Search

Key Message The first bottleneck in Spanish black pine survival through afforestation is the lack of resistance to drought in their initial life stages. Abstract Spanish black pine (Pinus nigra Arn ssp. salzmannii) is the most widely distributed pine species in mountain areas of the Mediterranean Basin and is commonly used for afforestation in endangered and degraded areas. Despite its importance, little is known regarding the factors driving seedling survival for this species, which may hamper afforestation success in Mediterranean areas. In this study, we assessed the effects of seed origin and plantation site along a natural gradient with contrasting elevation and climatic conditions in a Mediterranean forest in Central-Eastern Spain. Our results showed: (1) higher seedling survival rates when seed origin differed from plantation site (25.3 ± 5.4%) compared to same origin and plantation site (5.3 ± 2.7%); (2) higher survival probability (~ 20%) for high and medium elevation seeds (colder and wetter locations) compared to the warmer and drier low elevation sites (15%); (3) higher seedling survival (~ 40%) at higher elevation sites compared to low-elevation sites (

Spanish black pine showed greater resilience and resistance, but generally lower recovery to drought events in managed than in unmanaged forest stands under Mediterranean humid climate. Drought negative effects on forest ecosystems are projected to increase under global warming all over the world. In this context, forest management can be an effective option for reducing drought impacts and increasing tree growth stability to extreme drought events. Here, we aim to evaluate black pine (Pinus nigra subsp. salzmannii) growth response to climatic variability and drought events in managed and unmanaged stands under similar Mediterranean climatic conditions. Drought events were identified using long-term climatic data, and basal area increments were calculated for 100–120-year old trees cored in managed and unmanaged plots. Results showed that tree size, temperature, and the interaction between management treatment and water availability significantly influenced tree growth. Basal area increment was reduced in response to the 1983, 1991, 1994‒1995, 1999–2000 and 2005 drought events. Trees in managed plots showed lower growth reductions in response to drought than those located in unmanaged plots, probably experiencing higher competition for soil water, whereas the reverse happened under wet climate conditions. Black pines showed greater resilience and resistance, but generally lower recovery to drought events in managed than in unmanaged stands. Our results suggest that forest management enhances drought tolerance in black pine stands, which may help to ameliorate the negative impacts of global warming across Mediterranean forest ecosystems.

The magnitude of drought impact in forest ecosystems depends on which group of trees are more severely affected, greater mortality of smaller trees can modulate the trajectories of succession, while the mortality of larger trees can disproportionately offset the ecosystem’s carbon balance. Several studies have documented a greater vulnerability of large trees to extreme droughts while some other studies reported a greater growth reduction in smaller trees during droughts. We tested these hypotheses by comparing tree basal area increment (BAI), drought resistance (i.e., magnitude of growth decline during drought), and resilience (i.e., magnitude of growth recovery after drought) across five different age-classes in black pine (Pinus nigra Arn. Ssp salzmannii) forests in Spain. Our results showed that the BAI patterns, drought resistance, and resilience were strongly influenced by tree age-classes. In addition, the effect of climatic water balance (precipitation minus potential evapotranspiration) on BAI significantly varied among age-classes. The effect of water balance on BAI was lower for younger age-classes (1–39 years of age) compared to older age-classes. We observed a greater growth reduction (i.e., lower resistance) in older trees (&gt, 40 years of age) during droughts compared to younger trees (&lt, 40 years of age). However, all trees, irrespective of their ages, were able to recover the growth rates after the drought. In general, younger trees showed a greater capacity in recovering the growth rate (i.e., more resilient) than older trees. We detected no significant effects of stand basal area and stand density on BAI, drought resistance, and resilience. Overall, our results indicated that growth of older trees was more negatively affected during drought. Therefore, these older/larger trees can be selected for commercial thinning, or can be released from competition, which can minimize the potential impacts of future droughts in black pine forests in Spain.

