The water and energy exchange of a shaded coffee plantation in the lower montane cloud forest zone of central Veracruz, Mexico

Abstract

The water and energy fluxes of a shaded coffee plantation in the lower montane cloud forest (LMCF) zone of central Veracruz, Mexico, were measured over a two-year period (September 2006–August 2008) using the eddy covariance method. Complementary measurements of throughfall and stemflow were made to study rainfall interception. The sum of the observed sensible (H) and latent (λE) heat fluxes was almost 95% of the net radiation (Rn) minus the canopy heat storage fluxes, indicating very good energy balance closure. The mean annual evapotranspiration was 1066mm, and 95% of the corresponding FAO Penman-Monteith reference evapotranspiration (ET0) of 1117mm yr−1. Interception loss was 8% of annual rainfall (1386mm). Both the eddy covariance, and the throughfall and stemflow measurements showed average wet-canopy evaporation rate to be very low (0.05mmh−1) compared to the corresponding rainfall rate (3.06mmh−1). As a result, and despite the low canopy storage capacity of the coffee plantation (Cm, 0.50mm), interception was dominated by post-event evaporation of intercepted water rather than by within-event evaporation. Comparing the results for the coffee plantation with interception data from mature and secondary LMCFs in the study area suggests that the conversion of LMCF to shade-coffee may lead to a decrease in interception loss of 8−18% of incident rainfall. This decrease is caused by a three- to seven-fold decrease in Cm, probably due to the lower leaf area and smaller epiphyte biomass of the coffee plantation. The mean annual dry-canopy evaporation was 992mm, and 89% of ET0. Comparing the eddy covariance-based estimate of dry-canopy evaporation for the coffee plantation with sapflow-based estimates of transpiration for the LMCFs did not show any clear differences.