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Humboldt-Universität zu Berlin (2012)

Land use change and its effects on vegetation trends and fire patterns in Mediterranean rangelands

Sonnenschein, Ruth

Titre : Land use change and its effects on vegetation trends and fire patterns in Mediterranean rangelands

Auteur : Sonnenschein, Ruth

Université de soutenance : Humboldt-Universität zu Berlin

Grade : Doctor Rerum Naturalium 2012

Résumé
Drylands cover about 41% of the earth’s surface, sustain the livelihoods of 2 billion people, harbor unique biodiversity and provide important ecosystem services, but land use and climate change exert considerable pressure on these ecosystems. However, pattern and drivers of land use change are weakly understood. Remote sensing can monitor these changes for large areas but methods to detect both gradual and abrupt events like fires are missing. The main objectives of this thesis were to develop remote sensing based methods to better quantify the impact of land use change on fire-prone Mediterranean ecosystems, and to apply these methods to better understand the influence of different land use processes on fire regimes. The island of Crete (Greece) served as study region where diverging land use transformation are extensive, fires are frequent and environmental gradients are large. First, the trade-off between different vegetation estimates when using Landsat-based trend analyses was quantified. The results suggested that simple vegetation estimates perform equally well and thus, allow for effective mapping of large areas. Second, a trajectory change detection approach was applied to separate gradual changes from abrupt events and to answer the question how land use systems and fire regimes have affected Crete’s rangelands. Statistical modeling was then used to quantify the relative importance of land use processes in driving the fire regime. The results show that vegetation changes resulted in complex pattern of gradual changes and fires likewise. The fire regime appeared to be mainly driven by changing grazing systems. Fires were frequent in foothills whereas mountains showed increasing vegetation as a result of land abandonment. The statistical modeling confirmed that land extensification and climate are the primary drivers of fire regimes on Crete. The results suggest that the former fuellimited fire regime will likely shift towards a drought-driven fire regime.

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Page publiée le 30 juin 2013, mise à jour le 28 décembre 2018