Maritime Pine Stands Research Articles

Unraveling the shifts in the belowground microbiota and metabolome of Pinus pinaster trees affected by forest decline.

Pinus pinaster Aiton (maritime pine) stands are suffering a generalized deterioration due to different decline episodes throughout all its distribution area. It is well known that external disturbances can alter the plant associated microbiota and metabolome, which ultimately can entail the disruption of the normal growth of the hosts. Notwithstanding, very little is known about the shifts in the microbiota and the metabolome in pine trees affected by decline. The aim of our work was to unravel whether bacterial and fungal communities inhabiting the rhizosphere and root endosphere of P. pinaster trees with symptoms of decline and affected by Matsucoccus feytaudi in the National Park of Sierra Nevada (Granada, Spain) showed alterations in the structure, taxonomical profiles and associative patterns. We also aimed at deciphering potential changes in the rhizosphere and root metabolome. Trees infected by M. feytaudi and healthy individual harbored distinct microbial communities at both compositional and associative patterns. Unhealthy trees were enriched selectively in certain plant growth promoting microorganisms such as several ectomycorrhizal fungi (Clavulina) and Streptomyces, while other beneficial microorganisms (Micromonospora) were more abundant in unaffected pines. The rhizosphere of unhealthy trees was richer in secondary metabolites involved in plant defense than healthy pines, while the opposite trend was detected in root samples. The abundance of certain microorganisms was significantly correlated with several antimicrobial metabolites, thus, being all of them worthy of further isolation and study of their role in forest decline.

Trade-offs and management strategies for ecosystem services in mixed Scots pine and Maritime pine forests

AbstractMixed forests are increasingly recognized for their resilience to climate change and enhanced ecosystem services (ESs) provision, making them a focal point for sustainable forest management strategies. This study examines the trade-offs in ESs provision between pure and different proportions of mixed stands of Scots pine (Pinus sylvestris L.) and Maritime pine (Pinus pinaster Ait.) in the Northern Iberian Range, Spain. Using the SIMANFOR simulation platform, we evaluated various silvicultural scenarios developed to obtain different ESs such as carbon sequestration, timber and mushroom yields. Our findings reveal that ESs provision varies depending on the forest type (pure or mixed) and the mixture proportion, following different trends on each ES. The initial species proportions and their maintenance were less critical than the management approach itself, which significantly influenced ESs outcomes. Focusing solely on individual ESs can lead to trade-offs, as highlighted by our study on silviculture focused on large saw timber yields. However, adopting a balanced approach that considers multiple ESs can mitigate these trade-offs. Our findings underscore the effectiveness of this approach in maximizing yields of mushrooms, sequestered carbon, and small saw timber. This research provides valuable insights for forest managers aiming to balance productivity and sustainability in ESs provision, providing strategies to maximize compatible ESs effectively.

Height increment patterns in Pinus pinaster seedlings emerging in naturally regenerated gaps

Abstract The group selection cutting system provides a promising technique for transforming monospecific even-aged stands into uneven-aged, mixed stands. However, this system has scarcely been used to regenerate Mediterranean shade-intolerant species. In this study, we analyze the height increment patterns of Pinus pinaster seedlings emerging in naturally regenerated gaps. P. pinaster is a shade-intolerant pine species distributed throughout the Mediterranean basin. An experimental trial was established in a 50-year-old P. pinaster (maritime pine) plantation located in the mountains of central Spain. Gaps of two different sizes (diameter equal to 1.5 and 2.5 times the dominant height of the stand, 26 and 44 m, respectively) were opened during winter 2017–18. A total of 531 subplots with a 1-m radius were installed in spring 2018, distributed within the gaps as well as in control plots adjacent to the gaps. Seedlings were tagged individually and variables including height, along with other ecological variables, were collected twice a year (in spring and autumn), providing six time intervals for the development of our models. We applied seemingly unrelated regression to analyze the height growth in this polycyclic species, allowing us to model spring and autumn height increments at the same time. Our results showed that seedling height growth depended on the silvicultural treatment, meteorological conditions during the spring growth season, inter-specific scrub competition, position within the gap, and seedling characteristics, such as the ontogenetic development or the size of the seedling itself. This work, along with germination and survival analysis, aims to provide a holistic perspective on the suitability of the group selection cutting system to regenerate maritime pine stands, taking into account current and future climate change scenarios.

