Invasive Plant Removal Projects
Friends of Bidwell Park
June 2003 through December 2004
This report summarizes our volunteer invasive plant removal projects in Bidwell Park from the time we started in June 2003 through the
end of 2004. During this time period, Friends of Bidwell Park volunteers
contributed 2021 hours of on-site labor to the park. Currently we're working 3
mornings a week in Bidwell Park and will be adding a monthly 4th
There are many reasons to remove invasive plants from Bidwell Park,
e.g., to improve wildlife habitat, to increase botanical diversity by removing
faster-growing invasives, for fire prevention and flood control, to prevent
erosion, to eliminate plants that reduce the aesthetic or recreational value of
an area, to elevate the sight lines to improve security, to remove the seed
source reducing future problems.
Our goals were to (1) compile a
list of the park's potentially invasive plants,
(2) provide preliminary rankings as to their impact on the park, (3) provide
photos to aid in the identification of these plants, (4) to research control
methods for each plant, (5) and to map their locations. Another goal was to
start a volunteer program that would provide regular opportunities for
individuals to help the park by removing invasive plants. As we worked in the
park, we've also identified other ways that we can provide support for Bidwell
Park, such as picking up trash, mapping, removal of wire fence remnants,
picnic table maintenance, and clearing abandoned homeless camps.
We focus our removal efforts on invasive plants that are high priority
for removal, can be removed by volunteers using hand tools, and, once removed,
either won't come back or be controlled by periodic monitoring of removal
sites. Generally this means that we must remove the roots of the plant. We
usually work on only one plant species at a time; both to avoid making
volunteers identify an array of plants and also to avoid denuding an area.
When we don't have the resources to remove an entire plant species in one area
or it's the wrong time of year to pull out the plants, we try to reduce the
potential for future seedlings by removing the plant's seeds (e.g. bladder
senna, pokeweed). If the plant is a potential food source for wildlife we try
to make sure that alternative foods are available. Finally, we also have to
select plants that volunteers are willing to remove.
The first plant species we removed, bladder senna, had a long taproot,
requiring a levering tool for removal. We borrowed 6 Weed Wrenches from the
California Native Plant Society Mt. Lassen Chapter (they use them for Spanish
broom removal in Upper Park). We also wrote to Chico businesses
and individuals asking
them to consider donating a Weed Wrench to the Park Dept. One business
responded by donating 4 wrenches, one of each size, which FOBP also borrowed.
Eventually, both groups needed their tools back for their projects. In the
meantime, we raised money to buy our own tools. A variety of tools are needed
for efficient removal of invasive plants. The purchase (almost $2000 so far)
and maintenance of these tools are, by far, our most significant cost to date.
Many of the plants we're removing are fairly large (5'-20'), woody and
bushy so on-site composting isn't feasible; we would soon run out of areas to
pile the pulled plants and it would be difficult to monitor for new seedlings
in these areas. The technique we use is to pile the plants on tarps and pull
the tarps to areas, such as parking lots or streets, where the Park Dept. can
bring a loader and dump truck to remove the debris to either the solid waste
facility or the compost yard. They've hauled off several hundred loads in the
last 1½ years.
We recruit all of our own volunteers by posting flyers at CSUC
and elsewhere, putting notices in newspaper calendars, making brief
presentations at meetings of other organizations and in classrooms, handing out
business cards, staffing an occasional booth at the Saturday Farmer's Market,
through word of mouth, our web calendar, and a weekly email that describes
upcoming park-related activities. Many volunteers are active retirees, some
living in other communities around Chico where park volunteerism
apparently isn't encouraged. We could accommodate many more volunteers. Once
we've planned a workday and lugged all of the tools and supplies to the site,
it would be just as easy to work with 10 volunteers as 5. We could use help
from the BPPC and Park Dept. in identifying and recruiting volunteers.
