Modeling of light transmission under heterogeneous forest canopy: model description and validation

International audienceGrowth and survival of regeneration saplings and understorey vegetation development is closely related to light available below the forest trees. Manipulating the forest structure by thinning adult trees is a major tool to control light transmission to the understorey. The transmission is related to the attenuation of light which is usually estimated with the Beer-Lambert law assuming homogeneous foliage within the canopy. However forest canopies are far from homogeneous, which requires models that can take into account the effect of clumping between and within trees. In this work we present a model that can be readily used with both coarse or detailed parameterization to generate any type of stand and compute the distribution of light transmitted below the canopy. To evaluate the accuracy of the model, we compared model results with field measurements from several stands of Pinus sylvestris L. in the French Massif Central.no abstrac

Characterisation and correction of the shape of hardwoods planted at low densities without woody accompanying vegetation

Pour réduire les coûts de plantation et limiter la concurrence entre arbres afin d'optimiser leur croissance initiale, les feuillus précieux sont de plus en plus plantés à faible densité. Il est généralement admis que ces conditions conduisent au développement de nombreux défauts de forme compromettant la production d'une bille de pied de qualité. De 1991 à 1997, nous avons suivi l'évolution des défauts de forme de près de 1 500 arbres (Merisier, Érable sycomore et Frêne commun) plantés à large espacement en l'absence d'accompagnement ligneux afin de vérifier ce postulat. Nous avons également évalué les capacités de la taille de formation à corriger les défauts de forme potentiels. À partir de ces résultats, nous avons calculé l'intensité de taille nécessaire pour parvenir à l'obtention d'une bille de pied droite et sans noeud

Light-dependent development of two competitive species (Rubus idaeus, Cytisus scoparius) colonizing gaps in temperate forest

Forest regeneration can be inhibited by competition for environmental resources (water, nutrients, light) between tree seedlings and some competitive species that are generally light-demanding species developing in gaps. The study's aim was to quantify the development of two competitive species (Rubus idaeus and Cytisus scoparius) present in the chaine des Puys, France, relatively to light in gaps inside Picea abies stands. On 29 transects linking the stand to the gap centre (223 points), light intensity was measured (0-80% of relative light) and floristic measurements (cover and height of the different species) were done. Development of both competitive species is positively connected to fight, with a bell-shaped curve with a maximum of 40-50% for R. idaeus and a quite constant increase to 80% (maximum of light recorded in the experimentation) for C scoparius. These results are discussed relatively to understorey vegetation management in order to favour forest regeneration

Investigations sur la stratégie de survie des jeunes hêtres (Fagus sylvatica L.) sous faibles conditions de lumière avec une approche de modélisation intégrative

International audienceBeech (Fagus sylvatica L.) is a shade tolerant species of broadleaved temperate forests from the northern hemisphere. However, how it manages to survive low irradiance conditions is debated. This must involve both carbon balance components (mainly photosynthesis vs. respiration) and efficient utilization / partitioning of the available C resource among the different sinks (mainly growth vs. reserve storage). This survival strategy was investigated through a combined experimental and modelling approach. Four-year-old beech seedlings growing in the understorey of natural Scots pine stands were 3D-digitized in summer for architecture, including woody parts (growth units) and leaves. Then seedlings were harvested in autumn and winter to quantify biomass and carbohydrate reserve contents of each organ, both above and below ground. Roots were separated into 3 classes: taproot, main lateral roots and fine roots, and shoot segments according to their age. These data were used to construct 3D-digital mockups of the young trees and to parameterize and initialize the carbon-based functional-structural model PIAF-1. Additional beech-specific parameters relevant to phenology and gas exchange rates were derived from similar experiments or literature. Meteorological data (daily radiation and temperature) were generated for each tree based on recorded weather data. Transmitted solar irradiance above each seedling was calculated from hemispherical photographs and the global radiation above the stand. The first results suggest that under the most restrictive light conditions, the reserve store was just sufficient for the spring outgrowth. The major factor allowing the seedling to pass the short but critical near-zero-reserve phase appeared to be the leaf growth strategy, with surface area expanding prior to structural hardening. The reserve mobilization strategy showed only as a second factor, with the mobilization rate likely not limiting in contrast to the total reserve store

Investigating survival strategy of regenerating youg beech (Fagus sylvatica L.) under low light condition through integrative modeling

Investigating survival strategy of regenerating youg beech (Fagus sylvatica L.) under low light condition through integrative modeling. 2016 IEEE International Conference on Functional-Structural Plant Growth Modeling, Simulation, Visualization and Applications (FSPMA 2016

Evolution des besoins en lumière avec la dimension des individus et lien avec la croissance de plants de hêtre de 8 ans dans le massif central

International audienceIt is well know that light requirements for significant growth increase with individual's size rather than with age for most young forest trees. We tested this assumption for the European beech (Fagus sylvatica), a particularly shade-tolerant species. Growth, crown morphology, light capture, photosynthesis and biomass allocation were recorded since beech plantation in 2000 in central France under the shelterwood of Pinus sylvestris thinned to get different light intensities. Beech growth rate increased with light availability with a plateau at 40-50%. The biomass shoot:root ratio was unaffected by light, whereas the ratio between leaf area and total plant biomass (LAR) logarithmically decreased with increasing light. This effect almost disappeared when taking into account individual biomass. It seems that the proportion of non-photosynthetic tissues (root, stem) increased faster than that of photosynthetic tissues (leaf). Therefore light availability to beech sapling should be continuously increased to maintain the same growth rate with time.Les besoins en lumière des jeunes plants forestiers ne sont pas constants et évoluent notamment avec la dimension des individus. Cette relation a été étudiée pour le hêtre (Fagus sylvatica) dans le Massif Central en France, sous différents couverts de pin sylvestre

Evolution of light requirement with individual's size and links with growth performance of eight-year-old beech saplings in central France

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