No description available.

Abstract In this study, mineral nutrition and its relation to the vigour of Scots pines growing under the influence of sulphur, copper and nickel stress were investigated. This was done by analysing the nutrient status and needle damage of pines along a pollution transect extending from the proximity of a large S, Cu and Ni emitters on the Kola Peninsula to a background area in Finnish Lapland. Additionally, pine seedlings were exposed to Cu and Ni stress in order to gain more detailed information about the mechanisms behind metal stress. The total sulphur concentrations of the youngest needles in the vicinity of the largest point source were about double compared to those in the reference area (< 800 mg in kg of dry needles vs. > 1900 mg kg-1). In the case of Cu and Ni, this difference was close to 100-fold (from 2-3 mg kg-1 to over 250 mg kg-1). While the elevated sulphur concentrations were not attributable to particle deposition, the particles on needle surfaces raised the total concentrations of Cu and Ni occasionally over 1.5-fold compared to the inside concentrations. The Mn and Zn concentrations showed a decreasing trend, whereas K and P slightly increased towards the Monchegorsk smelters. Enhanced needle senescence and tip necrosis were related to high total foliar levels of Cu, Ni and S and low levels of Zn and Mn. Stomatal chlorosis and other discolourations showed a distinct relation to high SO2 levels in the air and also to high foliar concentrations of Ca, Fe, Si and Cl. Particles deposited on needle surfaces did not cause directly visible injuries in pines. In seedlings, Cu and Ni were enriched in roots: the Ni concentration was up to 16-fold and the Cu concentration 6-fold compared to that added into the soil. While Cu was mostly retained in roots, Ni had much easier access to foliage. The effect of metal stress on other nutrients varied between nutrients, plant parts and metals added. Soil analyses from both the field study and the seedling experiment gave mostly a weak estimation about the plant availability of nutrients. Foliar nutrients remained above the deficiency limits in all studies and were hence not the primary cause for the decrease of pine vigour and the consequent growth retardation and forest decline.

Yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) forests of coastal British Columbia are apparently experiencing decline in a manner similar to that observed in southeastern Alaska. In this pilot study, we collect tree-ring data from live and standing dead yellow-cedar trees from four declining sites on the North Coast of British Columbia. We use this data to compare growth patterns at our sites to those of yellow-cedar trees at non-declining and declining sites in southwestern British Columbia and southeastern Alaska and, in addition, to assess the possibility of reconstructing yellow-cedar population dynamics in declining stands using dendrochronology. We found coherent growth patterns (i.e. marker years and periods of suppression) among yellow-cedar chronologies from non-declining and declining sites across a broad geographic range as well as unique growth patterns between our chronologies from declining sites and those from declining sites in nearby Alaska. Using outer-ring dates of increment cores, we were able to estimate time since death of decade- to century-old standing dead yellow-cedar trees, although the precision of the estimates was influenced by partial cambial mortality and erosion of outer rings. Our results provide baseline dendrochronological information that will be useful for planning future studies that assess growth-climate relations and reconstruct the long-term population dynamics of yellow-cedar in declining stands.

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.

<p>This study presents the extent, history and process of forest decline in Awassa watershed, south central Ethiopia. By combining different data sources such as satellite images, social surveys and historical documents, forest decline is described quantitatively and qualitatively and the main causes behind this process are identified. Forest decline in the study area is interpreted as the result of a combination of socio-political changes, economic activities, population growth, cultural patterns and agricultural developments while local conflicts over resources also play an important role. The findings of this study reveal forest decline to be a continuous process associated with spatial fragmentation and location specific losses. The recent increase in production of the cash crop khat has made a significant impact on the forest through several mechanisms: it relocates the agricultural/forest frontier; it causes intrusion and permanent settlement within forests; and fragments remaining forest. The analysis of human-spatial boundaries indicates unsystematic management of the natural forests by several administrative units. As a result, multiple claims have been made on the forests simultaneously as weak control and accountability conditions have negatively affected forest management. The main conclusions are as follows: Forest decline in the study area has a long history, spanning at least one century. The causes are identifiable as both temporally spaced individual events as well as chains of events. These interact with each other at different levels and scales as well as with the geographical properties of the study area. Land users’ rationale in weighing the advantages between keeping and replacing the forest is affected by economic gain, market conditions and transport facilities. Multiple claims to the forest land and weak accountability contribute to inefficient management, which accelerates forest decline.</p>

This study presents the extent, history and process of forest decline in Awassa watershed, south central Ethiopia. By combining different data sources such as satellite images, social surveys and historical documents, forest decline is described quantitatively and qualitatively and the main causes behind this process are identified. Forest decline in the study area is interpreted as the result of a combination of socio-political changes, economic activities, population growth, cultural patterns and agricultural developments while local conflicts over resources also play an important role. The findings of this study reveal forest decline to be a continuous process associated with spatial fragmentation and location specific losses. The recent increase in production of the cash crop khat has made a significant impact on the forest through several mechanisms: it relocates the agricultural/forest frontier; it causes intrusion and permanent settlement within forests; and fragments remaining forest. The analysis of human-spatial boundaries indicates unsystematic management of the natural forests by several administrative units. As a result, multiple claims have been made on the forests simultaneously as weak control and accountability conditions have negatively affected forest management. The main conclusions are as follows: Forest decline in the study area has a long history, spanning at least one century. The causes are identifiable as both temporally spaced individual events as well as chains of events. These interact with each other at different levels and scales as well as with the geographical properties of the study area. Land users’ rationale in weighing the advantages between keeping and replacing the forest is affected by economic gain, market conditions and transport facilities. Multiple claims to the forest land and weak accountability contribute to inefficient management, which accelerates forest decline.