First through fourth growing season responses of planted loblolly pine to thinning in the Western Gulf RegionThis article is part of a larger document. View the larger document here.
Thinning is commonly used in managing loblolly pine (Pinus taeda L.) plantations in the Western Gulf Region. While long-term loblolly pine growth responses to thinning have been well documented, understanding of the response in the first couple of years after thinning is limited. Data were collected for a loblolly pine thinning study from 16 sites across east Texas and western Louisiana over the first four growing seasons following thinning. Three thinning intensities, with residual stockings of 150, 225, and 300 trees per acre after thinning, and an un-thinned control were implemented across a range of sites with varying edaphic conditions. Thinning was performed at a stand age of approximately 12 years by removing every fifth row and then thinning from below poor quality trees from remaining rows. Thinning responses were expressed in relative terms by calculating the difference between a treatment mean and the control mean and expressing it as a percentage of the control mean. Results showed that (1) growth responses in diameter at breast height (d.b.h.) were positive at all thinning intensities, and the responses were stronger for the heavier thinning intensities and increased with year after thinning; (2) growth responses in total height were negligible, especially for heavier thinning intensities; and (3) tree size affected thinning responses both in d.b.h. and height growth, depending on the year post-thinning. Small trees (d.b.h. class of 6 inches) had the largest responses in d.b.h. growth but the responses of the medium (d.b.h. class of 8 inches) and large trees (d.b.h. class of 10 inches) increased with year until year 3. Responses in height growth of small trees were positive at year 1, in particular for heavier thinning, but became negligible
after three growing seasons, while medium and large trees showed an opposite pattern, with the responses being small and negative initially but becoming positive, although small, at year 4. These results provide important information regarding early response of loblolly pine plantations to thinning in the Western Gulf Region.