Abstract: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 1Ð91 mm for relatively dry weeks with a regression model and at 2Ð46 mm for all weeks with the analytical Gash model; the respective estimates of mean S t were 0Ð04 mm and 0Ð09 mm, of mean p were 0Ð42 and 0Ð63, and of mean p t were 0Ð003 and 0Ð012. The LAI ranged from 5Ð19 to 9Ð32. 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 D 0Ð77 and 0Ð35 respectively, n D 40). Bryophyte and lichen coverage tended to decrease S t 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.

Abstract:The water budget of forested catchments controls the local water supply and influences the regional climate. To assess the anthropogenic impact on the water cycle, we constructed a water budget for three ¾10 ha catchments under lower montane forest on the east-facing slope of the Andes in south Ecuador at 1900-2150 m elevation. We used field hydrological measurements and modelled surface flows with TOPMODEL, a semi-distributed catchment model. We measured incident precipitation, throughfall, stemflow, and surface flow between May 1998 and April 2002 in hourly to weekly resolution, and determined all variables needed to parameterise TOPMODEL. On average, of the four monitored years and three catchments, incident precipitation was 2504 š SD 123 mm, throughfall 1473 š 197 mm, and stemflow 25 š 2 mm yr 1 . Fog water input was negligible. Mean annual interception loss in the forest was 1006 š 270 mm, and mean annual surface flow, calculated with TOPMODEL in an hourly resolution was 1039 š 48 mm. The resulting mean annual evapotranspiration was 1466 š 161 mm of which 32% (D471 š 162 mm) was transpiration if evaporation from the soil was neglected. Our study catchments show a high evapotranspiration attributable to the strong solar insolation near the equator, the small impact of fog, the generally low intensity of incident precipitation and additional wind-driven advective energy input.

The N, P, and S cycles in pristine forests are assumed to differ from those of anthropogenically impacted areas, but there are only a few studies to support this. Our objective was therefore to assess the controls of N, P, and S release, immobilization, and transport in a remote tropical montane forest. The study forest is located on steep slopes of the northern Andes in Ecuador. We determined the concentrations of NO 3 -N, NH 4 -N, dissolved organic N (DON), PO 4 -P, dissolved organic P (DOP), SO 4 -S, dissolved organic S (DOS), and dissolved organic C (DOC) in rainfall, throughfall, stemflow, lateral flow (in the organic layer), litter leachate, mineral soil solution, and stream water of three 8-13 ha catchments (1900-2200 m a.s.l.). The organic forms of N, P, and S contributed, on average, 55, 66, and 63% to the total N, P, and S concentrations in all ecosystem fluxes, respectively.The organic layer was the largest source of all N, P, and S species except for inorganic P and S. Most PO 4 was released in the canopy by leaching and most SO 4 in the mineral soil by weathering. The mineral soil was a sink for all studied compounds except for SO 4 . Consequently, concentrations of dissolved inorganic and organic N and P were as low in stream water (TDN: 0.34-0.39 mg N l À1 , P not detectable) as in rainfall (TDN: 0.39-0.48 mg N l À1 , P not detectable), whereas total S concentrations were elevated (stream water: 0.04-0.15, rainfall: 0.01-0.07 mg S l À1 ). Dissolved N, P, and S forms were positively correlated with pH at the scale of soil peda except inorganic S. Soil drying and rewetting promoted the release of dissolved inorganic N. High discharge levels following heavy rainstorms were associated with increased DOC, DON, NO 3 -N and partly also NH 4 -N concentrations in stream water. Nitrate-N concentrations in the stream water were positively correlated with stream discharge during the wetter period of the year. Our results demonstrate that the sources and sinks of N, P, and S were element-specific. More than half of the cycling N, P, and S was organic. Soil pH and moisture were important controls of N, P, and S solubility at the scale of individual soil peda whereas the flow regime influenced the export with stream water.

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