Cristina Branquinho
Centro de Biologia Ambiental
Faculdade de Ciências da Universidade de Lisboa

Global change is expected to cause several impacts at the global scale. Range shifts and phenological changes in species and systems have already been observed worldwide and attributed in part or totally to climate change, nitrogen pollution and/or loss of biodiversity. Ecosystems have critical thresholds, the so-called tipping points, at which the system changes abruptly to a contrasting alternative state. Once that threshold is crossed, a switch back to the initial state of the system may be impossible, leading to a degradation of biodiversity, a loss of ecosystem services and human well-being. These abrupt and irreversible transitions are expected to increase due to climate change and to the depletion of natural resources, but its forecast is still extremely difficult. Some authors suggest that is possible to find early‐warning signals that may indicate if a critical threshold is approaching. Transitions to arid ecosystems are one of this sudden discontinuous changes from a vegetated to a desert state as a result of human pressure and climate change. Desertification and Land Degradation (DLD) affects a large area of the worlds land. The UN convention has recognized that although great deals of data on land resources are available, global and universal indicators are still needed. Ecosystem functioning is extremely complex and thus monitoring the effects of environmental change factors in ecosystems in an integrative perspective can make use of ecological indicators. Vegetation functional traits are measurable characteristics that are functional related to some environmental factor that influence organisms’ performance and ultimately are responsible for determining which species survive and which do not under an environmental factor. By relying on the use of vegetation functional traits, rather than using a blind perspective such as total species richness, we will be able to focus on ecosystem process. We will use vegetation and lichen functional groups (that have traits such as tolerance to drought and water use efficiency) as potential ecological indicators of DLD. For that we defined a DLD gradient based on climatic data and restricted the location of sampling points for other confounding factors such as altitude, type of soil, land-use, slope, etc, by fixing them. Both lichen and vegetation functional groups were assessed along this desertification gradient. The results showed that both lichen functional diversity and annual plants functional diversity can be used as early warning indicators of DLD in the south of Portugal. The more universal use of these indicators will be further discussed.

Acknowledgments to DesertWarning (PTDC/AAC-CLI/104913/2008)