The promotion of mixed forests represents an adaptation strategy in forest management to cope with climate change. The mixing of tree species with complementary ecological traits may modify forest functioning regarding productivity, stability, or resilience against disturbances. Litter decomposition is an important process for global carbon and nutrient cycles in terrestrial ecosystems, also affecting the functionality and sustainability of forests. Decomposition of mixed-leaf litters has become an active research area because it mimics the natural state of leaf litters in most forests. Thus, it is important to understand the factors controlling decomposition rates and nutrient cycles in mixed stands. In this study, we conducted a litter decomposition experiment in a Scots pine and European beech mixed forest in the province of Navarre (north of Spain). The effects of forest management (i.e., different thinning intensities), leaf litter types, and tree canopy on mass loss and chemical composition in such decomposing litter were analysed over a period of three years. Higher decomposition rates were observed in leaf litter mixtures, suggesting the existence of positive synergies between both pine and beech litter types. Moreover, a decomposition process was favoured under mixed-tree canopy patches. Regarding thinning treatments significant differences on decomposition rates disappeared at the end of the study period. Time influenced the nutrient concentration after the leaf litter incubation, with significant differences in the chemical composition between the different types of leaf litter. Higher Ca and Mg concentrations were found in beech litter types than in pine ones. An increase in certain nutrients throughout the decomposition process was observed due to immobilization by microorganisms (e.g., Mg in all leaf litter types, K only in beech leaves, P in thinned plots and under mixed canopy). Evaluating the overall response in mixed-leaf litters and the contribution of single species is necessary for understanding the litter decomposition and nutrient processes in mixed-forest ecosystems.

Droughts chronically alter resource availability in forest ecosystems. The increased frequency and severity of such extreme climate events challenge the acclimation potential of tree species especially across the drought-prone Mediterranean region. Pinus nigra is a widely distributed tree species in the Mediterranean region and considered vulnerable to extreme droughts. We used a 1000 km latitudinal gradient from northern Morocco to north-eastern Spain incorporating four regions (Edge-South, Core-South, Core-North and Edge-North) and including different P. nigra provenances. We aim to identify the climate and forest structure related drivers that influence tree radial growth (BAI, basal area increment). We developed statistical models for BAI by incorporating the potential effects of climate and forest structure (diameter and age distributions). Then, we forecasted the future growth of P. nigra forests during the 21st century considering the emission scenario A2 with an expected increase of +2.7 °C at the end of this century. Our results showed large variability across P. nigra populations in terms of environmental conditions, forest structure, and growth. The northernmost P. nigra populations, subjected to wetter and cooler conditions were those presenting the lowest BAI (4.9 cm2), whereas the southernmost P. nigra populations subjected to drier and warmer conditions presented the highest BAI values (11.5 cm2). Pinus nigra growth was enhanced by high spring precipitation, but this positive effect was probably modulated by forest structure. Temperature explained a higher proportion of the BAI variance than precipitation, with warmer summer conditions decreasing growth. Growth projections forecasted a decline in BAI (from 9.6 to 7.0 cm2) across all ecological regions starting around the mid-21st century but being lower in Edge-North populations compared to the other populations. Our study provides quantitative knowledge related to how P. nigra populations have been growing across four distinctive ecological regions. We also provide a forecasting tool that incorporates both climate and stand structure related information to project dynamics in tree populations.

The intentional movement of tree genotypes, or assisted migration, is an operational approach proposed to adapt forest management to climate change. Assisted migration assumes that tree populations are locally adapted to environmental conditions, but this fact should be tested specifically. In this study, both a reciprocal transplant and a common garden experiment were carried out to test local adaptation to variable environmental conditions of seedling emergence and survival of the tree species Pinus nigra. Reciprocal sowing experiments involved the cross-sowing of four seed origins among four destination habitats, located in high- and low-altitude sites within central and peripheral populations of Pinus nigra. Evidence of local adaptation was taken to be a significant destination x origin interaction. Then, the possibility of local adaptation was further evaluated under the ‘‘local versus foreign’’ and the ‘‘home versus away’’ criteria. Results showed negative evidence of local adaptation to the emergence and survival environment faced by Pinus nigra seedlings, which would reduce the utility of assisted migration as an effective tool to adapt forests to ongoing climate change.

