Assessing longleaf pine (Pinus palustris) restoration after southern pine beetle kill using a compact experimental design

Abstract

A compact experimental design and analysis is presented of longleaf pine (Pinus palustris) survival and growth in a restoration project in the Piedmont region of Georgia, USA. Longleaf pine seedlings were planted after salvage logging and broadcast burning in areas of catastrophic southern pine beetle (Dendroctonus frontalis) attacks on even-aged mixed pine–hardwood forests. The split-plot design with randomized complete blocks was replicated on four sites. Main treatments were: chemical control of competing vegetation with herbicides; mechanical mowing to remove above-ground competition; and an untreated control. Nested within fixed-area treatment plots were single-tree plots centered on longleaf pine seedlings where adjacent vegetation was assessed immediately before treatment in years 1 and 2. Treatments applied to single-tree plots comprised three sizes of sprayed area around seedlings in chemical treatment plots. Logistic mixed-effects models indicated that initial survival was impacted by herbaceous vegetation but remained unaffected by the various vegetation control treatments applied later in year 1. Control of above- and below-ground competition around planted seedlings by mowing in conjunction with herbicide treatments resulted in significantly greater frequency of emergence from the grass stage, accelerating development of longleaf pine planted to restore beetle-killed areas in the Piedmont region of Georgia.

Keywords:

• logistic mixed-effects model
• Pinus palustris
• split-plot design
• stand establishment
• weed control

Acknowledgements

Support was provided by the USDA Forest Service Southern Research Station Center for Disturbance Science, the Georgia Forestry Commission and the Humboldt State University Sponsored Programs Foundation. John Moore planned and managed the site preparation and tree planting operations, assisted in study design and planning, and provided logistical support and valuable advice on mechanical and chemical weed control. David Combs performed the botanical survey, and provided extensive technical support and field assistance. Field assistance was also provided by Rex Dagley, Eric Everett, Aaron Green and Greta Langhenry.