Research Highlights: Seedlings of different Quercus suber L. populations and half-sib families differ in their response to multiple stressors, which may have consequences on the future distribution of this Mediterranean species. Background and Objectives: Global change will likely increase the frequency and severity of drought in drylands. Plant species' distributions will largely depend on their ability to respond to the combined effect of drought and other environmental stressors. Genetic diversity in morpho-functional traits are key components of this response. Yet, information on the response to multiple stresses is scarce for many iconic species. The present study assessed the variability in the response of populations and half-sib families of a Mediterranean acidophilous tree, cork oak, to drought and changes in soil conditions. Materials and Methods: We sampled acorns of half-sib families from two cork oak populations genetically introgressed with the alkaline-tolerant species Quercus ilex L., and from a non-introgressed cork oak population located in its core habitat. We germinated the acorns and subjected seedlings to contrasted levels of water availability and additions of calcium and magnesium carbonate, and assessed their morpho-physiological response. Results: Response to drought and soil chemistry composition differed between populations and families. For some traits, introgressed populations responded similarly to drought than the non-introgressed population. Conversely, the response to soil chemistry was not clearly related to introgression. When considering half-sib families within populations, the population effect diminished, which revealed the importance of intra-population variation. However, relevant traits for water scarcity adaptations, such as specific leaf area and root:shoot ratio, remained significantly different at the population level, which highlights the relevance of these traits for management. Conclusions: Our study shows that the adaptive management and restoration of cork oak forests should consider not only geographic provenances, but also half-sib lines within populations.
Under the ongoing climate change with more frequent and prolonged drought and heat waves, the future of the forests ecosystems in the Mediterranean is unpredictable. Pinus halepensis, a native tree species forms large forests in extensive areas. Its morpho-functional characteristics show high plasticity to tolerate the variability and the severity of Mediterranean climatic conditions. After an extreme drought event occurred few years ago, an extensive tree mortality was observed in different forests in SE Spain, with visible signs of bark beetles attacks. The occurrence of frequent and prolonged droughts must have an important role on tree-growth decline. Previous studies reported on delayed effects, stating not to be caused by a single drought event but likely an accumulative effect of previous ones. Their recurrence may weaken the trees making them more vulnerable for bark beetles attacks, which may trigger their mortality. In this study we analysed the impact of droughts on Pinus halepensis forests and their recovery capacity. We tested whether the triggering factor for tree-growth decline was an extreme drought occurred 2014 or a delayed effect of previous ones which together with pest outbreaks could be the cause for tree mortality. We analysed ecophysiological and dendrochronological variables of tree vigour and growth during the last decades to determine the causes of forest decline. The main results pointed out that pine mortality was the consequence of the extreme dry conditions, since no differences in dendrochronolgical analysis were found among living and dead pines in the years before the mortality episode.
Cork oak (Quercus suber L.) is a suitable species for restoring Mediterranean ecosystems due to its capacity to resprout after wildfires and its economic importance for the use of cork. Several studies have focused on improving the seedling quality and abiotic conditions at the outplanting site to favour the field performance of Q. suber, however, most studies have been conducted by independently testing treatments. The aim of this study was to assess the combined effect of three techniques that focused on reforestation success with Q. suber in Mediterranean degraded shrubland: (i) a nursery technique to improve root system development, such as the use of deep containers to develop a longer tap root, combined with two field techniques such as (ii) the use of tree shelters to diminish solar radiation stress, and (iii) shrubland treatments to reduce competition for soil water and nutrients. For this purpose, 1-year-old Q. suber seedlings were grown in two containers types: a shallow container (CCS-18) and a deep container (CCL-30). Seedlings were established in a degraded shrubland at three experimental sites in the Calderona mountain range of Castellón, Spain. A factorial design was combined based on container type (CCS-18 and CCL-30), shrubland management (undisturbed shrubland and cleared shrubland in strips) and tree shelters (vegetable fibre tree shelters and no tree shelters). After 2 years of monitoring, the outplanting results indicated that using: (i) a deep container produced a longer taproot, but did not favour better survival or better field performance of seedlings; (ii) tree shelters improved the microweather conditions around seedlings, particularly by reducing excess incoming solar radiation; (iii) cleared shrubland strips reduced competition for soil water by favouring a higher water potential, better maximum photochemical PSII efficiency and higher survival rates for the seedlings established into cleared sites. The results indicate that the cleared shrubland treatment effects overlap the effects of using deep containers and tree shelters. This, in turn, reveals that shrubland clearing is the most suitable technique for favouring the introduction of a resprouter species like Q. suber into ecosystems characterized by predominantly degraded shrublands.
Introduction: Resprouter species, by regenerating rapidly, can maintain an optimal carbon balance and improve the resilience of ecosystems that have been disturbed or are at high risk of fire. Objective: To assess the effect of light availability and soil moisture on the ecophysiological variables of six resprouter species planted under cover of Pinus halepensis Mill. Materials and methods: Arbutus unedo L., Rhamnus alaternus L., Quercus ilex L., Quercus faginea Lam., Fraxinus ornus L. and Acer granatense Boiss. were planted in plots with three pine densities per hectare: HD = 800 to 1 100, MD = 300 to 600 and LD = 100 to 250. The species were also grown in the nursery, trying to maintain the same solar radiation conditions. Photosynthesis (A), stomatal conductance (Gs), photosystem II maximum efficiency (Fv/Fm) and water use efficiency (IWUE) were measured. Results and discussion: Evergreen sclerophyll species (A. unedo, R. alaternus and Q. ilex) showed higher photosynthetic capacity, lower photoinhibition and lower IWUE than deciduous species. In HD, plants showed lower photosynthetic capacity (P < 0.01) and higher photoprotection (P < 0.001). The IWUE was similar under the three pine forest densities. In the nursery, A was high under 100 % and 50 % light conditions; Gs was higher under 20 % conditions; and IWUE was high under 100 % light. Conclusion: The physiological variables of the species were conditioned by shading and changes in water demand produced by tree cover.
