Rosebay willowherb

Key traits

Offsite coloniser, able to invade burned sites rapidly. Secondary colonisation by on-site seed (Pavek, 1992). Seeds are only viable in soil for around 18 months (Comeau et al, 1989).

Plant response to fire

Rosebay willowherb is able to colonise burned areas, and exposed mineral soil and peat rapidly (Comeau et al, 1989) and is named fireweed in North America for this reason. Rosebay willowherb’s rhizomes can withstand low intensity fires being typically buried in the top 5cm of the soil. McLean, (1969) suggests rosebay willow herb is 'moderately susceptible to fire’ because of the relatively shallow roots but notes that where more deeply rooted it can survive fire allowing it to reproduce vegetatively. Hence it is not anticipated to survive frequent burning (Myerscough, 1980). Seed production is high (Comeau et al, 1989) but seed viability is relatively short. Archibold, (1980) suggested that rapid invasion of burned areas occurs from soil seed banks that are known to survive fires. However, it seems the timing of the fire would have to correspond within the limited life-span of seed viability. However, its plumed seeds are well distributed by wind and rapidly cover recently denuded of burned landscapes (Comeau et al, 1989). It has been noted that the greatest cover is attained on high severity sites, where it can form uniform cover of large areas (Comeau et al., 1989). Once established from seed it continues to expand vegetatively. Seedling have been noted to be found following summer fires in Molinia caerulea (Myerscough, 1980) in the UK.

Timing of life history

Perennial species. Seeds can be produced from the first growing season. Flowering June to September.