The path back: oaks ( Quercus spp.) facilitate longleaf pine ( Pinus palustris ) seedling establishment in xeric sites

Listen to a brief audio clip by author E. Louise Loudermilk describing this publication. • Text Transcript


Understanding plant–plant facilitation is critical for predicting how plant community function will respond to changing disturbance and climate. In longleaf pine (Pinus palustris Mill.) ecosystems of the southeastern United States, understanding processes that affect pine reproduction is imperative for conservation efforts that aim to maintain ecosystem resilience across its wide geographic range and edaphic gradients. Variation in wildland fire and plant–plant interactions may be overlooked in “coarse filter” restoration management, where actions are often prescribed over a variety of ecological conditions with an assumed outcome. For example, hardwood reduction techniques are commonly deemed necessary for ecological restoration of longleaf pine ecosystems, as hardwoods are presumed competitors with longleaf pine seedlings. Natural regeneration dynamics are difficult to test experimentally given the infrequent and irregular mast seed events of the longleaf pine. Using a long-term, large-scale restoration experiment and a long-term monitoring data site at Eglin Air Force Base, Florida (USA), this study explores the influence of native fire-intolerant oaks on longleaf regeneration. We test for historical observations of hardwood facilitation against the null hypothesis of competitive exclusion. Our results provide evidence of hardwood facilitation on newly germinated longleaf pine seedlings (<2 yr old) after two mast seeding events (1996, 2011). Using regression-tree and Kaplan–Meier survival analyses, we found that deciduous oak midstory density was the most significant variable associated with longleaf pine seedling survival rates in the first 2 yr after germination. We found that as few as 43 oak midstory stems ha−1 were sufficient to facilitate seedling survival, but as many as 1400 stems ha−1 maintained facilitation without competitive exclusion of seedlings. We found that 1.5-yr- old pine seedlings were more moisture stressed under more open canopy conditions when compared to those immediately adjacent to a midstory oak canopy. Recognition that deciduous oaks are important facilitators of longleaf seedling establishment on xeric sites represents a significant departure from conventional wisdom and current management practices that has largely focused on competitive exclusion. This points to a critical role of a deciduous oak midstory of moderate densities for long-term ecosystem resilience in xeric longleaf pine ecosystems in light of climate uncertainty.

Sound Research audio clip of this publication is available.

  • Citation: Louise Loudermilk, E.; Kevin Hiers, J.; Pokswinski, Scott; O'Brien, Joseph J.; Barnett, Analie; Mitchell, Robert J. 2016. The path back: oaks ( Quercus spp.) facilitate longleaf pine ( Pinus palustris ) seedling establishment in xeric sites . Ecosphere, Vol. 7(6): e01361-. 14 p. DOI:10.1002/ecs2.1361
  • Keywords: deciduous oaks, Eglin Air Force Base, Kaplan Meier, longleaf pine, management, plant facilitation, regression trees, restoration, seed masting, turkey oak, xeric sandhill
  • Posted Date: September 15, 2016
  • Modified Date: July 6, 2021
  • Print Publications Are No Longer Available

    In an ongoing effort to be fiscally responsible, the Southern Research Station (SRS) will no longer produce and distribute hard copies of our publications. Many SRS publications are available at cost via the Government Printing Office (GPO). Electronic versions of publications may be downloaded, printed, and distributed.

    Publication Notes

    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
    • Our online publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact the SRS webmaster if you notice any errors which make this publication unusable.
    • To view this article, download the latest version of Adobe Acrobat Reader.