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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 [...]

Eastern white cedar (Thuja occidentalis) and red spruce (Picea rubens) contribute to the biodiversity and resilience of mixedwood forests. However, cuts that remove most or all the forest cover can cause the decline of these species. Among partial cutting options, the irregular shelterwood system (ISS) can create successful conditions for the development of advance regeneration and enrichment planting. We studied 6 years of ecophysiology of lower advance regeneration and planted seedlings of eastern white cedar and red spruce growing under a first ISS cut according to three cutting intensities: light cut (35% removal, 20 [m.sup.2]*[ha.sup.-1] residual basal area), moderate cut (42%, 18 [m.sup.2]*[ha.sup.-1]), and heavy cut (52%, 15 [m.sup.2]*[ha.sup.-1]). Light-saturated photosynthesis and height growth of planted cedar and both spruce types decreased with increasing cutting intensity, in response to an increase in competing vegetation. Therefore, to limit the negative impact of competing species on cedar and spruce regeneration, we recommend protecting tall advance regeneration (2 m+) during partial cut operations and using large-sized containerized seedlings (40-50 cm height) for enrichment planting. Results also suggest that a mechanical release could help optimize the physio-morphology and growth of both regeneration types of cedar and red spruce. Key words: continuous cover forestry, declining species, ecological silviculture, enrichment planting, natural regeneration, uneven-aged management Le thuya occidental (Thuja occidentalis) et l'epinette rouge (Picea rubens) contribuent a la biodiversite et a la resilience des forets mixtes. Cependant, les coupes qui suppriment la majeure partie ou la totalite du couvert forestier peuvent entrainer le declin de ces especes. Parmi les options de coupe partielle, le procede de regeneration par coupes progressives irregulieres (CPI) peut creer des conditions favorables au developpement de la regeneration preetablie et a la plantation d'enrichissement. Nous avons etudie pendant 6 ans l'ecophysiologie de la basse regeneration preetablie et de semis plantes de thuya occidental et d'epinette rouge poussant sous une premiere CPI selon trois intensites de coupe: coupe legere (35% de prelevement, 20 [m.sup.2]*[ha.sup.-1] de surface terriere residuelle), coupe moderee (42%, 18 [m.sup.2]*[ha.sup.-1]) et coupe forte (52%, 15 [m.sup.2]*[ha.sup.-1]). La photosynthese sous lumiere saturante et la croissance en hauteur du thuya plante et des deux types d'epinette ont diminue avec l'augmentation de l'intensite de la coupe, en reponse a une augmentation de la vegetation concurrente. Par consequent, pour limiter l'impact negatif des especes concurrentes sur la regeneration du thuya et de l'epinette, nous recommandons de proteger la regeneration preetablie de grande taille (2 m+) pendant les operations de coupe partielle et d'utiliser des semis en conteneur de grande taille (40-50 cm de hauteur) pour la plantation d'enrichissement. Les resultats suggerent egalement qu'un degagement mecanique pourrait contribuer a optimiser la physio-morphologie et la croissance des deux types de regeneration de thuya occidental et d'epinette rouge. Mots-cles : foresterie a couvert permanent, especes en declin, sylviculture ecologique, plantation d'enrichissement, regeneration naturelle, amenagement inequienne, Introduction The temperate mixedwood forest of Quebec (Canada) represents a rich, diversified, and complex ecosystem providing many economic and ecological services to society. Located in the balsam fir (Abies balsamea [...]

