Invasive Species Upon Mount Sutro

Introduction

Mount Sutro is located within the city of San Francisco and is located close to the eastern most part of Golden Gate Park. This mountain is known for having exposed chert and sandy soils. It is often exposed to mild temperatures and is frequently moistened by a rainy period from October to February with frequent periods of fog year-round. Much of the mountain is currently covered in invasive species, especially species commonly known as Blue Gum Eucalyptus, Cape Ivy, English Ivy, and Himalayan Blackberry. Non-native species have dominated the area and have severely limited the growth of most native species. The forest floor is currently being smothered by many ivy species which directly causes the inability of native species to grow, in addition to the inability for new tree seedlings to sprout. This is causing the mountain to lose its biodiversity and hinders its regenerative capabilities.

Background Research

My research site is located within San Francisco upon Mount Sutro. The Sutro Stewards Nursery is located at 476 Johnstone Dr, San Francisco CA, 94131. Mount Sutro historically was originally purchased by Prussian immigrant Adolph Sutro, who originally intended to use the land as a timber farm for Blue Gum Eucalyptus, Cypress, and Pine. In 1998 the University of California San Francisco (UCSF) devised a management plan to begin restoring the mountain for locals and native flora and fauna. Their goals were improving the general health of the forest, protecting native plant species, providing habitat for native wildlife, preserving aesthetics, and improving public access for recreation. In 2003 a large donation allowed for the creation of the Rotary Meadow which gave rise to the growth of many native grass species. In 2006 many volunteers worked together to create trails for recreational purposes. Today the Sutro Stewards work to remove high priority invasive species, cultivate and sow natives during planting season (Sutro Stewards 2018).

As of 2014, Mount Sutro Stewards released a checklist of all vascular plants found upon the mountain. Species were classified based upon if they were native to the state of California or not, native to the city of San Francisco or not, and if the species was considered invasive or not. There have been 140 recorded plant species on Mount Sutro, with 84 species being believed to be native and 57 species believed to be non-native. Of these non-native species 28 have been identified as invasive species. (UCSF 2018). Some of the most notable invasive species upon the mountain are the following: Delairea odorata (Cape Ivy), Myosotis latifolia (Forget-me-not), Eucalyptus globulus (Blue Gum Eucalyptus), Rubus armeniacus (Himilayan Blackberry), Tropaeolum majus (Garden Nasturtium), and Hordeum marinum spp. leporinum (Farmers Foxtail) (Sutro Stewards 2014). The majority of these species were introduced by human activity, either directly through planting or indirectly through cross contamination and human travel. Many of these species exist across various locations upon the mountain and are not confined to certain patches. Many of these invasive species are considered critical by either the CAL-IPC or by the Sutro Stewards due to their tendency to dominate the landscape and outcompete native species.

UCSF and Sutro Stewards have organized and recognized up to four types of forests upon the mountain and have developed plans on how to care for all variations. Forest 1 is recognized to be the forest with the most significant health problems and is the focus for the majority of restoration work for at least the first five years of the project. Forest 2 and Forest 3 are close in health issues and are both facing similar problems that UCSF intends to mitigate in the middle of the project. Forest 4 is considered the healthiest on the mountain and will receive restoration efforts the latest.

Impacts

It has been found that the majority of the understory consists of invasive non-native species that include but are not limited to Himalayan blackberry, Cape Ivy, English Ivy, Algerian Ivy and other species to a much lesser extent. The overwhelming presence of these invasions is causing a decline in native species population. Additionally, tree seedlings are struggling to grow, and the forest has been unable to maintain a sufficient rate of regeneration (UCSF 2018). This is a huge problem that is compromising the overall health of the forest. It’s important to have species diversity in an ecosystem and having a few key species dominating the area and preventing others from growing is detrimental. Native species often provide more natural system services to the area unless an invasive has taken over a niche. The native species will have evolved to the environment and should be capable of providing the ecosystem with what it requires. These jobs vary and may include nutrient recycling, comprehensive root structures, or forage for wildlife. Ivys that suffocate surrounding natives are unlikely to have replicated all ecological niches that would have been covered by native species. Furthermore, it is important for the future health of the forest that it is able to regenerate. This means the forest trees should produce a certain number of seedlings that will eventually grow to replace old and dying trees. If this fails to occur, then the forest will not continue to maintain itself over the course of many decades or centuries.

