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.