced declines in crown foliation affect the provision of multiple ecosystem services from understory vegetation. We selected holm (Quercus ilex) and cork oak (Q. suber) trees in a Spanish oak woodland and evaluated three proxies of canopy effects. One proxy (crown defoliation) solely captured Seca-dependent effects, one proxy solely captured Seca-independent effects (tree dimensions such as diameter and height), while the third proxy (tree vigor) captured overall canopy effects. We then used the best-performing proxies to assess canopy effects on key ecosystem services (ESs) such as above-ground net primary production (ANPP), grass and legume biomass, species diversity, litter decomposition rates, and a combined index of ecosystem multifunctionality.We found that both types of canopy effects (i.e. Seca-dependent and Seca-independent effects) were related, indicating that ANPP was disproportionally more affected by Seca when defoliated trees were large. Responses of other ESs were mostly not significant, although lower species diversity was found under trees with intermediate vigor. Our results underline that a Seca-related decline in canopy density triggered a homogenization of ecosystem service delivery on the ecosystem scale. The ecosystem functions (EFs) under trees of low vigor are similar to that in adjacent open microsites indicating that the presence of vigorous (i.e. old and vital) trees is critical for maintaining EFs at a landscape level. Our results also highlight the importance of quantifying not only defoliation but also tree dimensions as both factors jointly and interactively modify canopy effects on ecosystem multifunctionality.

Ungulates mediate trade‐offs between carbon storage and wildfire hazard in Mediterranean oak woodlands

AbstractUngulates influence ecosystem services in important ways, including by altering the amount of standing plant biomass and species composition. Browsing, for example, removes biomass and, in consequence, can decrease the risk of wildfires. The influence of ungulates on carbon storage is more complicated. Browsers reduce carbon stocks directly by consuming biomass, but if browsing reduces fine fuel loads, then long‐term carbon storage may increase.We investigated how wild ungulates mediate trade‐offs between carbon stocks and wildfire hazard in a Mediterranean oak woodland. We assessed the effects of deer (Cervus elaphusandDama dama) on the colonization by gum cistus (Cistus ladanifer), a highly flammable Mediterranean shrub, through a long‐term ungulate exclusion experiment.We established fenced (unbrowsed) and open (browsed) plots in areas where shrubs were previously cleared, and compared shrub density, height, biomass, and above‐ground carbon stocks 6 and 14 years after fencing.There were no significant differences in shrub density between treatments after 6 years of browsing exclusion but, by this point, height was already significantly greater in fenced plots. At the end of the experiment, shrub density and height were both significantly greater in fenced plots. Biomass and carbon stocks of gum cistus increased and reached a plateau in fenced plots, while in open plots biomass and carbon stocks increased initially but then decreased. Ungulates also prevented accumulation of litter carbon stocks, which was significantly higher in fenced plots after 14 years of browsing exclusion.We also modelled fire behaviour in fenced and open plots. Browsing reduced fine fuel load, an important contributor to fire spread, by 80%. In browsed plots, modelled wildfire rate of spread, flame length, and fireline intensity decreased by 50%, 65%, and 90%, respectively, which also decreased the probability of canopy fire and of oak mortality.Synthesis and applications. By decreasing fire hazard and the probability of canopy fire, ungulates may ultimately increase ecosystem carbon stocks through improved adult oak survival. These critical, indirect trade‐offs need to be assessed when addressing the effects of ungulates on ecosystems and the management of their populations.

Variability of beetle assemblages in Mediterranean cork oak woodlands: does the higher taxa approach reliably characterize a specific response to grazing?

Studying macroarthropod community responses to different land uses is particularly interesting in agroforestry for the conservation of Mediterranean landscapes, which need to be managed in terms of ecological and functional sustainability. Because of the sensitivity of many taxa to human impacts, we assessed the response of beetle assemblages at low taxonomic resolution (i.e. family level) to grazing in Mediterranean cork oak woodlands in northern Sardinia (Italy). Scarab assemblages were also analysed at the species level because of their ecological role in grazed areas. Cork oak woodland descriptors were also recorded in order to relate beetle assemblages to the forest structure. Over the entire sampling period, 4550 beetles belonging to 47 families were captured using pitfall traps. Multivariate analyses performed on ground-dwelling beetle data showed a distinct separation in terms of assemblages between grazed and ungrazed sites. The average diameter of cork oak trees and the degree of shrub cover were significantly linked to the beetle family assemblages. Constrained multivariate analyses indicated the significance of grazing, by both large and small domestic herbivores, and altitude, as variables determining the pattern of scarab beetle assemblages. Mantel test showed a significant correlation between the beetle and scarab dissimilarity matrices indicating a similar pattern for the two levels of identification. Our results show the predictive power of beetles at the family taxonomic level, as well as scarab beetles at the species level. These turned out to be valuable indicators in biomonitoring programmes in Mediterranean cork oak woodlands in order to increase the resilience of cork oak agroforestry systems under future global change scenarios.

