Fire effects on soils erodibility in rainforest conversion in southern Brazil

Abstract

The conversion of rainforests through fire alters the erosive processes impacting the physical properties and soil erodibility. To date, no studies have directly investigated the impact of this transformation on soil erodibility. This study evaluates a recent subtropical rainforest conversion system with the use of fire – from three months to four years post-fire – in two types of soil (Ferralsol and Cambisol). We are seeking to answer the following questions: (a) How does the conversion of subtropical rainforests with the use of fire affect the physical dynamic of different soil types? (b) How do the erosion mechanisms and the erodibility of these soils respond to these forest conversions? (c) How does subtropical rainforests conversion alter the root dynamic of the soils and how does this correlate with the physical properties and the erodibility? Thus, undeformed soil samples were collected using erosion plots (0.135 m² of area x 10 cm depth) in the following areas of each soil type: (1) native forest; (2) ninety days post-fire; and (3) four years post-fire, for experimental evaluation under simulated rain. The results showed changes of 50 % in the physical properties of the Ferralsol and 33 % in the Cambisol. The Ferralsol microaggregates increased by 27.7 % post-fire and the Cambisol microaggregates increased by 34 % post-fire. Rainsplash accounted for more than 83 % of the total soil loss in both soils. Interrill detachment varied from 2.38 × 10⁻³ to 7.43 × 10⁻³ kg m⁻² s⁻¹, increasing in the Ferralsol four years post-fire and decreasing in the Cambisol ninety days post-fire. Interrill erodibility varied between 2.86 × 10⁶ and 7.68 × 10⁶ kg s m⁻⁴ with a post-fire decrease only in the Cambisol. Correlation analysis indicated that the organic matter, aggregate stability, bulk density, and shear strength influenced the rainsplash and sheetwash) while root dynamic influenced the erodibility.