Contexte : L’influence de la végétation urbaine sur le développement de l’asthme infantile est controversée. Il est avancé que les arbres (canopée urbaine) réduisent la pollution atmosphérique, un facteur de risque de l’asthme mais également, que certains peuvent émettre des pollens et des composés organiques volatils biogéniques, tout-autant des facteurs de risque pour le développement de l’asthme chez l’enfant. Cependant, les risques associés à la canopée urbaine ont été étudiés à l’aide de données rudimentaires souvent, sans considération pour la saison. Objectifs : 1) Caractériser l’association entre la végétation urbaine et le développement de l’asthme en distinguant la végétation totale et de la canopée des feuillus et de conifères, en fonction des saisons de production de pollens et de feuilles des arbres. 2) Évaluer l’influence de la canopée d’arbres sur l’association entre les particules fines (PM2.5) et le développement de l’asthme infantile. Méthodes : Nous avons utilisé les données d’une cohorte de naissance ouverte contenant tous les enfants nés sur l’île de Montréal (Canada) entre 2000 et 2015 et suivis jusqu’à leurs 12 ans, créée à partir de données médico-administratives agrégées. L’exposition à la végétation totale a été estimée à l’aide d’une mesure satellitaire appelée l’indice de végétation par différence normalisée (NDVI) et l’exposition à la canopée urbaine, a été estimée à l’aide de données de télédétection laser aéroporté - LiDAR permettant d’estimer l’aire de la canopée des feuillus et des conifères dans un rayon de 250 m autour de la résidence des participants, tout au long du suivi. En dehors des saisons de pollens et de feuilles des arbres, les variables d’expositions ont été fixées à zéro. Des modèles de risque proportionnels de Cox ont été développés pour estimer le risque associé au NDVI et aux canopées d’arbres lors de la saison de pollens et de feuilles des arbres. La non-linéarité a été modélisée à l’aide de catégories et de splines cubiques pour les expositions. Nous avons ensuite évalué l’effet de la canopée urbaine sur l’association entre les particules fines (PM2.5) et le développement de la maladie. Résultats : Parmi les 352 946 enfants inclus dans la cohorte et suivis pour un total de 1,7 millions de personnes-années, 30 816 nouveaux cas d'asthme ont été identifiés pour un taux moyen de nouveaux cas d’asthme était de 17,79 nouveaux cas par 1 000 personnes-années. Le NDVI moyen annuel s’élevait à 0,365 (Écart-type (ET) : 0,106) dans un rayon de 250 m centré sur la résidence des participants. En saison de pollens, le NDVI moyen se réduisait à 0,089 (ET : 0,106) et à 0,15 (ET : 0,185) en saison de feuilles. En moyenne, les enfants étaient exposés à trois fois plus de canopées de feuillus (moyenne = 12,3 (ET : 17,0) ×103 m2) que de conifères en saison de feuilles (moyenne= 4,5 (ET : 4,3) ×103 m2), et sept fois plus en saison de pollens. Nos analyses ont révélé des associations distinctes en fonction des saisons pour le NDVI et la canopée de feuillus. Trop peu de conifères étaient présents pour tirer des conclusions quant à leur effet. Les analyses à l’aide des splines cubiques pour les expositions ont indiqué la présence de relations non-linéaires. La catégorisation des expositions a indiqué que des niveaux moyens de canopée de feuillus en saisons de feuilles avaient un effet protecteur lorsque comparés aux non-exposés (Rapport de Risque (RR): 0,694 ; Intervalle de confiance (IC95%) : 0,680 – 0,708). À l’inverse, pour les journées de pollens, la canopée de feuillus autour de la résidence était associée à l’augmentation du risque (RR =1,082 (IC95% 1,056 – 1,108)). Pour les catégories de NDVI annuel (non subdivisé par saisons), aucune association n’a été détectée. Pour finir, la canopée d’arbres et le NDVI n’ont influencé que très faiblement l’association entre les PM2.5 régionaux et le développement de l’asthme infantile. Cependant, une légère interaction a été observée entre les feuillus en saison de feuilles et les PM2.5. Des niveaux élevés de feuillus autour de la résidence en période de feuilles diminueraient le risque d’asthme associé à l’exposition aux PM2.5. Discussions : Les résultats suggèrent que l’effet de la végétation varie en fonction des saisons. L’effet capté par le NDVI semble être en grande partie attribuable à la canopée de feuillus. L’influence de la végétation sur l’association entre les PM2.5 et le développement de l’asthme est très faible. / Background: The influence of urban vegetation and tree canopy on the development of childhood asthma is controversial. It is argued that trees reduce air pollution, a risk factor for asthma, but at the same time, some species emit pollens and biogenic volatile organic compounds, all of which are risk factors for the development of asthma in children. Yet, the risks associated with the urban canopy have been studied using rudimentary data, often without consideration for the season. Objectives: 1) To characterize the association between urban vegetation and asthma development by distinguishing between total vegetation and deciduous and evergreen tree canopy, according to the pollen and leaf-on seasons. 