Cattle foraging in Mediterranean oak woodlands – Effects of management practices on the woody vegetation

Vegetation structure and composition of woodlands in the Mediterranean Basin have experienced extensive land-use change during recent decades. Decline in traditional foraging by goats is leading to more closed and spatially homogeneous woody vegetation, reduced plant diversity, and increased fire risk because of accumulation of inflammable material. We studied the use of cattle foraging as an alternative to goat foraging in Mediterranean oak woodlands. Our main goal was to provide basic information on the responses of woody vegetation to cattle foraging intensity, and on the factors affecting spatial patterns of woodland utilization. We conducted the study in the Western Galilee, Israel, in oak woodland dominated by Palestine oak (Quercus calliprinos Webb.) interspersed with patches of shrubs and herbaceous vegetation. Effects of two animal population densities, moderate (0.33 cow⋅ha−1) and high (0.55 cow⋅ha−1), on the structure, composition, and regeneration potential of dense and of open woody formations were examined. Four consecutive annual seasons of cattle foraging resulted in relatively large amounts of woody vegetation removal, especially under high animal density, but had no negative effects on woody species richness or regeneration potential from saplings. The type of vegetation formation and initial state of the woody vegetation were important factors affecting the degree of change. Woody biomass removal by cattle, as shown in this study, can reduce fire hazards and increase vegetation heterogeneity and plant diversity. These findings support the use of cattle as an efficient alternative tool for multi-purpose, sustainable management of Mediterranean oak woodlands.

What to save, the host or the pest? The spatial distribution of xylophage insects within the Mediterranean oak woodlands of Southwestern Spain

The Mediterranean oak forests are currently in severe decline. Although the oak decline has been mainly related to Phytophthora sp. and extreme climatic conditions, there are other biotic factors - such as the beetle Cerambyx “complex” - which are also implicated. The future climate change scenarios might aggravate this situation but also might enhance the dispersal and establishment of new beetle populations. We used the Andalusian forest health monitoring network (SEDA Network) to assess the current distribution of the beetles, using the Kernel Density Estimation approach, and the current and future distributions using ensemble Species Distribution Models. Model predictions revealed that dasometric (normal diameter and frequency of oak trees) and climatic (number of days with mean temperature above 30°C) variables were important to estimate the distribution of the Cerambyx “complex”.The model performance was analyzed by K, TSS, and AUC, which gave accurate (K>0.56; TSS>0.59 & AUC>0.87) to very accurate (K>0.63; TSS>0.64 & AUC>0.89) results for the models developed only with dasometric variables and with the combination of climatic and dasometric variables, respectively. We found four main regions where the xylophage beetles occur in Andalusia and a larger area which satisfies the environmental requirements of these beetles. The current potential habitat suitability of the xylophage beetles might increase under future climate scenarios, which might enhance the dispersal, colonization, and establishment of new populations of xylophage beetles in Andalusia.

Spatial and temporal activity of cattle grazing in Mediterranean oak woodland

We examined the temporal and spatial variation patterns of the grazing activity of free-ranging cattle in Mediterranean oak woodland in the Western Galilee, Israel, as affected by seasonal and management factors.The vegetation is dominated by scrub-oak woodland (Quercus calliprinos Webb.), interspersed with patches of semi-dwarf shrubs and herbaceous vegetation. High and moderate animal population densities of 0.55 and 0.33cowha−1, respectively, were replicated twice. Cattle behavior was monitored with activity sensors on GPS collars, and pedometers, and spatial data were processed with Geographic Information System (GIS) tools.Overall, cattle devoted 9.7±0.7h/day to grazing, mostly in woodland areas, although they are natural herbaceous grazers. Behavior was associated with seasonal changes in biotic and abiotic factors. Preference for the woody vegetation types was detectable over the annual time scale but large seasonal differences in preference canceled out to a large extent when viewed at that time scale. Cattle under high density spent more time grazing and made more use of woody vegetation and steeper slopes. Thus, relatively high population densities may be required for landscape-oriented management. The present findings should contribute to rational management of cattle grazing in Mediterranean woodlands.