Climate models predict increasing mean temperatures and reduced precipitation for Mediterranean ecosystems already subjected to major hydrological fluctuations. Forest decline phenomena relate extreme droughts or heat waves with other organisms, e.g., insects or microorganisms acting as pests, but their role needs to be elucidated. A biotic factor responsible for forest diseases is Candidatus Phytoplasma pini which is a phloem-parasitism that negatively affects Spanish pine forests in drought-prone areas. In several healthy and declining Aleppo pine stands, we monitored pine infection by PCR (Polimerase Chain Reation), determined the tree phloem tissue terpene composition, carbohydrate content, measured several relevant morpho-physiological variables and examined trees affected by bark beetles. PCR confirmed C. P. pini infection was widespread in all stands, regardless of to the presence of symptomatically affected trees. However, visible symptomatic decline only occurred in trees living under more stressful conditions. The terpene composition of pines in declining stands differed from those in healthy ones, and could be related with bark beetle attacks when pines were previously weakened by the phytoplasma disease. Our results indicate that biotic factors, such as C. P. pini, affecting phloem tissue may be triggering factors for drought-mediated forest decline and suggest that phloem diseases can play a key role in forest declining processes during extreme drought.
Predictions of warmer droughts causing increasing forest mortality are becoming abundant, yet fewer studies have investigated the mechanisms of forest persistence. To examine the resistance of forests to warmer droughts, we used a five-year precipitation reduction (~45% removal), heat (+4°C above ambient) and combined drought and heat experiment in an isolated stand of mature Pinus edulis-Juniperus monosperma. Despite severe experimental drought and heating, no trees died, and we observed only minor evidence of hydraulic failure or carbon starvation. Two mechanisms promoting survival were supported. First, access to bedrock water, or 'hydraulic refugia' aided trees in their resistance to the experimental conditions. Second, the isolation of this stand amongst a landscape of dead trees precluded ingress by Ips confusus, frequently the ultimate biotic mortality agent of piñon. These combined abiotic and biotic landscape-scale processes can moderate the impacts of future droughts on tree mortality by enabling tree avoidance of hydraulic failure, carbon starvation, and exposure to attacking abiotic agents.
Forests provide many environmental services, especially those related to the water cycle. In semiarid areas where water is a limiting factor for ecosystem functioning, forested areas can have a strong impact on ground water recharge. In these areas, proper knowledge of forests’ water balance is necessary to promote management practices that may ensure ecosystem properties and environmental services like water or carbon fixation. In this article, we review several ecohydrology topics within the framework of Mediterranean water-limited environments in two representative ecosystems: Kermes oak (Quercus ilex L.) and Aleppo pine (Pinus halepensis Mill.) forests. Both are the commonest species in countries that surround the Western Mediterranean Basin. We analysed the Blue and Green water components, i.e., green water is the water demand of forests, represented by evapotranspiration and interception; while blue water is the part of the balance involving runoff and deep percolation, which can be regarded as water directly usable by society. In general, different studies conducted in Mediterranean areas have pointed out that the water balances of Q. ilex and P. halepensis forests have low values for the Blue to Green water (B/G) ratios. Adaptive forest management like forest thinning can compensate for these ratios. Thinning has demonstrated to reduce losses by interception, but at same time, it can also increase individual tree transpiration and evaporation rates. However, these practices lead to higher B/G ratios when considering the whole stand. In future global change scenarios, in which drought conditions are expected to intensify, management practices can improve the water balance in these ecosystems by minimizing the risk of plant mortality and species replacement due to intense competence by water resources.
Climate warming should result in hotter droughts of unprecedented severity in this century. Such droughts have been linked with massive tree mortality and data suggest warming interacts with drought to aggravate plant performance. Yet, how forests will respond to hotter droughts remains unclear, as does the suite of mechanisms trees use to deal with hot droughts. We used an ecosystem‐scale manipulation of precipitation and temperature on piñon pine (Pinus edulis) and juniper (Juniperus monosperma) trees to investigate nitrogen (N) cycling‐induced mitigation processes related to hotter droughts. We found that while negative impacts on plant carbon and water balance are manifest after prolonged drought, performance reductions were not amplified by warmer temperatures. Rather, increased temperatures for five years stimulated soil N cycling under piñon trees and modified tree N allocation for both species, resulting in mitigation of hotter drought impacts on tree water and carbon functions. These findings suggest that adjustments in N cycling are likely after multi‐year warming conditions and that such changes may buffer reductions in tree performance during hotter droughts. The results highlight our incomplete understanding of trees’ ability to acclimate to climate change, raising fundamental questions about the resistance potential of forests to long‐term, compound climatic stresses.
What are the changes at individual and community level derived from altered climatic regime in a typical secondary Mediterranean shrubland?
