Évaluation du potentiel de croissance des arbres feuillus et de leur sensibilité aux conditions climatiques

En Amérique du Nord, la coupe de jardinage a été implantée en réponse à plusieurs décennies de mauvaises pratiques forestières ayant laissé de grandes superficies de peuplements feuillus dégradés et de faible vigueur. Or, l’application de la coupe de jardinage dans un contexte industriel a produit des résultats variés et parfois peu convaincants sur sa capacité à améliorer la vigueur générale des peuplements et à fournir un rendement soutenu en bois de haute valeur. L’objectif général de ce projet de recherche était d’améliorer les prévisions de la croissance et de la mortalité des arbres feuillus à partir d’une meilleure évaluation de leur potentiel de croissance sur pied et de leur sensibilité aux conditions climatiques. Nos résultats ont d’abord montré un effet marginal du taux de dégagement induit par la coupe de jardinage sur la croissance et le taux de survie des arbres résiduels. Ce résultat s’explique en partie par une concentration de la récolte des arbres à l’intérieur et aux abords des sentiers de débardage, laissant ainsi de larges zones non traitées dans les peuplements résiduels. Dans les années suivant l’application du traitement, uniquement 24 % des arbres ont connu une hausse de croissance significative, un pourcentage de réaction de croissance légèrement inférieur à celui induit par les perturbations naturelles au cours des décennies précédentes. Nos analyses ont également montré qu’une réduction marquée de la croissance sur plusieurs décennies précédait 88 % des événements de mortalité post-récolte, et que les prévisions de ces événements pouvaient être significativement améliorées en considérant les tendances de croissance 25 ans avant la coupe. De plus, la présence de défauts affectant la vigueur des arbres au moment de la coupe était positivement reliée à la probabilité de mortalité et négativement reliée à la probabilité d’avoir une hausse de croissance après la coupe. Par ailleurs, nos analyses ont montré qu’une évaluation visuelle de la densité du houppier est l’indicateur le plus efficace pour estimer la vigueur et le potentiel de croissance sur pied de l’érable à sucre. Finalement, nos analyses des relations entre la croissance et les conditions climatiques ont montré un lien fort entre l’occurrence des stress climatiques ponctuels et une diminution de la croissance de l’érable à sucre. Les épisodes de gel-dégel de forte intensité ont été particulièrement dommageables en provoquant des baisses abruptes de la croissance dans les deux régions étudiées. À l’inverse, les analyses provenant des tendances climatiques mensuelles ont indiqué une relation faible et instable dans le temps avec la croissance. Nos résultats indiquent que l’effet synergique d’une accumulation de plusieurs stress climatiques et d’épidémies d’insectes défoliateurs au début des années 1980 a induit un changement important dans la dynamique de croissance de l’érable à sucre et sa réponse aux conditions climatiques mensuelles

An accumulation of climatic stress events has led to years of reduced growth for sugar maple in southern Quebec, Canada

Understanding the influence of climatic variation on forest dynamics is of great ecological and economic interest, and is essential to prescribe silvicultural interventions that will facilitate ecosystem acclimation to global change. However, the retrospective identification of climatic events responsible for the inter-annual variation of tree growth is challenging, notably because both their duration and their subsequent effects can be highly variable in time. In this study, we aimed to (1) quantify empirically the effect of climatic stress events on the short- and long-term growth dynamics of sugar maple trees; (2) compare the effects of different types of climatic events, that is, drought and thaw–freeze; and (3) compare the effects of climatic stress events to those of traditional monthly level climate metrics. To achieve this, we paired cross-dated tree-ring series to monthly and daily-level climate metrics over more than 50 yr in two distinct regions of southern Quebec. While the analysis from monthly level metrics first suggested a weak and non-stationary relationship between climatic conditions and tree growth, the analysis from daily-level metrics showed that climatic stress events, and more particularly thaw–freeze events, were strongly related to the growth of sugar maple trees. Our results suggest that the synergic influence of cumulative climatic stress events, which was exacerbated by insect outbreaks during the early 1980s, induced an important shift in the growth dynamics of sugar maple and in its response to variation in climatic conditions. These results highlight the potential negative impact of global climate change on our capacity to predict stand productivity accurately, especially if climate-sensitive growth models are based on projections of future monthly metrics. Because adverse climatic events are expected to increase both in frequency and in severity over the next decades, a general decrease in the growth rate of sugar maple is apprehended in southern Quebec

Local Geometric Consensus: A General Purpose Point Pattern-Based Tracking Algorithm

