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Summary: The climatic significance and ecosystem implications of latewood intra-annual density fluctuations (IADFs) are still not fully understood in Mediterranean ring-porous oak species. To solve this issue, we investigated: (i) the climate drivers of radial growth and latewood IADFs in the Mediterranean oak Quercus faginea , and (ii) whether they were correlated to increased canopy cover and greenness as recorded by the Normalized Difference Vegetation Index (NDVI). IADFs were formed in the mid to late latewood and they were characterized by rows of parenchyma cells. Such IADFs were uncommon and only present in 30–50% of sampled trees during 1999 and 2014, both years characterized by high precipitation in late July and early August. This relationship between IADFs formation and summer wet conditions differed from the conditions that enhance Q. faginea annual growth, wet winter-spring conditions, and low summer temperatures. Furthermore, IADFs formation showed a positive relationship with August NDVI values, indicating a correspondence of canopy greenness with secondary growth reactivation. We conclude that latewood IADFs in Q. faginea are a robust proxy of rare late-summer wet conditions and enhanced canopy activity as reflected by increased August NDVI values. Further monitoring of xylogenesis in other Mediterranean hardwoods along climatic gradients is suggested to mechanistically explain IADF production in seasonally dry biomes. [ABSTRACT FROM AUTHOR]

As climate change increasingly affects forest ecosystems, detailed understanding of major effects is important to anticipate their consequences under future climate scenarios. The Mediterranean region is a prominent climate change hotspot, and evergreen cork oak (Quercus suber L.) woodlands are particularly climatically sensitive due to cork (bark) harvesting. Cork oak's drought avoidance strategy is well-known and includes structural and physiological adaptations that maximise soil water uptake and transport and limit water use, potentially leading to reduced stem and cork growth. Trees' responses to cope with water-limited conditions have been extensively described based on cork-rings width and, more recently, on cork-rings density, in dendroecological studies. However, so far, tree functional attributes and physiological strategies, namely photosynthetic metabolism adjustments affecting cork formation, have never been addressed and/or integrated on these previous cork-rings-based studies. In this study, we address the relation between carbon and oxygen stable isotopes of cork rings and precipitation and temperature, in two distinct locations of southwestern Portugal-the (wetter) Tagus basin peneplain and the (drier) Grândola mountains. We aimed at assessing whether the two climatic factors affect cork-ring isotopic composition under contrasting conditions of water availability, and, therefore, if carbon and oxygen signatures in cork can reflect tree functional (physiological and structural) responses to stressful conditions, which might be aggravated by climate change. Our results indicate differences between the study areas. At the drier site, the stronger statistically significant negative cork δ13C correlations were found with mean temperature, whereas strong positive cork δ18O correlations were fewer and found only with precipitation. Moreover, at the wetter site, cork rings are enriched in 18O and depleted in 13C, indicating, respectively, shallow groundwater as the water source for physiological processes related with biosynthesis of non-photosynthetic secondary tissues, such as suberin, and a weak stomatal regulation under high water availability, consistent with non-existent water availability constrains. In contrast, at the drier site, trees use water from deeper ground layers, depleted in 18O, and strongly regulate stomatal conductance under water stress, thus reducing photosynthetic carbon uptake and probably relying on stored carbon reserves for cork ring formation. These results suggest that although stable isotopes signatures in cork rings are not proxies for net growth, they may be (fairly) robust indicators of trees' physiological and structural adjustments to climate and environmental changes in Mediterranean environments. [ABSTRACT FROM AUTHOR]

