Seedling bank demography over 11 years in an island laurel forest, Tenerife, Canary Islands

Abstract

Confined to the humid cloud belt of the Macaronesian Islands the Laurel-forests are sensitive to climate changes. Intense natural disturbances are rare and regeneration includes asexual regeneration and dominance of shade intolerant species in the seedling bank. Long-term monitoring of the seedling bank showed that even under these relatively stable conditions high variations occurred. Studies point out to a downward shift of the trade winds cloud belt that confined laurel cloud forests. Only long-term studies can detect the effects of rare extreme events or the influence of slow processes on seedling dynamics. In nine 10 × 10 m plots (six in windward and three in leeward) we monitored the seedling bank monthly from 2000 to 2003 and recount it in 2005 and 2011. Our aim was to estimate seedling dynamics in a Laurel forest. We hypothesized that this forest seedling bank is relatively stable over time. Under present mild temperate climate, we hypothesized that this forest seedling bank is relatively stable over time; seedling recruitment will be positively related to rainfall; sprouting-species will be poorly represented in the seedling bank and growth rate will be higher than observed in other forests. Composition and abundance in seedling bank were stable across 2000–2003. The fluctuation in density, recruitment and mortality for Laurus novocanariensis was determinant for seedling community dynamic, and composition and abundance in seedling bank were stable across first three years and relative seeding growth rate is higher than observed in another subtropical wet montane forests. There was no significant relationship between mortality and recruitment and precipitation. However, in the 2011 count, an increase in density for all species. Except for a hot year in 2010 and a humid one in 2009 for the Canary Islands, there was no record of exceptional weather events or large-scale disturbance episodes in the previous eight years, and these are unlikely to explain the observed increase. Species with seedling banks were more abundant. Nonetheless, few seedlings survive more than two years. We emphasise the importance of long-term studies with fine-scale disturbance monitoring for understanding the dynamic processes of this unique forest.