A study led by the Forest Science Centre of Catalonia (CTFC), in collaboration with CREAF, enables to assess drought stress for Catalan tree species at regional scale by coupling forest inventory data with mathematical models. This will make it possible to anticipate and mitigate drought effects, promoting the health of our forests


Drought episode in a Mediterranean forest. Photo: CTFC

When trees need more water than the amount available for a certain period of time, they suffer water stress or drought stress. Having the ability to anticipate this phenomenon at regional scale is the aim of the study led by Miquel de Caceres, a CEMFOR group researcher (Center for Mediterranean Forest Research) from CTFC and associated to CREAF. Using soil and vegetation data from Spanish forest inventories, they have developed and validated a mathematical model in order to obtain reliable predictions of soil moisture changes and drought stress over large areas.

The model is based on the daily balance between processes providing water to the ground and those extracting it, and requires detailed information about vegetation and soil characteristics. With this information, the model is able to simulate plant species competition for local water resources, since each of them has different extractive capacity and a different strategy to cope with drought.

The study focuses on drought stress between 1990 and 2010 in forests of Catalonia, a region with 60% of its area covered by forests and shrublands. Using data from Spanish forest inventories, the researchers of this study were able to characterize spatial and temporal variation in leave area and root distribution, both drought stress key factors.

Drought is more affected by forest growth than by weather conditions

Predictions made by the model show how changes in vegetation structure may play a key role. According to De Caceres, “increased drought stress observed for many species between 1990 and 2010 is given more by forest growth than by weather conditions,” adding “this growth is the result of rural abandonment and the reduction forest management activities”.

Since the mid-twentieth century, forest cover in northwest of the Mediterranean basin is increasing by the progressive abandonment of rural areas. Therefore, it is recommended to consider forest structure when assessing drought stress patterns, either in specific localities or over large geographic areas.

Findings will enable to anticipate drought effects by means of regional strategies

These models, combined with meteorological data, enable to anticipate the place, the time and the tree species affected by drought, identifying highly vulnerable areas to its impacts. In addition, they also enable to obtaining assessments at regional level, allowing the design of strategies based on adaptation and mitigation of drought impacts, which are usually designed and implemented at these scales. Therefore, they can be a useful complement to monitoring programs of drought impacts, such as the one already existing in Catalonia.

Authors also warn further efforts are required to calibrate mortality processes related to drought events in order to predict in more detail the impact of drought stress on forests.

More information:

De Cáceres M., Martínez-Vilalta J., Coll L.,Llorens P., Casals P., Poyatos., Pausas J. G., Brotons L. (2015) Coupling a water balance model with forest inventory data to predict drought stress: the role of forest estructural changes vs. climate changes. Agricultural and Forest Meteorology. 213, 77-90