Rainfall interception in a lower montane forest in Ecuador: effects of canopy properties

Rainfall interception in forests is influenced by properties of the canopy that tend to vary over small distances. Our objectives were: (i) to determine the variables needed to model the interception loss of the canopy of a lower montane forest in south Ecuador, i.e. the storage capacity of the leaves S and of the trunks and branches S(t), and the fractions of direct throughfall p and stemflow p(t); (ii) to assess the influence of canopy density and epiphyte coverage of trees on the interception of rainfall and subsequent evaporation losses. The study site was located on the eastern slope of the eastern cordillera in the south Ecuadorian Andes at 1900-2000 m above sea level. We monitored incident rainfall, throughfall, and stemflow between April 1998 and April 2001. In 2001, the leaf area index (LAI), inferred from light transmission, and epiphyte coverage was determined. The mean annual incident rainfall at three gauging stations ranged between 2319 and 2561 mm. The mean annual interception loss at five study transects in the forest varied between 591 and 1321 mm, i.e. between 25 and 52% of the incident rainfall. Mean S was estimated at 1(.)91 mm for relatively dry weeks with a regression model and at 2(.)46 mm for all weeks with the analytical Gash model; the respective estimates of mean S(t) were 0(.)04 mm and 0(.)09 mm, of mean p were 0(.)42 and 0(.)63, and of mean pt were 0(.)003 and 0(.)012. The LAI ranged from 5(.)19 to 9(.)32. Epiphytes, mostly bryophytes, covered up to 80% of the trunk and branch surfaces. The fraction of direct throughfall p and the LAI correlated significantly with interception loss (Pearson's correlation coefficient r = -0(.)77 and 0(.)35 respectively, n = 40). Bryophyte and lichen coverage tended to decrease S, and vascular epiphytes tended to increase it, although there was no significant correlation between epiphyte coverage and interception loss. Our results demonstrate that canopy density influences interception loss but only explains part of the total variation in interception loss. Copyright (c) 2004 John Wiley & Sons, Ltd.