ainforest Agroforestry: A comparative study of the productivity of traditional tree crops with special reference to their effects on associated crops and the forest zone of S.W. Province, Cameroon. (Contract no. TS2*0280-UK(SMA)

[biotec at goliat.ugr.es]

Rainforest Agroforestry:  A comparative study of the productivity 
of traditional tree crops with special reference to their effects 
on associated crops and the forest zone of S.W. Province, Cameroon. 
 (Contract no. TS2*0280-UK(SMA)

Agroforestry is an intensive land use system that facilitates the 
diversified production  of trees, agricultural crops and / or 
livestock from the same land area,  ideally through the use of 
sustainable land management practices.  Transmission of light 
through the canopy and root competition for moisture and other soil 
resources are major environmental factors that affect the design 
and viability of such systems.

This EU funded project sought to establish optimal conditions for 
the incorporation of    agroforestry systems employing woody 
perennials, in particular oil palm, into the agriculture of  rain 
forest buffer zones of S.W. Province, Cameroon.  The research 
programme was co-ordinated by Drs.S.M.Newman and J.Wainwright of 
Fountain Renewable Resources, U.K. with the collaboration of the 
Institute of Terrestrial Ecology,  Edinburgh,  the Department of 
Silviculture & Forest Ecology,  Wageningen Agricultural University, 
 Netherlands and Institute de la Recherche Agronomique,  Cameroon.

The main objectives were as follows:  to determine how interactions 
between trees and the major environmental  factors of light 
transmission and soil moisture influenced growth of understorey 
crops;  to develop and test models that could be used to help 
design agroforestry system by predicting how interactions between 
tree height, canopy dimensions affect light transmission and hence 
understorey productivity;  and to select and to improve native 
fruit and nut tree species of potential for use in agroforestry.  

Field experiments were established in an existing oil palm spacing 
trial,  which facilitated investigation of the effects of palm tree 
planting density on understorey crop growth.  Locally important 
herbs, Ameranth (Ameranthus cruentus) and Basil (Oscimum 
basilicum), were grown in the understorey both  in pots and in soil 
in order to distinguish between aerial and underground interactions 
in the agroforestry system. Canopy transmission of 
photosynthetically active radiation was measured at different tree 
planting densities and capacitance probes were used to measure 
variations in soil moisture to a depth of 1m.  Separate shading 
experiments established  specific relationships between yield of 
pot herbs and incident radiation.  A mathematical model was written 
to predict the light received beneath a single tree and published 
models were applied to predict how variations in total absolute 
light received by a plot varied in response to canopy shape, 
diameter and solar aspect.  Techniques for propagation of native 
nut and culinary leaf tree species Ricinodendron heudelottii, 
Irvingia gabonensis and Gnetum africanum) were also investigated 
and showed that rooting of cuttings was best achieved in sawdust 
following application of hormone (indole butyric acid).  

It was shown that while there was no significant effect of density, 
 aspect or tree proximity on soil moisture in the agroforestry 
plots,  tree spacing had a large effect on  transmission of light 
to the understorey.   Ameranth could be grown at 50% total incident 
radiation without significant yield loss and it was predicted that 
this light intensity would be achieved in the understorey of oil 
palm trees planted at a density of 39 stem ha-1 and  spaced at 16m. 
 In an agroforestry system with these planting densities,  palm oil 
yield would be 47% of that harvested at the optimum planting 
density of 140 stems ha-1  but the yield of ameranth grown in the 
understorey would more than compensate for the lower yield of palm 
oil compared to a monoculture. Mathematical modelling showed the 
importance of tree form in designing agroforestry systems. Small, 
spherical and tall, slender canopies cast light, widely dispersed 
shade whilst larger, spherical or widely spreading canopies cast 
deep shade centred over the tree.
	
Use, ease of propagation, cultivation and management are all major 
factors determining the choice of species for an agroforestry 
system.  The study emphasises that selection of understorey species 
with a shading tolerance compatible with the shading characteristic 
of the canopy form of a particular tree species is essential for 
the design of systems that will optimise yield and maximise 
economic returns at harvest.