Proceedings of ACM ISMAR 2015, Fukuoka, JapanInternational audienceWe present a method which can quickly and robustly match 2D and 3D point patterns based on their sole spatial distribution , but it can also handle other cues if available. This method can be easily adapted to many transformations such as similarity transformations in 2D/3D, and affine and perspective transformations in 2D. It is based on local geometric consensus among several local matchings and a refinement scheme. We provide two implementations of this general scheme, one for the 2D homography case (which can be used for marker or image tracking) and one for the 3D similarity case. We demonstrate the robustness and speed performance of our proposal on both synthetic and real images and show that our method can be used to augment any (textured/textureless) planar objects but also 3D objects

Practical and precise projector-camera calibration

International audienceProjectors are important display devices for large scale augmented reality applications. However, precisely calibrating projectors with large focus distances implies a trade-off between practicality and accuracy. People either need a huge calibration board or a precise 3D model [12]. In this paper, we present a practical projector-camera calibration method to solve this problem. The user only needs a small calibration board to calibrate the system regardless of the focus distance of the projector. Results show that the root-mean-squared re-projection error (RMSE) for a 450cm projection distance is only about 4mm, even though it is calibrated using a small B4 (250 × 353mm) calibration board

Characterization of geological boundaries using 1‐D wavelet transform on gravity data: Theory and application to the Himalayas

International audienceWe investigate the use of the continuous wavelet transform for gravity inversion. The wavelet transform operator has recently been introduced in the domain of potential fields both as a filtering and a source-analysis tool. Here we develop an inverse scheme in the wavelet domain , designed to recover the geometric characteristics of density heterogeneities described by simple-shaped sources. The 1-D analyzing wavelet we use associates the upward continuation operator and linear combinations of derivatives of any order. In the gravity case, we first demonstrate how to localize causative sources using simple geometric constructions. Both the upper part of the source and the whole source can be studied when considering low or high altitudes, respectively. The ho-mogeneity degree of the source is deduced without prior information and allows us to infer its shape. Introducing complex wavelets, we derive analytically the scaling behavior of the wavelet coefficients for the dyke and the step sources. The modulus term is used in an inversion procedure to recover the thickness of the source. The phase term provides its dip. This analysis is performed on gravity data we measured along a profile across the Himalayas in Nepal. Good agreement of our results with well-documented thrusting structures demonstrates the applicability of the method to real data. Also, deeper, less constrained structures are characterized

FaDIn: Fast Discretized Inference for Hawkes Processes with General Parametric Kernels

Temporal point processes (TPP) are a natural tool for modeling event-based data. Among all TPP models, Hawkes processes have proven to be the most widely used, mainly due to their simplicity and computational ease when considering exponential or non-parametric kernels. Although non-parametric kernels are an option, such models require large datasets. While exponential kernels are more data efficient and relevant for certain applications where events immediately trigger more events, they are ill-suited for applications where latencies need to be estimated, such as in neuroscience. This work aims to offer an efficient solution to TPP inference using general parametric kernels with finite support. The developed solution consists of a fast L2 gradient-based solver leveraging a discretized version of the events. After supporting the use of discretization theoretically, the statistical and computational efficiency of the novel approach is demonstrated through various numerical experiments. Finally, the effectiveness of the method is evaluated by modeling the occurrence of stimuli-induced patterns from brain signals recorded with magnetoencephalography (MEG). Given the use of general parametric kernels, results show that the proposed approach leads to a more plausible estimation of pattern latency compared to the state-of-the-art

GDMS-R: A mixed SQL to manage raster and vector data

11pInternational audienceTo evaluate urbanization impact on territories, an accurate knowledge of the urban and peri-urban fabrics is unavoidable. To provide advanced characterization of the terrain, modern GIS applications target even wider geographic areas at finer resolutions but they also have to mix data of different types such as Digital Elevation Model (raster layer), buildings (polygonal layer) and roads (polylines layer). Processing both raster and vector data with the same semantic and in an efficient way presents significant challenges to GIS insofar as underlying granularities but also data layout and processing patterns might be absolutely different. We have already focused on the definition and the implementation of an abstraction layer called GDMS (Generic Datasource Management System) to handle and process vector data. Main objectives with GDMS, were to provide the user not only a simple and powerful API but also a spatial SQL derived language. Moreover, as an intermediate layer between the user and the information source, GDMS intends to reduce the coupling between the processes and the specificities of each underlying format. As a consequence, former work may easily be reused in a much larger set of scenarii. The learning curve is consequently even simpler. In this paper, we propose a raster extension to the GDMS layer called GDMS-R. Even if, there is currently no OGC standard concerning raster processing (using well-known SQL language), there already exists a de facto standard called Map Algebra defined by C. D. Tomlin in 1990 and commonly implemented in a wide set of GIS. Our objective is a bit different insofar as we propose to extend SQL language. We present the integration of Map Algebra concepts in GDMS through the GRAP (GeoRAster Processing) language. As for GDMS, reuse is enhanced by the possibility of being vendor-independent (middle-ware approach) and the extension capabilities of the underlying SQL language. To demonstrate the capabilities of GDMS-R, we present a use case relative to the deep impact of increased urbanization on the vulnerability of peri-urban hydro-systems: impact of the linear constraints on the runoff water pathways and accumulation that uses both vector and raster data in an unified way

