Fire shifts the soil fertility and the vegetation composition in a natural high-altitude grassland in Brazil

Abstract

The Serra da Calçada Mountain (Minas Gerais State, Brazil) hosts a natural grassland with high biodiversity and endemism, locally known as campo rupestre, which grows over hematite and quartzite outcrops, protecting several headwaters. However, this mountain has been severely threatened by anthropogenic fires and its restoration has been challenged by the lack of knowledge on the effect of fire on plant species and soil fertility. Thus, this study aimed to assess a burned campo rupestre site after 1 year concerning plant biodiversity and soil properties as compared to a preserved site. Aside from the high plant biodiversity, the preserved site (with no fire history) showed a high natural soil fertility, particularly regarding soil organic matter (SOM): ∼3.48%, Cationic Exchange Capacity (CEC): ∼8.4 meq/100g, soil ammonium (NH4+-N): ∼11 ppm and soil phosphorus (P): ∼6.9 mg/Kg. However, the fire reduced not only the plant species composition, abundance, richness and biodiversity, but also disrupted the natural soil fertility. There was a change in N chemical species from ammonium to nitrate as well as an increase in sodium (Na) content, in addition to a depletion of SOM and CEC. The variations of nitrogen chemical species, sodium, SOM, CEC and soil moisture explained 79% of the changes in plant composition as revealed by the Mantel matrix permutation test. Increased soil nitrate and sodium were considered the main factors determining changes in vegetation composition after fire. Therefore, fires should be strictly avoided for the management of the campo rupestre grassland, and for the rehabilitation purposes, the improvement of SOM and ammonium in detriment of nitrate is recommended.