Introduction: discussion of classification, seral assignment and monitoring. Instructions: plot setup and data collection using the Excel spreadsheet.

Transcription

1 Shallow Clay (Big bluestem-sideoats grama-western wheatgrass) Page 1. Page 2. Page 3. Page 4. Introduction: discussion of classification, seral assignment and monitoring. Graph. Instructions: plot setup and data collection using the Excel spreadsheet. 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.

2 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 Year LINT Year LINT Difference.158 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 Year 1 Year 5 Change Page 1 of 4

3 Big bluestem-sideoats grama-western wheatgrass Ecological Type by Seral Stages Big bluestem Sideoats grama Western wheatgrass Blue grama 4000 Index values LATE L.INTERMEDIATE E.INTERMEDIATE EARLY Mean Index Big bluestem 4, Sideoats grama 197 2,558 1, Western wheatgrass ,219 Blue grama ,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

4 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 Cover Class Mid Point 1 >0-5% 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

5 REFERENCES Daubenmire, R A canopy-coverage method of vegetational analysis. Northwest Science. 33(1): SPSS 12.0 for Windows SPSS Inc. 444 N Michigan, Ave, Chicago, IL Uresk, D. W Using multivariate techniques to quantitatively estimate ecological stages in a mixed grass prairie. J. Range Mgt. 43(4): Page 4 of 4