Ecological strategies of tree species in the laurel forest of Tenerife (Canary Islands): an insight into cloud forest natural dynamics using long-term monitoring data

Abstract

In Tenerife (Canary Islands), the laurel forest is considered one of the most biodiverse ecosystems of the archipelago. This study aims at providing useful information about tree species strategies and their natural dynamics in order to improve understanding of the functioning of this ecosystem. The knowledge gained would be of great importance for laurel forest conservation, not only in the Canaries, but also in Madeira and the Azores. Our main research question is: 'Are the ecological groups of laurel forest tree species, described in earlier studies based exclusively on regeneration strategies, consistent with species functional traits, growth patterns and spatial distributions?' We used data from six 50 × 50 m permanent plots established in 1999 and re-measured in 2015, combined with information on twelve functional traits from newly produced data or extracted from previous studies. For each species we analyzed the abundance of seedlings/suckers, saplings and adults inside the permanent plots. Two ordination methods were used to assess multivariate differences in functional traits between species. Different mixed-effect models were tested to investigate effects of sites, individual tree size and competition on tree growth rates. Finally we analyzed the spatial distribution of both saplings and adults and their interaction within the six permanent plots. Our results were consistent with a classification of species into different ecological groups based on (1) their shade-tolerance: light-demanding vs. shade-tolerant species and (2) their reproductive strategies: sexual (i.e. seedlings), asexual (i.e. suckers) or both. These differences between light-demanding vs. shade-tolerant and/or seedling-producing species vs. sucker-producing species were consistently observed across the species functional traits, growth patterns and spatial distributions. Only one species, Viburnum rigidum Vent., presented singularities compared with its previously established group. Because V. rigidum is mostly an understory species, we proposed to add a third aspect to the classification scheme: understory vs. canopy species. This led to a total of six ecological groups within fourteen laurel forest tree species. Finally, this study also showed that the Tenerife laurel forest is still maturing and becoming richer in species, which outlines the importance of its preservation.