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A decrease in the average diameter of commercially harvested tree species in the Eastern boreal forest of Canada has led to a decrease in availability of quality wood for the forest industry. Commercial thinning has been proposed as a means to increase stem diameter growth. However, little is known about physiological responses underlying species responses to thinning. We assessed the effect of canopy opening on the photosynthetic response of mature jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP) trees. Two years after thinning and for each species, light response curves and the diurnal course of photosynthesis were characterized from measurements taken in a completely randomized block experiment on current-year and one-year-old needles of 12 trees from stands subjected to different levels of canopy opening. Soil water content, air and soil temperatures, and needle N concentration were not affected by thinning for either species. However, light availability increased with basal area removed and could explain the significantly positive relationship between thinning intensity and diurnal course of photosynthesis for one-year-old needles of jack pine. Black spruce photosynthesis did not respond to increases in light. Light-saturated rate of net photosynthesis (A), photosynthetic efficiency (α), light compensation point (LCP), and diurnal respiration (R) did not vary with thinning for either of the species. Jack pine and black spruce responses to thinning should be interpreted in light of species autecology.maxd

To explain the transition between the southern mixedwood and the northern coniferous bioclimatic domains that are dominated, respectively, by balsam fir (Abies balsamea (L.)Mill.) and black spruce (Picea mariana (Mill.) B.S.P.), 59 sites were selected throughout the two bioclimatic domains. The regeneration (seedling abundance) and mortality (difference between seedlings and saplings) of balsam fir seedlings were compared within and between bioclimatic domains. We also determined the soil types (clay and till), summer growing degree-days above 5[degrees]C (GDD_5), and total summer precipitation (PP_MA). Balsam fir regeneration was strongly linked to parental trees and was higher in the mixedwood bioclimatic domain than in the coniferous domain, with higher regeneration occurring on till than on clay soils. Mortality was higher on till than on clay soils due to competition between balsam fir seedlings, with other species having either no effect or decreasing mortality. Unlike PP_MA, GDD_5 positively influenced balsam fir regeneration. The dynamics of balsam fir stands in the coniferous bioclimatic domain were attributed to a decrease in balsam fir regeneration and to an increase in its mortality, most likely due to a lack of suitable establishment substrates (till soils) and cooler temperatures. Small balsam fir populations still persist in the northernmost latitudes of the species' range, mainly where parental trees occur on good establishment substrates. Our study contributes to a better understanding of the effect of species, climate, and site condition on latitudinal vegetation dynamics at a global scale. Key words: balsam fir, seedlings, coniferous domain, mixedwood domain, climate change. Pour expliquer la transition entre les domaines bioclimatiques des forets mixtes du sud et des forets resineuses du nord, qui sont respectivement dominees par le sapin baumier (Abies balsamea (L.) Mill.) et l'epinette noire (Picea mariana (Mill.) B.S.P.), 59 stations ont ete selectionnees dans les deux domaines bioclimatiques. La regeneration (abondance des semis) et la mortalite (difference entre le nombre de semis et de gaules) des semis de sapin baumier ont ete compares dans chacun des domaines bioclimatiques et entre eux. Nous avons aussi determine le type de sol (argile et till), les degres-jours de croissance au-dessus de 5[degrees]C pendant l'ete (DJC_5) et les precipitations estivales totales (PP_MA). La regeneration en sapin baumier etait fortement liee aux arbres parentaux et etait plus elevee dans le domaine bioclimatique des forets mixtes que dans celui des forets resineuses, avec des valeurs plus elevees sur les tills que sur les sols argileux. La mortalite etait plus forte sur les tills que sur les sols argileux a cause de la competition entre les semis de sapin baumier, alors que la mortalite des autres especes n'etait pas influencee ou diminuait. Contrairement aux PP_MA, les DJC_5 influencaient positivement la regeneration en sapin baumier. La dynamique des peuplements de sapin baumier dans le domaine bioclimatique des forets resineuses a ete attribuee a une diminution de la regeneration en sapin baumier et a une augmentation de sa mortalite, qui ont probablement ete causees par un manque de substrats d'etablissement approprie (tills) et des temperatures plus froides. De petites populations de sapin baumier sont toujours presentes sous les latitudes les plus nordiques de son aire de distribution, surtout aux endroits ou les arbres parentaux sont presents sur de bons substrats d'etablissement. Notre etude contribue a une meilleure comprehension des effets de l'espece, du climat et des conditions des stations sur la dynamique latitudinale de la vegetation a l'echelle globale. [Traduit par la Redaction] Mots-cles : sapin baumier, semis, domaine des forets resineuses, domaine des forets mixtes, changements climatiques., Introduction Tree population dynamics are closely related to seed availability and recruitment potential, which may be limited by many factors (Clark et al. 1998). Tree seedlings, which constitute the first [...]

Jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) B.S.P.) total stem volume increment and vertical growth distribution after thinning were quantified and related to foliage biomass, foliage density, and growth efficiency (GE) (stem to foliage biomass ratio). Significant positive stem volume increments were observed following thinning for jack pine (3 years after) and black spruce (4 years after). Both species reacted differently in terms of the distribution in specific volume increments (SVI) (annual stem volume increment to cambial surface ratio): (i) for jack pine, an increase in SVI was first observed at the base of the tree, with the increase moving upwards, showing that the taper was likely to increase following thinning and (ii) for black spruce, the vertical distribution of SVI was constant, leading to no modifications in stem taper. For jack pine, total stem volume growth was related to an increase in GE and a greater foliage biomass at midcrown, with foliage density staying constant. For black spruce, however, no changes in GE, foliage biomass, and foliage mass density were observed. Resume: L'accroissement total du volume de bois de la tige et la distribution de cette croissance le long de la tige du pin gris (Pinus banksiana Lamb.) et de l'epinette noire (Picea mariana (Mill.) B.S.P.) ont ete quantifies apres une eclaircie et relies a la biomasse foliaire, la densite foliaire et l'efficacite de croissance (EC) (rapport de la biomasse de bois de la tige sur la biomasse foliaire). Le volume de bois de la tige du pin gris et de l'epinette noire s'est accru de facon significative, respectivement 3 et 4 ans apres l'eclaircie. Des differences ont ete observees entre les especes dans l'accroissement specifique en volume (ASV) (rapport de l'accroissement annuel du volume de bois de la tige sur la surface cambiale): (i) dans le cas du pin gris, l'accroissement a commence a la base de la tige et s'est propage vers le haut indiquant que le defilement etait susceptible d'augmenter a la suite de l'eclaircie et (ii) dans le cas de l'epinette noire, l'ASV a ete plut?t constant tout au long de la tige, ce qui n'a pas beaucoup modifie son defilement. Chez le pin gris, la croissance totale de la tige etait reliee a une augmentation de l'EC et a une plus grande biomasse foliaire a mi-cime, la densite foliaire demeurant inchangee. Par ailleurs, aucun changement dans l'EC, la biomasse foliaire et la densite de la masse foliaire n'a ete observe chez l'epinette noire. [Traduit par la Redaction], Introduction Thinning forest stands can induce a sudden increase in resource availability for the residual trees (Aussenac 2000), leading to physiological and morphological modifications such as increases in stem volume [...]

Resume : En foret boreale, les effets benefiques du passage du feu sur le substrat de germination ont souvent ete lies a la presence de charbon et a son effet [...]

Author(s): Venceslas Goudiaby (corresponding author) [1]; Pieter A. Zuidema [1]; Godefridus M. J. Mohren [1] We suggest some pointers to guarantee the long-term storage, accessibility and reliability of international research [...]

Water use by mature trees of Acacia tortilis (Forsk.) Hayne ssp. raddiana (Savi) Brenan var. raddiana growing in the northern Sahel was continuously recorded over 4 years. Water use was estimated from xylem sap flow measured by transient heat dissipation. Concurrently, cambial growth, canopy phenology, leaf water potential, climatic conditions and soil water availability (SWA) were monitored. In addition to the variation attributable to interannual variation in rainfall, SWA was increased by irrigation during one wet season. The wet season lasted from July to September, and annual rainfall ranged between 146 and 367 mm. The annual amount and pattern of tree water use were stable from year-to-year despite interannual and seasonal variations in SWA in the upper soil layers. Acacia tortilis transpired readily throughout the year, except for one month during the dry season when defoliation was at a maximum. Maximum water use of about 23 l (dm sapwood area)−2 day−1 was recorded at the end of the wet season. While trees retained foliage in the dry season, the decline in water use was modest at around 30%. Variation in predawn leaf water potential indicated that the trees were subject to soil water constraint. The rapid depletion of water in the uppermost soil layers after the wet season implies that there was extensive use of water from deep soil layers. The deep soil profile revealed (1) the existence of living roots at 25 m and (2) that the availability of soil water was low (−1.6 MPa) down to the water table at a depth of 31 m. However, transpiration was recorded at a predawn leaf water potential of −2.0 MPa, indicating that the trees used water from both intermediary soil layers and the water table. During the full canopy stage, mean values of whole-tree hydraulic conductance were similar in the wet and dry seasons. We propose that the stability of water use at the seasonal and annual scales resulted from a combination of features, including an extensive rooting habit related to deep water availability and an effective regulation of canopy conductance. Despite a limited effect on tree water use, irrigation during the wet season sharply increased predawn leaf water potential and cambial growth of trunks and branches. [ABSTRACT FROM PUBLISHER]

It is important to understand price premiums related to certified raw wood to predict the future of forest certifications from the perspective of forestry enterprises. We focused on identifying the trading roundwood market data in the economic center of power in Tokyo. This study aimed to clarify Tama-certified raw wood prices under the local area certification scheme, forest-certified raw wood prices, and the handling volumes at the Tama Roundwood Market Center in Tokyo. Sales details of the Tama Roundwood Market Center were used to identify the handling volumes, Tama-certified raw wood prices, and FSC (Forest Stewardship Council) or SGEC (Japan-specific Sustainable Green Ecosystem Council)-certified raw wood prices. The FSC and SGEC have operated from the center since 2016. Data were collected from the 2006–2018 fiscal years. Our results showed that the volume of raw wood handled increased due to the regeneration-cutting project conducted by the Tokyo Metropolitan Government. On the other hand, there was no price premium for Tama-certified raw wood under the local certification scheme or for FSC- or SGEC-certified raw wood. Price premiums for forest certifications are necessary for ongoing sustainable forest management. There is a need to increase consumer awareness of forest certifications and to differentiate quality certifications further, and these would likely create price premiums. [ABSTRACT FROM AUTHOR]