Silvergran, Abies alba, är en ursprungligen odlad art som har fått snabb spridning i södra och mellersta Sverige de senaste 100 åren. Risk finns att denna art är invasiv och kan påverka vår inhemska flora och fauna negativt. I ett lövskogsområde norr om Uppsala finns en ungefär 70 år gammal plantering av silvergran som är nära 1200 kvadratmeter stor. I området kring planteringen har ett stort antal plantor av silvergran etablerat sig och syftet med denna studie är att kartlägga spridningen av arten i området. Studien kan bidra till att skapa ett generellt spridningsmönster för silvergran i liknande miljöer i Sverige. Att kartlägga spridningsmönstret kan vara fördelaktigt både för att kunna avgöra om arten måste klassas som invasiv, och om åtgärder behöver vidtas mot den möjligt invasiva ädelgranen. Skogsområdet är omgivet av åkermark och har inventerats genom transekter indelade i rutor. Från inventeringen är en generell spridning av silvergran kartlagd för skogsområdet. Granarna uppmättes i olika storlekskategorier, vilket är representerat i de framställda kartorna. På så sätt får man direkt en visuell överblick över spridningen av silvergran i skogsområdet från ursprungskällan. Tydligt är att silvergranen har stor möjlighet att på egen hand sprida sig i den sydliga, svenska lövskogen och hur spridningen av silvergran i framtiden kommer se ut är ett ämne för diskussion och studier.

When making decisions on which areas to harvest in a sustained yield, even-flow manner in mountainous areas such those in coastal British Columbia, it is important to know how timber productivity changes with elevation. This information allows foresters to decide at what elevation to start increasing the rotation age and to decide at what elevation sustainable harvesting becomes infeasible due to low productivity. Since Pacific silver fir (Abies amabilis Dougl. ex Forbes) has an elevation range that extends from sea level nearly to the tree line (0 m to approximately 1,650 m; from the Coastal Western Hemlock zone, through the Mountain Hemlock zone; to the lower limits of the Alpine Tundra zone), productivity-elevation relationships are especially important. To acquire quantitative measures of productivity decrease with increasing elevation a regression equation relating site index (the height of the dominant trees at a base age of breast height age of 50 years) to elevation in southern coastal BC was developed. In turn, we used this regression as an input into the height driven yield model named the Variable Density Yield Prediction model (VDYP). The use of the VDYP model allows the site index values to be translated into actual productivity measures (e.g., volume per hectare, mean annual increment at culmination age).

Site classification in the biogeoclimatic ecosystem classification system is based on three differentiating properties: climatic regimes (expressed by biogeoclimatic subzones or variants), soil moisture regimes (SMRs), and soil nutrient regimes (SNRs). A SNR represents a segment of a regional soil nutrient gradient, i.e., soils which provide similar levels of plant-available nutrients over a long period. SNRs are identified in the field using a number of easily observable soil morphological properties and indicator plant species. However, we need to know to what extent soil nutrient properties support these indirect field-estimates. There have been several studies that quantitatively characterize regional soil nutrient gradients in different climatic regions, but no study has yet been done in the subalpine coastal forest (Mountain Hemlock zone). Influenced by a maritime subalpine boreal climate, high-elevation coastal soils differ from low-elevation soils by having a thicker forest floor and a higher organic matter content. In the study summarized here, relationships between soil chemical properties and field-estimated SNRs are examined and soil chemical properties and field-identified SNRs are related to the site index of Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Forbes) - one of the major timber crop species in the Coastal Western Hemlock and Mountain Hemlock zones.

