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Browsing by Author "Shannon, Joseph"

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    Canopy transpiration and water yield changes following forest canopy conversion in Northern Minnesota.
    (2011-03) Shannon, Joseph
    In 1980, the upland aspen (Populus tremuloides & P. grandidentata) portion of the S6 watershed of the Marcell Experimental Forest was clearcut and subsequently converted to red pine (Pinus resinosa) and white spruce (Picea glauca). Comparisons of water yield observed at S6 and that predicted using the aspen dominated S2 control watershed, suggest that streamflow from S6 has decreased over the past two decades as the conifers have matured. Granier-style thermal dissipation probes were used to quantify sap flux in 36 trees in S2 and S6 throughout the growing season to determine if transpiration rates differed between the two watersheds. Representative sample trees were selected according to factors which may cause sap-flux rates to differ: tree species, slope position, and slope aspect. Using forest inventory data, sap-flux rates were up-scaled to watershed canopy transpiration. Transpiration losses in the S6 watershed were 30% greater than those in S2 for the duration of the study period. Differences were primarily driven by a longer growing season in conifers and greater forest basal area in S6. By representatively sampling forest species it is possible to show that 40 - 50% of transpiration in each watershed is the result of one dominant species, red pine or aspen, in the experimental or control watersheds respectively. Future use of these data will include combination with concurrent interception and flow routing studies to better evaluate hydrologic impacts of similar management decisions in the future. Forest conversion is an ongoing management strategy that brings about long-term effects on streamflow. Understanding these effects allows better prediction of the effect of management on water resources.