Oak forests can naturally regenerate from seed or from sprouts. Both strategies result in the establishment of a tree layer, but they involve a crucial difference: i.e. regeneration from seeds affects population genetics while sprouting assures the recovery of biomass after a disturbance but it does not involve sexual reproduction. In addition the two regeneration mechanisms differ in their complexity and are affected by different constraints: i.e. regeneration from seed is a more intricate pathway with several potential bottlenecks (e.g. seed and micro-sites availability, predation, seedling-saplings conflicts) while sprouting is a much more straightforward process benefiting from the presence of an already established root system and more independent from environmental stochasticity. Ultimately, regeneration from seeds or sprouts will result in contrasting forest structures (respectively, high-forests and coppices) with a different functioning and dynamics and requiring particular forestry practices. When natural regeneration is not possible, oak forest restoration must be done using artificial regeneration by seeding or planting (traditionally, both methods have been recommended), provided that acorn predators are controlled. Although similar results have been obtained with regard to survival, under Mediterranean conditions, shoot growth patterns clearly differ for both methods. Indeed, one-year seedlings often discontinue their shoot elongation shortly after transplanting, especially under drought or competition. At this time, a new taproot and fine lateral roots are formed. This observation suggests that the seeding and planting techniques may bear different consequences with regard to root system development, which may ultimately affect seedling establishment. Survival and growth planted seedlings depends on morphological and physiological attributes (Burdett in Can J For Res 20:415–427, 1990; Villar-Salvador et al. in New For 43:755–770, 2012; Grossnickle in New For 43:711–738, 2012). Cultivation techniques strongly determine the functional attributes of seedlings by manipulating the amount of resources (water, mineral nutrients, light, space) and the conditions (temperature, growing medium pH, photoperiod) for seedling growth. Consequently, how seedlings are cultivated impacts on the performance of forest plantations. Cultivation practices improve the ‘‘seedling physiological potential’’, increasing the chances of survival immediately after field planting. Each of these has an influence and interacts with the others (Ketchum and Rose in Interaction of initial seedling size, fertilization and vegetation control. Redding, CA, pp 63–69, 2000), which should be taken into consideration when evaluating a reforestation proposal; otherwise, artificial forest regeneration often results in unacceptably poor seedling performance. Planting date and site preparation, since they increase water availability, have been shown to be the factors most relevant to the survival of Mediterranean species. However, in less restrictive conditions, the use of less intensive soil preparation, on dates more favorable to the initial growth of the seedlings in the field, might be more efficient. Similarly, the use of tree shelters in oaks plantations is under debate, as its effects are species and environmental dependent. A better understanding of the ecophysiological seedling response under the microenvironment of the tree shelter is needed to improve the management of this protection tool. On the other side, the effects of cultivation practices can be linked closely to newly established seedlings (the post-planting phenological cycle), and such benefits are ephemeral in nature; thus, the effects of cultivation practices have their greatest importance during the initial growing seasons (1–2 years), diminishing with time.
Resumen. Las proyecciones del cambio climático indican que en el área mediterránea se producirá un aumento en la frecuencia de sequías extremas, lo que causará impactos en sus masas forestales y en los servicios ecosistémicos que estas prestan. En los últimos años se han registrado eventos de decaimiento y mortalidad asociados a fuertes sequías, los cuales se pueden considerar representativos de los previstos por el cambio climático, por lo que su estudio es una oportunidad para comprender y predecir cómo se verán afectados los bosques mediterráneos en el futuro. Este es el principal objetivo del nuevo proyecto de investigación liderado por la Universidad de Alicante y el CEAM y cuyo propósito es profundizar en el conocimiento de estas cuestiones. Para ello se está llevando a cabo el análisis detallado de distintas variables ecohidrológicas y ecofisiológicas en masas forestales de distintas zonas experimentales de la Comunidad Va-lenciana, dos de las cuales se hallan en el Parque Natural del Carrascal de la Font Roja. En este artículo se presentan los principales objetivos del citado proyecto, así como sus instalaciones experimentales en el Parque Natural. Palabras clave. cambio climático, sequía, mortalidad, balance hídrico, estrés, transpiración. Resum. Les projeccions de canvi climàtic indiquen que a l'àrea mediterrània es produirà un augment en la freqüència de sequeres extremes, el que causarà impactes en les seues masses forestals i en els servicis ecosistèmics que aques-tes presten. En els últims anys s'han registrat esdeveniments de decaïment i mortalitat associats a fortes sequeres, les quals es poden considerar representatives de les previstes pel canvi climàtic. Per tant, el seu estudi és una oportunitat per a comprendre com es veuran afectats els boscos mediterranis en el futur. Aquest és el principal objectiu d'un nou projecte d'investigació liderat per la Universitat d'Alacant i el CEAM i es tracta d'aprofundir en el coneixement d'aquestes qüestions. Per a això s'està duent a terme l'anàlisi detallat de distintes variables ecohidrológiques i ecofisiológiques en masses forestals de diferents zones experimentals de la Comunitat Valenciana, dues de les quals es troben en el Parc Natural del Carrascal de la Font Roja. En aquest article es presenten els objectius específics de l'esmentat projecte, així com les seues instal·lacions experimentals al Parc Natural. Paraules clau. canvi climàtic, sequera, mortalitat, balanç hídric, estrés, transpiració. Summary. Global change projections point out an increase in the number of severe droughts in the Mediterranean region, which may have a deep impact in forests and in environmental services they provide. In the past years, events of drought-induced decay and plant mortality have been registered in this region, which are considered representative of climatic change consequences. Hence, their study is a good chance to understand and foresee how Mediterranean forests will be affected by climate change in the future. This is the main purpose of the new research project carried out by University of Alicante and CEAM foundation whose main goal is improve our actual knowledge in this topic. To achieve this, an exhaustive study of forest's ecohydrological and ecophysological variables is being carried out in several experimental sites through the Valencian Communiy, two of them located within kermes oak forest of Font Roja Natural Park. In this paper, we introduce the main project goals and the experimental design of Natural Park's study sites.
