Unprecedented herbivory threatens rear‐edge populations of Betula in southwestern Eurasia
Mediterranean rear‐edge populations of Betula, located at the southwestern Eurasian margin of the distribution range, represent unique reservoirs of genetic diversity. However, increasing densities of wild ungulates, enhanced dryness, and wildfires threaten their future persistence. A historical per...
| Published in: | Ecology |
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| Main Authors: | , , , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Ecological Society of America
2019
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| Subjects: | |
| Online Access: | https://boris.unibe.ch/132578/1/2019_Ecology.pdf https://boris.unibe.ch/132578/8/2019_Ecology_100_e02833.pdf https://boris.unibe.ch/132578/ |
| Summary: | Mediterranean rear‐edge populations of Betula, located at the southwestern Eurasian margin of the distribution range, represent unique reservoirs of genetic diversity. However, increasing densities of wild ungulates, enhanced dryness, and wildfires threaten their future persistence. A historical perspective on the past responses of these relict populations to changing herbivory, fire occurrence and climatic conditions may contribute to assessing their future responses under comparable scenarios. We have reconstructed vegetation and disturbance (grazing, fire) history in the Cabañeros National Park (central‐southern Spain) using the paleoecological records of two small mires. We particularly focused on the historical range of variation in disturbance regimes, and the dynamics of rear‐edge Betula populations and herbivore densities. Changes in water availability, probably related to the North Atlantic Oscillation (NAO) index, and land‐use history have played a crucial role in vegetation shifts. Our data suggest that heathlands (mainly Erica arborea and E. scoparia) and Quercus woodlands dominated during dry phases while Sphagnum bogs and Betula stands expanded during wet periods. Betula populations survived past moderately dry periods but were unable to cope with enhanced land‐use, particularly increasing livestock raising since ~ 1100‐900 cal. BP (850‐1050 CE), and eventually underwent local extinction. High herbivore densities not only contributed to the Betula demise but also caused the retreat of Sphagnum bogs. Ungulate densities further rose at ~ 200‐100 cal. BP (1750‐1850 CE) associated with the historically documented intensification of land‐use around the Ecclesiastical Confiscation. However, herbivory reached truly unprecedented values only during the last decades, following rural depopulation and subsequent promotion of big game hunting. For the first time in temperate and Mediterranean Europe, we have used the abundances of fossil dung fungal spores to assess quantitatively that current high herbivore ... |
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