As climate change increasingly affects forest ecosystems, detailed understanding of major effects is important to anticipate their consequences under future climate scenarios. The Mediterranean region is a prominent climate change hotspot, and evergreen cork oak (Quercus suber L.) woodlands are particularly climatically sensitive due to cork (bark) harvesting. Cork oak’s drought avoidance strategy is well-known and includes structural and physiological adaptations that maximise soil water uptake and transport and limit water use, potentially leading to reduced stem and cork growth. Trees’ responses to cope with water-limited conditions have been extensively described based on cork-rings width and, more recently, on cork-rings density, in dendroecological studies. However, so far, tree functional attributes and physiological strategies, namely photosynthetic metabolism adjustments affecting cork formation, have never been addressed and/or integrated on these previous cork-rings-based studies. In this study, we address the relation between carbon and oxygen stable isotopes of cork rings and precipitation and temperature, in two distinct locations of southwestern Portugal–the (wetter) Tagus basin peneplain and the (drier) Grândola mountains. We aimed at assessing whether the two climatic factors affect cork-ring isotopic composition under contrasting conditions of water availability, and, therefore, if carbon and oxygen signatures in cork can reflect tree functional (physiological and structural) responses to stressful conditions, which might be aggravated by climate change. Our results indicate differences between the study areas. At the drier site, the stronger statistically significant negative cork δ13C correlations were found with mean temperature, whereas strong positive cork δ18O correlations were fewer and found only with precipitation. Moreover, at the wetter site, cork rings are enriched in 18O and depleted in 13C, indicating, respectively, shallow groundwater as the water source for physiological processes related with biosynthesis of non-photosynthetic secondary tissues, such as suberin, and a weak stomatal regulation under high water availability, consistent with non-existent water availability constrains. In contrast, at the drier site, trees use water from deeper ground layers, depleted in 18O, and strongly regulate stomatal conductance under water stress, thus reducing photosynthetic carbon uptake and probably relying on stored carbon reserves for cork ring formation. These results suggest that although stable isotopes signatures in cork rings are not proxies for net growth, they may be (fairly) robust indicators of trees’ physiological and structural adjustments to climate and environmental changes in Mediterranean environments.

Over recent decades, climate change has been particularly severe in the Mediterranean basin, where the intensity and frequency of drought events have had a significant effect on tree growth and mortality. In this context, differences in structural and physiological strategies between tree species could help to mitigate the damage inflicted by climate variability and drought events. Here, we used dendroecological approaches to observe common associations (synchrony) between indexed ring width in Pinus pinea and P. pinaster, as a measure of degree of dependence on climate variation or growth sensitivity to climate, as well as to analyze species growth responses to drought events through the Lloret's indices of resistance, recovery and resilience. Based on data from 75 mixed and pure plots installed in the Northern Plateau of Spain, we used modeling tools to detect the effect of the mixture, along with climate and stand-related variables, on the short-term responses and long-term growth sensitivity to climate. Our results showed a trade-off between resistance and recovery after the drought episodes. In addition, different attributes of tree species, such as age and size as well as stand density seemed to act synergistically and compensate drought stress in different ways. The presence of age and quadratic mean diameter as covariates in the final synchrony model for P. pinaster reflected the influence of other variables as modulators of growth response to climate. Furthermore, differences in growth synchrony in mixed and monospecific composition suggested the existence of interactions between the two species and some degree of temporal niche complementarity. In mixed stands, P. pinaster exhibited a lower sensitivity to climate than in monospecific composition, whereas P. pinea enhanced its resistance to extreme droughts. These results allowed us to identify the species-specific behavior of P. pinea and P. pinaster to mitigate vulnerability to climate-related extremes. [ABSTRACT FROM AUTHOR]

Global warming modulates the spatial and temporal occurrence of insect outbreaks, leading to as-yet-unknown effects on forests ecosystems. Warmer trends may favour the upward and northward expansion of pests, albeit increased exposure to heat events and droughts may also hamper insect growth and development. Thus far, further research is needed about the balance of climate warming on pine processionary moth (PPM) (Thaumetopoea pityocampa) development stages, especially at broader scales, despite being the main conifer-defoliating insect in the Mediterranean area. This research analyses the relationships of PPM with the climatic conditions during its most vulnerable development phases in Spain to provide base-information for forest managers. We hypothesize that warmer winter temperatures will increase PPM growth at their larval feeding stage, whereas summer-heat events will reduce PPM rates from egg and early larval stages, leading to counterbalanced effects of climate warming. Furthermore, we expect dry springs will allow an earlier development of PPM and higher incidence of outbreaks. To analyse climate effects on PPM populations in Andalusia, Castilla-La Mancha, and Navarre (37 to 42°N), we compiled information from the Regional Forest Services comprising up to 26 years of monitoring data from 2465 forest stands dominated by Pinus nigra and Pinus sylvestris. We fitted Cumulative Link Mixed Models (CLMM) to test the climate effects on four PPM defoliation severity levels. Our results support higher PPM larvae survival and incidence due to warmer winter conditions, but also the reduction of PPM population size under summer heat conditions. Particularly, the increasing incidence associated to warmer winters during the larval defoliating stage is counterbalanced by the decreasing population at earlier life stages during summer heat events. Spring drought also plays an important role on PPM incidence rates, but its effect is idiosyncratic to each region, suggesting an adaptation of PPM populations to regional conditions, claiming to tailor-made forest management endeavours. This study reveals that a better comprehension of abiotic effects along the whole PPM life cycle is paramount to understand the impact of climate warming on insect outbreaks which shorten wood production and carbon sequestration of Mediterranean forests. • Understanding novel environmental conditions on pest outbreaks is paramount to forecast their future incidence. • Positive effects of warmer winters for PPM populations is counterbalanced by the negative impacts of summer heat events. • Spring drought plays an important role on PPM incidence rates, but its effect is idiosyncratic to each region. [ABSTRACT FROM AUTHOR]

