Search

In boreal old-growth forests, advance regeneration typically attains canopy dominance through growth release events following partial disturbances. We sampled competing Picea mariana (Mill.) and Abies balsamea (L.) in disturbed old-growth stands in Quebec, Canada, to understand the intra- and interspecific size hierarchy development. We reconstructed tree size development and examined the role of initial size difference, time between germination and a disturbance, and the strength of response to the disturbance in determining tree size hierarchies. Trees that regenerated first generally dominated their intraspecific competitors also following a disturbance event. However, prolonged time between germination and disturbance resulted in a less deterministic outcome. Tree size difference prior to disturbance also influenced the development of size hierarchies. In interspecific competition between individuals of the same diameter, A. balsamea had a 61% probability of gaining dominance over P. mariana, the probability being 50% if P. mariana was 5 mm larger than A. balsamea. Dominant trees generally had the strongest response to the disturbance, reinforcing the existing size hierarchies. The largest trees typically gain dominance after a partial disturbance. However, interspecific competition is less predictable than intraspecific competition, small initial size difference, and prolonged time in suppression potentially changing tree size hierarchies. Key words: tree size hierarchy, advance regeneration, partial disturbance, competition, Abies balsamea, Picea mariana, old-growth forest, boreal forest Dans les vieilles forets boreales, la regeneration pre-etablies atteint generalement la canopee par le biais d'un ou de plusieurs evenements de liberation de la croissance a la suite de perturbations partielles. Cependant, on ne sait toujours pas comment les differences dans les strategies vitales des especes d'arbres influencent le developpement des hierarchies de taille entre les arbres concurrents. Pour comprendre le developpement de ces hierarchies de taille intra- et interspecifiques des especes arborescentes, nous avons echantillonne des Picea mariana (Mill.) et des Abies balsamea (L.) en competition dans des peuplements anciens perturbes du nord-est du Quebec, au Canada. Nous avons reconstitue l'evolution de la taille de paires d'arbres adjacents et examine le role de la difference de taille initiale, du temps ecoule entre la germination et une perturbation, ainsi que la force de la reponse a la perturbation dans la determination des hierarchies de taille des arbres. Les arbres qui se sont regeneres en premier ont generalement domine leurs concurrents intraspecifiques, meme apres une perturbation. Toutefois, un delai prolonge entre la germination et la perturbation a donne lieu a un resultat moins deterministe. La difference de taille des arbres avant la perturbation a egalement influence le developpement des hierarchies de taille. Dans la competition interspecifique entre individus de meme diametre, A. balsamea avait une probabilite de 61% de gagner la dominance sur P. mariana, la probabilite etant de 50% si P. mariana etait 5 mm plus grand que l'A. balsamea en competition. Les arbres dominants ont generalement reagi a la perturbation par une croissance plus forte que leurs concurrents, renforcant ainsi les hierarchies de taille existantes. Les differences de taille entre les arbres concurrents influencent fortement l'individu qui devient dominant a la suite d'une perturbation partielle. Cependant, la competition interspecifique est moins previsible que la competition intraspecifique, une faible difference de taille initiale et un temps prolonge de suppression pouvant modifier les hierarchies de taille des arbres. Mots-cles : hierarchie des tailles d'arbres, regeneration, perturbation partielle, concurrence, Abies balsamea, Picea mariana, foret ancienne, foret boreale, Introduction Advance regeneration is crucial in determining how forest ecosystems reorganize after a disturbance (Yamamoto 2000; Seidl and Turner 2022). Hence, if the changes in disturbance regimes change the competitive [...]

Silvicultural regeneration methods focus on manipulating the forest canopy, but success can depend on the use of site preparation to control competing vegetation, including the density of advance regeneration, and create suitable microsite conditions for germination and seedling establishment. Tip-up mounds are known to provide favorable conditions for some tree species, but the creation of tip-up mounds as a method of site preparation has scarcely been investigated. We assessed effects of artificial tip-up mounds on tree seedling composition across a gradient of regeneration methods and residual overstory densities 2-4 years post-implementation. We found that tree seedling communities on mounds in some treatments were compositionally distinct from untreated reference plots. However, no tree species exhibited a strong affinity for mounds when analyzed independently from the regeneration method, and much of the difference in composition was associated with lower dominance of maples (Acer spp. L.) on mounds. As maples are strong competitors in forests regenerated with selection systems, reduced maple competition on artificial mounds could advantage desired under-represented species and aid in natural regeneration over time. Therefore, in stands where promoting tree species diversity is desirable, implementing artificial tip-up mounds as part of a long-term strategy may be beneficial. Key words: site preparation, seedling composition, forest regeneration, Acer saccharum, shelterwood, Introduction Natural forest regeneration is a complex process influenced by factors that interact across space and time scales. These factors can interact with life history characteristics, including seed size and [...]