Unraveling the Effect of Fire Seasonality on Fire-Preferred Fuel Types and Dynamics in Alto Minho, Portugal (2000–2018)

Socio-demographic changes in recent decades and fire policies centered on fire suppression have substantially diminished the ability to maintain low fuel loads at the landscape scale in marginal lands. Currently, shepherds face many barriers to the use of fire for restoring pastures in shrub-encroached communities. The restrictions imposed are based on the lack of knowledge of their impacts on the landscape. We aim to contribute to this clarification. Therefore, we used a dataset of burned areas in the Alto Minho region for seasonal and unseasonal (pastoral) fires. We conducted statistical and spatial analyses to characterize the fire regime (2001–2018), the distribution of fuel types and their dynamics, and the effects of fire on such changes. Unseasonal fires are smaller and spread in different spatial contexts. Fuel types characteristic of maritime pine and eucalypts are selected by seasonal fires and avoided by unseasonal fires which, in turn, showed high preference for heterogeneous mosaics of herbaceous and shrub vegetation. The area covered by fuel types of broadleaved and eucalypt forest stands increased between 2000 and 2018 at the expense of the fuel type corresponding to maritime pine stands. Results emphasize the role of seasonal fires and fire recurrence in these changes, and the weak effect of unseasonal fires. An increase in the maritime pine fuel type was observed only in areas burned by unseasonal fires, after excluding the areas overlapping with seasonal fires.

The Importance of Using Permanent Plots Data to Fit the Self-Thinning Line: An Example for Maritime Pine Stands in Portugal

Density-dependent mortality occurs in the evolution of even-aged populations when these approach crown closure age. This density-dependent mortality is regulated by the so-called “3/2 power law of self-thinning” that assumes a constant slope for the line relating the log of stand density with the log of the average tree size, the self-thinning line or maximum size–density relationship, MSDR. A good estimate of the self-thinning line is therefore an essential component to any forest growth model. Two concepts for the MSDR have emerged: (1) a static upper limit for the species; and (2) a dynamic self-thinning line influenced by several factors (e.g., management techniques, site quality and/or genetics). The objective of this study was to estimate a new static self-thinning line based on the quadratic mean diameter at breast height (Reineke’s self-thinning line) for the generalized use in maritime pine growth models in Portugal. Data from 41 observations obtained in nine long-term permanent experimental trials of maritime pine species were carefully selected from a data set of 186 plots as being under self-thinning. Two methods were used: OLS and mixed linear models. An exploratory analysis on the impact of each environmental variable on the slope and intercept of the self-thinning line led to the selection of a subset of environmental variables later used in an all possible regressions algorithm to find the subsets leading to the lowest values of Akaike information criterion (AIC). The OLS procedure showed that the differences between the plots could be explained by site index, by climate variables (e.g., evaporation or climatic indices) and the use of more than one covariable slightly improved the fit. Nevertheless, the best MSDR line fitted with mixed linear models (ln N = 12.97158 − 1.83926 ln dg) having the plot random effect in the intercept, largely outperformed the best OLS model and is therefore recommended for generalized use in forest growth models.

The footprint of large wildfires on the multifunctionality of fire-prone pine ecosystems is driven by the interaction of fire regime attributes