- 1. American pokeweed (Phytolacca americana)
- This plant is spreading rapidly in Bidwell Park and
elsewhere in Chico. In the last few years, it has moved upstream into the Five
Mile area. It develops an enormous taproot in just a few years and produces
large quantities of seeds. Our goals are to identify the boundaries of its
spread, first removing outlying patches and working towards the densest
populations. We also plan to focus on removing the berries in the fall.
According to Dr. Paul Maslin, a retired CSUC biology professor, it's only
necessary to remove the crown of the root to kill the plant so that's the
technique we're using.
- 2. Bladder senna (Colutea arborescens)
- This is our largest single removal project to date.
Through December 2004,
FOBP volunteers spent 850 hours removing this shrub and
another park volunteer, Laura Nissim, has spent an equal amount of time on
removing it too. Before we started, we mapped 62 locations of the plant in the
park, which occurred from One Mile to Five Mile. The number of plants at these
locations ranged from a few plants to many thousands, in some cases such dense
stands that we could only see a foot into the growth area.
We believe that all of the ~250,000 bladder senna
plants came from one shrub planted
in the Experimental Forestry Station in 1895. During the first year of the
removal process we focused on picking all of the seedpods to reduce future
infestations and then pulled as many plants as we could before the soil became
too dry. We're in our second year of removal and, by spring, should have
eliminated virtually all of the plants that are larger than seedlings. The
seeds may be viable for as long as 40 years, however, so the site monitoring
and removal must continue for a very long time, although it should only take a
few hours a year in the future.
What we learned:
- Bladder senna can only be removed in the
winter when the soil is wet. Attempted removal at any other time will just
break off the tap root, which can resprout from at least 6" below the soil
surface. Broken roots must be dug out, a process that takes many times as long
as using a Weed Wrench.
- The plant is apparently not good wildlife
food or habitat; we seldom found branches or pods that had been nibbled and
little evidence that it was used for shelter.
- Pod removal appeared to have a significant
effect on the number of seedlings the next year, indicating that the seed's
greatest viability is in its first year.
- 3. Bur chervil (Anthriscus caucalis)
- Bur chervil is a plant that produces thousands of tiny Velcro-like
burrs that stick to socks, pants legs and dog fur. At the suggestion of Dr.
Paul Maslin, last summer we pulled out bur chervil plants from the north side
of Five Mile, filling 40 33-gallon trash bags from a 100' x 100' area. We're
monitoring this site to see whether this focused removal reduces the number of
new plants this summer. If it does, we'll identify other areas with dense bur
chervil populations and remove those plants.
- 4. European Olive (Olea europaea)
- The olive fruit fly is a serious threat to the area's olive industry.
According to the Butte County Agricultural Commission, Butte County
currently has about 1000 acres of producing, commercial olive orchards, at
least 500-600 acres of non-producing orchards and as much as 100 acres of
ornamental and feral olive trees. Because of the fruit fly, Butte County
commercial growers are unable to sell their olives for the table market, but
must instead sell it for olive oil, which generates less revenue. The Ag.
Commission is encouraging the owners of non-producing olive trees to remove or
spray these trees, to reduce the occurrence of the fruit fly. Bidwell Park has
an abandoned olive orchard on the south side of the golf course, with numerous
olive trees spreading up the watershed on both sides of the creek. There are
also a smaller number of olive trees in the Cedar Grove area and in the
riparian area of Lower Park. We're currently removing olive trees in Lower Park
whenever they're in our work area, and hope to obtain a grant to facilitate
their removal in Upper Park. Successful elimination of the olive trees in Bidwell
Park will require cooperative efforts from the Bidwell Park Golf Course, who
may be reluctant to remove their trees as they provide some landscaping
- 5. Hackberry (Celtis species)
- Hackberry trees are found throughout Lower Park and Five
Mile. Even the smallest hackberry seedlings are difficult to remove by hand
and a 2" tall plant requires the use of pliers to pull out. We've decided that
it's futile to try to remove these plants until the mature trees that provide
the seed source are cut down or girdled.