2) To assess the influence of tree canopy on the association between fine particulate matter (PM2.5) and the development of childhood asthma. Methods: We used data from an open birth cohort containing all children born on the island of Montreal, Canada, between 2000 and 2015 and followed up until their 13th birthday, created from aggregated medico-administrative data. Exposure to total vegetation was estimated using a satellite measure called the normalized difference vegetation index (NDVI). Exposure to the urban canopy was estimated using LiDAR, an airborne remote laser sensing technology that was used to estimate the area of the deciduous and coniferous canopy within a 250 m buffer centered on participants' residential postal codes, updated throughout the follow-up. Outside of the pollen and tree leaf-on seasons, exposure variables were set to zero. Cox proportional hazard models were developed to estimate the risk associated with NDVI and tree canopies for the pollen and tree leaf-on seasons. Nonlinearity was modeled using categories and restricted cubic splines for exposures variables. We then assessed the effect of the urban canopy on the association between fine particulate matter (PM2.5) and asthma development. Results: Among the 352,946 children included in the cohort and followed for a total of 1.7 million person-years, 30,816 new asthma cases were detected, for an average incidence rate of 17.79 new cases per 1,000 person-years. The mean annual NDVI was 0.365 (Standard Deviation (SD): 0.106) within a 250 m buffer centered on participants' residential postal codes. In the pollen season, the mean NDVI was reduced to 0.089 (SD: 0.106) and to 0.15 (SD: 0.185) for the leaf-on season. On average, children were exposed to three times as much deciduous canopy (mean= 12.3 (SD: 17.0) ×103 m2) as coniferous canopy in leaf-on season (mean= 4.5 (SD: 4.3) ×103 m2), and seven times as much in pollen season. Our analyses revealed distinct associations by season for NDVI and deciduous trees. Too few evergreens were present to draw conclusions about their effect. Cubic spline analyses for exposures indicated the presence of nonlinear relationships. Exposure categorization indicated that average levels of deciduous trees canopy in the leaf-on season had a protective effect when compared to unexposed (Hazard Ratio (HR): 0.694; Confidence Interval (CI95%): 0.680 - 0.708). Conversely, for pollen days, the residential deciduous canopy was associated with increased risk (HR =1.082 (CI95% 1.056 - 1.108)). For annual NDVI categories (not subdivided by season), no association was detected. Finally, tree canopy and NDVI only weakly influenced the association between regional PM2.5 and childhood asthma development. However, a slight interaction was observed between leaf-on-season deciduous canopy and PM2.5. High levels of deciduous trees canopy at residential postal codes during the leaf-on season decrease the risk of asthma associated with PM2.5 exposure. Discussion: Our results suggest that the effect of vegetation varies with season. The effect captured by NDVI appears to be largely due to the deciduous canopy. The influence of vegetation on the association between PM2.5 and asthma development appeared to be marginal.

La hausse de l’urbanisation et la hausse d’introduction des espèces exotiques qui l’accompagne sont parmi les plus grands risques pour la biodiversité. Les espèces exotiques peuvent non seulement affecter la diversité alpha et réduire les populations d’espèces indigènes, mais également entrainer des changements de la biodiversité bêta. Toutefois, ces phénomènes sont complexes et la littérature sur le sujet présente des résultats variés. C’est pourquoi le but de cette recherche est d’étudier l’influence des espèces exotiques et envahissantes sur la diversité alpha et bêta de 61 boisés urbains de la grande région de Montréal. Nos résultats ont montré que les espèces envahissantes ont un effet plus grand que les espèces non envahissantes sur la diversité alpha. Elles sont toutes deux associées à une hausse de la richesse totale et de la diversité alpha. Toutefois, une hausse du couvert des espèces envahissantes est associée à une diminution de la richesse et du couvert des espèces indigènes. Nos résultats ont également montré qu’un grand couvert en espèces envahissantes provoque des changements significatifs de la diversité bêta en réduisant la différence entre les sites. À l’opposé, lorsque la richesse en espèces exotiques est grande, nous avons observé une différenciation en espèces indigènes qui serait expliquée par la diminution de leur richesse. Pour finir, nous avons constaté que les espèces exotiques et envahissantes sont associées à un changement significatif de la composition en espèces. Nos résultats suggèrent que les espèces exotiques, tout particulièrement les espèces envahissantes, sont associées à des changements importants de la diversité des boisés urbains. Toutefois, des études supplémentaires sont nécessaires pour confirmer si elles sont responsables de ces changements ou simplement le symptôme de perturbations sous-jacentes. / Urbanization and exotic species introduction associated with it are among the most important causes of the current biodiversity crisis. These disturbances are associated with a decrease in native species alpha diversity and with changes in beta diversity worldwide. However, those changes are complex, and studies on this subject show mixed results. Consequently, the impact of exotic species on native flora is still up for debate. In this context, we aimed to study the relationship between exotic and invasive species on the diversity of 61 forest patches in the Metropolitan region of Montreal. Our analysis showed that invasive species had slightly more impact on native diversity than non-invasive ones. However, the effects of invasive and non-invasive species were similar. They both added to the total richness, and their richness was associated with an increase of alpha diversity. They were also associated with a decrease in native species cover and the invasive species with a reduction of native richness. We also found that a high cover in exotic species, especially invasive ones induced homogenization in urban forest patches. However, at high richness, they tend to induce differentiation in native species beta diversity, caused by a decrease in native species richness. Finally, we found that exotic species induce significant changes to the species composition of the forest patches. Our results suggest that exotic species, especially invasive ones, are associated with significant changes in urban forest diversity. However, further research is needed to verify if they are direct actors in those changes or symptoms of underlying disturbances.

