FIRE CASE STUDIES
SPECIES: Muhlenbergia montana | Mountain Muhly 



CASE NAME : 
Fort Valley Experimental Forest, AZ/Prescr. Fire/Grass & Shrub Response

Vose, J. M.; White, A. S. 1991 [15570]
White, A. S.; Cook, J. E.; Vose, J. M. 1991 [16885]


SEASON/SEVERITY CLASSIFICATION : 
fall/moderate in ponderosa pine (Pinus ponderosa) sawtimber stands
fall/severe in ponderosa pine pole stands


STUDY LOCATION : 
Prescribed fires were conducted at the Fort Valley Experimental Forest
near Flagstaff, Arizona.


PREFIRE VEGETATIVE COMMUNITY : 
The ponderosa pine overstory occurred in three kinds of spatially
distinct patches.  Sawtimber patches had average dbh of 25 inches (63
cm) and density of 49 trees per acre (120 trees/ha).  There was a thick
accumulation of litter 12 to 20 inches (30-50 cm) beneath the canopies
of sawtimber trees; between canopies, openings received full sunlight
and had minimal litter accumulation.  Pole patches had average dbh of 6
inches (15 cm) and density of 700 trees per acre (1,730 trees/ha).
Sapling patches had average dbh of 1.8 inches (4.5 cm) and density of
4,075 trees per acre (10,070 trees/ha).  The groundlayer was heavily
shaded in sapling patches because of high tree density.  Understory
grasses were mountain muhly (Muhlenbergia montana), Fendler bluegrass
(Poa fendleriana), and bottlebrush squirreltail (Elymus elymoides).
Shrubs included Fendler's ceanothus (Ceanothus fendleri) and Wood's rose
(Rosa woodsii var. ultramontana).


TARGET SPECIES PHENOLOGICAL STATE : 
Not given.


SITE DESCRIPTION : 
The study site is at 6,890 feet (2,100 m) elevation.  Soil is stony clay
loam.  Annual precipitation averages 19.7 inches (500 mm).  There is
pronounced drought in May and June, frequent rain in July and August,
and scattered snowfall and rain in winter.  Prior to prescribed burning,
the site was relatively undisturbed, with no evidence of grazing.  The
study area was fenced in 1982, prior to plot establishment, to prevent
future livestock grazing.


FIRE DESCRIPTION : 
Fire history of the study area suggests that fires occurred at
approximately 2-year intervals until the late 1800's, after which fires
were excluded until the time of the study.  Ungrazed ponderosa pine
stands were prescribed burned on 2 consecutive days in late October
1982.  Mean air temperatures were 64 and 57 degrees Fahrenheit (18 and
14 deg C).  Relative humidity was 21 percent on both days.  Backfires
were used on sawtimber patches; both back- and headfires were used on
pole and sapling patches.  Fires were restricted to the understory and
little immediate damage to overstory trees was apparent.  Using
heat-yield data and observations, fire severity in the burned patches
was ranked:  below-canopy sawtimber sites > pole > sapling > open-canopy
sawtimber sites.  On below-canopy sawtimber sites, fires consumed 95
percent of the fuel load and smoldered for several days.  Fire behavior
was as follows:

                         Open-ST    Below-ST     Pole       Sapling

Intensity (kW/m)      
   Backfires                 5         NA           14          17
   Headfires                NA         NA          346         294
Rate of spread (m/min)
   Backing fires             0.2       NA            0.2         0.3
   Head fires               NA         NA            4.5         7.6
Total heat yield
   (kJ/sq m)             1,600         NA       42,082      15,866
Fuel load (Mg/ha)           17.1      145.9         46.2        30.5
Fuel Consumption, %         25         95           55          33

Note:  Open sawtimber (Open-ST); below-canopy sawtimber (Below-ST); not
       available (NA)


FIRE EFFECTS ON TARGET SPECIES : 
Mountain muhly was common on the experimental sites before and after the
prescribed fires.  From mid-September through October 1982, prior to
burning, mountain muhly cover was estimated on burn sites and control
sites in below-canopy sawtimber, open sawtimber, pole, and sapling
stands.  Postfire inventory was conducted from mid-October to
mid-November 1983, on all sites.  Mountain muhly cover and biomass on
control sites were similar in 1982 and 1983.  Mountain muhly average
percent cover was lower on burned sites in 1983 due to high mortality,
no increased growth of surviving plants, and almost no seedling
recruitment.  Mountain muhly biomass was significantly (p<.05) lower on
burned plots than on control plots on open sawtimber sites and on pole
sites; biomass analysis in below-canopy sites and sapling patches was
not possible.

Mountain muhly seedling recruitment was monitored under burned and
unburned conditions.  Seed rain was monitored for a full year after
burning.  Mountain muhly total seed rain for 1 year was 81 seeds per
square meter on burned open sawtimber sites and 27 seeds per square
meter on unburned open sawtimber sites.  There was no mountain muhly
seed rain in closed-canopy sawtimber, pole, or sapling stands.  No
mountain muhly seeds germinated in greenhouse tests of buried seed.  A
very few mountain muhly seedlings appeared on burned, open timber sites
(0.1 seedling/sq m), but none appeared at other burned sites.  It
appears that buried seed is not important in contributing new seedlings
after burning.

