Dry Valleys (Prairie sandreed-Little bluestem-Sedge)
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
Dry Valleys.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 ‘Dry Valleys.pxl’ file on your PDA and,
•
Save the file under a new name after finishing data collection on each site, e.g. ‘Dry Valleys site1.pxl’, ‘Dry
Valleys site2.pxl’…….. to avoid overwriting previous files with data.
Monitoring Seral Stages in Prairie sandreed-Little bluestem-Sedge Ecological Type
Classification, seral assignment, and monitoring of prairie sandreed-little bluestem-sedge 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 prairie sandreed-little bluestem-sedge ecological type, the key species are Calamovilfa longifolia
(CALO), Schizachyrium scoparium (SCSC), and Carex spp. (CARX). 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: CALO=500, SCSC=2200, and
CARX=1500. Four years later the index values obtained were: CALO=1000, SCSC=2900, and CARX=600.
Calculating the probabilities, we find:
CALO SCSC
CARX
LATE LINT
EINT
EARLY
Stage
Year1
500
2200
1500
.000
.589
.224
.186
LINT
Year5
1000
2900
600
.000
.791
.161
.048
LINT
Difference
In both years, the site was classified and assigned
to the late intermediate seral stage; the greatest
probability values (.589 in Year1 and .791 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 (.224 for Year1 and .161 for Year5) which are
associated with an earlier seral stage (EINT). The site
shows an upward successional change of about .2,
which is the difference between the probabilities in
Year1 and Year5.
.202
Late
Late Intermediate
.59
Early
Year 1
1.0
.5
Late
1.0
.5
Late Intermediate
.79
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
1.0
Early Intermediate
Late Intermediate
.20
1.0
.5
Early
Change
1.0
.5
1.0
.5
1.0
.5
1.0
Page 1 of 4
Monitoring Seral Stages in Prairie sandreed-Little bluestem-Sedge Ecological Type
Prairie sandreed-Little bluestem-Sedge
Ecological Type by Seral Stages
3500
Prairie sandreed
Little bluestem
Sedge spp.
3000
Index Values
2500
2000
1500
1000
500
0
LATE
L.INTERMEDIATE E.INTERMEDIATE EARLY
Mean Index
Prairie sandreed
Little bluestem
Sedge spp
1,810
4
1,921
157
3,122
1,448
449
665
2,445
338
468
237
Mean indices of plant species through four seral stages of succession in a prairie sandreed, little
bluestem sedge 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 Prairie sandreed-Little bluestem-Sedge Ecological Type
1. Establish two parallel 30 m permanent
transects, 20 m apart, as a plot within the
prairie sandreed-little bluestem-sedge
ecological type. Recommendations are to
establish two plots per section within the
ecological type.
2. Using the ‘Dry Valleys.xls’ spreadsheet (see
figure at left) installed on your PDA, record
canopy cover within a 20cm x 50cm quadrat
for Calamovilfa longifolia (CALO)
Schizachyrium scoparium (SCSC) and Carex
spp. (CARX) 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.
Dry Valleys.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 Prairie sandreed-Little bluestem-Sedge 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