Profitability analysis of southern plantations through timber alone or timber and carbon integration in pine-sweetgum mixes

Due to their high degree of heterogeneity, mixed forest plantations give rise to numerous questions regarding the economic feasibility of this type of forest management. We simulated the growth of loblolly pine mixed in various proportions with white oak and sweetgum (75–25%, 50–50%, and 25%–75%), two commercially important hardwood species of the southeastern United States, to obtain a better understanding of the optimality of mixed plantation management. The most relevant result was that, in all scenarios, the maximum land expectation values of mixed plantations are higher than the maximum land expectation values of monoculture plantations established for timber production only, and for plantations managed for combined timber production and carbon sequestration. Economically, the optimal mixed forest plantation scenario contains 1125 loblolly pine trees and 375 sweetgum trees per hectare. We identified the density effect between the loblolly pine trees within the mixed plantations as the main factor driving the value of mixed plantations. The mixed white oak and sweetgum trees also increased the maximum land expectation values of the mixed stands in comparison to the less dense monoculture loblolly pine stands. This implies that the incorporation of hardwoods adds timber, but the trees do not represent a substitute for pine. Our analysis showed that mixed forest plantations can be a feasible economic option to diversify the production of timber in the region.