Tree stems have been identified as globally significant methane (C[H.sub.4]) sources; however, little information exists on emissions from tree wounds and branches. C[H.sub.4] emissions can occur from the decomposition of anaerobic heartwood, which is also associated with wounds; C[H.sub.4] may also be transported through the transpiration stream and emitted from branches. We compared C[H.sub.4] emissions between tree stems and branches and assessed whether trees with major wounds emit more than those without. C[H.sub.4] fluxes were measured from stems, branches, and wounds (classified as major or minor) of two dominant tree species in an upland temperate forest, and from the soil, and scaled up to the stand level. Branches and stems of both species emitted C[H.sub.4], and the per unit area emission rates from branches were similar to (or in some cases greater than) stems. Trees with major wounds had greater C[H.sub.4] emission rates than those without, from unblemished sections of their stems and from the wounds. At the stand scale, branches, stems, and wounds accounted for 83%, 9%, and 8% of net C[H.sub.4] emissions from trees, respectively, and collectively offset 63% of the soil C[H.sub.4] sink. These results indicate that tree branches and wounds can be important C[H.sub.4] sources in forests. Key words: methanogens, heartwood rot, decomposition, stem, trunk, upland temperate forest Les tiges des arbres ont ete identifiees comme des sources de methane (C[H.sub.4]) importantes au niveau mondial; cependant, il existe peu d'informations sur les emissions provenant des blessures et des branches des arbres. Les emissions de C[H.sub.4] peuvent provenir de la decomposition du bois de coeur anaerobique, qui est egalement associe aux blessures; le C[H.sub.4] peut egalement etre transporte par le biais de la transpiration et emis par les branches. Nous avons compare les emissions de C[H.sub.4] entre les tiges et les branches des arbres et evalue si les arbres presentant des blessures importantes emettent davantage que ceux qui n'en presentent pas. Les flux de C[H.sub.4] ont ete mesures a partir des tiges, des branches et des blessures (classees comme majeures ou mineures) de deux especes d'arbres dominantes dans une foret temperee de haute terre, et a partir du sol, et mis a l'echelle au niveau du peuplement. Les branches et les tiges des deux especes ont emis du C[H.sub.4], et les taux d'emission par unite de surface des branches etaient similaires (ou dans certains cas superieurs) a ceux des tiges. Les arbres presentant des blessures importantes avaient des taux d'emission de C[H.sub.4] plus eleves que ceux qui n'en presentaient pas, que ce soit a partir des sections non endommagees de leurs tiges ou a partir des blessures. A l'echelle du peuplement, les branches, les tiges et les blessures representaient respectivement 83%, 9% et 8% des emissions nettes de C[H.sub.4] des arbres, et compensaient collectivement 63% du reservoir de C[H.sub.4] du sol. Ces resultats indiquent que les branches et les plaies des arbres peuvent etre des sources importantes de C[H.sub.4] dans les forets. Mots-cles: methanogenes, pourriture du bois de coeur, decomposition, tige, tronc, foret temperee de haute terre, Introduction Methane (C[H.sub.4]) is a greenhouse gas with a global warming potential 32-45 times greater than carbon dioxide (C[O.sub.2]) over a 100-year timeframe (depending on whether pulsed or continual emissions [...]

