Title: Amazon Rainforest Regrowth under Nutrient Stress: results from a biosphere-atmosphere interaction numerical study

Author: Marcos Heil Costa, the Federal University of Viçosa, Brazil

Marcos Heil Costa received his bachelor's degree in Agricultural Engineering from the University Federal of Viçosa (1986), his masters in Agricultural Meteorology from the Federal University of Viçosa (1991) and his doctorate in Atmospheric and Oceanic Sciences from the University of Wisconsin - Madison (1998). Currently, he is an associate professor of the Federal University of Viçosa. He has experience in the area of Geosciences, with emphasis in Climatology, concentrating mainly on the following subjects: interactions atmosphere-biosphere-hydrosphere, micrometeorology of ecosystems, and large-scale hydrology.

He has published 32 scientific articles, 1 book and 2 book chapters, and advised 11 master's students and 3 doctoral students.


This seminar investigates how the climate feedback and the nutrient feedback interact to regulate the patterns in the regrowth of the Amazon tropical forest after a large-scale deforestation. The study is performed using the fully coupled biosphere-atmosphere model CCM3-IBIS. Initially, the model was validated against observed climate and vegetation dynamics and structure variables. The Amazon climate (annual mean and seasonality) is well simulated for both precipitation and incident solar radiation. Vegetation cover patterns reproduce well the observed patterns. The simulated net primary production and respiration rates are within 5% and 16% of observed data, respectively. The performance of simulated variables that depend on carbon allocation, like net primary production partitioning, leaf area index and biomass, although good on a regional mean, is good at the regional scale, but low when spatial patterns are considered. A better representation of these spatial patterns depends on the understanding of the spatial variation in carbon allocation and its relationship to environmental factors. To evaluate the rainforest regrowth two experiments were done. The first experiment considers different types of nutrient stress and a hypothetical full deforestation. The second experiment considers the most realistic type of nutrient stress and different deforestation scenarios, looking for a threshold of deforestation that could cause dangerous interference on the Amazon recovery. Results show that the reduction in rainfall is proportional to the amount of deforestation and is more drastic when the deforested area is higher than 40% of the original forest extent. In addition, this simulated precipitation reduction alone is not sufficient to prevent the rainforest regrowth. However, when the precipitation reduction is associated with a soil nutrient stress, a savannization process may start over northern Mato Grosso, no matter how much is deforested. This is concerning because this region has the highest clearing rates in Amazonia. The low resilience of the forest under nutrient stress indicates that northern Mato Grosso should be a major target for conservation initiatives.