Live fast and die young: The aquatic macrophyte dynamics in a temporary pool in the Brazilian semiarid region

We sampled the community composition, dynamics, and life- and growth-forms of plant species in a 4.57 ha temporary pool (4°11′13.04″S; 39°06′11.75″W, 200–300 m a.s.l.) in semiarid region of Northeastern Brazil for 13 weeks. We recorded 30 species, five of them being from the surrounding thorny woodland vegetation which appeared only as seedlings in the first sampling round. Only a small number of species were present in each sampling round, indicating that few species could co-exist. Emergent therophytes and cryptophytes predominated among the aquatic species because they were able to withstand the contrasting wet and dry phases, however temporary pools in other regions of the world were found to have different biological spectra which were responsive to climate variables according to Raunkiaerian phytoclimates. In this study, species quickly substituted one another over time, in a replacement gradient in which five groups were distinguished: (1) non-aquatics from the surrounding vegetation (e.g. Croton sp., Angelonia sp., Senna sp.); (2) early species that appeared only in the initial expansion period (e.g. Heliotropium elongatum, Callisia filliformis, Panicum dichotomiflorum); (3) late species that appeared in the contraction period (e.g. Bacopa aquatica, Eleocharis barrosii, Apalanthe granatensis); (4) sporadic species (e.g. Thalia geniculata, Eleocharis interstincta, Utricularia foliosa); and (5) persistent species that were present from the beginning of the expansion period until the end of the contraction period (e.g. Eleocharis mutata, Neptunia oleracea, Nympahea lasyophylla). Only E. mutata and N. lasiophylla persisted as dominant populations throughout the wet phase. The complementary life growth form of these two species probably favored their co-existence.

► Aquatic plant communities change very quickly during the rainy season in a temporary pool.
► These changes are characterized by: species that cannot tolerate inundation, species that can tolerate flooding for short periods of time, early species, late species, and sporadic species.
► Emergent therophytes and cryptophytes were predominant in the community.
► Temporary pools have different biological spectra responding to climatic variables in accordance with Raunkiaerian phytoclimates.
► Surviving the harsh conditions of the dry phase could be more important for determining the community composition of temporary pools than surviving the wet phase.