Silene occidentalis ssp longistipitata
Deadhorse Mechanical Thinning Treatment Effects
Monitoring Report – Preliminary Results, 1 year after treatment
Nov 10, 2010
Colin Dillingham
I.
Introduction
The Nature Conservancy (W-1, 1996) currently lists Silene occidentalis ssp.
longistipitata as a G4T1 plant indicating that the taxon is imperiled worldwide. The Grank reflects the condition of the entire species (secure), whereas the T-rank reflects the
global situation of just the subspecies. The Nature Conservancy (W-1, 1996) gives the
taxon as S1.2 in California, indicating that it is critically imperiled and the occurrences
are threatened. The California Native Plant Society (W-4) lists the species as 1B.2,
which indicates that it is rare, threatened, or endangered in California and 20-80% of
occurrences are threatened.
It is not clear which environmental factors limit the distribution or abundance of the longstiped campion (Dillingham and Sanger 2007). It may be lack of disturbance regime.
There may be too little light reaching the forest floor outside of the forest opening
currently occupied by long-stiped campion.
Monitoring at Silene occidentalis ssp longistipitata locations indicate that there is a large
natural variability in the number of plants present each year. A review of annual
monitoring plant census at populations on the Lassen National Forest indicate that
occurrences can have annual population fluctuation of 50% and return to previous
population levels without any vegetation treatment (i.e. South Fork Antelope Creek Site,
Dillingham and Sanger 2007). Therefore, we can expect that some populations will
increase or decrease by 50% because of natural variation and not as a response to
treatment. With statistical analysis, we may be able to determine that a population has
changed by a smaller amount when comparing controls to treatment areas. However,
small changes in the population are not considered significant in terms of management.
II.
Methods
We are primarily concerned with maintaining self-sustaining populations at each site.
The mean post-treatment population (at least 3 years of data) shall be at least equal to the
minimum total number of long-stiped campion plants found during pretreatment
conditions. A decrease of up to 50% of the pre-treatment population level, although not
considered desirable, would be considered within the range of natural variability for any
individual year. It is the longer term population means that we are trying to maintain.
The populations should be maintained at this level through 2015 (5 years after
implementation of the thinning project).
Both positive and negative effects from proposed management activities are possible.
At the Deadhorse site, mechanical thinning operations were completed in the fall of 2009
(retain 100 trees per acre greater than 6 inches diameter at breast height). One hypothesis
is that the new disturbance could provide a suitable seedbed for the species and the
opening of the canopy could provide more light to the forest floor for population
expansion. An alternate hypothesis is that the timber harvest and prescribed burning
operations may also cause direct impacts to individual plants, displace or remove existing
duff and eliminate seeds from the seed bank.
Table 1. Monitoring Areas Included in this Monitoring Report
Site Name
Occurrence
Treatment Type
Number
Deadhorse Falls
13
Mechanical Thin
Monterey Point
8
Control (for Deadhorse)
“Smitty Camp”
A complete census of the adult plants within the macroplots was conducted in July of
each year. Although data exists for subplots within the macroplots, no analysis at this
small scale has been attempted. It appears that the thinning treatment was applied
relatively evenly across the macroplot and no data stratification appears necessary.
All data presented is for adult plants within the entire macroplot. Although we
present our data as a census, we recognize that some plants may be missed. We feel
that the percent of adult plants missed is very small, likely less than 5%.
In order to capture some of the effects of the proposed treatments, photo points were
completed and the following measurements were recorded in the four corners of each
subplot:
duff depth (cm)
canopy cover (using densitometer or “moosehorn”)
shrub height in meters
A. Monitoring location
The Deadhorse and Smitty Camp long-stiped campion monitoring macroplots are
located in Tehama County. Previous versions of the monitoring protocol indicated
that the Scott’s John Creek occurrence in Butte County would be used as the control
plot. Upon further investigation, it was determined that the habitat (red fir), elevation
difference and lack of juxtaposition made the Scott’s John Creek less desirable as a
control for comparison to the Deadhorse site. The Smitty Camp control at Monterey
Point was much more similar in habitat, adjacency, plot size, population size and
elevation and is considered to be a superior control plot. Specific locations are
available in the HFQLG rare plant monitoring database.