An anomalous event of drought and heat occurred in central Italy during the summer of 2017. Based on the SPI (Standardized Precipitation Index) and data from the European Space Agency, this event started in November 2016 and was characterized by a strong reduction of precipitation and soil moisture, especially in lowland areas with Mediterranean climate. The aim of this case report were to describe the impact of this event on representative forest communities in central Italy, to analyze the different responses of deciduous and evergreen tree and shrub species in contrasting environmental conditions and to assess their subsequent capacity of recovery or, if not, mortality. Trees suffered severe impacts consisting of widespread crown defoliation, leaf desiccation, crown dieback and whole tree mortality. Deciduous tree species (Fagus sylvatica, Quercus pubescens, Quercus cerris) shed their leaves during the summer, but apical buds and twigs were preserved. This allowed these species to produce new shoots in the following year (2018) and to restore the canopy closure of the stands. Mediterranean evergreen broadleaves, such as Quercus ilex and Phillyrea latifolia suffered of total or partial crown desiccation with wilting leaves and branch dieback. These species partially resprouted in 2018 from axillary and latent buds. The case presented here is discussed within the wider context of the impacts of climate change on Mediterranean forests. Future research directions should include an effective forest monitoring system that combines terrestrial and remote sensing surveys, ad hoc field climate change experiments and silvicultural trials from the perspective of proactive management for the adaptation of forests to future climatic conditions.

Mixed forests of Quercus ilex L. and Pinus pinea L. are widely found throughout the Mediterranean Basin, being representative of two co-existing functional types: evergreen-sclerophyllous drought-resistant species and Mediterranean-adapted drought-avoidant conifers. Their contrasting physiological strategies to cope with water deficit influence all the processes regulating their growth such as wood formation, leading to peculiar tree-ring anatomical features such as intra-annual density fluctuations (IADFs). Intra-annual density fluctuations are abrupt changes in wood anatomical traits within a tree ring, appearing as latewood-like cells within earlywood or earlywood-like cells within latewood, and are frequently found in Mediterranean species as a response to seasonal climate changes. In this study, we characterized the anatomical traits and composition of carbon and oxygen stable isotopes in IADFs occurring in tree rings of Q. ilex and P. pinea trees co-existing at a same site in Southern Italy, in order to link their xylem hydraulic properties with the related physiological mechanisms. The relationships between IADF occurrence and seasonal mean temperature and total precipitation were investigated, with the aim of assessing whether they can be used as indicators of species-specific responses to intra-annual climate fluctuations. Results show that IADF period of formation is during autumn months for both species. The influence of climate on IADF occurrence was found to be an indicator of species-specific response to climate: an increased stomatal conductance associated to the formation of a wood safer against embolism was found in Q. ilex, while a tighter stomatal control associated to a more efficient wood with regard to hydraulic conductivity occurred in P. pinea. Moreover, the assessment of the influence of climate on IADF occurrence indicates that, with rising temperatures, Q. ilex would form fewer IADFs compared with P. pinea. Other study cases are desirable to assess the suggested forecasts and to link the plasticity of the species to form IADFs with their effective adaptive capability to compete for resources, and to explain how it may influence future population development. [ABSTRACT FROM AUTHOR]

Abstract: Over the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire‐induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade‐offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post‐fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the “resprouter exhaustion syndrome,” a condition where pre‐fire drought stress, or short fire return intervals, seriously restrict post‐fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire‐free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate. [ABSTRACT FROM AUTHOR]

