Restoring Native Habitats
by Sharon Farrell, Plant Ecologist, Marc Albert, Natural Resource Specialist, and Janice Cooper, Park Ranger, Presidio
Within the Presidio of San Francisco lies an “ecological island” known as Inspiration Point. Surrounded by non-native vegetation, residential neighborhoods, and other hallmarks of urban development, Inspiration Point’s grasslands support a rich diversity of native plant species. These plants now struggle to survive in their reduced habitat, and several are officially designated as federally endangered species.
During the fall of 1995, the National Park Service embarked on a three-year program to restore the native grassland community that once existed at Inspiration Point, thereby protecting these plants and encouraging their growth. To do so, however, required the removal of some introduced trees. For example, the non-native Monterey pine trees that flourish at Inspiration Point have now created their own microclimate, one which conflicts with the needs of the native species. As part of the restoration process, several pines were removed.
The Presidio’s Natural History
Imagine a rough peninsula, bounded on three sides by ocean and bay, full of low hills and wide valleys. San Dunes migrate eastward across much of the landscape, formed and reformed by off-shore winds. Hardy shrubs cling to the high coastal bluffs, while tule reeds edge the bayshore. Bands of blue-gray serpentine rock snake across the landscape, carpeted in bunch grasses and wildflowers. Oak trees mark the occasional creek or pool. This diverse landscape abounds with equally diverse animal life: insects and reptiles, birds, fish, and a host of mammals, from mice and gophers to deer, elk, and bear.
Such was the northernmost tip of the San Francisco peninsula when Spanish colonizers arrived in 1776 to build a Presidio, or military post. With wonder, Father Pedro Font noted the abundant wildlife and “so many lilies that I had them almost inside my tent.” The Spanish brought their religious and military traditions, their methods of agriculture and architecture. They built permanent shelters, grazed cattle and sheep, and planted European grasses to feed themselves and their stock. The landscape began to change. After seventy years of Spanish, then Mexican rule, the U.S. Army occupied the land in 1846. By 1900, soldiers had planted a forest of hundreds of thousands of trees.
Ironically, military interests both promoted Inspiration Point’s development and protected it from urban sprawl. After more than two centuries, the Presidio of San Francisco still contains remnants of ecosystems that once flourished here. The serpentine grassland at Inspiration Point continues to provide habitat for more than seventy-five native plant species. The National Park Service is managing this grassland in accordance with its mission of preserving and restoring native landscapes.
What Makes Inspiration Point Unique?
Inspiration Point contains the only serpentine grassland within Golden Gate National Recreation Area’s 74,000-plus acres of land. A fragmented band of serpentinite, the California state mineral, traverses San Francisco, emerging on the Presidio from Inspiration Point and continuing to the coastal bluffs. Numerous small grasslands once flourished along this band. Inspiration Point is the site of one of the few intact remnant serpentine grasslands in the San Francisco peninsula because of development. Serpentine soils are very unusual, and are hosts to many endemic plants. While containing high levels of certain heavy metals that can be toxic to plants, they are low in other elements needed for plant growth, such as calcium. Over hundreds of thousands of years, many plant species have evolved mechanisms that allow them to survive in serpentine soils, and some are found only in these unique habitats. As their habitat diminishes, these specially adapted plants become rare or endangered. Inspiration Point is home to three rare plants, including one of the last remaining natural populations of Presidio clarkia.
The trees being removed in the current habitat restoration project are primarily Monterey pines. The Army first introduced Monterey pines to the Presidio in the late 1800s to slow down the relentless coastal winds and to distinguish the military outpost from the surrounding area. While they do grow naturally in other areas of California, these pines were not historically found on the Presidio, and are considered to be non-native. They quickly became established, and soon dominated large areas within sand dune and serpentine habitats. As the pine trees grew, they had an impact on the grassland and shrub communities, by creating a shady, moister, more nutrient-rich environment. This new microclimate altered natural growing conditions and soil composition to the point that few native species could tolerate the changes, and allowed more weedy species to become established. The National Park Service, local Conservation Corps workers, and community volunteers removed some of the pine trees at Inspiration Point in phases, while monitoring what happened after each removal. The long-term goal is to bring back the original natural serpentine grassland system.
