342 Agricultural Revolutions and Change
Land-use intensification pathways
The pathway of agricultural intensification depends to some extent on the bio-
physical environment but is modified by the demographic composition and pres-
sures, production technologies, and natural resource management practices,
infrastructure, institutions and policy environment present at the time. The usual
pathway begins with the reduction of the fallow period to less than 10 years and
more commonly less than 5 years. These short fallows are incapable of accumulat-
ing sufficient nutrient stocks in the biomass and suppressing weeds by shading.
Unlike shifting cultivation, where soil erosion is seldom a problem, slash-and-burn
systems have less vegetative cover and often exposed, compacted soils that increase
water run-off and soil erosion rates (Lal et al, 1986). This change in vegetation and
soil structure may lead to changes in the hydrologic cycle, with negative conse-
quences downstream (Bruijnzeel, 1990; Tinker et al, 1996). The combined effects
of shortened fallows result in systems with declining productivity, depending more
and more on less and less fallow biomass. In some cases, the systems reach a point
at which the trees are replaced by other, highly degraded systems such as Imperata
cylindrica (L.) Beauv grasslands in South-East Asia and West Africa (Garrity, 1997)
and degraded pastures in Latin America (Serrāo and Homma, 1993). This path-
way of land-use intensification, land degradation and the resulting losses of carbon
stocks, nutrients and biodiversity is depicted in the left-hand, declining curve in
Figure 15.1, line a. It is important to remember that those and other ecosystem
services have been traded for private benefits, including food, feed, fibre and
cash.
With further increases in population density come increased access to markets
and decreased access to forest products. A point may be reached when land degra-
dation begins to be reversed with changes in land tenure institutions that facilitate
investments in improved land management. This process was recognized by Boserup
(1965) and is sometimes called induced institutional innovation (Hayami and
Ruttan, 1985). Land rehabilitation usually is accomplished by replenishing lost
plant nutrients; using improved crop germplasm, agronomic practices and soil
conservation methods; introducing livestock; and planting more trees.
Farmers will invest in improved land management and care for the environ-
ment when they have reasonably secure land or tree tenure and if it is profitable
compared with other investment options within the context of household con-
straints and individual time preferences and attitudes toward risk. Examples of soil
and land rehabilitation with increasing population pressure are well documented
as ‘more people, less erosion’ (Tiffen et al, 1994) and ‘more people, more trees’
(Sanchez et al, 1998). They are accompanied by increasing productivity and prof-
itability. Ecosystem stocks of carbon and nutrients increase and other ecosystems
services also return, the level of which depends on the previous state of degradation
and on the type of land-use system that is established. Livelihoods may continue
to improve as more and more valuable economic products are obtained from the
system. The trade-offs between the environmental services and profitability are