Shallow Clay (Big bluestem-Sideoats grama-Western wheatgrass)
Page 1.
Introduction: discussion of classification, seral assignment and monitoring.
Page 2.
Graph.
Page 3.
Instructions: plot setup and data collection using the Excel spreadsheet.
Page 4.
References.
Caution
Shallow Clay.xls is an Excel workbook containing the datasheet for field data collection. Copy the Excel file to a PDA.
The .xls file will be converted to a Pocket Excel file with a .pxl extension. The file contains a spreadsheet with formulas
that provide calculations necessary for classification of a site, using the variables defined for this ecological type.
Be careful with the spreadsheet when loaded on a PDA. Although the formulas and cells are protected on the PC version
of Excel, protection of spreadsheets/worksheets is not an option on the Pocket version of Excel. It is possible to erase
formulas and stop the classification system. Be sure to make changes only within the empty cells, and not in any of the
calculation or formula cells such as cov%, probabilities, etc.
In addition, always:
•
Keep a backup copy of the original ‘Shallow Clay.pxl’ file on your PDA and,
•
Save the file under a new name after finishing data collection on each site, e.g. ‘Shallow Clay site1.pxl’,
‘Shallow Clay site2.pxl’…….. to avoid overwriting previous files with data.
Monitoring Seral Stages in Big bluestem-Sideoats grama-Western wheatgrass Ecological Type
Classification, seral assignment, and monitoring of big bluestem-sideoats grama-western wheatgrass
ecological type seral stages is according to the method of Uresk (1990). Statistical analysis of field-collected
data indicates the presence of four seral stages: early, early intermediate (EINT), late intermediate (LINT)
and late. A site is classified, and assigned to a seral stage by entering a set of key plant indices into the set of
canonical discriminant functions developed for this ecological type and estimating posterior probability for
each seral stage (SPSS, 1995). The site monitored is assigned to the stage with the highest posterior
probability.
For the big bluestem-sideoats grama-western wheatgrass ecological type the key species are Andropogon
gerardii (ANGE), Bouteloua curtipendula (BOCU), Agropyron smithii (AGSM) and Bouteloua gracilis
(BOGR). Indices for these species are developed from data collected using the Daubenmire (1959) canopy
cover method. This method requires field collection of canopy cover and frequency of occurrence for each of
the three plant species. The index is produced by multiplying total cover by frequency of occurrence (as a
percent) for each species for the overall site.
The seral stage assigned to a set of plant indices is always associated with the greatest probability value. If
that value is 1, then succession is at the middle of the assigned seral stage. If the greatest probability value is
less than 1, then the second greatest probability value is used to determine the successional status relative to
middle of the assigned stage. For instance, if the second greatest probability is associated with an earlier seral
stage, succession is at the lower end of the assigned seral stage. On the other hand, if the second greatest
probability is associated with a later seral stage, succession is at the upper end of the assigned stage (see
example below).
When permanent macroplots are established to assess the vegetational trend of a site, re-sampling and
comparing the previously assigned seral stage to the current stage provides information about succession or
retrogression. On a finer scale, within-stage changes in vegetation successional status can be quantified by
comparing the probability values. For example, first-year field measurements collected for canopy cover and
frequency of occurrence on a site resulted in the following index values: ANGE=400, BOCU=2100,
AGSM=2100, and BOGR=800. Four years later the index values obtained were: ANGE=400, BOCU=2400,
AGSM=1800, and BOGR=400. Calculating the probabilities, we find:
ANGE BOCU AGSM BOGR
LATE LINT
EINT
EARLY
Stage
Year1
400
2100
2100
800
.000
.763
.155
.000
LINT
Year5
400
2400
1800
400
.000
.921
.009
.000
LINT
Difference
In both years, the site was classified
and assigned to the late intermediate seral
stage; the greatest probability values (.763
in Year1 and .921 in Year5) are associated
with LINT. Placement within the late
intermediate seral stage is at the lower end
of the stage, as indicated by the second
greatest probability values (.155 for Year1
and .009 for Year5) which are associated
with an earlier seral stage (EINT). The site
shows an upward successional change of
about .16, which is the difference between
the probabilities in Year1 and Year5.
