The Park Division has a small budget for invasive plant removal in the park so they can target only the species that are considered to be the “worst of the worst”. These include Giant reed (Arundo), Perennial Pepperweed, Starthistle, Himalayan blackberry, Tree of Heaven (Ailanthus) and Privet.
Arundo sites in the Big Chico Creek Watershed were recently mapped by Kim Klementowski, a CSU, Chico graduate student. She found 100 infestation points in Upper Park and 11 in Lower Park. When they have time and money available, the Park Division’s maintenance staff and hired Salt Creek (correctional facility) crews cut down the Arundo and paint the stumps with herbicides. Because even a tiny piece of Arundo can re-root, all of the material removed is taken to the landfill for disposal.
Two small infestations of pepperweed were found in the walnut orchard area in the summer of 2003. Because this plant is incredibly invasive and can develop roots 20 feet deep, it was immediately sprayed with a herbicide.
Currently, goats are brought in for a few weeks a year to control blackberries and starthistle. Generally, crews cut down the blackberries in an area, piling them to be burned when they dry out. When the new growth appears, the goats are put on the site for a few days. In a recent year, the goats cleared the above-ground vegetation in 40 acres at a cost of $15,000. The hope is that after several years of grazing the same area, the root structure of the blackberries will be weakened. Since a single starthistle plant can produce tens of thousands of seeds, goat grazing only works if the plant hasn’t yet gone to seed. In the past, some starthistle areas were controlled with prescribed burns. Because the goats are so visible, many park visitors consider them to be the Park’s primary weed control method. However, at only 40 acres per year cleared, with some weed regrowth expected, this assumption is certainly not true.
Ailanthus is generally treated or removed at the same time the Arundo work is done. Larger trees are girdled. Trees that are cut down have herbicide applied to the stumps.
Olive trees have been cut down, and perhaps treated with herbicides, in past years by the Park Dept, but many of them have resprouted. Friends of Bidwell Park (FOBP) has started an experimental olive tree removal project in the cork oak section of Cedar Grove, using Weed Wrenches® and picks to remove the trees.
Recently the Park Division has begun cutting down the large seed-producing privet trees in the Five Mile area, in order to reduce the huge number of new seedling plants that appear each year. A volunteer group, Kids & Creeks, and an individual, Laura Nissim, have removed thousands of the smaller privets from this area. Privets are also found in Lower Park, but no removal program is underway there yet.
For a number of years, the California Native Plant Society has been removing broom in Upper Park. Because it is more difficult to access the south side of Big Chico Creek, much more removal has been done on the north side of the creek.
Bladder senna shrubs were cut to the ground by Salt Creek crews in past years. Unfortunately, this resulted in vigorous resprouting. In mid-2003, FOBP mapped all of the infestation points for this plant (about 60 sites in Lower Park and Five Mile) and began an eradication program, removing seedpods and pulling out the plants.
Kids & Creeks and Streaminders remove other invasive plants in small areas of the park as part of their riparian restoration projects. These include hackberry, blackberry, catalpa, pyracantha, pokeweed, English ivy, and Periwinkle (vinca). Laura Nissim has also done a significant amount of ivy removal in Lower Park and the Five Mile area.
Lynn Thomas has been controlling puncturevine in Lower Park for a number of years. More recently, she and John Burge have started control efforts along the bike trail next to Upper Park Road.
In summary, the invasive plant removal program for Bidwell Park is in its infancy. Presently, there is little city funding for such a program, inventory and mapping of current infestations has just begun and a prioritized master management plan for controlling invasives doesn’t exist yet. Volunteer efforts, while effective in small, focused areas, may find that their removal work is quickly overrun by invasives creeping in from the edges of their projects. Also, although the Park Division hopes to use volunteers for a significant part of invasive plant removal projects, it is unlikely that this will be a viable solution due to the current condition of the park and their volunteer program, which has failed to attract the large number of workers needed.
As an example of the resources that might be needed, the FOBP Bladder senna removal project is targeting a plant that has slowly spread throughout Lower Park in the last 100 years. It’s found only in areas that are easily accessible, since it was spread primarily by park walkers picking and popping seed pods as they moved through the park. FOBP did their own plant location mapping, recruits their own labor, and provides group supervision and most of the expensive Weed Wrenches and other tools and supplies needed for plant removal. The Park Division has provided 2 additional wrenches and they also pick up the piles of plants that have been removed. So far, the project has logged about 800 volunteer hours. About 1/4 of the visible plants have been removed, along with the current year’s crop of seedpods. It will take an estimated 1500 hours to remove the rest of the shrubs. Seeds in the ground may be viable for as long as 20 years so monitoring and removal must be done annually. Some plants were found overhanging or in creek banks so new downstream infestations are also possible. This is probably one of the easiest invasive plants to remove from the park. Despite that, it may still consume a total of 3000 volunteer hours, including future monitoring.