Vorliegende Arbeit zeigt die jüngsten Möglichkeiten hochauflösender Fernerkundung am Beispiel von Stadtbäumen in Berlin, Deutschland. Es wurden neuste methodische Ansätze eingesetzt, wie beispielsweise maschinelles Lernens und individuelle Baumdetektion. Sie erwiesen sich von großem Vorteil für die detaillierte Analyse urbaner Ökosystemdienstleistungen in einer heterogenen Umwelt. Neueste Fernerkundung von hoher zeitlicher Auflösung hat Möglichkeiten gezeigt, Veränderungen des Stadtwaldes präziser zu untersuchen. Diesbezüglich konnten Baumspezies klassifiziert werden auf Grundlage saisonaler Veränderungen, die mittels Fernerkundungsdaten aufgenommen wurden. Dies ist für den urbanen Bereich einmalig und über große Flächen noch nicht durchgeführt worden. Darüber hinaus haben diese Baumarten einzelnen Bäumen zugeordnet werden können, deren Abmessung fernerkundlich erfasst worden ist. Diese neu erzeugten Umweltinformationen einzelner Bäume können damit verbundene urbane Ökosystemdienstleistungen präzise aktualisieren. Zum Beispiel haben so Unsicherheiten in der Schätzung zur Kohlenstoffspeicherung städtischer Wälder reduziert werden können. Es ist zudem von Vorteil gewesen, den gegenwärtigen Mangel an räumlich expliziten dreidimensionalen Informationen über Stadtwälder anzusprechen. Allerdings ist die Rolle städtischen Wälder, das Treibhausgas CO2 langfristig auszugleichen, immer noch wenig untersucht. Gerade der Mangel an präzisen, konsistenten und aktuellen Details führt zu großen Unsicherheiten im Rahmen von Lebenszyklus-Analysen. Auf Grund des aktuellen Fortschritts in hochauflösender Fernerkundung könnten diese Unsicherheiten reduziert werden. Dazu werden Möglichkeiten ausgiebig kritisch bewertet und anhand einer Lebenszyklus-Analyse am Beispiel Berlin andiskutiert, inwieweit sie präzisere langfristige Prognosen zum Stadtwald als Kohlenstoffspeicher liefern. / This work shows recent options for implementing high resolution remote sensing in assessing urban trees in Berlin, Germany. State-of-the-art methodological approaches like machine learning and individual tree detection proved to be highly advantageous for analyzing details of urban ecosystem services within a heterogeneous urban environment. Recent remote sensing of high temporal resolution offers new options for more precisely addressing urban forest dynamics. This successfully shows that tree species could be identified from seasonal changes of remotely sensed imagery, though this has not yet been applied across cities. Furthermore, these tree species results could be combined with remotely sensed individual tree dimensions. This newly generated data can be suggested to update spatially explicit information on related urban ecosystem services. For example, this could reduce the uncertainties of such estimates as urban forest carbon storage, and also address the present lack of spatially explicit three-dimensional information on urban forests. However, few studies have considered the local scale of urban forests to effectively evaluate their potential long-term carbon offset. The lack of precise, consistent and up-to-date forest details is challenging within the scope of life cycle assessments. This can cause high uncertainties in urban forest carbon offset. Although, recent progress in high resolution remote sensing is promising to reduce these uncertainties. For this purpose, remote sensing options are extensively reviewed and briefly discussed using an example of life cycle assessment for Berlin, which allow more precise long-term prognoses of urban forest carbon offset.