The increase in aridity, mainly by decreases in precipitation but also by higher temperatures, is likely the main threat to the diversity and survival of Mediterranean forests. Changes in land use, including the abandonment of extensive crop activities, mainly in mountains and remote areas, and the increases in human settlements and demand for more resources with the resulting fragmentation of the landscape, hinder the establishment of appropriate management tools to protect Mediterranean forests and their provision of services and biodiversity. Experiments and observations indicate that if changes in climate, land use and other components of global change, such as pollution and overexploitation of resources, continue, the resilience of many forests will likely be exceeded, altering their structure and function and changing, mostly decreasing, their capacity to continue to provide their current services. A consistent assessment of the impacts of the changes, however, remains elusive due to the difficulty of obtaining simultaneous and complete data for all scales of the impacts in the same forests, areas and regions. We review the impacts of climate change and other components of global change and their interactions on the terrestrial forests of Mediterranean regions, with special attention to their impacts on ecosystem services. Management tools for counteracting the negative effects of global change on Mediterranean ecosystem- services are finally discussed. Keywords: climate change; drought; global change; mediterranean forests; ecosystem services; resilience; management; migration; extinction; diversity; communities; CO2; plant invasion [ABSTRACT FROM AUTHOR]

Climate change-induced rainfall reductions in Mediterranean forests negatively affect the decomposition of plant litter through decreased soil moisture. However, the indirect effects of reduced precipitation on litter decomposition through changes in litter quality and soil microbial communities are poorly studied. This is especially the case for fine root litter, which contributes importantly to forests plant biomass. Here we analyzed the effects of long-term (11 years) rainfall exclusion (29% reduction) on leaf and fine root litter quality, soil microbial biomass, and microbial community-level physiological profiles in a Mediterranean holm oak forest. Additionally, we reciprocally transplanted soils and litter among the control and reduced rainfall treatments in the laboratory, and analyzed litter decomposition and its responses to a simulated extreme drought event. The decreased soil microbial biomass and altered physiological profiles with reduced rainfall promoted lower fine root-but not leaf-litter decomposition. Both leaf and root litter, from the reduced rainfall treatment, decomposed faster than those from the control treatment. The impact of the extreme drought event on fine root litter decomposition was higher in soils from the control treatment compared to soils subjected to long-term rainfall exclusion. Our results suggest contrasting mechanisms driving drought indirect effects on above-(for example, changes in litter quality) and belowground (for example, shifts in soil microbial community) litter decomposition, even within a single tree species. Quantifying the contribution of these mechanisms relative to the direct soil moisture-effect is critical for an accurate integration of litter decomposition into ecosystem carbon dynamics in Mediterranean forests under climate change. [ABSTRACT FROM AUTHOR]

Context: Tree populations at the rear edge of species distribution are sensitive to climate stress and drought. However, growth responses of these tree populations to those stressors may vary along climatic gradients. Aims: To analyze growth responses to climate and drought using dendrochronology in rear-edge Pinus nigra populations located along an aridity gradient. Methods: Tree-ring width chronologies were built for the twentieth century and related to monthly climatic variables, a drought index (Standardized Precipitation-Evapotranspiration Index), and two atmospheric circulation patterns (North Atlantic and Western Mediterranean Oscillations). Results: Growth was enhanced by wet and cold previous autumns and warm late winters before tree-ring formation. The influence of the previous year conditions on growth increased during the past century. Growth was significantly related to North Atlantic and Western Mediterranean Oscillations in two out of five sites. The strongest responses of growth to the drought index were observed in the most xeric sites. Conclusion: Dry conditions before tree-ring formation constrain growth in rear-edge P. nigra populations. The comparisons of climate-growth responses along aridity gradients allow characterizing the sensitivity of relict stands to climate warming. [ABSTRACT FROM AUTHOR]