La gestión de bosques mixtos se ha convertido en una estrategia de adaptación para reducir los riesgos relacionados con el cambio climático. A su vez, los modelos ecológicos pueden ser una herramienta útil para el estudio del crecimiento y la productividad de dichas masas. En este trabajo se presenta una evaluación de la capacidad del modelo híbrido “FORECAST Climate” de simular el estrés hídrico y la productividad en bosques mixtos de pino silvestre y haya en Navarra (norte de España) y su interacción con distintos niveles de densidad de regenerado. En el estudio se incluyeron tres escenarios climáticos para comprobar la capacidad del modelo para simular los flujos de agua bajo condiciones de cambio climático. Las estimaciones del modelo tanto de estrés hídrico como de acumulación de biomasa se mostraron sensibles a la reducción en la densidad de regeneración inicial. Los resultados indicaron que el modelo muestra la suficiente capacidad para simular los efectos de la competencia entre especies en la mortalidad de árboles en bosques mixtos y estimar variables relacionadas con los flujos hídricos. Por un lado, los efectos más significativos de la densidad del rodal sobre la disponibilidad hídrica aparecen durante la primera etapa de desarrollo, mientras que, por otro, el estrés hídrico es mayor en el caso del haya, aunque la reducción de la competencia podría compensar dicho aumento. Las implicaciones de este trabajo para la gestión adaptativa de bosques mixtos sugieren el actual control de la densidad para que los efectos acumulativos sean significativos en próximas décadas. Management of mixed forest has become an adaptation strategy to reduce the risks related to climate change. At the same time, ecological models can be a useful tool for studying the growth and productivity of these stands. This work introduces an assessment of the capacity of the ‘FORECAST Climate’ hybrid model to simulate water stress and productivity in mixed Scots pine and beech forests in Navarre (northern Spain), and their interaction with different levels of regeneration density. The study included three climate scenarios to test the model capacity to simulate water flows under climate change conditions. Model estimations of water deficit and biomass accumulation were sensitive to the reduction in the initial regeneration density rates. The results indicated that the model shows sufficient capacity to simulate the effects of competition between species on tree mortality in mixedwoods, and to estimate the variables related to water flows. On the one hand, the most significant effects of stand density on water availability occur during the first stage of development, while on the other hand, water stress is greater in the case of beech, although the reduction in competition could offset this increase. The implications of this work for adaptive management of mixed forests suggest applying density control soon in order to have significant cumulative effects in coming decades. Este trabajo ha sido financiado por medio de los proyectos AGL2012-33465 del Ministerio de Economía y Competitividad, y el proyecto CIG-2012-326718-ECOPYREN3 de las Acciones Marie Curie del 7º Programa Marco de la Comisión Europea.

International audience; The study tested the hypothesis that future changes in the composition of tree communities, as predicted by species distribution models, could already be apparent in the current regeneration patterns of three pine species (Pinus pinaster, P. nigra and P. sylvestris) inhabiting the central-eastern mountains of Spain. We carried out both an observational study and a seed-sowing experiment to analyze, along an altitudinal and latitudinal gradient, whether recent recruitment patterns indicate an expansion of P. pinaster forests to the detriment of P. nigra ones in the low-altitude southern sites of these mountains; or whether P. sylvestris is being replaced by P. nigra in the high-altitude sites from the same area. The observational study gathered data from 561 plots of the Spanish National Forest Inventory. The seed-sowing experiment tested the effects of irrigation and stand basal area on seedling emergence and survival. Data were analyzed by means of Generalized Linear Models and Generalized Linear Mixed Models. Regeneration of the three pine species responded similarly to the explicative factors studied, but the density of tree seedlings and saplings exhibited a wide spatial heterogeneity. This result suggested that a mosaic of site- and species-specific responses to climate change might mislead model projections on the future forest occupancy of tree species. Yet, we found no indications of neither an expansion nor a contraction of the near future forest occupancy of the tree species studied.