BackgroundMediterranean ecosystems dominated by Pinus pinaster Ait. (maritime pine) are subject to a shift from fuel-limited to drought-driven fire regimes, characterized by an increasing wildfire extent, recurrence, and severity. Previous studies have not addressed the interacting effects of fire recurrence and severity on the ecosystem multifunctionality (EMF) of maritime pine forests, although complex relationships between such fire regime attributes are expected. Here, we evaluated the medium-term effects of fire recurrence and severity on the EMF response of unmanaged, native pine ecosystems dominated by Pinus pinaster in the western Mediterranean Basin. We considered four key ecosystem functions computed from functional indicators (carbon regulation, decomposition, soil fertility, and plant production), which were pooled into an EMF construct. The fire regime effects on the trade-offs and synergies between the considered ecosystem functions were also analyzed.ResultsMultiple ecosystem functions responded differentially to fire recurrence and severity. Fire recurrence had a strong effect on soil fertility, decomposition, and plant production functions. No significant effects of fire severity on any of the individual functions were detected. However, both fire regime attributes interacted to determine soil fertility and decomposition functions, suggesting that their performance is only impaired by fire severity when fire recurrence is low. The differing responses to the fire regime attributes among ecosystem functions fostered a significant EMF response to fire severity and its interaction with fire recurrence, indicating that the effect of fire severity on EMF was stronger under low fire recurrence scenarios, even when relationships between individual functions and fire severity were weak. Fire recurrence caused significant trade-offs between functions to emerge. However, these trade-offs were not strong enough to differ significantly from the intrinsic trade-offs (i.e., regardless of the fire regime) of maritime pine ecosystems.ConclusionsOur results indicated the need to use an integrative approach to assess the response of ecosystem functioning to the fire regime in maritime pine ecosystems. Adaptive management responses are necessary towards the minimization of repeated burnings and the reduction of the fuel load in unmanaged maritime pine stands of the western Mediterranean Basin with similar characteristics to those analyzed in this study.

Predicting forest stand attributes using the integration of airborne laser scanning and Worldview-3 data in a mixed forest in Turkey

The aim of this study is to examine the capability of the combined LiDAR/WorldView-3 data in estimating the plot-level stand attributes (stem number-N, mean diameter-D, mean height-H, basal area-BA and volume-V) in a complex forest located in the northwest of Turkey. Total 135 plots were measured to determine the forest attributes. Prediction models were developed at three levels which are: i) the general level for all stands (including all plots), ii) forest type level (coniferous forest, broad-leaved forest), and iii) tree species level (Black pine stands, Maritime pine stands, Oak stands, Mixed stands). Multiple Linear Regression (MLR) and Random Forest (RF) modelling approaches were tested to predict stand attributes. The MLR regression modelling showed that the stand attributes were estimated with R 2 ranging from 0.71 (N and V in Mixed) to 0.94 (H in Maritime pine) at tree species level, from 0.73 (BA in Broadleaved) to 0.95 (H in Conifer) at forest types level and from 0.77 (V) to 0.89 (H) at general level. The RF modelling indicated that the stand attributes were estimated with R 2 ranging from 0.69 (V in Mixed and Oak) to 0.94 (H in Maritime pine) at tree species level, from 0.72 (N in Broadleaved) to 0.95 (H in Conifer) at forest types level and from 0.81 (N and V) to 0.88 (D) at general level. The mean height had the highest prediction accuracy for almost all levels in both approaches. However, the stem number and basal area were generally estimated with the lower accuracies. The homogeneous coniferous stands provided the higher estimation accuracy than the broadleaved stands. Our results showed that the modelling approaches used here provide different performance for predicting different stand attributes. While the MLR approach performed better in estimating the stand attributes at the tree species level, the RF approach towards the general level provided higher accuracy estimation. In conclusion, the combination of aerial laser scanning and high resolution satellite data has high potential for predicting stand attributes in complex forest ecosystems.

Nitrogen accumulation in forest floors with introduced Pinus pinea and Pinus pinaster in dune site.

Introduced stone pine (Pinus pinea L.) and maritime pine (Pinus pinaster Aiton) stands were sampled 60years after plantation in Istanbul-Durusu (Terkos), Turkey. Sampling was conducted at four different developmental stages (mean diameter of trees at 1.3-m height (DBH) in stands: SDF = < 8cm, MDF = 8-20cm, LDF = 20-36cm, and UDF > 36cm), with 15 replicated sample plots for each species and developmental stage, for a total of 120 sample plots. The forest floor was sampled in 5 replications in each sample plot. The forest floor samples were divided into two layers: L + F (litter + fermentation) and H (humus), and the oven dry mass and nitrogen (N) content were determined. As a result, the masses of the total forest floor and of both layers were significantly different among the development stages with an increasing trend in maritime pine stands despite no significant difference found in the mass of the humus layer in stone pine stands. However, total forest floor accumulation significantly increased with the development stage (28-60 t/ha in stone pine and 17-64 t/ha in maritime pine). In both species, the N concentrations in the forest floor layers differed significantly among the development stages, and the N concentrations tended to increase as the development stage increased in the L + F layer, whereas a fluctuating trend was observed in the H layer. Although the N content of the humus layer of stone pine did not show a significant difference among the development stages, the N content in the total forest floor was determined to be 0.1-0.5 t/ha in maritime pine and 0.2-0.5 t/ha in stone pine. The relationship between the mean stand DBH and the N stock of the total forest floor was determined to have a higher correlation in maritime pine (R2 = 0.8) than stone pine (R2 = 0.4). In conclusion, the nitrogen concentrations and nitrogen contents of the forest floor were remarkably different in stands introduced with different tree species, indicating the accumulation of forest floor nitrogen.