Forest Type 1 spans twenty-four acres of the eastern forest and it’s composed of Blue Gum Eucalyptus, Blackwood Acacia, Monterey Cypress, Monterey Pine, Redwoods, Plum, Cherry, Bay, Coast Live Oak, and Willows. This type of forest has 110 dead trees per acre with 60% of dead trees being Eucalyptus and 24% being Blackwood Acacia. There is little to no tree sprouting within this area. The majority of the understory is entirely covered in Himalayan Blackberry, Poison Oak, and vine species (UCSF 2018). This area has been deemed a priority and is the focus of much of the work earliest in the project. It is of great importance to remove dead or dying trees from the area for both the health of the forest and the safety of visitors. Dead trees may potentially fall and injure visitors walking the trails of the mountain. Furthermore, dying trees can make good fuel for wildfires and it is important to attempt to mitigate the severity of any wildfires that occur atop the mountain.

Forest Type 2 is the remaining nine acres of easternmost forest and is composed of almost entirely blue gum eucalyptus and Monterey Cypress. There are very few trees with small diameters, with no trees having below a 14” diameter. The majority of living trees within this area have a living crown ratio of 20% or significantly less. This is a strong indication the health of these trees is in strong decline as tree’s generally require a healthy crown to take in sunlight necessary for photosynthesis. Within the last twenty years there has been little to no tree sprouting within this area which has severely impacted the forest’s ability to regenerate. Much of the understory is heavily covered in various ivy species with the addition of Poison Oak and Himalayan blackberry. Forest Type 3 is eight acres in the northernmost part of the forest and is comprised of Blue Gum Eucalyptus, Blackwood Acacia, Plum, Cherry, Bay, and Coast Live Oak. The understory of the forest is entirely covered by various species of ivy and Himalayan blackberry. There are no living trees within this area that have diameters below 12”. Within this area there is no records of new tree sapling growth within the last three years (UCSF 2018). Both of these forests are viewed to have similar problems as both have heavy understory coverage and a significant lack of new seeding growth. This is an issue that impacts the long-term survivability of the forest. Currently the forest in these areas is alive but if left unmanaged it is not expected to regain its health. It is of great importance to remove a lot of the invasive species currently occupying the undergrowth of the forest to make the forest floor more accessible. Native species should be planted in restoration efforts to maintain control over invasive species if possible.

Forest Type 4 is eighteen acres and takes up the west side of the mountain, and 82% of this forest is Blue Gum Eucalyptus, with few noted Monterey Cypress, Cherry, and Coastal Live Oaks. These trees are considered to be the healthiest with a living crown ratio of 40% on average. It has been found that there are 55 dead trees per acre in this forest, with most dead trees being young in age and having a diameter at or below 12”. The understory of this area is also covered in invasive species like Himalayan Blackberries and various ivy species (UCSF 2018). This area is of the least concern because it receives the most fog from the western side of San Francisco. As California has been experiencing longer periods of more extreme drought in the past twenty years, we should expect that many species are going to struggle. The additional moisture provides for the forest in periods of drought which helps maintain the overall long-term health of the forest. Much of the areas understory will require work to remove significant portions of invasive species and replant native species.