A stand density index (SDI) was derived from three hypotheses, of which two concern mortality and growth up to the age at which there is an inflection point in growth, and the third relates mean tree volume and dbh (quadratic mean diameter at breast height) up to that age. The equations are log (no. of trees) = K - [[lambda]/1-[beta]] log dbh or SDI = trees/unit area x [([dbh/reference dbh]).sup.[lambda].sub.1-[beta]], reference dbh = 25.4 cm or 10 inches. The parameters [lambda] and [beta] relate mean tree volume to dbh and stand volume to number of trees. Either equation provides a simple alternative to determining the self-thinning line and finding its slope, and also provides a direct comparison to the Reineke equation. Comparison of SDI values and exponents from the above equations to others' results indicates the equations tend to produce smaller exponents, and larger SDI values, for dbh less than 25.4 cm. Values of [[lambda]/1-[beta]] varied with species and site quality, generally with smaller values than 1.605 for conifers, and larger values for angiosperms, when these were determined from yield tables, while values from experimental plots were always smaller than those from yield tables. Parameters must be estimated from data that are not significantly beyond the inflection age, and [beta] and the ratio of growth to mortality parameters must be comparable. Key words: stand density index, self-thinning, sigmoid growth, exponential growth, exponential mortality Un indice de densite de peuplement (IDP) a ete derive a partir de trois hypotheses, dont deux concernent la mortalite et la croissance jusqu'a l'age auquel il y a un point d'intersection dans la croissance, et la troisieme concerne le volume moyen des arbres et le diametre a hauteur de poitrine (dhp) jusqu'a cet age-la. Les equations sont les suivantes : log (no. d'arbres) = K - [[lambda] /1-[beta]] log dhp ou IDP = arbres/unitede surface * (dhp/dhp reference)[lambda]/1-[beta]], dhp reference = 25,4 cm ou 10 pouces. Les parametres [lambda] et [beta] relient le volume moyen des arbres a la hauteur de 10 dhp et le volume du peuplement au nombre d'arbres. L'une ou l'autre de ces equations offre une alternative simple pour determiner la ligne d'autoepaississement et determiner sa pente, et fournit egalement une comparaison directe a l'equation de Reineke. La comparaison des valeurs de l'IDP et des exposants a partir des equations ci-dessus aux resultats d'autres auteurs indique que les equations ont tendance a produire des exposants plus petits et des valeurs d'IDP plus grandes, pour les dhp inferieurs a 25,4 cm. Les valeurs de [[lambda]/1-[beta]] varient en fonction de l'espece et de la qualite du site, en general avec des valeurs inferieures a 1,605 pour les coniferes, et des valeurs plus grandes pour les angiospermes, lorsque celles-ci ont ete determinees a partir de tableaux de rendement, tandis que les valeurs des parcelles experimentales etaient toujours plus petites que celles des tableaux de rendement. Les parametres doivent etre estimes a partir de donnees qui ne sont pas significativement au-dela de l'age d'inflexion. Les parametres doivent etre estimes a partir de donnees qui ne depassent pas de maniere significative l'age d'inflexion, et [beta] et le rapport entre les parametres de croissance et de mortalite doit etre comparable. Mots-cles : indice de densite de peuplement, autoeclaircie, croissance sigmoide, croissance exponentielle, mortalite exponentielle, Introduction The log-log equation relating number of trees per unit area at full density to the quadratic mean diameter at breast height (dbh) proposed by Reineke (1933), (1) log N [...]

Treeline advance is a well-established response of treeline ecotones to climate change. However, the degree to which tree growth and establishment drives treeline movement is widely debated. We used geographic information system (GIS) analysis of aerial photographs and dendrochronological analysis of tree growth and age structure to examine treeline dynamics on Pikes Peak (Colorado). The rate of treeline advance at the site (1938-2017) was 0.235 m [year.sup.-1], and it accelerated through time. Several sites have transformed from abrupt to diffuse topology. Regional temperatures significantly increased after the 1890s, particularly in the last half-century. Tree growth was inhibited by late spring snow in the 1935-1985 window and enhanced by growing season temperature in the 1965-2009 window. Tree establishment above treeline appears to have transformed treeline topology and set up the potential for further treeline advance. We conclude that if current climatic trends and system relationships continue, treeline should continue to advance because (i) there are large numbers of seedlings and saplings above the treeline due to continuous significant seedling recruitment and (ii) growth of trees in the treeline ecotone is positively related to growing season temperatures, which are increasing. Other limits to the system, such as drought or topographic barriers, may arise in the future. Key words: treeline advance, tree establishment, tree growth, GIS. L'avancee de la limite des arbres est une reaction au changement climatique bien connue des ecotones de la limite des arbres. Cependant, la mesure dans laquelle l'etablissement et la croissance des arbres determinent le mouvement de la limite des arbres fait l'objet d'un vaste debat. Nous avons utilise l'analyse de photographies aeriennes a l'aide d'un systeme d'information geographique (SIG) et l'analyse dendrochronologique de la croissance et de la structure d'age des arbres pour etudier la dynamique de la limite des arbres au Pic Pikes, dans l'Etat du Colorado. Le taux de deplacement de la limite des arbres au site d'etude (1938-2017) etait de 0,235 m [an.sup.