Consequências do corte periódico do componente lenhoso da vegetação de cerrado
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Data
2016-02-29
Autores
Giles, André Luiz [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O cerrado em seu sentido amplo apresenta fisionomias que englobam formações campestres, savânicas e florestais, que estão associadas a uma interação de fatores, principalmente climáticos, edáficos e históricos de perturbação. É evidente que na ausência de qualquer agente perturbador, formações vegetais abertas, como campo e savana, se adensem pelo aumento no recrutamento de espécies arbóreas, transformando-se em formações florestais. O contrário também ocorre, formações florestais na presença de incêndios frequentes modificam-se para formações abertas, como savana e campo. No entanto, aqui mostramos que essa evolução é ocasionada por outro agente perturbador além do fogo. Demonstramos que a perturbação pelo corte periódico do componente lenhoso em fisionomia florestal favorece a instalação de espécies mais frequentes em formações savânicas. O principal fator ecológico que se modifica com a perturbação é o microclima, principalmente pelo aumento na intensidade luminosa. Esse aumento provavelmente age na quebra de dormência do banco de sementes e no auxílio do desenvolvimento de espécies que provavelmente rebrotaram através de estruturas subterrâneas. O solo não apresentou diferenças físico-químicas capazes de favorecer ou ser um fator determinante na seleção de espécies campestres ou savânicas nas áreas perturbadas. O que constatamos é que a quantidade de recursos no solo influencia as respostas das comunidades vegetais de cerradão após a perturbação. Desse modo, a supressão do componente lenhoso do cerradão induz mudanças florísticas discretas nas comunidades vegetais sobre solo com maior quantidade de nutrientes, menor acidez e menores teores de alumínio e variações mais acentuadas em ambientes com solo de menor quantidade de nutrientes, mais ácido e com maiores teores de alumínio. Isso indica que ambientes com maior disponibilidade de recursos conseguem se recuperar mais rapidamente que os ambientes com menor disponibilidade de recursos, conferindo maior resiliência após um evento de perturbação.
The cerrado sensu lato includes physiognomies such as field, savanna and forest formations, which are associated with an interaction of factors, especially climate, soil and disturbance history. There is evidence that, in the absence of a disturbing agent, open plant formations, such as fields and savannas, become denser after an increase in the recruiting of tree species and convert to forest formations. The opposite also occurs: forest formations burned by frequent fires change into savanna and field formations. However, here, we demonstrate that other disturbing agent, besides fire, causes this evolution, it is the periodical cutting of the woody component that leads to the establishment in forest formations of species more frequent in savanna formations. The main ecological factor that changes after this disturbance is the microclimate, as a result of an increase in light intensity, which probably breaks seed dormancy and helps the growth of species that have probably resprout from underground structures. We have not found physicochemical differences in the soil that could lead to or act as a determining factor in the selection of savanna species or change the composition of the community. However, we confirmed that the responses of woodland savanna plant communities to disturbance, associated with the higher light derived from canopy suppression, are more intense in environments with lower nutrient soils. Therefore, the cutting of the woody component of the woodland savanna leads to subtle floristic changes in plant communities on soils with higher levels of nutrients, lower acidity, and lower aluminum content, and to sharper changes in environments with soils with lower levels of nutrients, higher acidity, and higher aluminum content. It means that environments with higher resource availability manage to recover faster than environments with lower resource availability, which contributes to greater resilience to disturbance.
The cerrado sensu lato includes physiognomies such as field, savanna and forest formations, which are associated with an interaction of factors, especially climate, soil and disturbance history. There is evidence that, in the absence of a disturbing agent, open plant formations, such as fields and savannas, become denser after an increase in the recruiting of tree species and convert to forest formations. The opposite also occurs: forest formations burned by frequent fires change into savanna and field formations. However, here, we demonstrate that other disturbing agent, besides fire, causes this evolution, it is the periodical cutting of the woody component that leads to the establishment in forest formations of species more frequent in savanna formations. The main ecological factor that changes after this disturbance is the microclimate, as a result of an increase in light intensity, which probably breaks seed dormancy and helps the growth of species that have probably resprout from underground structures. We have not found physicochemical differences in the soil that could lead to or act as a determining factor in the selection of savanna species or change the composition of the community. However, we confirmed that the responses of woodland savanna plant communities to disturbance, associated with the higher light derived from canopy suppression, are more intense in environments with lower nutrient soils. Therefore, the cutting of the woody component of the woodland savanna leads to subtle floristic changes in plant communities on soils with higher levels of nutrients, lower acidity, and lower aluminum content, and to sharper changes in environments with soils with lower levels of nutrients, higher acidity, and higher aluminum content. It means that environments with higher resource availability manage to recover faster than environments with lower resource availability, which contributes to greater resilience to disturbance.
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Palavras-chave
Cerrado, Comunidades vegetais, Espécies savânicas, Fatores abióticos, Perturbação antrópica