Growth and injury patterns of eastern white pine (Pinus strobus L.) seedlings as affected by hardwood overstory density and weeding treatments

Abstract

White pine seedlings were underplanted under a range of overstory densities in a hardwood stand in northern Minnesota. Vegetation surrounding seedlings was left untreated (control), weeded annually, or completely removed through monthly weeding. After 4 years, the benefit of weeding woody competition for diameter growth of seedlings was limited to areas with relatively open overstory conditions. Seedling height growth was reduced in areas with higher overstory density, but improved through weeding treatments that removed woody vegetation. The removal of herbaceous vegetation did not improve growth of seedlings in any conditions. Open growing conditions created by overstory removal and weed control resulted in higher incidences of seedling injuries, e.g., through infection by white pine blister rust. Conditions for pine bark adelgids also were enhanced in areas with low overstory densities and weeding treatments. The incidence for white pine weevil seems to follow a similar pattern, although the number of trees infected was minimal. Results show that improving growing conditions through management of the overstory and understory vegetation improves seedling growth rates, but must be balanced with potentially higher incidences of seedling injuries under more open conditions.