Old-field succession of taxonomic and functional diversity in the iconic humid evergreen laurel forest of the Canary Islands

Socio-economic changes on islands have led to wide-spread land abandonment in low productive and low accessible areas as a result of a transition from agriculture to tourism, leaving a starting point for successional processes (old-field succession) potentially relevant for nature conservation. The humid, evergreen laurel forest of Macaronesia is iconic for its tree species diversity and endemism and plays an important role in regulating ecosystem services on these islands. For these reasons it is of high conservational value.

Our study analyses the successional dynamics and trajectories of taxonomic and functional diversity, biogeographic origin, growth forms and individual traits in a ~60 year chronosequence using relevés of all vascular plant species and trait databases in the laurel forest of La Palma, Canary Islands. As a reference we included relevés in the nearly pristine old-growth forest of Los Tilos in a nature reserve area.

We find that both species composition and functional composition follow a clear temporal trajectory towards old-growth forests. While taxonomic and functional diversity as well as non-native species decrease, endemism increases with time. Woody species, climbers and maximum growth height increase with time, while forbs decrease.

Unassisted old-field succession in the laurel forest is taxonomically as well as functionally on a trajectory towards old-growth forests, whereas non-native species only play a subordinate role during later successional stages. This offers accessible pathways for natural regeneration and ultimately nature conservation in this important system on the Canary Islands and Macaronesia and sheds new insights into the dynamics of succession in this system.