Mediterranean plants are subjected to high levels of drought stress during summer periods and, in some cases, dry conditions surpass security levels producing xylem cavitation. One of the key questions when analyzing the capacity of survival is: what is the capacity to recover xylem functionality after intense drought events with high levels of xylem embolism?. The objective of this study was to analyze the effect of xylem recovery after intense drought conditions in several Mediterranean trees and shrub species. We analyzed this factor under controlled conditions (drought cycles in the nursery) but also under field conditions. We measured water potential and xylem conductivity during the maximum level of drought stress (in summer) and also after recovery, one or two months later, when autumn rains fall in the natural ecosystems, or after rewatering in the nursery. Results showed that plants were able to recover some hydraulic conductivity but this capacity was species-dependent and also related to the levels of drought stress experienced by plants. We discuss the results in terms of tolerance and avoidance strategies and also when comparing early-successional with late-successional species.
In a climate variability context, knowledge about Alpha grass (Stipa tenacissima) seed germination and seedling establishment requirements is a key factor given the relevance of this species in wide areas of North Africa and southern Europe. Such knowledge can help to collect information about current S. tenacissima populations allowing the conservation and restoration in these ecosystems. According to this objective, we conducted a series of laboratory studies to investigate the effects of several ecological factors as temperature, light, salinity, burial depth and drought, in relation to germination capacity and development of new seedlings. The main results revealed that germination was delayed with increasing drought conditions generated by osmotic solutions. Seeds germinated at all the concentrations of NaCl solutions, but germination was completely inhibited at a PEG 6000 solution of −1.6 MPa. Further, an osmotic potential of −0.8 MPa inhibited root and shoot growth. Variations in temperature also promoted variable germination rates (GR50). The base germination temperature (Tb (50)) was less than 2 °C for the different osmotic potentials. Burial depth was another limiting factor required for establishment. Despite significant seed production, this study has identified several key limiting points affecting seed germination and seedling establishment which can affect the viability of their populations in the near future.
Drought is one of the main constraints determining forest species growth, survival and productivity, and therefore one of the main limitations for reforestation or afforestation. The aim of this study is to characterize the drought response at the physiological and molecular level of different Pinus halepensis (common name Aleppo pine) seed sources, previously characterized in field trials as drought-sensitive or drought-tolerant. This approach aims to identify different traits capable of predicting the ability of formerly uncharacterized seedlings to cope with drought stress. Gas-exchange, water potential, photosynthetic pigments, soluble sugars, free amino acids, glutathione and proteomic analyses were carried out on control and drought-stressed seedlings in greenhouse conditions. Gas-exchange determinations were also assessed in field-planted seedlings in order to validate the greenhouse experimental conditions. Drought-tolerant seed sources presented higher values of photosynthetic rates, water use efficiency, photosynthetic pigments and soluble carbohydrates concentrations. We observed the same pattern of variation of photosynthesis rate and maximal efficiency of PSII in field. Interestingly drought-tolerant seed sources exhibited increased levels of glutathione, methionine and cysteine. The proteomic profile of drought tolerant seedlings identified two heat shock proteins and an enzyme related to methionine biosynthesis that were not present in drought sensitive seedlings, pointing to the synthesis of sulfur amino acids as a limiting factor for drought tolerance in Pinus halepensis. Our results established physiological and molecular traits useful as distinctive markers to predict drought tolerance in Pinus halepensis provenances that could be reliably used in reforestation programs in drought prone areas.
Tropical Andean ecosystems have been identified as very vulnerable to climate change. Changes in climatic conditions, especially drought as envisaged by climate change projections, could affect the establishment of new individuals that are responsible for ensuring the persistence of species and plant communities. The aim was to study the main morpho-functional traits related to water use and drought resistance of native plant species from Ecuadorian ecosystems during imposed drought periods. Seedlings of six native species representative of the Ecuadorian Andes were studied: lower montane evergreen forest (Alnus acuminata and Cedrela montana), montane cloud forest (Podocarpus sprucei and Aegiphila ferruginea) and montane dry shrubland (Schinus molle and Caesalpinia spinosa). Morphological characterisation, a root growth capacity test and stomatal conductance measurements during two controlled drought periods were used to investigate biomass allocation patterns, the root system morphology and gas exchange patterns of species, respectively. The main results indicated that species-specific differences in morpho-functional traits and allocation patterns determined responses to water availability and drought conditions. Low relative growth rate, leaf area ratio and specific leaf area, and high specific root length, were related to drought-resistant species as P. sprucei and C. spinosa. In contrast, a high or moderate relative growth rate, leaf area and root biomass, but low specific root length as in A. ferruginea, S. molle, C. montana, were related to lower resistance to drought conditions. Despite A. acuminata showed high specific root length, it was reported as a species sensitive to drought. Overall, patterns of stomatal conductance, linked to biomass allocation patterns and root system morphology, especially specific root length, seemed to be related to differences in vulnerability to drought in these species. Drought response was independent of species habitats. Unexpectedly, P. sprucei, belonging to montane cloud forest showed higher drought resistance than S. molle, belonging to montane dry shrubland.
