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The Eucalyptus genus is extensively planted in Brazil for industrial use, and with the expansion of forest frontiers and climate changes, studies are needed on how these changes affect wood density (WD). The aim of this study was to evaluate the effect of some climate variables on WD of an Eucalyptus urophylla clone for a 4-5 year period. WD from trees collected in 12 sites were evaluated. Five growth rings were identified using a magnifying glass, X-ray densitometry, and forest inventory. WD was correlated with temperature (T), precipitation (P), soil water deficit, ring width, and current annual increment. There was no variation in WD in the first 20 months among sites. From that age on, WD was mainly correlated with T (r > 0.6). The 1 [degrees]C increase in T resulted in a WD reduction of 0.014 g [cm.sup.-1], and increases of 10 [m.sup.-3] [ha.sup.-1] in the final volume were related to an increase of 0.004 g [cm.sup.-1] in WD. Researchers and managers should continue to put efforts into broad experimental networks to assess the effects of climate change on the adaptation and wood quality of Eucalyptus clones. Highlights The influence of climate on E. urophylla wood density was greater after the third year of growth. The mean air temperature was the best correlated climatic variable with E. urophylla wood density. The cross-site climatic gradient was more important in wood density variation of E. urophylla than the variability among the years. Key words: wood quality, climate conditions, annual growth, densitometry, forest expansion, 1. Introduction Plant secondary (radial) growth is a dynamic process and related to external factors such as climate and soil (Pillai et al. 2013; Zhang et al. 2014; Mendivelso et [...]

Herbivores affect plants via direct consumption, but also indirectly via changes in the vegetation. These indirect effects may only manifest after decades of exposure and, as a result, their impact is rarely accounted for. To better understand the direct and indirect impacts of a large herbivore, moose (Alces alces), on forests, we measured tree growth in areas that were both subjected to and excluded from herbivory for over 80 years. Growth data were gathered from five tree species, ranging from low to high palatability. We found that at small sizes, Betula papyrifera, a preferred species, benefited from herbivore exclusion. However, larger individuals grew more when exposed to herbivory, a response we attribute to lower competition in heavily browsed conditions. Populus tremuloides, a highly preferred tree, did not show any differences between levels of herbivory. Abies balsamea, a preferred winter browsed, was only marginally affected by browsing at smaller sizes. The two non- preferred species, Picea glauca and Picea mariana, did not show differential growth between herbivory levels. We conclude that herbivores can impact forests through both direct and indirect effects, that these effects are size specific, and that effects vary among species in ways not always predicted by consumption patterns. Key words: Abies, Alces alces, Betula, Isle Royale National Park, Picea, Populus, Introduction Understanding the forces impacting ecological communities is critical for evaluating their current and future functioning. In the case of forest ecosystems, which are essential for humans in terms of [...]

We investigated how the surrounding environment influences the growth of dominant trees and their responses to temperature and insect epidemics in boreal forests of eastern Canada. We focused on 82 black spruce and jack pine focal trees in stands spanning a double gradient of species diversity and soil texture within a 36 [km.sup.2] area of western Quebec. For these trees, we compared their diameter at breast height, growth rates, temperature-growth relations, and growth during insect defoliator epidemics. We used linear models to study how surrounding tree attributes and soil properties affected the growth of focal trees. Models showed that tree growth responses and responses to temperature and insect epidemics were generally negative with higher intraspecific competition and positive with greater tree species diversity. Growth of both species benefitted from lower soil sand content. Our research offers novel insights on the potential role of the surrounding environment, notably tree competition and species diversity, in mitigating the vulnerability of eastern Canada's boreal trees to anthropogenic climate change and insect epidemics. Key words: basal area increments, forest tent caterpillar, growing season length, eastern spruce budworm, summer heat stress Nous avons etudie comment le milieu environnant influence la croissance d'arbres dominants et leurs reponses a la temperature et aux epidemies d'insectes dans les forets boreales de l'est du Canada. Nous nous sommes concentres sur 82 epinettes noires et pins gris dans des peuplements couvrant un double gradient de diversite d'especes et de texture du sol dans une zone de 36 [km.sup.2] de l'ouest du Quebec. Pour ces arbres, nous avons compare leur diametre a hauteur de poitrine, leur taux de croissance, les relations temperature-croissance et la croissance pendant les epidemies d'insectes defoliateurs. Nous avons utilise des modeles lineaires pour etudier comment les attributs des arbres environnants et les proprietes du sol affectaient la croissance des arbres focaux. Les modeles ont montre que les reponses de la croissance des arbres et les reponses a la temperature et aux epidemies d'insectes etaient generalement negatives avec une competition intraspecifique accrue entre arbres et positives avec une plus grande diversite d'especes d'arbres. La croissance des deux especes a beneficie d'une teneur en sable plus faible dans le sol. Notre recherche offre de nouvelles perspectives sur le role potentiel du milieu environnant, notamment de la competition et de la diversite des especes d'arbres, dans l'attenuation de la vulnerabilite des arbres boreaux de l'est du Canada au changement climatique anthropogenique et aux epidemies d'insectes. Mots-cles: accroissement de la surface terriere, livree des forets, longueur de la saison de croissance, tordeuse des bourgeons de l'epinette, stress thermique estival, 1. Introduction Anthropogenic climate change is expected to impact the growth of trees in boreal forests of Northeastern America directly through increasing temperatures (D'Orangeville et al. 2016; Pau et al. [...]

Water deficit or drought is the most important abiotic stress limiting plant growth performance and plant community development; this is typical in the Mediterranean area where plants are often severely and permanently water limited. Such is the case of the argan tree (Argania spinosa (L.) Skeels), one of the tree species most affected by desertification and global warming. To advance knowledge on how this tree can withstand drought stress, inoculation with a native complex of arbuscular mycorrhizal fungi (AMF), composed mainly of the genus Glomus, was studied in connection with a set of growth and physiological parameters. Under controlled conditions, inoculated and non-inoculated argan seedlings were grown for 3 months under three water regimens: 25%, 50%, and 75% relative to the field capacity of used soil substrate. The results showed that the argan tree had different growth abilities to develop and withstand the various applied water limitations. The AMF complex stimulated the growth and mineral nutrition of argan seedlings under the different imposed levels of water deficiency. Relative water content (RWC) in leaves, water potential, and stomatal conductance in argan leaves showed a general improvement in inoculated seedlings compared to non-inoculated ones. Soluble sugar and proline contents significantly increased in non-inoculated seedlings compared with inoculated seedlings under water-limiting conditions (25%). Similarly, oxidative enzyme (catalase, peroxidase, superoxide dismutase) activity increased significantly in drought-stressed seedlings. Non-inoculated seedlings showed the highest accumulation of these enzymes. Moreover, mycorrhizal symbiosis establishment positively correlated with argan tree seedlings in terms of growth, mineral nutrition, soluble sugar and proline contents, and enzymes activities. The main results from the current study suggest that AMF improve the ability of A. spinosa to tolerate drought by enhancing mineral nutrition and the transport of high levels of water by enhancing the RWC and water potential in leaves. Finally, the alleviation of the destructive effects of reactive oxygen species was modulated by enzymatic scavenging activity. Hence, the use of AMF in the technical process of argan seedlings production is highly recommended in different ecofriendly restoration strategies, with the aim of producing high quality seedlings capable of tolerating drought stress. Key words: mycorrhizae, drought, plant growth, Argania spinosa. Le deficit hydrique ou la secheresse est le stress abiotique le plus nefaste pour la croissance des plantes et le developpement des communautes vegetales; ce qui est typique en region mediterraneenne ou les vegetaux sont souvent severement et en permanence prives d'eau. C'est le cas de l'arganier (Argania spinosa (L.) Skeels), une des especes d'arbre parmi les plus affectees par la desertification et le rechauffement global. Pour elargir les connaissances sur la facon dont cet arbre peut resister au stress cause par la secheresse, l'inoculation avec un complexe indigene de champignons mycorhiziens a arbuscules (CMA), compose surtout de champignons du genre Glomus, a ete etudiee en lien avec un ensemble de parametres physiologiques et de croissance. En conditions controlees, des semis d'arganier inocules et non inocules ont ete soumis a trois regimes hydriques (25, 50 et 75% de la capacite au champ du sol utilise comme substrat) pendant trois mois. Les resultats montrent que l'arganier possede differentes capacites de croissance pour se developper et supporter les differents degres de privation d'eau qui ont ete appliques. Le complexe de CMA a stimule la croissance et la nutrition minerale des semis d'arganier malgre les differentes intensites de deficit hydrique. La teneur relative en eau dans les feuilles, le potentiel hydrique et la conductance stomatique dans les feuilles de l'arganier se sont generalement ameliores chez les semis inocules comparativement aux semis non inocules. La teneur en sucre soluble et en proline a significativement augmente chez les semis non inocules relativement aux semis inocules dans les conditions d'irrigation restreinte (25 %). Cela etait similaire aux enzymes oxydatifs (catalase, peroxydase, superoxyde dismutase) dont l'activite a significativement augmente chez les semis stresses par la secheresse. L'accumulation de ces enzymes a atteint un sommet chez les semis non inocules. De plus, l'etablissement de la symbiose mycorhizienne etait positivement correle avec les semis d'arganier en termes de croissance, de nutrition minerale, de teneur en sucre soluble et d'activite enzymatique. Les principaux resultats qui decoulent de cette etude indiquent que les CMA augmentent la tolerance a la secheresse de l'arganier en ameliorant la nutrition minerale et le transport de quantites elevees d'eau en augmentant la teneur relative en eau et le potentiel hydrique dans les feuilles. Finalement, l'attenuation des effets nefastes des types reactifs d'oxygene etaient modules par l'activite de piegeage enzymatique. Par consequent, l'utilisation des CMA dans l'itineraire technique de production de semis d'arganier est fortement recommandee dans differentes strategies de restauration respectueuses de l'environnement fondees sur l'arganier dans le but de produire des semis de grande qualite capables de tolerer le stress cause par la secheresse. [Traduit par la Redaction] Mots-cles : mycorhizes, secheresse, croissance des plantes, Argania spinosa., 1. Introduction Drought stress is one of the most severe factors impeding plant production worldwide, especially in the Mediterranean since it is one of the most vulnerable regions of the [...]

