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Universität zu Köln (2014)

Advancing Functional Understanding of Primary Production in Drylands : Insights from a Data-Integration Approach

Ruppert, Jan Christian

Titre : Advancing Functional Understanding of Primary Production in Drylands : Insights from a Data-Integration Approach

Auteur : Ruppert, Jan Christian

Université de soutenance : Universität zu Köln

Grade : PhD thesis 2014

Résumé
Dryland ecosystems are highly vulnerable and degradation-prone regions, especially under the premises of global change. Since drylands are preponderantly used as rangelands for livestock production, reliable provision of natural resources and basic ecosystem services, such as forage, are indispensable for local livelihoods. Even though climate projections for drylands still exhibit considerable variation and uncertainty across scenarios and regions, there is a general trend that most dryland regions are facing unbeneficial changes. In particular, climatic aridity and variability are projected to increase even above the already high level of today. Simultaneously, population growth will further increase the demand for ecosystem services from drylands, with negative feedbacks on ecosystem functioning. Given the high natural variability in drylands, as well as future projections, the assessment of drylands’ current and future provision of ecosystem services is challenging, yet essential. The most common estimate for a major ecosystem service of dryland ecosystems (i.e. forage) is aboveground net primary production (ANPP). This cumulative dissertation aimed at advancing our understanding of dryland ecosystems’ functioning and ecosystem service provision, taking a global perspective. Particularly, data integration and standardization techniques were used to derive new insights from available data on drylands’ primary production. With this innovative approach, it could be shown that dryland primary production is mainly driven by precipitation and grazing, not only locally but also on a global scale (Chapter 2.1). Another important outcome was that effects of grazing and rainfall are not merely additive, but could mask each other (Chapter 2.1) or interact in complex ways (Chapter 2.3). Similarly, drought severity may influence primary production either linearly or non-linearly, depending on vegetation characteristics (Chapter 2.3). These findings underline the complex dynamics of dryland ecosystems. Besides these general findings, the established methodological toolbox as well as the assembled global database of dryland primary production are among the main merits of this dissertation. The combination of a large global database, the normalization of ANPP and precipitation data (Chapter 2.2), and the collection of additional site- or study-based information allowed the assessment of ecosystem functioning and stability on a global scale, which thus far could only be done on a theoretical or anecdotal basis.

Mots clés : Drylands, Primary Production, Aboveground Net primary Production, ANPP, Meta-Analysis

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Page publiée le 20 octobre 2014, mise à jour le 8 janvier 2019