Disentangling the relative impacts of precipitation reduction and vapor pressure deficit (VPD) on plant water dynamics and determining whether acclimation may influence these patterns in the future is an important challenge. Here, we report sap flux density (FD), stomatal conductance (Gs), hydraulic conductivity (KL) and xylem anatomy in piñon pine (Pinus edulis) and juniper (Juniperus monosperma) trees subjected to five years of precipitation reduction, atmospheric warming (elevated VPD) and their combined effects. No acclimation occurred under precipitation reduction: lower Gs and FD were found for both species compared to ambient conditions. Warming reduced the sensibility of stomata to VPD for both species but resulted in the maintenance of Gs and FD to ambient levels only for piñon. For juniper, reduced soil moisture under warming negated benefits of stomatal adjustments and resulted in reduced FD, Gs and KL. Although reduced stomatal sensitivity to VPD also occurred under combined stresses, reductions in Gs, FD and KL took place to similar levels as under single stresses for both species. Our results show that stomatal conductance adjustments to high VPD could minimize but not entirely prevent additive effects of warming and drying on water use and carbon acquisition of trees in semi-arid regions.
http://medpine5.ctfc.es/ Session Stand dynamics and forest management, Thursday 25 th Sept 56 Developing silvicultural methods to adapt pine forests to climate change has become a priority. Recommended management include in particular stand thinning in order to reduce competition for water and re-introduction of resprouting hardwood species to promote diversity and resilience through a faster vegetation recovery and soil protection after new wildfires. In this study, we examined the effect of Aleppo pine thinning on early establishment of a set of introduced hardwood seedlings with different shade and drought tolerance, in relation to environmental factors under different canopy covers. Stands were selected in 2 sites -South-East France and South-East Spain, corresponding to wetter and dryer conditions, respectively-and thinned at three levels (control=30 m 2 /ha, moderate=13-20m 2 /ha or heavy thinning= 7-10m 2 /ha). Hardwood species performances were higher under thinned treatments in France, whereas in Spain thinning was detrimental for the survival and height growth of most species, but positive for basal diameter growth. Best performing species were shade-tolerant in France and drought-tolerant in Spain. Thinning increased light transmittance (control=10-15%, moderate=20-30%, heavy thinning=40-60%) and accentuated the daily extremes (maximum and minimum) of air temperature and vapor pressure deficit in both sites. Thinning effect on soil water content was different between the two sites: no or slight effect in France but an increase of soil humidity in the most intense thinning treatment in Spain. In France, thinned plots were rapidly colonized by an abundant layer of tall understorey shrubs but not in Spain. This shrub layer may explain the difference of thinning effect on soil water content. Surprisingly, species survival was lower in the thinned treatments in the dry conditions of Spain in spite of higher soil water content. This suggests that reduction of air vapor pressure deficit, temperature and light irradiation may be more critical than soil water content for species survival in Spain whereas in France light availability is the most crucial parameter. This study highlights the major importance of shading for species survival in the Mediterranean. Pine thinning can be a tool for accelerating the transition towards mixed stands but with contrasted impacts according to site conditions. In wetter sites, intense thinning is adapted to enhance growth and survival whereas in drier sites moderate thinning producing enough shade to ensure saplings survival can be recommended. However, further investigation is needed to fully understand the role of understorey shrubs in modifying this pine density -sapling interaction.
Background and aims: Several studies show apparently contradictory findings about the functional convergence within the Mediterranean woody flora. In this context, this study evaluates the variability of functional traits within holm oak (Quercus ilex) to elucidate whether provenances corresponding to different morphotypes represent different ecotypes locally adapted to the prevaling stress levels. Methods: Several morphological and physiological traits were measured at leaf and shoot levels in 9-year-old seedlings of seven Q. ilex provenances including all recognized morphotypes. Plants were grown in a common garden for 9 years under the same environmental conditions to avoid possible biases due to site-specific characteristics. Key results: Leaf morphometry clearly separates holm oak provenances into 'ilex' (more elongated leaves with low vein density) and 'rotundifolia' (short and rounded leaves with high vein density) morphotypes. Moreover, these morphotypes represent two consistent and very contrasting functional types in response to dry climates, mainly in terms of leaf area, major vein density, leaf specific conductivity, resistance to drought-induced cavitation and turgor loss point. Conclusions: The 'ilex' and 'rotundifolia' morphotypes correspond to different ecotypes as inferred from their contrasting functional traits. To the best of our knowledge, this is the first time that the combined use of morphological and physiological traits has provided support for the concept of these two holm oak morphotypes being regarded as two different species.