Forest sustainability depends on reliable tree regeneration but seedling survival is affected by climate change and disturbance. Based on seed introduction experiments, we compared recruitment of native pine species in central Spain in totally burned, thinned, and dense stands of Spanish black pine ( Pinus nigra Arn. ssp salzmannii ). Seed sources included P. nigra from three elevations bracketing its range, as well as the fire-adapted species maritime pine ( P. pinaster ) and the mesic-adapted species Scots pine ( P. sylvestris ). In addition, seed predation effect was also tested. Small and large herbivores as well as rodents were excluded using cages. All seeds had high viability in laboratory germination tests and all displayed high emergence in field trials. However, unprotected seedlings and those that emerged in thinned or dense stands did not survive the first growing season. Surviving seedlings were only found in totally burned stands. Protected P. nigra seedlings had the highest survival, reaching 23%. Protected seedlings of P. pinaster and P. sylvestris averaged 11.5% and 10.9%, respectively. Unprotected seedlings of any species had less than 2% survival. The unexpected result of higher mortality under a sheltering canopy compared with open post-wildfire conditions may be due to wetter spring during the experiment. Overall, the results indicate that native species currently still regenerate best within the environment of their present range, even though future climate or fire disturbance may lead to distributional shifts. Protection is necessary for successful pine regeneration in the study region.

El cambio climático, la expansión urbanística o el aumento del uso recreativo en zonas forestales están aumentando la probabilidad de ocurrencia de incendios forestales. Las comunidades rurales pueden afrontar la oportunidad de combinar actividades silvícolas para reducir el riesgo de incendios con el desarrollo energético basado en el aprovechamiento de la biomasa forestal generada. Para demostrar la viabilidad de este tipo de gestión, se ha creado una herramienta informática demostrativa de apoyo a la toma de decisiones. Mediante la modificación y calibración del modelo ecológico FORECAST, se simularon las condiciones de diferentes localidades y especies forestales de Navarra. Sobre dichas simulaciones, se ha desarrollado la interfaz de usuario de esta calculadora (Fire Interface Rural Screening Tool for Heating: FIRST-Heat Navarra), que pretende estimar la sostenibilidad ecológica y socio-económica del uso de la biomasa forestal a nivel local. Esta herramienta se muestra capaz de simular los efectos del cambio en las condiciones de crecimiento del bosque mediante un modelo ecológico dinámico. También presenta la capacidad de integrar, resumir y comunicar de forma efectiva el último conocimiento científico sobre ecología forestal, y el conocimiento técnico, económico y social sobre la tecnología de calefacción de distrito a partir de biomasa. Climate change, urban expansion or increased recreational use in forest areas are increasing the likelihood of forest fires. Rural communities can take advantage of the opportunity to combine silvicultural activities to reduce fire risks with energy development based on the use of the forest biomass generated. In order to demonstrate the feasibility of this type of management, a computer tool has been created to support decision-making. The conditions of different locations and forest species in Navarre (Spain) were simulated by modifying and calibrating the FORECAST ecological model. On these simulations, the user interface of this calculator (Fire Interface Rural Screening Tool for Heating: FIRST-Heat Navarra) has been developed, aiming to estimate the ecological and socio-economic sustainability of the use of forest biomass at local level. This tool is able to simulate the effects of growth changes in forests through a dynamic ecological model. It features the ability to effectively integrate, synthesize and communicate the latest scientific knowledge on forest ecology, but also technical, economic and social knowledge about district heating technology from biomass.

