The Brazilian freshwater wetscape: Changes in tree community diversity and composition on climatic and geographic gradients

Abstract

Wetlands harbor an important compliment of regional plant diversity, but in many regions data on wetland diversity and composition is still lacking, thus hindering our understanding of the processes that control it. While patterns of broad-scale terrestrial diversity and composition typically correlate with contemporary climate it is not clear to what extent patterns in wetlands are complimentary, or conflicting. To elucidate this, we consolidate data from wetland forest inventories in Brazil and examine patterns of diversity and composition along temperature and rainfall gradients spanning five biomes. We collated 196 floristic inventories covering an area >220 ha and including >260,000 woody individuals. We detected a total of 2,453 tree species, with the Amazon alone accounting for nearly half. Compositional patterns indicated differences in freshwater wetland floras among Brazilian biomes, although biomes with drier, more seasonal climates tended to have a larger proportion of more widely distributed species. Maximal alpha diversity increased with annual temperature, rainfall, and decreasing seasonality, patterns broadly consistent with upland vegetation communities. However, alpha diversity-climate relationships were only revealed at higher diversity values associated with the uppermost quantiles, and in most sites diversity varied irrespective of climate. Likewise, mean biome-level differences in alpha-diversity were unexpectedly modest, even in comparisons of savanna-area wetlands to those of nearby forested regions. We describe attenuated wetland climate-diversity relationships as a shifting balance of local and regional effects on species recruitment. Locally, excessive waterlogging strongly filters species able to colonize from regional pools. On the other hand, increased water availability can accommodate a rich community of drought-sensitive immigrant species that are able to track buffered wetland microclimates. We argue that environmental conditions in many wetlands are not homogeneous with respect to regional climate, and that responses of wetland tree communities to future climate change may lag behind that of non-wetland, terrestrial habitat.

Woody plant subregions of the Amazon forest

“…A high correspondence was also found between some subregions and the gradient extending from Colombia to southeastern Amazon (Emilio et al, 2010;Oliveira & Nelson, 2001;ter Steege et al, 2000ter Steege et al, , 2006, characterized by an increased presence of Burseraceae (Protium and Tetragastris), Bignoniaceae (Jacaranda and Tabebuia) and Rutaceae (Fagara) in drier forests at the southeastern margin of the Amazon basin (ter Steege et al, 2000(ter Steege et al, , 2006. At the same time, we found a striking similarity between the clustering of subregions into broader zones, with an east-west Andes-Craton division (Quesada et al, 2012;Tuomisto et al, 2016;Wittmann et al, 2017). This result confirms that, besides the better known genus gradual replacement over large distances, floristic discontinuities also make a great contribution to compositional patterns in the Amazon forest (Higgins et al, 2011;Tuomisto et al, 2016Tuomisto et al, , 2019.…”

“…These are two broad floristic gradients that run from the Guiana Shield in the northeast to Peru/ Bolivia in the southwest (Emilio et al, 2010), and from southern Colombia in the northwest to the southeast of the Amazon basin (Emilio et al, 2010;Oliveira & Nelson, 2001;ter Steege et al, 2000ter Steege et al, , 2006. These compositional gradients include the wetland flora of large river floodplains, riparian zones, and hydromorphic whitesand savannas and campinaranas heath vegetation (Wittmann et al, 2017). They are related to the stresses that poor soil nutrition and reduced light availability pose in the Guiana Shield, and that seasonal drought impose in the southern Amazon rim (ter Steege et al, 2006;Wittmann et al, 2017).…”

Fostering water resource governance and conservation in the Brazilian Cerrado biome

“…The Cerrado's most tree species‐rich habitats are its riparian forests, with up to 800 flood‐tolerant tree species (Wittmann et al, ). They provide refuge for many moist‐sensitive tree species that overcome seasonal drought and wildfires by tapping into the high groundwater along rivers.…”

Respostas morfológicas ao alagamento em espécies arbóreas de florestas ribeirinhas subtropicais brasileiras

“…A frequência de inundações está associada com as variações climáticas e influencia a estrutura das comunidades vegetais (Wittmann et al 2017). Nos trópicos, muitas destas comunidades são naturalmente expostas à inundação (Medri et al 2012).…”

“…Nos trópicos, muitas destas comunidades são naturalmente expostas à inundação (Medri et al 2012). Em alguns ecossistemas brasileiros, a inundação ocorre de maneira definida ao longo do ano devido a ocorrência das estações secas e chuvosas (Wittmann et al 2017). Todavia, em outros ecossistemas como os que ocorrem na região Sul do Brasil, marcada por clima subtropical, os fenômenos de inundações conduzidos pelas variações topográficas são imprevisíveis e de baixa magnitude, ocorrendo com alta frequência ao longo de todo ano (Budke et al 2010).…”