Premium
The absorption and evaporation of water vapor by epiphytes in an old‐growth Douglas‐fir forest during the seasonal summer dry season: Implications for the canopy energy budget
Author(s) -
Pypker Thomas G.,
Unsworth Michael H.,
Van Stan John T.,
Bond Barbara J.
Publication year - 2017
Publication title -
ecohydrology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.982
H-Index - 54
eISSN - 1936-0592
pISSN - 1936-0584
DOI - 10.1002/eco.1801
Subject(s) - epiphyte , canopy , vapour pressure deficit , environmental science , lichen , latent heat , atmospheric sciences , botany , horticulture , hydrology (agriculture) , ecology , biology , photosynthesis , transpiration , geography , physics , geology , meteorology , geotechnical engineering
Our goal was to determine how epiphytic lichens and bryophytes affect canopy latent heat fluxes in an old‐growth Douglas‐fir forest when the canopy was dry. The epiphyte water content (WC e expressed as a percent of dry weight) of representative epiphytic foliose lichens, fruticose lichens, and bryophytes was measured in the laboratory after 1 to 12 hr of exposure at five different values of vapor pressure deficit (VPD). After 12 hr of exposure, WC e increased fivefold to sixfold as VPD decreased from 1849 to 132 Pa. In addition, we measured WC e in the field using strain gauges. These field measurements were used to calibrate the models described below. Two models were created to estimate the potential latent heat flux from epiphytes at the canopy scale (LE e ). The first model combined measured total biomass of epiphytes with a model that estimated the laboratory determined VPD‐dependent changes in WC e of the lichens/bryophytes (VPD method). The second model estimated LE e by scaling the change in WC e of epiphyte‐laden branches that were continuously monitored in situ in the canopy by a strain gauge (SG method). Both methods showed a strong diurnal trend in LE e when VPD was less than 645 Pa. Prior to sunrise, the epiphytes absorbed water, corresponding to a latent heat flux of 5 to 15 W/m 2 per unit ground area, whereas after sunrise, the epiphytes lost water at a rate of −10 to −20 W/m 2 . For short periods, epiphytes may contribute a significant portion of the latent heat flux from Douglas‐fir forests.