Sampling Methods
There are five components of data sampling used
for this study
Conditions During the Fires
We will monitor fuel and fire weather conditions, fire
behavior, and soil heating profiles during fires. Fuel
characteristics will be described separately for the shrub,
grass/forb, and litter fuel layers. For each fuel layer,
we will measure mean height, load, percent cover, live
to dead ratio, and gravimetric moisture content. These
variables will be measured separately for 1, 10, and 100
hour fuels. Fire weather will include temperature, wind
speed, and relative humidity. Fire behavior data will be
measured
visually during each fire using pre-positioned reference
points within the fire and will include rates of spread,
flame length, flame height, and flame depth. Measurements
of fire behavior may be crosschecked using digital images
recorded at fire-resistant recording stations located adjacent
to the visual reference points. Soil heating will be monitored
using arrays of type-K transition joint thermocouple probes
(Omega Engineering) located -2, 0, and 10 cm from the soil
surface and attached to Campbell CR10X data-loggers. Fuel
conditions, fire behavior, and soil heating samples will
be collected at 5 replicate locations within the burned
area, which will allow us to evaluate variation within,
and inter-relationships among, these variables. These data
are necessary to precisely characterize each fire, since
we will only study two sites, and to evaluate the effectiveness
of seeding treatments given specific fire characteristics.
Total Plant Cover and Species Diversity
At the center of each 9 x 9 m treatment plot, we will
establish a 3 x 3 m sampling plot such that the plot edge
will be
3 m from the outside edge of the treatment plot. Plant
cover will be visually estimated using Braun-Blanquet cover
classes
for each species rooted within each of nine 1 m x 1 m subplots
in each sampling plot. This sampling method will provide
a coarse measure of plant cover, and is suited for documenting
changes in shrub and perennial grass cover before and after
burning. These methods will also allow us to calculate
plant species richness at three nested scales (1, 4, and
9 m2), and species evenness at two nested scales
(4 and 9 m2).
Herbaceous Plant Biomass and Density
Above-ground live biomass and density of cheatgrass, other
herbaceous plants, and perennial plant seedlings will be
measured separately for beneath-canopy (within the shrub
canopy dripline) and interspace (1 m outside the dripline)
microhabitats. Prior to burning, we will randomly chose
2 woody shrubs within each 3 x 3 m sampling plot, around
which we will measure herbaceous biomass and density. Two
10 x 10 cm sampling stations (100 cm2) will be established
in each microhabitat on the north and south side of each
shrub (n=2 sampling stations/microhabitat/shrub).
Samples will be collected during spring when above-ground
live biomass of winter annuals is highest and most species
have flowered and begun to set seed. All annual plants
and perennial seedlings rooted within each 10 x 10 cm sampling
station will be clipped at ground level, sorted by species
groups, counted to determine density, dried to a constant
mass at 60ºC, and weighed to determine above-ground
live dry biomass (0.0001 g precision). Species groups will
consist of the following: cheatgrass, other alien grasses,
each of the seeded species (3 introduced and 3 native grasses,
1 introduced and 1 native forb), alien forbs, native grasses,
native forbs, and native shrubs. Second year samples will
be located 5 cm from the first year samples and will be
considered repeated measures.
Soil Seedbank
Soil seedbank samples will be collected directly
adjacent to each plant biomass sample. Methods for sampling
were adapted from those developed early in this century,
and later modified. Soil samples will be collected by pressing
a tin soil canister (diameter 6.0 cm and height 4.4 cm)
firmly into the ground (3.0 cm deep) and sliding a metal
scraper
underneath (85 ml sample). Each sample will be placed into
a bowl and thoroughly homogenized. Rocks >1cm diameter
will be removed and soil aggregations will be broken so
that there will be no soil particles >1cm diameter.
One-half cup of the soil sample will be placed into a bulb
pot that is 6.5 inches in diameter and 3 inches tall and
is lined with a large natural coffee filter. One-half cup
of vermiculite will then be added to the top of each soil
sample to aid in moisture regulation. The pots will be
arranged randomly on a table in a greenhouse, and subjected
to four treatments including two wetting phases with tap
water, a third wetting phase with the addition of 50 ml
of 0.01 molar solution of potassium nitrate, and a fourth
wetting phase with the addition of a 6.5 * 10-4 molar solution
of gibberellic acid. These chemicals are known to trigger
germination of some types of seeds. Between each treatment
there will be a drying phase when the samples will be allowed
to dry out, in theory simulating the type of drying experienced
during annual dry seasons and thus tricking additional
seeds to germinate after a period of quiescence. The pots
will be allowed to dry for three to four weeks, before
starting the next wetting phase.
Seedling vouchers of all species germinated from the soil
samples will be collected, photographed, and preserved
permanently on 3 x 5 cards under clear tape. These vouchers
will be identified using a digital library of images, seedlings
preserved in a herbarium, or by allowing them to mature
and identifying the adult plants.
Soil Nutrients
Soil nutrients will also be measured at each sampling
station, using the same sampling protocol as described
above for the soil seedbank. Each sample will be sieved
to remove particles >2 mm, and sent to the UC Davis-DANR
lab or the BYU soil lab for analyses. We will measure NO3,
NH4, and PO4 to evaluate the effects of the nutrient manipulations
on plant available nitrogen and phosphorous. A sub-sample
will also be initially analyzed for soil texture, pH, organic
matter, and CaCO3 to characterize the general soil conditions
at the two study sites.
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