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Understanding the growth efficiency of individual trees, or growth per unit of resource utilization, can inform silvicultural management strategies to maximize tree and stand growth. Stand structure—the size and spatial distributions of trees within the stand—strongly influences water, light, and nutrient availability, as well as the resource-use efficiency of each tree. Key silvicultural tools for stand management include manipulating tree density, size distribution, and arrangement by controlling natural regeneration, artificial seeding, planting seedlings, and/or subsequent thinning of established trees. We analyzed two sets of plots from even-aged stands of common coniferous species in central Spain, 106 pure Scots pine (Pinus sylvestris) and 92 pure Mediterranean pine (Pinus pinaster), to examine the dynamics of the dominance hypothesis, the relationship between stand structure and growth, and the relationship between structure and growth efficiency. Our main findings revealed a negative impact of size-class uniformity on stand growth in both Scots pine and Mediterranean pine, while the positive effect of tree size on growth efficiency was supported for Mediterranean pine stands but uncertain for Scots pine. At the operational level, our results highlight how thinning intensity is more important than the thinning method in Mediterranean pinewoods and how thinning can benefit the provision of multiple ecosystem services. We also recommend integrating dominance effects on growth into individual tree modelling. [ABSTRACT FROM AUTHOR]

Forest dynamics are undergoing profound alteration due to the fact that climate change is increasing the frequency and severity of abiotic and biotic forest disturbances. Because of the unpredictable nature of the drought periods and the variation in their severity, Mediterranean forests are typically more vulnerable. Mediterranean Pinus pinaster forests are showing decay symptoms linked to climate change. There is clear evidence that promoting mixtures can serve as an effective forest adaptation strategy. In this regard, we sought to better understand the responses of P. pinaster radial growth dynamics to various factors, in both mixed and pure forest stands, and provide valuable insights into P. pinaster dynamics when mixed with P. sylvestris. In this study, we examined the variation of intra-annual cumulative radial increment patterns in response to the climate of P. pinaster between pure and mixed stands with P. sylvestris. Using data from band dendrometers collected over five consecutive climatically distinct years (2016–2020), a nonlinear mixed-effect model approach was used to analyze the differences in intra-annual cumulative radial increment patterns for P. pinaster between years in mixed and pure stands. The intra-annual radial increment pattern of P. pinaster showed significant year-to-year variation and varied with tree size, with greater increment in larger trees. Trees in mixed stands had a higher mean radial increment compared to corresponding ones in pure stands. Increased summer maximum temperatures negatively affected tree cumulative annual increment regardless of composition, but with a lower impact on trees in pure stands. Spring precipitation increased the length of the growing season, while higher spring maximum temperatures triggered an earlier inflection point. Our results highlight the high plasticity of P. pinaster in adapting to varying intra- and inter-annual environmental conditions and competition with other species and suggest that promoting mixtures with P. sylvestris may be an interesting management strategy for adaptation to climate change. [ABSTRACT FROM AUTHOR]

Seedling size-related functional attributes of Mediterranean forest species are critical traits to be considered in nursery practices aimed at improving the survival and performance of seedlings exposed to summer drought in dryland reforestation projects. We looked at how nursery light regimes and nitrogen fertilization affected the survival and performance of Pinus pinaster Ait. under contrasting post-planting watering regimes. Seedlings grown in the nursery for 13 months were given low or high nitrogen doses and exposed to three light regimes (full sun, medium light and low light). After outplanting, half of the seedlings were watered fortnightly during the hottest months of the first summer and the other half were left unwatered. Seedling size-related variables (shoot height, basal diameter, stem volume and sturdiness quotient) were measured at the beginning and at the end of the study, and summer drought survival was checked three times. Our results showed that fertilization and the nursery light regime influenced initial seedling quality and transplant stress. Post-planting first summer watering also increased seedling survival probability. The medium-light and especially the full-sunlight regimes in the nursery decreased the probability of seedling mortality after outplanting. However, a low-light regime in the nursery negatively affected plant traits and increased the probability of post-planting seedling mortality. In comparison with low-N seedlings, high-N fertilization increased post-planting stress (evaluated in the change of sturdiness quotient after one field growth season), but did not affect survival. [ABSTRACT FROM AUTHOR]