-1] et a augmente avec le temps. Plusieurs sites se sont transformes, passant d'une topologie abrupte a diffuse. Les temperatures regionales ont significativement augmente apres les annees 1890, particulierement au cours du dernier demi-siecle. La croissance des arbres a ete inhibee par la neige tardive au printemps durant la periode de 1935 a 1985 et favorisee par la temperature durant la saison de croissance durant la periode de 1965 a 2009. L'etablissement des arbres au-dela de la limite des arbres semble avoir transforme la topologie de la limite des arbres et enclenche la possibilite d'une avancee ulterieure de la limite des arbres. En conclusion, si les tendances courantes du climat et des relations du systeme persistent, la limite des arbres devrait continuer a avancer parce que : (i) il y a un grand nombre de semis et de gaules au-dela de la limite des arbres a cause du recrutement important et continu de semis et (ii) la croissance des arbres dans l'ecotone de la limite des arbres est positivement reliee a la temperature qui va en augmentant durant la saison de croissance. D'autres limites du systeme, telles que la secheresse ou des barrieres topographiques, pourraient survenir dans le futur. [Traduit par la Redaction] Mots-cles: avancee de la limite des arbres, etablissement des arbres, croissance des arbres, SIG., Introduction As average global temperature continues to increase (IPCC 2018), ecosystems that have climatically constrained boundaries are beginning to undergo significant geographical shifts (Walther et al. 2002). The alpine treeline [...]

Acclimation of leaf respiration to a 3-5-year period of warming by 3.4 °C for 10 North American tree species in forest conditions eliminated 80% of the increase in leaf respiration expected of non-acclimated trees; this suggests that the increase in respiration rates of terrestrial plants from climate warming, and the associated increase in atmospheric CO.sub.2 levels, may be less than anticipated. How tree acclimation limits CO.sub.2 output Increasing plant respiration in a warming world might be expected to further accelerate warming by releasing additional CO.sub.2 into the atmosphere, but the extent to which plants acclimate to high temperatures in the long-term is poorly quantified. Peter Reich et al. have measured acclimation of leaf respiration to a three- to five-year period of warming (by 3.4 °C) for ten North American tree species in forest conditions. They find that acclimation eliminated 80% of the increase in leaf respiration expected of non-acclimated trees. This result suggests that the increase in respiration rates of terrestrial plants resulting from climate warming -- and the associated increase in atmospheric CO.sub.2 concentration -- may be less than anticipated. Plant respiration results in an annual flux of carbon dioxide (CO.sub.2) to the atmosphere that is six times as large as that due to the emissions from fossil fuel burning, so changes in either will impact future climate. As plant respiration responds positively to temperature, a warming world may result in additional respiratory CO.sub.2 release, and hence further atmospheric warming.sup.1,2. Plant respiration can acclimate to altered temperatures, however, weakening the positive feedback of plant respiration to rising global air temperature.sup.3,4,5,6,7, but a lack of evidence on long-term (weeks to years) acclimation to climate warming in field settings currently hinders realistic predictions of respiratory release of CO.sub.2 under future climatic conditions. Here we demonstrate strong acclimation of leaf respiration to both experimental warming and seasonal temperature variation for juveniles of ten North American tree species growing for several years in forest conditions. Plants grown and measured at 3.4 °C above ambient temperature increased leaf respiration by an average of 5% compared to plants grown and measured at ambient temperature; without acclimation, these increases would have been 23%. Thus, acclimation eliminated 80% of the expected increase in leaf respiration of non-acclimated plants. Acclimation of leaf respiration per degree temperature change was similar for experimental warming and seasonal temperature variation. Moreover, the observed increase in leaf respiration per degree increase in temperature was less than half as large as the average reported for previous studies.sup.4,7, which were conducted largely over shorter time scales in laboratory settings. If such dampening effects of leaf thermal acclimation occur generally, the increase in respiration rates of terrestrial plants in response to climate warming may be less than predicted, and thus may not raise atmospheric CO.sub.2 concentrations as much as anticipated., Author(s): Peter B. Reich [sup.1] [sup.2] , Kerrie M. Sendall [sup.1] , Artur Stefanski [sup.1] , Xiaorong Wei [sup.1] [sup.3] , Roy L. Rich [sup.1] [sup.4] , Rebecca A. Montgomery [...]