The Presidio
Background
A place ingrained with a rich history, and a product of both natural processes and human alterations, the Presidio Forest is an integral component of the cultural landscape of the city. This area symbolizes both a forested refuge, and a cultural landmark amid a densely urbanized setting (NPS & Presidio Trust, 2001). The name Presidio – stands for a fortified military settlement, and its history dates back to 1776, when the Spanish arrived in the region, and established the northernmost outpost of their empire in western North America (National Park Service, 2015). The Presidio fell under Mexican rule for 24 years.
In 1846, the U.S. Army took control of the region and further established military fort on the northern tip of the San Francisco Peninsula (National Park Service, 2015). The area was transformed between the 1880s and the 1940s, form sandy dunes and coastal scrub to a green forest, home to a preeminent military post. Located in a strategic place, the post quickly grew into an important military installation which served as an embarkation point for troops sent to the Pacific to fight in the 1898 Spanish-American War, the Philippine-American War, and later WWII. The Presidio became the headquarters for the Western Defense Command during the war (National Park Service, 2015). The Presidio expanded in the 1920's, when Crissy Airfield was established along the bay front. Given its 350 historically significant buildings, the area was designated a National Historic Landmark in 1962. In 1989, when the military base was closed, the Presidio was the oldest continuously operating military base in the country. In 1994 the Presidio was transferred to the National Park Service, and became part of the Golden Gate National Recreation Area (National Park Service, 2015).
Currently, the 1,480-acre former military post is home to native plants, species introduced as landscaping, and prominent stands that have matured into an extensive forest composed primarily of Monterey pine, Monterey cypress, and eucalyptus trees. The Vegetation Management Plan (VMP) for the Presidio of San Francisco was designed as a collaborative planning effort between the National Park Service (NPS) and the Presidio Trust (Trust), the two agencies that share land management responsibilities for the area.
Environmental regulations
As a federal facility, the Presidio is subject to the provisions of NEPA, which require an evaluation of impacts associated with federal actions (NPS & Presidio Trust, 2001). Part of the NEPA compliance process, management interventions must also be in compliance with the Endangered Species Act (ESA). In addition to this, since the Presidio of San Francisco is a National Historic Landmark, any action that would change the appearance of the site must be in compliance with the National Historic Preservation Act (NHPA) (NPS & Presidio Trust, 2001).
Recognizing that the vegetation resources found at the Presidio have both natural and historical significance, the goal of the VMP was to: improve the Presidio's natural and recreational qualities, maintain and enhance the historic plantings, reduce the potential for adverse impacts to park resources, and establish a framework for rehabilitating and restoring the native plant, historic forest, and landscaped areas of the park (NPS & Presidio Trust, 2001). Some of the recommendations of the VMP such as the proposed forest treatment strategies, and selection of species for replanting have gathered significant public interest and civic engagement.
The VMP is separated into five different sections, three sections address management recommendation relevant to each newly defined vegetation management zone (the Native Plant Communities Zone; the Historic Forest Management Zone – the most visible area of the park; and the Landscape Vegetation Management Zone), while the remaining two sections are relevant to all three vegetation management zones, and address issues related to soil erosion control (an issues that has been increasingly problematic) and fire management control (NPS & Presidio Trust, 2001). To focus on specific conditions in the area (such as sewer discharge from the construction of the Richmond Transport Sewer project), the southwest corner of has been designated a Special Management Zone (SMZ). Each vegetation zone has been defined based on resource characteristics and values, historic land uses, and practical management concerns.
Defining the boundaries of these distinct vegetation management areas was a critical step for a number of reasons. First, it is important to take into account that forest boundaries have shifted over time. Even though, the historic forest management zone generally follows the extent of the original planted forest, it is recognized that, in some cases, trees in the historic forest have expanded beyond the original planted areas, while in other cases, historic plantings have been lost (NPS & Presidio Trust, 2001). Second, when managing native plant communities, it is important to attempt to connect remnant natural areas, and establish large continuous areas part of the same management zone to facilitate seed dispersal and to allow more sustainable management. At the interfaces of the three vegetation zones concepts of "edge" management and vegetation transition are important considerations when developing effective vegetation management strategies (NPS & Presidio Trust, 2001). Minimizing the edge of a vegetation management zone is seen as desirable, since rare or endangered species are less likely to persist over time if the edge zone of the native plant community is large. Third, the zones needed to be designed in a way to preserve essential wildlife habitat and wildlife diversity (NPS & Presidio Trust, 2001).
The following section will describe the characteristics of each vegetation zone and discuss the management objectives and recommendations defined by the VMP.
1. Native Plant Community Zone
The VMP describes and maps 11 native vegetation types and identifies the native plant habitat of particular concern such as the last remaining areas of serpentine grassland at Inspiration Point and the native dune community at Crissy Field, and the dune scrub community above Baker Beach (NPS & Presidio Trust, 2001). In addition to this, the Presidio is home to a number of rare species due to its combination of soils and climate. The VMP defines and identifies the special-status (rare) species present on the site.
Objectives: restoring, protecting, and enhancing the native plant communities by reclaiming habitat from past development and non-native species; monitoring rare and endangered plant species; planting native vegetation in areas where forests were previously removed; removing invasive species from the habitat; preserving rare plant species; and enhancing wildlife habitat by avoiding disturbance and increasing habitat diversity (NPS & Presidio Trust, 2001).