Intra-seasonal growth responses of co-occurring European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) to weather variability in montane forests can provide useful information on their future growth trends. To improve growth predictions, we aimed to identify (i) the main seasonal windows during which weather variability influences tree-ring growth, (ii) species-specific differences in the response to weather fluctuations, and (iii) teleconnections to remote sites in the Western Carpathians. We monitored intra-seasonal growth dynamics based on proxies extracted growth signals detected by high-resolution dendrometers in the transition zone between the beech and spruce altitudinal belt. Over 12 consecutive seasons in the natural montane forest (1350 m a.s.l.), the main part of spruce (68% to 10 July) and beech (95% to 26 August) annual increment was under the prevailing influence of temperature. After this, precipitation pattern (regarding spruce) and day length became the most influential variables during deceleration and cessation of growth. In addition, synchronous patterns with remote sites in the Western Carpathians were found. The results emphasize the importance of studying the influence of shorter-term weather fluctuations during the season. Our findings suggest that montane spruce tends to be less temperature-demanding and more drought-sensitive than beech, which may favor beech over the spruce under the future climate. Key words: European beech, Norway spruce, intra-seasonal growth, weather response, high altitude. Les reactions de la croissance intra saisonniere du hetre commun (Fagus sylvatica L.) et de l'epicea commun (Picea abies (L.) Karst.), deux especes cooccurrentes, a la variabilite des conditions meteorologiques dans les forets alpestres peuvent fournir des informations utiles concernant les tendances de leur croissance future. Afin d'ameliorer les predictions de la croissance, nous avions pour objectif d'identifier : (i) les principales fenetres saisonnieres durant lesquelles la variabilite des conditions meteorologiques influence la croissance des cernes annuels; (ii) les differences propres a chaque espece dans leur reaction aux fluctuations des conditions meteorologiques; et (iii) les teleconnections avec des stations eloignees dans les Carpates occidentales. Nous avons suivi la dynamique de la croissance intra saisonniere sur la base des signaux de croissance extraits de substituts detectes par les dendrometres haute resolution dans la zone de transition entre la ceinture altitudinale du hetre et de l'epicea. Au cours de 12 saisons consecutives dans la foret naturelle alpestre (1350 m a.s.l.), la principale portion de l'accroissement annuel de l'epicea (68 % jusqu'au 10 juillet) et du hetre (95 % jusqu'au 26 aout) etait sous l'influence preponderante de la temperature. Apres cela, le patron de precipitation (dans le cas de l'epicea) et la duree du jour sont devenus les variables les plus influentes durant le ralentissement et l'arret de la croissance. De plus, des patrons synchrones avec des stations eloignees dans les Carpates occidentales ont ete detectes. Les resultats mettent en evidence l'importance d'etudier l'influence des fluctuations des conditions meteorologiques a court terme durant la saison de croissance. Nos resultats indiquent que l'epicea alpestre tend a etre moins exigeant pour la temperature et plus sensible a la secheresse que le hetre, ce qui peut avantager le hetre plutot que l'epicea dans le contexte des conditions climatiques a venir. [Traduit par la Redaction] Mots-cles : hetre commun, epicea commun, croissance intra saisonniere, reaction aux conditions meteorologiques, haute altitude., Introduction High-altitude montane forests provide important ecosystem services and are sensitive to the changing climate, which probably seriously influences their functioning (Lindner et al. 2010; Treml et al. 2012), as [...]

Abstract: Wetland restoration is a common practice in the southeastern United States, where changing land use patterns have resulted in the widespread degradation of coastal ecosystems. Re-establishment of indigenous vegetation [...]

We examined modulus of elasticity (MoE) derived from SilviScan in white spruce (Picea glauca (Moench) Voss) at the site, tree, and ring levels across the Boreal Plains ecozone in Canada. Area-weighted averages of MoE were calculated for juvenile and mature wood and were examined in relation to radial growth, climate, and location. Correlations indicated that there was a negative relationship between radial growth and MoE in the juvenile wood that was detectable at the site and tree levels; however, the relationship weakened in the mature wood, particularly at the site level. Few climate variables were correlated with MoE in juvenile wood, whereas multiple summer and fall climate variables showed a significant correlation with MOE in mature wood. A model describing the radial profile of MoE explained 58% of the variability in MoE, with 10% of the random variability attributed to between-tree differences. Elevation and summer water balance accounted for nearly all of the betweensite variability. A decrease in MoE with increasing elevation was noted and has been previously linked to a decrease in cell wall thickness due to a shorter growing season at higher elevations. Integration of the MoE profile model into an individual-tree growth and yield simulator is the next logical step. Key words: wood stiffness, white spruce, climate, Boreal Plains, radial growth. Nous avons etudie le module d'elasticite (MoE) derive de SilviScan chez l'epinette blanche (Picea glauca (Moench) Voss) a l'echelle de la station, de l'arbre et du cerne annuel a travers l'ecozone des plaines boreales au Canada. Des moyennes du MoE ponderees par la superficie ont ete calculees pour le bois juvenile et le bois mature et ont ete etudiees en relation avec la croissance radiale, le climat et la station. Les correlations indiquent qu'il existe une relation negative entre la croissance radiale et le MoE dans le bois juvenile qui est detectable a l'echelle de la station et de l'arbre. Cependant, cette relation s'attenue dans le bois mature, particulierement a l'echelle de la station. Peu de variables climatiques sont correlees avec le MoE dans le bois juvenile tandis que de multiples variables climatiques d'ete et d'automne sont significativement correlees avec le MoE dans le bois mature. Un modele decrivant le profil radial du MoE explique 58 % de la variabilite du MoE et 10 % de la variabilite aleatoire est attribuee aux differences entre les arbres. L'altitude et le bilan hydrique estival expliquent presque toute la variabilite entre les stations. Une diminution du MoE avec l'augmentation de l'altitude a ete notee et a precedemment ete reliee a une diminution de l'epaisseur de la paroi cellulaire due a une saison de croissance plus courte a plus haute altitude. L'integration du modele du profil du MoE dans un simulateur de croissance et rendement d'arbres individuels est la prochaine etape logique. [Traduit par la Redaction] Mots-cles : rigidite du bois, epinette blanche, climat, plaines boreales, croissance radiale., Introduction White spruce (Picea glauca (Moench) Voss) is often used for the production of structural lumber or plywood because of its relatively low mass and high stiffness (i.e., modulus of [...]