Growth release of trees following canopy disturbances is of interest to ecological scientists and forest managers. Using dendroecological techniques, I examined growth release of canopy and subcanopy trees following the formation of natural, fine-scale canopy gaps in old-growth, western red cedar-western hemlock forests of coastal British Columbia. I aimed to quantify detailed information on release of the three shade-tolerant tree species that constitute these stands: western red cedar (Thuja plicata), western hemlock (Tsuga heterophylla), and Pacific silver fir (Abies amabilis). As a first step, I calibrated the radial-growth averaging method to account for regional-scale variability and capture a more complete range of growth releases that may occur following the formation of fine-scale gaps in the study stands. A 25% threshold, 5-year moving average, and 10-year window emerged as appropriate parameters for detecting releases using radial-growth averaging. Basal area increment was also the most appropriate growth index for detecting releases. Establishing these empirically-based criteria was important for quantifying the magnitude and duration of releases. Tree diameter and growth rate prior to release were the most important predictors of the magnitude and duration of releases, but identity of the tree species and distance from the gap center were also important predictors. Western hemlock and Pacific silver fir were often growing slowly both in the canopy and subcanopy, giving them tremendous potential to release. For these species, releases were generally intensive and persistent. In contrast, western red cedar were often growing quickly both in the canopy and subcanopy, giving them less potential to release. Compared to western hemlock and Pacific silver fir, western red cedar releases were less intensive and persistent. Patterns related to distance from the gap center emerged for trees growing along the north-south axis of gaps. Regardless of species, increasing distance from the gap center resulted in decreasing magnitude and duration of releases. However, patterns for duration were complex, as the distance effect was greater for trees north of the gap center. Information on growth release of trees is useful for reconstructing the history of past canopy disturbances, elucidating mechanisms of tree species coexistence, and assessing and predicting stand changes due to forest management in coastal British Columbia.

Growth release of trees following canopy disturbances is of interest to ecological scientists and forest managers. Using dendroecological techniques, I examined growth release of canopy and subcanopy trees following the formation of natural, fine-scale canopy gaps in old-growth, western red cedar-western hemlock forests of coastal British Columbia. I aimed to quantify detailed information on release of the three shade-tolerant tree species that constitute these stands: western red cedar (Thuja plicata), western hemlock (Tsuga heterophylla), and Pacific silver fir (Abies amabilis). As a first step, I calibrated the radial-growth averaging method to account for regional-scale variability and capture a more complete range of growth releases that may occur following the formation of fine-scale gaps in the study stands. A 25% threshold, 5-year moving average, and 10-year window emerged as appropriate parameters for detecting releases using radial-growth averaging. Basal area increment was also the most appropriate growth index for detecting releases. Establishing these empirically-based criteria was important for quantifying the magnitude and duration of releases. Tree diameter and growth rate prior to release were the most important predictors of the magnitude and duration of releases, but identity of the tree species and distance from the gap center were also important predictors. Western hemlock and Pacific silver fir were often growing slowly both in the canopy and subcanopy, giving them tremendous potential to release. For these species, releases were generally intensive and persistent. In contrast, western red cedar were often growing quickly both in the canopy and subcanopy, giving them less potential to release. Compared to western hemlock and Pacific silver fir, western red cedar releases were less intensive and persistent. Patterns related to distance from the gap center emerged for trees growing along the north-south axis of gaps. Regardless of species, increasing distance from the gap center resulted in decreasing magnitude and duration of releases. However, patterns for duration were complex, as the distance effect was greater for trees north of the gap center. Information on growth release of trees is useful for reconstructing the history of past canopy disturbances, elucidating mechanisms of tree species coexistence, and assessing and predicting stand changes due to forest management in coastal British Columbia.