GDMS: An abstraction layer to enhance Spatial Data Infrastructures usability

15pInternational audienceThe practical exploitation of SDI (Spatial Data Infrastructures) raises number of issues as far as it grows. Among them is the heterogeneity of data sources and thus the difficulty for GIS users not to depend on the data source format and of course to learn different systems. This a major flaw with respect to reuse and data sharing. The purpose of our work is to propose a new semantic layer derived from the SQL language that is independent of the underlying data source. This layer, called GDMS (Generic Data source Management System) can first be seen as an abstraction layer between data sources and the SDI tools. We will also show how this layer extends both SQL and spatial semantics and improves the exploitation of the SDI, by providing feedback both in terms of work and data reuse. A simple example mixing heterogeneous data sources will be presented

Vaporization of bi-component droplets in a turbulent over-heated flow : Experiments and Numerical Simulation

This paper deals with an experimental study of bi-component droplets evaporation in a turbulent over-heated channel flow. Droplets are made of a mixture of n-octane and 3-pentanone (15% in volume). Planar Laser Induced Fluorescence (PLIF) of 3-pentanone is used to derive both concentration of this molecule in liquid and gas phases. Concomitant dispersion of the liquid droplets and evaporation can be clearly observed with a trend to homogenisation of the 3-pentanone vapour in the flowfield due to high turbulence rate, on the order of 40%. The experimental results, in term of concentration of 3-pentanone in both liquid and gas phases have been compared to a simplified numerical simulation based on the discrete component model, taking into account the droplet composition, associated to the isolated droplet model. It appears that the measurements performed on the liquid phase overestimate the calculated evaporation, as the gas phase measurements performed far from the injection point are in correct agreement with the calculations. One of the explanations is that the PLIF CCD camera dynamic is not sufficient to detect simultaneously the biggest and smallest droplets. In the present cases, most of the numerous smallest droplets seem to be ignored by the measurement, which tends to overestimate the droplet evaporation. The second important cause of discrepancy between experimental and numerical results is linked to the strong extinction of the fluorescence signal issuing from the liquid phase, due to the absorptio

Direct and indirect paths leading to contraceptive use in urban Africa

Résumé Cet article examine le recours à la contraception dans les capitales de quatre pays africains, le Burkina Faso, le Ghana, le Maroc et le Sénégal. L’article cherche à répondre à deux questions : (i) quel est l’ordre hiérarchique des relations causales entre les caractéristiques individuelles associées au recours à la contraception dans les quatre populations urbaines considérées ? Plus particulièrement, (ii) comme l’instruction est un facteur majeur de la transition démographique, les données confirment-elles les deux chemins indirects allant de l’instruction au recours à la contraception qui ont été proposés dans la littérature, à savoir un chemin union-re­production et un chemin socio-culturel ? À partir d’une analyse secondaire des En­quêtes Démographie et Santé (EDS), la méthodologie se base sur des modèles structurels récursifs représentés par des graphes acycliques orientés. L’analyse em­pirique confirme l’importance de variables telles que le désir d’enfants et l’accord parental en matière de planification familiale pour expliquer le recours à la contraception. L’analyse met aussi en relief un chemin structurel union-reproduction as­sociant instruction féminine et recours à la contraception. En revanche, l’analyse aboutit à rejeter l’existence d’un chemin socioculturel, celui-ci étant infirmé par les données disponibles. La validité de ces résultats est discutée. Abstract This study examined contraceptive use in the capital cities of four African countries, Burkina Faso, Ghana, Morocco and Senegal. The article sought to answer two questions: (i) what is the hierarchical ordering of causal relationships among the individual factors involved in the use of contraception in the four urban populations considered? More particularly, (ii) as education is a major factor of fertility transition, are two main indirect pathways that have been proposed in the literature (a union-reproductive path and a socio-cultural one), leading from women’s education to contraceptive use, confirmed by the data? Having recourse to a secondary analysis of Demographic and Health Survey(DHS) data, the methodology is based on recursive structural models represented by directed acyclic graphs. The empirical analysis confirms the importance of variables such as the desire for children and partner agreement on family planning in explaining contraceptive use. It also highlights a structural union-reproductive path linking female education and contraceptive use. On the contrary, the analysis leads to a tentative rejection of the socio-cul­tural path, as it is falsified by the data available. The validity of these results is discussed