Stand characteristics of inter-cropped loblolly pine and black locust

Abstract

Inter-cropping conifers and hardwoods provides greater economic flexibility, biological diversity and aesthetic benefits, relative to traditional, single species plantations. This study evaluates the biological feasibility of inter-cropping loblolly pine ( Pinus taeda L.) and black locust ( Robinia pseudoacacia L.). Seedlings of both species were established from 1-0 seedlings in pure stands and 25:75, 50:50 and 75:25 mixtures under tall fescue ( Festuca arundinacea Schreb.) cover or maintained weed-free conditions. Both species established well under weed-free conditions but black locust survival and growth were severely reduced by herbaceous cover. After 5 years, herbaceous cover reduced mean stem volume 45% and 88% for loblolly pine and black locust, respectively, relative to weed-free conditions. When grown in mixture, both species had larger stem volume, and crown volume, relative to monocultures. Height to the lowest living branch decreased for both species as the proportion of pine decreased. In loblolly pine, live crown ratio increased and stem height:diameter ratio decreased as the proportion of pine decreased, indicating that intensity of competition for aboveground resources was directly related to the proportion of pine in these stands. Pine foliar N did not vary with stand type or herbaceous cover. The results of this study suggest that mixed stands of loblolly pine and black locust can be established from seedlings, provided herbaceous vegetation is controlled. If the present growth patterns continue, inter-cropping will result in the production of merchantable trees of both species earlier than in monoculture stands.