Control & Removal

UCSF and the Sutro stewards plan to create restoration sites across the mountain for invasive understory removal. This will be done in the hopes that species of blackberry and ivy are permanently removed or reduced to promote the growth of native species. Removal of these plants cannot be done with herbicides; thus, other methods must suffice. UCSF has planned to remove these species by hand and the use of equipment. Volunteers working with the Sutro stewards will remove these species to the best of their ability by hand and with the assistance of using small picks and trowels. Volunteers will be instructed to attempt to remove as much of root structures as possible to limit regrowth. This will be repeated up to four times a year until invasive species fail to regrow or are deemed as adequately controlled. UCSF will additionally hire goats to graze areas on the mountain that are dominated by invasive (UCSF 2018). This cannot be done in areas with high concentrations of native species as goats are not objective consumers. After the use of goats volunteers and paid staff will remove remaining debris and plant natives within the area. Goats are to be used in areas difficult for humans to access due to topography or overgrowth of harmful species.

Many individuals from the species Eucalyptus globulus (Blue Gum Eucalyptus) will be removed due to their poor health. In various forest areas there are a number of dead or dying Eucalyptus trees which are planned to be removed. UCSF intends to replant many eucalyptus saplings with the addition of a few native species of tree within the forest. UCSF and the Sutro Stewards recognize the limits of their capabilities and try to base this project on what may realistically be feasible. They do not promise to remove all invasive species. They intend to replant new seedlings of Eucalyptus species despite this being considered invasive for two main reasons. Eucalyptus trees are a very popular species and well loved by the local communities that visit the mountain, and they have adapted well to the area’s native climate. This should theoretically revitalize the forest in the future and create a healthy canopy that is not overcrowded or dying.

Future

Through the use of grazing animals, human labor and equipment it is hoped that over many years some areas will be able to be restored to having higher concentrations of native species. This plan is excellent as it utilizes the management strategy of manually removing plant species and goats as biological agents against invasive species and the plan is tailored towards what invasive species are specifically being removed. A strong population of native species may by themselves be able to limit the regrowth of invasive species. It is also hoped that by frequently removing foliage that over the course of time, energy will be drained from underground root structure and the plants will eventually be unable to grow. It should not be expected that all invasive species on this mountain will be eradicated, nor is it likely that the complete eradication of the most threatening invasive species is possible. It should be hoped that the range of the most invasive species will be contained to specific areas. This will require a staggering amount of work over the course of many years and after the project’s completion there will frequently need to be upkeep upon the mountain to maintain the containment of invasive species. It can be hoped that upkeep will require less manpower than the current project which hopes to restore all four forests upon the mountain.

Conclusion

Mount Sutro is an area that is nearly entirely covered by an assortment of invasive species. There may be up to 28 invasive species upon the mountain, but the majority is dominated by a few key species. It should be noted that by limiting the spread of the current most widespread species that the other less intrusive invasive species will replace their range. There will need to be a significant amount of labor in order to remove the vast majority of these invasions during the current project and afterwards there will need to be constant maintenance on the land to prevent the invasive species from returning. The many invasive species upon this mountain are likely to never be fully removed but it should be possible to maintain and contain their populations. If this occurs, we should see more native species growing upon the mountain which should restore natural levels of biodiversity and provide the area with key system services that may have been erased by the overwhelming presence of invasive species. Mount Sutro is a beautiful location in the middle of the city of San Francisco and is an excellent location for locals to visit if they seek to feel surrounded by nature and lessen the stress of being within a large metropolitan area. Most visitors enjoy seeing both invasive and non-invasive species within the park. With restoration and close management, we can increase the beauty of the area while most importantly ensuring that it can continue to be enjoyed far into the future.

References Cited

Sutro Stewards. (2018). “History of Mount Sutro”. Sutro Stewards. Retrieved from https://www.sutrostewards.org/mount-sutro-history

Sutro Stewards (2014). “Annotated Checklist of the Vascular Plants of Mount Sutro”. Sutro Stewards.

UCSF. (2018). “Vegetation Management Plant”. UCSF Mount Sutro Open Space Reserve. Retrieved from https://www.ucsf.edu/about/locations/mount-sutro-open-space-reserve#tabs-3