Tree growth at the treeline ecotone is known to be sensitive to climate variability and is thus considered to be a worldwide biomonitor of climate change. However, our understanding of within-region variation in growth responses through space and time is limited. A dry south-facing slope dominated by Pinus wallichiana A.B. Jacks. and a wet north-facing slope dominated by Abies spectabilis (D. Don) Spach in Nepal, central Himalaya, were used to analyze the intersite (i.e., dry vs. wet sites) and intrasite (i.e., treeline vs. forest line elevations) tree-growth relationships, as well as response to monthly and seasonal temperature and precipitation at annual and bidecadal time scales. At both study sites and at two elevations within each site, growth can be strongly affected by growing-season and nongrowing-season factors; however, there are inconsistencies in terms of the climate-growth relationship across space and over time. At the dry site, only a weak positive growth response to summer temperature is observed. At both sites, there is a negative growth response to winter precipitation at both high and low elevations, and this response is markedly independent of the summer and winter temperature trends of the respective site. At the wet site, growth at the higher elevation is negatively correlated to the early summer temperature, whereas a positive growth response to spring precipitation is observed at the lower elevation, indicating a possible drought effect. The results illustrate how different climatic drivers may govern tree-growth responses both between sites with contrasting climates within a region and along elevational gradients within the treeline ecotone. This underlines the need for multiscale studies and a focus on multiple climate variables when analyzing treeline ecotone responses to climate change. Key words: Abies spectabilis, climate-growth relations, forest line, Pinus wallichiana, treeline, tree rings. On sait que la croissance des arbres dans l'ecotone de la limite des arbres est sensible aux variations du climat et qu'elle est par consequent consideree comme un indicateur biologique du changement climatique global. Cependant, notre comprehension de la variation intraregionale des reactions de la croissance dans l'espace et le temps est limitee. Une pente seche exposee au sud dominee par Pinus wallichiana A.B. Jacks. et une pente humide exposee au nord dominee par Abies spectabilis (D. Don) Spach au Nepal, dans l'Himalaya central, ont ete utilisees pour analyser le comportement de la croissance des arbres entre les sites (c.-a-d. sec vs. humide) et dans les sites (c.-a-d. altitude de la limite des arbres vs. celle de la limite de la foret commerciale) ainsi que sa reaction a la temperature et a la precipitation mensuelles et saisonnieres a des echelles temporelles annuelle et bi-decennale. Dans les deux sites a l'etude, et aux deux altitudes dans chacun des sites, la croissance peut etre fortement influencee par des facteurs associes ou non a la saison de croissance. Cependant, la relation entre le climat et la croissance n'est pas coherente dans l'espace ni dans le temps. Dans le site sec, seulement une faible reponse positive de la croissance a la temperature estivale a ete observee. Dans les deux sites, la croissance reagit negativement aux precipitations hivernales, aux altitudes elevee et faible, et cette reaction est manifestement independante des tendances des temperatures estivales et hivernales dans chacun des sites. Dans le site humide, la croissance a l'altitude la plus elevee est negativement correlee a la temperature en debut d'ete tandis qu'on observe une reponse positive de la croissance aux precipitations printanieres a l'altitude plus basse, l'indication d'un effet de secheresse potentiel. Les resultats illustrent de quelle facon differents facteurs climatiques peuvent controler les reponses en croissance des arbres tant entre les sites dont le climat differe a l'interieur d'une region que le long de gradients altitudinaux dans l'ecotone de la limite des arbres. Cela met en evidence la necessite d'etudes a differentes echelles, avec un accent sur de multiples variables climatiques lorsqu'on analyse les reponses de l'ecotone de la limite des arbres au changement climatique. [Traduit par la Redaction] Mots-cles: Abies spectabilis, relations entre la croissance et le climat, limite de la foret commerciale, Pinus wallichiana, limite des arbres, cernes annuels., Introduction The treeline ecotone, which marks the transition from closed forest to the treeless alpine or arctic tundra, is highly responsive to climate (Germino et al. 2002; Dullinger et al. [...]

We analyzed a series of increment cores collected from 260 adult dominant or co-dominant quaking aspen (Populus tremuloides Michx.) trees from national forests across Colorado and southern Wyoming in 2009 and 2010. Half of the cores were collected from trees in stands with a high amount of crown dieback, and half were from lightly damaged stands. We define the level of stand damage based on stand survey data in which lightly damaged stands had average crown dieback of 16% and heavily damaged stands averaged 41%. Upon analysis, two-thirds of the cores collected did not exhibit radial growth correlated with region-wide patterns (e.g., climate) and were classified as having a low cohesive response. The site variable most predictive of whether a stand exhibited high cohesive response or low cohesive response was site elevation, followed by aspect, slope, and canopy closure. Sites with high cohesive response stands were more likely to have aspen bark beetle damage, white rot, and Cryptosphaeria canker. We did not detect relationships between tree growth and summer precipitation from 1900-2008, but there was a relationship between growth and annual precipitation. A growth model included maximum May and July temperatures, as well as the current and previous year's annual precipitation. Key words: aspen, Populus tremuloides, drought, increment, mortality. Nous avons analyse une serie de carottes prelevees sur 260 peupliers faux-tremble (Populus tremuloides Michx.) adultes dominants ou codominants dans des forets nationales a travers le Colorado et le sud du Wyoming en 2009 et 2010. La moitie des carottes ont ete prelevees sur des arbres dans des peuplements severement touches par le deperissement de la cime et l'autre moitie dans des peuplements legerement endommages. Nous avons defini le niveau de dommage du peuplement sur la base de donnees d'inventaire de peuplement selon lesquelles les peuplements legerement endommages avaient un taux moyen de deperissement de 16 % alors que les peuplements severement endommages avaient un taux moyen de deperissement de 41 %. Apres analyse, les deux tiers des carottes ne montraient pas de correlation entre la croissance radiale et des profils regionaux (p. ex. le climat) et ont ete classees comme ayant une faible reponse cohesive. Parmi les variables de site, l'altitude predisait le mieux la reponse cohesive du peuplement, suivie de l'exposition, de la pente et de la fermeture du couvert. Le peuplier faux-tremble avait plus de chance d'etre endommage par les scolytes, la carie blanche et le chancre cryptosphaerien dans les sites oU les peuplements avaient une forte reponse cohesive. Nous n'avons pas detecte de relation entre la croissance des arbres et la precipitation estivale de 1900 a 2008, mais il y avait une relation entre la croissance et la precipitation annuelle. Un modele de croissance incluait les temperatures maximum des mois de mai et juillet ainsi que la precipitation annuelle de l'annee en cours et de l'annee precedente. [Traduit par la Redaction] Mots-cles: peuplier faux-tremble, Populus tremuloides, secheresse, accroissement, mortalite., Introduction Quaking aspen (Populus tremuloides Michx.) is the primary pioneer tree species and one of a few hardwood tree species found in forests throughout the southern Rocky Mountain region (Mueggler [...]