Regeneration of Riparian and Maritime Pine Forests after a Large Wildfire on the Largest Public Forest of Portugal

Eighty-six percent of the largest Portuguese public forest, Leiria National Forest (Mata Nacional de Leiria—MNL), central west, was burned in a wildfire in October 2017. Most of the area was covered by maritime pine stands (Pinus pinaster Aiton) crossed by riparian forests along small-sized streams. This work aims to characterize the post-fire vegetation and evaluate its natural regeneration. Sampling was carried out c. 6 months after the fire in 28 plots distributed at pine stands (3.5 × 3.5 m2) and in 24 plots (5 × 20 m2) at stream channels and riverbanks. These latter surveys were repeated in 2019. Data include the floristic composition and cover data of pine stands and streams, and the number of pine seedlings. Six months after the fire, 60% and 93% of the pre-fire species were observed at streams and pine stands, respectively. Fire severity was not related to differences in flora composition, nor with species richness. Pine seedlings were significantly more abundant in pine stands &gt;60 years old compared to younger (&lt;25 y) stands, but no significant differences were observed in the regeneration of understory. On riparian landscapes, the germination and resprouting of invasive exotic species, such as Acacia sp., created dense vegetation formations with decreased native plant diversity and altered the ecosystem structure. Following large wildfires, such as the one in MNL, managers should prioritize preserving the natural regeneration potential in the soil and aerial seed banks.

Characterization of mixed and monospecific stands of Scots pine and Maritime pine: soil profile, physiography, climate and vegetation cover data

• Key messageThis document provides valuable environmental information about a triplets’ essay of Scots pine and Maritime pine in Spain. The dataset characterizes the soil profile (physicochemical parameters of organic and mineral horizons), climate, physiography, understory and overstory. Dataset access is athttps://doi.org/10.5281/zenodo.4384530and associated metadata is available athttps://metadata-afs.nancy.inra.fr/geonetwork/srv/fre/catalog.search#/metadata/21cca830-daf9-4913-9b5b-a185d77943d5

Can mixed pine forests conserve understory richness by improving the establishment of understory species typical of native oak forests?

A positive effect of mixed pine forests ( Pinus sylvestris L. and Pinus pinaster Ait.) on the understory richness and tree regeneration was observed with respect to monospecific stands. Understory species typical of the native Pyrenean oak forests in the Iberian Peninsula contribute to maintaining high understory richness in such mixed pine forests. The influence of stands characteristics on the understory in mixtures that combine coniferous tree species of the same genus deserves more study since they are frequent in Spain. To assess the effect of mixed versus monospecific stands of Pinus sylvestris L. and Pinus pinaster Ait. on the main tree species regeneration and understory species composition. Tree regeneration and understory species composition were inventoried in eighteen forest plots (6 triplets) in North-Central Spain. Each triplet consisted of two plots dominated either by Scots pine or Maritime pine and one mixed plot that contained both species. The basal area (%) of both Pinus species was the only characteristic of the stands that significantly influenced the understory composition and tree regeneration. Characteristic species of humid and temperate zones, including P. sylvestris regeneration, dominated in Scots pine stands, and typical species of well-drained Mediterranean areas, including P. pinaster regeneration, dominated in Maritime pine stands. In mixed stands, the highest regeneration of the native Pyrenean oak with respect to monospecific stands was accompanied by understory species typical of native oak forests that share the same regeneration niche. Mixed pine forests allow the development of understory species better than monospecific forests.