Mountain muhly flowering response was measured in ponderosa pine
sawtimber (closed-canopy and open-canopy combined) and pole patches.
Sapling patches were not measured.  Only plants that had occurred on the
sites prior to burning were monitored.  Mountain muhly failed to flower
the first year after burning on both the ponderosa pine sawtimber and
pole patches.  During the second year, no significant differences in
mountain muhly flowering existed between burned sawtimber and pole
patches and their controls.  The percentage of mountain muhly plants
producing seeds the second year was approximately the same in burned and
unburned areas.  Percent of mountain muhly plants that reached flowering
stage each year was as follows:

                           Plants Flowering (%)

                   Pole                     Sawtimber
            Burned     Unburned         Burned     Unburned

    1983      0*          38              0*           54
    1984     25           33             42            33

* Indicates significant difference (p<.05) between burned and unburned
    sites.   


FIRE MANAGEMENT IMPLICATIONS : 
Mountain muhly cover and biomass decrease in response to fire, and
flowering is suppressed for 1 postfire year.



FIRE CASE STUDIES
SPECIES: Muhlenbergia montana | Mountain Muhly 



CASE NAME : 
Fort Apache Indian Reservation, AZ/Prescr. Fire/Fuel,Timber & Forage Effects



SEASON/SEVERITY CLASSIFICATION : 
spring/moderate


STUDY LOCATION : 
Prescribed fires were carried out on the Fort Apache Indian Reservation
7 miles (11 km) east of McNary, Arizona.


PREFIRE VEGETATIVE COMMUNITY : 
Prefire vegetation was in uneven-aged variable density ponderosa pine
(Pinus ponderosa) stands with open grassy glades which included mountain
muhly (Muhlenbergia montana), with cover of about 70 percent, and
bottlebrush squirreltail (Elymus elymoides). 


TARGET SPECIES PHENOLOGICAL STATE : 
Not given.


SITE DESCRIPTION : 
The study site is at an elevation of 7,400 feet (2,256 m).  The ground
is flat, and the soil is "rather heavy."  The area was selectively
logged in 1924. Grass density was low because of the relatively dense
trees.  Forage was similar on all plots.


FIRE DESCRIPTION : 
There were six burned plots and six unburned control plots in a
ponderosa pine habitat type.  Three plots were burned September 30,
1950; another three were burned October 10, 1950.

Average fuel weights before burning (in tons per acre) were as follows:

                            Control     September      October
         Size of Fuel        Plots      Burn Plots    Burn Plots

    Large (diam. > 12 in)     4.49         8.00*         3.73*
    Medium (2-11 in. diam.)   3.81         3.08          1.40
    Small (< 2 in. diam.)     6.94         6.21          4.83
    Total                    15.24        17.29**        9.96**

*  Difference between September and October plots significant (p<.05).
** Difference between September and October plots significant (p<.01).

Small fuels included needles, dead grass, cones, and partly rotted wood.

Weather conditions were different on the 2 burning days, and the effects
of the fires were markedly different.  The September fire was conducted
from 10:00 a.m. to 3:40 p.m.  Air temperature was 59 to 67 degrees
Fahrenheit (15-19 deg C).  Relative humidity was 62 to 37 percent.  Fuel
moisture was 14.0 to 11.6 percent.  Wind velocity was 18 to 25 miles per
hour (29-40 km/hr).  A light shower fell during burning of two of the
three plots, and 0.25 inches (0.64 cm) rain fell after 6:00 pm, cooling
the site.

The October fire was conducted from 12:00 m. to 3:30 p.m.  Air
temperature was 73 to 75 degrees Fahrenheit (23-24 deg C).  Relative
humidity was 19 to 17 percent.  Fuel moisture was 10.0 to 8.5 percent.
Wind velocity was 3 to 12 mph (5-19 km/hr).  Wind was variable and
gusty, causing spot blowups during burning.

The effect of the fires on surface fuel weight was as follows:

                           Percent Change

                 September Fire        October Fire

        Large        -63*                  -74*
        Medium       -62*                  +83* 
        Small        -48                   -51
        Total        -57                   -40

* Difference between September and October fires significant (p<.05).


Reduction of heavy fuel by the October fire was partially offset by an
increase in medium fuel.  Both fires raised the lower level of tree
crowns in sapling thickets and killed almost all trees less than 3 or 4
feet (0.9-1.2 m).


FIRE EFFECTS ON TARGET SPECIES : 
Mountain muhly was reduced on all burned plots the first year after
burning, as were other grasses.  Two years later mountain muhly
comprised about 60 percent of total grass density, 10 percent less than
prefire levels. 


FIRE MANAGEMENT IMPLICATIONS : 
Mountain muhly usually declines the first growing season after fire.  It
usually does not regain its former cover until at least 3 years after
fire.

Related categories for Species: Muhlenbergia montana | Mountain Muhly