ABSTRACT Wildfire events cause considerable environmental disturbance but few studies have examined changes in soil properties due to fire. This study aimed to assess the effect of a wildfire event on chemical, physical, and biological properties of the soil in a eucalyptus forest in the Pampa biome. Part of a seven-year-old eucalyptus forest was affected by a wildfire event that lasted for two days. Soil and plant litter sampling was performed in three areas: in the forest that was not affected by the fire, in the forest affected by it, and in an adjacent natural pasture area (the original vegetation). Seven samples were collected from the 0.00-0.05 and 0.05-0.20 m layers of each plot for biological analysis, and three samples were collected for chemical and physical analyses. Disturbed soil samples were collected in order to determine pH, organic matter, acidity, and nutrient content. Undisturbed samples were collected to determine soil microporosity, macroporosity, total porosity, and density. Soil macrofauna was assessed through the Tropical Soil Biology and Fertility method, and biological activity was tested through substrate consumption in the bait-lamina test. The fire increased soil pH values, CEC, and base saturation, as well as K, Ca, and Mg content; it decreased potential acidity and P content in the soil. Soil physical properties were not altered by the wildfire. The total abundance of macrofauna and of annelids, arachnids, coleoptera, and isoptera decreased due to the wildfire, resulting in lower soil diversity. Hymenoptera abundance increased because of the fire event. The feeding activity of organisms in the soil surface layer decreased due to the fire. The wildfire in the eucalyptus forest in the Pampa biome altered soil chemical and biological properties.

As voçorocas podem ser estabilizadas pelo restabelecimento da vegetação original ou de outro tipo de cobertura vegetal adaptada à nova condição. Este estudo teve como objetivo caracterizar a revegetação natural de uma voçoroca localizada em área de pastagem cultivada, isolada do gado, em Mato Grosso do Sul. Foram obtidos dados florísticos e fitossociológicos de maio/2009 a abril/2010, e informações referentes à biologia das espécies envolvidas. Foram encontradas 23 famílias, 49 gêneros e 71 espécies. Predominaram as herbáceo-subarbustivas (78,9%), eretas (63,4%), hemicriptófitas (43,7%) e autocóricas (60%). O período chuvoso contou com 90% das espécies em floração e 77,1% em frutificação. O atributo "solo descoberto" apresentou elevado VI (51,6%) e CR (72,50%) em maio/2009, valores gradualmente reduzidos a 34,2% (VI) e 45,3% (CR) em fevereiro/2010. Conclui-se que a revegetação natural está em curso e sugere-se que o estudo seja repetido daqui a alguns anos, para monitorar a evolução da sucessão da vegetação.

Gullies can be stabilized by restoration of original vegetation or another type of vegetation cover adapted to the new condition. This study aimed to characterize the spontaneous revegetation of a gully in cultivated pasture, isolated from cattle, in Mato Grosso do Sul State. We obtained data floristic and phytosociological and information related to the biology of the species involved of May/2009 to April/2010. We found 23 families, 49 genera and 71 species. Herbaceous-subshrubby (78.9%), erect (63.4%), hemicryptophyte (43.7%) and autochoric species (60.0%) predominated in the study area. The rainy period had 90% of the species in flower and 77.1% in fruit. The attribute "bare soil" was high in terms of IV (51.6%) and RC (72.5%) in May/2009, values gradually reduced to 34.2% (IV) and 45.3% (RC) in February/2010. It is concluded that natural revegetation is under way. Such survey should be repeated within some years to monitore plant succession.

RESUMO Em áreas florestais, o uso contínuo do solo altera seus atributos físicos e geralmente deteriora sua qualidade, em decorrência do tráfego de máquinas nas operações florestais, com redução da produtividade das culturas. Diante disso, avaliou-se a relação entre a qualidade do solo em diferentes sítios com a produção de Pinus taeda, em solos do Planalto Catarinense. Foram utilizadas quatro fazendas, com dois sítios em cada uma delas, escolhidos pelo tipo de solo e produtividade da floresta (alta e baixa produtividade). Foi descrita a morfologia e amostras de solo foram coletadas em cada horizonte pedogenético para análises físicas e químicas. Existe grande variação nas características físicas dos perfis, especialmente na sequência e espessura dos horizontes. Foi constatada compactação na camada superficial dos perfis mais rasos, evidenciada pela maior densidade e/ou, resistência à penetração do solo, nos quais, a produtividade foi reduzida entre 14 a 36 %, comparados aos perfis mais profundos e com menor grau de compactação.

ABSTRACT In forest areas, the continual use of the soil alters its physical attributes and deteriorates its quality, in consequence of the traffic of machines used in forest operations, resulting in lower yields of crops. The relationship between soil quality at different sites and the production of Pinus taeda was evaluated in soils of the Planalto Catarinense region. Four farms were used, with two sites on each farm, chosen for the soil type and yield of the forest. The soil morphology was described and samples were collected in each pedogenetic horizon for physical and chemical analyses. Great variation exists in the physical attributes of the profiles, especially in the sequence and thickness of the horizons. Compaction was verified in the surface layer of the shallow profiles, evidenced by the higher bulk density and, or, soil resistance to penetration. In these profiles, the yield was reduced by between 14 and 36%, compared to the deeper profiles with a smaller degree of compaction.