ABSTRACT There is a need for greater knowledge about the medium- and long-term effects of prescribed fire management on soil in ecosystems prone to wildfires and more vulnerable to climate change. This study examined the short- and medium-term effects of prescribed fire on soil chemical properties and chemical fractions of soil organic matter (SOM) in two positions of the landscape in a high-elevation grassland environment. The ecosystem is located in the mountain peaks of southeastern Brazil associated with the Atlantic Forest biome. Prescribed fire was conducted in 2017 to reduce understory vegetation and thus prevent potential severe wildfires. Soil samples were collected at the layers of 0.00-0.10, 0.10-0.20, and 0.20-0.40 m, at eight composite sampling. The composite samples were collected on five different occasions: before the prescribed fire, and 10, 30, 90, and 240 days after the prescribed fire. Soil chemical properties, total organic carbon, labile C, and chemical fractionation of SOM were analyzed. All soil properties investigated were affected by the prescribed fire, with variations in landscape position, duration of effect, and soil layer. In the backslope area, the medium-term effect of fire was negative and induced soil degradation and induced soil degradation. In the footslope area, the system showed greater resilience to the effects of fire, as indicated by the recovery of the soil’s chemical properties. These results can help assess the suitability of controlled burning of vegetation for managing risks of fire in mountainous regions, such as high-elevation grasslands.

O objetivo deste trabalho foi avaliar a longevidade de sementes de mutamba (Guazuma ulmifolia) em diferentes tempos de enterrio e profundidades no solo, em banco de sementes induzido. O delineamento utilizado foi blocos casualizados, em esquema fatorial 3x3, com quatro repetições. Os tratamentos empregados foram três profundidades de semeadura (0, 2 e 4cm) e três épocas de avaliação (3, 4 e 5 meses). Cada repetição consiste em 500 sementes, colocadas em sacos tipo filó (10x10cm) e enterradas em sementeira. Em cada época, foi avaliada a viabilidade das sementes por meio de teste de germinação, obtendo-se o percentual de emissão de raiz; plântulas normais e sementes firmes/duras. Foi avaliado, ainda, o percentual de saída do banco (contado através das perdas). As sementes de mutamba (G. ulmifolia) mantiveram-se viáveis no solo (25% do total das sementes enterradas apresentando 72% de viabilidade), mesmo após cinco meses enterradas. As sementes colocadas na superfície do solo e enterradas a 2cm de profundidade apresentam maior taxa de emergência de plântulas no campo do que as sementes enterradas a 4cm. O percentual médio de perdas é de, aproximadamente, 61%, independente da profundidade de semeadura e do tempo de permanência no solo.

The objective of this research was to evaluate the seed viability of mutamba (G. ulmifolia) at different times of burying and depth in the soil in an induced soil seed bank. A randomized block design was used in a 3 x 3 factorial scheme with four plots. The treatments used were three soils depths (0, 2 and 4cm) and three times (3, 4 and 5 months after burying). Each plot had 500 seeds in a bag (10x10cm) buried in nursery soil. The evaluations were seed viability with intact seed, using germination tests, obtaining the number of root emergences, normal seedlings and hard seeds. Further, the number of losses in the soil seed bank were evaluated. The results obtained showed that the mutamba seeds (G. ulmifolia) could stay viable in the soil seed bank after 5 months (25% of total seed buriying showing 72% viability). Seeds on the soil surface and 2cm deep had better average of root emergence and normal seedling percentage than that 4cm deep. The percentage of losses in soil seed bank is 61%, regardless of depth or time.

A viabilidade de sementes de espécies florestais tropicais, em banco de sementes do solo, ainda é pouco estudada. No entanto, pode fornecer informações sobre o potencial de restabelecimento da floresta após distúrbios naturais ou em áreas que sofreram intervenções antrópicas. Os objetivos deste trabalho foram avaliar o vigor e a viabilidade potencial de sementes de S. multijuga e S. macranthera, em semeadura direta, em condições de viveiro e testar a eficiência do teste de tetrazólio para avaliar a viabilidade delas em laboratório. Foram realizados testes de germinação, tetrazólio e emergência de plântulas para avaliar a viabilidade inicial das sementes de ambas as espécies. O teste de tetrazólio (0,075% e 30ºC), foi utilizado, ainda, para avaliar a viabilidade potencial das sementes presentes no solo, aos 6, 12 e 18 meses. Sementes de S. multijuga apresentaram viabilidade potencial de 93,1; 65,3; 52,5 e 17,7% aos 0, 6, 12 e 18 meses, respectivamente, enquanto as sementes de S. macranthera apresentaram viabilidade potencial de 79,3; 73,9; 32,5 e 14,7% aos 0, 6, 12 e 18 meses, respectivamente. As espécies estudadas apresentaram comportamento típico daquelas que formam bancos de sementes persistentes.

Seed viability of tropical forest species in seed soil banks is not well known. This research aimed to evaluate the seed vigour and potential viability of S. multijuga and S. macranthera in direct sowing under nursery conditions and to test the efficiency of the tetrazolium test to determine quickly the seed viability of these species. The germination test, tetrazolium test and seedling emergence test can be used to evaluate seed viability of two species. The tetrazolium test (concentration 0,075%, and 30ºC) was also used to evaluate the potential viability at 6, 12 and 18 months from seeds in a soil bank. S. multijuga seeds presented 93,1%; 65,3%; 52,5% and 17,7% potential viability at sowing and after 6, 12 and 18 months, in the soil bank respectively, and S. macranthera presented 79,3%; 73,9%; 32,5% and 14,7% at sowing and after 6, 12 and 18 months in soil bank, respectively. The species studied had typical behavior of a persistent seed bank.