Pyrogenic flowering of Aristida beyrichiana following 50 years of fire exclusion

Abstract

Fire-stimulated or pyrogenic flowering is one of many traits that enable plants in fire-prone ecosystems to persist or dominate following frequent fires. Obligate pyrogenic flowering has long been observed in wiregrass (Aristida beyrichiana), a foundation bunchgrass in frequently burned longleaf pine ecosystems in the southeastern United States. Widespread fire exclusion in this ecosystem has contributed to well-documented declines in plant and animal biodiversity prompting the need for restoration efforts. We studied the effect of fire reintroduction on the flowering of wiregrass in northern Florida, USA. Prescribed fires were ignited in a 50-yr unburned site and an adjacent frequently burned site in the summer of 2017. Wiregrass was measured eight months after the burns in both stands. As expected, the frequently burned stand had higher density, basal area, and percent flowering of wiregrass tussocks. Logistic regression revealed that wiregrass initiated flowering at significantly larger sizes in the long-unburned stand. Despite these differences, wiregrass size distributions were similar in both stands, with the long-unburned stand lacking tussocks in the largest (100+ cm 2 ) size class. We did not find differences in the number of flower culms per unit of mass between the two stands. Even though diminished in nearly every measure, the ability of wiregrass to flower after five decades of fire exclusion, and presumably no sexual reproduction, provides evidence of resilience of the dominant herb of these ecosystems.

Fire‐triggered flowering is the dominant post‐fire strategy in a tropical savanna

“…Quantifying PFF at the community scale is less conducted in savannas than in other regions, and most observations have been made for single, mainly shrub, species (Franceschinelli & Bawa, 2005; Conceição & Orr, 2012; de Sousa & da Cunha, 2018; Dodonov et al, 2018; Shearman et al, 2019, but see Massi et al, 2017; Pilon et al, 2018). In Lamont and Downes’ (2011) review of PFF in Australasia and South Africa, the vast majority of species identified as having this strategy (>70%) were from mediterranean climate regions, whereas only ~14% were from savanna.…”

“…However, although some observations of this phenomenon were made, studies quantifying the PFF responses in the Cerrado are lacking. Mass PFF events have been documented (Coutinho, 1976;Massi et al 2017;Pilon et al, 2018); however, in general, most studies have focused on the responses of single species rather than at the community level (e.g., Franceschinelli & Bawa, 2005;Conceição & Orr, 2012;Dodonov et al, 2018;Shearman et al, 2019;Sousa and Cunha, 2019). The speed of PFF (i.e.…”

Morphological and molecular characterization of Langdonia walkerae sp. nov. infecting Aristida stricta and A. beyrichiana in longleaf pine-grassland ecosystems in the southeastern USA

“…These perennial bunchgrasses are adapted to fire, enabling them to persist and reproduce despite frequently recurring fires ( Platt 1999 , Means 2007 ) as well as to survive for decades without burning ( Shearman et al . 2019 ).…”

Wiregrass (Aristida beyrichiana) survival and reproduction after fire in a long-unburned pine savanna

“…Aristida beyrichiana (wiregrass) is a perennial, endemic C4 bunchgrass that commonly dominates pine savanna understories, contributing to vegetation-fire feedbacks and biodiversity dynamics [ 16 – 18 ]. In savannas where fire has been excluded however, the size and number of wiregrass individuals are greatly reduced [ 19 , 20 ], which could be attributed to competition, lower light levels from overstory shading, or heavy litter [ 21 – 23 ]. Moreover, because sexual reproduction in wiregrass is primarily stimulated by fire, lack of fire inhibits wiregrass seed production [ 16 ].…”

“…In a stand that had been fire-suppressed for at least 35 years, [ 13 ] found that wiregrass declined after a reintroduction fire and still had not reached pre-burn levels of cover after eight years. In addition, wiregrass’ inflorescence production has been shown to be lower after the reintroduction of fire in long-unburned areas relative to that in frequently burned areas [ 20 ], although it is unknown how this translates to seed viability and germination. None of these studies, however, examined the burning of accumulated fuels as a mechanism by which reintroduction fires affect wiregrass plants.…”