Importance of structure for species richness and tree species regeneration niches in old-growth Patagonian swamp forests

Abstract

Swamp forests have high ecological value and significantly contribute to the productivity of the zones in which they are located because they provide important ecosystem benefits to society. Tepualia stipularis-dominated swamp forests, also called tepuales, are the most common but endangered swamp forests in Patagonia. In these forests, T. stipularis develops very complex structures and accumulates large amounts of biomass due to its horizontal growth habit, which leads to the formation of arboreal soils and nearly impenetrable networks of trunks. Here, we hypothesize that the complex structure of old-growth T. stipularis-dominated forests influences species abundance and the regeneration niches of the different tree species that grow in them. In addition, in these forests with restricted drainage, elevated microsites facilitate the development of regeneration. Using pre-harvesting inventory data from two silvicultural experiments in T. stipularis-dominated forests of Chiloé Island, North Patagonia, we aim to (a) characterize the structure and composition of old-growth, undisturbed stands, (b) evaluate how their structure influences the regeneration niches of the main tree species, and (c) explain the implications of these findings in the context of the traditional silvicultural management of these forests. Our results show for the first time that these forests present low anthropogenic influence (no exotic species) and contain high tree-species richness, which exceeds that of several old-growth swamp forests around the world. Also, their characteristic gap-phase dynamics and complex structures influence the regeneration niches of different coexisting tree species, which mostly germinate and establish on trunks. In this context, silvicultural methods that maintain a continuous cover should be encouraged to increase the ability of different species to reorganize and adapt to new conditions.