FINAL

Impact Evaluation Report

Washington Conservation Corps Restoration Methods

October 25, 2018

Prepared for: 

Laura Schlabach

WCC IP, Compliance, and 

Communications Coordinator

Washington Conservation Corps 

Washington State Department of 

Ecology PO Box 47600, Olympia, WA 

98504

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Title-page image: Washington Conservation Corps crew setting up monitoring plots. 

The Watershed Company Reference Number: 170840

The Watershed Company Contact: Sarah Sandstrom, PWS and Nell Lund, PWS

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TABLE OF CONTENTS

Page #

1 Introduction ...................................................................................... 1

2 Purpose ............................................................................................ 1

3 Methods ............................................................................................ 2

3.1 Study Participants.............................................................................................. 2

3.2 Site Layout.......................................................................................................... 2

3.3 Planting and maintenance ................................................................................ 5

3.4 Data collection.................................................................................................... 6

3.5 Statistical Approach .......................................................................................... 8

4 Results.............................................................................................. 8

5 Discussion...................................................................................... 10

6 References ..................................................................................... 11

Appendix A ............................................................................................. 1

Reference Photographs ......................................................................... 1

Appendix A: Photos

LIST OF FIGURES 

Figure 1. Lake Whatcom Watershed map with the City of Bellingham-owned property 

where the restoration area is located marked in pink. ......................................3

Figure 2. NWI map showing wetland conditions within the proposed study site...............4

Figure 3. Outline of study area in black with locations of experimental plots....................5

Figure 4. Diagram showing approximately layout of experimental plots, center posts, and 

sampling subplots. As shown above, the sub-plot does not need to be precisely 

aligned with the boundaries of the experimental plot.......................................6

Figure 5. Percent survival, deer browse, and string trimmer damage for each treatment..9

LIST OF TABLES

Table 1. Summer data collection summary for each treatment......................................7

Table 2. Total costs of installation and maintenance for all plots in each treatment........9

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IMPACT EVALUATION RE PORT

WASHINGTON CONSERVATION CORPS RESTORATION METHODS

1 INTRODUCTION

The Washington Conservation Corps (WCC) is a service program that has been 

providing opportunities to young adults to protect and restore our natural 

environment since 1983. Improving habitat for state and federally listed species, 

including anadromous fish, is a primary goal of the WCC. WCC projects include 

wetland enhancement and restoration, and riparian corridor enhancement and 

restoration. The Washington State Department of Ecology (Ecology) administers 

the WCC program. Since 1994, WCC has been an AmeriCorps program.

To comply with AmeriCorps grant requirements and review their internal site 

restoration practices, the Washington Conservation Corps (WCC) hired The 

Watershed Company to prepare this Evaluation Plan. For this evaluation, the 

WCC chose a restoration project they are implementing in partnership with the 

City of Bellingham, Washington. 

The purpose of this impact evaluation report is to assess the effectiveness of 

different WCC restoration methods. As the independent reviewer, staff from The 

Watershed Company tabulated and analyzed the data WCC crews collected. 

2 PURPOSE

This evaluation seeks to answer the question, “Does additional investment in 

initial restoration techniques and post-restoration care of installed plants lead to 

increase in successful outcomes?” 

More specifically, this study compares the relative benefits of two products 

commonly used to improve plant survival following installation: 1) solid tube 

tree protectors and 2) deer repellant. A literature review did not find any 

comparable studies of wetland native plant survival using these methods; 

however, both tube tree protectors and herbivore repellants have been reviewed 

for protection of agricultural crops (e.g., Zabadal and Dittmer 2000, Olmstead 

and Tarara 2001) and upland trees (e.g., Ward and Williams 2010, Randall 2012). 

This study evaluates the cost-effectiveness of the use of each of these two 

products relative to standard planting methods. The study uses native plant 
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survival, evidence of plant damage, and persistence of treatment materials to 

determine the relative cost-effectiveness of each treatment method. 

3 METHODS

3.1 Study Participants

This study was a collaborative project lead by WCC, in partnership with the City 

of Bellingham. The City of Bellingham provided the restoration project site, a 

property owned by the City of Bellingham Water Department. Staff from City of 

Bellingham, WCC, and The Watershed Company collaborated on restoration 

methodologies, study questions of interest, and study design. WCC staff was 

responsible for coordination with the City of Bellingham and The Watershed 

Company. WCC supervisors and crew members implemented the planting 

project and collected and compiled field data. City of Bellingham and WCC 

funded the restoration project through a cost-share partnership (75/25). WCC 

funded the evaluation. City of Bellingham contributed staff time toward 

development of the evaluation plan, provided oversight, and assisted with

maintenance activities at the site. Staff from The Watershed Company 

developed the Evaluation Plan, assisted with plot set up, analyzed data provided 

by WCC, and summarized results in this report. 

