Plant-Derived Smoke Influences Germination of Native and Invasive Plant Species

Plant-derived smoke stimulates seed germination in many fire-prone ecosystems (Keeley 1987, Abella 2006). Historically, the northern Great Plains experienced frequent fire return intervals between five and ten years (Vinton et al. 1993, Umbanhowar Jr. 1996). Current land use changes including conversion to agriculture, changes in grazing regimes, and the cessation of anthropogenic burning has resulted in a reduction in fire occurrence (Samson and Knopf 1994, Ryan et al. 2013). This reduction in fires may have consequences for seed germination and plant community dynamics (Abella et al. 2007, Barnes et al. 1983, Van Staden et al. 2006).

Seed germination is known to be influenced by fire and smoke (Abella et al. 2007, Van Staden et al. 2006) although responses are species specific (Tieu et al. 2001, Gashaw and Michelsen 2002, Ooi et al. 2006, Nelson et al. 2009, Dayamba et al. 2010). Fire, and the smoke derived from fire, can break dormancy, increase total germination, and increase germination rate through temperature changes (i.e., heat shock), and release of chemical compounds such as nitrates, nitric oxides, and butenolides (Dixon et al. 1995, Blank and Young 1998). For example, germination rates in four Brassicaceae weeds have been found to be 26%–400% higher than control rates once exposed to aerosol fire and aqueous smoke solution (smoke-water; Mojzes and Kalapos 2014). Fire can increase seedling performance after germination through the removal of aboveground biomass, creating available nutrients, space, and other resources that can be utilized by newly-germinated seedlings (Chou et al. 2012).

The species-specific response of seeds to smoke (Adkins and Peters 2001, Rokich et al. 2000, Dayamba 2010) has potential to impact species composition and successional trajectory (Hanes 1971, Ewing and Engle 1988, Keeley 1991, Scheiter et al. 2012). Cool-season and warm-season species may have divergent responses to fire seasonality (Ewing and Engle 1988, Toderich et al. 2007, Scheiter et al. 2012). If a fire stimulates germination too early in the growing season, seedlings may not have adequate resources or suitable environmental conditions to survive (Ooi et al. 2006, Walck et al. 2011). This effect has been observed for species in the northern Mixed-grass Prairie (Walck et al. 2011) and cool-season grasses (Benson and Hartnett 2006). Further, heat shock or smoke-derived chemical cues from early spring fires can cause warm season grass seeds to germinate early in the growing season when climatic conditions are not adequate for plant growth (Ooi et al. 2006). Contrary to the former, if fires stimulate germination in cool season grasses too early in the season, climatic conditions and perturbation may reduce seeding survival (Benson and Hartnett 2006). Thus, timing of fire can have adverse effects on overall biomass production, life cycles, and population dynamics of warm-season species (Benson and Hartnett 2006).

The purpose of this study was to examine how exposure to two different types of plant-derived smoke (grass smoke and wood smoke) affects the germination of common native and invasive plants found in the northern Great Plains. First, we hypothesize that smoke (both grass-derived and wood-derived) will increase total germination. Second, we hypothesize that wood-derived smoke will influence germination differently than will grass-derived smoke. Lastly, we hypothesize that native and non-native plants will respond differently to the exposure to the two plant-derived smoke treatments.

We evaluated effects of grass-derived and wood-derived smoke on germination of ten native and invasive plant species found in the northern Great Plains. A total of 100 seeds/species (five replicates of 20 seeds per species) were exposed to each smoke treatment: grass-derived, wood-derived, or no smoke (control). Species included native grasses: Andropogon gerardii (big bluestem), Bouteloua curtipendula (sideoats grama), Elymus canadensis (Canada wildrye), and Pascopyrum smithii (western wheatgrass); invasive grasses: Agropyron cristatum (crested wheatgrass), Bromus inermis (smooth brome), Psathyrostachys juncea (Russian wildrye), Poa pratensis (Kentucky bluegrass); and native forbs: Symphyotrichum ericoides (white heath aster), Dalea candida (white prairie clover), Echinacea angustifolia (blacksamson echinacea), and Geum triflorum (prairie smoke). Using a bee-keeper's smoker, we applied dense smoke...