We evaluated effects of topsoil scarification by heavy machinery on growth of two valuable, shade-intolerant tree species--Nothofagus dombeyi (Mirb.) Oerst. (evergreen and considered to be very plastic to different soil fertility levels) and Nothofagus alpina (Poepp. & Endl.) Oerst. (deciduous and considered to be sensitive to soil fertility) - seedlings that were underplanted in Nothofagus old-growth forests, which were subjected to shelterwood cuttings without the final cut in the Chilean Andes. We compared tree basal diameter growth as it responds to light availability and soil compaction (as measured by resistance to penetration) by fitting a growth model based on the Michaelis-Menten equation. Predicted growth of N. dombeyi was greater than N. alpina in high and low light levels; however, there were no significant differences between the species. Both species showed significant differences at high levels of penetration resistance (>2000 kPa). Differences for N. dombeyi occurred above ~40% in total light, and differences occurred for N. alpina above ~20% in total light. However, they were not different when compared at low and intermediate levels of penetration resistance. The results suggest that partial shelterwood cuts may provide adequate light levels to achieve appropriate growth of underplanted Nothofagus seedlings. However, if regeneration of N. alpina is desired, scarification of topsoil needs to be implemented with more caution in canopy openings, as traffic and soil removal by heavy machinery can have detrimental effects on growth of this species and other species that are more sensitive to soil compaction. Key words: Michaelis-Menten, shade tolerance, soil resistance to penetration, stress conditions, underplanting. Nous avons evalue les effets du scarifiage de la couche superieure du sol avec de la machinerie lourde sur la croissance de semis de deux especes d'arbre precieuses et intolerantes a l'ombre, Nothofagus dombeyi (Mirb.) Oerst. (espece a feuilles persistantes qui est consideree comme etant tres plastique a differents niveaux de fertilite du sol) et Nothofagus alpina (Poepp. & Endl.) Oerst. (espece decidue qui est consideree comme etant sensible a la fertilite du sol). Ces semis ont ete plantes sous le couvert de vieilles forets de Nothofagus soumises a des coupes progressives sans la coupe finale dans les Andes chiliennes. Nous avons relie la croissance en diametre au collet des semis a la disponibilite de la lumiere et a la compaction du sol (mesuree par la resistance a la penetration) en ajustant un modele de croissance fonde sur l'equation de Michaelis-Menten. La croissance predite de N. dombeyi etait plus grande que celle de N. alpina sous des intensites lumineuses forte et faible, mais sans qu'il y ait de differences significatives entre les especes. Des differences significatives ont ete observees chez les deux especes lorsque la resistance a la penetration etait elevee (>2000 kPa). Les differences ont ete observees chez N. dombeyi au-dessus de ~40 % de la lumiere totale alors qu'elles l'ont ete au-dessus de ~20 % dans le cas de N. alpina. Toutefois, aucune difference n'a ete observee lorsque la resistance a la penetration etait faible ou intermediate. Ces resultats indiquent que les coupes progressives peuvent procurer des niveaux de lumiere adequats pour obtenir une croissance appropriee des semis de Nothofagus plantes sous couvert. Cependant, si on desire que la regeneration de N. alpina s'etablisse, le scarifiage de la couche superieure du sol doit etre realise plus prudemment dans les ouvertures du couvert parce que la circulation et l'enlevement du sol par la machinerie peuvent avoir des effets nefastes sur la croissance de cette espece et d'autres qui sont plus sensibles a la compaction du sol. [Traduit par la Redaction] Mots-cles: Michaelis-Menten, tolerance a l'ombre, resistance du sol a la penetration, conditions de stress, plantation sous couvert., Introduction Silvicultural practices manage canopy structures with the objective of regenerating and reallocating growing space for desired crop species (Nyland 2002; Puettmann et al. 2008a). Questions on which resource levels [...]

European beech (Fagus sylvatica L.) is an economically and ecologically important forest tree species in Europe. Expected future temperature increases due to global climate change may significantly affect growth of beech trees and consequently influence carbon cycling in beech forests. We tested the hypothesis that soil temperature influences the growth of both belowground and aboveground parts of beech seedlings. One-year-old seedlings were transferred into rhizotrons and subjected to two different soil temperatures for 2 years while the soil moisture level was kept constant. The main effect of the soil temperature was a changed biomass of the woody part of the seedlings. Soil temperature significantly influenced the biomass of shoots and roots and diameter of the stem, which were the highest for the seedlings grown in conditions of soil temperatures maintained in the range of summer soil temperatures from the site of origin of the seedlings. Increased soil temperature also resulted in increased specific root length and specific root tip density. Root-to-shoot ratio and leaf parameters (leaf mass, number of leaves, and specific leaf area), except for leaf area ratio, were not influenced by soil temperature. Key words: Fagus sylvatica, biomass allocation, fine roots, rhizotrons, cooling of the root system, soil warming, specific root length. Le hetre commun (Fagus sylvatica L.) est une essence forestiere ecologiquement et economiquement importante en Europe. L'augmentation anticipee de la temperature due aux changements climatiques globaux peut avoir un effet nefaste significatif sur la croissance des hetres et par consequent sur le recyclage du carbone dans les hetraies. Nous avons teste l'hypothese voulant que la temperature du sol influence la croissance des parties souterraine et aerienne des semis de hetre. Des semis d'un an ont ete transferes dans des rhizotrons et soumis a deux temperatures du sol differentes pendant deux ans en gardant le meme degre d'humidite du sol. Le principal effet de la temperature du sol a ete le changement dans la biomasse des tissus ligneux des semis. La temperature du sol a eu une influence significative sur la biomasse des pousses et des racines et sur le diametre de la tige dont les valeurs etaient les plus elevees chez les semis cultives dans un sol dont la temperature etait maintenue dans la gamme de temperatures estivales observees dans le sol des sites d'oU provenaient les semis. L'augmentation de la temperature a aussi augmente la longueur racinaire specifique et le nombre d'apex racinaires par unite de poids. Le rapport racines-pousses et les parametres foliaires (masse foliaire, nombre de feuilles, et surface foliaire specifique) a l'exception de l'indice de surface foliaire, n'ont pas ete influences par la temperature du sol. [Traduit par la Redaction] Mots-cles : Fagus sylvatica, allocation de biomasse, racines fines, rhizotrons, refroidissement du systeme racinaire, rechauffement du sol, longueur racinaire specifique., Introduction Currently, European beech (Fagus sylvatica L.) is a widely spread tree species in central and western Europe. In the northern part of its range, it prefers low altitudes, whereas [...]

The aim of this study is to analyze the relationships between black spruce (Picea mariana (Mill.) B.S.P.) growth and climate at a large spatial scale in North America's northeastern boreal forest. The study area (approximately 700 000 [km.sup.2]) is located in the taiga zone of the Quebec--Labrador Peninsula. A network of tree-ring chronologies from 93 black spruce populations was developed. A hierarchical cluster analysis was conducted to analyze tree-ring series affinities, and response functions were calculated to analyze relationships between tree rings and climate. The cluster analysis results showed well-marked spatial affinities among the tree-ring series. These affinities were strongly linked with the spatial variability of the relationships between tree rings and climate. The interannual growth variations were governed mainly by the temperature variables that preceded the growing season (November (negative influence), December-January (positive influence), and April (positive influence)). The growing-season temperature (July temperature) mainly influenced the northernmost populations. Relationships between tree rings and climate in the northeastern boreal forest varied at a large spatial scale. This variability was expressed by a north-south contrast, which appears to be related to a temperature gradient, and an east-west contrast linked to a humidity gradient, which favors winter snow cover. Key words: dendroecology, relationships between tree rings and climate, taiga, black spruce, Quebec--Labrador peninsula, spatial variability. Le but de cette etude est d'analyser la variabilite spatiale des relations entre la croissance de l'epinette noire (Picea mariana (Mill.) B.S.P.) et le climat dans la foret boreale Nord-Americaine. La zone d'etude (environ 700 000 [km.sup.2]) se trouve dans la region de la taiga de la peninsule Quebec-Labrador. Un reseau de dendrochronologies provenant de 93 peuplements d'epinette noire a ete construit. Une analyse de groupement hierarchique a ete realisee pour analyser les affinites entre les series et des regressions lineaires multiples associees a la technique << bootstrap >> ont ete utilisees pour calculer les fonctions de reponse des arbres au climat. Les variations interannuelles de la croissance sont regies principalement par des variables de temperature qui precedent la saison de croissance (temperature des mois de novembre (influence negative), decembre- janvier (influence positif) et avril (influence positif)). Les temperatures ayant une influence durant la periode de vegetation (temperature de juillet) ne s'exerce que sur les peuplements les plus septentrionaux. Les relations cerne-climat dans le nord de la foret boreale varie fortement sur la zone etudiee. Cette variabilite est exprimee par un contraste nord-sud qui semble etre reliee a un gradient de temperature et par un contraste est-ouest lie a un gradient d'humidite qui favorise la couverture de neige en hiver. Mots-cles : dendroecologie, relations cerne-climat, taiga, epinette noire, peninsule Quebec--Labrador, analyse spatiale., Introduction North America's boreal forest is dominated by black spruce (Picea mariana (Mill.) B.S.P.), a species indigenous to North America (Farrar 1995). Black spruce forests can be divided into three [...]

