Abstract
A 27-month-long study was conducted to compare the impacts of Imperata cylindrica (L.) (Beauv.) and native vegetation competition on the productivity of Pinus taeda (L.) seedlings. In March 2003, 1-year-old pine seedlings were planted in the following treatments: vegetation free (VF), native competition (NC), and I. cylindrica (IC) competition. At the end of the study, only 26% of the IC seedlings survived, half of what was observed in the NC treatment. The IC seedlings had significantly smaller root collar diameter than the NC seedlings (P < 0.0001) after the first growing season and by the end of the third growing season the height and stem volume index were significantly less as well (P < 0.0001). After one full growing season, the NC and IC pine seedlings had 21 and 11.5% of the total biomass of the VF seedlings, respectively. After three growing seasons, the IC pine seedling total biomass was 2.4% of that of the VF seedlings and 18% of that of the NC seedlings (P < 0.0001). The greatest difference was in the pine needle biomass with the IC pine needle biomass being only 11% of that of the NC. During the first growing season, the IC pine seedlings maintained the lowest levels of light-saturated net photosynthesis and stomatal conductance. These results may be explained by reduced amounts of foliar nitrogen and water stress that result from I. cylindrica competition. The pines in the IC treatment had the lowest total foliar surface area and the lowest specific leaf area, which may explain the reduced productivity. Evidence from this study suggests that I. cylindrica competition significantly reduces the productivity and growth of P. taeda seedlings compared with that from native vegetation.