The area has a seasonal climate with a distinct dry period of 6–8
months. Most of the annual precipitation occurs as rainstorms
during August and September and most of it is drained to
ephemeral streams via surface runoff (Udomchoke and Mingtipon,
1995). Between 1992 and 1997 the average annual rainfall in Maejo was 1026 mm, with a 95% confidence interval of 882–1231 mm (Maejo University meteorological station data). Soils are
predominantly sandy with gravel and rock fragments, poor
nutrient status and low water-holding capacity (Vongtanaboon,
1998).