1. Light and water interactions in silvopastoral systems in a seasonally dry region of Costa Rica
Hernán J. Andrade C.1
Robert M. Brook2
Muhammad Ibrahim3
1 Ecofriendly Production of Tropical Crops Research Group , Faculty of Agronomy, University of Tolima. Ibagué, Colombia,
2 School of the Environment, Natural Resources & Geography, Bangor University, Wales, UK;
3 Livestock & Environmental Management Group, CATIE, Costa Rica.

2. Introduction
Deforestation: Around 13 million ha year-1 , most for agriculture (FAO 2005).
Permanent pastures: 63% agricultural land in Central America and 82% in Costa Rica.
Increasing adoption of Brachiaria pasture species in milk and beef production in Costa Rica
Silvopastoral systems (SPS): trees in pastures, low adoption due mainly to perceived competition for water in dry periods in semi-arid environments
Main goal: To understanding light and water interactions in silvopastoral systems with native timber tree species in dry tropics: key for the appropriate management: radiation, water, fine root dynamics.

3. Description of experimental site
Materials and methods
Description of experimental site
(Cañas, Costa Rica)
Tropical dry forest zone:
50 m altitude
Rainfall: 1500 mm year-1
Reference evapotranspiration: 1800 mm year-1
Temp: 28ºC (23-36ºC)
Soils: Lithic Ustorthent – Lithic Dystropept Complex
Treatments: indigenous trees
Pithecellobium saman,
Diphysa robinioides
Dalbergia retusa
planted in double lines in pastures:
Hyparrhenia rufa (‘juaragua’) or
Brachiaria (syn. Urochloa) brizantha (palisade grass)
Flexible grazing system with 2.0 AU ha-1 and free access to all experiment
Source: Google Earth 2006

4. Evaluated variables Radiation and water use efficiency
Photosynthetically active radiation (PAR)
Hemispherical photographs analyzed by Gap Light Analyzer
Sunscan PAR sensors (Delta T Devices)
Meteorological data
Dry matter production
Water use
Granier sap flow gauges (heat dissipation method) on trees
Simplified water balance (gravimetric) for pasture and trees
Radiation and water use efficiency
1 m
0.5 m

5. Transmission of PAR (PARt)
Results
Transmission of PAR (PARt)
Hemispherical photography Sunscan measurements
Mean values of PARt:
P. saman 65.5%
D. retusa 47.5%
D. robinioides 39.4%

6. Dynamics of water use of trees at stand level
Tree water use: D. robinioides: Bb = Hr D. retusa: Bb > Hr P. saman: Hr > Bb

7. Water use per unit leaf area (from sap flow)

8. Biomass accumulation rates (t DM ha-1 y-1)
Trees
Diphysa robinoides 5.2
Dalbergia retusa 1.7
Pithecellobium saman 0.8
Pastures
Hyparrhenia rufa 5.3
Brachiaria brizantha 14.7

9. Pasture resource use efficiency
Water use efficiency
(no tree plots)
g DM kg-1 H20-1
1.2
3.7
Radiation use efficiency
g DM incident MJ-1
+ trees -trees
Hyparrhenia rufa
Brachiaria brizantha

10. Total carbon storage by biomass components (51 months after establishment)
From: Andrade et al. (2008) Growth, production and carbon sequestration of silvopastoral systems with
native timber species in the dry lowlands of Costa Rica. Plant & Soil 308:11–22

11. Conclusions
P. saman: highest PAR transmission, which allows a high initial tree density in SPS.
D. robinioides had the lowest PAR transmission & highest LAI
D. robinoides fastest growing, P. saman the slowest
Grasses did affect trees, B. brizantha inhibited P. saman growth, H. rufa inhibited D. retusa growth
However, no effect of tree treatments on grass production
B. brizantha productivity was almost three times that of H. rufa: water and radiation use efficiency of B. brizantha was three times than that of H. rufa
Tree-grass interactions in tree water use
Trees have different water use strategies: P. saman had the highest water use by leaf area
D. robinioides: Bb = Hr
D. retusa: Bb > Hr
P. saman: Hr > Bb

12. A final word of warning
Pithecellobium saman is the ‘rain tree’, and commonly
grows to a large size, as seen here in Lae, Papua New Guinea

13. Thank You!