Planting trees on agricultural land either as farm woodlands or agroforestry (trees integrated with farming) is one option for reducing the level of atmospheric carbon dioxide. Trees store carbon as biomass, and may increase carbon storage in the ground. A review of the literature outlined uncertainty relating to changes in carbon storage after planting trees on agricultural land. The aim of this thesis is to deter¬mine the impact of tree planting on arable and pasture land in terms of above and belowground carbon storage and thereby address these uncertainties, and assess the implications for the Woodland Carbon Code: a voluntary standard for carbon storage in UK woodlands. Measurements of soil organic carbon to a depth of 1.5 m were taken at two field sites in Bedfordshire in the UK: a 19 year old silvoarable trial, and a 14 year old silvopasture and farm woodland. On average 60% and 40% of the soil carbon (rel¬ative to 1.5 m) was found beneath 0.2 and 0.4 m in depth respectively. Whilst tree planting in the arable system showed gains in soil organic carbon (12.4 t C ha−1 at 0–40 cm), tree planting in the pasture was associated with losses of soil organic carbon (6.1–13.4 t C ha−1 at 0–10 cm). Evidence from a nearby mature grazed woodland indicate that these losses may be recovered. No differences associated with tree planting were found to the full 1.5 m, though this may be due to a lack of statistical power. Measurements of above and belowground biomass, and the root distribution of 19 year old poplar (Populus spp.) trees (at the silvoarable trial) and ash (Fraxinus excelsior) trees ranging from 7 to 21 years (at several field sites across Bedfordshire) were made, involving the destructive harvest of 48 trees. These measurements suggest that Forestry Commission yield tables overestimate yield for poplar trees grown in a silvoarable system. An allometric relationship for determining ash tree biomass from diameter measurements was established. The biophysical model Yield-SAFE was updated to take into account root growth, and was parameterised using field measurements. It was successfully used to describe existing tree growth at two sites, and was then used to predict future biomass carbon storage at the silvoarable trial. Measurements indicate that losses in soil carbon at relatively shallow depths can offset a large proportion of the carbon stored in tree biomass, but assessing changes on a site by site basis may be prohibitively expensive for schemes such as the Woodland Carbon Code.

<ul><li>As the human population expands, agricultural expansion and intensification will exert an increasing pressure on remaining habitats, especially in the tropics. Oil palm is one of the most rapidly expanding crops in these regions, and identifying management strategies that conserve biodiversity and ecosystem services in these landscapes is therefore a priority. I assess whether riparian forest fragments (riparian reserves) conserve species and the functions they support within oil palm landscapes. Riparian forests are legally required for their beneficial impact on hydrological dynamics and their potential to contribute to the conservation of terrestrial species is poorly documented. I focussed on two ecologically important indicator groups (ants and dung beetles) and the ecosystem processes that they support. Whilst protecting primary forest will remain the most important strategy for biodiversity conservation, I found that riparian reserves do support species of ants and dung beetles that would not otherwise persist in oil palm landscapes. However, the extent to which riparian reserves maintained key ecological functions differed between these two taxa. The amount of nutrient distribution carried out by ants in riparian reserves was similar to logged forest areas, and higher than in oil palm. In contrast, dung removal functions did not vary between these land uses. I also investigated how the vegetation structure and landscape context of riparian reserves affects the dung beetle communities they support. Increasing reserve width and proximity to other forest fragments had a positive impact on the species richness and diversity of dung beetles in riparian reserves. There was little evidence that riparian reserves enhance the provision of dung removal or pest control services in adjacent areas of oil palm. >The results provide evidence to support the introduction and/or enforcement of legislation to protect riparian forest reserves in order to conserve biodiversity and ecological processes in oil palm landscapes.

