The three-level structure in the coffee canopy occurs if it is considered that shaded leaves have higher net photosynthesis than leaves exposed to full sunlight (Cannell 1985). Several data showed that stomatal conductance is larger in shaded coffee leaves (Butler 1977; Fanjul et al. 1985; Gutiérrez et al. 1994). Field assays with the C. arabica varieties ‘Bourbon’ and ‘Caturra’ have shown that despite the stomata of plants growing at full sun remaining open at dawn, they close in the morning with an increase in temperature, irradiation and atmosphere air saturation deficit (Fanjul et al. 1985). According to Da Matta (2004b, and references there in), this stomatal behavior should be attributed to the sensitivity of the stomata to decreases in vapour pressure deficit (VPD) than to solar radiation. The relationship between stomatal conductance and VPD has been described either by a curvilinear and simple linear decay function for Arabica (Fanjul et al. 1985; Gutiérrez and Meinzer 1994; Gutiérrez et al. 1994; Kanechi et al. 2005) probably due to the nutritional demand in the flowering and Robusta (Pinheiro et al. 2005) coffees, respectively