- 6. Himalayan Blackberry (Rubus discolor)
- It is very difficult to totally remove blackberries manually, since
even a tiny root segment can resprout. Also, volunteers generally aren't
willing to work in tall, dense blackberry patches. We've taken out
blackberries to facilitate removal of other invasive plants, but haven't
focused on eradication of them except where the patch was very small. Removal
of this invasive plant is compounded by the fact that the fruits are used by
many songbirds and by other animals in the park.
- 7. Ivy (English and Algerian) (Hedera species)
- Currently, we're only removing small, self-contained patches of ivy.
Ivy spreads by runners and by seeds (only present on the mature form of ivy,
which may take many years to reach maturity). There's a considerable amount of
interest in ivy removal both from park users and volunteers, but first we need
to map its locations in Lower and Middle Park and identify and
eliminate the seed sources within and encroaching from the park's boundary on
the south side.
- 8. Japanese Privet (Ligustrum japonicum)
- Japanese privets are considered to be one of Butte County's
worst invasive plant species. There are several other privet species in the
park, but they don't seem to develop such a dense monoculture. In March 2004,
FOBP met with Park Department staff at Five Mile Recreation Area to discuss a
privet eradication project there. The Park Dept. agreed to cut down all of the
large privet trees, the seed source for the tens of thousands of smaller
privets surrounding the three lawn areas. An attempt to stop future growth by
girdling the tree stumps failed, with most of the cut stumps resprouting; now
the Park Dept. is using a backhoe to remove these large stumps. Since March,
FOBP and Kids & Creeks volunteers have removed about 80% of these smaller
privets from Five Mile. Working with the Park Dept., we expect to eliminate privets
from this site by the end of 2005.
In November 2004, FOBP met with Park Dept. staff at the 4th
Street entrance to Lower Park to discuss a major privet removal project along
Woodland Ave. Since few of these trees seemed to be large seed producers, we
agreed that FOBP first would remove all smaller privets manually, followed by
the Park Dept. removing the larger trees over two years. The Park Director
asked that we notify the neighbors along Woodland Ave.
and indicated that the old woven and barbed wire fence would be replaced with a
split rail fence once the privet removal was completed. It has been necessary
to remove this wire fence, both to pull out privets and also to eliminate wire
that was embedded in the oak trees there.
We've also removed all of the privets between One Mile and Hwy 99 on
the north side of the creek (with the exception of one very large tree). There
are other areas in Bidwell Park that have significant numbers of privets,
including the areas between Caper Acres and Hwy 99 along South Park Drive area,
the west side of Cedar Grove, by picnic site #25, west of CARD, in Camellia Way
Park, in Lost Park and on the north side of Lower Park by Crister Avenue. To
eliminate privets from the park will require a cooperative effort from
Cal-Trans, since Hwy 99 is lined with privet trees from Hwy 32 to Cohasset
Rd. The city hopes to work with Cal-Trans on invasives removal during the
Teichert Ponds restoration project, hopefully leading to a broader pact.
Through December 2004, we spent 598 hours removing privets.
What we learned:
- Privets that had been cut to the ground in
an attempt to improve the security of an area were much more difficult to
remove later because they had developed more extensive root systems and also
the remaining stump was too large in diameter or too short to use a Weed
- Privet trees up to 4" in diameter can be
removed manually by digging around the root area, cutting off the side roots
and rocking the tree back and forth to expose more roots, if the tree truck
hadn't previously been cut down to the ground.
- Privets can be removed year-round because
of their shallow root structure, especially in areas that are irrigated.
- In areas where there is other vegetation,
privet removal has little visual impact.
- Because they are evergreen, it is easiest
to map their locations in the winter, when most other plants have lost their
- Privet seed viability drops off
tremendously after the first year so removing the seed trees is key to a
successful privet elimination project.
