Abstract:
To accomplish an economic evaluation of vegetation management in
loblolly pine (Pinus taeda L.) at regeneration and a subsequent release
time, two existing growth models were linked together in a dynamic
programming analysis. The first model (Burkhart and Sprinz, 1984) provides
a projection of stands regenerated with varying hardwood components but
does not allow intermediate thinning or release entries. The second model
(Cao et a/.,, 1982) permits density control through intermediate thinning in
pure conifer stands without hardwoods. The combined growth model covers a
whole rotation and, hence, vegetation control, intermediate thinnings, and
final harvest can be optimized jointly.
The resulting analytic model can be used to assess most vegetation
management and thinning alternatives including site preparation treatment
without subsequent density control of hardwoods. It excludes alternatives that
involve conifer density control without previous or concurrent total hardwood
removal. The performance of the model indicates that the dynamic programming formulation was able to characterize the economic problem and
the interrelationships between vegetation management and further stand
development.
The economic gains with high interest rates (8 Z) are comparable to
current vegetation management costs experienced, while at lower rates the
gains are several times current costs. Additional insights to vegetation
management impacts are provided through observations on the rotation
lengthening impact of any sizeable hardwood component, and through the
Impacts of hardwood vegetation on both volume and large diameter tree
production.
The optimization model also gives new opportunities for analysis of pure
loblolly pine stands. The three dimensional dynamic programming network
takes Into account the acceleration in diameter growth resulting from thinnings.
Quality premiums in sawtimber prices and thinning entry costs can be varied to
provide flexibility for economic analysis.
Keywords: Dynamic programming optimization, economic analysis, loblolly
pine (Pinus Teede L.), thinning regime, vegetation management.