Density is an important wood mechanical property and an indicator of xylem architecture and hydraulic conductivity. It can be influenced by forest management and climate. We studied the impact of thinning and climate variables on annual stem radial growth (ring width and ring density, and their earlywood and latewood components) in two contrasting Scots pine (Pinus sylvestris L.) stands in northern Spain (one continental, one Mediterranean). At each site, three thinning regimes (control or T0, removing 20% basal area or T20, and removing 30% or T30) were randomly applied to nine plots per site (three plots per treatment) in 1999. Thinning was repeated at the Mediterranean site in 2009 (increasing thinning intensity in T30 to 40%). Eight trees per plot were cored in spring 2014. Second thinning at the Mediterranean site and first thinning at the continental site generally caused significantly wider ring (RW), earlywood (EW) and latewood (LW) widths, although no differences between T20 and T30/40 were found, supporting in part the common observation that radial growth is enhanced following thinning as competition for water and nutrients is reduced. At the Mediterranean site, values of latewood density (LD) and maximum density (Dmax) relative to pre-thinning conditions were significantly lower in T0 than in T30. However, at the continental site, relative changes of ring density (RD) and LD were significantly higher in T0 than in T20 and T30. Climate significantly affected not only RW but also RD, with significant RD drops during or right after unusually warm-dry years (e.g., 2003, 2011), which were characterized by LD reductions between 5.4 and 8.0%. Such RD decreases were quickly followed by recovery of pre-drought density values. These results indicate trees temporarily reduce LD as a way to enhance hydraulic conductivity during dry summers. However, climate effects on wood density were site-dependent. We also detected that the thinning effect was not intense enough to prevent drought-induced changes in wood density by altering water availability, but it could help to reduce wood properties fluctuations and therefore maintain more homogeneous wood mechanic features., E.G.A. was funded through a Spanish Predoctoral Research Grant (ref. BES-2013-066705). Funding for this research has been provided by the Spanish Ministry of Economy and Competitiveness (project AGL2012-33465), which also funded Y.-H.L. J.A.B. was funded through a Ramón y Cajal contract (ref. RYC-2011-08082) and a Marie Curie Action (ref CIG-2012-326718-ECOPYREN3), which also funded D.C.-P. Funds to cover the costs of publishing in open access were provided by the OpenAIRE pilot program of the European Union 7th Framework Programme

Forest biomass, the most ancient of fuels, is again in the center of renewable energy production. This chapter provides an introductory view of the main factors that condition the ecological sustainability of this energy source. The basic concepts of ecological sustainability, ecological rotation, and ecological thresholds (among others) are presented. The state of the art on approaches to assess the sustainability of forest biomass production for heat and electricity is discussed, and tools available for decision-makers to evaluate the sustainability of forest biomass production and management are described. This chapter then describes the main advantages and drawbacks of forest certification, growth and yield tables, and ecological models in relationship to their use in sustainable forest management for biomass and energy production. This research was funded by a Government of Navarre’s (Spain) research action (ref. PI037 InFORest, which also funded David Candel-Pérez), and a project funded by the Spanish Ministry of Economy and competitiveness (ref. AGL2016-76463-P TIMENUTRIENT). Yueh-Hsin Lo was funded through a Marie Skłodowska-Curie Action (ref. MSCA-IF-2014-EF656810-DENDRONUTRIENT). The FP7 post-grant Open Access publishing funds pilot funded the publication of this manuscript.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Current decreasing precipitation and increasing temperatures promote the likelihood of extreme drought events and may alter the recruitment capacities of tree species. Spanish black pine (Pinus nigra ssp. salzmannii) initial recruitment is being one of the most affected pine species by changing conditions with alterations in the future species distribution. In this context, a cross-exchange experiment was implemented using an outdoor nursery located in a warmer and drier location for testing different Spanish Black pine seeds and soil provenance combinations in relation to early recruitment and initial seedling growth. Soil and seeds were collected at a high (HA, 1641 m.a.s.l.) and low (LA, 1099 m.a.s.l.) altitude in Cuenca Mountains (Spain). Then, a cross-sown experiment using HA and LA soils and seeds was set up in an outdoor nursery, which is located in Albacete (704 m.a.s.l.). Soil quality, seedling emergence, seedling survival, initial seedling growth and total seedling dry mass were measured after one year. We found higher seed emergence and seedling survival by combining LA soil with LA seeds or HA soil with HA seeds. Seedlings from LA seeds with both soil origins and seedlings from HA seeds with LA soils allocated more biomass to roots than seedlings from HA sites growing in HA soils under drier and warmer conditions. These results support the idea that autochtonous provenances have the potential to adapt to changing climatic conditions in their habitats.

