Fire effects on a fire-adapted species: response of grass stage longleaf pine seedlings to experimental burning

Benjamin O Knapp,Lauren S Pile,Joan L Walker,G Geoff Wang

doi:10.1186/s42408-018-0003-y

Benjamin O Knapp, Lauren S Pile + Show 2 more

Open Access

https://doi.org/10.1186/s42408-018-0003-y

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Abstract

BackgroundLongleaf pine (Pinus palustris Mill.) seedlings have a morphological “grass stage” that is considered to be an adaptation to frequent surface fire regimes. However, fire can kill longleaf pine seedlings and thus may play an important role in longleaf pine regeneration dynamics. We used a prescribed burn simulation tool designed to treat individual grass stage longleaf pine seedlings with controlled delivery of fire treatments and then measured survival and growth responses through two growing seasons. Naturally regenerated grass stage longleaf pine seedlings were randomly selected from three size classes and each assigned one of four treatments (Control, no treatment; Clip, mechanical needle removal; LB, a low-temperature burn treatment; or HB, a high-temperature burn treatment) in both the dormant season (January) and the growing season (May).ResultsSeedlings greater than 15 mm root collar diameter had greater than 0.5 probability of survival after the first growing season in the HB treatment, regardless of the season of treatment application, and seedlings across all sizes had greater than 0.6 probability of survival in the LB treatment after the first growing season. The growing season treatment application resulted in additional mortality during the second growing season, across all seedling size classes, which was not observed in the dormant season application. Burning reduced root collar growth through two growing seasons, likely due to needle mortality and the subsequent prioritization of growth to needle production rather than to root or stem growth.ConclusionsOur results suggest that the interplay between seedling size and fire intensity likely contributes to the success of longleaf pine natural regeneration and that seedling size should be considered when scheduling the first burn following planting of longleaf pine seedlings.

Highlights

Longleaf pine (Pinus palustris Mill.) seedlings have a morphological “grass stage” that is considered to be an adaptation to frequent surface fire regimes
Prescribed fire is commonly used in longleaf pine forests at Brosnan Forest, and the stand had been previously burned in spring 2011
We modeled survival probability of all seedlings based on treatment (Control, Clip, high-temperature burn treatment (HB), low-temperature burn treatment (LB)), initial root collar diameter (RCD), and application month

Summary

Introduction

Longleaf pine (Pinus palustris Mill.) seedlings have a morphological “grass stage” that is considered to be an adaptation to frequent surface fire regimes. Much of the southeastern Coastal Plain region was historically dominated by longleaf pine ecosystems that were maintained with fire return intervals generally < 5 yr (Frost 2006, Huffman 2006, Stambaugh et al 2011). In these ecosystems, frequent fire generates a positive feedback among vegetation, fuels, and fire (O’Brien et al 2008, Mitchell et al 2009). Consumption of the forest floor creates space for regenerating individuals of the characteristically species-rich ground flora (Hiers et al 2007, Veldman et al 2014) and germination sites for longleaf pine seed (Croker and Boyer 1975, Brockway et al 2006). Longleaf pine ecosystems can quickly transition to alternative states and may be difficult to re-establish without intensive treatments (Martin and Kirkman 2009)

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