Inflamabilidade de espécies do estrato herbáceo do Cerrado
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Data
2019-11-29
Autores
Zanzarini, Vagner Augusto [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Sistemas savânicos são compostos por espécies herbáceas, principalmente gramíneas C4, as quais se expandiram há milhões de anos atrás, alterando a ocorrência de fogo nas regiões sub e tropicas do globo terrestre. Assim sendo, em sistemas como o Cerrado, onde o fogo está presente há pelo menos 4 milhões de anos, as espécies selecionadas por este fator possuem atributos inflamáveis que contribuem para a propagação das chamas. A essa capacidade que diversas espécies possuem de entrarem em combustão e serem consumidas, chamamos de inflamabilidade, sendo um componente essencial dos sistemas inflamáveis, contribuindo para o regime de fogo do ambiente, a partir de fatores ambientais, como a sazonalidade, e composição de espécies. Sendo assim, este trabalho teve como objetivo compreender a inflamabilidade das espécies herbáceas de ambientes savânicos do Cerrado, bem como entender quais são os grupos e os atributos vegetais que mais influenciam a inflamabilidade do sistema de acordo com a sazonalidade do ambiente. Diferentes espécies de herbáceas, arbustos e gramíneas foram coletadas em áreas de campo sujo do Cerrado durante a estação chuvosa e ao longo da estação seca (começo, meio e fim). Medições dos atributos de inflamabilidade (temperatura máxima, taxa de queima e biomassa consumida) e morfofisiológicos (biomassa morta, teor de umidade e área específica foliar) dessas espécies foram realizadas durante tais épocas, afim de compreender se existia variações na inflamabilidade. Além disso, 21 espécies de gramíneas também foram coletadas no meio da estação seca em duas regiões de Cerrado campo sujo diferentes, onde os atributos citados acima também foram mensurados. Com isso, avaliamos a variabilidade na inflamabilidade entre as diversas espécies de gramíneas, além de compreender qual atributo vegetal estaria mais relacionado com o aumento da inflamabilidade. Assim sendo, concluímos que as gramíneas são as espécies que estão influenciando significativamente a inflamabilidade das vegetações savânicas, principalmente durante o meio da estação seca, pois é quando esse grupo encontrou-se mais inflamável. Por otro lado, os arbustos e as herbáceas se mostraram com baixa inflamabilidade, independente da época do ano. As gramíneas apresentaram tais variações entre as estações devido as mudanças na quantidade de biomassa morta e no teor de umidade, os quais foram considerados os principais influenciadores da inflamabilidade. Por fim, também foi possível observar que nem todas as espécies de gramíneas possuem a mesma inflamabilidade, havendo espécies menos e mais inflamáveis no sistema, contribuindo para a propagação heterogênea do fogo. Além disso, constatamos que a quantidade de biomassa morta foi o atributo vegetal que contribuiu para o aumento da inflamabilidade das espécies. Portanto, diante de tais resultados, concluímos que a presença das gramíneas compondo o estrato herbáceos dos sistemas savânicos, como o Cerrado, torna-se imprescindível para manter a inflamabilidade do sistema, bem como o regime de fogo, além de manter as características ambientais e estruturais das fisionomias abertas, fazendo com que espécies como arbustos e herbáceas sejam também consumidas pelo fogo e, consequentemente, persistam na comunidade.
Savanna ecosystems are essentially covered by herbaceous species, mostly C4 grasses, which have a huge expansion million years ago, altering the fire occurrence in the sub and tropical regions of the world. Therefore, fire-prone ecosystems as the Cerrado, have fire present about 4 million years ago, which selected species with flammable traits enhancing the flames propagation. That capacity that several species possess to be consumed and spread the fire is called flammability, which is an essential component of flammable systems, contributing to fire regime, together with environmental factors, as seasonality and species composition. Thus, this study had the main aim understand the flammability of herbaceous species of the Cerrado open savannas physiognomies, besides understand which are the species groups and traits that most influence the system flammability, according to seasonality. Different species of forbs, shrubs and graminoids were collected in areas of Cerrado campo-sujo during the wet season and over the dry season (early, mid and late-dry). Flammability (maximum temperatures, burning rate and burnt biomass) and morphophysiological traits (dead biomass, moisture content and specific leaf area) measurements were taken across seasons, to understand the flammability changes. Moreover, 21 grass species were also collected in the middle of the dry season in two different regions of Cerrado campo-sujo, where the same traits were measured, to evaluate the variability of flammability among grass species, besides understand which is the plant trait that most increase the flammability. We conclude that grasses significantly influence the open savannas flammability, especially in the middle of the dry season, when the group reached the highest flammability, while forbs and shrubs have low flammability in all seasons. Grasses showed this variability across seasons due to changes in the quantity of dead biomass and moisture content, which were considered strongly flammability influencers. Finally, we observed that grasses did not burn at the same way, having species less flammable than others in the system. Indeed, we concluded that the dead biomass percentage was the most increased flammability. In conclusion, the grass presence is indispensable in the open savanna systems, as the Cerrado, besides affect the fire regime, maintaining the open physiognomies characteristics, making that forbs and shrubs species burn and persist in the community.
Savanna ecosystems are essentially covered by herbaceous species, mostly C4 grasses, which have a huge expansion million years ago, altering the fire occurrence in the sub and tropical regions of the world. Therefore, fire-prone ecosystems as the Cerrado, have fire present about 4 million years ago, which selected species with flammable traits enhancing the flames propagation. That capacity that several species possess to be consumed and spread the fire is called flammability, which is an essential component of flammable systems, contributing to fire regime, together with environmental factors, as seasonality and species composition. Thus, this study had the main aim understand the flammability of herbaceous species of the Cerrado open savannas physiognomies, besides understand which are the species groups and traits that most influence the system flammability, according to seasonality. Different species of forbs, shrubs and graminoids were collected in areas of Cerrado campo-sujo during the wet season and over the dry season (early, mid and late-dry). Flammability (maximum temperatures, burning rate and burnt biomass) and morphophysiological traits (dead biomass, moisture content and specific leaf area) measurements were taken across seasons, to understand the flammability changes. Moreover, 21 grass species were also collected in the middle of the dry season in two different regions of Cerrado campo-sujo, where the same traits were measured, to evaluate the variability of flammability among grass species, besides understand which is the plant trait that most increase the flammability. We conclude that grasses significantly influence the open savannas flammability, especially in the middle of the dry season, when the group reached the highest flammability, while forbs and shrubs have low flammability in all seasons. Grasses showed this variability across seasons due to changes in the quantity of dead biomass and moisture content, which were considered strongly flammability influencers. Finally, we observed that grasses did not burn at the same way, having species less flammable than others in the system. Indeed, we concluded that the dead biomass percentage was the most increased flammability. In conclusion, the grass presence is indispensable in the open savanna systems, as the Cerrado, besides affect the fire regime, maintaining the open physiognomies characteristics, making that forbs and shrubs species burn and persist in the community.
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Palavras-chave
Ecossistemas savânicos, Cerrado, Ecologia do fogo, Ecossistemas inflamáveis, Savanna ecosystems, Fire ecology, Fire-prone ecosystems