Chemistry Reference
In-Depth Information
extremely low organic carbon and total nitrogen content. Soil carbon and
nitrogen content of the 0-10 cm layer is lower after 53 years of cultivation than it
is in nearby natural forests.
197
Cultivation also reduces soil aggregate
stability,
198
exemplified by the fact that average bulk density of a rainforest
soil is lower than in deforested areas.
199
These reductions in soil porosity lead to
soil degradation due to changes in water infiltration and percolation.
200
d
n
1
r
2
n
g
|
8
4.1.3 Repairing Soil Degradation
The challenge the world now faces is how to manage forests and agricultural
lands proactively to deliver food and water to humans, while also preserving
biodiversity and other ecosystem services.
201
Strategies to reduce or even reverse
soil degradation include no-till farming, water conservation and harvest, cover
cropping, woodland regeneration, agroforestry, improved grazing practices,
more efficient irrigation and erosion control.
181,179
Soil organic-matter content
is of the utmost importance and can be improved by management practices that
add biomass to the soil, reduce disturbance and improve soil structure.
4.1.4 The Agroforestry Alternative
From Conte,
202
''A forest understood as an agrarian landscape can include
many centuries of forest-based husbandry.''
203,204
For centuries, farmers in the
eastern Arc Mountains of Africa used agroforestry in the mountains to cultivate
native and introduced plants.
205-209
At Mt. Kisagau, traditional botanical
knowledge is tightly connected to a 1000 m elevation gradient and conveyed to
generations through oral history that details the agro-ecological use of the entire
mountain.
202
Farming once entailed a mosaic of forest ecosystems at varying
stages of exploitation and regeneration that emphasised mobility, since water
rather than temperature was a key factor of tree migration across Africa.
210
Farmers combined imported grain species with African beans, sorghum and
millet,
211,212
and there is evidence that Asian banana was possibly a feature in
African agroforestry for more than 5000 years.
212
More recently, western-style
agricultural and forestry practices ignored lessons of indigenous land-use and
forest evolution, emphasising timber yields only, and the landscape was quickly
degraded to a point where indigenous trees could not even be replanted.
202
Agroforestry practices have been common for thousands of years in Europe,
Africa and South America, and may hold the key to understanding how to use
fertile forest soils to support all life without denuding and degrading them.
5 Soil Characteristics as Tools for Adaptive
Management
Scientists are currently developing new tools based on soil characteristics to
help farmers and land managers evaluate the potential effects of climate
