Effects of Ponderosa Pine Treatments on Water Yield in Arizona

Annual water yields were determined for three levels of overstory removal and three levels of strip cut with thinning applied on ponderosa pine watersheds. Water yield increases from a completely cleared watershed were statistically significant for 7 years, losing significance after recovery and growth of Gambel oak and herbaceous vegetation. Water yield increases were maintained 6 years after a light overstory removal and 10 years following a heavy overstory removal cut. Significant increases were obtained for 3–4 years following two levels of strip cut with thinning, but were then lost on watersheds with a high percentage of southern exposure or low slopes. Water yield increase remained at a 15% level during the first 6 years on a strip‐cut watershed with 60% of its area on northern aspects.