We examined the effects of a root-feeding beetle larva (Anomala cuprea Hope) on the survival and biomass of Lolium perenne L. and Plantago lanceolata L. plants at various ages. We hypothesized that belowground herbivory would kill more juveniles than mature plants because of greater root damage. We predicted that for juvenile plants, mortality would be higher for P. lanceolata than for L. perenne, because the thin taproot of P. lanceolata is less tolerant to herbivory. We hypothesized that for mature plants, herbivory of fibrous roots would negatively affect biomass; thus, L. perenne would be less tolerant than P. lanceolata. Plants of L. perenne or P. lanceolata at four ages were grown in pots with or without a herbivore. Herbivores killed juvenile plants, but not mature plants, of both species. More juveniles of P. lanceolata than L. perenne were killed by herbivory. In P. lanceolata, the low biomass of juveniles was attributed to herbivory, but herbivory did not affect the biomass of mature plants. In contrast, herbivory negatively affected the biomass of L. perenne plants of all ages. We concluded that the effects of belowground herbivory depend on plant age and, thus, on plant growth stage and root architecture. Key words: grubs, plant-soil interactions, plant tolerance, root architectures, root herbivore. Les auteurs ont examine les effets d'une larve de coleoptere qui se nourrit de racines (Anomala cuprea Hope) sur la survie et la biomasse de Lolium perenne L. et Plantago lanceolata L. a des ages differents. Ils ont pose l'hypothese que l'activite herbivore souterraine tuerait davantage de juveniles que de plants matures a cause d'un dommage racinaire plus important. Ils ont predit que pour les plants juveniles, la mortalite serait plus elevee chez P. lanceolata que pour L. perenne, car la racine pivotante de P. lanceolata est moins tolerante a l'herbivorisme. Ils ont egalement pose l'hypothese que chez les plants matures, l'herbivorisme des racines fibreuses affecterait negativement la biomasse; ainsi, L. perenne serait moins tolerant que P. lanceolata. Les plants de L. perenne ou de P. lanceolata de 4 ages differents ont ete cultives en pots en presence ou en absence d'herbivores. Les herbivores ont tue les plants juveniles mais non les plants matures des deux especes. Davantage de juveniles de P. lanceolata que de L. perenne ont ete tues par l'herbivorisme. Chez P. lanceolata, la faible biomasse des juveniles etait attribuable a l'herbivorisme, mais l'herbivorisme n'affectait pas la biomasse des plants matures. Au contraire, l'herbivorisme affectait negativement la biomasse des plants de L. perenne de tous les ages. Les auteurs concluent que les effets de l'herbivorisme souterrain dependent de l'age du plant, et par consequence, du stade de croissance et de l'architecture racinaire. [Traduit par la Redaction] Mots-cles: larve, interaction plante-sol, tolerance de la plante, architecture racinaire, herbivore des racines., Introduction Belowground herbivores significantly shape many ecosystem processes, such as plant successional patterns (Brown and Gange 1989,1990,1992; De Deyn et al. 2003; Rasmann et al. 2011). This is because belowground [...]

: Atmospheric pollution levels in China are increasing quickly. Experience from other polluted regions shows that tree growth could be affected, but long-term effects of N deposition and soil acidification on Chinese forests remain mostly unknown. Soil acidification and N deposition were simulated for Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations managed for three consecutive 20-year rotations in southeastern China. A factorial experiment combined four rain pH levels (2.5, 4.0, 5.6, and 7.0), four N deposition rates (1, 7.5, 15, and 30 kg N * [ha.sup.-1] * [year.sup.-1]), and two site qualities (poor and rich). Results indicate that atmospheric pollution effects are not immediate, but after one to two rotations, soil acidification effects could reduce ecosystem C pools significantly (-25% and -11% in poor and rich sites, respectively). N deposition rates above 15 kg N * [ha.sup.-1] * [year.sup.-1] could offset some of the negative effects of soil acidification and lead to more ecosystem C (19 and 28 Mg C * [ha.sup.-1] more in poor and rich sites, respectively, than in low N deposition). However, at high N deposition rates (> 15 kg N * [ha.sup.-1] * [year.sup.-1]), N leaching losses could greatly increase, reaching 75 kg N * [ha.sup.-1] * [year.sup.-1]. Moderate N deposition could increase tree biomass production and soil organic mass, resulting in increased ecosystem C, but these gains could be associated with important N leaching. Atmospheric pollution could also result in the long term in nutrient imbalances and additional ecological issues (i.e., biodiversity loss, eutrophication, etc.) not studied here. Resume: Les niveaux de pollution atmospherique augmentent rapidement en Chine. L'experience d'autres regions aux prises avec la pollution montre que la croissance des arbres pourrait etre ralentie mais les effets a long terme des depots azotes (N) et de l'acidification des sols dans les forets chinoises sont pratiquement inconnus. L'acidification du sol et les depots de N ont ete simules dans des plantations de sapin de Chine (Cunninghamia lanceolata (Lamb.) Hook.) amenagees pendant trois rotations consecutives d'une duree de 20 ans dans le sudest de la Chine. Une experience factorielle a combine quatre niveaux de pluie acide (pH 2,5, 4,0, 5,6 et 7,0), quatre taux de deposition de N (1, 7,5, 15 et 30 kg N * [ha.sup.-1] * [year.sup.-1]) et deux qualites de station (pauvre et riche). Les resultats montrent que les effets de la pollution atmospherique ne sont pas imme-diats, mais qu'apres une a deux rotations, les effets de l'acidification du sol pouvaient reduire de facon significative les reserves de carbone (C) de l'ecosysteme (-25 et -11 % respectivement dans les stations pauvres et riches). Les taux de deposition de N plus eleves que 15 kg N * [ha.sup.-1] * [year.sup.-1] pouvaient attenuer certains des effets negatifs de l'acidification du sol et ont mene a plus de C de l'ecosysteme (19 et 28 Mg C * [ha.sup.-1] de plus respectivement dans les stations pauvres et riches qu'a-vec un faible taux de deposition de N). Cependant, les pertes de N par lessivage pouvaient augmenter de facon importante, jusqu'a 75 kg N * [ha.sup.-1] * [an.sup.-1], lorsque le taux de deposition de N etait eleve (> 15 kg N * [ha.sup.-1] * [year.sup.-1]). Un taux de deposition de N modere pouvait augmenter la production de biomasse des arbres et la masse de sol organique, ce qui a entraine une augmentation du C de l'ecosysteme, mais ces gains pouvaient etre associes a un lessivage important de N. La pollution atmosphe-rique pourrait aussi entrainer des desequilibres nutritifs a long terme et d'autres problemes d'ordre ecologique (c.-a-d. perte de biodiversite, eutrophisation, etc.) qui n'ont pas ete etudies ici. [Traduit par la Redaction], Introduction Concern about the possible effects of acid rain in China emerged in the late 1970s (Fan and Wang 2000), with the first reports appearing in the international literature in [...]

