Abstract
ABSTRACT Information on the recovering of areas of gravel extraction of the Caatinga biome are scarce. Thus, the objective of this work was to assess the soil fauna as bioindicator of soil quality, evaluating areas with addition of topsoil (WAT) and control areas (CWT) without the addition of topsoil used for forest plantations, which were implemented for recovering gravel extraction areas. A native forest of the Caatinga biome (NFC) was taken as a reference. Ten traps with three replicates were installed in each area, which were evaluated in a randomized block design in split-plot arrangement at the end of the rainy season of different years, 0, 1, 3 and 6 years after the experiment implementation. A total of 45,740 specimens were captured. These specimens were from 36 taxonomic groups. The Acari, Diptera, Entomobryomorpha, Formicidae, Poduromorpha and Symphypleona were the predominant groups in all areas (WAT, CWT and NFC). Nine groups (25% of the total) had restricted occurrence. The fauna richness and diversity were higher in the NFC, followed by the WAT and CWT. The uniformity and total abundance of the soil fauna community showed no defined patterns. The abundance of most groups was inhibited in the treatments evaluated, compared with NFC, however, this adverse effect was more significant in CWT compared with WAT. The CWT and WAT had high similarity and both had very low similarity with NFC. The ecological complexity of soil fauna community was higher in NFC. The soil fauna was efficient as a bioindicator of soil quality, which was higher in WAT, compared with CWT.
Highlights
Different human activities can modify landscapes, reducing the resilience of the altered areas, requiring in some cases, human intervention to facilitate and accelerate the recovery of the ecosystem functions
The subsoil exposed after the gravel extraction in areas of the Caatinga biome is usually rich in nutrients, this expensive practice, does not necessarily leads to an increase in fertility of the remaining subsoil (RESENDE et al, 2010)
According to the hierarchical cluster diagram (Figure 7), the treatments CWT and with addition of topsoil (WAT) were relatively distant from each other and formed a group that showed comparatively low similarity compared with the native forest of the Caatinga biome (NFC). This pattern confirmed the results found by comparing the averages, indicating that the WAT treatment was more favorable to the soil fauna, compared with the CWT
Summary
Different human activities can modify landscapes, reducing the resilience of the altered areas, requiring in some cases, human intervention to facilitate and accelerate the recovery of the ecosystem functions. The removal of the soil surface layer (topsoil) for extraction of gravel, which is a mineral material found in the subsoil, mainly composed of silt, sand and grit (RESENDE et al, 2010), is common in the Caatinga biome of the State of Rio Grande do Norte (RN), Brazil. This material is used for ground levelling of onshore sites of oil extraction and processing, which is one of the main economic activities of this state (LIMA et al, 2015), as well as for landfill, and dam and road constructions. Several authors recommend this practice to increase the richness of species that regenerate these areas, through the seed bank of the topsoil
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