La disminución de las precipitaciones y el incremento de la temperatura registrados en las últimas décadas, junto con el aumento de la probabilidad de ocurrencia de eventos extremos de sequía, hacen muy probable una mayor vulnerabilidad de las poblaciones forestales mediterráneas. Sin embargo, el impacto de los diferentes escenarios climáticos previstos para el futuro sobre el crecimiento de las especies forestales ha sido poco desarrollado. Analizamos el patrón de crecimiento del pino laricio (Pinus nigra Arn. ssp salzmannii) a lo largo de un gradiente altitudinal en la Serranía de Cuenca (este de la Península Ibérica). Estos datos, expresados como incremento de área basal, se usaron para ajustar modelos lineales mixtos de clima-crecimiento. A partir de estos modelos se realizó una predicción del crecimiento de los individuos en el futuro, usando como variables independientes los modelos de cambio climático CGCM2 y ECHAM4 y los escenarios de emisiones A2 y B2 del IPCC, disponibles a escala regional para el área de estudio. Hipotetizamos que las poblaciones situadas a menor altitud tendrán una menor tasa de crecimiento medio y serán las más vulnerables al aumento de la aridez climática. Los datos climáticos locales y regionales registrados durante el siglo XX, así como los modelos de clima futuro considerados (2011-2070), coinciden en mostrar una tendencia de calentamiento y un aumento de los episodios de sequía extrema. En las poblaciones de P. nigra situadas a menor altitud la tasa de crecimiento medio no fue inferior pero las correlaciones entre temperatura y crecimiento fueron siempre negativas y por tanto, los modelos predicen para estas poblaciones una drástica reducción del crecimiento y su virtual desaparición. Sin embargo, las poblaciones más envejecidas y las situadas en su límite superior altitudinal mostraron predicciones similares o ligeramente inferiores al crecimiento actual, a pesar de mostrar la menor tasa de crecimiento medio. Las muestras procedentes del centro del rango altitudinal mostraron tendencias positivas de crecimiento, ofreciendo una correlación positiva con las temperaturas de invierno y otoño. Los resultados permiten concluir que los efectos del cambio climático sobre P. nigra serán probablemente heterogéneos, existiendo poblaciones con alto riesgo de declive, poblaciones que aumentarían su crecimiento potencial en el futuro y poblaciones que podrían persistir de forma similar a la actualidad. Current decreasing precipitation and increasing temperatures, together with the growing likelihood of extreme drought events, may heighten the vulnerability of several tree populations in the Mediterranean. However, the effects of expected climate change on tree growth are poorly understood. We analysed growth pattern in black pine (Pinus nigra) across an altitudinal gradient in the Cuenca Mountain Range (central-eastern Spain). Data on the increment of tree basal area were used to fit climate-growth models. Then, we forecasted future tree growth using as predictors the climate data from CGCM2 and ECHAM4 models, and the IPCC emission scenarios A2 and B2, at a regional scale. We hypothesized that the populations showing the lowest mean growth rates are the most vulnerable to impending climate change. Local climatic data spanning the 20th century, as well as the future (2011-2070) climate projections, yielded a warming trend and increasing extreme drought events. Low-elevation P. nigra stands did not yield the lowest growth rate but showed negative correlations among temperature and climate, and therefore, growth models forecasted growth decline and virtual extinction of these populations. Nonetheless, old-growth and higher-elevation stands yielded steady and slightly declining growth predictions, despite they showed very low mean growth rates. Core populations showed positive growth trends related to positive correlations with winter and autumn temperatures. Our results allow to expect contrasting climate change effects on P. nigra, where some populations are likely to decline, others populations might improve their potential growth, and some old-growth stands could endure long-term persistence in a similar manner as they currently do. Este trabajo ha sido financiado por la Junta de Comunidades de Castilla-La Mancha [POII10-0112-7316].