The Forest’s Future
Most of the forest is protected as a cultural resource that honors the Presidio’s history as a military post and provides a quiet refuge from a highly populated urban community. The National Park Service will not remove any trees where the original historic plantings were located unless they have a negative impact upon endangered species habitats or present a public hazard. Natural resource specialists have identified several areas where non-native tree removal is appropriate: the Lobos Creek Valley, the serpentine grasslands at Inspiration Point, and within the sensitive sand dune habitats along North Baker Beach. Fewer than a hundred trees have been removed -- a very small number compared to the 400,000 originally planted. The park is developing a vegetation management plan that will outline the future management of the Presidio’s forested areas.
Wildflowers Will Return
Many of the pine trees that will be removed at Inspiration Point are between thirty and seventy years old. Over time, their falling needles and cones, and the shade produced by the trees, have had an impact on the grassland environment. It may take many years for the natural processes and species to fully re-establish within these areas, but some natural features should begin to rebound quickly. Park staff and volunteers removed trees during the late summer months, after bird nesting season was over and the grass herb seeds had fallen to the ground. Tree stumps were cut flush with the ground and the thick thatch was raked from the soil surface by community volunteers. Removing this organic material will allow native species, which are adapted to the low-nutrient serpentine soils, to vigorously compete with the weedy non-native plants.
Inspiration Point supports numerous perennial native bunch grasses - California oat grass, California needle grass, and red fescue -- found in few other places today. Many of these grasses will regenerate naturally in the spring. In some denuded areas, park staff and community volunteers will also replant hundreds of nursery-grown grasses, which must be cared for and nurtured. These grass plantings will limit erosion problems and reduce the spread of weedier non-native annual grasses.
Wildflowers will regenerate at their own pace, without additional plantings. In late spring, community volunteers and schools will weed the newly planted areas in hopes of providing habitat for wildflower and other native plants. With continued community support, park visitors should see poppies, irises, buttercups, blue-eyed grass, yarrow, buckwheat, wild onion, sanicles, and other native species growing and blooming within the next two years.
Park staff will continue to monitor the effectiveness of the non-native tree removal and other restoration activities. Particular attention will be given to the range and size of endangered species populations -- including the Presidio clarkia -- and the change in the overall plant community in areas that were once under the tree canopy.
Wildlife will return
The native insects, amphibians, reptiles, birds, and mammals of San Francisco all evolved over the span of thousands of years with specific species of native plants. Since plants are the original source of food and shelter in this food web, restoring native plant communities provides the nectar, seeds, leaves, and stems to feed wildlife, as well as habitat for nesting and egg-laying. Quail and other ground-nesting birds and small animals will benefit from the cover provided by the grasslands as well as from anticipated increases in insect diversity and abundance. The large surrounding trees that are not removed will continue to provide habitat for nesting birds, including raptors such as red-tailed hawks, red-shouldered hawks, and kestrels. Raptors often perch in trees on the edges of grasslands, reaping the best of both worlds -- protection for the nest plus good feeding grounds. Raptors eat small mammals such as gophers and mice, which will become increasingly available as grassland habitat is restored.
Restoring Natural Processes
Park staff and community volunteers -- the Presidio Park Stewards -- share the work and the fun of habitat restoration on thirteen sites within the Presidio. Park Stewards work year-round to restore natural habitats and protect twelve species of rare or endangered plants through activities such as collecting native plant seeds, growing plants in the Presidio Native Plant Nursery, planting them at restoration sites during the rainy season, and removing invasive exotic weeds. The work is accomplished through a community-based program that provides educational and recreational opportunities to the public and job training for volunteers, interns, and local Conservation Corps members.
We cannot leave nature alone because nature has not been left alone on the Presidio. When a natural area has been affected by human change it is no longer “natural” -- it is a manipulated landscape. The National Park Service wants to keep part of the historic Army landscape while restoring and protecting some of the last remnants of the native California environment. The richness and beauty of San Francisco’s unique natural areas will continue to diminish without our careful and committed involvement.