Stand density management diagrams (SDMDs) are robust decision-support tools available to forest managers under limited information. SDMDs which are based on empirical models at stand level, graphically represent the temporal relationships among stand density, and different stand variables such as quadratic mean diameter, dominant height, and mean tree volume. They are used to define initial planting spacing or thinning interventions, to meet various management objectives. Nowadays, there is a growing interest in mixed-species forests as an option for adaptive forest management, where they are considered a guarantor to safeguarding a wide variety of ecosystem services within the framework of sustainability. But there is still a lack of knowledge and efficient tools and models for mixed stands such as SDMDs. This study aims to develop an SDMD for Pinus sylvestris L. and Pinus pinaster Ait. mixed stands in the Sierra de la Demanda (Spain) using data from the third Spanish National Forest Inventory. Both species are two of the most important conifers in Europe and the western Mediterranean basin. Different variables can be used to develop an SDMD. In this case, quadratic mean diameter, dominant height, total stand volume, number of trees per hectare, and stand density index were used. These equations were fit by simultaneous fitting including a new variable representing the proportion of both species in the mixed stand. The results of the simultaneous fitting showed the new variable representing the proportion of both species was not significant. Based on that, the SDMD was constructed without including mixture degree. This SDMD can be used by forest managers as an efficient tool to plan thinning operations. [ABSTRACT FROM AUTHOR]

There is growing interest in mixed-species forests but also a lack of studies that analyse them at the regeneration phases or any stage other than mature stands. Information is particularly scarce about relatively unproductive species such as Pinus pinaster and Pinus halepensis in Mediterranean ecosystems. The objective of this study was to investigate inter- and intra-specific interactions of both species at different tree densities during the first years of establishment. Five Nelder wheel plots were planted to test densities ranging from 1000 to 80 000 seedlings/ha and simulate establishment sub-processes at high densities. Further, P. pinaster and P. halepensis were mixed along the spokes, to obtain three mixture levels in which 100, 80 or 60 per cent of the seedlings were of the same species. Cox proportional-hazards models and binomial logistic regressions were fitted to analyse seedling survival. Early growth (basal diameter and height at one and four years after plantation) was analysed by fitting linear mixed-effects models. In this regard, P. halepensis showed higher survival rates and basal diameter increments but more time is needed to know how P. pinaster responds to density and mixture. Both competitive and facilitating seedling interactions were observed at higher densities, which fostered seedling survival but decreased early growth. [ABSTRACT FROM AUTHOR]

The main objective of this study was to analyse biomass production and distribution among the constituent parts of 4-year-old Pinus pinaster and Pinus halepensis trees. Young trees were harvested from a Nelder wheel experimental site and their biomass weight was determined. With the Nelder design, the effect of stand density can be included in the biomass analysis. We analysed biomass production at test densities ranging from 1000 to 80 000 seedlings/ha by fitting two types of equations: (1) Dirichlet regressions to estimate the biomass proportions of constituent tree parts and (2) allometric equations to simultaneously predict the biomass content of constituent tree parts. Results from this innovative approach showed that the effect of stand density in tree-level biomass was significant for P. halepensis but not for P. pinaster. We observed a general increase of total biomass from P. halepensis at lower densities. More precisely, the proportion of root biomass increased at the expense of aboveground biomass, which is considered a positive effect in terms of resilience and adaptation. This new set of equations fills a fundamental knowledge gap for these species in central Spain and can readily be used by silviculturists and scientists to quantify carbon stocks for young planted forests. [ABSTRACT FROM AUTHOR]

• Key message: This 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 [ABSTRACT FROM AUTHOR]

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Forest decline may be a complex disease caused by the interaction of a number of interchangeable factors (both abiotic and biotic), leading to gradual deterioration of the forest. These factors have been classified as predisposing, inciting or contributing factors. Pinus pinaster Ait. is one of the most important forest species in Spain because of its protective value and the high timber yields obtained. Maritime pine decline has been observed in several forests in the centre of the Iberian Peninsula, manifested as transparency at the crown, small needles, foliage discolouration and premature tree death. The aim of this study was to unravel the role of predisposing, inciting and contributing factors in Mediterranean maritime pine decline in Spain. Various parameters were measured in 27 circular plots of radius 15 m in natural stands of P. pinaster ssp. mesogeensis . The data obtained indicated better forest health status in pure stands, in which thinning has been carried out, than in unthinned mixed stands. High values of total height and spring precipitation showed better forest health, whereas high tree density was associated with the poorest forest health status. The results suggest that predisposing factors such as competition and water deficit have triggered the decline of P. pinaster. [ABSTRACT FROM AUTHOR]

