INVESTING IN TREES AND LANDSCAPE ... - PROFOR

than shade-grown systems (at 10–20 years compared with 40–60 years), so the limited availability
of planting material is also a constraint (Ruf and Zadi 1998). However, a WWF-led global study on
best practice models indicates that smallholder cocoa has potential as both an agent of ecosystem
fragmentation and as protection, depending on whether it is grown in extensive systems (largely
responsible for forest thinning or clearing) or intensive systems such as the multistrata cocoa
agroforests, which typically also provide farmers with a diversified range of edible tree fruits and
other food crops for nutritional and economic sustainability (WWF 2006).
Recent studies (see Somarriba and Beer 2011) indicate that shade trees do not reduce cocoa yields,
at least during the initial 10–12 years of production, but another motivation of cocoa farmers to clear
existing forest without replanting lies in the lack of policies favoring ownership and use of timber
trees by farmers. For example, lack of private rights to trees is a major factor behind Ghanaian cocoa
farmers’ shift toward full-sun varieties (Ruf 2011).
In their detailed financial analysis of shaded coffee production in Ghana, Obiri and others concluded
that “cocoa production is, in general, profitable. The change from the traditional system to one
with hybrid cocoa raised the Internal Rate of Retrun [internal rate of return] from 31 percent to
57 percent with planted shade and 67 percent without, although extra agrochemical costs would
tend to reduce the profitability of unshaded hybrid cocoa in particular.” The study determined that
the “optimum economic rotation for the hybrid cocoa is between 18 and 29 years, much less
than the traditional system” (Obiri et al. 2007). So the integration of improved varieties into shade
systems can be competitive with cocoa monocrops and can become even more profitable with an
appropriate selection of other fruit or timber trees.
Agroforestry Systems for Improved Cereal Crop Productivity
The addition of trees into agricultural landscapes has been shown to positively alter the soil-crop
environment by improving soil aggregation and enhancing water infiltration and waterholding
capacity, which reduces water runoff and soil erosion and thus contributes to reduction of the effects
of drought periods on soils under trees (Phiri et al. 2003). Experiments lasting more than a decade
in Zambia and Nigeria showed that rainfall use efficiency (crop production per unit of rainwater)
was consistently higher in agricultural fields where trees were grown than where they were not
(Sileshi et al. 2011). Equally important, nitrogen-fixing trees used in fallow or intercrop systems
enrich soils through the generation and application of more than 200 kgs of nitrogen per hectare.
They can also provide other nutrients and, of course, important mulch cover that can suppress
weed growth. There are several examples of the large-scale use of agroforestry for soil and crop
improvement. One example is the parkland system, in which indigenous trees are regenerated in
cropfields. In Niger, more than 5 million hectares have been rehabilitated through farmer-managed
natural regeneration (Reij, Tappan, and Smale 2009). Faidherbia albida, an indigenous nitrogenfixing
species in many Sahelian parklands, is being planted at scale in Zambia (200,000 farms) as
part of a conservation program of farming with trees (Aagaard 2011). Finally, exotic leguminous
trees that can withstand frequent cutting, such as Gliricidia, are being used in a wide scaling up
of agroforestry for food security in Malawi (Akinnifesi et al. 2010). Some of these systems are
described in more detail below.
32 INVESTING IN TREES AND LANDSCAPE RESTORATION IN AFRICA