Effects of aerial strip spraying on mixedwood stand structure and tree growth

Abstract

Herbicide application in strips offers a cost-effective way to accelerate spruce growth in young mixedwood stands, while also retaining the mixedwood character of the stand. In June of 2006 data were collected to evaluate the effects of aerial strip spraying on subsequent growth of treated stands. These blocks had been planted in 1991 and treated in 2000 with Triclopyr ester herbicide applied in strips. Treated and untreated strips averaged 5.8 m and 8.4 m in width, respectively, with 38% of the block area being effectively treated. In 2006 aspen density, DBH, and height were significantly lower in the treated strips compared to either untreated strips or completely untreated blocks. Spruce growth was significantly larger in treated strips with diameter growth responses beginning in the first and height growth responses in the second growing season following treatment. Yield estimates from the Mixedwood Growth Model (MGM) indicate that the strip spray treatments result in the highest spruce yields. However, when understory protection (harvesting aspen at age 70 and spruce at 120) is applied, the untreated blocks provided higher total yield and net present value.