On the rocks: Biogeography and floristic identity of rocky ecosystems in eastern South America

Abstract

The geodiversity of rocky ecosystems includes diverse plant communities with specific names, but their continental-scale floristic identity and the knowledge on the role of macroclimate remain patchy. Here, we assessed the identity of plant communities in eastern Brazil across multiple types of rocky landscapes and evaluated the relative importance of climatic variables in constraining floristic differentiation. We provided lists of diagnostic species and an assessment of the conservation status of the identified floristic groups. We compiled a data set of 151 sites (4498 species) from rocky ecosystems, including campos rupestres, campos de altitude, granitic-gneiss lowland inselbergs, and limestone outcrops. We used unsupervised clustering analysis followed by ANOSIM to assess floristic groups among sites. We performed a random forest variable selection to test whether the identified floristic groups occupy distinct climatic spaces. Six groups (lithobiomes) segregated floristically according to lithology and climate. Alongside campos de altitude and limestone outcrops, inselbergs were divided according to the biome in which they occur (Atlantic Forest or Caatinga), and campos rupestres were largely segregated according to their lithological matrix (ironstone or quartzitic). Plant communities of Caatinga inselbergs were more similar to limestone outcrops, while Atlantic Forest inselbergs communities resembled campos de altitude. The composition of plant communities on outcrops seems to be largely constrained by lithology, but climatic factors are also meaningful for sites with similar lithology. The current network of protected areas does not cover these unique ecosystems and their floristic heterogeneity, with Caatinga inselbergs and limestone outcrops being the least protected.

Key words： campos de altitude; campos rupestres; geodiversity; inselberg; ironstone; karst; limestone outcrops; lithophytes; rupicolous plant communities