Validation et comparaison de divers indicateurs des changements à long terme dans les écosystèmes méditerranéens arides: Application au suivi de la désertification dans le Sud Tunisien.
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UNCCD Library
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Validation and comparison of various indicators of long term changes in arid Mediterranean ecosystems: Application for desertification monitoring in southern Tunisia. ( These Pour obtenir le grade de: Docteur de l’université de droit, d’économie et des sciences d’Aix-Marseille Discipline: Ecologie)
As many rangelands surrounding the Mediterranean Basin, the Tunisian arid zone, characterised by
scattered steppic vegetation, is commonly viewed as degraded landscapes. In Arid Mediterranean regions,
vegetation dynamics is indeed affected by human and non-human disturbances and stresses which induce
desertification processes.
In this context, the objectives of this research were to identify and validate various indicators of long
term changes to provide information useful for the management of arid lands. The study is focussed on the
understanding of 1) the structure and functioning of ecosystems and 2) the changes that occur in space and time in response to degradation. The ecological indicators allow us to describe different organisation levels from species to the ecosystem and the landscape. The diachronic comparison of vegetation maps of 1975 and 2000 allow a more complete diagnosis about the evolution of ecosystems and landscapes over the last three decades.
Some of these ecological indicators have been also linked with remote sensing data acquisition and processing strategies.
The results indicate that degradation has involved the reduction of perennial plant cover, the homogeneisation of the flora and a decrease in grazing value of these rangelands since the 1970s. However,
degradation seems to have slown down since the end of 80s as a result of actions to combat desertification. An evolution towards recovery has indeed been observed since this date. Remote sensing, particularly unmixing, provides a useful tool to quantify vegetation and soil changes. This work constitutes a first step to assess degradation or restoration using indicator data collected on the ground through ecological studies linked with remote sensing data ; a second step will need to take into account socio-economic systems.
As many rangelands surrounding the Mediterranean Basin, the Tunisian arid zone, characterised by
scattered steppic vegetation, is commonly viewed as degraded landscapes. In Arid Mediterranean regions,
vegetation dynamics is indeed affected by human and non-human disturbances and stresses which induce
desertification processes.
In this context, the objectives of this research were to identify and validate various indicators of long
term changes to provide information useful for the management of arid lands. The study is focussed on the
understanding of 1) the structure and functioning of ecosystems and 2) the changes that occur in space and time in response to degradation. The ecological indicators allow us to describe different organisation levels from species to the ecosystem and the landscape. The diachronic comparison of vegetation maps of 1975 and 2000 allow a more complete diagnosis about the evolution of ecosystems and landscapes over the last three decades.
Some of these ecological indicators have been also linked with remote sensing data acquisition and processing strategies.
The results indicate that degradation has involved the reduction of perennial plant cover, the homogeneisation of the flora and a decrease in grazing value of these rangelands since the 1970s. However,
degradation seems to have slown down since the end of 80s as a result of actions to combat desertification. An evolution towards recovery has indeed been observed since this date. Remote sensing, particularly unmixing, provides a useful tool to quantify vegetation and soil changes. This work constitutes a first step to assess degradation or restoration using indicator data collected on the ground through ecological studies linked with remote sensing data ; a second step will need to take into account socio-economic systems.
Geographical Keywords
Tunisia
Keywords
desertification
ecological indicators
remote sensing
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