Value of Tree Measurements Made at Age 5 Years for Predicting the Height and Diameter Growth at Age 25 Years in Loblolly Pine Plantations

Abstract

Early growth measurements Of pine plantations are often used to predict the productivity of the stand later in the rotation when assessing the effect Of management on productivity. A loblolly pine (Pinus taeda L.) study established at 35 locations (2 to 3 plots/location) was used to test the relationship between height measurements at age 5 years and productivity at age 25. Mean heights of dominant and codominant trees at age 25 were used to represent site index at a locatIon; basal area growth per tree from ages 20 to 25 was used as an index of individual tree growth. The plot data showed a relatively weak relationship (r²=0.40) between heights at age 5 and site index. Ranking age-5 heights and using only taller trees did little to improve the relationship. The fit of the regression equation changed gradually from an 12 of 0.45, when only the tallest tree was used, to an 12 of 0.43 when the tallest one-half of all trees was used. Using more trees did not degrade that relationship. As all trees must be measured to determine the tallest group, little is gained by attempting to designate dominant and codominants or crop trees for use in analyses and interpretations. Overall, predictions of stand productivity at age 25 using only individual tree parameters based on height at age 5 were of little value, accounting for only about 20 percent of the variation. Although plot location and rank of the tree within a plot each accounted for about 10 percent of the variability at age 25, a nearest-neighbor competition index and height at age 5 accounted for less than 0.1 percent each. However, rank by height at age 5 was an excellent predictor of individual tree survival, with 95-percent survival at age 25 for the tallest pines and almost no survival for the shortest pines. Based on the results of this study, we surmise that accurate modeling of stand development from early measurements probably requires more site information, such as amount and type of competing vegetation, soil properties, and a history of the land management.

Citation

Tiarks, Allan E.; Meier, Calvin E.; Baldwin, V. Clark, Jr.; Haywood, James D. 1998. Value of Tree Measurements Made at Age 5 Years for Predicting the Height and Diameter Growth at Age 25 Years in Loblolly Pine Plantations. Proceedings of the Ninth Biennial Southern Silvicultural Research Conference