Our objective was to study how changes in the light spectra affect growth; the concentration of carbohydrate, chlorophyll, carotenoid, terpene, alkaloid, and phenolic compounds; and the emissions of BVOC (biogenic volatile organic compound) of Norway spruce (Picea abies (L.) Karst.) seedlings. This study was conducted during the growth of the third needle generation in plant growth chambers. The plants were exposed to two light spectra with equal photon flux densities but different proportions of blue light (400-500 nm) produced by LED (light-emitting diode) lamps: (i) control (white light +12% blue light) and (ii) increased blue light (+B) (white light + 45% blue light). The +B treatment increased the concentrations of total flavonoids and acetophenones in needles. The major changes in the phenolic profile were an accumulation of astragalin derivatives and the aglycone of picein. The +B treatment also decreased concentrations of the main alkaloid compound, epidihydropinidine, and its precursor, 2-methyl-6-propyl-1,6-piperideine; the emission rates of limonene, myrcene, and total monoterpenes; and the concentrations of a few terpenoid compounds, mainly in stems. Growth as well as the carbohydrates and pigments present in the needles were not affected. The results suggest that supplemental blue light shifts carbon allocation between secondary metabolism routes--from alkaloid and terpenoid synthesis to flavonoid and acetophenone synthesis. The changes may affect herbivory and abiotic stress tolerance of Norway spruce. Key words: blue light, Norway spruce, biogenic volatile organic compounds, phenolic compounds, alkaloids. Notre objectif consistait a etudier de quelle facon les changements dans le spectre lumineux influencent la croissance, la concentration des hydrates de carbone, de la chlorophylle, des carotenoides, des terpenes, des alcaloides et des composes phenoliques, ainsi que les emissions de composes organiques volatiles biogeniques chez des semis d'epicea commun (Picea abies (L.) Karst.). Cette etude a ete effectuee en phytotrons durant la croissance des aiguilles de troisieme generation. Les plants ont ete exposes a deux spectres lumineux avec une densite egale du flux photonique qui se distinguaient principalement par la proportion de lumiere bleue (400-500 nm) produite par des lampes a DEL (diode electroluminescente) : (i) temoin (lumiere blanche + 12 % de lumiere bleue) et (ii) plus forte proportion de lumiere bleue (+B) (lumiere blanche + 45 % de lumiere bleue). Le traitement +B a augmente la concentration totale des flavonoides et des acetophenones dans les aiguilles. L'accumulation de derives de l'astragaline et de l'aglycone de la piceine est le changement majeur observe dans le profil des composes phenoliques. Le traitement +B a aussi reduit la concentration du principal compose alcaloide, l'epidihydropinidine et son precurseur, la 2-methyl-6-propyl-1,6-piperideine, les taux d'emission du limonene, du myrcene et des monoterpenes totaux, ainsi que la concentration de quelques composes terpenoides, principalement dans la tige. La croissance, ainsi que les pigments et les hydrates de carbone presents dans les aiguilles n'ont pas ete modifies. Les resultats indiquent que le supplement de lumiere bleue modifie l'allocation du carbone vers les sentiers metaboliques secondaires, de la synthese des alcaloides et des terpenoides vers la synthese des flavonoides et des acetophenones. Ces changements pourraient avoir un impact sur la tolerance de l'epicea commun aux herbivores et aux stress abiotiques. [Traduit par la Redaction] Mots-cles : lumiere bleue, epicea commun, composes organiques volatiles biogeniques, composes phenoliques, alcaloides., Introduction Quality and quantity of light are primary factors affecting plant germination, morphogenesis, growth, reproduction, and defence. Several photoreceptors participate in perceiving different wavelengths of light, such as phototropins and [...]