: This paper calibrates climate controls over radial growth of floodplain white spruce (Picea glauca (Moench) Voss) and examines whether growth in these populations responds similarly to climate as upland trees in Interior Alaska. Floodplain white spruce trees hold previously unrecognized potential for long-term climate reconstruction because they are the source of driftwood that becomes frozen in coastal deposits, where archeological timbers and beach logs represent well-preserved datable material. We compared ring width chronologies for 135 trees in six stands on the Yukon Flats and Tanana River with temperature and precipitation at Fairbanks from 1912-2001. Our sample contains a stable common signal representing a strong negative relationship between summer temperature and tree growth. We developed a floodplain temperature index (FPTI), which explains half of the variability of the composite chronology, and a supplemental precipitation index (SPI) based on correlation of monthly precipitation with the residual of the temperature-based prediction of growth. We then combined FPTI and SPI into a climate favorability index (CFI) in which above-normal precipitation partially compensates for temperature-induced drought reduction of growth and vice versa. CFI and growth have been particularly low since 1969. Our results provide a basis for building longer chronologies based on archeological wood and for projecting future growth. Resume: Cet article quantifie le controle qu'exerce le climat sur la croissance radiale de l'epinette blanche (Picea glauca (Moench) Voss) de la plaine inondable et examine si la croissance dans ces populations reagit au climat de la meme facon que les arbres des hautes terres de l'interieur de l'Alaska. Les epinettes blanches de la plaine inondable possedent un potentiel jusqu'a present meconnu pour reconstituer le climat sur le long terme parce qu'ils sont la source de bois flotte qui finit gele dans les depots cotiers ou les bois archeologiques et les bois de plage constituent un materiau bien preserve et qui peut etre date. Nous avons compare les series dendrochronologiques de 135 arbres provenant de six peuplements des Yukon Flats et de la riviere Tanana avec les temperatures et les precipitations a Fairbanks de 1912 a 2001. Notre echantillon contient un signal commun stable qui represente une relation negative etroite entre la temperature estivale et la croissance des arbres. Nous avons developpe un indice de temperature des plaines inondables (ITPI) qui explique la moitie de la variabilite de la serie dendrochronologique composite et un indice de precipitation supplementaire (IPS) fonde sur la correlation des precipitations mensuelles avec les valeurs residuelles de la prediction de la croissance basee sur la temperature. Nous avons ensuite combine l'ITPI et l'IPS dans un indice de climat favorable (ICF) dans lequel des precipitations plus elevees que la normale compensent en partie une reduction de la croissance due a la secheresse provoquee par la temperature et vice versa. L'ICF et la croissance ont ete particulierement faibles depuis 1969. Nos resultats fournissent une base pour la construction de chro-nologiques plus longues a partir de bois archeologiques et pour les projections de la croissance futures. [Traduit par la Redaction], Introduction Significant climate change impacts in high-latitude boreal ecosystems are already evident, and impacts are expected to become even more pronounced in the future (Juday et al. 2005), posing major [...]

: 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, [...]

In light of a significant increase in the warming trend observed in recent decades in semi-arid Mongolia, tree-ring attributes and anomalies were analysed to detect potential changes in the growth-climate relationship. In a moisture-limited environment, an increase in temperature could cause a shift in the seasonal response of trees to climate. Chronologies were developed for the dominant tree species (Larix sibirica Ledeb, Pinus sibirica Du Tour, and Pinus sylvestris L.) from north-central Mongolia. In addition to annual ring width, both earlywood and latewood width were measured, and tree-ring anomalies such as false rings and light rings were systematically identified. Earlywood width was mainly associated with precipitation in the year prior to ring formation and early growing season conditions. Temperature was associated with cur rent year growth and mainly influenced latewood development. False rings were good indicators of early summer droughts, whereas light rings were mainly associated with a cold end of summer. A seasonal shift in the significance of monthly climate variables was observed in recent decades. This displacement presumably resulted from changes in the timing and duration of the growing season. Tree growth starts earlier in spring and is now affected by late summer to early autumn climate conditions. En lien avec la tendance significative au rechauffement observee depuis les dernieres decennies en Mongolie semi-aride, des attributs et des anomalies des cernes annuels ont ete analyses pour detecter les changements potentiels dans la relation entre la croissance des arbres et le climat. Dans des milieux ou la disponibilite en eau est un facteur limitant, des augmentations de temperature pourraient engendrer, une modification de la reponse saisonniere des arbres au climat. Des series dendrochronologiques ont ete developpees pour les trois especes dominantes du centre-nord de la Mongolie (Larix sibirica Ledeb., Pinus sibirica Du Tour et Pinus sylvestris L.). En plus de la largeur des cernes annuels, la largeur du bois initial et du bois final a ete mesuree et des anomalies des cernes telles que les faux-cernes et les cernes pales ont ete systematiquement identifiees. La largeur du bois initial etait principalement associee aux precipitations de la saison precedant la formation du cerne ainsi qu'o celles du debut de la saison de croissance. La saison de croissance en cours etait pour sa part associee a la temperature qui influencait surtout le developpement du bois final. Les faux cernes etaient de bons indicateurs de secheresses en debut d'ete, tandis que les cernes pales etaient surtout associes a des fins d'ete froides. Une modification saisonniere des associations significatives avec les variables climatiques mensuelles a ete observee au cours des dernieres decennies. Cette modification pourrait etre reliee a des changements dans l'initiation et la duree de la saison de croissance. La croissance des arbres commence plus tot au printemps et est maintenant influencee par les conditions climatiques qui prevalent a la fin de l'ete et au debut de l'automne., Introduction Global temperatures are expected to increase by 1.5 to 6 °C over the next 100 years, with the greatest warming projected to occur at high latitudes (Intergovernmental Panel on [...]

The influence of site index on growth efficiency was studied for 411 dominant and codominant Abies balsamea (L.) Mill. and Picea rubens Sarg. from 10 sites across Maine, USA. Young A. balsamea (n = 204) were from stands precommercially thinned 15-20 years ago and ranged in site index from 18.4 to 24.3, while the older P. rubens (n = 207) were from stands that were not precommercially thinned and ranged in site index from 13.1 to 17.8. We hypothesized that site index positively influences growth efficiency. The results showed that volume increment--leaf area relationships and growth efficiency increased significantly with site index for A. balsamea but were unaffected by site index for P. rubens. A monotonic decreasing pattern of growth efficiency over increasing leaf area was found for both species. When standardized per unit site index, growth efficiency behaved nonlinearly for both species. L'influence de l'indice de qualite de station sur l'efficacite de croissance a ete etudiee a partir de 411 Abies balsamea (L.) Mill. et Picea rubens Sarg. des etages dominants et codominants de 10 stations situees a travers l'Etat du Maine, aux Etats-Unis. Les jeunes A. balsamea (n = 204) provenaient de peuplements ayant subi une eclaircie precommerciale 15 a 20 ans auparavant et dont l'indice de qualite de station variait de 18,4 a 24,3. De leur cote, les P. rubens (n = 207) provenaient de peuplements plus vieux n'ayant pas subi d'eclaircie precommerciale et dont l'indice de qualite de station variait de 13,1 a 17,8. Nous avons pose l'hypothe'se que l'indice de qualite de station influence positivement l'efficacite de croissance. Les resultats indiquent que la relation entre l'accroissement en volume et la surface foliaire ainsi que l'efficacite de croissance augmentent significativement avec l'indice de qualite de station dans le cas d'A. balsamea, mais pas dans celui de P. rubens. Une decroissance monotone de l'efficacite de croissance en fonction de l'augmentation de la surface foliaire a ete observee chez les deux especes. Lorsqu'elle est standardisee par unite d'indice de qualite de station, l'efficacite de croissance se comporte de facon non lineaire chez les deux especes. [Traduit par la Redaction], Introduction Growth efficiency (GE), the ratio of stemwood volume increment (VINC, dm3) to projected leaf area (LA, [m.sup.2] x [m.sup.-2]), is a useful metric for describing tree and stand growth [...]