Seed bank dynamics constitute a pool of natural regeneration, a complex and key process for stand persistence. The present work analyzes post-dispersal predation on a Pinus pinaster Ait. (maritime pine) belowground seed bank. The study was carried out at the experimental site of Mata de Cuellar (Segovia, central Spain), where an integrated analysis of maritime pine regeneration has been underway since 2004. Seed predation was monitored every month from 2010 to 2013. A generalized linear model was fitted using 'next spring seed density' as the response variable and seed rain, micro-site conditions and annual climate variability as explanatory variables. Seed rain, distance to the nearest stump, basal area and Walter's drought index, along with percentage cover of herbaceous species, pine needle litter and shrub species, had significant positive effects. The number of neighboring trees had a significant negative effect on seed density. These results demonstrate how seed rain, summer drought and micro-site conditions are crucial to understand the effects of predation on the belowground seed bank. Though greater than null, the final seed bank might be insufficient for successful natural regeneration due to high mortality caused by difficult germination and establishment conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Significant variation in interannual cone production correlated across years. [•] Fertility differences between stands are high. [•] Annual seed dispersal kernels fitted lognormal or 2Dt models depending on the stand. [•] Median seed dispersal distances vary between 14 and 25m. [•] Dispersion capacity is strongly influenced by mating system, fertility and LDD events. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nitrogen effects on Pinus pinaster seedlings plasticity depend on the light availability. [•] Better seedling performance with full sunlight and high-N. [•] Higher dry weight allocation to needles in full sunlight and medium light/high-N. [•] Higher dry weight allocation to stem with shade, regardless N availability. [•] Higher allocation to root in low-N seedlings in full sunlight and medium light. [ABSTRACT FROM AUTHOR]

Background: How environmental factors affect forest regeneration is relevant for systems that depend partially or fully on natural regeneration. Methods: P. pinaster post-disturbance regeneration and its relationship to environmental factors was studied in five P. pinaster forest populations of central Spain. We expected that: 1) different harvesting methods or wildfire would promote natural regeneration in all populations, but with local and regional variations,or 2) alternatively, different site-dependent stand factors would affect natural regeneration, although generalized climate effects would be seen. Analysis of variance and multivariate analysis were used to test differences, to classify ecological variations, and to search for the most important factors affecting regeneration. Results: The results suggest that the recovery of P. pinaster forest in burnt stands, and stand replacement in harvested stands, can be achieved soon after disturbance if climatic conditions and other local-site factors (e.g., soil and overstory structure in harvested stands, cone bank in burnt stands) make the stand suitable for natural regeneration. Heterogeneous regeneration can be expected in all cases. The time of precipitation strongly influenced seedling density and successive regeneration development stages. Conclusion: Edaphic properties, combined with water availability from precipitation, can seriously limit the natural establishment of P. pinaster in xeric systems or during years of intense drought. Although many factors contribute to high variability, natural regeneration has been very effective (successful) in P. pinaster forests, which contributes to the generalization that natural regeneration is a viable forestry option in many forest types. [ABSTRACT FROM AUTHOR]

Abstract: Germination and survival in the initial months represent a critical period for forest species. Many factors have significant influences and can produce a negative effect on regeneration. To prevent this, these factors must be known and their influence must be evaluated. The influence of light and of water availability has been studied in the most important pine species in the Iberian Peninsula, the Pinus pinaster. An experimental seed-sowing was conducted in the Cuéllar experimental site (central Spain), where four different harvest intensities were applied in 2004. Four different watering regimes were performed during two consecutives summers (2006 and 2007) and seedling development was monitored during 18 months. Main findings reveal that, regarding germination and survival in the initial months, light was more important than water availability. Higher germination and survival rates were obtained when the lowest level harvest was applied. However, in terms of biomass and growth, water availability was more influential than harvest intensity. Results improved when there was greater water availability after a few months. The main conclusion of this study is that light shows a higher impact that summer rainfall with respect to germination and survival in the early stages of Mediterranean Maritime Pine. [Copyright &y& Elsevier]

We established a circular experimental plot (radius=100 m) that consists of 380 trees of maritime pine (Pinus pinaster Ait.). The plot is located in central Spain (Segovia province) and within a pure, even-aged and naturally regenerated stand of the species. Every tree was initially mapped using polar coordinates. The objective of the study was to explore the spatial arrangement of some stand attributes such as age of trees, diameter at breast height (DBH), total height, diameter increment and number of female strobili and cones. Genetic data (three highly polymorphic nuclear microsatellites) were used to investigate extend of relatedness within the stand and differentiate between genetic and environmental causes of spatial aggregation. We employed, in the analysis of tree attributes, only geostatistical tools (direct and cross variograms as well as their indicator counterparts). The results revealed that all the studied attributes are spatially correlated and some of them cross-correlated. Competition and height were found to be key-variables in stand dynamics, which influence the rest of the attributes. Fine-scale genetic structure exists within the stand (0–30 m range). Relatedness between neighboring trees can partially explain the spatial aggregation of individual tree attributes. Geostatistical tools are recommended for this type of spatial analysis of forest stands. Their use can provide useful insights into the nature of stand organization and can guide future silvicultural treatment toward higher stand productivity or better and faster regeneration. [Copyright &y& Elsevier]

