Effects of deer browsing in a Mediterranean coastal juniper stand

Abstract

I studied the effects of browsing by red deer (Cervus elaphus) on the growth, composition, structure and succession of a stand of the dioecious maritime juniper (Juniperus macrocarpa) in the moving dunes of the Dona National Park (SW Spain). A deer exclosure experiment was initiated in 1999 and plant growth was monitored for 22 months. In 2007, height and sex were determined in 100 juniper plants inside the exclosure and 100 in the adjacent open area. Finally, in 2010 woody plant composition, structure and diversity was measured in both treatments and compared with previous data. Junipers showed continuous growth throughout the year, with the highest growth being recorded in the rainiest part of the year (autumn, winter or spring). Browsing took place mainly in autumn and winter, but extended to spring and summer. Junipers inside the exclosure showed higher growth when compared to junipers in the open area except for the summer, when herbivory decreased and unfenced junipers showed a compensatory response. In 2007, there were more female plants in the exclosure (35%) than in the open area (3%), while the number of unsexable individuals was larger in the open area (74%) than inside the exclosure (38%), suggesting a selective browsing on female individuals by red deer. Plant species richness did not change during the study period, but the community previously dominated by Helichrysum picardii became dominated by maritime juniper, increasing in cover from less than 7% to 46%. These results supported the hypothesis that browsing by red deer led to a state of arrested succession, maintaining small plants and open zones. Control of red deer density or access may be an option for improving maritime juniper reproduction and for releasing maritime juniper woodlands from arrested succession.