Understanding microsite preferences of species at the sapling stage is crucial for successful forest restoration, as efforts can be concentrated onto the most promising sites, and invaded sites can be manipulated toward more suitable conditions for target species. The Hawaiian Lowland Wet Forest is a highly endemic and endangered ecosystem that has received limited attention in terms of research on recruitment dynamics. Our study combined density records and sapling-based measurements within a forest reserve, an invaded forest, a traditional restoration project and a novel restoration project. We recorded substrate type, soil depth, surface roughness, and light availability for 382 saplings of the four native tree species Metrosideros polymorph'a, Myrsine lessertiana, Pipturus albidus, and Psychotria hawaiiensis, and 146 spots where the target species were absent. The invaded forest had the lowest native sapling density, lower light availability, and lower surface roughness than the remaining management units. The novel restoration project had more moss/nurselog sites and higher light availability than the remaining management units. The traditional restoration project was mainly characterized by rocky substrate. Metrosideros and Pipturus showed significantly higher light demand than Myrsine and Psychotria. Pipturus was associated with rough microsites and Metrosideros with moss/nurselog substrates. Our findings suggest that restoration strategies considering manipulation of the canopy light environment and microsite preferences of target species can better facilitate native recruitment into heavily invaded forests. Keywords: abiotic microsite preferences, restoration ecology, Metrosideros polymorpha, Psychotria hawaiiensis, Pipturus albidus, Myrsine lessertiana, forest restoration planning, THE ABUNDANCE AND DIVERSITY OF SAPLINGS in a forest ecosystem provide information about future forest conditions as forest composition and dynamics are predominantly influenced by variation in the survival of [...]

Belowground herbivory under nutrient-poor conditions is known to significantly decrease plant biomass and root:shoot ratios. However, the mechanisms behind the changes in belowground plant-herbivore interactions that occur under different nutrient conditions remain unclear. We performed a pot experiment using Lolium perenne L. and the third-instar larva of Popillia japonica Newman. The experiment used a three-way factorial randomized-block design; the three factors were nutrient amount (rich/poor), nutrient heterogeneity (homogeneous/heterogeneous), and belowground herbivore (present/absent). Relative water content (RWC) of shoots under nutrient-poor conditions was smaller than that under nutrient-rich conditions, and a single herbivory significantly reduced the RWC under the nutrient-poor conditions. Plant biomass was larger under nutrient-rich conditions than under nutrient-poor conditions. A herbivore decreased plant biomass more under nutrient-poor conditions than under nutrient-rich conditions. Nutrient heterogeneity had no effect on plant biomass, but herbivory and nutrient amount interactively affected root proliferations to nutrient patches. Plants were smaller under nutrient-poor conditions; thus, a larger proportion of the roots was removed by a belowground herbivore. A loss of a larger proportion of roots would cause the small RWC, which restricts compensatory growth. Consequently, growth of L. perenne is more severely limited by a belowground herbivore under nutrient-poor conditions. Keywords: nutrient patches, plant-herbivore interactions, relative water content, root foraging, root:shoot ratio. L'herbivorisme souterrain dans des conditions pauvres en nutriments est connu pour diminuer de maniere tres importante la biomasse vegetale et les ratios racine : pousse. Cependant, les mecanismes derriere les changements dans les interactions souterraines plante-herbivore qui surviennent dans differentes conditions nutritives demeurent flous. Les auteurs ont realise une experience en pot avec Lolium perenne L. et la larve du troisieme stade de Popillia japonica Newman. Ils ont utilise un plan experimental factoriel aleatoire triple; les trois facteurs etaient la quantite de nutriments (riche/pauvre), l'heterogeneite des nutriments (homogene/heterogene) et l'herbivore souterrain (present/absent). Le contenu relatif en eau (RWC pour << relative water content >>) des pousses dans des conditions pauvres en nutriments etait similaire a celui obtenu dans des conditions riches en nutriments, et un herbivore unique reduisait de maniere tres importante le RWC dans des conditions pauvres en nutriments. La biomasse vegetale etait plus importante dans des conditions riches en nutriments que dans des conditions pauvres en nutriments. L'herbivore diminuait davantage la biomasse vegetale dans des conditions pauvres en nutriments que dans des conditions riches en nutriments. L'heterogeneite en nutriments n'avait pas d'effet sur la biomasse vegetale, mais l'herbivorisme et la quantite de nutriments affectaient de maniere interactive la proliferation des racines vers les patchs de nutriments. Les plants etaient plus petits dans des conditions pauvres en nutriments; ainsi, une plus grande proportion de racines etait eliminee par un herbivore souterrain. La perte d'une plus grande proportion de racines pourrait etre la cause du faible RWC, ce qui restreint la croissance compensatoire. Consequemment, la croissance de L. perenne est plus severement limitee par un herbivore souterrain dans des conditions pauvres en nutriments. [Traduit par la Redaction] Mots-cles: patchs de nutriments, interactions plante-herbivore, contenu relatif en eau, ravitaillement des racines, ratio racine/pousse., Introduction The belowground parts of plants, such as roots, rhizomes, and storage organs, are estimated to account for over 80% of total plant biomass in temperate grasslands, tundra, and deserts [...]

