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ND-08 Abstract

Soil Organic Matter Fluxes in Amazonian Forests: Natural Vs Intensively Managed Systems

Luiz Gonzaga da Silva Costa — FCAP (SA-PI)
Ken McNabb — Auburn University (US-PI)

Objectives





We propose to study the carbon dynamics of intensively managed tree plantations and

directly compare them to those of adjacent undisturbed primary forest. There are at least

four current plantation operations in the Amazon basin and these intensively managed

systems are sometimes regarded as a strategy to increase fiber production per unit of land

area and relieve pressures for harvesting native forests. There are questions, however, as

to how conversion to plantations from primary forest or abandoned agriculture land will

modify or restore normal ecological processes, particularly, what is the long term

sustainability of these plantation systems? We propose to address this issue by comparing

the carbon cycling processes of intensively managed plantations to adjacent undisturbed

primary forest. In collaboration with the Agriculture College of the State of Pará, we

will make a comparison of soil carbon inputs, soil carbon fractions, and the chemical

differences between the soils of these two forest types. We assume that land use

conversion will result in significant and measurable changes in the carbon inventory of

the site and that a stable level of biologically active soil organic matter is the

determining factor in long-term site productivity. We seek to identify those components of

the carbon cycle most affected by intensive plantation management.






In relation to the stated objectives of the LBA program, our research (1) addresses a

specific data gap, (2) measures changes in carbon cycling caused by a land use conversion

in the Amazon, and (3) specifically attempts to address the sustainability of this

conversion. This data will be essential to determine the suitability of intensively

managed plantations as a viable and acceptable land use option in the Amazon.





Approaches





Two sites will be investigated -- a clay soil and a sandy soil. Eight sample blocks of

10 m radius will be established at each site, 4 in the plantation and 4 in primary

undisturbed forests adjacent to the plantation. The following measurements will be made in

the 16 blocks.





Soil Carbon Inputs





LITTERFALL will be sampled monthly for 24 months and separated into foliar, stem, and

reproductive components. To measure LITTERFALL DECOMPOSITION nylon mesh bags containing

litterfall will be placed within each forest type and followed over a 24 month period,

initiated twice, once in the dry season and once in the wet season. A similar technique

will be used to follow DECOMPOSITION OF STEM LITTER in two diameter classes of small

stems; <2.5 cm diameter. And 2.5 - 10 cm diameter LITTER QUALITY will be determined by

analysis of C, N, P, lignin, and cellulose contents at 3-month intervals. ROOT BIOMASS

will be sampled every other month for 12 months using soil cores. An estimate of COURSE

WOODY DEBRIS will be conducted during the dry season.





Soil Carbon Pool





Soil sampling will be done in close proximity to each litter trap by bulking a

composite of at least three samples. TOTAL SOIL CARBON will be sampled during both the wet

and dry season. LABILE/STABLE C RATIO will be analyzed from both wet and dry season

samples using a series of sonication, sieving, and densiometric separations to fractionate

various soil organic components including an "enriched labile fraction"

hypothesized to be the major organic matter pool depleted by cultivation.





Nutrient Dynamics





Extractable P, K, Al, Mg, Ca, pH, and CEC will be analyzed for soil samples taken

during both the wet and dry seasons. Soil bulk densities will be determined for wet season

samples at two depths. Total soil N will be sampled along with total soil C. Foliar litter

samples will be analyzed at 3 month intervals for C, N, P, lignin, and cellulose contents.





Research Site





We will conduct this study on the property of Jari Cellulose, a private enterprise

located on the Jari river, the first south flowing major tributary of the Amazon river.

This location offers an exceptionally unique situation to compare natural and artificial

systems. The company manages approximately 80,000 ha of plantations which, for the most

part, are surrounded and immediately adjacent to primary forest that has no history of

human intervention with the possible exception of extractive practices. Auburn University

has signed a research agreement with Jari Cellulose and has worked collaboratively with

the company in the past.





Schedule







  • Litterfall collection April 1998 to April 2000, monthly samples


  • Litter quality Three month intervals from July 1998 to April 2000


  • Litter decomposition Two initiation points - April 1998 and October 1998, 18 months

    duration


  • Root coring October 1998 to October 1999, monthly


  • Coarse Woody Debris October 1998


  • Soil N and C October 1998 and April 1999


  • Soil chemistry October 1998


  • Soil bulk density April 1999






Research Team Responsibilities







  • Ken McNabb: Project coordinator, silva-culture and management


  • Graeme Lockaby: Soil carbon dynamics, biogeochemistry


  • Luiz G. da Silva: Carbon and nutrient cycling


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