Growth release of trees following canopy disturbances is of interest to ecological scientists and forest managers. Using dendroecological techniques, I examined growth release of canopy and subcanopy trees following the formation of natural, fine-scale canopy gaps in old-growth, western red cedar-western hemlock forests of coastal British Columbia. I aimed to quantify detailed information on release of the three shade-tolerant tree species that constitute these stands: western red cedar (Thuja plicata), western hemlock (Tsuga heterophylla), and Pacific silver fir (Abies amabilis). As a first step, I calibrated the radial-growth averaging method to account for regional-scale variability and capture a more complete range of growth releases that may occur following the formation of fine-scale gaps in the study stands. A 25% threshold, 5-year moving average, and 10-year window emerged as appropriate parameters for detecting releases using radial-growth averaging. Basal area increment was also the most appropriate growth index for detecting releases. Establishing these empirically-based criteria was important for quantifying the magnitude and duration of releases. Tree diameter and growth rate prior to release were the most important predictors of the magnitude and duration of releases, but identity of the tree species and distance from the gap center were also important predictors. Western hemlock and Pacific silver fir were often growing slowly both in the canopy and subcanopy, giving them tremendous potential to release. For these species, releases were generally intensive and persistent. In contrast, western red cedar were often growing quickly both in the canopy and subcanopy, giving them less potential to release. Compared to western hemlock and Pacific silver fir, western red cedar releases were less intensive and persistent. Patterns related to distance from the gap center emerged for trees growing along the north-south axis of gaps. Regardless of species, increasing distance from the gap center resulted in decreasing magnitude and duration of releases. However, patterns for duration were complex, as the distance effect was greater for trees north of the gap center. Information on growth release of trees is useful for reconstructing the history of past canopy disturbances, elucidating mechanisms of tree species coexistence, and assessing and predicting stand changes due to forest management in coastal British Columbia. / Arts, Faculty of / Geography, Department of / Graduate