Cold stress is a major factor that limits the success of environmentally sound cultivation of maize in central and northern Europe. This study evaluated the early growth of seven groups of Swiss Flint maize landraces (Zea mays L. ssp. mays) of different geographic origin under controlled cool conditions by assessing shoot and root traits. Measurements of plants, subjected to a permanent cold stress of 15/13[degrees]C (day/ night), were made at the three-leaf stage of the check Magister, a hybrid of approved good early vigor. The ranking (univariate analysis of variance) and the multivariate clustering of the groups of landraces differed when root and shoot traits were included in the evaluation. Furthermore, the association of phenotype with geographic parameters was successful only when root traits were considered. Groups of Swiss landrace accessions expressed three types of phenotypes under cold conditions: (i) large leaf area and an extensive axile root system for landraces from the Tessin and the Poschiavo valley (i.e., south of the Alps), (ii) large leaf area and a short axile root system in landraces from the Linth valley, the lower Rhine valley, and the posterior Rhine valley, all of which are north of the Alps, (iii) small leaf area and a short axile root system in landraces from the anterior Rhine valley and the Swiss Rh6ne valley. The method of root phenotyping (i.e., a simple and rapid determination of traits of axile roots) proved suitable for the characterization of a large number of samples, as is typically required in quantitative genetic analysis.

Information on the distribution of vernalization genes and their association with growth habit is crucial to understanding the adaptability of wheat (Triticum aestivum L.) cultivars to different environments. In this study, 278 Chinese wheat cultivars were characterized with molecular markers for the vernalization genes Vrn-A1, -B1, -Dl, and -B3. Heading time was evaluated in a greenhouse under long days without vernalizaton. The dominant Vrn-D1 allele showed the highest frequency in the Chinese wheat cultivars (37.8%), followed by the dominant Vrn-A1, -B1, and -B3 alleles. Ninety-two winter cultivars carried recessive alleles of all four vernalization loci, whereas 172 spring genotypes contained at least one dominant Vrn allele. All cultivars released in the North China Plain Winter Wheat Zone were winter type. Winter (53.0%), spring (36.1%), and early-heading (10.9%) cultivars were grown in the Yellow and Huai River Valley Winter Zone. Most of the spring genotypes from this zone carried only the dominant Vrn-Dl allele, which was also predominant (64.1%) in the Middle and Lower Yangtze Valley Winter Zone and Southwestern Winter Wheat Zone. In three spring-sown wheat zones, all cultivars were early-heading spring types that frequently possessed the strongest dominant Vrn-Ala allele and combinations with other dominant Vrn gene(s). The Vrn-D1 allele is associated with the latest heading time, Vrn-A1 the earliest, and Vrn-Bl intermediate values. The information is important for breeding programs in countries interested in using Chinese wheats.

Growth response functions (GRFs) that relate the growth of a population to the climate of the sites in which it is tested are gaining attention for their ability to predict impacts of climate change on tree growth. However, nonclimatic site to site variation introduces error into GRFs. Using data from a large lodgepole pine (Pinus contorta Dougl. ex Loud.) provenance test in British Columbia and the Yukon, Canada, a technique is presented that accounts for the effect of nonclimatic variation in GRFs. The mean height of the 'local' provenances at each test site was used to predict 'site height' from site climate variables in multiple regression. Residuals from the site height equation provided an index of the nonclimatic effect for each site and were included as a covariate in quadratic GRFs that related provenance height at each test site to mean annual temperature at each test site. Inclusion of the nonclimatic index in the model resulted in a moderate or large displacement of GRFs for 25% of the provenances, while increasing mean [R.sup.2] values for 138 of 140 provenances and decreasing the root mean squared error for 113 of 140 provenances. These results suggest that inclusion of the nonclimatic index in GRF models could substantially affect height predictions for some provenances and reduce prediction error for most provenances. Les fonctions de reaction de la croissance (FRC) qui relient la croissance d'une population au climat des stations oh elles sont testees gagnent en popularity; a cause de leur capacity; a predire les impacts des changements climatiques sur la croissance des arbres. Cependant, les variations non climatiques entre les stations introduisent des erreurs dans les FRC. A partir des donnees d'un test de provenance de pin tordu latifolie (Pinus contorta Dougl. ex Loud.) de grande envergure en Colombie-Britannique et au Yukon, au Canada, nous presentons une technique qui tient compte de l'effet des variations non climatiques dans les FRC. La hauteur moyenne des provenances <> a chaque endroit oU le test a ete etabli a ete utilisee pour predire, a l'aide de la regression multiple, la <> a partir des variables climatiques de la station. Les residus de l'equation de la hauteur specifique a la station ont fourni un indice de l'effet non climatique dans chaque station et ont etes inclus comme covariable dans des FRC quadratiques qui reliaient la hauteur de la provenance dans chaque station a la temperature annuelle moyenne de la station. L'introduction de l'indice non climatique dans le modele a produit un dylplacement modere a grand des FRC chez 25 % des provenances, a augmente la valeur moyenne du [R.sup.2] de 138 des 140 provenances et a diminue l'erreur quadratique moyenne chez 113 des 140 provenances. Ces resultats indiquent que l'introduction de l'indice non climatique dans les modeles de FRC pourrait substantiellement affecter les predictions de hauteur pour quelques provenances et diminuer l'erreur de prediction pour la plupart des provenances. [Traduit par la Redaction], Introduction With climate change raising the spectre of significant changes to forest productivity due to altered adaptation, provenance tests have encountered a resurgence of interest, as modellers attempt to mitigate [...]

Impacts of elevated tropospheric ozone and soil nitrogen amendment on two native European aspen (Populus tremula L.) and eight hybrid aspen (P. tremula L. * Populus tremuloides Michx.) clones were studied in a free-air ozone exposure system. Potted saplings were exposed to ambient (ca. 20 ppb) or 1.5 * ambient ozone and two levels of soil nitrogen (39 and 78 kg N * [ha.sup.-1] * [year.sup.-1] in the first year, 60 and 140 kg N * [ha.sup.-1] * [year.sup.-1] in the second year for low-nitrogen and high-nitrogen treatments, respectively) over two growing seasons. The plants were measured for photosynthesis, chlorophyll fluorescence, and biomass accumulation. Ozone decreased leaf-level net photosynthesis (Asat) in particular early in the growing season and maximum quantum yield of photosystem II ([F.sub.v]/[F.sub.m]) at the end of the growing season. Nitrogen amendment increased the growth of all plant parts and mitigated the adverse ozone effects. There were significant differences in ozone responses among the clones, and we were able to cluster the clones into sensitivity groups based on their growth responses. The most ozone-tolerant genotypes were hybrid aspen clones, indicating that populations that have already experienced selection for ozone-tolerant genotypes should be used to cross-breed with ozone-sensitive populations to achieve tolerance of a climate with increasing tropospheric ozone concentrations. Les impacts d'une teneur en ozone tropospherique elevee et d'un amendement azote du sol sur deux clones de peuplier tremble (Populus tremula L.) indigenes d'Europe et huit clones d'hybrides de peuplier (P. tremula * Populus tremuloides Michx.) ont [Traduit par la Redaction], Introduction Background ozone levels have doubled in the past 100 years from mean annual concentrations of approximately 10-20 parts per billion (ppb) to the current 20-45 ppb (Vingarzan 2004). In [...]

