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Harvard Forest REU Symposium Abstract 2023
- Title: Seedling persistence and passage in a hemlock-hardwood forest: filling in the gaps
- Author: Isabella L Stone (Willamette University)
- Abstract:
Natural disturbance events often create canopy gaps, driving changes in forest structure and composition. Understory individuals compete for resources made available by canopy tree death. We investigated how gap-phase dynamics impact seedling regeneration to understand how long it takes for a seedling to reach the sapling layer and how many seedlings it takes to make a sapling for five temperate forest tree species. We related seedling height and age while controlling for gaps. We collected data in 402 plots (1 m2), located in the Harvard ForestGEO plot, arrayed around recently dead canopy trees (n = 53) and 16 live control trees. All woody seedlings with a DBH less than 1 cm were identified, mapped (within the 1 m2 plot), and measured for height in 2021, 2022 and 2023. Canopy cover was rated 1-5 from complete shade to complete sun per plot. We projected the number of seedlings required to make one 1.5 m sapling and passage time to that height. We found that the passage time for seedlings varied across species with a maximum of 48 years for eastern hemlock under closed canopies, and minimum of 13 years for birch in full canopy gaps. We simulated that it would require at least 20 seedlings for birch in canopy gaps and at the other extreme hemlocks needed an average of 115 seedlings under closed canopies to make one sapling. We harvested seedlings under different light levels to compare to our predicted age-to-height correlations. We found that our estimated age for a given height was significantly less than the observed age for the same height suggesting our projects of passage time were conservative. Our results highlight the longevity of seedlings in the understory and the importance of canopy gaps for sapling recruitment.
- Research Category: Physiological Ecology, Population Dynamics, and Species Interactions; Large Experiments and Permanent Plot Studies
