1,721,038 research outputs found
Fine-scale benthic biodiversity patterns inferred from image processing
No full textAbstract not availableJason E. Tanner, Camille Mellin, Lael Parrott, Corey J.A. Bradsha
Modelling the effect of fire, insect, and logging disturbances on climate and vegetation across various spatial and temporal scales
No full textFire, insect, and logging disturbances affect ecosystems worldwide and often lead to spectacular local changes in vegetation characteristics, as well as biogeochemical and biogeophysical fluxes. Despite a growing body of empirical and modelling studies, many key questions remain unanswered, and even unasked, about the effect of these disturbances on climate and vegetation. In this thesis, I explored some of these questions at different spatial and temporal scales, and mostly from a modelling perspective. In Chapter 2, I simulated various future (2015–2300) fire regimes in the University of Victoria Earth System Climate Model and estimated the resulting impacts on global carbon stocks and surface temperature, with and without the effect of the main fire-related non-CO2 emissions. This global-scale study in a fully coupled climate–carbon model allowed me to differentiate the net from the gross carbon emissions in response to changes in fire frequency, a crucial distinction that is sometimes overlooked in the literature, and to also highlight the possibly dominant effect of fire-emitted aerosols on the net climatic impact from non-deforestation fires. In Chapter 3, I investigated, with a new model developed for this purpose, how different approaches to represent fire and logging in climate models affected the simulation of albedo over boreal forests. This methodological study showed that the simplest approach, which was the one applied in Chapter 2, noticeably underestimates the long-term fire-induced albedo increase over boreal forests, but that substantial improvements can be obtained without undue additional computing requirements. Having focussed on stand-clearing disturbances in the previous two chapters, I looked at the role of insect outbreaks in Chapter 4. I assessed, with a modified version of the Integrated BIosphere Simulator dynamic vegetation–land surface model, the long-term impacts (up to >1,000 years) from recurrent mountain pine beetle (MPB) outbreaks at three different locations in British Columbia on different vegetation- and climate-related variables, namely merchantable biomass, ecosystem carbon, albedo, and net radiative forcing. This study emphasized the major role of the non-target vegetation in MPB-induced changes and illustrated various non-linearities in the responses to recurrent outbreaks. In Chapter 5, I finally performed a critical review of the literature relevant to the climate–forest–disturbances triad in Canada. More precisely, I proposed five principles relevant for the management of Canadian forests in the context of carbon cycling, climate regulation, and disturbances, and then applied these principles to address four questions of current interest. One conclusion from this study was the need to perform >100-year analyses of disturbances in Canadian forests, as I did in Chapter 4. Overall, suggesting that fire or insect disturbances seem to generally have less impact per event as they become more frequent (i.e., sub-linear scaling) is the most important scholarly contribution from this thesis. Another major outcome consists of identifying sources of uncertainty that prevent sound conclusions on the net warming or cooling impact from natural disturbances, namely the strength of cloud-mediated aerosol effects in the case of fire and the response from the non-target vegetation in the case of MPB outbreaks. Other contributions to knowledge include the possible influence of fire-emitted aerosols on land–atmosphere and ocean–atmosphere carbon exchanges, the impact of dead standing trees on the post-disturbance carbon response due to their interactions with energy and water exchanges, and the idea that the spatial distribution of trees killed by insects can modulate the resulting biogeophysical and biogeochemical consequences. Finally, this thesis illustrates that fire, insect, and logging disturbances lead to both large and small impacts, depending upon the specific scale and element considered.Les perturbations causées par les feux, les insectes et les coupes forestières affectent de manière souvent spectaculaire la végétation locale, ainsi que les échanges biogéochimiques et biogéophysiques. Malgré l’augmentation des études empiriques et de modélisation abordant l’effet de ces perturbations sur le climat et la végétation, plusieurs questions centrales sur le sujet demeurent sans réponse ou n’ont pas encore été posées. Dans cette thèse, j’ai exploré certaines de ces questions à différentes échelles spatiotemporelles. Dans le Chapitre 2, j’ai simulé divers futurs (2015–2300) régimes des feux dans le University of Victoria Earth System Climate Model afin d’en estimer les impacts globaux sur les réservoirs de carbone et la température de surface, avec et sans l’effet des principales émissions causées par les feux en plus du CO2. Cette étude m’a permis de différencier les émissions nettes des émissions brutes de carbone en réponse à des changements dans la fréquence des feux, une distinction cruciale qui est parfois négligée dans la littérature, ainsi que de mettre en évidence l’effet possiblement dominant des aérosols émis par les feux. Dans le Chapitre 3, j’ai examiné, à l’aide d’un modèle développé à cet effet, comment différentes approches visant la représentation des feux et des coupes forestières dans les modèles climatiques affectaient la simulation de l’albédo des forêts boréales. Cette étude a montré que l’approche la plus simple sous-estime notablement l’augmentation à long terme de l’albédo résultant des feux dans les forêts boréales, mais que des améliorations substantielles peuvent être obtenues sans conséquences déraisonnables sur le temps de calcul. Dans le Chapitre 4, j’ai évalué, à l’aide d’une version modifiée du modèle de végétation dynamique et de surface terrestre Integrated BIosphere Simulator, les impacts à long terme (jusqu’à >1000 ans) d'épidémies récurrentes de dendroctone du pin ponderosa (DPP) à trois locations différentes en Colombie-Britannique sur diverses variables reliées à la végétation et au climat. Cette étude a mis l’accent sur le rôle majeur que joue la végétation épargnée dans les changements causés par le DPP et a illustré plusieurs non-linéarités dans les réponses aux épidémies récurrentes. Dans le Chapitre 5, j’ai finalement réalisé une revue critique de la littérature pertinente concernant la triade climat–forêt–perturbations au Canada. Plus précisément, j’ai proposé cinq principes pour la gestion des forêts canadiennes en tenant compte du cycle du carbone, de la régulation du climat et des perturbations, en plus d’aborder quatre questions d’actualité en utilisant ces principes. Dans l’ensemble, l’idée selon laquelle les perturbations par les feux ou les insectes semblent en général avoir moins d’impact individuel lorsqu’elles deviennent plus fréquentes s’avère la contribution académique la plus importante de la présente thèse. Un autre résultat majeur provient de l’identification de sources d’incertitude qui empêchent d’obtenir des conclusions solides sur l’impact net (réchauffement ou refroidissement) des perturbations naturelles, soit les effets aérosols–nuages dans le cas des feux et la réponse de la végétation épargnée dans le cas d’épidémies de DPP. D’autres contributions scientifiques incluent l’influence possible des aérosols émis par les feux sur les échanges de carbone terre–atmosphère et océan–atmosphère, l’impact des arbres morts encore debout sur les flux de carbone post-perturbation étant donné les interactions de ces arbres avec les échanges d’énergie et d’eau, ainsi que l’idée selon laquelle la distribution spatiale des arbres tués par les insectes peut moduler les conséquences biogéophysiques et biogéochimiques résultant de cette mortalité. Finalement, cette thèse illustre le fait que les perturbations par les feux, les insectes et les coupes forestières ont des impacts grands et petits tout à la fois, selon l’échelle et l’élément qui sont considérés
The modelling spiral for solving ‘wicked’ environmental problems: guidance for stakeholder involvement and collaborative model development
No full textHybrid modelling of complex ecological systems for decision support: Recent successes and future perspectives
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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