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Forecasted scenarios of climate change are expected to result in a dramatic reduction in the provision of Ecosystem Services (ES) from forests. Increasing tree species diversity has been proposed as a measure for adapting forests and warrantee the provision of services, since mixed forests, if compared with monospecific forests, are expected to be more productive, resilient and stable facing disturbances. In the present work we use a modelling approach in order to quantify the provision of different ES under expected climate scenarios, comparing pure forests of Pinus pinea L. with mixed forests where the species grows accompanied by different Quercus and Juniperus species. To this aim we first adapted the existing individual tree level model PINEA2, originally constructed for pure even-aged stands of P. pinea, in order to consider the interspecific interactions acting in mixed forests. In a second step we used the so adapted model for forecasting and comparing the provision of different ES – focusing on stocking, growth, yield, CO2 fixation, economic income and structural diversity – under current climate and expected scenarios RCP 4.5 & 8.5. Our results indicate that although growth and allometry in P. pinea trees is enhanced in mixtures, this effect is currently counterbalanced by the expected reduction in growth in the species occupying the understorey, thus under current climate conditions little differences due to composition are observed in the provision of ES. On the other hand, our simulations point to a generalized decrease in the ES supply under more severe climate change scenarios, being this reduction mitigated – at least in part - in mixed P. pinea forests, which are more competitive under the most restrictive environmental conditions. As a consequence, the promotion of mixtures by under-planting and/or releasing of pre-existing advanced regeneration of complementary species may be postulated as a management concept for adapting these forests to climate

Key message: Our modelling approach shows the predominance of the facilitative over the competition effects in controlling the regeneration of the studied species, thus pointing out to intra- and inter-specific coexistence mechanisms. Abstract: Natural regeneration is a main issue in the management of continental Mediterranean forests. Ensuring natural forest regeneration is therefore vital for preserving ecosystem function under climate warming and increased frequency and intensity of extreme droughts. In this study, we evaluated intraspecific and inter-specific relationships between saplings and adult trees in mixed Pinus pinea-Quercus ilex-Juniperus stands in the Spanish Northern Plateau. Data were gathered from five 50 m × 60 m plots that covered different stand densities. Adult trees, saplings, and stumps were positioned, and height and diameter were measured. We developed a patch model to predict the probability of occurrence and abundance of saplings of the three species in 2.5 m × 2.5 m patches using a zero-inflated model. We considered as predictive variables abundance of adult trees, stumps, and saplings of each species, both in a patch and in its adjacent patches. Saplings of the three species showed a cluster pattern. The abundance of saplings of the three species was positively related with the current or past presence of their conspecific adult trees. The presence of adult trees of Pinus pinea plays a main role in both Quercus ilex and Juniperus dissemination. Our modelling approach shows the predominance of the facilitative effects over the competition effects in controlling the regeneration of the three species, pointing out to intra- and inter-specific coexistence mechanisms. The simulations suggested that to perpetuate the mixture, it is necessary to apply intense release cuttings in Pinus pinea trees once seedlings have been successfully established.

Recent studies show that several tree species are spreading to higher latitudes and elevations due to climate change. European beech, presently dominating from the colline to the subalpine vegetation belt, is already present in upper montane subalpine forests and has a high potential to further advance to higher elevations in European mountain forests, where the temperature is predicted to further increase in the near future. Although essential for adaptive silviculture, it remains unknown whether the upward shift of beech could be assisted when it is mixed with Norway spruce or silver fir compared with mono-specific stands, as the species interactions under such conditions are hardly known. In this study, we posed the general hypotheses that the growth depending on age of European beech in mountain forests was similar in mono-specific and mixed-species stands and remained stable over time and space in the last two centuries. The scrutiny of these hypotheses was based on increment coring of 1240 dominant beech trees in 45 plots in mono-specific stands of beech and in 46 mixed mountain forests. We found that (i) on average, mean tree diameter increased linearly with age. The age trend was linear in both forest types, but the slope of the age–growth relationship was higher in mono-specific than in mixed mountain forests. (ii) Beech growth in mono-specific stands was stronger reduced with increasing elevation than that in mixed-species stands. (iii) Beech growth in mono-specific stands was on average higher than beech growth in mixed stands. However, at elevations > 1200 m, growth of beech in mixed stands was higher than that in mono-specific stands. Differences in the growth patterns among elevation zones are less pronounced now than in the past, in both mono-specific and mixed stands. As the higher and longer persisting growth rates extend the flexibility of suitable ages or size for tree harvest and removal, the longer-lasting growth may be of special relevance for

