Inundation and Fire Shape the Structure of Riparian Forests in the Pantanal, Brazil

Abstract

Inundation and fire can affect the structure of riparian vegetation in wetlands. Our aim was to verify if there are differences in richness, abundance, basal area, composition and topographic preference of woody species in riparian forests related to the fire history, flooding duration, or the interaction between both. The study was conducted in the riparian forests of the Paraguay River some of which were burned three times between 2001 and 2011. We sampled trees with a girth of at least 5 cm at breast height in 150 5 × 10 m plots (79 burned and 71 unburned). We also measured height of the flood mark and estimated the flooding duration of each plot. We performed Generalized Linear Mixed Models to verify differences in richness, basal area, and abundance of individuals associated to interaction of fire and inundation. We used an analysis of similarity (ANOSIM) and indicator species analysis to identify differences in composition of species and the association with burned and unburned area according to different levels of inundation. Finally, we used a hierarchical set of Generalized Linear Models (GLM), the so-called HOF models, to analyse each species’ specific response to inundation based on topography and to determine their preferred optimal topographic position for both burned as well as unburned areas. Richness was positively associated with elevation only in burned areas while abundance was negatively influenced by inundation only in burned areas. Basal area was negatively associated with time of inundation independent of fire history. There were 15 species which were significant indicators for at least one combination of the studied factors. We found nine species in burned areas and 15 in unburned areas, with response curves in HOF models along the inundation gradient. From these, five species shifted their optimal position along the inundation gradient in burned areas. The interaction of fire and inundation did not appear to affect the basal area, but it did affect the richness, number of individuals, success of some species, and seemed to shape the boundary of these forests as shown by the difference in the positioning of these species along the inundation gradient.

Analysis of the landscape complexity and heterogeneity of the Pantanal wetland

“…This justifies the highest standard deviation of the sub-region Tuiuiú. Although most sub-regions are under the dry season in August, by then the Tuiuiú is still flooded due to the delayed flow of the Paraguay river from the upper basin (Arruda et al, 2016). Such aquatic vegetation over water bodies was described in that area (Catian et al, 2012).…”

Soil Seed Bank in Pantanal Riparian Forest: Persistence, Abundance, Functional Diversity and Composition

“…The climate of Corumbá is Awa, i.e., tropical megathermic, with a mean annual rainfall of 1100 mm, and an average annual temperature of 21-31°C (Soriano 1997). The Paraguay River riparian forest is composed primarily of alluvial seasonal semi-deciduous forest (Damasceno-Junior et al 2005, Arruda et al 2016.…”

“…However, the opposite can occur in habitats with strong seasonal environmental filters, where the plant community is more prone to such filters than to competition (Lohbeck et al 2014). Therefore, the smaller effect of competition in the plant communities of the Pantanal can occur due to the recurrence of seasonal floods and fire events (Arruda et al 2016), that set the vegetation back to initial succession stages.…”

“…Floodplains such as the Pantanal are dynamic environments, whereby vegetation types are structured mainly by seasonal flood (Damasceno-Junior et al 2005, Catian et al 2018 and fire (Arruda et al 2016). To overcome such environmental filters, plants have different strategies related to persistence (Bond & Midgley 2001) and regeneration niches (Grubb 1977).…”

Fire can weaken or trigger functional responses of trees to flooding in wetland forest patches

“…Riparian vegetation in floodplains may undergo regular fire episodes owing to nearby combustible grass, as well as biomass deposited into piles by flooding (Dwire & Kauffman, ; Petit & Naiman, ). These events interact in environmental filtering processes by shaping vegetation structure, excluding species intolerant to fire and flood (Arruda et al., ; Petit & Naiman, ).…”