Big Sagebrush
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
Big Sagebrush.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 ‘Big Sagebrush.xls’ file on your PDA and,
•
Save the file under a new name after finishing data collection on each site, e.g. ‘Big Sagebrush site1.pxl’, ‘Big
Sagebrush site2.pxl’,….. to avoid overwriting previous files with data.
Monitoring Seral Stages in Big sagebrush-Western wheatgrass-Blue grama Ecological Type
Classification, seral assignment, and monitoring of big sagebrush-western wheatgrass-blue grama
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, 1989-2003). The site monitored is assigned to the stage with the highest posterior
probability.
For the big sagebrush-western wheatgrass-blue grama ecological type the key species are Artemisia
tridentata (ARTR), 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: ARTR=1100, AGSM=1500, and
BOGR=1900. Four years later the index values obtained were: ARTR=1100, AGSM=1800, and BOGR=1700.
Calculating the probabilities, we find:
ARTR AGSM BOGR
LATE LINT
EINT
EARLY
Stage
Year1
1100
1500
1900
.000
.842
.155
.003
LINT
Year5
1100
1800
1700
.000
.991
.009
.000
LINT
0
300
200
Difference
In both years, the site was classified and
assigned to the late intermediate seral stage;
the greatest probability values (.842 in Year1
and .991 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 (.115 for Year1 and .009 for Year5)
which are associated with an earlier seral
stage (EINT). The site shows an upward
successional change of about .15, which is
the difference between the probabilities in
Year1 and Year5.
.151
Late
Late Intermediate
.84
Early
Year 1
1.0
.5
Late
1.0
.5
Late Intermediate
.99
1.0
1.0
.5
Early Intermediate
Early
Year 5
1.0
.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.
Early Intermediate
1.0
.5
Late Intermediate
.15
1.0
1.0
.5
Early Intermediate
Early
Change
1.0
.5
1.0
.5
1.0
.5
1.0
Page 1 of 4
Monitoring Seral Stages in Big sagebrush-Western wheatgrass-Blue grama Ecological Type
Big sagebrush-Western wheatgrass- Blue grama
Ecological Type by Seral Stages
5000
Big sagebrush
Western wheatgrass
Blue grama
4000
Index Values
3000
2000
1000
0
Late
L. Intermediate
E. Intermediate
Early
Mean Index
Big sagebrush
Western wheatgrass
Blue grama
4,666
458
191
1,297
1,738
863
222
605
2,707
835
343
6
Mean indices of plant species through four seral stages of succession in a big sagebrush , western
wheatgrass, blue grama, 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 sagebrush-Western wheatgrass-Blue grama Ecological Type
Instructions
1. Establish two parallel 30 m permanent transects,
20 m apart, as a plot within the big sagebrushwestern wheatgrass-blue grama ecological type.
Recommendations are to establish two plots per
section within the ecological type.
2. Using the ‘Big Sagebrush.xls’ spreadsheet (see
figure at left) installed on your PDA, record
canopy cover within a 20cm x 50cm quadrat for
Artemisia tridentata (ARTR) Agropyron smithii
(AGSM) and Bouteloua gracilis (BOGR) at onemeter 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.
Big Sagebrush.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 sagebrush-Western wheatgrass-Blue grama Ecological Type
REFERENCES
Benkobi L, DW Uresk, and RD Child. 2007. Ecological classification and monitoring model for the
Wyoming big sagebrush shrubsteppe habitat type of northeastern Wyoming. Western North
American Naturalist: Vol. 67, No. 3 pp. 347–358.
Benkobi, L. and D.W. Uresk. 1995. Seral stage classification and monitoring model for big
sagebrush/western wheatgrass/blue grama habitat. . Gen. Tech. Rep. INT-338. Ogden,
UT/USA: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range
Experiment Station. 5.
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