Water and Agroforestry
Chin Ong, 29 June 2007
ICRISAT Center, Patancheru, India, 1985
ICRAF’s research on water,1991-2007
• Past, present and future issues
• Machakos (‘Mecca’ for land recovery & agroforestry)
• Challenges of more trees & climate change
Source: Anyango, 2005
More people, less erosion
Tiffin & Gichuki,1997
Majjia Valley,Niger, 1975-2002
More rain or more soil conservation? Source: C. Reij
Impacts of land recovery in Niger &
• More adoption of water
• Increase in dry season
• Higher incomes
• Improved nutrition
• More firewood
• More fodder
• Less time fetching water Quickbird image of Lare, Nakuru District, 2006
Malesu et al. 2006
Hypothesis: Trees can capture and use resources more efficiently than crops
Machakos Research, 1985-1992
Strong focus on alley cropping and erosion
However, large plots indicate little or no improvement in
Controls plots invaded by tree roots.
(Ayeampong et al. 1995)
Hypothesis: Improvements in microclimate lower soil evaporation & promote
Maturity delayed by 2 weeks due to lower temp (-4C). Soil water benefit is not as
Climate change benefits?
Ong et al. 2000. Agric. Ecosyst. Environ. 80: 121-145
Complementarity in water uptake
Focus attention on Grevillea robusta-maize in different arrangements
Hypothesis: Deep roots of grevillea is highly compatible with maize.
Howard et al. 1997. Agrofor Sys. 35: 15-29
Fast-growing trees & competition
RAC: Root studies of fast-growing trees
Is the answer below-ground?
Ong et al, 2002. Agr. Water Manag. 53: 171-186
Fractal index & root studies
Fractal index = ratio of lateral vs vertical roots
Index determined for a range of species. How useful?
Ong et al.1999. Agrofor.Syst.44: 87-103
Total transpiration by sole maize was only 50% rainfall
85% by agroforestry systems, including 25 % during the dry season
Lott et al . 2003. For. Ecol. Mange 180: 45-59
Long-term consequences of different resource
Melia volkensii, 13 yr
Cautious spender: deciduous & lateral rooting
Machakos, July 2006
Grevillea, 15 yr
Big spender: evergreen & deep rooting
Comparison of deciduous & evergreen trees
Melia volkensii, Machakos, 1997 Paulownia fortunei, Naro Moro, 2001
Land use change & stream flow
Loss of watershed function
of the Mau Complex
Sondu-Miriu hydropower plant
Mau Forest Change 1973 - 2005
Key areas of
Stream flow of Nyando River
Cumulative streamflow (mm)
0 5000 10000 15000 20000 25000 30000 35000 40000
Cumulative rainfall (mm)
Long term river flow is 4% of annual rainfall ( Sang, 2007)
More erosive rain is predicted for Lake Victoria Basin!
Katuk Odeyo, 1998 Quickbird, Katuk Odeyo, 2004
Source : Meshak
Green and blue water fluxes in Kenya
Eucalyptus: an ecological time-bomb?
• Millions of eucalyptus were planted in
Mau & Central Kenya.
• What will be the ecological impacts?
• Promoted by Forest Department & for
Carbon Trade by TIST.
• 250m3 of water for one ton of carbon!
1 year old eucalyptus uses 30 litres of water per
day! Juja 2007
Sap flow equipment for water uptake
Map of Eucalyptus Impact on Streamflow in South Africa
Source: Mark Gush,2005
More trees with less water?
Naro Moro: Muthuri et al. 2004
Lessons & challenges for ICRAF
• Predicted changes in land use & climate will
have serious impacts on water supply &
• Strong tradeoffs with carbon credits: which
profitable trees to plant without loss of
• Machakos lessons: long-term evidence is
needed, reserve water for ecosystem De Wit 2006
• Make science more meaningful to policy
makers e.g. eucalyptus, bioenergy & water
• Connecting upstream & downstream,
combining land management across scales
e.g. Green blue water initiative with
Stockholm Environment Institute on Lake
• Where are the future Machakos?
Contributions & dedication of countless
students & technicians.
Partners: Nottingham, Bangor, Dundee,
JKUAT, IH, UWA, Sokoine, Cornell, Florida
Donors: DFID, Sida, ACU, DAAD, BMZ
ICRAF: Peter Huxley, Tony Young
Meka Rao, Ahmed Khan
The future is bamboo
Economy class Club class
For zero carbon footprints!