Size–Density Trajectory in Regenerated Maritime Pine Stands after Fire

Research Highlights: This study bridges a gap of knowledge about the maximum size–density trajectory for juvenile stands of maritime pine. The continuity of the trajectory along the development stages to maturity is assured with a straightforward approach providing support to determine optimum density along all the revolution periods for the species. Background and Objectives: Forest fire is a significant threat to forests in the Mediterranean regions, but also a natural disturbance that plays a vital role in the perpetuation of forest stands. In recent decades, there has been an increase of burnt area in maritime forests in Portugal, followed by an increased interest in managing the natural and usually abundant regeneration occurring after the fires. The gap in the knowledge of growth dynamics for juvenile stages, for these forest systems, currently constrains their correct management, for forest planning, particularly in determining the optimal densities. The study aims to identify the maximum attainable density trajectory at the early stages of development of the species that could support a non-empirical definition of silvicultural prescriptions and thinning decisions, along the revolution. Materials and Methods: A representative data set collected in stands regenerated after fire supports the analysis of the maximum size–density trajectory for the species. Results: The maximum size–density trajectory for the juvenile stands deviates from the expected trajectory defined in the self-thinning line published for the species. Significant deviation occurs at the lower end of the line, indicating the need for a reevaluation of the existing self-thinning line. We propose a new self-thinning model for the species that explicitly considers the behavior of size–density for juvenile stands. The new model assures a logical continuity for the trajectory from the young stages of development to maturity. Conclusions: The proposed model based on the maximum attainable size–density trajectory provides ecological-based support to define silvicultural guidelines for management of the species.

Predicting Mushroom Productivity from Long-Term Field-Data Series in Mediterranean Pinus pinaster Ait. Forests in the Context of Climate Change

Long-term field-data series were used to fit a mushroom productivity model. Simulations enabled us to predict the consequences of management and climate scenarios on potential mushroom productivity. Mushrooms play an important ecological and economic role in forest ecosystems. Human interest in collecting mushrooms for self-consumption is also increasing, giving forests added value for providing recreational services. Pinus pinaster Ait. is a western Mediterranean species of great economic and ecological value. Over 7.5% of the total European distribution of the species is found on the Castilian Plateau in central Spain, where a great variety of mushrooms can be harvested. The aim of this study was to model and simulate mushroom productivity in Maritime pine (Pinus pinaster Ait.) ecosystems in northern Spain under different silvicultural and climatic scenarios. A mixed model was fitted that related total mushroom productivity to stand and weather variables. The model was uploaded to the SiManFor platform to study the effect of different silvicultural and climatic scenarios on mushroom productivity. The selected independent variables in the model were the ratio between stand basal area and density as a stand management indicator, along with precipitation and average temperatures for September and November. The simulation results also showed that silviculture had a positive impact on mushroom productivity, which was higher in scenarios with moderate and high thinning intensities. The impact was highly positive in wetter scenarios, though only slightly positive and negative responses were observed in hotter and drier scenarios, respectively. Silviculture had a positive impact on mushroom productivity, especially in wetter scenarios. Precipitation had greater influence than temperature on total mushroom productivity in Maritime pine stands. The results of this paper will enable forest managers to develop optimal management approaches for P. pinaster forests that integrate Non-Wood Forest Products resources.

Fire-severity mitigation by prescribed burning assessed from fire-treatment encounters in maritime pine stands

Maritime pine (Pinus pinaster Ait.) stands are prone to high-intensity fire. Fuel treatments lessen potential fire behaviour and severity, but evidence of their effectiveness when tested by wildfire is extremely scarce in Europe. We assess the longevity of prescribed burning in maritime pine plantations in decreasing fire severity. Heights of crown scorch and stem-bark char were measured in treated and untreated adjacent areas after fire-treatment encounters in Portugal, Italy, and Australia. Treatment effect was quantified as the log-transformed ratio between prescribed-burned and untreated fire-severity data. Linear mixed modelling indicated that for typical wildfire conditions, the effect of prescribed burning in crown scorch height lasts 2–6 years. The persistence of prescribed burning benefits is higher for fire control operations than for fire-severity mitigation. Regression tree analysis of data from one wildfire highlighted the roles of wind direction, topography, and stand height in explaining variability in fire severity. A 4-year interval between prescribed burning treatments in maritime pine stands is recommended in general, depending on site quality and stand age and structure. Improved fuel-consumption prescriptions and monitoring procedures are advisable to foster prescribed-burning effectiveness and its evaluation.