The research aim was to assess the vegetation and soils of the Rora /' Habab plateau, Eritrea and to develop methods of propagating the native tree species, juniper and olive. The research consisted of vegetation and soil surveys, interviews with local people, archival research, and experiments on propagation of olive and juniper. Junipers are now confined to the north of the plateau. Olives are more abundant in the north but have very few individuals in the centre, where there are many dead trees, or south. Soil erosion was ubiquitous and often severe. Soil morphology and nutrient status were related to vegetation, topography, land use, and erosion status, and varied greatly over short distances. Soil texture was coarser and most chemical factors (except total Ca and exchangeable Na) were lower in the south. Organic C, total N, exchangeable Ca, percent day, CEC and the sum of bases were higher in soils from grazed land than in cultivated fields. Germination of olive seeds was 92% when the endocarp was removed; stratification had little effect. Rooting of olive stem cuttings attained 76% under mist when parent plants were fertilised and cuttings were treated with rooting hormone. Germination for juniper was 56% after stratification at 5°C for 30 to 60 days. Juniper stem cuttings rooted in only one of three experiments, where rooting was 78% in a well ventilated, cool, low-mist environment. Olive seedlings which were fertilised and watered every 7, 14, or 21 days for two months, were taller, had lower root:shoot ratios and soil moisture than unfertilised plants. Fertilised seedlings watered every 28 days died. Root volume was less for plants watered every 21 days but watering interval had little effect on other variables in unfertilised seedlings. Ecological restoration is urgently required to rehabilitate the Rora plateau, which has Africa's most northerly remnant juniper / olive woodlands.

Today's arid and semi-arid zones of the Mediterranean are affected by desertification, resulting from various factors, including climatic variations and human activities such as overcultivation, overgrazing and deforestation. Afforestation programs are one of the most effective means in preventing desertification. For many years Libya has had afforestation programs in order to restore degraded land and in response to rapid desert encroachment in the north east of Libya, in the area called the Jabal Akhdar (Green Mountain), which has been investigated in this study. The purpose of this research was to investigate the relative roles of exotic compared to native tree species in preventing desertification and enhancing degraded land restoration in the Jabal Akhdar. The effect of environmental factors on exotic compared to native tree species have been assessed by observations on growth and reproductive success of the species, including variables of stocking rate, trunk diameter, tree height, crown diameter, tree coverage, natural mortality, felling and seedling regeneration, as well as calculated variables, derived from these measurements. The effects of methods and age of afforestation on the promotion of biological diversity have been investigated using the Shannon-Wiener diversity index. The effects of tree species on soil depth have also been investigated. Multivariate statistical analyses of site, species and environmental data, using both cluster analyses and factor analyses have been performed, with the aim of determining what is influencing the species, crops or differentiating between the sites, based on soil depth, angle of slope, altitude, rainfall and air temperature values. Pinus halepensis showed success in its growth and regeneration, particularly at higher altitudes and steeper slopes. Cupressus sempervirens was successful in growth and regeneration in the mountains. The exotic Eucalyptus gomphocephala was very successful in its growth, but did not regenerate well, while the exotic Acacia cyanophylla trees had a failure of both growth and regeneration. E. gomphocephala species appeared to favour relativley the flatter (non-mountain) sites, while A. Cyanophylla appeared to favour relativly the mountain sites. All the species responded positively to greater rainfall and deep soil, but they differed in where they were most likely to be successful. Environmental factors such as climate, terrain and soil are the main determinants of species distribution in the study area, in addition to their impact on the growth of the main trees. There appeared not to be any relationship between biodiversity and whether the main trees were native or exotic, and only P. halepensis showed any negative effect on the abundance of shrubs. There was greater diversity of trees and shrubs generally at the younger sites than the old sites. The present study emphasises the current mismanagement of planted forests, particularly with overgrazing contributing to desertification, through preventing tree growth and eliminating most sapling regeneration. This study concludes by making recommendations for more effective choice of tree species to plant, and for subsequent management to improve afforestation programmes in the Jabal Akhdar area.