- 9. Puncturevine (Tribulus terrestris
- In July 2004 we decided to remove puncturevine in Upper Bidwell
Park. A park volunteer, Lynn Thomas, had gradually eliminated puncturevine
from Lower Park over several years, with only one small patch remaining in an
area where Park employees regularly use a weedeater, spreading the plant's
seeds. One of our first steps in this project was to distribute a
poster to the local bike shops
as part of an educational process and to recruit volunteers for our initial
puncturevine removal day. We didn't get any volunteers, but several of the
bike shops, along with Chico Velo, donated money to buy Hula-Hos, an
oscillating hoe that can cut the plant's root. We spent 38 hours removing all
of the puncturevine along Upper Park Road and its side roads, the Horse Arena
area, Centennial Ave. on the park side, and a small area by the children's play
equipment at One Mile.
What we learned:
- Puncturevine will not resprout if broken
off at the root.
- Removal should start earlier in the year
before any seeds form and before it gets too hot to work in full sun.
- Each fruit (seed) breaks into 3-4 parts and
each of these "punctures" is viable for 3-5 years.
- Since the seeds are carried to new
locations by shoes and bike tires, we need to expand the removal program to
other areas, especially along Sycamore Channel and the Durham bike path.
- There's a
bio-control available in Butte County, the puncturevine weevil. However the
weevil doesn't like areas with much activity so it's not a very useful control
along bike paths.
- 10. Pyracantha (Pyracantha angustifolia)
- After seeing the effect of uncontrolled pyracantha growth in the
Teichert Ponds area, we decided to remove pyracantha whenever it's in our work
area. Smaller plants can be pulled out with a Weed Wrench, while the large
ones (up to 20' high and equally wide) require several hours of cutting and
- 11. Tree-of-heaven (Ailanthus altissima)
- At the request of the Urban Forester, in November 2004, an FOBP
volunteer mapped the locations of all tree-of-heaven trees in Lower
Park. He found 82 locations that had one or more trees. There are also a few
tree-of-heaven in the Five Mile Area, possibly due to several large trees on
the south side of Centennial Avenue in this area.
- 1. Annie's Glen
- In June 2004 we started a weekly Sunday morning trash pickup and
invasive plant removal project in Annie's Glen .
Because this is a small self-contained area, it's perfect for a restoration
project. We've identified numerous problems and possible solutions for this
area and recently contacted the Glen's four neighbors to offer to help replace their
invasive plants with suitable alternatives. So far, we've identified 22 native
plants and 55 non-native plants in the Glen .
Through December 2004, we spent 324 hours working here.
- 2. Lost Park
- We occasionally picked up trash in Lost Park but recently
decided that this area needed its own regular,
focused effort -- [Press Release].
The Park Dept. had a major invasive plant removal project a few years ago to
discourage camping, but without more usage of the area by the Chico community,
it continues to be used mostly for alcohol consumption and camping. Remaining
invasive plants include American pokeweed, black locust, giant reed, Himalayan
blackberry, Italian arum, ivy (English and Algerian) Japanese privets, Johnson
grass, periwinkle, Northern catalpa, photinia, and tree-of-heaven.
We've found that, with very few exceptions, park users approve of
invasive plant removal. So far, our efforts have focused on invasive plant
species that either the Park Dept or our volunteers wanted to remove. As part
of the Master Management Plan update and its associated Vegetation Management
Manual, we hope that a comprehensive plan will be developed for control of all
of the high priority invasive plants. It's likely that an analysis of these
plants will show that certain of them present a more immediate threat than
others. Some of these plants can be removed by volunteer labor, while others
require mechanical removal or chemical treatment. Some are relatively easy to
remove permanently while others require constant vigilance.
One topic to include in the manual would be to clarify the rationale
for targeting one plant for removal over others. Occasionally members of the
public ask why efforts are being made against one plant species, when attacking
a different plant may seem to be more urgent. Another topic might be to set criteria
to help park maintenance staff decide when it is appropriate for them to take
additional time to totally remove invasive vegetation rather than just pruning
it back year after year. We also need to develop more scientific methods to
evaluate the effectiveness of treatments and to monitor sites to prevent