B. Intended data analysis approach
The potential population changes will be compared against the pre-treatment and
control population estimates. Under the assumption that the control population mean
does not have a greater than 25% change from the mean during the same sampling
period, the population responses would be considered to be caused by management
activities, unless other evidence suggests otherwise. In the event that the control area
also changes, a more rigorous statistical evaluation would be coordinated between
Lassen NF botanists Kirsten Bovee and Allison Sanger, and SPI monitoring
coordinator Cajun James and USDA Forest Service Herger-Feinstein Quincy Library
Group monitoring coordinator Colin Dillingham.
III.
Preliminary results
The data indicates that the population increased between 2009 and 2010 at the
Deadhorse site in the immediate year after the treatment was completed (Figure 1).
However, the plant count remained in the range of the pretreatment population level
and therefore the population appears to have remained the same following the
definitions established in the long-stiped campion monitoring protocol (Dillingham et
al. 2007, revised 2010). The thinning treatment reduced the canopy from a
pretreatment mean of 66 percent canopy closure down to 48 percent post-treatment
(Figure 1). There were little environmental changes to duff depth or shrub cover or
height. There was no association between annual rainfall and annual plant counts.
Although the treatment population increased between 2009 and 2010 by 170%, the
control population at Smitty Camp also increased by 210% during the same period
(Figure 2). It appears that some environmental factor could be partially responsible
for the large increase in long-stiped campion in the treatment plot.
140
120
100
Plants
80
% Canopy
60
Duff Depth mm
Rainfall (inches)
40
20
0
2007
2008
2009
2010
Figure 1. Preliminary Results of Deadhorse Site Plant and Environmental Data. The
Deadhorse site was treated in the fall of 2009, after the 2009 pretreatment data was
collected.
200
180
160
140
120
Plants at Deadhorse
100
Plants at Smitty Camp
80
60
40
20
0
2007
2008
2009
2010
Figure 2. Preliminary Results of Deadhorse site plant data as compared to the control
at Smitty Camp. No data was collected at the control plot in 2007 or 2008. The
Deadhorse site was treated in the fall of 2009, after the 2009 pretreatment data was
collected.
Figure 3. Photo point at Deadhorse treatment site established to show effects of
treatment at this site. The photo on the left taken during 2009 prior to treatment
can be compared against the post-treatment photo on the right taken in 2010. The
thinning of the forest canopy is evident as is the increased light reaching the forest
floor.
IV.
Preliminary Management Implications
The long-stiped campion monitoring protocol (Dillingham et al. 2007) recommends
that at least 3 years of post-treatment data be collected prior to making final
management recommendations. Nevertheless, it is appropriate to recognize the
current trend and make preliminary management implications now that the first year
of data has been collected and analyzed. Management implications are from the
monitoring protocol prepared in 2007.
Post-treatment monitoring determined that the 2010 flowering population (104 plants)
is between the lower count (61 - 2009) and upper count (118 - 2007) of pre-treatment
population counts. Therefore, preliminary results indicate that the treatment would be
considered to have no change. The treatment would be considered to have no effect
to the species. If continued monitoring results are similar, forest thinning would be
permitted in other long-stiped campion occurrence locations.
Literature Cited:
Dillingham, Colin P. and Allison Sanger. 2007. Conservation Assessment and Strategy
for Long-stiped Campion Silene occidentalis Watson ssp. longistipitata. Report
available from Lassen National Forest. 35 pp.
Dillingham, Colin P. 2007. Silene occidentalis ssp longistipitata Monitoring Protocol
Version 1.2, revised Nov 2, 2010. Report available from Herger-Feinstein Quincy
Library Group Implementation Team, Plumas and Lassen National Forest. 6 pp.