Abstract
Road networks cause land degradation by mean of 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 hypotheses. 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 conduits of land degradation causing taxonomic, phylogenetic
and functional impoverishment of Caatinga vegetation.