Season of fire manipulates bud bank dynamics in northern mixed-grass prairie

Authors: RUSSELL, MORGAN - Texas A&M University; Vermeire, Lance; GANGULI, AMY - New Mexico State University; Hendrickson, John

Submitted to: Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2014
Publication Date: 4/14/2015
Citation: Russell, M.L., Vermeire, L.T., Ganguli, A.C., Hendrickson, J.R. 2015. Season of fire manipulates bud bank dynamics in northern mixed-grass prairie. Journal of Applied Ecology. 216:835-846.

Interpretive Summary: Below ground accumulation of vegetative buds provides a reservoir of meristems that can be utilized following disturbance. Perelll1ial grass bud banks are the primary source of nearly all tiller growth, yet understanding of season of fire effects on bud banks is limited. We tested effects of summer, spring, and fall on bud banks of the C4 grass blue grama (Bouteloua gracilis), the C3 caespitose grass needle and thread (Hesperostipa comata), and the C3 rhizomatous grass western wheatgrass (Pascopyrum smithii). Fire (no fire, summer fire, fall fire, spring fire) treatments were applied and axillary buds were evaluated in southeastern Montana one and two years after fire. Tillers were harvested from two individuals of each grass species for immediate and seasonal bud assessments. Tillers were harvested from randomly determined individuals 12 to 24 hours before and following prescribed burns to determine immediate bud mortality or activation. Bud activity (i.e. active buds, dormant buds, and dead buds) were confirmed using staining procedures. Blue grama bud mortality did not occur immediately following fire in any season. Short-term changes in blue grama bud mortality due to season were minimal throughout the two post-fire growing seasons and, overall, the number of dead buds was very low. Summer burns resulted in 35% more active blue grama buds than fall or spring burned plots throughout winter. Fall burns tripled new active blue grama buds by the end of the second post- fire growing season compared to non-burned plots. Spring burns increased active blue grama buds 77% at the begilll1ing of the second post-fire growing season compared to non-burned plots and by then all buds were active. Summer, fall, and spring burning increased active blue grama buds compared to non-burned plots during the drought of the first post-fire growing season (6.0, 5.4 and 5.5 vs. 2.3 ± 0.6 buds• tiller-1). Needle and thread bud activity was not immediately impacted by fire. Fire also had no immediate effect on needle and thread bud mortality regardless of season. Active needle and thread buds were reduced entering the second post-fire growing season by summer and spring burns. These fire effects on needle and thread bud banks continued throughout the second growing season for summer, fall and spring bums 81, 85 and 65% reductions, respectively. Summer, fall, and spring fire had no immediate effect on dormant or dead buds for western wheatgrass. However, development of active western wheatgrass buds increased 37% immediately following fall fire. Development of active western wheatgrass buds primarily occurred during the second year following fire. Active, overwintering western wheatgrass buds increased following summer and fall fire compared to spring burns and non-burned plots. Increased activity of western wheatgrass buds continued through the winter and summer, fall, and spring burns increased active buds by 84, 82, and 80% compared to non-burned plots. By the beginning of the second post-fire growing season, only fall and summer fires increased western wheatgrass bud activity, and active bud counts became similar across all fire treatments by the middle of the second growing season. Belowground bud banks respond positively by increasing in bud activity and having minimal bud mortality following moderate fire intensity. Both blue grama and western wheatgrass responded to fire with increased bud activity throughout winter dormancy in order to replenish bud bank reserves and capitalize upon early spring precipitation. Differences in season of fire responses due to different growth patterns of mixed grass prairie grasses can influence future patterns of grass growth and community dynamics. Manipulating bud bank dynamics by season of fire illustrates potential to improve management strategies following wildfires or planning prescribed burns based on the

Technical Abstract: In perennial grassland dominated systems, belowground bud banks regulate plant community dynamics. Plant community responses to disturbance are largely driven by the ability to generate future aboveground growth originating from belowground axillary buds. This study examined bud bank dynamics for Bouteloua gracilis, Pascopyrum smithii, and Hesperostipa comata, following fire in northwestern mixed-grass prairie in eastern Montana, USA. Belowground axillary buds were counted and classified for three growing seasons to determine immediate and short-term effects of summer, fall, and spring prescribed burns on patterns of bud bank activity, dormancy, and mortality. Prescribed burns did not result in immediate mortality of B. gracilis, P. smithii, or H. comata buds (P > 0.05). Surprisingly, spring prescribed burns immediately increased the number of active B. gracilis buds (P < 0.01). Summer fire, however, reduced B. gracilis active bud numbers (P < 0.01). Fall burns immediately activated P. smithii buds (P < 0.01), whereas fire did not influence any immediate bud dynamics for H. comata (P > 0.05). Reduced bud numbers of H. comata may limit the ability to respond to fire. Season of fire directly manipulated bud activity, dormancy, and mortality for these species throughout the growing and dormant seasons following fire. Using season of fire to manipulate bud bank dynamics illustrates potential to improve post-fire management strategies based on known bud development trajectories and bud dynamics following fire.