FIRE EFFECTS
SPECIES: Sonchus arvensis | Perennial Sowthistle 



IMMEDIATE FIRE EFFECT ON PLANT : 
Fire probably top-kills perennial sowthistle.  Buried seed and
perennating buds on rhizomes probably remain undamaged by most fires.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Perennial sowthistle response to fire is variable.  Perennial sowthistle
cover and frequency may increase, decrease, or remain the same after
fire in grasslands [24,27].  Fire in wetlands may increase perennial
sowthistle cover [16,40].

Perennial sowthistle occurred as a minor species on five mixed grassland
study sites within the Tewaukon National Wildlife Refuge in North
Dakota.  Prescribed fires were conducted in late spring and the
vegetation was sampled in postfire year 2.  Two sites had no significant
difference (p=0.05) in perennial sowthistle canopy cover between burned
areas and an unburned control, two sites had higher canopy cover on the
unburned controls, and one site had higher canopy cover on the burned
area [27].

In a northwestern Iowa prairie, perennial sowthistle frequency 1 year
after an early April fire was higher than prior to burning.  For two
sites, perennial sowthistle prefire frequency was 8.1 and 18.9 percent
and postfire frequency was 15.9 and 22.0 percent, respectively [24].

Low-severity fire in early May stimulated flowering of perennial
sowthistle in a northwestern Minnesota grassland dominated by Canada
bluegrass, Kentucky bluegrass, and smooth brome (Bromus inermis).  The
total number of flowering plants per unit area was greater on burned
sites than unburned controls [29].

Fire in wetlands may increase the cover of dry-adapted forbs, including
perennial sowthistle.  Perennial sowthistle cover increased following
both low-severity and high-severity simulated fire in two vegetation
zones (willow savanna zone and reedgrass [Calamagrostis spp.] meadow
zone) on the Peace-Athabasca Delta, Alberta.  In early July, a propane
torch was used to simulate low-severity and high-severity fires.  All
aboveground biomass including litter was combusted in the low-severity
fire treatment.  In order to simulate a severe fire which burns into
organic soils, 2 to 4 inches (5-10 cm) of soil was removed and the new
surface was heated with the torch for 1 minute.  Perennial sowthistle
cover was measured in August, 1 year after treatments.  In the willow
savanna zone, perennial sowthistle cover was 10 percent on the unburned
control and 15 percent on both burns.  In the reedgrass meadow zone,
perennial sowthistle cover was 1 percent on the unburned control, 2
percent on the low-severity burn, and 4 percent on the severe burn.  The
authors did not specify whether the perennial sowthistle sprouted from
undamaged rhizomes, or germinated from buried seed or recently dispersed
seed [16].

In a common reed stand in Delta Marsh, Manitoba, perennial sowthistle
seedlings established at a density of 1.4 seedlings per square foot
(15.5/sq m) 1 month after an August fire.  Seedlings did not establish
after a spring fire and only a few established in the first growing
season after a fall fire.  Perennial sowthistle was not present in the
prefire community; seedlings may have established from buried seed [40].

Perennial sowthistle seed germinated at a density of 43,600 seedlings
per acre (109,000/ha) in a greenhouse from soil collected from a red
pine (Pinus resinosa) stand in Minnesota which had burned 3 years
previously.  Perennial sowthistle seeds were not present in the soil of
an unburned portion of the stand.  The seeds were probably dispersed by
wind onto the burn from an off-site source.  No perennial sowthistle
plants were present on the burn at postfire year 3 [1].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
Fire does not appear to control perennial sowthistle effectively
because fire may increase the cover and/or frequency of perennial
sowthistle [16,24,27,40] and may stimulate flowering [29].

Related categories for Species: Sonchus arvensis | Perennial Sowthistle