3.2 Site Layout

The evaluation was conducted at a 1.04-acre site in unincorporated Whatcom 

County near the City of Bellingham. The site is southeast of Lake Whatcom, in 

the Lake Whatcom Watershed (Figure 1). The restoration site is within a National 

Wetland Inventory (NWI) mapped wetland near Anderson Creek and 

downstream of Mirror Lake (Figure 2). Prior to restoration, the roughly 

rectangular site was initially covered in an existing reed canarygrass 

monoculture (Figure 3). 

The site was divided into 45 experimental plots. The center of each plot was

marked in the field using a sturdy metal or wood stake, marked with the 

assigned plot number (1-45) and treatment (R-reference, D-deer deterrent, or Tprotective tubes). Each experimental plot was approximately 1,000 square feet in 

area. 

One treatment was randomly assigned to each plot using a random number 

generator, until each treatment was assigned to 15 plots. A map of assigned plot 

numbers and treatment locations is shown in Figure 3. 
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Figure 1. Lake Whatcom Watershed map with the City of Bellingham-owned property 

where the restoration area is located marked in pink.
4 

Approximate 

site location

Mirror Lake

Figure 2. NWI map showing wetland conditions within the proposed study site. 
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Figure 3. Outline of study area in black with locations of experimental plots. 

3.3 Planting and maintenance

Plants were installed on January 29th and 30th, 2018. Planting methods, density, 

and species were established consistently among all of the experimental plots. 

Since the site is within an NWI mapped wetland, only wet-tolerant native plant 

species were planted. Plants included cottonwoods (Populus balsamifera), willows

(Salix spp.), red osier dogwoods (Cornus sericea), and spiraea (Spiraea douglasii). 

All plants were installed as stakes. Plants were marked with flagging tape to 

facilitate identification throughout the study period.

Following initial planting, each plot was treated according to the treatment 

assigned. Treatment plots were established on January 31st, 2018. For the deer 

deterrent, Plantskydd® was applied according to manufacturer specifications 

immediately following plant installation (February 6th, 2018) and once in spring 

during leaf out (April 23rd, 2018). The central plot posts and measuring tapes 

were used to identify the boundaries of each plot for application purposes. 

Maintenance practices were limited to mowing using a string trimmer, and these 

actions were consistent across the entire site. Mowing occurred on April 20th and 

July 30th through August 2nd, 2018. The second mowing occurred over multiple
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working days because crews shut down each day at 1 pm due to elevated 

industrial fire precaution levels at that time. 

3.4 Data collection

Experimental plots were monitored immediately after plant installation in the 

winter of 2018, and again in the late summer of 2018. 

Sampling occurred on August 15th, 2018 within a 15-foot by 15-foot sub-plot, as 

shown in Figure 4. When collecting survival plant counts, string trimmer damage 

counts, and blue tube counts, only installed plants with a main stem inside each 

sub-plot were counted. When assessing deer browse, overhanging branches 

within each sub-plot were included.

~40 ft

~25 ft

15 ft

15 ft

Experimental 

Plot

Sampling subplot

Center 

post

Figure 4. Diagram showing approximately layout of experimental plots, center posts, and 

sampling subplots. As shown above, the sub-plot does not need to be precisely 

aligned with the boundaries of the experimental plot. 

Using a random number generator, two plots of each treatment type were

selected for a permanent photo point. Photo points were taken at the same point 

and direction. Photo-points were recorded in winter and summer of 2018. Photopoints were documented at the following plots: 

Reference Deer Repellent Blue Tubes

Plots 10 and 27 Plots 22 and 31 Plots 12 and 14
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Winter 2018

All native plants within a 15-foot by 15-foot sub-plot near the center of each plot 

were counted immediately following initial installation (Figure 4). Winter data 

collection was limited to installed plant counts. A location near the center of each 

plot was selected to minimize the effect of potential drift from adjacent 

treatments. 