Climate change involves warmer temperatures, altered precipitation patterns, increased climatic variability and, in Mediterranean regions, increased frequency and severity of droughts. Tree species may show different growth responses to these components of climatic change, which may trigger changes in forest composition and dominance. We assessed the influence of recent climatic changes on secondary growth of mature trees from four species co-occurring in a Mediterranean continental forest: Quercus ilex, Quercus faginea, Pinus nigra and Juniperus thurifera. We used dendrochronology to relate radial-growth variables [earlywood and latewood widths, basal area increment (BAI)] to annual and seasonal climatic variables for the period 1977-2007. Our results showed that Q. faginea BAI has declined, whereas J. thurifera BAI has increased over time while Q. ilex and P. nigra have maintained their growth rates. Growth was mainly favored by higher precipitations and tree size for all species. Reduced growth during extremely dry years was observed for all study species, but all of them except Q. faginea recovered their growth levels 2 years after drought. Our findings illustrate how the effects of climatic changes on growth should include analyses of seasonal climatic trends and extreme events such as severe droughts. We conclude that the seasonal timing of warming and precipitation alterations leading to drought events caused contrasting effects on growth of co-occurring Mediterranean tree species, compromising their future coexistence. [ABSTRACT FROM AUTHOR]

Abstract: Current decreasing precipitation and increasing temperatures, together with the growing likelihood of extreme drought events, may heighten the vulnerability of several tree populations in Mediterranean areas. In this study, we analysed tree-ring-width chronologies of three coexisting pine species (Pinus nigra Arn., Pinus pinaster L., and Pinus sylvestris L.) across an altitudinal gradient in the Cuenca Mountain Range (central-eastern Spain), along with soil conditions and stand structure. We quantified climate–growth relationships between basal area increment indexes and regional mean temperature and precipitation minus potential evapotranspiration (P-PET); drought sensitivity was defined as the percentage of growth reduction during an extreme drought event. Local climatic data spanning the 20th century yielded a warming trend and increasing extreme drought events since the onset of the 1980s. The P. nigra populations located at the lower altitudinal border showed the most significant correlation (negative) between mean temperature and declining growth trends. Contrasting to P. nigra, the studied P. pinaster population, also located at lower elevations, showed the higher correlations (positive) between P-PET and the higher mean growth. Aside from growth–climate relationships our results suggest a major effect of soil conditions and stand structure on tree growth and climate–growth responses. Old P. nigra stands showed the lower mean growth, while thinned stands, about 130years old, located at the core of the elevation range showed positive growth trends resembling a positive relationship with winter-to-spring temperatures and the higher soil organic matter content. P. nigra and P. sylvestris trees growing on soils with low total nitrogen seem to be more negatively affected by drought than would be expected under a linear elevation-related response. [Copyright &y& Elsevier]

• Introduction: Millions of hectares of Quercus ilex forests dominate disturbed landscapes in the western part of the Mediterranean basin. Although these forests are very widespread, little is known about the composition and structure of their associated ectomycorrhizal fungal communities. • Results and discussion: We examined seasonal patterns in ectomycorrhizal communities and their response to increased drought using a rainfall exclusion experiment established in a Q. ilex coppice since 2003. Ectomycorrhizae were sampled four times in 2007-2009. By sequencing fungal ITS, we identified 129 species in 1,147 sequenced ectomycorrhizal root tips. The fungal community in the surface organic horizon was well described by the logseries theoretical model, with 47.9% of singleton species. The composition of the community was strongly dominated by Basidiomycetes, with three families (Thelephoraceae, Russulaceae and Cortinariaceae) accounting for 72.9% of the root tips. Relative abundance of Russulaceae and Thelephoraceae showed pronounced seasonal shifts. Experimental reduction of rainfall resulted in significant shifts in community composition and seasonal fluctuations but had no effect on global richness of the community. • Conclusions: Together, these results suggest that the predicted rainfall reduction in this region due to climate change will lead to shifts in species composition in ectomycorrhizal communities. [ABSTRACT FROM AUTHOR]

The understanding of regional vulnerability to climate change in Mediterranean mountain forests is not well developed. Climate change impacts on tree growth should be strongly related to the steep environmental gradients of mountainous areas, where a temperature-induced upward shift of the lower elevation limit is expected, particularly amongst drought-sensitive species. Trees will adapt not only to changes in mean climate variables but also to increased extreme events such as prolonged drought. In this paper, we investigate the sub-regional temperature and precipitation trends and measure the basal area increment (BAI) in Pinus nigra subsp. salzmannii (Dunal) Franco. Significant differences related to altitudinal and latitudinal gradients and stand-age structure were found in response to long-term trends in climate dryness. Old trees growing at higher elevations showed similar extreme drought sensitivity but maintained almost steady BAI. Declining BAI found in trees at lower elevations and drier sites may imply a higher vulnerability to temperature-induced drought stress, suggesting an impending growth decline and an enhanced die-off risk. Our results illustrate how the effects of long-term warming and short-term drought on tree BAI are influenced by both site conditions and mean stand age in a drought-sensitive Mediterranean pine. [ABSTRACT FROM PUBLISHER]