Key message Aleppo pine stands resilience can be increased by introducing local resprouting hardwood species. Pine density management impacts seedlings establishment by modifying resources availability and abiotic stress. Under Mediterranean conditions moderate pine density should be preferred to promote seedlings establishment. Abstract Context: Developing silvicultural methods to adapt Mediterranean forests to climate change is a priority. Introduction of resprouting hardwood species in pine stands can promote diversity and resilience in particular to forest fires. Aims: Examine how pine thinning influences understory environmental factors and establishment of various hardwood seedlings in two Mediterranean sites. Methods: Aleppo pine stands were thinned at three levels (uncut 30 m2/ha, moderate 13-20 m2/ha or heavy thinning 7-10 m2/ha) at two Mediterranean sites (South-East France and South-East Spain). Seedlings of six hardwood species were introduced in the understory. Their survival and growth were monitored and related to changes in environmental factors. Results: At both sites thinning improved light availability and seedlings diameter growth of all species. Thinning also increased extreme temperature and evaporative demand. Soil moisture increased in the heavy thinning treatment at the site of SE Spain but not at the site of SE France. The most limiting conditions for seedlings survival were uncut stands in SE France and low density stands in SE Spain. Conclusion: Thinning accelerates seedlings growth but a too heavy thinning leading to summer harsh conditions can affect seedlings survival. Moderate pine covers (15-20m2/ha) allow the successful introduction of several local hardwood species.
This protocol describes the construction of Vulnerability to Embolism Curves for plants via the bench dehydration method. The method involves naturally dehydrating detached samples on the bench top and measuring loss of hydraulic conductivity as a function of xylem water potential.
III Reunión del Grupo de Trabajo de Hidrología Forestal: La hidrología forestal: ciencia y técnicas útiles Balance hídrico del suelo en pinares con diferente densidad de arbolado. Efectos sobre el establecimiento de brinzales de especies rebrotadoras bajo el dosel Resumen El objetivo del presente trabajo fue determinar el balance hídrico del suelo en bosques de pino carrasco con diferente densidad de arbolado utilizando el modelo ecohidrológico HYDROBAL, y evaluar sus efectos sobre la introducción y establecimiento bajo el dosel, de brinzales de especies ampliamente utilizadas en la restau-ración forestal. En este contexto, en La Hunde (Ayora, Valencia), y como consecuencia de previas labores de aclareo con diferente intensidad, se definieron tres tratamientos experimentales de acuerdo a diferentes densi-dades de pinos: Baja (100-300 pies ha-1); Media (300-700 pies ha-1) y Alta (700-1100 pies ha 1). De cada trata-miento se establecieron tres parcelas experimentales de 900 m 2 , localizadas en tres sitios (El Aljibe, El Lobo y El Mojón). En cada parcela se plantaron quince individuos de seis especies rebrotadoras con características morfo-funcionales contrastadas (Arbutus unedo, Rhamnus alaternus, Quercus ilex, Quercus faginea, Fraxinus ornus, Acer opalus ssp granatense). Los resultados del balance hídrico indicaron que las parcelas con alta densidad de pinos mostraron menor transcolación, menor precipitación neta y en consecuencia, menor hume-dad del suelo; lo cual coincidió con los resultados observados en campo. No obstante, y contrariamente a los resultados esperados, las parcelas de alta densidad presentaron los mayores valores de supervivencia (85%) y crecimiento en altura; lo cual pudo ser favorecido por el efecto protector del dosel, que redujo significativa-mente la radiación solar (transmisividad de luz solar: 15%).
Understanding and predicting plant response to disturbance is of paramount importance in our changing world. Resprouting ability is often considered a simple qualitative trait and used in many ecological studies. Our aim is to show some of the complexities of resprouting while highlighting cautions that need be taken in using resprouting ability to predict vegetation responses across disturbance types and biomes. There are marked differences in resprouting depending on the disturbance type, and fire is often the most severe disturbance because it includes both defoliation and lethal temperatures. In the Mediterranean biome, there are differences in functional strategies to cope with water deficit between resprouters (dehydration avoiders) and nonresprouters (dehydration tolerators); however, there is little research to unambiguously extrapolate these results to other biomes. Furthermore, predictions of vegetation responses to changes in disturbance regimes require consideration not only of resprouting, but also other relevant traits (e.g. seeding, bark thickness) and the different correlations among traits observed in different biomes; models lacking these details would behave poorly at the global scale. Overall, the lessons learned from a given disturbance regime and biome (e.g. crown-fire Mediterranean ecosystems) can guide research in other ecosystems but should not be extrapolated at the global scale.
XIV World Forestry Congress, Durban, ZAF, 07-/09/2015 - 11/09/2015
Reforestation efforts in dryland ecosystems frequently encounter drought and limited soil productivity, although both factors usually interact synergistically to worsen water stress for outplanted seedlings. Land degradation in drylands (e.g. desertification) usually reduces soil productivity and, especially, soil water availability. In dry sub-humid regions, forest fires constitute a major disturbance affecting ecosystem dynamics and reforestation planning. Climate change projections indicate an increase of drought and more severe fire regime in many dryland regions of the world. In this context, the main target of plantation technology development is to overcome transplant shock and likely adverse periods, and in drylands this is mostly related to water limitations. In this paper, we discuss some selected steps that we consider critical for improving success in outplanting woody plants, both under current and projected climate change conditions including: (1) Plant species selection, (2) Improved nursery techniques, and (3) Improved planting techniques. The number of plant species used in reforestation is increasing rapidly, moving from a reduced set of well-known, easy-to-grow, widely used species, to a large variety of promising native species. Available technologies allow for reintroducing native plants and recovering critical ecosystem functions for many degraded drylands. However, climate change projections introduce large uncertainties about the sustainability of current reforestation practices. To cope with these uncertainties, adaptive restoration approaches are suggested, on the basis of improved plant quality, improved techniques for optimizing rain use efficiency in plantations, and exploring native plant species, including provenances and genotypes, for their resilience to fire and water use efficiency.
