Early competitive effects on growth of loblolly pine grown in co-culture with switchgrass
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This study: (1) examined competitive interactions between switchgrass and loblolly pine grown in co-culture, and (2) assessed early growth rates of loblolly pine as affected by differing switchgrass competition treatments. Co-cultures were established and monitored on two Upper Coastal Plain sites for 2 years. The Pontotoc site has a history of agricultural use with some likely residual fertility, while the Starr site has a history of forest use, although it has been maintained for several decades as a mowed field. Five treatments were employed at each site: (1) switchgrass only (SG); (2) pine only (Pine); (3) pine planted into switchgrass with a 1.2-m competition-free zone on either side of the row of trees (PS-4); (4) pine in switchgrass with a 0.6-m competition-free zone (PS-2); (5) and pine planted into switchgrass with no-competition free zone (PS-0). Switchgrass yields at Starr were roughly one quarter of those at Pontotoc, which led to differences in competitive intensities between species at the two sites. Loblolly pine heights at Pontotoc and Starr averaged 70 and 63 cm following year 1, and 161 and 176 cm following year 2, respectively. Planting pines directly into switchgrass significantly reduced tree heights, but seedlings in PS-4 treatments experienced growth ≥ Pine treatments. Switchgrass yields did not significantly differ by distance from tree row for any treatment. Ourresults suggest switchgrass dominates resource competition in early phases of this production system. However, these competitive pressures can be managed to effectively co-produce loblolly pine and switchgrass on southern lands.