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CD-11 Abstract

Selective logging, fire, and biomass in Amazonia

Ane Alencar — University of Florida (SA-PI)
Richard A. Houghton — Woods Hole Research Center (US-PI)





Biomass

and rates of disturbance are major factors in determining the net flux of carbon

between terrestrial ecosystems and the atmosphere, and neither of them is well

known for most of the earth's surface. Satellite

data over large areas are beginning to be used systematically to measure rates

of two of the most important types of disturbance, deforestation and

reforestation, but these are not the only types of disturbance that affect

carbon storage. Other examples

include selective logging and fire. Logging

and subsequent regrowth of forests have contributed more to the net flux of

carbon between the atmosphere and temperate zone and boreal forests in recent

decades than any other type of land use. In

the tropics logging is also becoming increasingly important. According to the FAO/UNEP assessment of tropical forests, about 25% of

total area of productive forests have been logged one or more times in the 60-80

years before 1980. The fraction must be considerably greater at present. Thus,

deforestation by itself accounts for only a portion of the emissions carbon from

land. Furthermore, as rates of deforestation become more accurately measured

with satellites, uncertainty in biomass will become the major factor accounting

for the remaining uncertainty in estimates of carbon flux. An approach is needed

for determining the biomass of terrestrial ecosystems.







LBA Ecology offers an excellent opportunity to obtain spatially detailed

estimates of both disturbance and biomass for the same region and time. The work

described here will be of value to LBA Ecology in integrating ground

measurements of biomass and satellite-derived estimates of disturbance. The

spatial data on biomass will help quantify the emissions and sinks of carbon

from land management in Amazonia. They should also help interpret direct

measurements of CO2 flux at tower sites. That is, what portion of a

measured carbon sink can be explained by recovery from past disturbances, as

opposed to other environmental influences?




Project Goals



1. determination of the rate of carbon accumulation (ha-1) in

logged forests;

 



2. determination of the rate, areal extent, and spatial distribution of

selective logging and fire in two regions within Amazonia;

 





3. determination of the spatial distribution of forest biomass as a

result of selective logging and fire; and

 





4. determination of the spatial distribution and the net flux of carbon

as a result of selective logging and fire.

 





The

work consists of (1) ground studies

in areas selectively logged and burned, where rates of wood removal, mortality,

and rates of forest growth are measured; (2) satellite

data (Landsat TM) to determine the rates, areal extent, and spatial

distribution of logging and fire in two areas along the arc of deforestation in

Amazonia; and (3) modeling to

determine the spatial distribution (a) of biomass resulting from current and

past rates of logging and fire and (b) of the net carbon flux associated with

these processes of disturbance and subsequent recovery. The goal is to develop

an approach to measurement of disturbance robust enough for use throughout

Amazonia as extensive satellite data become available for the region.





Study sites





Fieldwork

measuring biomass and rates of growth following logging will be conducted at two

to three sites yet to be determined.



Remote sensing



First,

Landsat TM will be used in two to three regions to identify selectively logged

and burned areas through identification of logging scars (areas indicating

logging by roads in primary forest and "patios" or clearing for log

storage). Second, the spatial distribution of 2000 sawmills in Para and

elsewhere throughout Amazonia will be used to evaluate how readily selective

logging can be monitored remotely, how important selective logging is for

changes in forest biomass and carbon balance in the region, and the relationship

between logging and fire.



Modeling



Extensive

data on disturbance (hectares logged and burned) will be used in a model with

site-specific data (carbon/hectare) on rates of mortality, decay and regrowth to

calculate the releases and accumulations of carbon resulting from logging and

fire. The model is a cohort model that tracks the area, age, and biomass of

lands subjected to different kinds of disturbance. 

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