COS 291-6 - Does longleaf pine cone production correlate with seed production, size, and germination rate?

Abstract: Successful natural regeneration of fire-dependent longleaf pine (Pinus palustris Mill.) ecosystems of the southeastern U.S. requires viable seed sources. Most studies focus on cone production, which is relatively easy to measure. However, it is unclear whether seed production and viability mirror cone production, which may be unrelated at high cone production levels. The objectives of our study were to 1) Determine the relationship between cone production and seed production across individual mature longleaf pine trees, 2) Determine whether cone production and seed size characteristics are related in mature longleaf pine trees, and 3) Determine whether seed germination rates vary with cone production. To better understand longleaf pine cone-seed relationships, we collected longleaf pine seeds from trees representing a gradient of cone production during seedfall (mid-October to early December) in 2021 and 2022. For the 2021 collection, we collected seeds from 10 trees at the Jones Center at Ichauway (Newton, Georgia, U.S.A.), using 10 0.25-m² seed traps placed under each tree. For the 2022 collection, we collected seeds from 10 trees each at Blackwater River State Forest (Milton, Florida, U.S.A.), Eglin Air Force Base (Fort Walton Beach, Florida, U.S.A.), and the Jones Center at Ichauway, using three 3-m² seed traps under each tree. We tallied seeds to determine seed production and measured seed characteristics (length, width, and mass) to explore seed size trends and their relationship with cone production and seed viability. Collected seeds were visually examined and classified as undeveloped (wing with no seed present), developed (wing with seed present), or damaged (visible damage to the seed). We are also conducting germination trials with collected seeds in a growth chamber under controlled conditions (20 °C, 16:8 hr light:dark). Preliminary results for 2022 indicate that total seed production across all 30 trees increases linearly with cone production (R² = 0.16, P = 0.026), with 2.84 (± 2.47; ± 95% C.I.) more seeds collected per additional cone produced. We observed a 1.17 (± 1.23; ± 95% C.I.) seed increase in developed seed production for every additional cone produced in 2022; however, these results were not statistically significant (R² = 0.12; P = 0.062). We found no relationships between seed size metrics and cone production. Identifying the relationships between cone production, seed production, and seed size will provide managers and landowners with a better method of predicting success of natural regeneration efforts in their longleaf pine stands.