The Effects of Tropical Forest Management on Biodiversity and Ecosystem Functioning Eleanor M. Slade 1. Between 35 % and 50 % of all closed-canopy tropical forest has been lost, and the rate of deforestation continues to increase throughout the tropics. Despite a wealth of literature on the effects of tropical forest disturbance on the diversity and composition of a variety of taxa, there is still no clear consensus on the value of disturbed forests for biodiversity. 2. If forest management practises are to be sustainable in the long-term they should maintain both biodiversity and ecosystem functioning (the interactions and processes of the ecosystem), as well as a timber harvest. However, few studies have investigated the extent to which ecosystem functioning is reduced in logged forests. The effects of different logging intensities on a variety of taxa, and the ecosystem processes with which they are associated, were assessed in the Danum Valley Conservation Area in Sabah (Malaysian Borneo). 3. Even under high logging intensities, the forests of Sabah appear to have been managed in a way that maintains timber yields in the short-term. However, other aspects of forest structure had been affected, which could have important consequences ecologically, and for the long-term sustainability of timber harvests. 4. Combining field studies with manipulative experiments allows assessment of the impacts of species changes associated with habitat modification on measures of ecosystem functioning. Dung beetle (Coleoptera: Scarabaeidae: Scarabaeinae) functional group richness and composition were manipulated in a series of field experiments. Certain functional groups and species were found to have a greater impact on ecosystem functioning than others; nevertheless a full complement of species was needed to maintain full ecosystem functioning. 5. Dung beetles appeared to be relatively robust to changes in forest structure associated with selective logging, but species richness was reduced with high-intensity logging. There was a corresponding decrease in ecosystem functioning (dung and seed removal) with a decrease in species richness, and a decrease in the biomass of large nocturnal tunnellers, suggesting that although some species are dominant, rare species are also needed to preserve full ecosystem functioning. 6. A complex interaction between birds and ants resulted in reduced herbivory of seedlings of the important timber tree, Parashorea malaanonan, in some instances. However, this interaction was not affected by either selective or high intensity logging. Seedfall of P. malaanonan, was reduced in logged forest compared to primary forest. Despite insect seed predation being higher in primary forest, there was still successful recruitment during a non-mast year. Parasitism of insect-predated seeds was found to be inversely density dependent, and was higher in logged forest where seed predation was lower. 7. The results of this thesis suggest that the forests of Sabah appear to be being logged under a management system that is compatible with sustainable timber management, but not necessarily sustainable forest management. Low intensity selective logging seems to preserve much of the original forest structure, biodiversity and ecosystem functioning compared to logging at higher intensities. However, ecosystem processes were variable in their response to logging, suggesting that management decisions should be based on the consideration of multiple taxa and processes.

Africa's miombo woodlands constitute one of the most important dry tropical forests on earth, yet the hydraulic function of these woodlands remains poorly researched. Given the current predictions of increased aridity by the end of this century in the miombo ecoregion, understanding the likely response of miombo woodlands tree species to water stress is crucial in planning adaptation strategies. Predicting the response of miombo woodlands to future climate trends is hampered by a lack of knowledge on the physiology of the common miombo woodlands tree species. In particular, plant-water relations for this woodlands type are not well understood. An understanding of plant-water relations for this woodlands type will provide insights into how water limits tree species distribution in this ecosystem. This will also improve our prediction model on the likely response of this ecosystem to predicted climate change. For this reason, the overall objective of this research was to evaluate the hydraulic architecture and xylem vulnerability to cavitation for nine principal miombo woodlands tree species differing in drought tolerance ability and habitat preference. This was achieved by; examining the hydraulic properties and evaluating the extent to which each hydraulic design was vulnerable to water stress-induced xylem cavitation; investigating how seasonal changes in plant-water relations influences seasonal patterns of leaf display and; analyzing the relationship between stem hydraulic supply and leaf functional traits related to drought tolerance ability. This research has found that drought-intolerant tree species with mesic specialization have more efficient stem hydraulic systems than co-occurring habitat broad ranging species. Broad ranging tree species attain wider habitat distribution by adjusting their hydraulic supply in response to changing ecosystem water availability. The finding that hydraulic properties differ significantly between tree species with contrasting habitat preference suggests that tree hydraulic design may have some adaptive ecological role in influencing species habitat preferences in miombo woodlands. The evaluation of xylem vulnerability to cavitation revealed that mesic specialized tree species were more vulnerable to water stress-induced cavitation than habitat broad ranging tree species. Vulnerability to cavitation in individuals from the same broad-ranging species growing in contrasting habitats showed only marginal and statistically insignificant (P > 0.05) differences between wet and dry sites. In the investigation of the influence of seasonal changes in stem water relations on seasonal leaf display, seasonal rhythms in stem water status were found to exert significant controls on leaf phenology. Mesic specialists had strong stem water controls throughout the year in comparison to broad ranging tree species. An analysis of the relationship between stem hydraulic supply and leaf functional traits suggests that stem hydraulic supply constrains leaf biomass allocation patterns among miombo tree species. Mesic specialists tend to invest more in leaf longevity than broad ranging tree species. This thesis has uncovered some interesting relationships between plant-water-relations and the distribution of miombo woodlands tree species. These results lead to the conclusion that in an event of increased ecosystem drying under future climate trends, tree species with mesic specialisation are at a greater risk of experiencing cavitation related species mortality than broad ranging ones.

