Stem flow is the water from precipitation that is intercepted by plant canopies and conveyed down the outside of stems to wet the soil at the base of the plant. For western juniper (Juniperus occidentalis Hook.) trees, stem flow was only a small fraction of the precipitation intercepted by the canopy. However, this moisture may be important in the nutrient flux of the trees. The first stem flow in the fall after the summer drought was enriched in nitrate-nitrogen although the quantity of nitrogen per unit area was small. The combination of favorable moisture and temperature conditions at the base of the tree leads to litter decay and nitrification. The root system of the trees had many fine roots in the area that received stem flow. Canopy interception and stem flow should be taken into consideration in application of soil active herbicides for control of western juniper.
