Coastal Freshwater Wetland Plant Community Response to Seasonal Drought and Flooding in Northwestern Costa Rica

Abstract

Wetlands in tropical wet-dry climates are governed by distinct and extreme seasonal hydrologic fluctuations. In this study, we investigated the plant community response to seasonal flooding and drought in Palo Verde Marsh, Costa Rica. Climate change models for the region predict reduced rainfall and a drier wet season which would likely alter seasonal hydrologic cycles and prompt vegetation change. We quantified compositional change following disturbance emphasizing seasonal differences in plant life-form abundance across life history stages via standing vegetation, seed bank, and seedling recruitment measurements. Whereas the dry season standing vegetation was dominated by emergent species, aquatic species (floating-rooted, free-floating, and submerged life forms) were more dominant during the wet season. Seed bank and seedling recruitment measurements indicated that many species are resilient with life history traits that enable them to respond rapidly to extreme hydrologic filters. Interestingly, species richness was highest during seasonal flooding. Our results highlight the importance of early-wet season rainfall for plant regeneration and community change. Our findings also indicate that a drier future would likely have a large impact upon wetland plant communities with a decrease in species richness and an increase in the abundance of drought-tolerant emergent species.

Climate and plant controls on soil organic matter in coastal wetlands

“…Drought has also been linked to mangrove die-off events in Senegal (Diop et al, 1997), shifts in marsh plant community composition in the northwestern Gulf of Mexico (Dunton et al, 2001), declines in marsh belowground production in the northern Gulf of Mexico (Stagg, Schoolmaster, Piazza, et al, 2017), and shifts in marsh biomass in the northwestern USA (Buffington et al, 2018). In tropical regions that have a long dry season (i.e., a tropical wet and dry climate), changes in the timing, intensity, and duration of the dry season can have large effects on wetland ecosystem structure and function (Barr et al, 2010;Fosberg, 1961;Malone, Starr, Staudhammer, & Ryan, 2013;Osland, González, & Richardson, 2011). In addition to a need to advance our knowledge of the effects of drought on salinity and plant productivity, our results indicate that there is a need to advance understanding of the effects of drought on soil organic matter, soil-surface elevation change, carbon storage, carbon cycling, and peat collapse.…”

Dinámica estacional de la vegetación litoral en el complejo lagunar inundable Zapatosa, Colombia

“…Similar results have also been reported by Rial (2006) for the Venezuelan Llanos. in accordance with the findings of Osland, González, and Richardson (2011), we considered that early rainfall periods at the beginning of the wet season initiate seed germination and re-sprouting of plants, therefore setting the community structure of the vegetation that will establish and persist during the following flooding phase. Aquatic and wetland plants surviving the dry season in permanently inundated areas of the lake and in lagoons also contribute to the fast re-colonization of shorelines.…”

“…Flooding phase: Persistent rainfalls, which start during March, initiate the wet season, yet water level of the CZFL only begins to raise approximately one month later when excess water of the Magdalena and Cesar Rivers start to flood the basin. Seed germination and vegetative regeneration by rhizomes or stolons of the rooted emergent plants are triggered by early-wet season rainfalls (Osland et al, 2011), leading to a fast re-growth of the mat forming vegetation. Low-lying flats and swales of the floodplain (Junk, 1986) Maltchik, de Oliveira, Rolon, and Stenert (2005) and Maltchik, Rolon, and Schott (2007) that small water-level fluctuations (~50cm) in wetlands may lead to changes in species dominance, moreover if fast clonal growing species are involved.…”

Genetic temporal dynamics in restored wetlands: A case of a predominantly clonal species, Berula erecta (Huds.) Coville

“…According to Casanova and Brock (2000) and Osland et al (2011), the seeds of most wetland plant species primarily germinate during drawdown conditions, and most post-disturbance plant recruitment occurs during the dry season. At BRO, in contrast to the other sites, two droughts occurred (the water level above the sediment was between 0 and 6 cm at most, unpublished data), the first in April and the second in July and August, during flowering and seed maturation.…”