This thesis describes a series of 1:75 scale wind tunnel experiments investigating the wind flow over, and through, three different forest models and the resultant wind loading on individual model trees. The experiments were designed to lead to a quantitative assessment of the wind stability of the particular forest arrangements and also to permit a study of the coherent gust structures in the flow. Forest canopy flow is dominated by a plane mixing layer flow regime with a shear layer close to the canopy top. It has been confirmed that data can be correlated usefully in terms of a shear length, Ls, related to the form of this shear layer. Frequency analysis has confirmed that the flow structures have the same frequency as the swaying of the tallest trees in each forest. A mechanism is proposed whereby upstream turbulence induces swaying of trees at and near the upwind edge region of the forest, which in turn perturbs the air in the unstable shear layer. This leads to a roll-up of the shear layer and the creation of coherent flow structures. Conditional sampling of the gust structures, using wavelet analysis, has also supported the theory of a plane mixing layer type flow. An eddy-pair structure was revealed, the arrangement of which accounts for the intermittent strong downward sweeps of air into the canopy that have been reported by many observers. The large downward sweep of air was also shown to be responsible for the highest bending moments experienced by individual trees. Assessments of the different forest formations showed that in a forest consisting of a 50/50 mix of 200 mm and 100 mm model trees, gusts did not penetrate the lower forest. This arrangement should improve the protection of younger trees and may be worth investigating in field trials.

Le changement climatique est connu pour entraîner une redistribution spatiale des conditions climatiques et avec elle une migration des espèces vers les pôles et les sommets. De tels changements impliquent une réorganisation des communautés végétales dont la nature, l'intensité et le déterminisme sont encore peu connus. L'objectif de cette thèse est d'évaluer, à large échelle spatiale et sur de longs pas de temps, les changements de composition des communautés végétales forestières induits par le réchauffement climatique, ainsi qu'analyser les facteurs écologiques et géographiques contribuant à ces changements à l'échelle de l'espèce et des communautés. La réponse de la flore forestière vis-à-vis du réchauffement climatique a été étudiée à l'échelle du territoire français (~546000 km²) à partir de larges bases de données d'observations floristiques, de données environnementales mesurées et modélisées, et d'une approche modélisatrice basée sur le concept de niche écologique et sur le caractère bio-indicateur des espèces. Dans un premier temps, nous avons montré que le remaniement des communautés végétales a permis la compensation de 0.54°C du réchauffement climatique ayant touché les forêts de montagne entre les périodes 1965–1986 et 1987–2008 (i.e. +1.07°C) contre seulement 0.02°C pour les forêts de plaine (réchauffement = 1.11°C). Cette compensation partielle démontre l'existence d'une dette climatique de la flore induite par le réchauffement climatique. L'importance de cette dette en plaine par rapport aux montagnes provient probablement de l'effet combiné d'un déficit d'extinction et de migration des espèces en plaine conduit respectivement par une plus large tolérance thermique des plantes forestières sur cette zone et par une migration des plantes a priori (i) limitée par l'importante fragmentation des forêts de plaine et (ii) inférieure au déplacement des conditions thermiques en plaine. Les particularités écologiques et géographiques des forêts de plaine et de montagne nous ont amené à considérer deux types de menaces induites par le changement climatique : (i) l'attrition biotique en plaine, et (ii) la perte d'une biodiversité historique et spécifique en montagne (réduction de l'habitat des espèces alpines aboutissant à leur disparition) remplacée probablement par des espèces plus communes. Dans un second temps, les effets de facteurs abiotiques, biotiques et géographiques pouvant amplifier ou réduire les changements de distribution des espèces et de composition des communautés induits par le réchauffement climatique ont été caractérisés. [...] Suite et fin du résumé dans la thèse. / Climate change is known to cause a spatial redistribution of climatic conditions which is driving poleward and upward range shifts. Such shifts imply a reorganization of plant communities which is still poorly understood. Here we aimed to assess the changes in plant communities' composition induced by climate warming at a global scale and over a long time period, as well as to analyze the effects of ecological and geographical factors that contribute to these changes at the species and community levels. The response of the forest flora to the raising temperature has been studied across the French metropolitan territory (~546,000 km²) from large floristic databases, measured and modeled environmental data, and a modeling approach based on the concept of ecological niche and the bioindicator properties of plant species. First, we showed that the reshuffling of plant communities allowed to recover 0.54°C of the temperature increase between the periods 1965–1986 and 1987–2008 in highland forests (i.e. +1.07°C), while it recovered only 0.02°C in lowland forest (warming = 1.11 °C). This partial compensation demonstrates the current occurrence of a climatic debt in forest vegetation caused by climate warming. The high climatic debt observed in lowland forest compared to the highland one is likely due to extinction and migration debts caused by a wider temperature tolerance of plants in lowland communities and a plant migration capacity (i) limited by the high spatial fragmentation of the lowland forest habitat and (ii) shorter than the shift of thermal conditions in lowland areas, respectively. The ecological and geographical specificity of lowland and highland forests led us to consider two different threats induced by climate change: (i) biotic attrition in lowland areas, and (ii) loss of a specific and an historic biodiversity in highland forest (mountaintop extinction of alpine species due the surface decrease of their potential habitat) likely replaced by more common species assemblage (increase of generalist plants). Second, the effects of abiotic, biotic and geographical factors which can amplify or reduce the magnitude of both the species range shifts and the reshuffling of plant communities induced by global warming were characterized. Last and final summary in the thesis.

