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A correction of this article has been published in: Forestry: An International Journal of Forest Research, Volume 94, Issue 3, July 2021, Page 477, https://doi.org/10.1093/forestry/cpab015; International audience; The translation of genetic gains into economic gains is important for evaluating the impact of using genetically improved forest reproductive material (FRM) in the forest sector. However, fewstudies based on European forests have been published to date. Here, we analyse the stand-level wood production and financial performance of planting genetically improved FRM in even-aged planted forests focusing on four European case studies with advanced breeding programme material and different management contexts: Scots pine (Pinus sylvestris L.) in southern Finland, central Sweden and central France, and maritime pine (Pinus pinaster Ait.) in southwestern France. The growth of improved stands was simulated using species-specific growth models by incorporating two levels of expected genetic gains (present and next generations of seed orchards, varying from 7 to 40 per cent depending on the breeding programme) into the estimated mean annual volume increment over a rotation (m3 ha(-1) yr(-1)). For each level of genetic gain, we tested the plantation of improved FRM managed with two silvicultural scenarios (maintaining the standard baseline rotation and thinning regime vs shorter rotation through the earlier achievement of the recommended felling criteria) in comparison with the plantation of the reference unimproved material (absence of genetic gain) managed according to the standard silvicultural regime. The use of improved FRM resulted in a larger financial performance in terms of soil expectation value (SEV (sic) ha(-1), discount rate 3 per cent) than planting unimproved reference material in all case studies and silvicultural scenarios for different wood price contexts (SEV gain from +20 to +190 per cent depending on the genetic and silvicultural context). The challenges associated with the economic assessment of realized gains fromgenetically improved FRM are discussed. We argue that silvicultural guidelines should be adapted to the use of improved FRM in order to gain better financial performance and flexible silvicultural response of planted forests to future environmental and socio-economic changes.

International audience; Climate change is impacting temperate tree species phenology, especially the timing of budburst, which is mainly driven by air temperature. However, interactions with biotic or other environmental factors also influence the timing of budburst and are usually overlooked. We studied the influence of forest stand composition on the budburst date of adult trees belonging to two species: sessile oak (Quercus petraea, Matt. (Liebl.)) and Scots pine (Pinus sylvestris, L.). We monitored their budburst dates for seven consecutive years at 18 experimental plots located in central France. We compared the budburst dates of oaks and pines growing in monospecific stands with those of their counterparts in an oak-pine mixture. Our results show that sessile oak budburst date in mixed stands with Scots pine was delayed by 2.2 days on average (SE = 0.6) compared to its budburst date in monospecific stands. In years with early budburst, the delay was more pronounced - up to four days. For Scots pine, our results showed no difference between budburst dates in monospecific and mixed stands. We hypothesize that the persistent foliage of the Scots pine in the mixed stand intercepted a part of the solar radiation, which affected the temperature perceived by the oak buds, thereby delaying the heat accumulation needed for sessile oak budburst. This effect may be of interest for the management of sessile oak in the context of global warming. In the future, sessile oak may experience more frequent frost damage due to an earlier budburst. Managing sessile oak with an evergreen species could limit late frost damage to some extent by delaying budburst. Stand composition must obviously be taken into account when monitoring the phenology of temperate tree species and to enable robust comparisons of phenological events for a given tree species at different sites.

International audience; Forecasted climate change impacts on temperate forest ecosystems include increased summer drought. Forest managers can increase the resistance of forest stands against summer drought by reducing stand density and favoring tree species mixtures. These strategies have been studied separately, but their combined effect on increasing forest stand resistance to summer drought is unknown.The main objective of our study was to quantify tree species interaction effects on radial growth during a water stress period and to determine whether these effects changed with different levels of competition reflected by stand density. The study was based in the Orleans state forest (Central France) at a long-term triplet experimental site (OPTMix) with pure and mixed stands of mature Quercus petraea and Pinus sylvestris. The experimental design comprised three repetitions of two densities (low and medium) in each composition (pure oak, mixed stands, pure pine). We monitored tree radial growth with 216 manual dendrometers placed throughout 18 plots, on small, medium and large trees. We analyzed three consecutive years with contrasted water stress: no water stress, a summer stress period, and a late summer stress period. We found that mixture did not improve tree growth of the either species during the summer water stress period. On the other hand, there was a mixture effect during the late summer water stress period but only in medium-density stands inversely for the two species studied. More growth occurred for oaks in mixtures while, inversely, more growth occurred for pines in monocultures. A density effect occurred only for oaks, which grew more in lower-density stands than in medium-density stands. Finally, tree size did not influence seasonal resistance to drought.

