Overstory‐derived surface fuels mediate plant species diversity in frequently burned longleaf pine forests

Dell, Jane E.; Richards, Lora A.; O’Brien, Joseph J.; Loudermilk, E. Louise; Hudak, Andrew T.; Pokswinski, Scott; Bright, Benjamin C.; Hiers, J. Kevin; Williams, Brett; Dyer, Lee A.

doi:10.1002/ecs2.1964

Cited by 43 publications

(48 citation statements)

References 53 publications

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“…The longleaf pine ecosystem is regarded as one of the most biodiverse, fire‐maintained ecosystems in North America (Noss et al ; Means ). Longleaf pine plays an important role in maintaining biodiversity through increasing understory flammability, helping to promote the frequent ignitions that maintain the open savanna structure (Fonda & Varner ; Dell et al ). Thus, regenerating longleaf pine is critical to the overall maintenance of the longleaf pine ecosystem.…”

Section: Discussionmentioning

confidence: 99%

Seed depredation negates the benefits of midstory hardwood removal on longleaf pine seedling establishment

Willis

Schnake

Wetzstein

et al. 2019

Restoration Ecology

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Midstory hardwoods are traditionally removed to restore longleaf pine on fire‐excluded savannas. However, recent evidence demonstrating midstory hardwood facilitation on longleaf pine seedling survival has brought this practice into question on xeric sites. Also, midstory hardwoods could facilitate longleaf pine seedling establishment, as hardwood litter may conceal seeds from seed predators or improve micro‐environmental conditions for seedling establishment. However, little is known about these potential mechanisms. In this study, we tracked longleaf pine seed depredation and germination in artificially seeded plots (11 seeds/m2) in a factorial design fully crossing hardwood retention or removal with vertebrate seed predator access or exclusion in the Sandhills Ecoregion of North Carolina, U.S.A. Seed depredation averaged 78% across treatments and was greatest in unexcluded plots. Hardwood retention did not affect seed depredation. Longleaf pine averaged 3.6 germinants/4 m2 across treatments, and was six times more abundant where vertebrates had been excluded. Hardwood removal had a strong positive effect on seedling germination, likely due to the removal of litter, but only when vertebrates were excluded. Our results indicated midstory hardwoods are not facilitating longleaf pine seedling establishment. Nevertheless, our results indicated that hardwood removal may not increase longleaf pine seedling establishment, as seed depredation diminished the effectiveness of hardwood removal under mast seed availability. Collectively, these results demonstrate the underlying complexity of the longleaf pine ecosystem, and suggest that planting may need to be part of the restoration strategy on sites where seed depredation limits longleaf pine natural regeneration.

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Section: Discussionmentioning

confidence: 99%

Seed depredation negates the benefits of midstory hardwood removal on longleaf pine seedling establishment

Willis

Schnake

Wetzstein

et al. 2019

Restoration Ecology

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“…Spatial heterogeneity in overstory tree distribution and differential fire energy release produced by fuels heterogeneity also play keys role in structuring understory conditions (O'Brien et al 2008, Dell et al 2017. A wide range in canopy closure produces gradients in light, water, wind, and fire exposure, which favor different plant traits and result in differing groundlayer composition.…”

Section: Spatial Heterogeneity and The Open Forest Spectrummentioning

confidence: 99%

“…Prescribed fire has been shown to trigger the germination of seed-banking species in oak woodlands and forests (Taft 2003, Hutchinson et al 2005 and in shortleaf pine woodlands (Sparks et al 1998). Indeed, fire energy release driven by overstory-derived fuels appears to have the greatest positive impact on diversity in relatively open-canopied, frequently burned stands (Dell et al 2017). …”

Section: Under-and Midstory Composition and Dynamicsmentioning

confidence: 99%

“…Variation in fuel loading helps to regulate the impacts of fire on tree establishment success (Loudermilk et al 2012) and the dispersion between overstory trees creates greater horizontal heterogeneity in canopy closure and stand density than found in closed forests (Hanberry et al 2014a. Uniform or random spacing typically may occur as individual trees claim the growing space around them, but factors such as differential fire severity, fire energy release driven by overstory contributions to fuels, patterns in fine-scale environmental gradients, and/or remnants of persistent soil seed banks may lead to patches of aggregated trees and clustered arrangements (Dell et al 2017). Additionally, dense pine establishment in particular may result in groups of trees that periodically fill overstory gaps.…”