Most hypotheses about controls over high-altitude forests, including treeline, the elevation for upright woody plants, or timberline, the upper elevation for aggregated forest, suggest that low temperature drives forest dynamics, either through effects on cell division and tree growth or indirectly through frost damage or nutrient availability. However, abiotic factors other than temperature, including water availability, may serve as other important controls at high elevations, particularly for seedlings. To test the hypothesis that the timing and amount of precipitation exerts a strong control over the high-elevation forest boundary on the Wasatch Plateau in central Utah, USA, we conducted a field experiment that manipulated water availability and monitored photosynthesis, growth, and survivorship in Picea engelmannii Parry ex Engelm. seedlings. Survivorship increased from the driest to the wettest conditions, whereas the timing of precipitation did not explain differences in survival. However, we found that large, infrequent rain events increased maximum photosynthetic flux density compared with small, frequent rain events. Our results highlight the potential role of growing season water availability in limiting timberline expansion below the low-temperature thermal limits of P. engelmannii. As a consequence, the infilling of trees below the treeline in this region in response to climate change is likely to be episodic and driven by multiyear periods of high water availability and frequency that overcome drought limitations. Key words: treeline, hydrology, Picea engelmannii, photosynthesis, survivorship. La plupart des hypotheses concernant les controles sur les forets de haute altitude, incluant la limite des arbres, l'altitude a laquelle on retrouve encore des plantes ligneuses dressees, ou la limite de vegetation des arbres, l'altitude superieure a laquelle il y a encore de la foret, indiquent que la basse temperature determine la dynamique forestiere, soit en ayant des effets sur la division cellulaire et la croissance des arbres, soit indirectement a cause des dommages dus au gel ou de la disponibilite des nutriments. Cependant, des facteurs abiotiques autres que la temperature, incluant la disponibilite en eau, pourraient etre d'importants facteurs alternatifs de controle a haute altitude, particulierement pour les semis. Pour tester l'hypothese que le moment et la quantite de precipitation exercent un controle significatif sur la limite de la foret a haute altitude sur le plateau des Wasatch dans le centre de l'Utah, aux Etats-Unis, nous avons realise une experience sur le terrain dans laquelle nous avons manipule la disponibilite en eau et suivi la photosynthese, la croissance et la survie des semis de l'epicea d'Engelmann (Picea engelmannii Parry ex Engelm.). La survie augmentait en passant des conditions les plus seches aux plus humides tandis que le moment des precipitations n'expliquait pas les differences dans la survie. Cependant, nous avons trouve que des episodes peu frequents de forte pluie ont augmente la densite du flux photosynthetique maximum comparativement a des episodes frequents de faible pluie. Nos resultats font ressortir le role potentiel de la disponibilite en eau durant la saison de croissance qui limiterait l'expansion de la limite de vegetation des arbres en deca des limites thermiques de temperature minimale de l'epicea d'Engelmann. En consequence, le recrutement des arbres en deca de la limite des arbres dans cette region en reponse au changement climatique sera probablement episodique et determine par des periodes de plusieurs annees de disponibilite en eau elevee et a une frequence qui surmonte les restrictions imposees par la secheresse. [Traduit par la Redaction] Mots-cles: limite des arbres, hydrologie, Picea engelmannii, photosynthese, survie., Introduction Renewed interest in upper treeline dynamics is, in part, driven by the hope that these systems will help us understand how ecosystems will respond to climate change (Harsch et [...]

