water and agroforestry - chin ong - icraf’s research on water,1991-2007
TRANSCRIPT
ICRAF’s research on water,1991-2007
• Past, present and future issues• Machakos (‘Mecca’ for land recovery & agroforestry)• Challenges of more trees & climate change
Upper Mbeere
Machakos
Thika
Source: Anyango, 2005
Thika
20001986
• More adoption of water harvesting
• Increase in dry season cultivation
• Higher incomes• Improved nutrition• More firewood• More fodder • Less time fetching water
Impacts of land recovery in Niger & Machakos
Quickbird image of Lare, Nakuru District, 2006Malesu et al. 2006
Machakos Research, 1985-1992
Strong focus on alley cropping and erosion
However, large plots indicate little or no improvement in crop yields.
Controls plots invaded by tree roots.
(Ayeampong et al. 1995)
1991 1991
Microclimate improvements
Hypothesis: Improvements in microclimate lower soil evaporation & promote hydraulic lift.
Maturity delayed by 2 weeks due to lower temp (-4C). Soil water benefit is not as important.
Climate change benefits?
Ong et al. 2000. Agric. Ecosyst. Environ. 80: 121-145
1993 1995
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
1992 1995
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
1997 1997
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
1994 1996
Water balance
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
1996 1996
Long-term consequences of different resource capture strategies?
Cautious spender: deciduous & lateral rooting
Big spender: evergreen & deep rooting
Grevillea, 15 yr
Melia volkensii, 13 yr
July 2006
Machakos, July 2006
Comparison of deciduous & evergreen trees
Melia volkensii, Machakos, 1997 Paulownia fortunei, Naro Moro, 2001
Land use change & stream flow
Sondu-Miriu hydropower plant
Loss of watershed functionof the Mau Complex
Evidence?
Mau Forest Change 1973 - 2005Key areas of deforestation include:
Eastern Mau
Western Mau
Masai Mau
Lowery, 2005
Stream flow of Nyando River
Nyando, 1968-1991
0
200
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600
800
1000
1200
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0 5000 10000 15000 20000 25000 30000 35000 40000
Cumulative rainfall (mm)
Cum
ulat
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amflo
w (m
m)
Long term river flow is 4% of annual rainfall ( Sang, 2007)
More erosive rain is predicted for Lake Victoria Basin!
Quickbird, Katuk Odeyo, 2004Katuk Odeyo, 1998
Source : Meshak
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
grevillea
Lessons & challenges for ICRAF
• Predicted changes in land use & climate will have serious impacts on water supply & erosion
• Strong tradeoffs with carbon credits: which profitable trees to plant without loss of ecosystem services?
• Machakos lessons: long-term evidence is needed, reserve water for ecosystem functions.
• 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 Victoria Basin
• Where are the future Machakos?
De Wit 2006
Acknowledgements
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 YoungMeka Rao, Ahmed Khan
RELMA team