Greasewood
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
Greasewood.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 ‘Greasewood.pxl’ file on your PDA and,
•
Save the file under a new name after finishing data collection on each site, e.g. ‘Greasewood site1.pxl’,
‘Greasewood site2.pxl’… to avoid overwriting previous files with data.
Monitoring Seral Stages in Greasewood-Western wheatgrass Ecological Type
Classification, seral assignment, and monitoring of greasewood-western wheatgrass ecological type seral
stages is according to the method of Uresk (1990). Statistical analysis of field-collected data indicates the
presence of three seral stages: early, intermediate (INT), 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 greasewood-western wheatgrass ecological type, the key species are Sarcobatus vermiculatus
(SAVE) and Agropyron smithii (AGSM). 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 two 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: SAVE=4300 and AGSM=1700. Four
years later the index values obtained were: SAVE=4300 and AGSM=2300. Calculating the probabilities, we
find:
SAVE AGSM
LATE
INT
EARLY
Stage
Year1
4300
1700
.325
.674
.001
INT
Year5
4300
2300
.196
.804
.000
INT
0
600
Difference
In both years, the site was classified
and assigned to the intermediate seral stage;
the greatest probability values (.674 in
Year1 and .804 in Year5) are associated
with
INT.
Placement
within
the
intermediate seral stage is at the upper end
of the stage, as indicated by the second
greatest probability values (.325 for Year1
and .196 for Year5) which are associated
with a later seral stage (LATE). The site
shows a downward successional change of
about .13, which is the difference between
the probabilities in Year1 and Year5.
.130
Late
Year 1
1.0
.5
Late
1.0
.5
Intermediate
.80
1.0
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
.67
1.0
.5
Intermediate
.13
1.0
Early
C hange
1.0
.5
1.0
.5
1.0
Page 1 of 4
Monitoring Seral Stages in Greasewood-Western wheatgrass Ecological Type
Greasewood-Western Wheatgrass
Ecological Type by Seral Stages
M ean In d ex V alu es o f K ey p lan ts
8000
G reasew o o d
W estern w h eatg rass
7000
Index Values
6000
5000
4000
3000
2000
1000
0
L AT E
IN T E R M E D IAT E
E AR L Y
Mean Index
Greasewood
Western wheatgrass
6769
1086
1964
2946
700
854
Mean indices of plant species through three seral stages of succession in a greasewood-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 Greasewood-Western wheatgrass Ecological Type
1. Establish two parallel 30 m permanent
transects, 20 m apart, as a plot within the
greasewood-western wheatgrass ecological
type. Recommendations are to establish
two plots per section within the ecological
type.
2. Using the ‘Greasewood.xls’ spreadsheet
(see figure at left) installed on your PDA,
record canopy cover within a 20cm x 50cm
quadrat for Sarcobatus vermiculatus
(SAVE) and Agropyron smithii (AGSM) 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.
Greasewood.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 Greasewood-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