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.

Alors que le département des Vosges connaît une importante industrialisation au XIXe siècle, dominée par l'industrie textile (tissages, filatures et blanchiments), comment ses activités traditionnelles du bois ont-elles participé à cet essor économique ? L'exploitation de ses forêts (plus de 200 000 hectares, près de 38 % de la superficie départementale) favorise, dès le début du XIXe siècle, le développement de la fabrication de produits sciés (planches et charpentes), transportés par flottage (sur la Moselle et surtout la Meurthe) pour être vendus hors du département, mais aussi de produits de boissellerie. Le travail du bois connaît ensuite d'importantes mutations à partir des années 1850-1860 et ne reste pas en marge du développement industriel. L'exploitation forestière s'intensifie, grâce à un aménagement plus rationnel des espaces forestiers (rythme annuel des coupes, multiplication des voies de transport), et fournit près de 800 000 m3 de bois par an. Les fabrications, organisées par une majorité de petites et moyennes entreprises familiales, forment progressivement une filière industrielle, par le développement d'activités de première transformation (essor des entreprises de sciage privées), de seconde transformation (industries de la menuiserie, du meuble, de la boissellerie) et d'un secteur de la papeterie utilisant les pâtes de bois. Constituée de 800 entreprises, mobilisant près de 10 000 Vosgiens (patrons et salariés), la filière bois marque fortement de son empreinte le département au début du XXe siècle, et constitue un bel exemple du rôle moteur de la petite industrie dans l' industrialisation progressive et sans révolution de certains territoires. / In the 19th century as the Vosges département was going through large scale industrialisation dominated by the textile industry, how did its traditional activities linked to logging take part in that economic boom? From the early nineteenth century the exploitation of its forests (occupying more than 200,000 hectares - nearly 38% of the surface of the département) was beneficial to the development of the production of sawn products (boards and roof timbers) floated down the waterways (the Moselle and mainly the Meurthe river) to be sold outside the Vosges. It also boosted the production of various wooden objects and implements. Then the logging industry experienced many changes from the 1850s and 1860s onwards, thus keeping pace with the increasing development of industry. Logging grew thanks to a more rational management of forested areas (annual rhythm of the cuttings, multiplication of the roads devoted to transport) and produced about 800,000 cubic metres of timber annually. The manufacturing organised in small and medium sized family-owned businesses gradually came to form the backbone of an industrial sector through the development of sawmilling activities (booming of family-owned sawmills), manufacturing activities (carpentry, cabinet-making and production of various wooden objects), and also a paper making sector using pulpwood. Comprised of almost 800 businesses employing a nearly 10,000 strong local workforce (managers and employees) the timber industry left a definite print on the Vosges at the turn of the 20th century and gives a fine example of the driving force played by small businesses in the progessive and smooth industrialisation of certain territories.