FIRE EFFECTS GUIDE - National Wildfire Coordinating Group

applied. Live tissue will turn bright blue within a few moments. A reddish purple color,
followed by the appearance of a blue color, also indicates life. A greenish blue color
probably means dead tissue. After using this technique for a while, the colors that
indicate dead or live cambium become readily recognizable. This test is preferable to
the tetrazolium test because it can be used in the field and provides almost immediate
results. However, caution is necessary because orthotolodiene has been found to be
carcinogenic in laboratory studies. Gloves should be worn as a precaution.
(3) General comments. Metabolic by-products being tested for may not break down
until a few days after a fire, even though the plant is dead. The proper location on the
plant must be tested to determine mortality. On coniferous trees with living foliage, the
cambium should be checked, and also the roots, if much heating occurred at the base
of the tree. Trees and shrubs sprout from different locations on stems, root crowns, and
roots, and it is these sprouting sites which should be tested to indicate whether the
shrub may sprout. Grass crowns should be tested where the buds and reproductive
meristems are found.
More than one test may be necessary per plant, because plants can survive some
amount of fire damage. Tree cambium requires a test on all sides, and a shrub at
several sprouting sites. Unburned meristems and buds of bunchgrasses should be
tested at both the center and edges of each plant, and at different depths below the
surface if the buds occur below the ground surface.
13. Burn Severity. Burn severity (discussed in II B.6.e), while not an attribute of
vegetation, is an exceptionally good predictor of fire effects on vegetation. It indirectly
measures the heat pulse below the surface, and provides an indicator of fire impacts on
buried plant parts. Burn severity classes can be developed that apply to the type of
vegetation and soil organic layer characteristics on the site being investigated. The
degree of burn severity can be assigned to one of five classes, including "unburned",
"scorched", and "light", "moderate", and "high" severity. Definitions for the latter three
classes can be based upon the information in section B.2.c. in this chapter. Burn
severity can be described as a percentage of area on plots of a specific size, or related
to specific inventory points. Although a qualitative measure, this descriptor can be
related to plant mortality, and amount and mode of reproduction, such as by rhizome
sprouting or seed germination.
Burn severity classes have been developed for bunchgrass plants. (See VI.B.2.d.(4))
Monitoring the relationship of these classes to postfire mortality or production of
specific species can provide a valuable tool for predicting postfire grass response when
considering emergency fire rehabilitation, or developing prescriptions for prescribed fire
use.
14. Moisture Conditions. The heat regime of a fire depends on the amount and
condition of the fuel on the site, how it burns, and the duration of burning. In order to
build a database that can be used to predict plant response to fire, moisture conditions
at the time of a fire must be documented, because moisture levels are a key regulator
of heat release during a fire. See Chapter III.B. and III.D. for a more complete
discussion of fuel moisture content and how it is measured.