Nestling food of three hole-nesting passerine species and experimental increase in their densities in Mediterranean oak woodlands

We studied nestling food of three species breeding in Mediterranean oak woodlands that collect food in different niches of trees: blue tit (Cyanistes caeruleus; foliage-gleaner), great tit (Parus major; bark–foliage-gleaner) and nuthatch (Sitta europaea; bark-gleaner) in 2013–2014. Species-specific functions were compared using size and composition of preyed caterpillars, and nest-boxes were used in a before-after control-impact (BACI) design to test increase in breeding densities by providing nest-boxes. Our results demonstrate a high importance of caterpillars in the nestling diet of the three passerine species and suggest their complementary predation on early and late instars of the same Lepidoptera species. According to results of our BACI experiment, species’ breeding density increased by providing nest-boxes, with blue tit showing the highest difference in percentage change between manipulated and control plots (38.2, 26.8 and 14.3 % for blue tit, great tit and nuthatch, respectively). Overall, we highlight the combined functions of different tree-foraging guilds in caterpillar predation and propose nest-box provision as a management method to prevent defoliator outbreaks in Mediterranean oak woodlands.

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.

Management of Montados and Dehesas for High Nature Value: an interdisciplinary pathway

Mediterranean oak woodlands, Montados in Portugal and Dehesas in Spain have long been acknowledged as potential land use systems of high nature and social value providing relevant ecosystem services and biodiversity conservation. Nevertheless, these systems are now under severe threat, both due to abandonment in certain areas and overuse in others, extremes that may be limited by appropriate management practices and strategies. The High Nature Value concept can be a pathway for the understanding and assessment of management practices best adapted to the balance of the Montado and Dehesa, and also to the assessment of the thresholds of change, so that the long term sustainability of the Montado systems is preserved. This special issue aims to contribute for the understanding of how the Montado and Dehesa classification as High Nature Value may be a path for sustainable management. This classification can be achieved by different ways and implies different components of the Montado, and thus the first four papers of this special issue address different approaches and methodologies for the identification of HNV Dehesas and Montados, the following seven papers deal mostly with the effect of management practices on biodiversity and other Dehesas and Montados values and finally the last two papers address the causes for Montado decline and suggest mitigation measures for that decline.

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.

Effects of dominant tree species on insectivorous birds breeding in Mediterranean oak woodlands

Capsule Differences in Cork Oak Quercus suber and Holm Oak Quercus rotundifolia dominance had little influence on bird communities though bark-gleaners showed a foraging preference for Cork Oak.Aims Examine the use of Cork and Holm Oak trees by insectivorous birds in Mediterranean oak woodlands.Methods Point-counts were used to compare species abundance among Cork Oak-dominated, Holm Oak-dominated and mixed woodlands. Focal foraging observations were used to evaluate the use of Cork and Holm Oaks in the three habitats and to relate tree characteristics with the foraging time of foliage- and bark-gleaners.Results Bird densities in the three habitats were not different for most foliage- and bark-gleaners. Tree preference index values and foraging time per tree showed no significant differences between tree species and foraging guilds, however bark-gleaners had positive index values for Cork Oak in the three habitats. The foraging time of foliage- and bark-gleaners on both tree species showed a positive relationship with characteristics associated with arthropod abundance.Conclusion Cork and Holm Oak trees are equally preferred by foliage-gleaners but bark-gleaners moderately preferred Cork Oak. Characteristics regarding morphology, phenology and physiological condition of trees can be used to predict habitat quality for insectivorous forest birds in Mediterranean oak woodlands.

Hemiparasite--host plant interactions in a fragmented landscape assessed via imaging spectroscopy and LiDAR.

Species interactions are susceptible to anthropogenic changes in ecosystems, but this has been poorly investigated in a spatially explicit manner in the case of plant parasitism, such as the omnipresent hemiparasitic mistletoe-host plant interactions. Analyzing such interactions at a large spatial scale may advance our understanding of parasitism patterns over complex landscapes. Combining high-resolution airborne imaging spectroscopy and LiDAR, we studied hemiparasite incidence within and among tree host stands to examine the prevalence and spatial distribution of hemiparasite load in ecosystems. Specifically, we aimed to assess: (1) detection accuracy of mistletoes on their oak hosts; (2) hemiparasitism prevalence within host tree canopies depending on tree height, and (3) spatial variation in hemiparasitism across fragmented woodlands, in a low-diversity mediterranean oak woodland in California, USA. We identified mistletoe infestations with 55-96% accuracy, and detected significant differences in remote-sensed spectra between oak trees with and without mistletoe infestation. We also found that host canopy height had little influence on infestation degree, whereas landscape-level variation showed consistent; non-random patterns: isolated host trees had twice the infestation load than did trees located at the core of forest fragments. Overall, we found that canopy exposure (i.e., lower canopy density or proximity to forest edge) is more important than canopy height for mistletoe infestation, and that by changing landscape structure, parasitic prevalence increased with woodland fragmentation. We conclude that reducing fragmentation in oak woodlands will minimize anthropogenic impact on mistletoe infestation at the landscape level. We argue that advanced remote sensing technology can provide baselines to quantitatively analyze and monitor parasite-host trajectories in light of global environmental change, and that this is a promising approach to be further tested in other temperate and tropical forests.