The aim of this work was to examine the effect of pine forests on the soil microbial community along an altitudinal gradient in the Cuenca Mountains, Spain. Six experimental forest areas and two tree diversity levels (monospecific and mixed pine forest) were selected according to the following types: (i) at lower altitudes (up to 960 m above sea level), a monospecific Spanish black pine (Pinus nigra Arn. ssp salzmannii) forest stand and a mixed forest stand (maritime pine (Pinus pinaster Ait.) and Spanish black pine); (ii) at medium altitudes (up to 1350 m), a monospecific Spanish black pine forest stand and a mixed forest stand (Scots pine (Pinus sylvestris L.) and Spanish black pine); and (iii) above 1670 m, a monospecific Spanish black pine forest stand and a mixed forest stand (Scots pine and Spanish black pine). Soil moisture and temperature and different forest stand variables such as tree species composition, tree height, basal area and shrub cover were measured. Physicochemical soil properties including texture, pH, carbonates, total organic carbon, organic matter, electrical conductivity, N, P, soil enzyme activities, soil respiration and soil microbial biomass carbon were analysed at the selected forest areas and tree diversity levels. Results showed that soil moisture and temperature differed significantly across the altitudinal gradient. Carbon:nitrogen ratio, total carbonates, total organic carbon, phosphorus and total N values also differed at each experimental area but tree diversity level was not an influential factor. Soil respiration, microbial biomass carbon and enzyme activities tended to be less at low altitudes whereas no differences were found between monospecific and mixed pine forests across the altitudinal gradient. This work suggests that the soils of the Cuenca Mountains may be more sensitive to some physical and chemical site-specific aspects such as soil temperature and moisture than changes in tree stand composition (when considering only pine species). In addition, differences in soil physicochemical properties found at each experimental area may also act as additional factors for regulating enzymatic activities.

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 130 years 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.

This study aimed to investigate the effects that stand age and forest structure have on microbiological soil properties, enzymatic activities and nutrient content. Thirty forest compartments were randomly selected at the Palancares y Agregados managed forest area (Spain), supporting forest stands of five ages; from 100 to 80years old to compartments with trees that were 19-1years old. Forest area ranging from 80 to 120years old and without forest intervention was selected as the control. We measured different soil enzymatic activities, soil respiration and nutrient content (P, K, Na, Mg, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb and Ca) in the top cm of 10 mineral soils in each compartment. Results showed that the lowest forest stand age and the forest structure created by management presented lower values of organic matter, soil moisture, water holding capacity and litterfall and higher values of C/N ratio in comparison with the highest forest stand age and the related forest structure, which generated differences in soil respiration and soil enzyme activities. The forest structure created by no forest management (control plot) presented the highest enzymatic activities, soil respiration, NH4(+) and NO3(-). Results did not show a clear trend in nutrient content comparing all the experimental areas. Finally, the multivariate PCA analysis clearly clustered three differentiated groups: Control plot; from 100 to 40years old and from 39 to 1year old. Our results suggest that the control plot has better soil quality and that extreme forest stand ages (100-80 and 19-1years old) and the associated forest structure generates differences in soil parameters but not in soil nutrient content.

Shrub cover has visible effects on Pinus nigra Arn ssp. salzmannii seedling emergence, but only in drier years under moderate basal area (25–30 m 2 ha −1 ). In the wetter year, shrub cover favours seedling survival without basal area influence. Shrubs are known to favour tree seedling recruitment in difficult climate environments, but facilitation may prove optimal in intermediate-level rather than harsh conditions, although such an effect remains to be specified. The main aim of this work was to evaluate the influence of stand basal area (15–20, 25–30 and 35–40 m2 ha−1) × with/without shrub facilitation on seedling recruitment in Spanish black pine (P. nigra Arn. ssp. salzmannii), which has been struggling to regenerate natural forests since the late nineteenth century, sometimes jeopardizing stand persistence. In spring 2012 and 2013, 72 subplots of 25 × 25 cm were established in Cuenca Mountains, central-eastern Spain (four replicates, each counting three subplots × 2 shrub conditions, both under and outside shrub cover, in three different stand basal areas). All plots were randomly distributed at least 500 m apart within each stand basal area. Each subplot comprised 20 seeds previously collected at the experimental forest site. Seedling emergence and early survival were monitored every month in 2012 and 2013. Seedling recruitment was strongly influenced by year. The year 2012 was drier and warmer than 2013. In 2012, seedling emergence was higher under the 25–30-m2 ha−1 stand basal area and favoured by shrub cover, whereas in 2013, neither basal area nor shrub cover had significant effects. No seedling survived the summer in 2012. Higher seedling survival was found outside shrub cover at every basal area interval in 2013 with living seedlings until the end of the year. Climate is the main factor controlling seedling emergence and survival. Shrub facilitation has visible effects on seedling emergence, but only in drier years under moderate light (moderate basal area). Facilitation collapses at extreme stress levels. In wetter years, shrub cover does not promote seedling survival and basal area is not an influential factor.