• The two species showed intra-annual stem radial variation synchrony. • Spring and autumn radial increment onset was earlier for maritime pine. • Maritime pine showed a higher sensitivity to summer drought. • Species differences in weather response may reduce competition for resources. Species complementarity by morphological and physiological trait differences could cause distinct temporal and spatial use of resources. Accordingly, mixed stands may enhance production, biodiversity and/or provide a better adaptation to future climate conditions. We aim to identify species differences in intra-annual stem radial variation patterns, and to recognize species-specific responses to contrasting weather conditions at key intra-annual growth phases. Stem radial variation was recorded from high temporal resolution point dendrometers (2012–2014) installed on twelve dominant maritime pine and Pyrenean oak trees in two mixed stands in central Spain. Species differences in stem radial variation were analyzed by synchrony statistics, intra-annual pattern modelling, and evaluating the dependence of main intra-annual growth phases on climate conditions. Both species showed important differences on intra-annual radial increment pattern despite general stem radial variation synchrony. Radial increment onset was earlier for maritime pine during the spring and rainy autumns. Species-specific responses to weather indicate that stem radial variation increased with autumn temperature in maritime pine, but decreased in Pyrenean oak trees. However, summer vapor pressure deficit may reduce stem radial variation for maritime pine. Therefore, maritime pine would adapt more efficiently to warmer temperatures associated with climate change, although summer water stress may reduce this competitive bonus. [ABSTRACT FROM AUTHOR]

• Crown characteristics in pine mixtures were examined with terrestrial laser scanning. • The mixing induced crowns with lower volume and upward displacement in Pinus pinaster. • P. sylvestris and P. pinaster had complementary strategies to occupy the canopy space. • Crown shifts are key to relate overyielding to the tree growing space efficiency. Forest canopy has been identified as a major contributor to explaining the potential of mixed stands to provide a greater amount of ecosystem services, including superior productivity. So far, most reports of mixture effects focused on combinations of species with contrasting functional traits. Hence, little is know about the mechanism behind positive effects in mixtures of species with similar traits. Here we used 3D terrestrial laser scanning data to inspect crown architecture of mature trees in pure and mixed stands of P. pinaster L. and P. sylvestris Ait., to gain insight on the observed overyielding of mixed stands. Differences in the crown dimensions of P. pinaster trees in response to mixing with P. sylvestris were observed. Mixture promoted an upward displacement of P. pinaster tree crowns while reduced its capacity to explore the canopy space. P. pinaster relies mainly on height growth to increase crown volume, whereas P. sylvestris increases crown volume by keeping branches lower in the crowns. Overall, we found mechanisms that could promote vertical stratification of tree crowns, in addition to evidence that P. pinaster undergoes greater competition in the upper canopy of mixed stands. These findings could be related to a better canopy space filling in the mixture, but also with more efficient use of the available space, both aspects closely related to overyielding. [ABSTRACT FROM AUTHOR]

• Mistletoe infestation was higher in pure Scots pine stands than in mixtures. • Associational resistance was partly driven by relative tree height. • Our study is the first to quantify associational resistance to a plant parasite. • In the study area Maritime pine was almost never infested with mistletoe. The pattern that a given tree species suffers less damage when growing with heterospecific neighbors than amongst conspecific plants, i.e. associational resistance, is common for insect herbivores and many fungal pathogens. However, associational resistance to parasitic plants has never been tested in a replicated study. Using paired forest plots, we investigated whether tree diversity triggered associational resistance to a tree parasite, the European mistletoe Viscum album ssp. austriacum , by comparing pure stands of Scots pine (Pinus sylvestris) with mixtures of Scots pine and Maritime pine (Pinus pinaster) in northern Spain. Maritime pine, with 1.2% of trees being infested, was considered a non-host species in the study area. The infestation level of Scots pines was significantly higher in pure plots (45.1%) than in mixed plots of Scots pines and Maritime pines (25.4%). Our study is the first to quantify associational resistance to a plant parasite in mixed vs. pure forest stands and suggests that mechanisms proposed to explain associational resistance to insects and pathogens also apply to plant parasites. Scots pine trees that were taller than the surrounding trees had a higher infestation probability, in both pure and mixed stands. Scots pine trees growing in mixtures were slightly lower than Maritime pines, suggesting that associational resistance was partly driven by reduced relative tree height. However, the effect of plot type (pure vs. mixed) remained significant after the effect of tree height was accounted for, thus indicating that other factors also contributed to lower mistletoe infestation in mixed plots. In particular, the behavior of birds dispersing mistletoe seeds might differ in mixed vs. pure stands. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]