Treefall gaps and regeneration composition in the laurel forest of Anaga (Tenerife):: a matter of size?

The size of treefall gaps is an important determinant of regeneration composition in tropical and temperate forests. Preliminary studies in the laurel forest of Tenerife have shown that small gaps (< 100 m(2)) were the most numerous. However, due to this small size, no significant differences were found between regeneration in gaps and regeneration below the canopy. Because infrequent large gaps (> 100 m(2)) are present in the laurel forest, we analyzed the regeneration in these large uncommon gaps, considering their potentially important role in the dynamics of the system. Our main hypothesis is that large gaps are important disturbance to ensure the regeneration and stablishment of shade intolerant species. Only five gaps larger than 100 m(2) (ranging from 125-268 m(2)) were found in the study area. Data from a further 20 small gaps (< 100 m(2)), analysed in a previous study, was also included. Control plots were examined close to the gaps in order to determine regeneration below the closed canopy. We did not find a significant difference between regeneration density in the gaps (< 100 m(2)) and regeneration below the canopy in the control plots. Contrary to our expectations, regeneration was lower in the large gaps than under the canopy. The open canopy in the large gaps increases light intensity, and has a negative effect on the germination and growth of shade-tolerant tree species like Viburnum tinus (although non-statistically significant); however, the increase in light intensity is not sufficient to stimulate the germination of shade-intolerant tree species. The effects of treefall gaps in the dynamics of the laurel forest of Anaga should be not considered as significant in comparison to other factors such as human disturbances or infrequent disturbances (land slides or hurricanes).