Old-growth Ficus trees provide soil water and carbon storage to urban greenspaces in a Brazilian metropolis

Abstract

Urban flooding has been considered one of the most severe natural disasters around the world, and urban greenspaces can provide important flood regulation ecosystem services. In Belo Horizonte (Brazil), the woody vegetation, especially the old-growth Ficus trees, appears to protect an urban park against the flooding of the Arrudas river. Thus, we compared the soil water content, soil water-holding capacity, soil aggregation and porosity among a highly permeable urban park planted with herbaceous and woody species, including Ficus, a semi-permeable parking lot with only Ficus and an impermeable site without trees (Disturbed Site-DS). The soil water content and water holding capacity of the urban park did not differ from that of the Ficus site, but it was lower than DS. These results were correlated with soil organic matter (SOM) content, soil aggregation and porosity, suggesting that Ficus trees play an important role in the hydrological cycle. To understand how the Fiscus species provide such soil permeability, we compared the aboveground plant biomass, soil fertility and soil carbon sequestration (total soil carbon, soil organic matter, humic and fulvic acids and soil isotopic δ13 C) in plots with Ficus and without this species within the park as well as in a preserved urban forest and a disturbed square. The outstanding plant biomass produced by Ficus species explained the high soil carbon sequestration, particularly in humic organic matter, favouring soil aggregation, porosity and water retention. Therefore, Ficus species may be considered an exceptional C-sequestering species, contributing for soil stabilization and the hydrological cycle in urban greenspaces.