The regeneration ecology of sugar maple (Acer saccharum Marsh.) has been impacted by acid rain leaching of base cations from the soils throughout much of its range. We tracked the survival and causes of death for a natural cohort of sugar maple seedlings across 22 sites in the Hubbard Brook Valley in New Hampshire, USA, where soil acidification has been documented. Survival over 7 years averaged 3.4%; however, significant differences in survival were observed among sites, which were classified into three main groups based on the shape of their survival curves. These site groups differed in position on the landscape, seedling nutrition and leaf size, and the prevalence of damage agents, but not in soil Ca. First-season mortality was high (71%), and the main damage agents were fungal infection (Rhizoctonia spp.) and caterpillar herbivory (Geometridae). Other principal causes of mortality in order of importance were winter injury, mechanical damage, and rodent (Myodes gapperi Vigors, 1830) tunneling, and all damage agents varied significantly in severity between years. This study highlights the importance of landscape-level variation in biotic factors for predicting sugar maple regeneration success. Predictions of sugar maple regeneration will require a better understanding of controls on initial seedling growth and the suite of biotic agents that damages seedlings. Key words: Geometridae, Hubbard Brook Experimental Forest, mortality, Rhizoctonia, winter injury. Le lessivage des cations basiques du sol par les pluies acides a eu un impact sur l'ecologie de la regeneration de l'erable a sucre (Acer saccharum Marshall) presque partout dans son aire de repartition. Nous avons suivi la survie et les causes de moralite d'une cohorte naturelle de semis d'erable a sucre dans 22 stations de la vallee de Hubbard Brook au New Hampshire, E.-U., oU l'acidite du sol a ete documentee. Sur une periode de 7 ans, le taux moyen de survie a ete de 3,4 %; cependant, des differences significatives ont ete observees entre les stations qui ont ete classees en trois groupes principaux sur la base de leur courbe de survie. Ces groupes de stations se distinguaient par leur position dans le paysage, la nutrition et la taille des feuilles des semis ainsi que par la predominance des agents deteriorateurs mais non par le Ca du sol. La mortalite a ete elevee (71 %) durant la premiere saison et les principaux agents deteriorateurs etaient les infections fongiques (Rhizoctonia spp.) et l'herbivorisme des chenilles (Geometridae). Les autres causes principales de mortalite etaient en ordre d'importance: les blessures hivernales, les blessures mecaniques et les galeries de rongeur (Myodes gapperi Vigors, 1830) et la severite des dommages causes par tous les agents deteriorateurs etait significativement differente d'une annee a l'autre. Cette etude fait ressortir l'importance de la variation a l'echelle du paysage des facteurs biotiques pour predire la reussite de la regeneration de l'erable a sucre. Les predictions concernant la regeneration de l'erable a sucre necessitent une meilleure comprehension des facteurs qui regissent la croissance initiale des semis et la serie d'agents biotiques qui causent des dommages aux semis. [Traduit par la Redaction] Mots-cles: Geometridae, foret experimentale de Hubbard Brook, mortalite, Rhizoctonia, blessures hivernales., Introduction Temperate forests are confronted with an unprecedented combination of human-accelerated environmental changes, including climate warming (Dale et al. 2001), air pollution (Tomlinson 2003), and introduced pests and pathogens (Fischer [...]