Une tendance à l’augmentation des dépérissements forestiers est observée et risque de s’accentuer dans le contexte actuel de changement climatique. La télédétection peut proposer des méthodes innovantes pour l’évaluation de l’état et du devenir des écosystèmes forestiers. Ce travail de thèse vise à proposer, valider et interpréter des mesures de baisse d’activité des résineux du Sud du Massif-Central et de la sapinière pyrénéenne. Le premier objectif est, par l’utilisation de séries temporelles d’images à moyenne résolution spatiale (images NDVI-MODIS), d’identifier les méthodes permettant de mesurer des baisses d’activité, et de vérifier qu’elles correspondent à des baisses de vitalité, dans des peuplements où se manifestent des phénomènes de dépérissement. La détection de changement d’activité, que l’on peut assimiler à des perturbations, repose sur deux approches : la première mesure des écarts ou des tendances de paramètres de phénologie de surface et la deuxième utilise une procédure de décomposition de la série temporelle. Les mesures de changement ont été réalisées sur la période 2000-2011. La détection des ruptures négatives et de forte amplitude dans la réponse de NDVI de 2003 à 2011 confirme l’influence de la sècheresse de 2003, qui se traduit à la fois par les baisses d’activité liées à l’état des arbres mais également par des coupes de dépérissement qui se sont succédées les années suivantes. Un travail préliminaire à l’étape de validation des baisses de vitalité détectées, a consisté à proposer et appliquer un modèle de détection des coupes afin d’éliminer ces situations des zones d’observation. Une procédure de validation des baisses de vitalité a été mise en place dans le cas de la sapinière des Pyrénées. Pour cela, deux approches ont été utilisées : (1) la confrontation à des données indirectes de l’état des peuplements mais spatialement exhaustives, à travers les inventaires des coupes de dépérissement sur la période 2000-2012 et une cartographie du dépérissement datant de 2001 et (2) la confrontation à des données d’observations directes de l’état des Sapins dans le Pays de Sault (Est des Pyrénées), en utilisant une méthode de diagnostic basée sur l’architecture des arbres (méthode ARCHI), avec un échantillonnage adapté à l’échelle des pixels MODIS (Lambert et al. 2013). Des relations ont été mises en évidence, permettant de valider les méthodes utilisées, mais aussi d’en ressortir des limites d’interprétation. Enfin, pour donner des éléments d’interprétation des phénomènes observés, les variations d’activité observées par télédétection ont été confrontées à des données climatiques et édaphiques spatialisées, adaptées à l’étude des milieux forestiers. Les résultats montrent que les baisses de vitalité constatées dans les peuplements de Sapins du Pays de Sault sont significativement corrélées au facteur climatique température et dans une moindre mesure, aux précipitations. Dans les Pyrénées Centrales, où les facteurs de causalité semblent être multiples, l’influence des conditions de sècheresse hydrique et édaphique n’a pas pu être démontrée. / An increasing trend of forest decline is observed and is likely to increase in the current context of climate change. Remote sensing can provide innovative methods for the forest ecosystems status assessment. This thesis aims at proposing, validating and interpreting activity measurements of some Southern Massif Central and Pyrenees mountains coniferous stands. The first objective is, using of time series of medium spatial resolution (MODIS-NDVI) images, to identify methods to measure decreases of activity, and to verify if they correspond to vitality decreases in stands in which has been observed forest decline. Change detection of activity, which can be considered as disturbances, is based on two approaches: the first allows to measure differences or trends of phenology surface parameters, and the second uses a method based on the time series decomposition. Changes that occur during the 2000-2011 times-period were measured. The detection of high magnitude negative breakpoints in NDVI time series from 2003 to 2011 confirms the influence of the 2003 summer drought, which both led to decreases in activity related to trees heath status and also to clear-cuts during the following years. Before the validation process, a clear-cut detection method was proposed in order to eliminate these situations in the study areas. A validation procedure was implemented on Pyrenean fir stands. For this step, two approaches were implemented: (1) the use of spatially extensive state stands proxies, through cuts inventory inventories during the 2000-2012 times-period and a 2001 forest decline map, and (2) the use of data from direct tree heath’s observations in the fir stands of Pays de Sault region (Eastern Pyrenees) using a diagnostic method based on the observation of tree architecture (ARCHI method). For this second approach, an appropriate sampling was assessed to deal with the MODIS pixels scale (Lambert et al. 2013). Relationships have been identified, allowing to validate the used methods, but also to highlight theirs interpretation’s limits. Finally, to provide an interpretation of the observed phenomena, the remote sensing activity variations were compared to climatic and soil spatial data which are adapted to the study of forest environments. The results show that vitality declines in Pays de Sault fir stands are significantly correlated with climatic factors, temperature and to a lesser degree to precipitations. In the Central Pyrenees, where the causal factors appear to be numerous, the influence of water and soil drought conditions has not been demonstrated.