Ecological envelope maps and stand production of eucalyptus plantations and naturally regenerated maritime pine stands in the central inland of Portugal

Eucalyptus and maritime pine forests provide most of the wood harvested in Portugal. Due mainly to forest fires maritime pine forest has been converted to eucalyptus plantations. In the central inland of Portugal these species are well represented, and their productivities are quite the same. The objectives of the study were: (1) to assess average wood volume, biomass production and carbon content of eucalyptus plantations and naturally regenerated maritime pine stands; (2) to evaluate biomass nutrients concentration of eucalyptus sprouts selection and maritime pine non-commercial thinning; (3) to analyse these forests cover change in relation to the annual burnt areas; and (4) to produce the species ecological envelope maps to foresee future environmental impacts of these forests current distribution. Simulation models were used to assess wood volume, biomass production and carbon content. Field data was collected to evaluate biomass nutrients concentration and to validated simulated data. Forest inventory data and forest cover maps were used to analyse forest cover change. Biogeographical variables were used to produce species ecological envelope maps. It was found that eucalyptus plantations provide higher mean annual wood volume, biomass production and carbon content. Biomass nutrients concentration in eucalyptus sprouts selection were higher than in maritime pine non-commercial thinning, particularly in calcium and potassium. Overall eucalyptus forests area did not increase substantially but the fires in maritime pine forests gave the opportunity for eucalyptus afforestation. That has precluded the opportunity for introducing native broadleaves to respond to climate changes, improve landscape biodiversity and mitigate fire hazard. Implementing good management practices to prevent losses of soil fertility by nutrients exhaustion, organic matter depletion or erosion were found more relevant in eucalyptus plantations than in naturally maritime pine forest. Species ecological envelope maps and production simulation models are key tools for supporting decision in afforestation planning.

Evaluation of Tree Species for Biomass Energy Production in Northwest Spain

Three types of forest stands (chestnut coppice, maritime pine stands, and poplar and willow short-rotation woody crops (SRWC)) were evaluated to determine their potential for energy production. The properties of the main aboveground biomass fractions (wood, bark and crown) and also the whole tree were analysed, thus providing data that could be used for management purposes and for evaluating potential forest, biomass energy yields and atmospheric emissions. Proximate, elemental and energetic analyses of the biomass provided important information for evaluating the fuel potential. The energetic value of the biomass derived from the maritime pine stands was higher than that of the poplar and willow clonal stands and chestnut coppice stands. The high ash content of the chestnut bark, relative to that of the wood and crown material, is also an important consideration in relation to energy production. The proportion of carbon concentration accumulated per tree was very similar in all types of material studied, although the N and S contents were higher in the maritime pine stands than in the other stands. For this reason, selection of species and fractions can help to improve fuel quality and the efficiency of the combustion processes, and to minimize atmospheric emissions.

A silvicultural stand density model to control understory in maritime pine stands

The aim of this study was to provide optimal silvicultural guidelines for the maintenance of low understory vegetation cover in maritime pine (Pinus pinaster Ait.) stands in Mediterranean areas prone to the occurrence of forest fires. An extensive data set from maritime pine stands of northern Portugal was used to assess the effect of stand density on the understory cover. A statistically significant relationship between the spacing-top height factor (Fw) and the understory cover was found. An ecologically-based density regulation model was developed based on Fw = 0.21, which provided the optimal stand density and canopy cover to prevent the understory growth and proliferation, thereby reducing the vulnerability to forest fire and ensuring at the same time the highest values of stand yield. The developed model represents a supporting tool for density regulation of maritime pine stands in areas prone to forest fires. The representativeness of the supporting data set (in terms of number of sample plots and variability of the stands characteristics) provides confidence in the generalization of our results to different maritime pine stands in the Mediterranean area. This study suggests that managing stand density may be an effective adaptive management procedure which can help reducing the forest fire hazard.

