The chemistry and flux of throughfall and stemflow in subalpine balsam fir forests

The fluxes of water and chemicals in throughfall and stemflow of three subalpine balsam fir forests of New Hampshire, USA were measured. The three fir stands were highly dissimilar in structural characteristics, serving as a test of the importance of stand structure on these fluxes. The sum of throughfall and stemflow water exceeded incident precipitation by more than 18 to 29%. This difference was attributed to the unmeasured input of cloud droplets impacted on canopy surfaces. The principal effect of stand structure was a positive relationship between stand density and stemflow. The flux of NH⁺₄, Na⁺, SO⁼₄ and Cl⁻ in stemflow was also significantly higher in the most dense stand. The fir canopy effects on capture and chemical alterations of elements were compared with analogous behavior of a nearby deciduous forest. There were several major contrasts, the most striking of which was a flux/canopy pool ratio (leachability index) in the hardwood canopy ranging from two to 32 times higher than in the fir canopy.