Fire promotes downy brome (Bromus tectorum L.) seed dispersal

Abstract

Particularly well-known among the many impacts of the invasive annual grass downy brome (Bromus tectorum, Poaceae) is its ability to alter fire cycles and increase in abundance after fire. However, little is known about how fire influences B. tectorum dispersal. We quantified fire effects on B. tectorum dispersal using three recently burned areas in the western region of the Colorado Rocky Mountains by marking diaspores (seeds) with fluorescent powder, and then recovering them at night using ultraviolet lights. Diaspores were of two types: with and without sterile florets attached. We also characterized vegetation cover and near-surface wind speed in burned and unburned areas. Diaspores travelled much farther in burned areas than in nearby unburned areas (mean ± standard error at the end of the experiment: 209 ± 16 cm and 38 ± 1 cm, respectively; maximal distance at the end of the experiment: 2,274 cm and 150 cm, respectively), indicating an increase in dispersal distance after fire. Diaspores with sterile florets attached dispersed longer distances than those without sterile florets (mean ± standard error at the end of the experiment: 141 ± 14 cm and 88 ± 7 cm, respectively). Vegetation cover was lower and wind speeds were higher in the burned areas. Our results indicate that at least one of the mechanisms by which the spread of B. tectorum is promoted by fire is through increased seed dispersal distance. Preventing movement of seeds from nearby infestations into burned areas may help avoid the rapid population expansion often observed.

Fire, humans and landscape in the European Alpine region during the Holocene

“…In recent times however, opening through fire results also in an increased susceptibility of the burnt ecosystems towards the colonization of invasive alien species (Grund et al, 2005;Lonati et al, 2009;Maringer et al, 2012) or animal communities, e.g., Lyet et al (2009) and Blant et al (2010). Similar to what is reported for the Mediterranean (Arianoutsou and Vilà , 2012) or other fire prone ecosystems (Franklin, 2010;Monty et al, 2013), also in the Alpine environments fire may represent an unrequested spread channel for alien invasive species with pioneer character, what reinforce the selective pressure of fire in favour of disturbance adapted species of both native (Delarze et al, 1992;Tinner et al, 2000;Moser et al, 2010) and alien origin (Lonati et al, 2009;Maringer et al, 2012) (Fig. 7).…”

Diaspore heteromorphism in the invasive Bromus tectorum L. (Poaceae): Sterile florets increase dispersal propensity and distance

“…In grasslands, where the vegetation cover is higher, seed entrapment strongly reduced average dispersal distances. These results confirm those of Johnston (2011) and Monty et al (Monty et al, 2013), who found even more important rates of secondary dispersal of B. tectorum in areas with almost no vegetation (reclamation and burned areas, respectively). Research on other species also found an influence of vegetation on ground level dispersal through a decrease in wind speed, changes in wind turbulence and seed entrapment (Chambers, 2000;Marushia and Holt, 2006;McEvoy and Cox, 1987).…”

“…The most distal florets are often sterile, and remain attached to the most distal fertile caryopsis after fruit set. This results in two types of diaspores (Monty et al, 2013): the simple ones, consisting of a single filled caryopsis with an awned lemma and the complex ones including one filled caryopsis and one or several sterile florets, resulting in a diaspore with two or more awns (Fig. 1).…”

“…On a spikelet, the most distal florets often abort and remain attached to the most distal mature caryopsis (McKone, 1985;Monty et al, 2013). Caryopses and sterile florets bear pubescent awns.…”

“…It is a highly problematic invasive plant in the western United States (US) that influences fire cycles and has profoundly altered some ecosystems of the North American West (D'Antonio and Vitousek, 1992;Knapp, 1996;Mack, 1981). Despite documentation of wind dispersal in this species in particular environments (Johnston, 2011;Monty et al, 2013), little is known about its dispersal ecology and the role in dispersal of diaspore heteromorphism caused by the presence or absence of sterile florets.…”