Initial constraints in seedling dynamics of Juniperus macrocarpa Sm.

The micro-forests dominated by Juniperus macrocarpa inhabiting coastal dunes in the Mediterranean Basin are European priority habitats. Their conservation is hindered by both anthropic and natural causes, although the regeneration problems for J. macrocarpa are still poorly understood. In this study, several factors influencing emergence and mortality of J. macrocarpa seedlings were investigated. For this purpose, permanent plots were placed in coastal dunes of Sardinia (Italy) and periodically monitored to record seedling parameters (emergence, survival and growth), as well as several biotic and abiotic variables (solar radiation, tree cover, herbaceous plus scrub cover, number of female cones on the soil and number of herbivory traces). Linear mixed models were fitted to test the effects of several types of explanatory variables on seedling dynamics. A total of 536 seedlings were marked, most of which emerged in winter. The microhabitat was the most important factor in models explaining emergence, with the number of emerged seedlings decreasing with solar radiation. Survival was very low, reaching the highest mortality percentage in the first summer. Herbivory and location in open interspaces had significant negative effects on seedling survival. In conclusion, the recruitment of J. macrocarpa is highly limited in the initial life cycle phases, with microhabitat and herbivory constraints influencing seedling dynamics. The identification of critical stages in the recruitment process of J. macrocarpa, together with factors influencing them, suggests some implication for management as well the hypotheses for future studies about conservation and recovery of the J. macrocarpa habitat.