Establishment and survival of tree seedlings in hard soils depends on production of deep root systems. This study evaluated the primary and lateral roots of an annual crop and several tree species growing in soils of varying strength. We grew peas and acacias by direct seeding, plus three eucalypts by direct seeding and transplanting, and measured various root characteristics. At all levels of soil compaction, the primary roots of acacia were thicker and they elongated faster than did those of the eucalypts. However, lateral roots of transplanted eucalypts elongated faster than their primary roots, and the rate of root elongation was negatively correlated with soil penetration resistance, especially for Eucalyptus camaldulensis. The primary root diameter of all plants increased with increasing penetration resistance, but acacia roots continued to elongate faster than pea roots. Pea plants produced most of their roots in the top 5 cm, whereas tree roots were more uniformly distributed with depth. Although not statistically significant at P = 0.05, the relative rate of root elongation in very hard soil correlated modestly (P = 0.11) with the maximum root growth pressure of four tree species. These variations in root growth behaviour can be related to the intrinsic variability of root characteristics for each plant species and the natural abundance of each species in different environments. Additional keywords: Acacia, compaction, direct seeding, Eucalyptus, Pisum, root penetration, transplanting., Introduction Revegetation of agricultural landscapes with trees has attracted much attention over the last three decades (e.g. Simpfendorfer 1975; Hillis and Brown 1984; Stirzaker et al. 2002; Donohue et al. [...]

Understory growth dynamics of northern conifer species were studied in four stands managed under multiaged silvicultural systems in eastern Maine. Height growth of Picea rubens Sarg., Abies balsamea (L.) Mill., and Tsuga canadensis (L.) Carr. saplings between 0.5 and 6.0 m in height was related to the proportion open sky (POS), using sapling height as a covariate. Height growth of T. canadensis equaled A. balsamea and exceeded P. rubens under very low light levels (POS < 0.1) but is much less responsive to both increasing POS and taller heights, reaching 50% of its maximum height growth at a POS of only 0.09. Abies balsamea outgrew P. rubens under similar dark conditions; at higher light levels (POS > 0.10), both species grew similarly. Evidently, no feasible overstory manipulation of light alone can promote more rapid height development of P. rubens saplings over A. balsamea. A nonlinear light-prediction model using stand basal area is linked with height-growth prediction equations to quantify sapling development from 0.5 to 6 m. Depending on overstory density, P. rubens requires a height advantage of 0.14-0.33 m over a 0.5 m tall A. balsamea to reach a height of 6 m over the same time period. La dynamique de la croissance en sous-etage des coniferes nordiques a ete etudiee dans quatre peuplements soumis a un regime sylvicole multi-age dans l'est de l'Etat du Maine. Avec la hauteur des gaules comme covariable, la croissance en hauteur des gaules d'epinette rouge (Picea rubens Sarg.), de sapin baumier (Abies balsamea (L.) Mill.) et de la pruche du Canada (Tsuga canadensis (L.) Carr.) entre 0,5 et 6,0 m de haut est reliee au pourcentage d'ouverture du couvert (POC). La croissance en hauteur de T. canadensis egale celle de A. balsamea et depasse celle de P. rubens dans des conditions de tres faible luminosite (POC < 0,1). Mais la croissance en hauteur de T. canadensis est tres peu sensible a l'augmentation du POC et a une hauteur initiale plus elevee, atteignant 50 % de sa croissance maximale en hauteur a une valeur de POC de seulement 0,09. Abies balsamea depasse P. rubens dans des conditions similaires de luminosite; dans des conditions de plus forte luminosite (POC > 0,10), les deux essences croissent de facon similaire. Evidemment, en pratique aucune manipulation de l'etage dominant pour augmenter la luminosite ne peut favoriser une croissance en hauteur des gaules de P. rubens plus rapide que celle de A. balsamea. Un modele non lineaire de prediction de la luminosite base sur la surface terriere est relie aux equations de prediction de la croissance en hauteur pour quantifier le developpement des gaules de 0,5 a 6 m. Dependamment de la densite de l'etage dominant, une tige d'epinette rouge doit avoir 0,14 a 0,33 m de plus qu'une tige de sapin de 0,5 m de haut pour atteindre une hauteur de 6 m au cours de la mdme periode de temps. [Traduit par la Redaction], Introduction A natural disturbance regime dominated by gap dynamics and a long history of partial cutting have made multiaged, mixed-species forest structures common in the Acadian Forest of northeastern North [...]