Sucessão vegetal em campo rupestre quartzítico sob recuperação: fatores bióticos e abióticos.

Abstract

The Serra da Calçada is a mountain located in the Minas Gerais State (Brazil) which host a vegetation with a special biodiversity and endemism over hematite and quartzite outcrops protecting several headwaters. However, it has been degraded by the practice of extreme sports, particularly motocross and off-road vehicle crossing which severely damaging the outcrops, headwaters and the native vegetation resulting in a strong erosion process. Erosion may be understood as the final process of soil disaggregation or the breakdown of soil aggregates which depend on the soil organic matter. These eroded areas were recovered in 2017 with a physical rehabilitation procedures, using large blocks of quartzite rocks to reconstruct the outcrops. Smaller rocks were used to fill the gully erosion as well as to pave the surface water flow system. In 2018 the biotic rehabilitation was conducted using native species that were planted and subjected to treatments without (R1) and with inoculation (R2) of arbuscular mycorrhizal fungi (AMF) (Case 1) and an area with bryophyte inoculation (Case 2). To assess the effect of bryophyte and AMF inoculation for the plant establishment as well as on soil fertility and water recovery in the rehabilitated areas, it was employed an experimental design with 4 sites: preserved area (PS), non-inoculated recovery area (R1), inoculated recovery area with AMF (R2) and degraded trail area (DS) where plant and soil samples were collected around quartzite outcrops, in halo “A” (1 m from the rock) and halo “B” (2 m from the rock). The dominant families in all areas were: Poaceae, Cyperaceae, Melastomataceae and Asteraceae. There was similarity between PS, R1 and R2 indicating the functional role of these families in plant succession, especially Poaceae, as they play an ecosystem role related to water distribution, functioning as a hydraulic carpet. Among the 5 dominant species in common between R1, R2 and PS, 3 belong to the Poaceae family and the majority were found in area R2. Area R2 showed an increase in fertility given by the higher content of nutrients, organic matter and CEC in relation to DS. This result was attributed to the presence of a high mycorrhizal population and the glomalin content of the soil, resulting in increased plant occupancy. In areas R1 and R2, a high soil water content was recorded, which determined the selection of tolerant species. PCA and Tukey's test showed greater similarity between R2 and PS, which indicates that R2 is ahead in the plant succession process, possibly due to mycorrhizal inoculation. PCA allowed the separation of halos “A” and “B”, indicating that soil fertility acted by selecting the species. Another study (Case 2) aimed to evaluate the effect of bryophyte inoculation on the establishment of vascular plants. The greater coverage of bryoflora in the area inoculated with bryophytes (RI) and non-inoculated area (RN), when compared to PS, indicates the participation of bryophytes in the plant succession process. There was a change in the floristic composition of those that had been inoculated in 2018, which was attributed to the selective pressure of spring water. Bryoflora is involved in the retention and distribution of water and nutrients, facilitating the plant succession of vascular plants, in addition to contributing to soil stabilization. Water and soil fertility were factors that contributed to the dynamics of plant succession in the area under recovery.