358 Agricultural Revolutions and Change
Quantifying environmental, agronomic and socioeconomic
parameters
Climate change
Tropical deforestation and land-use change contribute as much as 25 per cent of
the annual flux of carbon dioxide (CO 2 ) to the atmosphere (IPCC, 2001), yet
there is still much debate on this issue because of uncertainties in biomass esti-
mates, rates of deforestation and land-use change sequences. Changes in carbon
stocks and the associated sources or sinks of atmospheric CO 2 and fluxes of nitrous
oxide (N 2 O) and methane (CH 4 ), the three most important greenhouse gases,
were measured in the different land-use systems at the Brazil, Cameroon, Indone-
sia and Peru benchmark sites. Whereas most previous studies have focused on
measurements in the forest and grassland or continuous cropping systems – in
other words, the extremes – the dataset from ASB included measurements from
many of the tree-based systems that often dominate the landscape in the humid
tropics (Wood et al, 2000).
Carbon stocks in the above- and below-ground vegetation and in the top 20cm
of the soil were estimated by a combination of allometric equations (for converting
tree diameters into biomass) and destructive harvest. The concept of the average
amount of carbon stored in each of the land-use systems during the time course of
the rotations, or time-averaged carbon, was used for comparing land-use systems
with different rotation times. The standardized methods for sampling are pre-
sented in Woomer et al (2000) and Woomer and Palm (1998). Results are pre-
sented in Woomer et al (2000) and Palm et al (2002b).
Estimating N 2 O and CH 4 fluxes entails intensive, long-term sampling. This
was not possible at most of the ASB sites. To obtain some estimates for annual
fluxes and seasonal patterns for the different land-use systems, N 2 O and CH 4
fluxes were measured monthly over the course of 2 years in the Indonesia and
Peruvian benchmark sites using static chamber techniques. The sampling protocol
and results are detailed in Ishizuka et al (2002) and Palm et al (2002a).
Biodiversity
Tropical forests contain two-thirds of the estimated 250,000 world’s terrestrial
plant species, 90 per cent of world’s insects, and many bird species (Osborne,
2000), making tropical deforestation a primary cause of global biodiversity loss
(Heywood, 1995; Stork, 1997). The extent of biodiversity loss associated with dif-
ferent land-use systems has seldom been considered, although many traditional
land management strategies have supported biodiversity maintenance (McNeely
et al, 1995; McNeely and Scherr, 2003). Diversity of the above-ground vegetation
and below-ground biota were measured in the range of land-use systems at the
benchmark sites to address these issues.
Above-ground plant diversity was measured as the number of plant species
occurring in transects in each land-use type but also according to plant functional
types (PFTs) (Gillison and Carpenter, 1997). Assessing plant diversity in the tropics