Optimal prescribed burn frequency to manage foundation California perennial grass species and enhance native flora

Authors: CARLSEN, TINA - Lawrence Livermore National Laboratory; Espeland, Erin; PATERSON, LISA - Lawrence Livermore National Laboratory; MACQUEEN, D - Lawrence Livermore National Laboratory

Submitted to: Biodiversity and Conservation Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2017
Publication Date: 6/6/2017
Publication URL: http://handle.nal.usda.gov/10113/5807612
Citation: Carlsen, T.M., Espeland, E.K., Paterson, L.E., Macqueen, D.H. 2017. Optimal prescribed burn frequency to manage foundation California perennial grass species and enhance native flora. Biodiversity and Conservation Journal. 26(11):2627–2656. doi:10.1007/s10531-017-1376-y.

Interpretive Summary: Not much is known how perennial grass species management affects overall native plant diversity except for in a few instances. We used late spring prescribed burns over a span of eleven years on Poa secunda (pine bluegrass), a rare native annual forb Amsinckia grandiflora (the large-flowered fiddleneck) and local native and exotic species, with four additional years of measurements after the final burn. Annual burning resulted in a significant increase in P. secunda density, which was maintained for four years after the final burn. This treatment had the lowest thatch and exotic grass cover, the highest percentage of bare ground, but also had the lowest native forb cover and highest exotic forb cover. Burning every three years resulted in P. secunda population maintenance and resulted in the highest native forb cover and a low exotic grass cover. Burning every five years and no burning (control) generally resulted in a decline of P. secunda from the initial density, and had the highest exotic grass and thatch cover with the lowest percentage of bare ground. While local native forbs appeared to benefit from burning every three years, A. grandiflora generally performed best in the control treatment. A. grandiflora did not occur naturally at the site; therefore, no seed bank was present to provide across-year protection from the effects of the burns. Thus, solely focusing on managing perennial grass species without considering other local native species life history and phenology may be detrimental to overall native flora diversity.

Technical Abstract: Grasslands can be diverse assemblages of grasses and forbs but not much is known how perennial grass species management affects native plant diversity except for in a few instances. We studied the use of late spring prescribed burns over a span of eleven years on experimental plots in which the perennial grass Poa secunda (pine bluegrass) was established as the foundation species, with four additional years of measurements after the final burn. We evaluated the effects of the burns on P. secunda, the experimentally introduced rare native annual forb Amsinckia grandiflora (the large-flowered fiddleneck) and local native and exotic species. Annual burning (high frequency) resulted in a significant increase in P. secunda density, which was maintained for four years after the final burn. This treatment had the lowest thatch and exotic grass cover, the highest percentage of bare ground, but also had the lowest native forb cover and highest exotic forb cover. Burning every three years (medium frequency) generally maintained the initially established density of P. secunda and resulted in the highest native forb cover and a low exotic grass cover. Burning every five years (low frequency) and no burning (control) generally resulted in a decline of P. secunda from the initial density, and had the highest exotic grass and thatch cover with the lowest percentage of bare ground. While local native forbs appeared to benefit from the medium burn frequency, planted A. grandiflora generally performed best in the control treatment. A. grandiflora did not occur naturally at the site; therefore, no seed bank was present to provide across-year protection from the effects of the burns. Thus, solely focusing on managing perennial grass species without considering other local native species life history and phenology may be detrimental to overall native flora diversity.