Urbanization has destroyed and fragmented previously large areas of natural habitat. Small remnants that still exist in numerous cities will be unable to sustain many viable wild plant populations if they do not expand into the surrounding urban matrix. Residential gardens surrounding such remnants, and which form a significant component of urban green space in many cities, could play a role in redressing this problem. Riccarton Bush, a 7.8 hectare forest remnant, and its surrounding suburban residential area, in Christchurch, New Zealand, is a good example. Over 125 years the reported number of native vascular plants in the bush has declined by a third. My study was an attempt to understand: 1) the ecological, social and cultural factors influencing the dispersal and regeneration of 12 native bird-dispersed woody species from Riccarton Bush, into surrounding residential properties; and 2) the potential role residential properties could play in the future of the bush. To examine these diverse factors I adopted an interdisciplinary research approach combining methodologies, concepts and theories from ecology and the social sciences. In a broader context my work was an attempt to demonstrate how urban ecology can further develop and strengthen by adopting and integrating new methodologies, theories and concepts. The ecological component involved recording individuals of the study species found on 90 randomly selected properties within a 1.4 km radius of the bush. Soil samples were also collected from 31 of those properties and placed in a glasshouse and the study species that germinated were recorded. Results showed some species, particularly kahikatea (Dacrycarpus dacrydioides), the most abundant species in the bush, are being dispersed and establishing on properties predominantly within 250 m of the forest margin. These juveniles are not reaching maturity as most gardeners tend to remove all non-planted woody species. Qualitative interviews with 16 residents and a quantitative survey of the residents of 85 of the properties provided insights into the social context which these natural processes were operating. Using notions of place and performance I argue that gardens are continuously created and recreated by humans and non-humans. Residents attempt to create and maintain a garden that fulfils their individual and familial needs and desires (e.g., aesthetics, leisure and privacy), and public responsibilities such as ensuring they have a ‘neat’ and ‘tidy’ garden. This involves selecting plants for colour, shape and the care they require, and encouraging certain performances (e.g., flowering) while controlling other undesirable plants and performances (e.g. growth, spread and shading). While people make connections between native plants, belonging and identity; the ‘scientific’ demarcation between native and exotic species often becomes obscured as the garden is co-created by people and plants. Some plants become more significant than others but usually this is attributable to their performances rather than whether they are native or exotic. Residential gardens have the potential to play a major role in the conservation of species restricted to urban remnants. My research suggests that although the potential exists for woody species restricted to Riccarton Bush to naturally regenerate in nearby gardens, this will not happen without human intervention. Plants will need to be eco-sourced and propagated to avoid detrimental impacts on the genetic health of remnant populations, and then actively planted in gardens. The success of such planting initiatives will be increased by providing residents with information about the plants that are suitable for their performative needs and desires (e.g., the size, colour, and maintenance requirements of plants) and, most importantly, control over the location of plantings. In concluding, I argue that by adopting new concepts, theories and methodologies, the productivity, creativity and relevance of urban ecology can be significantly enhanced.

Current global agricultural practices are recognized as unsustainable. The increase in overall human population as well as the global trend of rural to urban migration, partially as a result of historically and continual unsustainable agricultural practices, exacerbates the vicious cycle of poverty and hunger in developing countries. Furthermore, cities and regions in developed countries practice unsustainable food production, distribution and consumption patterns, and as a result, exceed their global ecological footprint (Rees 2009). Consequently, the world is facing a global food (FAO 2009) and water crisis (UN Sick Water 2010). Cities and Regions must learn to feed themselves to address local food insecurity as well as protect from the climate effects of increased urbanization, including the Urban Heat Island effect (UHIe) by optimizing and fully integrating the local ecosystem services of food, water and forest within a tightly woven compact urban form through the implementation of strategic urban and regional food system planning. Cities can mitigate climate change and reduce the UHIe, by implementing sustainable intensive urban agriculture approaches through policy and zoning interventions that include concepts such as intensively productive urban agriculture that includes green roofs, vertical farming and greenways as continuously productive and edible urban landscapes, referred to in this paper as continuously productive urban agriculture and forestation (CPUAF) in the private and public realm. A highly participative, adaptive systems approach is explored as the key to sustainability within an economic world order that included corporate social responsibility and social enterprise as the foundation for the integration of multiple synergies. An increasing body of evidence often links urban forestation with urban greenery initiatives, as a carbon sink to reduce UHI effects, to reduce GHG emissions and as a tool for urban beautification and place making (ISDR: 2009,109). Urban agriculture, through the production of local food is increasingly recognized as a means to reduce fossil fuel emissions by reducing transportation and production outputs, to provide a secure local food source, enhance biodiversity and educate the public regarding food source while fostering a sense of community, environmental awareness and stewardship. This thesis explores the links between intensive urban agriculture and forestation, and the relationship between climate change, and the UHI’s as an adaptation and mitigation process in global cities, implemented as a interconnected, integrated, holistic urban management approach that has a further benefit of providing food security and a sustainable and local urban food source. / Dissertation (MTRP)--University of Pretoria, 2012. / Town and Regional Planning / unrestricted