Monardella follettii monitoring
Meadow Valley Group Selection Units
Michelle Coppoletta
November 18, 2010
In August of 2006, eight permanent plots were established within (and in the vicinity of)
Meadow Valley Group Selection Units 46 and 38 to evaluate the effects of group selection
treatments on Monardella follettii abundance. Three of the eight plots were designated as
controls where mechanical treatment and equipment were excluded. Group selection
treatments took place during the summer of 2007 and all eight plots were revisited and
monitored one year after treatment (August 27, 2008) and three years after treatment (August
23, 2010).
The following tables and figures present the pre and post-treatment monitoring data for the
eight M. follettii plots. Table 1 presents the number of M. follettii stems recorded in each plot.
Table 2 presents duff depth data, which were recorded to capture changes in the physical
characteristics of the eight M. follettii plots following treatment. Canopy cover was also
recorded, but is not presented due to the fact that the monitoring was insufficient to capture
change.
Table 1. The number of M. follettii stems within permanent plots prior to and following
treatment.
Plot #
Group Selection
1
2
3
4
6
Control
5
7
8
Pre-treatment
(2006)
1-year post treatment
(2008)
3-year post treatment
(2010)
564
109
119
37
203
312
47
47
60
2
451
163
163
219
60
291
625
180
182
349
144
291
Large snag fell into plot
165
Figure 1. The average number of M. follettii stems within treatment and control plots prior to
and following treatment. The error bars represent the 90 percent confidence intervals.
Table 2. Average duff depth (cm) in M. follettii permanent plots pre and post-treatment. The
control plots are highlighted in grey.
Plot #
Group Selection
1
2
3
4
6
Control
5
7
8
Pre-treatment
(2006)
1-year post treatment
(2008)
3-year post treatment
(2010)
0.7
0.9
1.3
1.2
1.1
2.8
0.6
1.1
2.9
0.9
0.7
0.5
1.2
1.5
0.2
0.8
0.7
1.2
0.9
1.3
1.8
1
Large snag fell into plot
3
Number of M. follettii stems
A repeated measures analysis (using a mixed-effects model) found no significant difference
between the plots that were treated with Group Selection harvest and the control plots. There
was also no significant interaction between the treatments and time. There was a significant
effect of year (p=0.01; ά = 0.05). The number of stems within all of the plots (whether they
were treated or controls) was significantly lower in 2008, than in either 2006 or 2010. The
number of stems was not significantly different between 2006 (pre-treatment) and 2010 (three
years post-treatment). This suggests that there may be relatively large natural variability in the
number of M. follettii stems between years.
Figure 2. The average number of M. follettii stems within treatment and control plots in 2006,
2008, and 2010. For all plots, the number of stems was significantly lower in 2008, compared
to 2006 and 2010.
During the 2008 monitoring effort, it became apparent that some plots were more heavily
impacted than others within the treatment area; for example, two of the five treatment plots
were in the middle of a skid trail and received a much greater degree of disturbance. The
photographs below provide an example of what we classified as “high” and “moderate”
disturbance within treatment plots.
“High” disturbance classification
Pre-treatment
Post-treatment
“Moderate” disturbance classification
Pre-treatment
Post-treatment
Those treatment plots located within skid trails were classified as having “high” disturbance
while those treatment plots that were located off of skid trails, but still within the area of
treatment, were classified as having “moderate” disturbance. It is important to note that even
the plots that were classified as “moderate” still experienced a great deal of disturbance (i.e.
debris piled on top of plants). In the analysis, there was no significant difference between
treatments of varying intensity.
The presence of M. follettii individuals within the treatment plots suggests that the species is
able to tolerate a fair amount of disturbance; M. follettii plants were found (albeit in much
lower abundance) in areas that were scraped of almost all of the duff and vegetation (i.e. skid
trails) and under woody debris. Many of the M. follettii within the treatment area were noted
to be robust with multiple flowering branches.
The lack of significance between the control and treatment plots suggests a few different
possibilities. First, that there is no difference between treatments and controls; or in other
words, the difference in the number of M. follettii stems before and after treatment is within
the natural range of variability observed for the species in the control plots. This seems to be
the most likely when considering the variability in both treatments and controls from year to
year.
A second, very important possibility is that we did not have enough experimental power to
detect a true difference between the control plots and the treatment plots. We need to do a
power analysis using the following objective:
Objective: To be 90% certain of detecting a 20% difference in mean plant density (i.e. the
number of stems per square meter) in group selection treatment units and in control
areas. We are willing to accept a 10% chance that a false-change error occurred
(conclude a change occurred when it really did not).
Environmental Data: There was no significant relationship between duff depth and number of
stems.
Photographs
Plot 1
Pre-treatment
Post-treatment
Plot 2
Pre-treatment
Post-treatment
Plot 3
Pre-treatment
Post-treatment
Plot 4
Pre-treatment
Post-treatment
Plot 5 (Control)
Pre-treatment
Post-treatment
Plot 6
Pre-treatment
Post-treatment
Plot 7 (Control)
Pre-treatment
Post-treatment
Plot 8 (Control)
Pre-treatment
Post-treatment