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“Apesar de sua fisionomia típica, devido à dominância da Araucária no dossel, esta floresta não pode ser considerada como uma formação floristicamente homogênea, pois, assim como as demais formações vegetacionais do globo terrestre, é influenciada por vários fatores, dentre eles o clima.”

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Foto de Leonardo F. Freitas

Afinal, quais fatores ambientais que poderiam explicar as variações espaciais nas taxas de crescimento de árvores em florestas tropicais? Clima, fertilidade do solo ou intensidade de distúrbios? Evidentemente, existe uma interação entre todos estes fatores. No entanto, foi observado em um estudo recente, desenvolvido em uma floresta tropical úmida de terras baixas na Bolívia, que o clima foi o fator mais determinante. Nos locais com maior quantidade de chuva, menor a estação seca e maior temperatura foram observadas as maiores taxas de crescimento.

Como destacado pelos autores, este estudo demonstra os possíveis impactos de mudanças climáticas sobre a produtividade primária e o sequestro de carbono em ecossistemas florestais tropicais.

Climate is a stronger driver of tree and forest growth rates than soil and disturbance: “

Summary

1. Essential resources such as water, nutrients and light vary over space and time and plant growth rates are expected to vary accordingly. We examined the effects of climate, soil and logging disturbances on diameter growth rates at the tree and stand level, using 165 1-ha permanent sample plots distributed across Bolivian tropical lowland forests.
2. We predicted that growth rates would be higher in humid than in dry forests, higher in nutrient-rich than nutrient-poor forests and higher in logged than non-logged forests.
3. Across the 165 plots we found positive basal area increases at the stand level, which agree with the generally reported biomass increases in tropical forests.
4. Multiple regression analysis demonstrated that climate variables, in particular water availability, were the strongest drivers of tree growth. More rainfall, a shorter and less intense dry period and higher temperatures led to higher tree growth rates.
5. Tree growth increased modestly with soil fertility and basal area growth was greatest at intermediate soil fertility. Surprisingly, tree growth showed little or no relationship with total soil nitrogen or plant available soil phosphorus.
6. Growth rates increased in logged plots just after logging, but this effect disappeared after 6 years.
7.Synthesis. Climate is the strongest driver of spatial variation in tree growth, and climate change may therefore have large consequences for forest productivity and carbon sequestration. The negative impact of decreased rainfall and increased rainfall seasonality on tree growth might be partly offset by the positive impact of increased temperature in these forests.

Toledo, M., Poorter, L., Peña-Claros, M., Alarcón, A., Balcázar, J., Leaño, C., Licona, J. C., Llanque, O., Vroomans, V., Zuidema, P. and Bongers, F. , Climate is a stronger driver of tree and forest growth rates than soil and disturbance. Journal of Ecology, no. doi: 10.1111/j.1365-2745.2010.01741.x

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