Late Summer 2018

In late summer 2018, one growing season after the restoration actions, each plot

was re-evaluated using a 15-foot by 15-foot sub-plot near the center of each plot

(Figure 4). Again, measuring tapes were used to mark the edges of the 225 SF 

sample area within each plot. Sample areas were located around the central stake 

in each plot. Summer data collection was recorded as summarized in Table 1 

below.

Table 1. Summer data collection summary for each treatment

Data to collect within each 225 SF sub-plot 

by treatment

Treatment

Reference

Deer 

deterrent

Protective 

tube

Installed plant live/dead counts X X X

Deer browse damage, 1-5 scale estimate X X X

Percent native plant cover, cover class 

estimate X X X

Blue tube counts X

Count of string trimmer damaged plants X X X

Each living native plant was counted within the sub-plot. Any dead plants 

within the sub-plot were counted separately. 

Evidence of deer browse was qualitatively evaluated in terms of intensity of 

browse damage. In addition, percent native plant cover within the sub-plot was

visually estimated using the cover class method. 

Where blue tubes were used, the number of blue tubes remaining on each live 

and dead plant within the sub-plot were counted. 

Each plant within the sub-plot was inspected for damage from string trimming. 

The number of plants with string trimmer damage was recorded. 

WCC crews estimated percent cover for native plants in each sub-plot. A Visual 

Cover reference data sheet was used to help standardize cover estimates. 
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Cost 

In order to understand the relative cost effectiveness of each treatment approach, 

the City of Bellingham provided invoices or total costs for all treatment 

materials. The City also provided an estimate of labor hours for each treatment, 

which were multiplied by $18 per hour to estimate total labor costs for each 

treatment. 

3.5 Statistical Approach

The study uses a quasi-experimental design with randomized control to ascertain 

correlations between site treatments and plant survival. The study consists of 

randomized plots, including untreated control (reference) plots as detailed in 

Section 3.2 above. 

Data collected on plant survival, deer browse, and string trimmer damage were 

analyzed using a one-way Analysis of Variance (ANOVA). The approach tested

the null hypothesis that there is no difference between native plant survival, deer 

browse, or stem damage among treatment groups. 

To keep the plot sizes at a practical scale and allow space for necessary replicates 

on the 1.04-acre site, the statistical significance was determined using an alpha of 

0.1. Given the statistical design, a sample size of 15 sites each for a control and

each treatment provided a power of 0.8 to detect a large effect (f=0.4). 

In addition, we identified the mean percentage of blue tubes remaining on plants 

in the blue tube treatment plots to determine longevity of that treatment method. 

The survival, browse, and damage measures were compared to the cost of each 

treatment method to provide a cost-benefit comparison among treatments. 

4 RESULTS

Plants protected with blue tubes exhibited significantly greater survival 

compared to reference plots and Plantskydd® plots (Figure 5, p=0.01). String 

trimmer damage was significantly lower in the blue tube treatments compared to 

the reference and Plantskydd® treatments (Figure 5, p=0.002). Damage from deer 

browse was low among all treatments (3% of less). There was no significant 

difference between the frequency of deer browse damage among treatments, 

although plants within blue tubes exhibited a slightly lower frequency of deer 

browse compared to reference plots and Plantskydd® plots (Figure 5, p=0.56). 
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Approximately 89 percent of blue tubes remained by the August sampling 

period. 

We did not observe a significant difference in the survival of any one plant 

species over another (p=0.45). Total cover was low (approximately 2 percent) 

across all treatments, and there was no difference between cover among 

treatments. 

68%

64%

86%

3% 2% 1%

22%

26%

6%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Reference Deer Skydd Blue Tubes

Survival Deer Browse Damage String Trimmer Damage

Figure 5. Percent survival, deer browse, and string trimmer damage for each treatment

Blue tube treatments cost more in both labor and materials compared to both 

Plantskydd® and reference treatments (Table 3). Assuming 667 plants were 

planted across all plots in each treatment, the total cost per plant surviving to 

Year 1 can be estimated (Table 3). 

Table 2. Total costs of installation and maintenance for all plots in each treatment

Reference Plantskydd® Blue Tubes

Materials $701.42 $819.79 $1,354.69

Labor $1,056.00 $1,344.00 $2,136.00

Total $1,757.42 $2,163.79 $3,490.69

Approximate cost per plant surviving Year 1 $3.87 $5.07 $6.09
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5 DISCUSSION

Based on the results of this experiment, blue tubes are the most effective method 

to support survival of plant stakes during the first year of establishment. The 

improved survival through the use of blue tubes can be attributed to a nearly 

equal reduction in the occurrence of string trimmer damage to plants protected 

by blue tubes. 

