Large Trees to Different Amounts of Available Soil Water 1

Introduction A method was developed to manipulate avai lable so i l water on large trees by intercepting thrufal l with gutters placed under tree canopies and irrigating the intercepted thrufal l onto other trees . With this design, trees were exposed for 2 years to either 25 percent less thrufal l , normal thrufal l , or 25 percent addit ional thrufal l . Undercanopy construction in these plots moderately af fected patterns of thrufal l entry onto the forest Boor when compared to a plot without construction. In this pilot study, a variety of aboveground and belowground measurements were recorded from trees over the 2-year period. Additional amounts of thrufall increased circumference growth, l i t ter fa l l , fine-root biomass , ectomycorrhizal development , and number of fruit ing bodies of ectomycorrhizal fungi . Intercepted thrufall decreased amounts of ergosterol, a surrogate for soil a n d r o o t o r i g i n fungal biomass. Recommendations are made to improve and simplify the design, including arranging gutters to intercept more or less thrufal l at any t ime of year .