Fir expansion not controlled by moderate densities of large herbivores: a Mediterranean mountain grassland conservation issue
Whilst livestock has maintained grasslands over centuries in south European mountains, current ungulate densities are insufficient to control tree and forest expansion effectively. The present results based on fir population dynamics and radial/height growth raise questions about the sustainable management of new forests that are former mountain grasslands. This empirical case study contributes to debate about methods for long-term management of grasslands in Mediterranean mountains.
Forest expansion following the cessation of grazing is a threat to biodiversity in mountain grasslands that are components of Mediterranean cultural landscapes.
We hypothesised that ungulates could mitigate tree recruitment, thus conserving mountain grasslands. We tested the efficiency of grazing and browsing by domestic and wild ungulates (sheep, roe and red deer) at inhibiting silver fir (Abies alba Mill.) encroachment in a conservation area, one of the main browsed trees.
The fir trees’ age structure was analysed by dendrochronology, and the individual growth patterns and scars were recorded in their tree-ring series.
Fir density has increased since the 1960s, simultaneously with the increase in ungulate populations. The scar occurrences only appeared during the 1970s. Most scars were observed on seedlings and small saplings. The impacts of ungulates are observed on the radial and height growth of trees, mostly on trees < 100 cm, but it did not however result in controlling the recruitment of fir.
The hypothesis that a moderate density of ungulates might inhibit tree encroachment is therefore rejected, even in the case of a highly palatable species such as silver fir. Ungulates, solely, would not be an appropriate policy for grassland conservation in Mediterranean mountains.
KeywordsConservation area Height growth Radial growth Age structure Grazing Browsing Ungulates Herbivory Tree-ungulate interactions
We are grateful to the Canjuers military camp for the access to its restricted territory. Data on roe deer and red deer were provided by Daniel Siméon (Fédération Départementale des Chasseurs, Alpes-Maritimes) and those on sheep grazing by Thierry Faure (Office National des Forêts, Canjuers Military Camp). We particularly thank Isabel Figueiral, Sarah Ivorra and André Thomas for their help during the field work or laboratory assistance. Finally, we warmly thank Dr. Laurent Bergès (Handling Editor) and two reviewers for their helpful suggestions for improving the manuscript and illustrations. The English text was edited by SEES-Editing Ltd.
Financial support was provided by the Centre National de la Recherche Scientifique (CNRS, France) and by the EPHE (to CC), and by a PhD grant from the CNRS (to SC).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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