ND-08 Group Augmented Abstract

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

Ken McNabb -- Auburn University
Luiz Gonzaga da Silva Costa -- Faculdade de Ciências Agrárias do Pará (FCAP)


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.


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.


Research Team Responsibilities