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.
Highlights
Fire in wetlands is an interesting phenomenon because its occurrence puts into play two opposing extreme events, fire and inundation, both of which have a profound effect in the riparian vegetation
We modelled the basal area, abundance and richness using a generalized linear mixed models (GLMM) with appropriate statistical distributions, and used fire, inundation and their interaction as fixed effects
In the Poisson-GLMM, we found a significant interaction between fire regime and position in the inundation gradient
Summary
Fire in wetlands is an interesting phenomenon because its occurrence puts into play two opposing extreme events, fire and inundation, both of which have a profound effect in the riparian vegetation. The seasonal inundation can promote changes in physiology and morphology of plants such as hypertrophied lenticels and anaerobic metabolism [2, 3]. Inundation is associated with changes in distribution of communities, species zonation in riparian forests, as well as richness and density of trees [1, 4,5,6]. Inundation can result in reduction of growth rates, biomass production, basal area, and increased resprouting ability [7,8]. It affects the recruitment efficiency of plants in the seedling phase [9] and interacts actively in seed dispersal [10]
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