Geoscience Reference
In-Depth Information
Fig. 12.8. Grasses, sedges, and forbs sprouting from un-
burned roots and rhizomes 3 years after a high-severity
crown fire in a lodgepole pine forest on the northeast side
of Yellowstone Lake (the east Fire of 2003). Such plants
sequester limiting nutrients as they become available after
the fire, preventing their loss from the ecosystem. Small tree
seedlings were becoming established at the time this photo
was taken but are too small to be seen. one effect of such
fires is to mineralize the forest floor and most of the leaves,
twigs, and small branches. However, most roots, tree boles,
and large branches are not burned; and most of the organic
matter and nutrients in this unburned biomass is eventually
incorporated into the soil. in burned lodgepole forests such
as this one, about 80 percent of the large-diameter wood is
not burned, about 10 percent is converted to persistent char-
coal, and the remainder is consumed.
intensity, amount of forest floor burned, water infiltra-
tion rate, the rate at which understory plant cover devel-
ops following the fire, and whether the burn was patchy
or uniform. the biggest erosion events usually follow
heavy summer rainstorms within the first year or two
after the fire. Snowmelt is less likely to produce serious
erosion than intense summer rain, even on a severely
burned site, because snow melts slowly and much of the
water percolates through the soil rather than flowing
over the surface.
in burned lodgepole pine forests, leaf area and total
plant growth return to pre-fire levels within a few
decades. the rate of recovery depends mainly on the
abundance of new lodgepole pine saplings, which can
vary immensely, as discussed in chapter 11. in gen-
eral, total plant growth in young stands increases with
increasing tree density, although this productivity may
be lower in stands having extreme densities (fig. 12.9).
only 10 years after the 1988 Yellowstone fires, a few
stands of lodgepole pine already supported leaf areas
and total plant growth rates close to values measured
in comparable mature forests. 29 Most stands required a
longer time.
Using data from young lodgepole pine forests devel-
oping after the 1988 fires, along with measurements
from older forests that grew after earlier fires in Yellow-
stone national Park, Dan Kashian and colleagues pro-
duced a model portraying the expected changes in
total plant growth over a 250-year period following
fire or other intense disturbances. 30 though initial
stand density makes a big difference in total productiv-
ity, both dense and sparse stands converge on a simi-
lar low level of net productivity near zero by age 250
years (fig. 12.10). this level of net productivity does not
mean the trees are dead. Photosynthesis continues, but
accumulation of new plant tissues declines, for reasons
not yet understood . 31 Lodgepole pine forests typically
recover more rapidly after an intense crown fire than do
any other forest types in the Rocky Mountains, except
aspen forests—which can be restored by sprouting from
 
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