Réponse du pin gris et de l'épinette noire à l'éclaircie commerciale en forêt boréale

En raison de la difficulté d'approvisionnement en bois de qualité que traverse le Québec, l'éclaircie commerciale a été préconisée comme un moyen sylvicole d'accroître le potentiel de croissance des espèces d'intérêt commercial. L'effet de l'éclaircie commerciale a été étudié chez le pin gris (Pinus banksiana Lamb.) et chez l'épinette noire (Picea mariana (Mill.) BSP). Notre hypothèse générale était que le pin gris, qui est intolérant à l'ombre, répondrait rapidement et intensément à l'éclaircie alors que l'épinette noire, modérément tolérante à l'ombre, répondrait plus faiblement. La thèse a été réalisée en Abitibi-Témiscamingue et aborde la réponse écophysiologique des deux essences à l'ouverture du couvert dans un contexte d'éclaircie commerciale à travers trois études prenant place à des échelles spatiales et temporelles différentes. Dans le cadre des deux premières études, des dispositifs expérimentaux distincts ont été mis en place pour chacune des deux essences. Dans chaque dispositif, un traitement témoin (sans intervention) et deux traitements d'éclaircie- des réductions relatives de surface terrière (G,) de 0,3 et 0,4 pour le pin gris, de 0,4 et 0,5 pour l'épinette noire (chapitre II) et de 0,4 et 0,5 pour les deux espèces (chapitre III), ont été assignées aléatoirement à des parcelles expérimentales dans deux blocs expérimentaux pour chacune des deux espèces (chapitre II) et dans cinq blocs expérimentaux pour le pin gris et quatre pour l'épinette noire (chapitre III). La première étude s'intéresse à la réponse des aiguilles et étudie la photosynthèse des deux essences sur une base journalière en même temps que les paramètres de la photosynthèse. La deuxième étude porte sur une période d'un à six ans après éclaircie et aborde la réponse des tiges individuelles mise en lumière à partir d'analyses de tiges effectuées sur 30 individus de pin gris et 24 d'épinette noire. Nous nous sommes intéressés à la distribution de croissance le long de la tige, aux modifications de structure de cime et à l'efficacité de croissance. Alors que les deux premières études utilisent une approche expérimentale, la troisième repose sur le modèle CroBas, un modèle de bilan de C, que nous avons paramétrisé pour chacune des deux essences en utilisant les données récoltées dans le cadre des deux premières études et des données provenant de la littérature. Le modèle simule la réponse des peuplements pour une période allant jusqu'à 20 ans après éclaircie. À l'échelle spatiale de l'aiguille, la concentration en Net la surface foliaire spécifique n'ont pas varié significativement à la suite de l'éclaircie aussi bien chez le pin gris que chez l'épinette noire. À l'échelle temporelle de la seconde, l'efficience photosynthétique (a), la respiration diurne (R,), la photosynthèse au point de compensation (LCP) et le taux de photosynthèse nette à lumière saturante (Amoxl n'ont également pas réagi significativement à l'éclaircie chez les deux espèces. À l'échelle journalière et pour les aiguilles âgées d'un an, la photosynthèse a connu une augmentation significative à l'image de la lumière chez le pin gris, ce qui n'a pas été le cas chez l'épinette noire. La réponse positive observée chez le pin gris a été liée à l'augmentation de la lumière après éclaircie, les réserves hydriques du sol étant demeurées inchangées. À l'échelle de l'individu et de l'année et sur une période de 6 ans, la réponse des arbres a été évaluée en fonction de la surface terrière prélevée relative [surface terrière prélevée 1 surface terrière initiale) x 100]. En l'absence d'éclaircie, l'accroissement en volume spécifique de bois ou SVI (rapport de l'accroissement annuel de la tige sur la surface cambiale) a été de 0,75 et 0,76 crn3 crn·2 an·' (1,30 rn du sol) respectivement chez le pin gris et chez l'épinette noire. Toutefois, on a noté des accroissements significatifs en SVI deux et trois ans après éclaircie respectivement chez le pin gris et chez l'épinette noire. À 6 ans après éclaircie, les SVI ont été chez le pin gris et chez l'épinette noire, respectivement de 1.77 crn3 crn·2 an·' et de 1.10 crn3 crn·2 an·' (1,30 rn du sol) pour la plus forte intensité d'éclaircie (réduction de surface terrière de 47,87 %). L'accroissement annuel absolu en volume de tige a été significatif dès les troisième et quatrième années après éclaircie respectivement chez le pin gris et chez l'épinette noire. L'accroissement en SVI a débuté en bas de la tige et s'est propagé en hauteur par la suite chez le pin gris alors que l'épinette noire a montré une réponse uniforme le long de la tige. L'efficacité de croissance (rapport de l'accroissement en biomasse de tige sur la biomasse foliaire) et la biomasse foliaire à mi -couronne ont significativement augmenté après éclaircie chez le pin gris et expliquent sa réponse positive alors que l'épinette noire a eu un choc d'éclaircie (réduction de SVI) les première et deuxième années après traitement. La réponse positive qui a suivi a été liée à une plus forte productivité associée à une allométrie inchangée. Les courbes de simulations de hauteur et de DHP obtenues à l'aide du modèle CroBas ont montré un bon ajustement à celles de Pothier et Savard (1998). Les accroissements en DHP, hauteur et volume ont également montré un bon ajustement aux accroissements issus de nos données expérimentales six ans après éclaircie aussi bien chez le pin gris que chez l'épinette noire avec généralement des précisions de prédiction de plus de 80% et des biais relativement faibles (0,01- 0,03). À partir de valeurs initiales de volume de peuplement et de surface terrière respectivement de 347 rn3 ha·' et de 37 rn2 ha·' chez le pin gris et de 320 rn3 ha·' et 48 rn2 ha·' chez l'épinette noire, nous avons obtenu des accroissements respectifs 20 ans après éclaircie de 38 et 32% chez le pin gris et de 25 et 20% chez l'épinette noire et ce, pour la plus forte intensité d'éclaircie ( 41% <S G, <S 66%; moyenne~ 47,87%). Toutefois, aucun effet compensatoire, à savoir une intensité d'éclaircie qui permette d'atteindre des valeurs de volume et de surface terrière d'avant traitement, n'a été noté chez les deux espèces. La meilleure réponse à l'éclaircie du pin gris lui confère un potentiel de production ligneuse plus intéressant pour l'industrie forestière alors que l'épinette noire apparaît plus intéressante si l'objectif est de produire des tiges dont la réponse a tendance à maintenir un défilement constant

