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
Western Wheatgrass.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 ‘Western Wheatgrass.xls’ file on your PDA and,
•
Save the file under a new name after finishing data collection on each site, e.g. ‘Western Wheatgrass site1.pxl’,
‘Western Wheatgrass site2.pxl’… to avoid overwriting previous files with data.
Monitoring Seral Stages in Western wheatgrass-Blue grama-Buffalograss Ecological Type
Classification, seral assignment, and monitoring of western wheatgrass-blue grama-buffalograss 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 western wheatgrass-blue grama-buffalograss ecological type the key species are Agropyron smithii
(AGSM), Bouteloua gracilis (BOGR) and Buchloe dactyloides (BUDA). 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: AGSM=200, BOGR=2400, and
BUDA=3800. Two years later the index values obtained were: AGSM=600, BOGR=2800, and BUDA=3200.
Locating these values in the tables, we find:
AGSM BOGR BUDA
LATE LINT
EINT
EARLY
Stage
Year1
200
2400
3800
.000
.118
.849
.033
EINT
Year3
600
2800
3200
.000
.318
.586
.096
EINT
Difference
In both years, the site was classified and
assigned to the early intermediate seral stage;
the greatest probability values (.849 in Year1
and .586 in Year3) are associated with EINT.
Placement within the early intermediate seral
stage is at the upper end of the stage, as
indicated by the second greatest probability
values (.118 for Year1 and .318 for Year3)
which are associated with a later seral stage
(LINT).
The site shows an upward
successional change of about .26, which is the
difference between the probabilities in Year1
and Year3.
.263
Late
Late Intermediate
Early Intermediate
Early
0.85
Year 1
1.0
0.5
Late
1.0
0.5
Late Intermediate
1.0
0.5
Early Intermediate
1.0
Early
0.59
Year 3
1.0
0.5
Late
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.
1.0
0.5
Late Interme diate
1.0
0.5
Early Intermediate
1.0
Early
0.26
Change
1.0
0.5
1.0
0.5
1.0
0.5
1.0
Page 1 of 4
Monitoring Seral Stages in Western wheatgrass-Blue grama-Buffalograss Ecological Type
Western wheatgrass-Blue grama-Buffalograss
Ecological Type by Seral Stages
6000
5000
Western wheatgrass
Blue grama
Buffalograss
Index Values
4000
3000
2000
1000
0
Late
L. Intermediate
E. Intermediate
Early
Mean Index
Western wheatgrass
Blue grama
Buffalograss
4,212
1,213
81
113
4,892
1,669
629
945
4,975
611
1,205
494
Mean indices of plant species through four seral stages of succession in a western wheatgrass-blue
grama-buffalograss vegetation 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 Western wheatgrass-Blue grama-Buffalograss Ecological Type
1. Establish two parallel 30 m permanent
transects, 20 m apart, as a plot within the
western wheatgrass-blue grama-buffalograss
ecological type. Recommendations are to
establish two plots per section within the
ecological type.
2. Using the ‘Western Wheatgrass.xls’
spreadsheet (see figure at left) installed on
your PDA, record canopy cover within a
20cm x 50cm quadrat for Agropyron smithii
(AGSM), Bouteloua gracilis (BOGR) and
Buchloe dactyloides (BUDA) 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.
Western Wheatgrass.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 Western wheatgrass-Blue grama-Buffalograss Ecological Type
REFERENCES
Daubenmire, R. 1959. A canopy-coverage method of vegetational analysis. Northwest Science.
33(1):43-64.
SPSS 12.0 1989-2003. SPSS Inc. 444 N Michigan, Ave, Chicago, IL 60611. Copyright SPSS, All
rights reserved.
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