Forest productivity in southwestern Europe controlled by coupled North Atlantic and Atlantic Multidecadal Oscillations

The North Atlantic Oscillation (NAO) depicts annual and decadal oscillatory modes ofvariability responsible for dry spells over the European continent. The NAO therefore holds agreat potential to evaluate the role, as carbon sinks, of water-limited forests under climatechange. However, uncertainties related to inconsistent responses of long-term forestproductivity to NAO have so far hampered firm conclusions on its impacts. We hypothesizethat, in part, such inconsistencies might have their origin in periodical sea surfacetemperature anomalies in the Atlantic Ocean (i.e., Atlantic Multidecadal Oscillation, AMO).Here we show strong empirical evidence in support of this hypothesis using 120 years ofperiodical inventory data from Iberian pine forests. Our results point to AMO+ NAO+ andAMO−NAO− phases as being critical for forest productivity, likely due to decreased winterwater balance and abnormally low winter temperatures, respectively. Our findings could beessential for the evaluation of ecosystem functioning vulnerabilities associated with increasedclimatic anomalies under unprecedented warming conditions in the Mediterranean

Risks, benefits, and knowledge gaps of non-native tree species in Europe

Changing ecosystem conditions and diverse socio-economical events have contributed to an ingrained presence of non-native tree species (NNTs) in the natural and cultural European landscapes. Recent research endeavors have focused on different aspects of NNTs such as legislation, benefits, and risks for forestry, emphasizing that large knowledge gaps remain. As an attempt to fulfill part of these gaps, within the PEN-CAFoRR COST Action (CA19128) network, we established an open-access questionnaire that allows both academic experts and practitioners to provide information regarding NNTs from 20 European countries. Then, we integrated the data originating from the questionnaire, related to the country-based assessment of both peer-reviewed and grey literature, with information from available datasets (EUFORGEN and EU-Forest), which gave the main structure to the study and led to a mixed approach review. Finally, our study provided important insights into the current state of knowledge regarding NNTs. In particular, we highlighted NNTs that have shown to be less commonly addressed in research, raising caution about those characterized by an invasive behavior and used for specific purposes (e.g., wood production, soil recultivation, afforestation, and reforestation). NNTs were especially explored in the context of resilient and adaptive forest management. Moreover, we emphasized the assisted and natural northward migration of NNTs as another underscored pressing issue, which needs to be addressed by joint efforts, especially in the context of the hybridization potential. This study represents an additional effort toward the knowledge enhancement of the NNTs situation in Europe, aiming for a continuously active common source deriving from interprofessional collaboration. Copyright © 2022 Dimitrova, Csilléry, Klisz, Lévesque, Heinrichs, Cailleret, Andivia, Madsen, Böhenius, Cvjetkovic, De Cuyper, de Dato, Ferus, Heinze, Ivetić, Köbölkuti, Lazarević, Lazdina, Maaten, Makovskis, Milovanović, Monteiro, Nonić, Place, Puchalka and Montagnoli

Reviewing the use of resilience concepts in forest sciences

Purpose of the review Resilience is a key concept to deal with an uncertain future in forestry. In recent years, it has received increasing attention from both research and practice. However, a common understanding of what resilience means in a forestry context, and how to operationalise it is lacking. Here, we conducted a systematic review of the recent forest science literature on resilience in the forestry context, synthesising how resilience is defined and assessed. Recent findings Based on a detailed review of 255 studies, we analysed how the concepts of engineering resilience, ecological resilience, and social-ecological resilience are used in forest sciences. A clear majority of the studies applied the concept of engineering resilience, quantifying resilience as the recovery time after a disturbance. The two most used indicators for engineering resilience were basal area increment and vegetation cover, whereas ecological resilience studies frequently focus on vegetation cover and tree density. In contrast, important social-ecological resilience indicators used in the literature are socio-economic diversity and stock of natural resources. In the context of global change, we expected an increase in studies adopting the more holistic social-ecological resilience concept, but this was not the observed trend. Summary Our analysis points to the nestedness of these three resilience concepts, suggesting that they are complementary rather than contradictory. It also means that the variety of resilience approaches does not need to be an obstacle for operationalisation of the concept. We provide guidance for choosing the most suitable resilience concept and indicators based on the management, disturbance and application context

Contrasting holm oak provenances show different field performance but similar resilience to drought events eight years after planting in a Mediterranean environment

Diversification of genetic plant material in forest plantations is viewed as a promising strategy to promote forest adaptation and resilience to ongoing climate change. However, there is an intense debate about whether foreign populations might outperform local ones under new climatic conditions. Unfortunately, long-term experiments using contrasting provenances are scarce, especially in the Mediterranean region. In this context, the evaluation of the resistance and resilience of individuals from different provenances to drought can help to forecast their performance under different climate change scenarios, and therefore to establish guideline regarding plant material selection in reforestation projects. We evaluated the performance (survival and drought) and drought sensitivity of Quercus ilex saplings from two contrasting provenances growing during eight years in a common garden experiment. For this, we used a combination of dendroecological methods and water-relation measurements, such as leaf water potential (Ψpd), cuticular transpiration (Ec), relative water content at the point of stomatal closure (RWCc) and specific leaf area (SLA). We also compared the resilience and resistance, in terms of radial growth to the intense drought event of 2012 between saplings from both provenances. Our results suggest a lack of idiosyncratic physiological response and growth sensitivity to drought between provenances. However, saplings from the drier provenance showed a superior performance in terms of survival and growth. Survival was greater in saplings from the dry provenance (100 vs. 91 %). Mean annual basal area increment was also greater in saplings from the dry provenance (158.8 ± 13.5 vs. 96.2 ± 8.4 mm2), which resulted in greater diameter eight year after planting (47.5 ± 2.8 vs. 38.3 ± 2.3 mm). The lower values of Ψpd, Ec and SLA in the summer of the first two years after planting suggest that climatic conditions after planting rather than isolated drought events was the most critical period for the success of these saplings. In view of our results, the selection of plant material for forest plantation should be carefully evaluated in forest restoration projects, while priority should be given to those actions oriented to increase the early survival of local Q. ilex seedlings

