Índices biofísicos para avaliação da desertificação no semiárido

• Autor(a) principal: Vendruscolo, Jhony
• Data de Publicação: 2017
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFPB
• Texto Completo: https://repositorio.ufpb.br/jspui/handle/123456789/25545
• topic: Caatinga; Cobertura arbórea; Atributos do solo; CNPQ::CIENCIAS AGRARIAS

The desertification process takes place in arid, semi-arid and sub-humid areas of the earth, causing losses of soil, organic matter and nutrients, and, consequently, the reduction of the productive capacity of the soils. In Brazil, areas susceptible to desertification encompass 9 states, including Paraíba, and it is observed that the process begins with the conversion of native forest to agriculture associated with inadequate soil management. The present work had as objective to select biophysical indicators and to provide indices for the evaluation of the level of desertification in the Semiarid of the Paraíba State. Twenty - two preserved areas were selected, with no clear cut in the last 30 years, and 22 desertified areas, with difficulties to re - establish the vegetation cover. In each area a plot of 100 m2 (10 x 10 m) was allocated. Initially, the tree species were identified, the perimeter at 0.30 m ground level (PGL), chest height perimeter at 1.30 m (PBH), absolute density (AD), relative density (RD), absolute frequency (AF), relative frequency (RF), absolute dominance (ADo), relative dominance (RDo), importance value index (IVI) and coverage value index (CVI) were calculated (I Chapter). After that, the number of species (NS), plant density (PD), mean canopy height (H-M), mean perimeter ground level (PGL-M), mean chest height perimeter (PBH-M) and total absolute dominance (ADo-T), and based on the results, the indicators of the level of desertification with paired T-test were selected (p < 0.05), the range of indicators was measured, considering the smallest detectable difference between the pairs of areas (conserved and desertified), the weights of the indicators were analyzed with principal component analysis and an index was prepared for the evaluation of the desertification level of the Paraíba semi-arid region (II Chapter). Soil samples were also collected in the 0-5 and 5-20 cm layers, and analyzed of the active acidity (pH in water), potential acidity (H + Al), sodium (Na+ ), aluminum (Al3+), potassium (K+ ), calcium (Ca2+), magnesium (Mg2+), total organic carbon (TOC), available P (Mehlich-1), soil texture and bulk density, and calculated the sum of bases, effective CEC, potential CEC, base saturation, aluminium saturation and percentage of exchangeable sodium (PES). The values of chemical and physical soil attributes were compared with reference values for the semiarid region, classified into three levels (1 - high, 2 - medium and 3 - low) and joined to the formation of a soil quality index, was compared to the climatic classification map to obtain the areas most susceptible to the desertification process and the most critical for restoration of forest cover (Chapter III). On the basis of the soil results, the indicators of xvi the desertification level with paired T-test (p < 0.05) were also selected, the range of indicators was measured, considering the smallest detectable difference between the pairs of areas (conserved and desertified), the weights of the indicators were analyzed with principal component analysis, and an index was prepared for the evaluation of the desertification level of the Semiarid of the Paraíba State (IV Chapter). In the first chapter, it is verified that the conserved areas presented a total of 63 tree species and 9 desertificated areas. The most frequent species in the conserved areas are Caesalpinia pyramidalis and Croton sonderianus, and in the desertified areas are Mimosa tenuiflora and Croton sonderianus. The conserved areas presented higher AD than the desertified areas, with total values of 4845 I ha-1 and 895 I ha-1 . The ADo followed the order Caesalpinia pyramidalis > Anadenanthera colubrina > Myracrodruon urundeuva, and Mimosa tenuiflora > Caesalpinia pyramidalis > Aspidosperma pyrifolium, for conserved areas and desertified areas, respectively. The Croton sonderianus (conserved areas) and Mimosa tenuiflora (desertified areas) species have the highest IVI and CVI. In the second chapter, it is verified that the loss of quality of the tree cover caused the desertification process, by reducing the protection of the soil against the action of water erosion. The parameters NS, ADo-T, PD, H-M, PBH-M and PGL-M, can be used as indicators in 100, 100, 97.9, 89.7, 71.6 and 56.8%, from the semi-arid region of Paraiba, respectively. The most important indicators are PBH-M (0.4210), PGL-M (0.4110), NS (0.4097), PD (0.3891), H-M (0.3614) and ADo-T (0.3407). The index of the level of desertification based on the tree cover allows to accurately assess the level of desertification of areas in the Semiarid of the Paraíba State. In the third chapter, it is observed that the conserved areas present a high level of soil quality. The attributes of the soil that makes the region naturally more sensitive to the desertification process are pH, P, TOC, potential acidity, potential CEC, effective CEC, base saturation and bulk density. The municipalities of Bonito de Santa Fé, Cacimba de Dentro, Campina Grande, Soledade, Picuí, Remígio and Uiraúna, present the lowest soil quality in conserved areas. The municipalities most susceptible to the desertification process, considering the soil quality in conserved areas and the availability of water, are Soledade and Picuí. The desertified areas present a high level of quality in the layer of 0-5 cm, and medium level of quality in the layer of 5-20 cm. The most limiting attributes to the growth and development of the vegetation cover in the desertified areas are TOC, P, bulk density, potential CEC, pH, effective CEC and calcium, respectively. The most critical regions for the restoration of vegetation cover in desertified areas are located in the municipalities of São Domingos do Cariri, Picuí and Taperoá. In xvii desertified areas, the use of integrated management is recommended prioritizing the accumulation of organic matter and the increase of water availability, aiming at the recovery of the vegetal cover. In the fourth chapter, the desertification process in the semi arid region of Paraiba tends to reduce the TOC content and increase the values of Na+ , PES and bulk density, independent of the layer, and decrease the values of Ca2+, H+Al, potencial CEC in the 0-5 cm layer, and K+ in the 5-20 cm layer. The range of the indicators in the semi-arid region for the 0-5 cm layer is as follows: TOC (100%), bulk density (100%), H+Al (68.0%), potential CEC (66.2%), Na+ (64.2%), Ca2+ (62.4%), PES (61.4%) and aluminium saturation (18.2%). In the 5-20 cm layer follows the order: TOC (91.2%), K + (78.0%), bulk density (55.6%), PES (53.0%) and Na+ (29.0%). The index of the level of desertification based on the soil atributes, allows to accurately assess the level of desertification in areas of the Semiarid region of Paraíba, and to point out which soil attributes are most limiting for restoring forest cover in specific regions.