El objetivo del presente trabajo fue determinar el balance hídrico del suelo en bosques de pino carrasco con diferente densidad de arbolado utilizando el modelo ecohidrológico HYDROBAL, y evaluar sus efectos sobre la introducción y establecimiento bajo el dosel, de brinzales de especies ampliamente utilizadas en la restauración forestal. En este contexto, en La Hunde (Ayora, Valencia), y como consecuencia de previas labores de aclareo con diferente intensidad, se definieron tres tratamientos experimentales de acuerdo a diferentes densidades de pinos: Baja (100-300 pies ha -1 ); Media (300-700 pies ha -1 ) y Alta (700-1100 pies ha 1 ). De cada tratamiento se establecieron tres parcelas experimentales de 900 m 2 , localizadas en tres sitios (El Aljibe, El Lobo y El Mojón). En cada parcela se plantaron quince individuos de seis especies rebrotadoras con características morfo-funcionales contrastadas (Arbutus unedo, Rhamnus alaternus, Quercus ilex, Quercus faginea, Fraxinus ornus, Acer opalus ssp granatense). Los resultados del balance hídrico indicaron que las parcelas con alta densidad de pinos mostraron menor transcolación, menor precipitación neta y en consecuencia, menor humedad del suelo; lo cual coincidió con los resultados observados en campo. No obstante, y contrariamente a los resultados esperados, las parcelas de alta densidad presentaron los mayores valores de supervivencia (85%) y crecimiento en altura; lo cual pudo ser favorecido por el efecto protector del dosel, que redujo significativamente la radiación solar (transmisividad de luz solar: 15%).
The frequency and magnitude of climate extremes are expected to increase in the future according to climate change forecasts.Forest mortality is, among others, a consequence of extreme drought events caused by of the increase of temperature and the decrease of precipitation. In the last years, forest mortality induced by events of extreme drought was observed in pine forests and shrublands in four sites in Mediterranean forests of Alicante province. However, under the closely same drought conditions the mortality rates observed in the different sites were distinct. In this work we intend to explore the role of vegetation structure in the observed differences in forest mortality rates in these four sites. A structural characterization of the different vegetation communities has been carried out by measuring tree density, specific composition, canopy cover and LAI.
Los incendios forestales son una perturbación recurrente en los ecosistemas mediterráneos, cuyas causas son básicamente de origen humano. Los regímenes de incendios forestales han cambiado en el este peninsular en las últimas tres décadas con un incremento en la superficie afectada y en la severidad, con la consecuente amenaza a la biodiversidad. A esto habría que añadir que la población, cada vez más, se distribuye en viviendas diseminadas en zonas forestales, con escasa gestión. El Centro de Estudios Ambientales del Mediterráneo (CEAM) viene estudiando desde los años 90 los ecosistemas mediterráneos con el fin de describir y comprender los procesos naturales y los asociados a las actividades humanas. Una de las líneas de investigación abiertas es el estudio del impacto de los incendios forestales y la respuesta de la vegetación al fuego y los procesos de degradación relacionados. Dentro de esta línea, se vienen realizando quemas experimentales de forma recurrente con el objetivo de conocer cómo se comporta el fuego en matorrales mediterráneos y su efecto sobre la estructura y la dinámica de la vegetación. Así pues, se dispone de una base de datos de incendios recurrentes que abarca los últimos 30 años. Con la finalidad de seguir avanzando en esta línea, entre finales de la primavera y verano de 2016 se han realizado tres nuevas quemas experimentales en las provincias de Alicante y Valencia, siguiendo la misma metodología que en quemas anteriores. Las parcelas de estudio ya habían sido quemadas anteriormente en tres ocasiones, por lo que poseen tres niveles de recurrencia, siendo el último fuego aplicado en el año 2006. Cada parcela tiene una extensión de entre 550 y 800 m2 y su composición antes de las quemas se correspondía con un modelo 5 de combustible, compuesto principalmente por pasto y matorral de jara menor de 1 m de altura. Durante las quemas experimentales se midieron las temperaturas alcanzadas en la superficie del suelo mediante termopares tipo K unidos a un datalogger. Asimismo, también se calculó la velocidad de propagación mediante la colocación de pértigas metálicas a una distancia conocida. Los resultados obtenidos muestran las variables descriptivas del comportamiento del fuego en unas condiciones ecológicas, topográficas y meteorológicas conocidas. La comparación de estos datos con los obtenidos en quemas anteriores con distintos niveles de recurrencia, nos permite, entre otros parámetros, conocer las características del comportamiento del fuego en unas condiciones de vegetación distintas para una misma parcela. Con las quemas experimentales podemos disponer de información del comportamiento del fuego en condiciones imposibles de realizar en fuegos no programados. Aparte de ser el punto fundamental para la disponibilidad de datos con fines de investigación, supone una ayuda en cuanto a formación para los servicios de prevención y extinción que actúan durante la realización de la quema, lo que redundará en una mayor capacitación durante actuaciones de extinción de fuegos naturales. Asimismo, pueden servir de referente en caso de la utilización de quemas prescritas como herramienta de modificación del combustible forestal; herramienta que se utiliza en otras partes del territorio nacional, compatibilizando las acciones de prevención de incendios con el mantenimiento de los procesos ecológicos. ******************************************************************************************************************* Forest fires are a recurrent disturbance in Mediterranean ecosystems whose causes are mainly of human origin. In the last three decades, wildfire regimes have changed in the eastern part of the Peninsula leading to burnings which are characterized with an increased area and severity, threatening to change the biodiversity of the affected ecosystems. Additionally, the population is increasingly distributed in scattered