This study did not yield any significant findings regarding Plantskydd®. Deer 

browse was low throughout the planted area, and Plantskydd® treatment plots 

did not exhibit significantly different extent of deer browse compared to other 

treatments. This is similar to the findings of Ward and Williams (2010). However, 

the results are also possibly an artifact of the site conditions. Herbivore damage 

may not have been a significant pressure at this site during the monitoring 

timeframe, the plants may not have had sufficient growth to attract substantial 

deer browse, and/or Plantskydd effectiveness may be limited due to leaf-out after

the first application. Other studies of the effectiveness of Plantskydd® have 

found that the repellent effect does not extend beyond one meter from the 

treated area (Nolte and Wagner 2000), so it is unlikely that the close proximity of 

treatments in this study design affected deer browse throughout the study area. 

In order to test this possibility, Plantskydd® could be applied at restoration plots 

with greater separation among plots. 

Although survival of plants using blue tubes was significantly high relative to 

the other treatments, blue tubes entailed the highest cost per surviving plant 

compared to the other treatments due to upfront materials and labor costs. It is 

important to recognize that this analysis only accounts for survival after the first 

growing season. Considering that the blue tubes remaining in place will continue 

to protect plants from string trimmer damage over successive growing seasons, 

and those without protection may continue to experience damage, it is possible 

that the cost per surviving plant may equilibrate over time. The cost per 

surviving plant measure also does not account for materials and labor associated 

with replanting if plant mortality exceeds allowable thresholds of success. 

Because blue tubes appear to be effective in promoting plant establishment, we 

recommend continued monitoring of this study site over a period of up to five 

years to understand the longer term costs and benefits of the blue tube treatment

method. An extended monitoring period could also help to evaluate the 

relationship between planting treatment and plant growth and cover. 

If WCC pursues extended monitoring, maintenance and treatment applications 

would need to continue at the site. This would include reapplication of 

Plantskydd®, and continued general maintenance. Maintenance, focused on 

weed control, is typically conducted at least twice annually, in spring and 
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summer. We would advise against any replanting at the site because it would 

confound long-term monitoring results and analysis. Performance monitoring 

should be conducted at least once annually in late summer. 

Most blue tubes remained on plants; however, approximately 11 percent of blue 

tubes were lost. In this study, we did not account for the number of lost blue 

tubes that were lost but recovered. This could be a consideration for cost; if blue 

tubes can be reused to support the establishment of other plants in the future, the 

total materials costs could be reduced. It is also a consideration of ecological 

impacts; if vinyl blue tubes are lost into the environment, the environmental cost 

of this pollution should be considered when weighing the benefit of their use in 

plant establishment. This also suggests that additional labor costs should be 

factored into the use of blue tubes to account for their removal once the plant 

establishment period is complete. 

6 REFERENCES

Randall, J. 2012. Tree shelters for hardwood plantings. Iowa State University Extension.

Nolte, D. and K. Wagner. 2000. Comparing the efficacy of delivery systems and active 

ingredients of deer repellents. P. 93–100 in Proc. of the Nineteenth Vertebrate 

Pest Conference, Salmon, T.P., and A.C. Crabb (eds.). University of California, 

Davis, CA.

Olmstead, M and J. Tarara. 2001. Physical principles of row covers and grow tubes with 

application to small fruit crops. Small Fruits Review. 1(3)29-46.

Ward, J. and S. Williams. 2010. Effectiveness of deer repellants in Connecticut. HumanWildlife Interactions. 4(1) 56-66.

Zabadal, T.J. and T.W. Dittmer. 2000. Grow Tubes: Are They Cost Efficient? 2000 

Research Executive Summaries of the Southwest Michigan Research and 

Agricultural Extension Center.

Appendix A

Reference Photographs 
Overview of site from Park Road looking south immediately after treatments established Winter 2018

Overview of site from Park Road looking south summer 2018
Deer repellent Plot 10 winter 2018

Deer repellent Plot 10 summer 2018
Blue tube Plot 12 winter 2018

Blue tube Plot 12 summer 2018
Blue tube plot 14 winter 2018

Blue tube plot 14 winter 2018
Reference Plot 22 winter 2018

Reference Plot 22 summer 2018
Deer repellent Plot 27 winter 2018

Deer repellent Plot 27 summer 2018
Reference Plot 31 winter 2018

Reference Plot 31 summer 2018