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LC-16 Abstract

The Effects of Rainfall Exclusion on Canopy Phenology, Water Dynamics, Carbon, Nutrients, and Survival of Plants of the Cerrado Projeto Seca-Cerrado

Eric A. Davidson — WHRC - Woods Hole Research Center (US-PI)
Carlos Augusto Klink — UnB - Universidade de Brasília (SA-PI)


In recent years severe droughts have

become common in tropical regions and may become more frequent in the

future.  Recent images of large,

extensive fires in the Amazonian and Cerrado regions remain fresh in our

memories.  Although characterized as a

biome with vegetation that explores deep soil to obtain nutrients and water,

the cerrado has suffered from land use change over a large geographic area

which has brought changes in the structure and function of this ecosystem.  Models that predict climate change show that

substitution of native vegetation by monocultures of pasture plants can change

precipitation patterns and the frequency dry periods in central Brazil.   These climatic changes can alter the

balance between woody plants with deep roots and herbaceous and grass species

with shallow roots.  The increase of

global temperatures and a concomitant decrease in precipitation may increase

the dominance of grasses to the detriment of deep-rooted woody vegetation in

the cerrado.  The cerrado vegetation has

the capacity to extract water and nutrients from deep soil layers during the

long dry season, which permits the foliage to continue to transpire.  Recharge of soil water after a long drought

is necessary for maintenance of the ecosystem. 

During periods of prolonged drought, such as the last El Nino event of

1997/1998, this recharge of soil water did not occur, resulting in pronounced

hydrologic stress.  The vertical

distribution of carbon inputs by roots, and hence the stocks of soil carbon,

could be substantially affected.  In

this research project, we propose to test these predictions in the cerrado by

provoking an experimental reduction in rainfall in an area of natural cerrado

in the Reserva Ecológica do IBGE (protected from fire for more than 20 years)

using a constructed cover over the vegetation with a removable top.  To understand the effects of rainfall

exclusion on the structure and function of the vegetation, we are studying

canopy phenology, growth and mortality of woody plants, production and quality

of litter, nitrogen mineralization, microbial biomass, retranslocation of

nutrients by woody species, production and distribution of roots, and soil

respiration.  These measurements will be

correlated with measures of soil water, using the same methodology that we have

used to study soil water in deep soil shafts. 

We will compare results from the experimental plot with an adjacent

control plot.  

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