The oxygen stable isotope composition ( δ18O) of CO2 is a valuable tool for studying the gas exchange between terrestrial ecosystems and the atmosphere. In the soil, it records the isotopic signal of water pools subjected to precipitation and evaporation events. The δ18O of the surface soil net CO2 flux is dominated by the physical processes of diffusion of CO2 into and out of the soil and the chemical reactions during CO2–H2O equilibration. Catalytic reactions by the enzyme carbonic anhydrase, reducing CO2 hydration times, have been proposed recently to explain field observations of the δ18O signatures of net soil CO2 fluxes. How important these catalytic reactions are for accurately predicting large-scale biosphere fluxes and partitioning net ecosystem fluxes is currently uncertain because of the lack of field data. In this study, we determined the δ18O signatures of net soil CO2 fluxes from soil chamber measurements in a Mediterranean forest. Over the 3 days of measurements, the observed δ18O signatures of net soil CO2 fluxes became progressively enriched with a well-characterized diurnal cycle. Model simulations indicated that the δ18O signatures recorded the interplay of two effects: (1) progressive enrichment of water in the upper soil by evaporation, and (2) catalytic acceleration of the isotopic exchange between CO2 and soil water, amplifying the contributions of ‘atmospheric invasion’ to net signatures. We conclude that there is a need for better understanding of the role of enzymatic reactions, and hence soil biology, in determining the contributions of soil fluxes to oxygen isotope signals in atmospheric CO2. [ABSTRACT FROM AUTHOR]

Abstract: The ecophysiological response to summer drought in seedlings of two co-occurring oak species (Quercus petraea and Quercus pyrenaica) outplanted below a dense Pinus sylvestris stand and a medium canopy gap was examined in two experiments carried out in central mountains of the Iberian Peninsula (Spain). Leaf water relations and gas exchange were studied in the first experiment. For both species, lower pre-dawn leaf water potential (Ψ pd) evidenced a higher degree of water stress in the understory seedlings, even though soil moisture was similar in both sites. Rates of photosynthesis (A sat) and stomatal conductance (g sat) at saturating light were higher in the gap seedlings in all measuring dates, but the earlier and more pronounced stress imposed in the understory precluded the comparison of tolerance responses between sites. Q. pyrenaica showed always higher A sat and g sat than Q. petraea, independently of Ψ pd, which did not differ significantly between species. At the end of summer, values of A sat/g sat and leaf carbon isotopic composition reflected a less efficient water use in Q. pyrenaica. In the second experiment, growth and root development were examined in a different set of seedlings planted in the same sites. Q. petraea allocated less biomass to roots, and attained 20% higher total plant dry mass than Q. pyrenaica at the end of the second growing season in the field. For both species total plant dry mass and coarse plus fine root dry mass reached at this time were approximately three-fold higher in the gap than in the understory. Poor root development could explain the more limited access to water of seedlings outplanted in the understory. This study reveals that seedlings of Q. petraea and Q. pyrenaica planted under a dense, mature pine stand are more susceptible to summer drought and present a delay in growth with respect to a medium canopy gap. [Copyright &y& Elsevier]

