FIRE EFFECTS
SPECIES: Rubus parviflorus | Thimbleberry 



IMMEDIATE FIRE EFFECT ON PLANT : 
Thimbleberry is described as resistant to fire [57,131].  Although often
top-killed, underground rhizomes generally survive.  High severity fires
which damage belowground regenerative structures may be most damaging to
rhizomes [98].  The aerial portions of relatively few plants actually
survive fire, except for those on unusual microsites [52].  Most seed
stored on-site is probably unharmed by fire.



DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Thimbleberry cover and vigor is generally enhanced by fire [20,57,100].

Vegetative response:  Thimbleberry is capable of rapid, vigorous
postfire spread through an extensive network of often deeply-buried
rhizomes [22,74,116].  Sprouting through surviving rootcrowns is also
possible, although rhizome sprouting probably represents the primary
mode of postfire regeneration [105].  Multiple sprouts often replace the
single stems observed in preburn communities [20].

Limited evidence suggests that sprouting of rhizomes is favored by fires
of low intensity and severity [20,98].  Hot fires presumably offer
greater potential for damaging underground regenerative structures.  In
western redcedar habitat types of northern Idaho, thimbleberry cover was
estimated at 10.9 percent 2 years after low severity fire.  However,
following a high severity fire, thimbleberry cover reached only 4.9
percent [98].

Seedling establishment:  Seed banking is an important postfire
regenerative strategy in thimbleberry, a prolific seed producer [57].
Birds and mammals also transport some viable seed to burned sites
[22,74].  Some seedlings have been observed to germinate from rodent
caches present on-site [99].  Thimbleberry seed is stimulated by fire
[52,120] and subsequently germinates in great numbers [116,120].
Researchers have observed up to 7.5 times more seedlings on plots which
have been burned than on adjacent untreated plots [120].  Most seedling
establishment occurs immediately after fire [57].

Some researchers have suggested that fires of high severity and
intensity can expose mineral soil, which serves as a favorable seedbed
for thimbleberry [98,105].  However, Morgan and Neuenschwander [99]
observed greatest seedling establishment on low severity burns where
duff reduction was incomplete.  The capacity to regenerate through seed
may be reduced by extremely hot, duff-reducing burns [99,127].

Rate of postfire recovery:  Both sprouting [56] and seedling
establishment occur soon after fire.  Growth is rapid and some plants
occasionally bear fruit during the first postfire year [22].
Thimbleberry generally reaches greatest abundance during the first years
after fire and decreases as the overstory canopy closes [57].  Dwindling
soil nutrients may also contribute to its decline [79].  On coastal
sites in British Columbia, thimbleberry typically attains greatest
height growth during the first few years after fire and remains abundant
for approximately 5 years [57].  Rhizome sprouting may produce dense
cover up to 3 feet (1 m) tall within 3 years after disturbance on some
particularly moist sites [15].  Thimbleberry reportedly dominates the
understory of many Northwestern Douglas-fir forests within just five
years after logging and slash disposal [96].  In Douglas-fir forests of
western Montana, thimbleberry was well-represented on many sites during
the first 2 to 3 years after fire [21,74].  Maximum cover values have
been observed within three to 5 years after fire in western redcedar
habitat types of Idaho [98].  In many areas, this shrub remains widely
distributed during the first several decades after fire [123].  Dense
early growth of aggressive species such as fireweed can slow
thimbleberry establishment and growth [121].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Rate of postfire recovery may be significantly related to fire severity
and intensity.  However, contradictory findings have been reported.
Hooker and Tisdale [66] observed rapid growth rates on severely burned
sites (0.25 inch/day [0.6 cm/day]) but slower growth on less severely
burned plots [66].  Slower growth may be expected where cover (and thus
increased intraspecific competition) is greatest, and these results do
not necessarily indicate that actual cover was greatest on these
severely burned plots.  Other research has suggested that thimbleberry
cover develops most rapidily after fires of low intensity [15].  

Some researchers suggest that, in general, rhizome sprouting may be
favored by fires of low intensity and severity, whereas seedling
establishment may be more effectively promoted by fires of relatively
high severity [98,105].  However, researchers in northern Idaho have
occasionally observed greater seedling establishment after fires of low
severity [99].  

Factors other than fire severity and intensity can also contribute to
the rate of postfire recovery.  Differences in the season of burn, plant
density and vigor in the preburn community, site differences, and
climatic factors all contribute to postfire recovery.  Fire severity and
intensity are not consistently defined in the literature, which
compounds the problems of interpreting plant response.  The rate of
postfire recovery is significantly related to climatic and topoedaphic
factors.  In coastal Oregon, 8,760 thimbleberry seedlings per acre
(21,382/ha) were present 1 year after fire on north aspects where 4,450
seedlings per acre (10,988/ha) had been observed prior to the fire.  On
south aspects, increases were even more dramatic, with 10,988 seedlings
per acre (24,640/ha) counted 1 year after fire where none had been
observed prior to the fire [120].

Mean frequency of thimbleberry by burn age and severity was documented
as follows after fire in a western redcedar/queencup beadlily habitat
type of northern Idaho [98]:

fire severity                      years

                        1     2     3     4     5     15
low                    83    80    80    59    56     98
high                   61    76    78    75    53    100   


FIRE MANAGEMENT CONSIDERATIONS : 
Timber harvest:  Thimbleberry typically increases dramatically after
timber harvest and subsequent slash burns [44,86].  In many areas, it
may provide formidable competition for regenerating conifer seedlings
[57].  Mueggler [100] reports that thimbleberry often assumes dominance
on broadcast burns in western redcedar and western hemlock habitat types
of northern Idaho [100].  Response may be rapid.  Maximum cover values
were reached within 5 years after fire in western hemlock and western
redcedar habitat types of northern Idaho [122].  This shrub can
establish as early as the first growing season after clearcutting and
broadcast burns in grand fir/pachistima habitat types of north-central
Idaho.  More serious disturbance may enhance the growth and recovery of
thimbleberry more than lighter disturbance.  In the Intermountain West,
Laursen [86] reported greater increases in ground cover in stands that
were clearcut and burned than in unburned shelterwood or selection cuts.
Maximum cover was typically reached within 20 to 25 years after
clearcutting and burning [86].  Thimbleberry commonly assumes importance
soon after timber harvest and slash burning in Douglas-fir forests of
the Oregon Cascades.  Frequency of occurrence by years after treatment
was documented as follows [136]:

site #                      1     4     5     (years)

  1                        15    32    36 
  2                         4    14    14

Wildlife:  Fire generally benefits animals that eat the fruits of Rubus
[83].

Related categories for Species: Rubus parviflorus | Thimbleberry