Contrasting holm oak provenances show different field performance but similar resilience to drought events eight years after planting in a Mediterranean environment

Diversification of genetic plant material in forest plantations is viewed as a promising strategy to promote forest adaptation and resilience to ongoing climate change. However, there is an intense debate about whether foreign populations might outperform local ones under new climatic conditions. Unfortunately, long-term experiments using contrasting provenances are scarce, especially in the Mediterranean region. In this context, the evaluation of the resistance and resilience of individuals from different provenances to drought can help to forecast their performance under different climate change scenarios, and therefore to establish guideline regarding plant material selection in reforestation projects. We evaluated the performance (survival and drought) and drought sensitivity of Quercus ilex saplings from two contrasting provenances growing during eight years in a common garden experiment. For this, we used a combination of dendroecological methods and water-relation measurements, such as leaf water potential (Ψpd), cuticular transpiration (Ec), relative water content at the point of stomatal closure (RWCc) and specific leaf area (SLA). We also compared the resilience and resistance, in terms of radial growth to the intense drought event of 2012 between saplings from both provenances. Our results suggest a lack of idiosyncratic physiological response and growth sensitivity to drought between provenances. However, saplings from the drier provenance showed a superior performance in terms of survival and growth. Survival was greater in saplings from the dry provenance (100 vs. 91 %). Mean annual basal area increment was also greater in saplings from the dry provenance (158.8 ± 13.5 vs. 96.2 ± 8.4 mm2), which resulted in greater diameter eight year after planting (47.5 ± 2.8 vs. 38.3 ± 2.3 mm). The lower values of Ψpd, Ec and SLA in the summer of the first two years after planting suggest that climatic conditions after planting rather than isolated drought events was the most critical period for the success of these saplings. In view of our results, the selection of plant material for forest plantation should be carefully evaluated in forest restoration projects, while priority should be given to those actions oriented to increase the early survival of local Q. ilex seedlings

Long term forest management drives drought resilience in Mediterranean black pine forest

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. Abstract Drought negative efects on forest ecosystems are projected to increase under global warming all over the world. In this context, forest management can be an efective 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 identifed 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 signifcantly infuenced 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

Climate and species stress resistance modulate the higher survival of large seedlings in forest restorations worldwide

Seedling planting plays a key role in active forest restoration and regeneration of managed stands. Plant attributes at outplanting can determine tree seedling survival and consequently early success of forest plantations. Although many studies show that large seedlings of the same age within a species have higher survival than small ones, others report the opposite. This may be due to differences in environmental conditions at the planting site and in the inherent functional characteristics of species. Here, we conducted a global-scale meta-analysis to evaluate the effect of seedling size on early outplanting survival. Our meta-analysis covered 86 tree species and 142 planting locations distributed worldwide. We also assessed whether planting site aridity and key plant functional traits related to abiotic and biotic stress resistance and growth capacity, namely specific leaf area and wood density, modulate this effect. Planting large seedlings within a species consistently increases survival in forest plantations worldwide. Species’ functional traits modulate the magnitude of the positive seedling size–outplanting survival relationship, showing contrasting effects due to aridity and between angiosperms and gymnosperms. For angiosperms planted in arid/semiarid sites and gymnosperms in subhumid/humid sites the magnitude of the positive effect of seedling size on survival was maximized in species with low specific leaf area and high wood density, characteristics linked to high stress resistance and slow growth. By contrast, high specific leaf area and low wood density maximized the positive effect of seedling size on survival for angiosperms planted in subhumid/humid sites. Results have key implications for implementing forest plantations globally, especially for adjusting nursery cultivation to species’ functional characteristics and planting site aridity. Nursery cultivation should promote large seedlings, especially for stress sensitive angiosperms planted in humid sites and for stress-resistant species planted in dry sites. © 2021 The Authors. Ecological Applications published by Wiley Periodicals LLC on behalf of Ecological Society of Americ

Forest productivity in southwestern Europe is controlled by coupled North Atlantic and Atlantic Multidecadal Oscillations

The North Atlantic Oscillation (NAO) depicts annual and decadal oscillatory modes of variability responsible for dry spells over the European continent. The NAO therefore holds a great potential to evaluate the role, as carbon sinks, of water-limited forests under climate change. However, uncertainties related to inconsistent responses of long-term forest productivity to NAO have so far hampered firm conclusions on its impacts. We hypothesize that, in part, such inconsistencies might have their origin in periodical sea surface temperature anomalies in the Atlantic Ocean (i.e., Atlantic Multidecadal Oscillation, AMO). Here we show strong empirical evidence in support of this hypothesis using 120 years of periodical inventory data from Iberian pine forests. Our results point to AMO+ NAO+ and AMO−NAO− phases as being critical for forest productivity, likely due to decreased winter water balance and abnormally low winter temperatures, respectively. Our findings could be essential for the evaluation of ecosystem functioning vulnerabilities associated with increased climatic anomalies under unprecedented warming conditions in the Mediterranean

Forest structure drives the expected growth of Pinus nigra along its latitudinal gradient under warming climate

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 droughtprone 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