
Fig. 2. A pole was used to measure the visual obstruction of 
residual vegetation. 
disc (Fig. 3) down the pole until the first piece of residual 
vegetation touched the bottom or edge of the disc. A 
height value was read at this point on the pole and 
rounded to the nearest half-decimeter. 
Between 1 July and 31 August, three sets of data were 
recorded for live plants within a square meter quadrat at 
12 stations per transect. These data sets included (1) a list 
of species present per transect, (2) an estimate of the per- 
centage composition of a plant species relative to all plant 
species within a quadrat (Brown 1954), and (3) an esti- 
mate of canopy coverage expressed as the percentage of 
ground area covered by the vertical projection of the maxi- 
mum spread of foliage (Cain 1932) of the above-ground 
parts of each species per quadrat (Brown 1954; Mueller- 
Dombois and Ellenberg 1974). No reduction adjustment 
was made for the small open spaces occurring in a canopy. 
The sum of percentage cover for all species within a quad- 
rat could exceed 100 % because of vertical structural strati- 
fication of the various plant species. A supplemental list 
was also kept of the plant species that occurred along each 
transect but not within the square meter quadrats. 
Scientific plant names correspond with the Atlas of the 
Flora of the Great Plains (Great Plains Flora Association 
1977). Table A-3 lists all plant species by name and pre- 
sents growth habit indices. 
Data Units and Analysis 
The original data were coded for keypunching and 
tabulated with the aid of Statistical Analysis System 
computer programs (SAS Institute Inc. 1979), 
Descriptive parameters for each species in SNC stands 
were estimated within square meter quadrats as follows: 
number quadrats in which a species occurred x 200 
- total number of quadrats 
percent 
frequency 
Fig. 3. A 30-cm-diameter plastic disc was used to measure the 
height of residual vegetation. 

relative _ number quadrats in which a species occurred x 100 
frequency total no. quadrats in which all species occurred 
percent estimated percent of ground area covered by a 
canopy = vertical projection of the canopy spread of a 
cover species x 100 
relative estimated % ground area covered by a species 
= — * 100 
canopy cover estimated % ground area covered by all species 
percent estimated number of a species in a quadrat 
100 
composition estimated numbers of all species in a quadrat 
importance relative frequency + relative canopy cover 
value + relative composition 
The sum of the importance values for all species in a stand 
sample equalled 300%. Importance values are synthetic 
values commonly used to position or rank a species within 
a stand or community or among different kinds of stands 
or communities. 
Twenty different measures were analyzed for their rela- 
tion to visual obstruction measurements taken in the same 
stand: seven measures of precipitation (the long-term 
average, total from initial planting year to measurement 
year, total from initial planting year to measurement year 
plus 1 year before planting, the previous year plus the 
initial year, the year before planting only, the 2 years 
before planting, and the standardized, expressed as the 
previous year’s precipitation minus the long-term average 
divided by the long-term average); three soil classes (soil 
capability Class II, soil capability Class III, and soil cap- 
ability Class IV); the percentage of grass estimated per 
stand; and nine age classes representing the nine growing 
seasons since planting. 
Scatter-plot diagrams indicated little or no relation be- 
tween visual obstruction and height measurements and the 
first six precipitation variates. The seventh or the stand- 

