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: In a forest stand, competition plays a central role, affecting individual growth. The size-growth relationship (SGR) indicates whether large trees grow proportionally more than (asymmetric SGR), equal to (symmetric), or less than (inversely asymmetric) smaller trees. SGR is thus an indicator of the growth partitioning and competition intensity within a stand. Using tree-ring analysis, we investigated long-term trends and interannual variability of SGR in several Norway spruce (Picea abies (L.) Karst.) stands in the Paneveggio Forest (eastern Italian Alps) over a 100-year period. The study plots were characterized by different stand structures (one multilayered and two monolayered) and disturbance histories (different dates of logging). Logging conducted until the 1940s induced an inversely asymmetric SGR in all the plots. During the successive five decades, in the monolayered plots, it shifted to direct asymmetric (plot 1) and to symmetric (plot 2). In the multilayered plot (plot 3), SGR remained inversely asymmetric. A direct effect of climate on SGR interannual variability was not found. However, fast-growing trees had a stronger climatic signal than slow-growing trees, indicating that growth rate affects tree response to climate. Moreover, we observed that sensitivity to climate was reduced in the monolayered plots over the study period, possibly as a consequence of increased competition. Resume: La competition joue un role central dans les peuplements forestiers etant donne l'influence qu'elle exerce sur la croissance des individus. La relation taille-croissance (RTC) indique si les gros arbres ont une croissance proportionnelle-ment plus grande (RTC asymetrique), egale (RTC symetrique) ou plus faible (RTC inversement asymetrique) que les arbres plus petits. La RTC est par consequent un indicateur de la repartition de la croissance et de l'intensite de la competition a l'interieur d'un peuplement. Al'aide de la dendrochronologie, nous avons etudie les tendances a long terme et la variabilite interannuelle de la RTC dans plusieurs peuplements d'epicea commun (Picea abies (L.) Karst.) de la foret de Paneveggio (Alpes italiennes orientales) sur une periode de 100 ans. Les parcelles echantillons etaient caracterisees par differentes structures de peuplement (une parcelle multietagee et deux parcelles monoetagees) et des historiques de perturbation distincts (differentes dates de recolte). Jusque dans les annees 1940, la recolte a engendre une RTC inversement asymetrique dans toutes les parcelles. Au cours des cinq decennies qui ont suivi, la RTC est devenue asymetrique (parcelle 1) et symetrique (parcelle 2) dans les parcelles monoetagees. La RTC est demeuree inversement asymetrique dans la parcelle multietagee (parcelle 3). Aucun effet direct du climat n'a ete observe. Cependant, les arbres a croissance rapide avaient un plus fort signal climatique que les arbres qui croissaient lentement, ce qui indique que le taux de croissance influence la reaction des arbres au climat. De plus, nous avons observe que la sensibilite au climat etait reduite dans les parcelles monoetagees pendant la duree de l'etude, possiblement a cause d'une plus forte competition. [Traduit par la Redaction], Introduction Competition between plants affects the ability of individuals to acquire resources, influencing growth and mortality patterns. In plant populations, partitioning of resources is defined as size-asymmetric when larger plants, [...]

Knowledge on the range of variability of montane European forests is hampered by limited data on the natural disturbance regime and by the small size of old-growth remnants. We studied the mixed Fagus--Abies--Picea Lom forest reserve (55.8 ha) in Bosnia and Herzegovina at three different scales: a grid of 40 sampling points to describe the structural characteristics and their range of variability, three transects to analyse gap size and gap fraction, and a 1.1 ha permanent plot to reconstruct age structure and disturbance history. The forest is characterized by a high volume of living trees (763 [m.sup.3] x [ha.sup.-1] in the 55.8 ha core area and 1160 [m.sup.3] x [ha.sup.-1] in the permanent plot) and of coarse woody debris (327 and 83 [m.sup.3] x [ha.sup.-1], respectively). The percentages of forest area in canopy and expanded gaps are 19% and 41%, respectively. The median canopy gap size is 76.9 [m.sup.2] and ranges from 11.1 to 708.0 [m.sup.2]. There are large (up to 120 cm diameter at breast height) and very old trees (441, 432, and 416 years for silver fir (Abies alba Mill.), Norway spruce (Picea abies (L.) Karst.), and European beech (Fagus sylvatica L.), respectively). During the last three centuries, the disturbance patterns have been characterized by single-tree or small group mortality. In central Europe, this forest is at the end of a gradient from forests characterized by intermediate disturbances to those where very small-scale processes predominate. Resume: On connait mal l'etendue de la variabilite des forets europeennes de montagne parce qu'il y a peu de donnees sur le regime de perturbations naturelles et a cause de la faible dimension des forets anciennes restantes. Nous avons etudie la foret mixte (Fagus--Abie--Picea) dans la reserve forestiere de Lom (55,8 ha) en Bosnie-Herzegovine a trois echelles differentes: une grille de 40 points d'echantillonnage pour decrire les caracteristiques structurales et leur variabilite, trois transects pour analyser la dimension des trouees et la fraction de troue, ainsi qu'une parcelle permanente de 1,1 ha pour reconstituer la structure d'age et l'historique des perturbations. La foret est caracterisee par un fort volume d'arbres vivants (763 [m.sup.3] x [ha.sup.-1] dans la zone centrale de 55,8 ha et 1 160 [m.sup.3] x [ha.sup.-1] dans la parcelle permanente) et de debris ligneux grossiers (respectivement 327 et 383 [m.sup.3] x [ha.sup.-1]). Le couvert et les trouees etendues occupent respectivement 19 % et 41 % de la superficie forestiere. La taille mediane des trouees est de 76,9 [m.sup.2] et varie de 11,1 a 708,0 [m.sup.2]. Il y a de gros (jusqu'a 120 cm au diametre a hauteur de poitrine) et tres vieux arbres (respectivement 441, 432 et 416 ans pour le sapin pectine (Abies alba Mill.), l'epicea commun (Picea abies (L.) Karst.) et le hetre commun (Fagus sylvatica L.). Durant les trois derniers siecles, les patrons de perturbation ont ete caracterises par la mortalite d'individus ou de petits groupes d'arbres. En Europe centrale, cette foret se situe a l'extremite d'un gradient allant de forets caracterisees par un niveau intermediaire de perturbation aux forets ou dominent des processus a tres petite echelle. [Traduit par la Redaction], Introduction Scientific understanding of the nature of disturbance events and successional or recovery processes in natural ecosystems has increased dramatically during the last decades (Pickett and White 1985; Frelich 2002). [...]