Screening cowpea [Vigna unguiculata (L.) Walp.] varieties by inducing water deficit and RAPD analyses

The effects of water deficit induced by polyethylene glycol-6000 on some cowpea varieties, which belong to the national germplasm in Senegal are reported. Our results showed that, the length of the epicotyl was not affected by water deficit but the length of primary root was influenced only in Mouride variety. Water deficit influenced mostly the number of lateral roots. The 985 variety showed a great increase of its lateral root numbers and could be considered a drought tolerant variety. In contrast, the IT81D-1137 variety is very sensitive to water deficit because its lateral root number were reduced 3.8 fold compared to the control. These physiological studies were complemented by analyzing the genetic diversity of these varieties with random amplified polymorphic DNA (RAPD). The RAPD analysis suggested that the samples were also genetically diverse. Key Words: Vigna unguiculata, drought tolerance, PEG, RAPD. African Journal of Biotechnology Vol.3(3) 2004: 174-17

EFO-LCI: A New Life Cycle Inventory Database of Forestry Operations in Europe

Life cycle assessment (LCA) has become a common methodology to analyze environmental impacts of forestry systems. Although LCA has been widely applied to forestry since the 90s, the LCAs are still often based on generic Life Cycle Inventory (LCI). With the purpose of improving LCA practices in the forestry sector, we developed a European Life Cycle Inventory of Forestry Operations (EFO-LCI) and analyzed the available information to check if within the European forestry sector national differences really exist. We classified the European forests on the basis of "Forest Units" (combinations of tree species and silvicultural practices). For each Forest Unit, we constructed the LCI of their forest management practices on the basis of a questionnaire filled out by national silvicultural experts. We analyzed the data reported to evaluate how they vary over Europe and how they affect LCA results and made freely available the inventory data collected for future use. The study shows important variability in rotation length, type of regeneration, amount and assortments of wood products harvested, and machinery used due to the differences in management practices. The existing variability on these activities sensibly affect LCA results of forestry practices and raw wood production. Although it is practically unfeasible to collect site-specific data for all the LCAs involving forest-based products, the use of less generic LCI data of forestry practice is desirable to improve the reliability of the studies. With the release of EFO-LCI we made a step toward the construction of regionalized LCI for the European forestry sector

The regeneration of balsam fir stands in their northern abundance limit is more related to their seed sources and soil types than the climate

To explain the transition between the southern mixedwood and the northern coniferous bioclimatic domains respectively dominated by balsam fir and black spruce, 59 sample plots 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 the two bioclimatic domains. We also determined the soil types (clay and till), summer growing degree-days above 5°C (GDD_5), and total summer precipitation (PP_MA). Balsam fir regeneration was strongly linked with parental trees and was higher in the mixedwood than in the coniferous bioclimatic domain, with higher regeneration occurring on till than on clay soils. Also, the mortality was higher on till than on clay soils, due to increasing competition on tills where the regeneration is higher. Unlike PP_MA, GDD_5 positively influenced balsam fir regeneration. The dynamic of balsam fir stands in the coniferous bioclimatic domain was attributed to a decrease of balsam fir regeneration and increase of its mortality most likely due to a lack of good establishment substrates (till soils), and cooler temperatures. However, balsam fir stands persist above this northern limit prospected, owing to patchy occurrences of good establishment substrates where parental trees are found.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Understanding Effects of Competition and Shade Tolerance on Carbon Allocation with a Carbon Balance Model

