FIRE EFFECTS
SPECIES: Larix occidentalis | Western Larch 



IMMEDIATE FIRE EFFECT ON PLANT : 
Mature western larch are able to withstand most fires; poles may survive
low to moderate fires [30,116].  Although young trees may survive high
temperatures for a short time, thin-barked seedlings and saplings are
readily killed by fire [19,33,116,117,118].  Bark thickness, crown
function, and tree vigor, as well as the characteristics of the fire,
are major factors that determine tree damage or death [110].  Trees that
are damaged by fire frequently succumb to insect attack or disease later
[110].

Mature western larch are most likely to be killed by fire after long
fire-free intervals in moist habitat types where true firs, western
hemlock, or western redcedar are potential climax.  These dense stands
include low-branching conifers and tall shrubs or ladder fuels that can
carry fire into the crowns of western larch [19].  When ground fires
smolder in deep, dry duff, they can girdle even thick-barked trees
[110].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
Several factors are considered when predicting and modeling mortality of
western larch [110].  Cambial mortality depends on the duration of the
fire and thickness of the bark, which can be estimated by an equation
using tree diameter [108,109].  Crown damage depends on the amount of
bud kill, which may be observed with binoculars.  Another indication of
crown kill is that a dead branch tends to retain the scorched needles
until they are removed by weather, while a live branch will drop the
dead needles promptly [109].  Nomograms have been developed that predict
mortality based on the bark thickness and crown scorch.  These nomograms
and others showing scorch height, flame length, and fire intensity can
be used to help plan prescribed fires [100,102].


PLANT RESPONSE TO FIRE : 
Even after large severe fires, scattered mature western larch survive
[147].  These survivers become seed trees for rapid restocking [2,70].
Fires that precede a good cone crop tend to favor western larch [63].
Western larch initiates new foliage growth shortly after being scorched
[110].

Western larch seedlings grow best on burned seedbeds [117,118].  Results
of a Montana study show numerous 3-year-old western larch seedlings
following a hot fire but very few on lightly burned areas [138].
Western larch seedlings and saplings have been found to grow one-third
faster on burned seedbeds than on bare mineral soil or duff-covered soil
[116].  This height increase might be due to changes in nutrients, water
infiltration, or competing vegetation.  Increases in manganese,
magnesium, nitrogen, phosphorus, and calcium in upper soil layers have
been observed after fire [116].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
When prescribed fire is used, western larch makes a good shelterwood
candidate in the Blue Mountains of Oregon [85].  Prescribed fire is
practical under a western larch shelterwood since the trees can
withstand normal prescribed fire intensities [113].  Planning such fires
is described in detail [64,85].  Such planning should recognize that
western larch needles have few surface deposits to slow moisture
movement and thus fuel moisture response times are shorter than those
for other conifer needles [1].  Near its southern limit in central
Idaho, western larch stands reflect past severe disturbance from
wildfire.  At present, however, it is not regenerating well following
broadcast burns or scarification.  Reasons for this may include
insufficient seed trees and marginal conditions for seedling
establishment [140].

Several researchers have modeled forest succession following fire,
including the life history and response of western larch [13,30,62].
Such information can be useful in setting management objectives.  The
response of western larch and other conifers following repeated fires at
10-, 20-, and 50-year intervals, a simulated natural fire frequency, or
fire supression has been described by a computer model [60].

Related categories for Species: Larix occidentalis | Western Larch