The effects of climate change on high‐latitude forest ecosystems are complex, making forecasts of future scenarios uncertain. The predicted lengthening of the growing season under warming conditions is expected to increase tree growth rates. However, there is evidence of an increasing sensitivity of the boreal forest to drought stress. To assess the influence of temperature and precipitation on the growth of black spruce (Picea mariana), we investigated long‐term series of wood anatomical traits on 20 trees from four sites along 600 km, the latitudinal range of the closed boreal forest in Quebec, Canada. We correlated the anatomical traits resolved at intraring level with daily temperature, vapor pressure deficit (VPD), and precipitation during the 1943–2010 period. Tree‐ring width, number of cells per ring and cell wall thickness were positively affected by spring and summer daily mean and maximum temperature at the northern sites. These results agree with the well‐known positive effect of high temperatures on tree ring formation at high latitudes. However, we captured, for the first time in this region, the latent impact of water availability on xylem traits. Indeed, in all the four sites, cell lumen area showed positive correlations with daily precipitation (mostly at low latitude), and/or negative correlations with daily mean and maximum temperature and VPD (mostly at high latitude). We inferred that drought, due to high temperatures, low precipitations, or both, negatively affects cell enlargement across the closed boreal forest, including the northernmost sites. The production of tracheids with narrower lumen, potentially more resistant to cavitation, could increase xylem hydraulic safety under a warmer and drier climate. However, this would result in lower xylem conductivity, with consequent long‐term hydraulic deterioration, growth decline, and possibly lead to tree dieback, as observed in other forest ecosystems at lower latitudes. [ABSTRACT FROM AUTHOR]

Detection of tree spatial patterns and structural attributes in a forest stand can provide critical information on occurring dynamics, and steer management decisions. However, since tree spatial distribution depends on factors that operate at different scales, including environmental heterogeneity and tree-to-tree interactions, both the extent to which measurements are taken and the choice of null model for spatial analysis (including site heterogeneity or not), can considerably influence investigation outcomes and related inferences. In this study, we aim to evaluate the effect of plot size, sampling design (single or combined plots), and null model for spatial analysis, on point pattern analysis and stand attribute assessment in temperate forests. Analyses were performed on 4-ha plots in two old-growth and two previously managed stands in central Europe. For each site, we calculated tree density, mean diameter, mean height and basal area, and performed point pattern analysis (pair-correlation function) under complete spatial randomness (CSR) and heterogeneous Poisson (HP) null models. We then assessed stand attributes and spatial patterns on subplots, and calculated their deviation from the 4-ha reference plot. As expected, accuracy of stand attribute assessment improved by increasing subplot size. However, while accuracy of small (0.25-ha) plots was quite high for basal area, it was rather low for tree density, especially in the old-growth stands. Outcomes of point pattern analysis in 0.25-ha plots were variable, generally presenting low agreement with the reference. Larger plots assured more consistent results, but deviations from the reference were still rather high when CSR null model was used. In all the sites, subplot agreement improved using HP model. Our investigation indicates that 0.25-ha plots are mostly reliable for assessing stand attributes in previously managed forests. However, tree distribution can be very variable both in these and in old-growth stands, therefore spatial patterns cannot be reliably detected with one small plot. Combining several small plots, and using null models accounting for site heterogeneity, are efficient strategies to detect small-scale spatial patterns, but plot larger than 1-ha should still be used to assess large-scale patterns in high-diversity forest stands. [ABSTRACT FROM AUTHOR]