Pyrrhic victory for bark beetles: Successful standing tree colonization triggers strong intraspecific competition for offspring of Ips sexdentatus

Most bark beetles living on standing trees must overcome the natural resistance of their host to succeed in colonization. For this they perform mass attacks to reach a critical threshold of attack density (CTAD) above which host defences are exhausted. However, this strategy can result in an intense intraspecific competition during larval development. Consequently, the ability of a bark beetle species to sustain outbreaks on standing trees would be conditioned by three key factors: the value of CTAD; the ability of attacking beetles to stop accumulating after CTAD has been reached; and the ability of offspring to tolerate intraspecific competition. To test these hypotheses, we assessed attack and colonization densities of Ips sexdentatus during an outbreak, and estimated CTAD, using a stand-scale approach, in nine maritime pine stands. We also estimated the effect of intraspecific competition on the productivity and fitness of I. sexdentatus offspring, testing increasing rearing densities in the laboratory. The overall CTAD of I. sexdentatus on standing maritime pines was 142 attacks/m2. CTAD varied among stands and ranged from 53 to 177attacks/m2. In several stands, attack densities raised much above local CTAD. Ips sexdentatus exhibited a low tolerance to intraspecific competition. The number of offspring per female and the fitness of emerging adults decreased exponentially with increasing rearing density. Excessive attack densities and negative feedback on offspring quantity and quality are likely to trigger rapid collapse of outbreaks. This supports the prediction that I. sexdentatus is an opportunistically aggressive species.

Responses of serpentine plants to pine invasion: Vegetation diversity and nickel accumulation in species with contrasting adaptive strategies

Introduction of non-native trees is one of the major threats to ecosystem integrity and biodiversity. Stands of maritime pine (Pinus pinaster Ait.) introduced decades ago represent a threat to the specialized plant communities of serpentine outcrops in Italy. This study investigates the effects of such invasions at the community and species level, based on vegetation sampling in three selected sites with comparable environmental conditions. Pine cover caused a decrease of α-diversity by lowering the species evenness of the community, though species richness was not negatively affected. Compositional changes between the two habitats were significant but not clearly associated with a decrease in taxonomic distinctness in the pine stands. As many as nine indicator species were found in the open vegetation, along with the obligate endemics Odontarrhena bertolonii and Armeria denticulata. Both of them declined in the pine stands. Here, an increase in the phytoavailable nickel fraction was associated with a decrease in total nickel concentration in the soil, via mobilization of the metal caused by lowering of pH induced by the conifer litter. The nickel-hyperaccumulator O. bertolonii was able to maintain high metal concentrations in the shoots despite a decrease in root concentration, resulting in a higher shoot/root ratio in the pine stands (~20). Conversely, shoot/root ratio in the non-accumulator Plantago holosteum was <1 and not affected by the conifer, as well as its abundance in this anthropogenic habitat. Contrasting responses of the two species were likely due to their different sensitivity to modified light and soil conditions, whereas stability of shoot nickel-concentration in O. bertolonii did not support increased predation by natural enemies as one of the causes for its decline under the conifer.Progressive thinning of these stands is advocated to limit soil nickel mobilization and to restore a unique ecosystem with its endemic metallophytes.

Water resources planning for a river basin with recurrent wildfires

Situated in the north of Portugal, the Beça River basin is subject to recurrent wildfires, which produce serious consequences on soil erosion and nutrient exports, namely by deteriorating the water quality in the basin. In the present study, the ECO Lab tool embedded in the Mike Hydro Basin software was used for the evaluation of river water quality, in particular the dissolved concentration of phosphorus in the period 1990–2013. The phosphorus concentrations are influenced by the burned area and the river flow discharge, but the hydrologic conditions prevail: in a wet year (2000, 16.3km2 of burned area) with an average flow of 16.4m3·s−1 the maximum phosphorus concentration was as low as 0.02mg·L−1, while in a dry year (2005, 24.4km2 of burned area) with an average flow of 2m3·s−1 the maximum concentration was as high as 0.57mg·L−1. Phosphorus concentrations in the water bodies exceeded the bounds of good ecological status in 2005 and between 2009 and 2012, water for human consumption in 2009 and water for multiple uses in 2010. The River Covas, a right margin tributary of Beça River, is the most appropriate stream as regards the use of water for human consumption, because it presents the biggest water potential with the best water quality. Since wildfires in the basin result essentially from natural causes and climate change forecasts indicate an increase in their frequency and intensity in the near future, forestry measures are proposed to include as a priority the conversion of stands of maritime pine in mixed stands of conifer and hardwood species.