International audience; Better knowledge and a more complete long-term monitoring of tree species phenology and tree foliage development are crucial to accurately estimating the impact of climate change on forest ecosystems functioning and on forest species distribution. We set up global solar radiation sensors under the forest canopy and continuously recorded solar radiation in order to follow the development of sessile oak (Quercus petraea L.) foliage in pure stands over four consecutive years and for two levels of stand density. At the same time, we made phenological observations to determine bud burst date. One of our goals was to link observed bud burst dates and transmittance measurements. Our results show that solar radiation transmittance during the leaf unfolding period followed a sigmoid-shaped curve; and that it was possible to fit a generalized logistic model to determine a set of parameters characterizing tree foliage and its development during the unfolding period. Among these parameters, we suggest that the date at which solar radiation interception by foliage reaches 50% could be used to monitor the beginning of the growing season over the long term. The relationship between observed bud burst date and the transmittance model parameters was more complex than we expected. We tested several indices to deduce the date of bud burst from transmittance. We showed that when radiation interception due to foliage reached 10%, this indicated the observed bud burst date. Finally, a linear model including parameters from the generalized logistic models of transmittance as predictors explained 57% of the variability in bud burst date. Complementary research combining light measurements and phenological observations over a longer period of time is needed to know whether these relationships could help estimate bud burst date regardless of the year or the stand density.

The IPCC previsions for the upcoming decades include an increase in frequency and intensity of drought events in several regions worldwide, including Northern Europe. Drought significantly affects forest ecosystems through decreased productivity, increased vulnerability to biotic disturbances and increased subsequent mortality. How forest ecosystems maintain resistance and resilience to drought events are important questions. Our study aimed to assess whether species mixture or an individual tree size within a stand alters a given tree’s resilience and resistance to drought. A retrospective study of tree-ring widths allowed us to calculate resistance, resilience and recovery indices for five recent drought events: 1976, the 1990–1992 period, 2003, 2006 and 2010. These drought events were selected based on the SPEI (Standardized Precipitation Evapotranspiration Index) drought index. Our study sample consisted of 108 individual sessile oak ( Quercus petraea (Matt.)) or Scots pine ( Pinus sylvestris L.) trees sampled in 2012 and 2013 (Orleans forest, central France) in pure and mixed stands, divided into three diameter classes corresponding to three sizes: large, medium and small trees. Scots pine performed better than sessile oak during the 1990–1992 and 2010 droughts while the contrary was observed for the 2003 and 2006 droughts. They performed equally in 1976. We suggest that the differing sensitivity of the two species to spring and summer drought explained this result. In our study, stand composition had no effect on resilience or resistance for either species. The size effect in oaks was unclear as small oaks displayed either a better performance or a worse performance than large oaks. Small pines displayed better resistance and resilience than pines of a larger size. This work stressed the importance of taking into account stand composition and trees size as well as soil and climatic conditions for each drought events to achieve a better understanding of the diversity of responses to climatic variations among forest ecosystems.

International audience; Coppice forestry is a conventional silvicultural practice that takes advantage of a tree's capacity to respond to disturbances by sprouting. Sprouting capacity is determined by many intrinsic and extrinsic factors such as parent tree age/size, understory light availability and deer browsing, which, under closed canopy conditions are important limiting factors for stump survival or sprout growth. However, the combined effect of potentially confounding abiotic and biotic factors on stump survival and sprout growth remains elusive, even more so under closed canopy conditions. This study aims to quantify the effect of deer browsing on stump mortality and sprout growth under closed-canopy conditions and to compare this effect with other known determinants. Here we show that stump survival and sprout growth in sessile oak (Quercus petraea Matt.) depend on deer browsing, understory light availability and the diameter of the parent tree. By studying paired fenced-unfenced plots, we confirmed that deer browsing decreased stump survival and inhibited sprout growth. Furthermore, by taking advantage of a gradient in understory light availability in monospecific and mixed stands of sessile oak and Scots pine (Pinus sylvestris L.), we showed a clear positive linear relationship between sprout growth and light availability. This relationship explained the observed differences among stand composition types. Finally, we found that increased understory light availability did not compensate for losses due to deer browsing. In the absence of deer browsing, our results demonstrate that sessile oak stumps regenerate well under closed-canopy conditions and maintain a moderate sprouting capacity at least until the age of 70-80 years old. Partial thinning could therefore be a potential tool to renew light-demanding tree species such as sessile oak in mixed high-forest stands. Nevertheless, we do not recommend coppicing sessile oak under closed canopies unless the oak stumps are protected from deer browsing and understory light availability is optimized as much as possible despite closed-canopy-management objectives.

