Date of Award

Spring 5-25-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

D. Paul Jackson

Abstract

Sonderegger pine (Pinus x sondereggeri H.H. Chapm.), the naturally occurring hybrid of longleaf (Pinus palustris Mill.) and loblolly pine (Pinus taeda L.), is considered a producer of poor-quality wood due to observations of stem forking and a high number of large-diameter branches at maturity. Because landowners generally decline planting Sonderegger pine seedlings, nursery workers cull putative hybrids from longleaf pine seedling stock during lifting and processing. However, over the past 100 years, very few studies have quantified stem quality of Sonderegger pine. To gain a better understanding of the early growth and development of Sonderegger pine, evaluations of height, diameter at breast height (DBH), bole (i.e., stem) form, and disease occurrence were made on five-year-old trees planted on the Catahoula Ranger District of Kisatchie National Forest in March 2018. Of the 102 trees evaluated, 65 (64%) were free of stem and branch defects, and less than 6% had fusiform rust (Cronartium quercuum f. sp. fusiforme). Branch frequency and branch diameter were strongly correlated with height and DBH. On an index scoring basis, 50% of trees had fewer branches or branches that were smaller in diameter when compared with other trees in the same height class (< 1.4 m, 1.4 to 3.0 m, > 3.0 m). Sonderegger pines showed a wide range in phenotype, which may suggest that (1) F1 hybrids can exhibit strong tendencies toward one parent species and (2) Sonderegger pine phenotypes are strongly influenced by the genetic quality of the hybridizing parent trees. Sonderegger pine seedlings commonly occur in longleaf pine seedlots grown in southern forest tree seedling nurseries. For decades, the initiation of height growth (12 to 15 cm) in longleaf pine seedlots has been used to indicate that hybridization with loblolly pine has occurred. However, research documenting Sonderegger pine seedling morphology has not been published for more than 60 years, and to our knowledge, no seedling quality assessments have been made. To better understand how morphological traits of longleaf and loblolly pine are expressed in hybrid seedlings, shoot height, root collar diameter (RCD), and hypocotyl length were compared among one-year-old container-grown longleaf, loblolly, and Sonderegger pine seedlings. Sonderegger pine seedlings had a range of stem development, with the majority (62%) of seedlings measuring less than 12 cm tall. Pure longleaf pine seedlings had up to 10 cm of stem elongation, but the cause of early height growth in these seedlings is unknown. More than 90% of Sonderegger pine seedlings met or exceeded RCD recommendations for loblolly (≥ 3.2 mm) and longleaf pine (≥ 4.75 mm).

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