Section: Spatial Heterogeneity and The Open Forest Spectrummentioning

confidence: 99%

“…A wide range in canopy closure produces gradients in light, water, wind, and fire exposure, which favor different plant traits and result in differing groundlayer composition. Overstory trees and understory herbaceous plants are functionally linked through interactions of fuel spatial distribution and subsequent energy release (O'Brien et al 2008, Dell et al 2017). Open forests have elements of grasslands because the growing space is not captured by trees, allowing for a diverse shade-intolerant herbaceous cover.…”

Section: Spatial Heterogeneity and The Open Forest Spectrummentioning

confidence: 99%

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A reconceptualization of open oak and pine ecosystems of eastern North America using a forest structure spectrum

2018

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We present a reconceptualization of forests in eastern North America by differentiating the ecological characteristics of open oak (Quercus) and pine (Pinus) forests from closed successional and oldgrowth forests. Despite historical abundance of savannas and woodlands, the fundamental ecology of open forest ecosystems remains ill-defined when compared to either closed forests or grasslands. Open forests were characterized by simple internal stand structure consisting of a single stratum of variably spaced, often very old overstory trees and limited midstory, maintained by understory disturbance that controlled tree regeneration and allowed instead a taxonomically rich herbaceous groundlayer. In contrast, closed forests have dense woody growth throughout the vertical profile, limiting herbaceous plants. To provide further clarity about these ecosystems, we developed a canopy closure spectrum model dependent on the interactions between prevailing disturbance regimes of the historical and current eras, which affect either the tree understory (regeneration) or overstory, and tree traits of fire and shade tolerance. Recognition of different stand structures, disturbance regimes, and their interrelationships should expand understanding of open forests and limit ecological misunderstandings and restoration misapplications, thereby improving management of these once historically extensive ecosystems.

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Allometry of the pyrophyticAristidain fire‐maintained longleaf pine–wiregrass ecosystems

Shearman

Varner

Robertson

et al. 2019

American J of Botany

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Premise of the Study Aboveground biomass (AGB) of herbaceous vegetation is a primary source of fuel in frequent surface fires that maintain grasslands, savannas, and woodlands. Methods for nondestructively estimating AGB are required to understand the mechanisms by which fuels affect fire behavior and the effects of time since the last burn. We developed allometric equations to estimate AGB in wiregrass (Aristida beyrichiana/A. stricta), a dominant bunchgrass in Pinus palustris ecosystems and a key species for ecological restoration. Methods We collected wiregrass from North Carolina to Florida, across a range of time‐since‐last burn and site types. We tested 32 mixed effect models to see which predictors were best at predicting live, dead, and total AGB. We also examined how time since burn (TSB) affected the live‐to‐dead ratio (LDR) using regression. Key Results Wiregrass AGB was found to increase with increasing latitude (relative to tussock volume), possibly due to an increase in precipitation, and was greater on more fertile clay soils and flatwoods than on sandy soils. The LDR decreased as a power function with TSB, resulting in rapid accumulation of dead, highly flammable, biomass in the fire‐free period. Conclusions Greater biomass will support fires of higher intensity. Our models can be useful in the parameterization of future physics‐based models to predict fire behavior. Understanding the environmental variables that influence the allometry of wiregrass should help increase the precision of AGB estimates and the subsequent effects on fire behavior and effects on neighboring vegetation.

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Overstory‐derived surface fuels mediate plant species diversity in frequently burned longleaf pine forests

Abstract: 2017. Overstory-derived surface fuels mediate plant species diversity in frequently burned longleaf pine forests. Ecosphere 8(10):

Cited by 43 publications

References 53 publications

Seed depredation negates the benefits of midstory hardwood removal on longleaf pine seedling establishment

Seed depredation negates the benefits of midstory hardwood removal on longleaf pine seedling establishment

A reconceptualization of open oak and pine ecosystems of eastern North America using a forest structure spectrum

Allometry of the pyrophyticAristidain fire‐maintained longleaf pine–wiregrass ecosystems

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