The importance of plant litter traits and decomposability for nutrient cycling processes and plant community dynamics through plant-litter-soil feedbacks has been largely emphasized. However, the role of biotic interactions as drivers of intraspecific variability in litter traits remains surprisingly little studied. In this study, we used a large-scale, multi-site network of long-term tree removal experiments manipulating the abundance of a foundation tree species, i.e., Quercus petraea, to assess how plant interactions control intraspecific variation in oak leaf litter traits and decomposability. We studied 19 plots across eight experimental sites covering a large gradient of oak abundance, stand age, and local abiotic context. Oak leaf litter quality strongly declined with tree removal in early forest successional stage. Litter became poorer in nutrients such as N and Mg and richer in secondary metabolites such as lignin and condensed tannins. This in turn slowed its decomposition. Importantly, litter N loss switched from N release to N immobilization. Variance partitioning indicated that oak abundance explained as much variation in oak leaf litter traits as oak age and twice as much as soil inherent fertility. Confirmatory path analysis revealed that the decline of oak leaf litter quality induced by tree removal was most likely driven by a shift in understory plant species composition. Plasticity of oak leaf litter traits to the shortage of nutrient supply related to the development of understory plants competitors with higher nutrient capture and retention ability could potentially explain this response pattern. Our data also give consistent but weaker support that the decline of oak leaf litter quality could be driven by alleviated competition for light among canopy trees and subsequent enhanced crown exposure to light. Overall, our study provides evidence that biotic factors such as plant interactions are major drivers of plasticity in leaf litter traits and decomposability. This finding contributes to the emerging view that phenotypic -plasticity is fundamentally related to biotic interactions for sessile organisms, especially for long-lived and large plant species such as trees. Taking this source of functional diversity into account could help us to better understand plant community dynamics and ecological processes in terrestrial ecosystems.

The sampling design was based on the OPTMix experimental plots (Irstea Nogent-sur-Vernisson, France); OPTMix provided a part of the soil and dendrometric data as well. We thank Deki Fourcin, Sebastien Mace, Vincent Seigner and Yann Dumas for their help with data collection. We thank Frederic Miller from the INRA Orleans, Pierre Gelhaye and Frederic Mothe from the INRA Champenoux, and Frederic Lagane from the INRA Bordeaux for their help with sample preparations and microdensitometer analyses. We are thankful to Victoria Moore for correcting the English.; Mixing species has been proposed as a forest management option to mitigate the effects of the increase in summer drought episodes predicted by climate change models in temperate zones. Studying how the relationship between tree rings and summer drought episodes is modified by species mixture is of primary importance in this context. Based on a dendroclimatology study, we (i) qualified and quantified the relationship between ring width (RW) or mean ring density (MRD) and soil water deficit (SWD) in a ring-porous species, Quercus petraea, and a coniferous species, Pinus sylvestris, and (ii) determined if the relationships between tree ring characteristics and SWD are modified in mixtures. We found interspecific differences in RW patterns depending on the seasonality of the drought periods: RW in Q. petraea responded mainly to SWD from May to July, and RW in P. sylvestris to SWD from May to September. The ring-width of both species was strongly reduced by SWD; however, inter-specific differences in response to SWD seasonality triggered RW variations of opposite directions between the two species, for several years. In contrast, MRD for both species was dependent on the SWD from June to July. MRD in Q petraea increased slightly with SWD whereas MRD in P. sylvestris decreased strongly with SWD. The relationship between RW and SWD was not modified in mixtures compared to pure stands. We found that the effect of SWD on MRD was stronger in mixtures. The impact of SWD on species may be worsened in mixtures, but mixture of species with different growth sensitivities to the seasonality of the drought periods and to the drought intensity might help to buffer the effects of climatic fluctuations on the overall mixed stands productivity compared to pure stands. (C) 2015 Elsevier B.V. All rights reserved.

Predicting growth and mortality of trees growing in the understorey requires estimates of their light requirements but would provide valuable help for the management of irregular forest stands, especially for light-demanding species like Scots pine (Pinus sylvestris L.). Sixty-five pine saplings from 0.4 to 6 m high and aged from 2 to 58 years were sampled in different light conditions in the understorey of mixed sessile oak-Scots pine stands in a temperate forest in central France. Each pine sapling was described by its height, diameter and age and by the light reaching its apex. Pine sapling height and diameter were positively correlated with light and age. The results highlighted that Scots pine, a tree species usually described as shade-intolerant, is able to grow, although slowly, in shaded conditions (less than 10 per cent of full sunlight). However, the results also showed that a more shaded growing environment leads to lower maximal pine sapling height whatever its age. Together with results from studies on other species, these results provide further evidence of a critical sapling size at a given light level beyond which the pine sapling is likely to die and suggest that this critical size increases with light availability.

National audience; Le Pin sylvestre couvre une surface importante en France (1,2 million d’hectares, chiffres IFN de 1999) et se place au deuxième rang des essences résineuses pour le volume sur pied. L’adaptation aux sols pauvres, acides et hydromorphes de cette essence et la qualité de son bois constituent des atouts considérables. Cependant, le Pin sylvestre restait l’une des rares essences d’importance pour laquelle on ne disposait pas encore de modèle de croissance orienté vers la gestion forestière en France. L’objectif de cet article est de présenter un modèle adapté pour les peuplements réguliers de Pin sylvestre pour les régions Centre et Alsace. Les différentes relations constituant le modèle sont passées en revue ainsi que son utilisation dans le simulateur CAPSIS. Une attention particulière est portée sur son domaine de validité ainsi que sur son évaluation. Des perspectives d’amélioration et d’enrichissement du modèle sont également discutées.