Prescribed fire has been widely used as a fuel reduction tool and silvicultural treatment in Mediterranean forest ecosystems. However, other than the fact that fire may alter microsite conditions, little is known about the impact of prescribed burning on the natural regeneration of Spanish black pine (Pinus nigra Arn. ssp. salzmanii). In this study, we compared the effects of post dispersal seed predation, prescribed burning and vegetation treatment (brushing) on initial recruitment of Spanish black pine in both pure and mixed (with maritime pine, Pinus pinaster Ait.) stands during one year (2014) in the Cuenca Mountains (central-eastern Spain). Seedling recruitment in both pure and mixed stands was negatively affected by prescribed burning but was improved by the vegetation treatment. Post dispersal seed protection was an important factor for seed emergence and early survival success. Prescribed burning must be carefully planned in forest management aimed at regeneration. The influence of fire on natural regeneration should be taken into account for developing guidelines for the management of black pine forests, mainly in the Mediterranean Basin. © 2016 Elsevier B.V.

The management of maritime pine in fire-prone habitats is a challenging task and fine-scale population genetic analyses are necessary to check if different fire recurrences affect genetic variability. The objective of this study was to assess the effect of fire recurrence on maritime pine genetic diversity using inter-simple sequence repeat markers (ISSR). Three maritime pine ( Pinus pinaster Ait.) populations from Northern Portugal were chosen to characterize the genetic variability among populations. In relation to fire recurrence, Seiros population was affected by fire both in 1990 and 2005 whereas Vila Seca-2 population was affected by fire just in 2005. The Vila Seca-1 population has been never affected by fire. Our results showed the highest Nei's genetic diversity (He = 0.320), Shannon information index (I = 0.474) and polymorphic loci (PPL = 87.79%) among samples from twice burned populations (Seiros site). Thus, fire regime plays an important role affecting genetic diversity in the short-term, although not generating maritime pine genetic erosion.

Eight Pinus nigra Arn. populations from Southern Spain and Northern Morocco were examined using inter-simple sequence repeat markers to characterize the genetic variability amongst populations. Pair-wise population genetic distance ranged from 0.031 to 0.283, with a mean of 0.150 between populations. The highest inter-population average distance was between PaCU from Cuenca and YeCA from Cazorla, while the lowest distance was between TaMO from Morocco and MA Sierra Magina populations. Analysis of molecular variance (AMOVA) and Nei’s genetic diversity analyses revealed higher genetic variation within the same population than among different populations. Genetic differentiation (Gst) was 0.233. Cuenca showed the highest Nei’s genetic diversity followed by the Moroccan region, Sierra Magina, and Cazorla region. However, clustering of populations was not in accordance with their geographical locations. Principal component analysis showed the presence of two major groups—Group 1 contained all populations from Cuenca while Group 2 contained populations from Cazorla, Sierra Magina and Morocco—while Bayesian analysis revealed the presence of three clusters. The low genetic diversity observed in PaCU and YeCA is probably a consequence of inappropriate management since no estimation of genetic variability was performed before the silvicultural treatments. Data indicates that the inter-simple sequence repeat (ISSR) method is sufficiently informative and powerful to assess genetic variability among populations of P. nigra.