Past failures of monocultures, caused by wind-throw or insect damages, and ongoing climate change currently strongly stimulate research into mixed-species stands. So far, the focus has mainly been on combinations of species with obvious complementary functional traits. However, for any generalization, a broad overview of the mixing reactions of functionally different tree species in different mixing proportions, patterns and under different site conditions is needed, including assemblages of species with rather similar demands on resources such as light. Here, we studied the growth of Scots pine and oak in mixed versus monospecific stands on 36 triplets located along a productivity gradient across Europe, reaching from Sweden to Spain and from France to Georgia. The set-up represents a wide variation in precipitation (456–1250 mm year−1), mean annual temperature (6.7–11.5 °C) and drought index by de Martonne (21–63 mm °C−1). Stand inventories and increment cores of trees stemming from 40- to 132-year-old, fully stocked stands on 0.04–0.94-ha-sized plots provided insight into how species mixing modifies stand growth and structure compared with neighbouring monospecific stands. On average, the standing stem volume was 436 and 360 m3 ha−1 in the monocultures of Scots pine and oak, respectively, and 418 m3 ha−1 in the mixed stands. The corresponding periodical annual volume increment amounted to 10.5 and 9.1 m3 ha−1 year−1 in the monocultures and 10.5 m3 ha−1 year−1 in the mixed stands. Scots pine showed a 10% larger quadratic mean diameter (p < 0.05), a 7% larger dominant diameter (p < 0.01) and a 9% higher growth of basal area and volume in mixed stands compared with neighbouring monocultures. For Scots pine, the productivity advantages of growing in mixture increased with site index (p < 0.01) and water supply (p < 0.01), while for oak they decreased with site index (p < 0.01). In total, the superior productivity of mixed stands compared to monocultures increased wit

Climate, competition and site conditions are the main drivers controlling annual secondary growth in tree species. These factors do no act independently on tree growth, but by means of interactions, resulting in mediated interactive effects. For example, the stress gradient hypothesis postulates alleviated interspecific competition under limiting spatial (site) or temporal (climate) resources. According to this, models predicting annual growth and yield for a given forest should consider these issues in their formulation. In this study, we present a modelling approach based on using data from permanent plots and dendrochronological analysis in order to describe annual tree growth in pure, even-aged stands of Pinus pinea L. in the Spanish Northern Plateau, a highly limiting environment due to its Mediterranean continental climate. Our method is based on identifying the different sources of variability by means of a multilevel linear mixed model, and thereby identifying the potential covariates explaining observed variability at the different spatiotemporal scales. Our results indicate that site related factors such as site index or dominant height exert a greater influence on annual secondary growth than size-symmetric competition. In addition, we found that the controlling influence of water stress is greater than that of temperatures on tree growth. Furthermore, our results allow evidence to be identified for the stress gradient hypothesis in temporal intraspecific interactions, since trees exposed to a higher degree of competition tend to grow more than expected in dry periods. In contrast, the effect of competition on growth, on average, tends to be aggravated at very poor sites. Finally, our modelling approach allows us to conduct growth and yield simulations under different climate scenarios at different spatial scales, providing results which point to significant decreases in timber and cone production under the more severe scenarios, which can be alleviated t

