PARENT SESSION
Poster Session # 14: Forest Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Overstory retention in longleaf pine forests: resource effects and regeneration responses.

Pecot, Stephen^*,1, Mitchell, Robert¹, Palik, Brian², Jones, Robert³, Mou, Paul⁴, ¹ Joseph W. Jones Ecological Research Center, Newton, GA, USA² USDA Forest Service, Grand Rapids, MN, USA³ Virginia Polytechnic Institute and State University, Blacksburg, VA, USA⁴ University of North Carolina, Greensboro, NC, USA

ABSTRACT- Recent interest in variable overstory retention silviculture has resulted from a desire to mimic the complex structure resulting from natural disturbances. However, overstory retention benefits are tempered by increased competition between the overstory and seedlings. To investigate these competitive interactions in longleaf pine ecosystems we used treatment plots 2 ha in size (with three replications) that were harvested to similar residual basal areas using three removal techniques: single–tree, small group (∼0.08 ha), and large group (∼0.18 ha) selection. Uncut control plots were also established. We sampled resources (light, soil water, and nutrients) as well as seedling growth and survival throughout the range of overstory density in each plot. Annual percent light transmittance varied greatly (35 to 80% of the maximum). Light reaching the understory was closely related to overstory abundance (r²=0.76) and was predicted well using hemispherical photographs (r²=0.77). Available nitrogen (measured with ion exchange resin membranes) greatly increased only in open areas where the understory was controlled (r²=0.59). Pine root production compensated for reduction in non-pine roots if understory vegetation was removed (P<0.001); however, in large gaps, non-pine roots quickly filled root gaps if the understory was left intact (P=0.015). Seedling growth was closely related to overstory density (r²=0.55). Large increases in resource availability in open areas (>65% gap fraction) suggest that grouped removal patterns facilitate greater seedling growth through higher light and N availability (though at a cost through increased belowground competition from non–pine roots) as well as less light captured by the overstory. These data argue that manipulation of the spatial distribution of overstory trees may allow for land managers to retain the benefits of overstory retention while allowing for regeneration of longleaf pine.

Key words: longleaf pine, variable overstory retention, regeneration, gaps