It is well known from Hardin's 'Tragedy of the Commons' [Hardin G (1968) Science 162:1243-1248] that, if open access is allowed, overgrazing typically results. Hardin, and most authors of the subsequent literature, adopted a static view of the underlying ecosystem. Here we extend this tragedy of the commons to consider the dynamics of the involved ecosystem as well. We consider a general model that allows for a variable carrying capacity of the pastures (due to variation in precipitation) and a stimulating effect on plant growth due to grazing. Our analysis further emphasizes the tragedy; in addition to overgrazing, the ecosystem may approach limit cycles. Thus, unless the pastoralists are able to coordinate themselves, the human capability of long-term planning will generally not stabilize the system. Although numerical optimization shows that a cooperative optimum would yield a high and stable harvest, the open-access system may produce limit cycles, in which even the peak harvest may be below the stable cooperative optimal harvest. Such fluctuations cause both losses in biomass production and utility losses. Our dynamic analysis also demonstrates that, in the absence of cooperation between herders, too much rain in an otherwise dry area might (temporally) destabilize the ecological grazing system through overstocking, subsequently leading to further overgrazing (which will be observed in, but not caused by, the typically dry conditions of landscapes where pastoralism is practiced). In short, through this study we have brought time (and temporal dynamics) into the Hardin's tragedy of the commons and show that the tragedy might be profoundly worsened. ecological dynamics | pastoralism | resource management | tragedy of the commons

The majority of wheat (Triticum aestivum L.) in the southern Great Plains is produced as a dual-purpose crop enterprise. Profitability of the system is highly dependent on removal of cattle (Bos taurus L.) from wheat pastures at the first-hollowstem stage of growth. A previous survey implied that earliness of first hollow stem and earliness of heading are independent traits, which would allow a grower to select a cultivar with late first hollow stem without sacrificing early maturity. We evaluated first hollow stem and heading records for 52 hard winter wheat lines (49 commercially available winter wheat cultivars and three advanced experimental lines) during a 7yr period at Stillwater, OK. Our analysis shows a positive, linear relationship between the occurrence of first hollow stem and heading in wheat when these phenological events were expressed as a function of cumulative thermal units after 1 January. When expressed in terms of calendar date, however, intervals between the earliest and latest cultivars for the first-hollow-stem stage were much greater than those for heading date. Overall, our analysis indicates that among commercially available cultivars and advanced experimental lines, choosing a cultivar with later occurrence of first hollow stem will also result in later heading in the same given environment.

Forages accumulate nonstructural carbohydrates during the day, with animals showing preference and improved daily responses from afternoon compared with morning cut hays. This study evaluated alfalfa (Medicago sativa L.) hay harvested at 0700, 1000, 1300, 1600, and 1900 h to determine how nutritive value changes during the day and to assess the impact of these changes on animal preference using cattle (Bos taurus L.), sheep (Ovis aries L.), and goat (Capra hircus L.) responses. Total nonstructural carbohydrates were altered by time of cut (cubic contrast, P < 0.01) ranging from 85 g [kg.sup.-1] at 0700 h to 83 g [kg.sup.-1] at 1000 h, then increasing to 97 g [kg.sup.-1] by 1600 h with little change at 1900 h (96 g [kg.sup.-1]). Fiber fractions also varied diurnally, with a quadratic decrease from 418 g [kg.sup.-1] at 0700 h to 387 g [kg.sup.-1] by 1900 h in neutral detergent fiber. A combined analysis of three animal trials showed a linear increase in dry matter intake (DMI) with later hay harvest, a cubic response for dry matter digestion (DMD), and a linear increase in digestible DMI. Mean DMI increased from 27.5 g [kg.sup.-1] body weight at 0700 h to a maximum of 30.8 g [kg.sup.-1] body weight at 1600 h, whereas DMD decreased from 658 g [kg.sup.-1] at 0700 to 647 g [kg.sup.-1] at 1300 h and peaked at 664 g [kg.sup.-1] at 1600 h. Digestible DMI increased from 18.1 g k[kg.sup.-1] body weight at 0700 h to a maximum of 20.5 g [kg.sup.-1] body weight at 1600 h. No additional advantages in animal responses were noted by cutting after 1600 h.

High temperature and drought stresses may reduce quality in cool-season turfgrasses during summer months in the transition zone. This growth chamber study was conducted to evaluate effects of high temperature and drought on physiology and growth of 'Apollo' Kentucky bluegrass (Poa pratensis L.) (KBG), 'Dynasty' tall fescue (Festuca arundincea Schreb.) (TF), and 'Thermal Blue', a hybrid (HBG) between KBG and Texas bluegrass (Poa arachnifera Tom). Turfgrasses were exposed for 48 d to supra-optimal (high temperature; 35/25[degrees]C, 14-h day/10-h night) and optimal (control; 22/15[degrees]C, 14-h day/10-h night) temperatures under well-watered (100% evapotranspiration [ET] replacement) and deficit (60% ET replacement) irrigation. Heat resistance was greater in HBG, which had greater visual quality, gross photosynthesis (Pg), dry matter production, and lower electrolyte leakage and soil surface temperatures than KBG and TF under high temperature. Cumulative Pg during the study was 16 and 24% greater in HBG than in KBG and TF, respectively. Green leaf area index (LAI) in HBG was not affected by high temperature, but LAI was reduced by 29% in KBG and 38% in TF. Differences in drought resistance were negligible among species. The combination of high temperature and drought caused rapid declines in visual quality and dry matter production, but HBG generally performed better. Results indicated greater heat resistance, but not drought resistance, in HBG than in KBG or TF.

Imidazolinone-resistant hard red wheat (Triticum aestivum L.) cultivars are occasionally injured by imazamox applications because a portion of the acetolactate synthase (ALS) remains susceptible to the herbicide. The growth and enzyme activity of two groups of hard red wheat near-isolines with spring or winter growth habit were examined following imazamox application. Each group of near-isolines contained a susceptible cultivar and cultivars with the imidazolinone-resistant trait on either the B or D genome. The spring wheat group also contained a line carrying both the B and D genome copies of the resistance gene. In whole plant experiments, growth of all single-gene resistant lines was delayed by both 35 and 105 g [ha.sup.-1] imazamox while the two-gene line was delayed at only the highest rate. There was a herbicide rate effect on biomass accumulation but no differences among genome locations in the single-gene resistant lines or among spring vs. winter growth habit. On an ALS enzyme basis, however, there were differences among B- vs. D-genome resistance and between winter and spring growth habit. Spring wheat cultivars with the B-genome resistance had greater reductions in ALS activity compared to the D-genome cultivars, while in winter wheat, B- and D-genome lines responded similarly. Differences among genotypes existed in the recovery of ALS activity in imidazolinone wheat but other factors also likely influence the injury occasionally observed in the field.

The growth rate (GR) hypothesis relates the evolution of plant defense to resource availability and predicts that plants that have evolved in abiotically stressful environments grow inherently more slowly and are more constitutively resistant to herbivory than plants from more productive habitats. Stress-adapted plants are also predicted to have reduced inducibility, but this prediction has not been previously tested. To evaluate this hypothesis, I compared the growth of nine species of herbaceous plants from Missouri glade habitats to congeners from more productive non-glade habitats. I also conducted bioassays using larvae of the generalist herbivore Spodoptera exigua to estimate constitutive and inducible resistance in these congeners. Glade congeners tended to grow more slowly and have higher constitutive resistance and lower inducibility than non-glade species. However, none of these comparisons was statistically significant due to the conflicting response of one congeneric pair (Salvia azurea and S. lyrata). Analyses without this genus were consistent with the GR hypothesis, as were analyses that categorized congeners by relative growth rate. These results highlight the complexity in searching for factors that determine plant growth rates and resistance traits across multiple genera and support the hypothesis that both constitutive and induced resistance may be influenced by selection on traits that alter plant growth rates. Future studies should attempt to determine whether variation in inducibility is better explained by habitat or relative plant growth rates. Key words: defensive syndromes; herbivory; induced defenses; Ozark glades; phenotypic plasticity; plant competition; plant-herbivore interactions; resource availability hypothesis.