Evaluating Native Shrub Plantings as a Control for Tall-Growing Woody Tree Species in Powerline Rights-of-Way

摘要

The effectiveness of planted native shrubs as a method for suppressing undesirable tall-growing trees is being evaluated at six recently constructed powerline right-of-way locations in northern Georgia. Three of the sites were formerly forested, and three were a herbaceous/grass/wooded mixture prior to line construction. At each site two shrub spacing treatments (1x1 and 2 x 2 m) and a control shrub spacing (1.5 x 1.5 m) of native shrub seedlings were established in a Randomized Complete Block design after an initial site vegetation survey. Shrub plantings were established without the use of herbicides or mechanical site preparation. Survivorship of planted shrubs across all sites declined from 72% in the first growing season to 38% at the end of the third growing season. Results show that in the first growing season after shrub planting the competition from tall-growing woody stems increased dramatically from 4 to 10 fold. In the second growing season, tall-growing woody stem densities on the formerly forested sites (high pre-planting tall-woody stems density) increased an additional 20-40. On sites with high grass /herbaceous coverage, tall-growing woody stem densities decreased by an average of 20% in the second growing season. Planted shrub spacing treatments so far have not significantly affected the numbers of tall-growing tree seedlings/sprouts after three growing seasons. The effectiveness of shrub plantings may have been further limited by early growing season drought effects on the growth and survival of the planted shrubs.