The figure to the right illustrates this
example. These quantitative changes in the
probabilities can be used to evaluate and
monitor the effects of management
alternatives.
.158
Late
Late Intermediate
.76
Early Intermediate
Early
Year 1
1.0
.5
Late
1.0
.5
Late Intermediate
.92
1.0
1.0
.5
Early Intermediate
Early
Year 5
1.0
.5
Late
1.0
.5
1.0
Early Intermediate
Late Intermediate
.16
1.0
.5
Early
Change
1.0
.5
1.0
.5
1.0
.5
1.0
Page 1 of 4
Monitoring Seral Stages in Big bluestem-Sideoats grama-Western wheatgrass Ecological Type
Big bluestem-Sideoats grama-Western wheatgrass
Ecological Type by Seral Stages
6000
Big bluestem
Sideoats grama
Western wheatgrass
Blue grama
5000
Index values
4000
3000
2000
1000
0
LATE
L.INTERMEDIATE E.INTERMEDIATE
EARLY
Mean Index
Big bluestem
Sideoats grama
Western wheatgrass
Blue grama
4,787
197
540
2
480
2,558
828
536
286
1,171
3791
700
0
536
1,219
4,740
Mean indices of plant species through four seral stages of succession in a big bluestem, sideoats
grama, western wheatgrass ecological type. Smoothed lines connect the means for each key plant
species at each stage. Graph provides a guide for an approximate mixture of species at each seral
stage.
Page 2 of 4
Monitoring Seral Stages in Big bluestem-Sideoats grama-Western wheatgrass Ecological Type
1. Establish two parallel 30 m permanent
transects, 20 m apart, as a plot within the Big
bluestem-sideoats grama-western wheatgrass
(Shallow Clay) ecological type.
Recommendations are to establish two plots
per section within the ecological type.
2. Using the ‘Shallow Clay.xls’ spreadsheet
(see figure at left) installed on your PDA,
record canopy cover within a 20cm x 50cm
quadrat for Andropogon gerardii (ANGE),
Bouteloua curtipendula (BOCU), Agropyron
smithii (AGSM) and Bouteloua gracilis
(BOGR) at one-meter intervals along each
transect (30 readings/transect) using
Daubenmire (1959) classes 1 through 6.
Class Code
1
2
3
4
5
6
Cover Class
>0 - 5%
5 - 25%
25 - 50%
50 - 75%
75 - 95%
95 – 100%
Mid Point
2.5%
15%
37.5%
62.5%
85%
97.5%
The spreadsheet calculates percent canopy cover,
frequency-of-occurrence, and index values for each
plant species for each transect and for the site. It also
provides the classification probabilities by seral
stage and the seral stage assignment.
Shallow Clay.xls
Calculations
Cover (%) = Sum Daubenmire midpoint values for each
species per transect, divide by 30. Site cover = mean
cover of the 2 transects.
Frequency (%) = Divide the number of plot frames in
which the species is present by the total number of plot
frames on the transect. Convert that value to a percent by
multiplying by 100. Site frequency = mean of the 2
transects.
Index = the Site Cover mean times the Site Frequency
mean. ((Xsect 1 cover + Xsect 2 cover) / 2) x ((Xsect 1
freq + Xsect 2 freq) / 2)
Page 3 of 4
Monitoring Seral Stages in Big bluestem-Sideoats grama-Western wheatgrass Ecological Type
REFERENCES
Daubenmire, R. 1959. A canopy-coverage method of vegetational analysis. Northwest Science.
33(1):43-64.
SPSS 12.0 for Windows. 1989-2003. SPSS Inc. 444 N Michigan, Ave, Chicago, IL 60611.
Uresk, D. W. 1990. Using multivariate techniques to quantitatively estimate ecological stages in a
mixed grass prairie. J. Range Mgt. 43(4):282-285.
Page 4 of 4