Community dynamics of stabilized dune xerophytic shrubs

Tese de doutoramento, Biologia (Ecologia), Universidade de Lisboa, Faculdade de Ciências, 2016

The overall goal of this thesis was to study the spatial and successional dynamics of plant communities at different scales. Stabilized dune xerophytic shrubs were selected since i) they are affected by severe environmental stress, and several biotic interactions are described for dune plant communities; ii) they are highly threatened habitats; and iii) a significant number of rare, endangered and endemic plant species occur in these communities. First, in the General Background, the main concepts addressed in the thesis, namely ecological community, succession, biotic interactions, functional diversity and functional traits, and ecological niche are analysed. Since these concepts have already been reviewed by a significant number of authors, our objective was to outline the framework where our work was developed rather than do a deep analysis. In the following chapters, the works where the different subjects related with the dynamics of xerophytic shrubs were addressed are presented. In Chapter 2 the main drivers acting on stabilized dune xerophytic shrubs in SW Portugal, namely Juniperus navicularis, Stauracanthus genistoides and Ulex australis communities, are analysed. Results indicate that these communities respond to edaphic site conditions, climate and human disturbance, confirming the existence of both Clementsian and Gleasonian processes. In addition, it is proposed a conceptual model of the inland dune community dynamics. In Chapter 3 the functional trait responses along the successions described in Chapter 2 are assessed. It was found that successional community changes in the studied system involve a turnover in key functional traits and imply variations in species richness and functional diversity. In Chapter 4, the effects of environmental factors and biogeographical limitations on the diversification patters of the genus Stauracanthus are studied. Finally, in Chapter 5 the successional models developed for a delimited area in Chapter 2 are evaluated to nearly all the geographic range of these communities. A significant consistence in the succession between S. genistoides and U. australis communities throughout most of the area of co-occurrence of both species was found even though the factors driving this successional gradient changed from one region to another: in Setubal and Comporta regions soil organic matter content was the main driver, while in South/South-Western region temperature seasonality and the habitat suitability of S. genistoides explained the most of the gradient. Finally, in the General Discussion, a synthesis of the major findings for the understanding of the xerophytic plant communities’ dynamics system is presented. Additionally, and aiming to improve the conservation measures of these communities, it is proposed the implementation of dynamic conservation strategies to ensure the preservation of the natural functioning of xerophytic shrub communities guaranteeing the successional pathways between them.