Past failures of monocultures, caused by wind-throw or insect damages, and ongoing climate change currently strongly stimulate research into mixed-species stands. So far, the focus has mainly been on combinations of species with obvious complementary functional traits. However, for any generalization, a broad overview of the mixing reactions of functionally different tree species in different mixing proportions, patterns and under different site conditions is needed, including assemblages of species with rather similar demands on resources such as light. Here, we studied the growth of Scots pine and oak in mixed versus monospecific stands on 36 triplets located along a productivity gradient across Europe, reaching from Sweden to Spain and from France to Georgia. The set-up represents a wide variation in precipitation (456–1250 mm year−1), mean annual temperature (6.7–11.5 °C) and drought index by de Martonne (21–63 mm °C−1). Stand inventories and increment cores of trees stemming from 40- to 132-year-old, fully stocked stands on 0.04–0.94-ha-sized plots provided insight into how species mixing modifies stand growth and structure compared with neighbouring monospecific stands. On average, the standing stem volume was 436 and 360 m3 ha−1 in the monocultures of Scots pine and oak, respectively, and 418 m3 ha−1 in the mixed stands. The corresponding periodical annual volume increment amounted to 10.5 and 9.1 m3 ha−1 year−1 in the monocultures and 10.5 m3 ha−1 year−1 in the mixed stands. Scots pine showed a 10% larger quadratic mean diameter (p < 0.05), a 7% larger dominant diameter (p < 0.01) and a 9% higher growth of basal area and volume in mixed stands compared with neighbouring monocultures. For Scots pine, the productivity advantages of growing in mixture increased with site index (p < 0.01) and water supply (p < 0.01), while for oak they decreased with site index (p < 0.01). In total, the superior productivity of mixed stands compared to monocultures increased wit

Studying intra-annual growth dynamics through a modelling approach has proved useful for characterizing differences in wood phenology between species and deviations from the expected tree growth due to climate change. The aim of this paper was to determine the climatic factors and the inter- and intra-specific competition traits that drive intra-annual secondary growth dynamics in three Mediterranean tree species that naturally co-exist in the Spanish Northern Plateau (Pinus pinea L., Juniperus thurifera L., and Quercus ilex subsp. ballota (Desf.) Samp.). For this purpose, we obtained girth increment data from band dendrometers installed on 58 trees from May 2012 to April 2015. Half of them were located in a high-density plot and half were in a low-density plot. These data were analysed through a nonlinear multifactorial model considering daily and cumulative climatic effects together with inter- and intra-specific competition indices. Our results provide evidence of a spatiotemporal niche separation between species. Compared with other species, Q. ilex subsp. ballota showed a wider thermal amplitude, a higher mean optimum temperature for growth, and a milder effect of drought on its secondary growth. Under current climate change projections, simulations based on our model predict a secondary growth reduction for P. pinea and a growth enhancement for Q. ilex subsp. ballota in these Mediterranean mixtures.

The management of species composition and competition are two of the main adaptive options that forest managers propose to cope with the expected negative impacts of climate change on forest growth in the Mediterranean basin. Species mixture can improve the resistance and resilience of forest ecosystems to face up global change. However, it seems likely that global change will modify mixed stands dynamics. Thus, studying inter-tree relationships on an annual basis is key to understanding ecosystem dynamics in the region. The aim of this paper was to evaluate the effects of tree species composition and competition on Pinus pinea annual secondary growth in mixed vs. monospecific stands over a period of 15. years with contrasting climatic conditions. We obtained basal area growth data from tree ring measurement on cores and cross section slices from 372 trees of P. pinea L. .;Juniperus thurifera L.;Quercus ilex subsp. ballota (Desf.)) Samp.;Quercus faginea Lam.;in the Spanish Northern plateau, approximately half of which were in monospecific stands and half in mixed stands. We analysed the effect of intra and interspecific competition on P. pinea secondary growth comparing the performance of several distance dependent competition indexes through linear mixed models. These competition indices were calculated for all trees within each plot for each year of study. The results showed competitive reduction and tree growth amelioration in mixed vs. monospecific stands of P. pinea indicating a spatial and temporal niche separation between species and size-symmetric effects for interspecific competition. Size-asymmetric results obtained for competition within pines indicated that the largest individuals obtain the majority of the contested resources suppressing the growth of their smaller pine neighbours. Intraspecific interactions were more negative than interspecific interactions.;we finally provide evidence of a growth enhancement in mixed vs. monospecific stands in water s