De nombreux cas de mortalité de Sapin pectiné (Abies alba Mill.) sont constatés en limite sud de son aire de répartition en Provence et semblent être liés aux sécheresses successives de la dernière décennie et à la répartition des propriétés hydriques du sol. L’enjeu est alors de mieux évaluer l’impact du stress hydrique sur le fonctionnement écophysiologique de cette espèce et de pouvoir caractériser et cartographier les zones les plus vulnérables à la sécheresse. Sur le Mont Ventoux, une expérimentation a été mise en place pour suivre pendant 3 ans différents paramètres écophysiologiques impliqués dans le comportement hydrique du Sapin pectiné sur des placettes pour lesquelles les propriétés du sol étaient caractérisées. Sur cette montagne de type karstique, les profondeurs de sols sont très variables et, à l'échelle stationnelle, les taux de mortalité et les intensités de stress hydrique étaient plus élevés sur les sols ayant une réserve hydrique plus importante. De plus, un arrière-effet de la sécheresse de 2009 a été observé réduisant durablement la transpiration de l'année suivante. Une approche par modélisation mécaniste a alors été adoptée en intégrant de nouveaux formalismes sur la dynamique racinaire permettant de prendre en compte cet arrière-effet. Elle a été évaluée sur les différents paramètres impliqués dans le cycle de l'eau et du carbone des arbres et le modèle a été validé sur les dynamiques de transpiration et d’accroissement en largeur de cernes des troncs. Des indices basés sur la mesure de température de surface ont été utilisés pour évaluer la possibilité de détecter le stress hydrique en forêt. Il existe une variabilité résiduelle liée aux facteurs climatiques et à la dimension réduite de la surface de mesure dans la relation entre transpiration et température de surface à l'échelle de l'arbre. A l’échelle du versant, la température de surface a permis d'identifier la répartition spatiale de la durée et de l'intensité du stress hydrique en accord avec la typologie de sol réalisées. La télédétection dans l'infrarouge thermique pourrait ainsi être un outil intéressant pour la gestion forestière. / Many reports of deaths of silver fir (Abies alba Mill.) are mentioned at the southern limit of its limit of distribution in Provence and appear to be related to the successive droughts of the last decade and to the distribution of soil water properties. The aim of the study is then to better assess the impact of water stress on ecophysiological functioning of this species and to characterize and map the areas more vulnerable to drought. On the Mont Ventoux, an experiment was set up to monitor for 3 years ecophysiological parameters involved in the water behaviour of silver fir on plots where soil properties were characterized. On this type of karstic mountain, soils depth is highly variable and, at forest stand scale, mortality rates and intensities of water stress were higher on soils with greater water reserve. In addition, a post-effect of the drought of 2009 was observed by reducing transpiration of the following year. A mechanistic modelling approach was then adopted by integrating new formalisms of root dynamics to take into account this post-effect. It was evaluated on various parameters involved in the water and carbon cycles of trees and the model was validated on the dynamics of transpiration and on annual rings width increment of tree trunks.Indices based on measured surface temperature were used to assess the possibility of detecting water stress in forests. At tree scale, there is a residual variability due to climatic factors and to the small size of the measurement surface in the relationship between transpiration and surface temperature. At the mountainside scale, surface temperature indices allowed identifying the spatial distribution of the duration and intensity of water stress according to the typology of soil done. Remote sensing in the thermal infrared could then be a useful tool for forest management.

In the wetter climates associated with the coastal forests of northwestern North America, coarse woody debris (CWD) accumulations in the form of snags, downed boles, and large branches can be large in natural forest ecosystems. Seedlings often regenerate on stumps and downed logs in the understory of old-growth coastal forests. The question remains though, whether CWD is a necessary component for seedling survival and growth in forests managed for commodity production. This study addresses one concern of forest managers: is there an immediate nutritional or moisture supply advantage conferred by CWD for the survival and growth of seedlings in the coastal climate of British Columbia? We compared survival and growth of seedlings planted in decaying wood compared to non-woody humus forms and mineral soil under heavy shade and full light conditions. Low light environments are of particular interest since reports of the strong association between CWD and regeneration has primarily referred to understory seedlings and saplings in old-growth forests.

The Mountain Hemlock (MH) zone includes all subalpine forests along British Columbia’s coast. It occurs at elevations where most precipitation falls as snow and the growing season is less than 4 months long. The zone includes the continuous forest of the forested subzones and the tree islands of the parkland subzones (Figure 1). Old-growth stands are populated by mountain hemlock, Pacific silver fir, and Alaska yellow-cedar, and are among the least-disturbed ecosystems in the world. Canopy trees grow slowly and are commonly older than 600 years, while some Alaska yellow-cedars may be up to 2000 years old. Early regeneration failures followed slashburning and the planting of unsuitable species. Currently, the most successful and feasible option for reforesting cutovers is natural regeneration with a mix of the three main tree species, but uncertainties remain about the temporal and spatial pattern of regeneration, changes in species composition, and the time required for stand establishment after cutting. Our study addressed these concerns by examining regeneration patterns on 6 sites that were clearcut 11-12 years prior to sampling and left to regenerate naturally. The sites were located at the lower limits of the zone in the Tetrahedron Range, near Sechelt, at elevations from 1060-1100m.