dwellings in forest areas, usually with poor management. The Mediterranean Center for Environmental Studies (CEAM) has been studying the Mediterranean ecosystems since the 90’s, in order to describe and understand natural processes and those amended by human activities. One of the current research projects, study the fire impact and its response on vegetation as well as the degradation processes related with fires. In the framework of this project, programmed experimental burnings have been conducted recurrently, with the aim of knowing how fire behaves in shrublands and its effect on the structure and dynamics of vegetation. Hence, a database of recurring fires covering the last 30 years is available. In order to make further progress, between late spring and summer of 2016, there have been three new experimental burnings in the provinces of Alicante and Valencia, following the same methodology as in previous ones. Such study plots had already been burned previously on three occasions, so they have three levels of recurrence, being the most recent in 2006. Each plot has an area between 550 and 800 m2 and the composition before burnings corresponds to a model 5 of fuel, i.e. composed mainly of grasses and rockrose shrubland less than 1 m in height. During the experimental burnings the soil surface temperature was continuously measured by the means of type K thermocouples attached to a datalogger. Furthermore, the propagation rate was also calculated by placing metal rods at a known distance. The obtained results show the fire behavior variables under known ecological, topographical and meteorological conditions. The comparison of these data with those obtained in previous fires with different levels of recurrence, enables us (among other parameters), to know the fire behavior characteristics under different vegetation conditions for the same plot. The experimental burnings offer valuable fire behavior information, which is impossible to carry out in unplanned fires conditions. Such experimental burnings, aside from being the main source of data for research purposes, constitute an important asset in terms of training for the prevention and extinction services, which could result in enhanced capacity to fight against wildfires. Finally, it can serve as a reference in case of prescribed burnings and its use as a tool for forest fuel modification; practice used in other parts of Spain that combines the fire prevention actions with the ecological processes conservation.
Wildfires are a recurrent disturbance in Mediterranean Basin ecosystems which in recent decades are becoming largest and more severe. Furthermore, climate change projections predict an increase in the frequency and severity of these fires due to an increase over time of the dry period of summer (either by advancing its beginning or by delaying its end). Our aim was to analyze the effect of induced drought after fire on the germination and sprouting capacity of typical species from these ecosystems. Concretely, our purpose was to investigate the effect of the summer prolongation to the detriment of the rainy season in autumn. For this purpose, experimental burns were performed in summer over three Mediterranean shrublands located in SE Spain. Then we applied rainfall exclusion treatments during the whole autumn rainy season (from October to December). Our results showed a decline in the germination, richness and coverage of species caused by this rainfall reduction in the first months after the fire. However, germination response varied among species. These changes in vegetation composition and coverage suggest that climate change can lead significant changes in Mediterranean vegetation by modifying the critical regeneration period just after fire. Therefore, these results suggest that ecosystem resilience could be threatened within the framework of future climate change by the interaction of two recurrent factors in the Mediterranean Basin such as fire and drought.
Water deficit is considered the main limiting factor for the establishment, survival, and growth of plants mainly in water-limited ecosystems. Plants have evolved a wide range of morphologic and functional mechanisms to adapt to arid environments. However, if the tension in the xylem conduits becomes too high, thus xylem cavitation can occur i.e., water column breakage. This results in the hydraulic disconnection of leaves and above-ground parts from roots because xylem conduits are filled with air and water vapor, and this phenomenon is called embolism. Therefore, the resistance of the xylem to cavitation and embolism is of paramount importance for plant functioning. In this chapter, we will review the role of plant hydraulics and xylem cavitation in the context of water-limited ecosystems and their relationship with other plant functional traits and with survival capacity. These topics will be analyzed and discussed on the basis of current knowledge and our research experiences.
Fire and drought are selective driving forces in Mediterranean plants, and thus their ability to resprout or recruit after these disturbances is of paramount importance. The contrast in regeneration niche between resprouters and seeders, and each group's different root characteristics, suggest that they are subjected to different degrees of environmental stress and, consequently, to different evolutionary forces. We compared leaf traits, xylem traits related to hydraulic efficiency and vulnerability to cavitation, and the physiological response to an imposed drought between seedlings of resprouters and seedlings of seeders. We used 12 species co-existing in Mediterranean basin ecosystems. Major differences were found in the xylem architecture and leaf traits, and in the response to drought conditions. Seeders were more efficient at transporting water to leaves but formed, in turn, a safer xylem network. They also presented higher photosynthesis and transpiration rates, and earlier stomatal closure with drought, but good leaf dehydration tolerance. Seeders and resprouters can be considered two syndromes whose different functional characteristics are related to water availability and drought responses. These characteristics, together with their differences in rooting habits, account for their distinct regeneration niches and, thus, their co-existence.