Technical resource bulletin. TRB-009, Comparing the growth of longleaf and loblolly pine on two soil types in North Carolina

Technical Resource Bulletin Comparing the Growth of Longleaf and Loblolly Pine on Two Soil Types in North Carolina Bill Pickens. NC Forest Service, Raleigh NC Longleaf pine has long had the reputation as a slow growing species unable to compete with loblolly pine. Boyer addressed what he called an “inherent bias’’ toward longleaf in a paper titled Longleaf Can Catch-up (Boyer 1996) in which he docu¬ mented longleaf growth rates to become equal and eventually surpass those of loblolly pine According to Boyer longleaf height catches up to loblolly between 25 to 30 years old espe¬ cially on medium to low quality sites. Studies show that only on the very best sites does loblolly maintain a growth advantage over longleaf (Scmidling 1987, Outcult 1993). Once height growth begins longleaf grows as quickly as loblolly on most sites, and better on some. The NCFS installed three demo sites to document longleaf growth rates after the grass stage, demonstrate its ability to catch-up to loblolly, and dispel the slow growth myth associat¬ ed with longleaf pine forest management. Two are both high quality (94 SI base 50 loblolly) Raines soil site typically thought of as more suitable for loblolly plantation. It was plant¬ ed in 1987, measured annually beginning at age 2, and last measured at age 10. The second site was also established in 1987, first measured at age 8, and last measured at age 17. The third is a lower quality site (80 — 85 SI base 50 loblolly) featur¬ ing Centenary and Lakeland sand soil type. This soil is often described as a typical longleaf site. It was established in 2000 and last measured at age 14. We abandoned both sites on the Raines soil after the first was adversely impacted by hurricane damage, and the second changed ownership and was harvested. We continue to measure the sand soil site. Results Raines Soil #1 After 10 growing seasons, we measured the average height of the longleaf trees at 25.2 feet and loblolly trees at 27.0 feet. The diameter at age 10 was 4.0 inches for the longleaf and 4.5 inch¬ es for the loblolly. The longleaf pine grew on average 2.52 feet per, while the loblolly pine grew at 2.70 feet per year. In this study we found that 88 % of the longleaf had initiated height growth after the first growing sea¬ son. If we calculate a mean annual incre¬ Figurel. Height from age 2 through age 10 measured on Raines #1. Height г i i • i i i Ml ment for the 9 years after height growth began, we find the longleaf trees grew on average 2.8 1 feet per year. Figure 1 . shows loblolly height advantage from age 2 through age 1 0. At Table 1 . Site #1 diameters, heights, and periodic annual increment from age 2 through age 10 on a high quality Raines soil type. Longleaf Loblolly Age DBH (in.) Longleaf HGHT (ft) LL Height PA1 LL Height РЛ1 (3 \r inter DBH (in.) Loblolly Height (ft) Lob Height PA1 Lob Hght PA1 (3 yr inter) 2 na 1.1 0.6 na 1.4 0.7 3 na 3.1 2 1 na 3.6 2.2 1.2 5 1.9 8.8 2.9 1.8 9.6 3 6 2.7 12.4 3.6 2.2 13.4 3.8 7 2.9 16.8 4.4 3.3 3 18.7 5.3 3.6 8 3.2 18.7 1.9 3.4 20.4 1.7 9 3.6 22.2 3.5 4 24.3 3.9 10 4 25.2 3 2.8 4.5 27 2.7 2.8 age 10 the height longleaf trees is 93 percent that of the loblolly trees. Raines Soil #2 After 1 7 growing seasons the dominant and codominant long¬ leaf and loblolly trees were on average 47.7 feet and 54.0 feet tall respectively. The measured trees averaged a DBI I of 6.6 inches for longleaf and 8.3 inches for loblolly. As expected loblolly outgrew longleaf in height by 0.4 feet per year. The mean annual increment (MAI) for loblolly is 3.2 feet per year compared to 2.8 feet per year for longleaf. From age 9 through 17 the difference in annual height growth was only 0.2 feet per year. For those nine growing seasons the periodic annual incre- Table 2. Site #2 : DBH. height, and periodic annua! increments from age 8-17 for loblolly and longleaf on a Raines soil trees planted on a Raines soil Diameter (inches) Height (feet) •Age 8 Age 11 •Age 17 PA1 AgcO - 8 РЛ1 Age 9 -17 MAI Age 0 - 17 AgeS •Age 11 Age 17 РЛ1 Age 0 - 8 PA1 Age 9 -17 MAI Age 0 - 17 Longleaf 3.12 4.55 6.55 0.39 0.38 0.39 18.34 27.20 47.70 2.29 3.26 2.81 Loblolly 4.36 5.61 8.25 0.55 0.43 0.49 22.70 32.10 54.00 2.84 3.48 3.18