A carbon-balance model based on mechanistic and allometric relationships (CroBas) was used to assess the effects of competition in C allocation in jack pine (Pinus banksiana Lamb.), a shade-intolerant species, and black spruce (Picea mariana (Mill.) B.S.P.), a moderately shade-tolerant species. For both species, model efficiencies ranged from 36 to 99%. The average model bias was lower than 11% and 18% for jack pine and black spruce, respectively. For both jack pine and black spruce, the total tree C increased over the years, with greater increases noted for decreasing competition. When considering a C compartment as a ratio of the total tree C, decreasing competition resulted for both species in decreasing stem C and increasing C in branches and foliage. When considering the amount of C in a given compartment, for jack pine, decreasing competition led to greater C stem, branches, foliage, and roots, whereas, for black spruce, it also increased its stem C but lately shifted at about 20 years, following thinning; thus, the changing C allocation over time results from both “passive plasticity”, reflecting environmentally induced variations in growth, and “ontogenetic plasticity”, referring to variations in the ontogenetic trajectory of a trait. Overall, the C allocation to stem and foliage relative to the total tree C generally decreased as competition decreased, supporting the optimal partitioning theory. These C-allocation patterns were related to the species’ shade tolerance and illustrated how jack pine and black spruce maximize their competitive fitness

Full Length Research paper - Screening cowpea [Vigna unguiculata (L.) Walp.] varieties by inducing water deficit and RAPD analyses

The effects of water deficit induced by polyethylene glycol-6000 on some cowpea varieties, which belong to the national germplasm in Senegal are reported. Our results showed that, the length of the epicotyl was not affected by water deficit but the length of primary root was influenced only in Mouride variety. Water deficit influenced mostly the number of lateral roots. The 985 variety showed a great increase of its lateral root numbers and could be considered a drought tolerant variety. In contrast, the IT81D-1137 variety is very sensitive to water deficit because its lateral root number were reduced 3.8 fold compared to the control. These physiological studies were complemented by analyzing the genetic diversity of these varieties with random amplified polymorphic DNA (RAPD). The RAPD analysis suggested that the samples were also genetically diverse

Stable annual pattern of water use by Acacia tortilis in Sahelian Africa

International audienceWater 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 onemonth during the dry seasonwhen defoliation was at amaximum.Maximumwater 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 fromdeep 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 leafwater potential of –2.0MPa, 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

Stable annual pattern of water use by Acacia tortilis in Sahelian Africa

International audienceWater 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 onemonth during the dry seasonwhen defoliation was at amaximum.Maximumwater 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 fromdeep 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 leafwater potential of –2.0MPa, 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

Patterns of genetic diversity resulting from bottlenecks in European black pine, with implications on local genetic conservation and management practices in Bulgaria

In the present study, we investigated the genetic structure and diversity of P.nigra populations in Bulgaria, using simple sequence nuclear repeats. Among-population structure was studied with distance and Bayesian frequency methods, assuming geometric distance and a “non-admixture” model. The “NJ” and “non-admixture” clusters confirm the “mountain effect” hypothesis of the black pine genetic structure in the study region. The analyses showed moderate among-population divergence (13.31 %; AMOVA) and evidence of genetic bottlenecks. The coalescent analyses suggest that P. nigra has survived for a long period (thousands of generations) under strong selection pressure and that its populations continued to be exposed to stochastic factors like climate fluctuation, forest fire and disease. The combination of recent and historic changes is responsible for the present population size and genetic diversity. Our results suggest that conservation and management practices should strive to maintain this genetic differentiation, specifically by emphasising reforestation efforts with stocks from local provenances to avoid non-local introductions

Species and soil effects on overyielding of tree species mixtures in the Netherlands

A growing number of studies provides evidence that mixed-species forests often have higher stand productivity than monospecific forests, which is referred to as overyielding. In this study, we explored how the combination of species and soil conditions affect overyielding in terms of periodic annual volume increment (PAIV) in Dutch forests. We studied Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), common beech (Fagus sylvatica L.), Scots pine (Pinus sylvestris L.), pedunculate oak (Quercus robur L.), and silver birch (Betula pendula Roth) growing in four two species combinations (Douglas-fir–common beech, Scots pine–pedunculate oak, pedunculate oak–common beech, and pedunculate oak–silver birch) from 398 long-term permanent field plots all over the Netherlands. We found that the Douglas-fir–common beech and Scots pine–pedunculate oak mixtures always showed overyielding. This overyielding was largely attributed to the Douglas-fir in the former mixture and to the pedunculate oak in the latter mixture, respectively. In both cases, overyielding was stronger at poor soils than at rich soils. The pedunculate oak–common beech mixtures overyielded at poor soils and underyielded at rich soils, which was attributed to the response of the common beech. Overyielding was not observed for the pedunculate oak–silver birch mixtures, irrespective of soil conditions. The results do not support our hypothesis since overyielding was not always driven by fast-growing light-demanding species. Overyielding was stronger for evergreen–deciduous species combinations, suggesting that differences in leaf phenology are a major driver of overyielding. Secondly, our results imply that overyielding is much stronger at poor soils than at rich soils, which is in line with the prediction of the stress-gradient hypothesis. We conclude that the growth of one species benefits from the admixture species, particularly in evergreen–deciduous species mixtures and that soils affect the extent of overyielding as studied in the Netherlands