• We obtained a 368 year-long fire history using the tree rings and documentary data. • Fire seasonality has remained unchanged over the past 350+ years. • Major fire years occurred during anomalously dry years in the region. • The sharp decline in fire frequency coincides with fire suppression activities. Forests in the Mediterranean basin frequently experience fires due to both anthropogenic and natural causes. There are concerns that the fire season will prolong in the Mediterranean basin, the fire frequency will increase with ongoing climate change, moreover, the fire regimes will shift from surface fires to local crown fires. Here, we aim to improve our understanding of the fire regime components of black pine forests in Turkey by 1) reconstructing a high-resolution fire chronology based on tree rings, 2) revealing the seasonality of fires, 3) investigating the relationship between fire and climate, and 4) comparing our reconstruction results with documentary data from forest management units. We collected 62 fire-scarred trees from three sites in Kütahya and developed a 368 year-long (1652–2019) composite fire chronology using dendrochronological methods. We found that at two sites major fire years coincided with dry years. Two major fire years (1853 and 1879) were common to all sites and two additional fire years (1822 and 1894) were found at two sites. Our results show a sharp decline in fire frequency after the beginning of the 20th century at all sites that can be attributed to increased fire suppression efforts and forest management activities in the 20th century. Our results suggest that the spread of fires has been actively suppressed since the first forest protection law in Turkey. Yet, tree-ring based and documentary data corroboration shows that seasonality did not change over the past +350 years. [ABSTRACT FROM AUTHOR]

Systematic forest networks of health monitoring have been established to follow changes in tree vigor and mortality. These networks often lack long-term growth data, but they could be complemented with tree ring data, since both defoliation and radial growth are proxies of changes in tree vigor. For instance, a severe water shortage should reduce growth and increase tree defoliation in drought-prone areas. However, the effects of climatic stress and drought on growth and defoliation could also depend on tree age. To address these issues, we compared growth and defoliation data with recent climate variability and drought severity in Abies pinsapo old and young trees sampled in Southern Spain, where a systematic health network (Andalucía Permanent Plot Network) was established. Our aims were: (i) to assess the growth sensitivity of old and young A. pinsapo trees and (ii) to test if relative changes in radial growth were related with recent defoliation, for instance, after severe droughts. We also computed the resilience indices to quantify how old and young trees recovered growth after recent droughts. Wet-cool conditions during the prior autumn and the current early summer improved the growth of old trees, whereas late-spring wet conditions enhanced the growth of young trees. Old trees were more sensitive to wet and sunny conditions in the early summer than young trees. Old and young trees were more responsive to the Standardized Precipitation-Evapotranspiration Index drought index of June–July and July–August calculated at short (one–three months) and mid (three–six months) time scales, respectively. Old trees presented a higher resistance to a severe drought in 1995 than young trees. A positive association was found between stand defoliation and relative growth. Combining monitoring and tree ring networks is useful for the detection of early warning signals of dieback in similar drought-prone forests. [ABSTRACT FROM AUTHOR]

• Phytophthora cinnamomi and soil moisture affected Quercus suber performance. • The inoculum density required to cause disease increased at lower soil moisture. • An average drier climate might imply a slower advance of the disease. • On the contrary, more frequent extreme rain events might favor the disease. Climate change and exotic pests and pathogens are causing alarming forest declines worldwide. However, we still lack a comprehensive understanding of how damage caused by exotic pests and pathogens might vary under the different scenarios of water availability imposed by a changing climate, particularly in water-limited forests as those that occupy Mediterranean areas. In this paper we aimed to experimentally analyse the interactive effects of the aggressive exotic pathogen Phytophthora cinnamomi and climate change-related reductions in soil moisture on seedling performance of the Mediterranean host Quercus suber. We conducted a full-factorial greenhouse experiment where the physiology and growth of Q. suber seedlings was measured in soils with different combinations of P. cinnamomi inoculum density (0, 30, 60 and 120 colony forming units per gram of dry soil) and soil moisture (15%, 40%, 50% and 100% soil water holding capacity) simulating different invasion and climate change scenarios. We found additive effects of P. cinnamomi and drought on Q. suber performance aboveground, although these effects were not always negative. In fact, seedlings showed a compensatory physiological response to P. cinnamomi infection by increasing their net photosynthetic rates. Our results also supported important interactive effects of pathogens and soil moisture on belowground performance. Thus, the inoculum density in the soil required to cause significant root damage in experimental seedlings decreased as soil moisture increased. From a climate change perspective, these results suggest that an average drier climate might imply sub-optimal conditions for P. cinnamomi infections allowing for a slower advance of the disease in invaded areas. However, this effect will be modulated by the also predicted more frequent extreme climatic events. A higher frequency of extreme rain events that saturate the soil might be particularly beneficial for P. cinnamomi , boosting its soil density beyond any possible response capacity of susceptible hosts. [ABSTRACT FROM AUTHOR]