Growth, yield, and structure of extended rotation Pinus resinosa stands in Minnesota, USA

Extended rotations are increasingly used to meet ecological objectives on forestland; however, information about long-term growth and yield of these systems is lacking for most forests in North America. Additionally, long-term growth responses to repeated thinnings in older stands have received little attention. We addressed these needs by examining the growth and yield of red pine (Pinus resinosa Ait.) in a growing stock experiment in northern Minnesota. Stands were 85 years old at the onset of this experiment and were repeatedly thinned to five levels of basal area (13.8, 18.4, 23.0, 27.5, and 32.1 m2·ha-1) over 58 years. Cumulative volume production and volume growth were lowest within the lowest stocking treatment and similar across other stocking levels. Late-successional structural attributes, such as the density of trees with ‡40 cm diameter at breast height, was similar across stocking levels. The mean annual volume growth culminated between 130 and 140 years. Additionally, positive growth responses were observed within the highest stocking-level treatments after thinning at 138 years, demonstrating the ability of older red pine to respond to reductions in competition. These results illustrate that extended rotations with repeated thinnings in red pine help achieve ecological goals, including the restoration of old-forest structure, while also maintaining high levels of stand productivity.