Thinning and Site Quality Effects on the Height-diameter Relationship of Pinus taeda

An experiment in pine (Pinus taeda) stands was conducted aiming to evaluate the thinning and site quality effect on the height-diameter relationship. We applied an analysis of variance in randomized blocks, with blocks representing the sites and treatments the mixed thinning, in which systematic and selective modalities were combined, harvesting every fifth row plus 66%, 54%, 42%, 30% and 19% of the lower canopy trees. Thinnings occurred at 8 and 9 years old interval, and diameters and heights of the trees were measured at age 12. We modeled height-diameter relationship and applied the Graybill test for reducing the number of similar selected models in a same block. We found statistical differences between treatments and blocks. As conclusion, height-diameter relationship varies less between treatments but the curve slope tends to reduce in lower quality sites. Same height-diameter equations can be used in different treatments.