Roads As Conduits Of Taxonomic, Functional And Phylogenetic Degradation In Caatinga Vegetation

Road networks cause disturbances that can alter the biodiversity and the functioning of the Caatinga ecosystems. We tested the hypotheses that (i) Caatinga vegetation near roads is less taxonomically, functionally and phylogenetically diverse, (ii) phylogenetically and functionally more clustered than vegetation further from roads, (iii) plant traits associated with herbivory deterrence are conserved within the phylogenetic lineages, and (iv) Caatinga vegetation near roads selects for disturbance-related traits. We sampled herbaceous and woody component of vegetation in four plots near roads and four plots further from roads to test these hypothesis. Sampled species were classified according to their resprouting capacity, nitrogen fixation, succulence/spines, urticancy/toxicity, lifeform, endozoochory, maximum height and maximum diameter, before we calculated the taxonomic, functional and phylogenetic diversity of plant communities. Species richness, taxonomic, functional and phylogenetic diversities were lower in plots close to the roads, confirming roads as sources of disturbances. The phylogenetic structure of the Caatinga vegetation near roads was clustered, indicating environmental filtering by herbivory as the main pervasive disturbance in Caatinga ecosystems, since traits related to herbivory deterrence were conserved within phylogenetic lineages and were filtered in near roads. Thus, roads should be considered degradation conduits causing taxonomic, phylogenetic and functional impoverishment of Caatinga vegetation.