Agriculture Reference
In-Depth Information
E3
a:
Ecosystem service
loss by cutting trees
from inside of a field
Ecosystem service
loss by cutting tree
lines at the edge of a field
Ecosystem service
loss by cutting trees
from corners of a field
a
b:
c:
E2
b
E1
c
0
III
T3
II
T2
I
T1
FIGURE 11.8
Theoretical model for added ecosystem services of increasing tree density
(e.g.,
F. albida
) on barley yield at farm level where E1, E2, and E3 refer to increasing barley
yield levels for three spatial density configurations of a tree on the corner, edge, and within
agricultural fields. (From Hadgu, K.M., L. Kooistra, W.A. Rossing, and A.H.C. van Bruggen,
Food Sec
., 1, 337, 2009. With permission.)
and lowland lakeshore areas in eastern and southern Africa, but are increasingly
being planted in uplands, especially in Zambia.
Use of different agricultural technologies to improve food security has been a
perennial subject in sub-Saharan Africa. However, managing the fate of C in food,
energy, and climate systems has become increasingly difficult (Lal 2010). It is
increasingly important to manage cropping systems with both food security and C
balance in mind.
11.3
ACCUMULATION OF CARBON IN BIOMASS AND SOIL
11.3.1 b
iomASS
A
ccumulAtion
in
A
groforeStry
in
e
AStern
And
S
outhern
A
fricA
Biomass buildup in agroforestry systems throughout eastern and southern Africa is
highly variable. This variation is partly explained by edaphic and climatic site condi-
tions, but it depends at least as strongly on the type of agroforestry that is practiced.
Management of the system is also an important factor. Unmanaged natural regenera-
tion of miombo woodlands, a typical vegetation type of eastern and southern Africa,
occurs slowly, with annual biomass increments estimated at 1 Mg ha
−1
in Zambia
(Stromgaard 1985) and 0.43 Mg ha
−1
in Tanzania (Aune et al. 2005).
11.3.1.1 Intercropping Agroforestry Systems
All agroforestry systems for which data are available accumulate biomass faster than
the natural systems they emulate. Montagnini and Nair (2004) bracket the range
of C sequestration by smallholder agroforestry in the tropics between 1.5 and 3.5
Mg C ha
−1
year
−1
. Most published studies of biomass accumulation in simultaneous
