FIRE EFFECTS
SPECIES: Melilotus alba | White Sweetclover 



IMMEDIATE FIRE EFFECT ON PLANT : 
Once the crown buds of second-year plants have expanded, growth
originates from branch tips or branch axils.  Thus once shoot growth has
begun, fire kills second-year plants simply by removing or scorching the
growing points, or on large individuals by charring the stem base
[15,18].  Numerous studies have shown that spring or summer burning in
prairies and old fields effectively kills most second-year plants.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
Burning of a remnant tallgrass prairie in Minnesota on May 1, when
second-year white sweetclover plants were 2 to 6 inches (5-15 cm) tall,
resulted in the virtual elimination of second-year plants from the site.
July burning on another portion of the same prairie similarly resulted
in killing all first- and second-year plants.  Although some large
second-year plants were not completely consumed by fire, none sprouted
by early September [15].

In the summer following early or mid-May burning on the Curtis Prairie
in Wisconsin, frequency of second-year plants ranged from 5 to 26
percent on burned plots and 93 to 100 percent on unburned plots [18].

In grass-dominated old fields in eastern North Dakota, late June burning
"completely eradicated" second-year white sweetclover [23].


PLANT RESPONSE TO FIRE : 
Numerous studies have documented that fire stimulates germination of
white sweetclover seed [9,15,18,23,25,28].  Seedling establishment
generally occurs as follows after burning at different times of the
year:

Spring burning - rapid seed germination and abundant seedling
establishment occur shortly after burning.  Additional seeds germinate
in the summer of the first postburn growing season, but few
late-germinating seedlings survive the winter.

Summer burning - poor to fair seed germination can occur after summer
burning, but few of these late-germinating seedlings survive the winter.
Additional seeds germinate in postfire year 2.

Fall burning - abundant germination occurs in the spring following fall
burning. 

Following spring burning of grasslands, frequency and cover of
first-year white sweetclover is much higher on burned than unburned
areas during the first postfire growing season.  During postfire year 2,
first-year plants are rare, while second-year plants are abundant.
White sweetclover frequency declines after postfire year 3.


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
White sweetclover thrives under a management program of periodic spring
burning on a 2-year or longer cycle, which has been a common practice in
many managed grasslands.  Under this regime, soil-stored white
sweetclover seed is scarified, resulting in abundant seedling
establishment.  The plants then overwinter, produce abundant seed in
their second year, and replenish the soil seed bank.  Because of these
life history attributes, the use of fire to suppress white sweetclover
is possible, but several successive annual or biennial burns are
probably required to exhaust the seed supply.  Dormant-season burns,
whether early spring or late fall, are not recommended because they do
not kill overwintering second-year plants.

Heitlinger [15] recommended the following strategies to suppress white
sweetclover and reduce seed supplies in tallgrass prairie: (1) burn
annually about early May (for Minnesota) when second-year shoots are
clearly visible, (2) burn every second year in early July before seed of
second-year plants ripens, or (3) burn annually in early September near
the beginning of the critical growth period [see Management
Considerations and Seasonal Development for more information on the
critical growth period].

In Wisconsin, a combination of an April burn followed the next year by a
May burn was more successful in reducing white sweetclover than other
burning combinations.  Heavily infested paririe stands where this
burning combination was conducted twice, separated by 2 years without
burning, became almost completly free of white sweet clover [18].

Related categories for Species: Melilotus alba | White Sweetclover