Existing Conditions: Once abundant, native plant communities have been currently limited to only 10% of the 1,480 acre reserve. Displacement and reduction of native plant communities was due to the modification of their natural habitat as a result of grazing, development, planting of introduced species for ornamental purposes, and naturalization of other invasive, non-native plants. The remaining native plant communities are small, impacted by invasive non-native plants, and fragmented by development or horticultural plantings.
Recommendations: Proposed management actions to maintain and enhance the native plant community at the Presidio can be broadly divided into four distinct parts.
First, efforts should be dedicated towards protecting remaining plant communities by: developing a long term inventory and monitoring program; establishing buffer areas (management of the edges between the native plant communities zone and historic forest management zone); restricting and containing forest trees (minimize shade and competition); and removing aggressive non-native species.
Second, management efforts should also be dedicated towards restoring native plant communities. Restoration activities should include and on-site evaluation, followed by the preparation of restoration site and an assessment of soil conditions. The restoration site should be planted with seed material generated form native plants propagated from Presidio stock. Maintenance (e.g. weeding, erosion control, preventing damage from human activities) and periodic evaluation of the restoration site would ensure that objectives are met, and would help assess the effectiveness of restoration efforts.
Third, attention should be given towards managing and enhancing habitat for rare plants by establishing new populations and protecting exiting species, populations, and habitats. A reliable and consistent monitoring program should be put in place to protect the thirteen special-status (rare) species have been identified at the Presidio. The vegetation management plan further go into details and offers specific recommendations for each of the rare species present on site. Some of the rare species documented include: California Sea Blite, Franciscan Thistle, Raven's Manzanita, San Francisco Lessingia, San Francisco Spineflower, Dune Gilia, and San Francisco Campion among others.
Lastly, the successful implementation of restoration and education programs can play a key role in maintaining the health of native plan communities. For example, native plant restoration projects have been ongoing on the Presidio since 1994 through the Presidio Park Stewards program. The Presidio Native Plant Nursery is a critical source for plant material needed for native plant community restoration and historic forest restoration. Education programs are also extremely valuable since they encourage public participation in restoration efforts, and raise public awareness and acceptance of changes to Presidio vegetation (NPS & Presidio Trust, 2001).
2. Historic Forest Management Zone
Objectives: restoring and rehabilitation the historic forest within its historical boundaries, while maintaining its windbreak function and preserving the visual appeal of the area; encouraging natural regeneration, while increasing the forest’s structural and species diversity; clearing non-historic forested areas to restore historic views and look-out points; protecting and enhancing wildlife habitats, while preserving historic planting configurations.
Background: The Presidio was designated a National Historic Landmark in 1962 and listed in the National Register of Historic Places. The Presidio Forest was planted in 1883 at the orders of Army Major W. A. Jones with the goal of creating a system of windbreaks and visually enhance the ridges, and the perimeters of the military post. To achieve this goal, a variety of evergreen and deciduous trees and shrubs were planted. The predominant species included: blue gum eucalyptus, Monterey pine, Monterey cypress, and blackwood acacia. Trees were planted with even spacing and with only one species in each planted area (NPS & Presidio Trust, 2001).
Existing Conditions: Particular attention has been given to the Historic Forest of Presidio since it is not only a significant feature of the historic landscape but also it is in an advanced stage of maturity. The forest is exhibiting reduced vigor, with little natural regeneration occurring due to overstocking, lack of maintenance thinning, and a reduced number of canopy openings that would allow light to reach the forest floor. Some areas of the forest are experiencing a state of decline due to lack of proper management (NPS & Presidio Trust, 2001). However, given the advanced state of maturity of the stands, corrective measures such as thinning of overstocked areas are no longer effective (NPS & Presidio Trust, 2001).
The current species composition within the forest is predominantly dominated by eucalyptus (42% of the forested acreage), followed by Monterey cypress (34 %), Monterey pine and mixed species stands (17 percent), and acacia and redwood (7%). Limited natural regeneration occurs based on species characteristics and site conditions. The forest has matured uniformly, and is entering a period of slower growth, and increase mortality rates as species planted in the late 1800s are reaching the end of their normal life spans (NPS & Presidio Trust, 2001). In the near future, it is expected that the extent of the forest will be reduced due to breakage, tree death and storm damage.
Recommendations (proposed management actions): Since the area covered by forest trees has shifted over time, it is essential to identify its species composition and structure, and design management actions that will rehabilitate the historic forest while maintaining its visual attributes, windbreak functions and historical value. Proposed management actions include the following:
First, it is important to encourage the development of species that have a range of ages from seedlings to dead snags, as well as increase species diversity. The tree age structure within the forest can be diversified by encouraging natural regeneration and conducting replacement planting, while also allowing fallen trees to remain as wildlife habitat (if they do not represent a threat to visitor safety, and if they do not have disease potential). Creating canopy openings within the forest is a key element to allow for the development of young seedlings and to encourage the regeneration of native plants in the understory. Species diversity can be enhanced by reintroduction of native trees and other native plant species (NPS & Presidio Trust, 2001). For example, in forests now dominated by Monterey cypress, Monterey pine might also be planted.
Second, management actions should be dedicated towards developing a variety of densities within the forest and developing a multi-layer forest structure. Currently in many forest stands tree density is 400 to 500 trees per acre, while it is thought that optimal density is between 30 to 50 trees per acres. Developing a multi-layer forest structure is also important not only to enhance wildlife habitat potential, but also to increase the structural diversity within the area (NPS & Presidio Trust, 2001).
Third, the vegetation management plan suggests exploring the benefits of developing native species buffer areas to increase forest species diversity, wildlife habitat potential, and reduce the need for containment. The buffer areas can effectively separate the historic forest area management zone from the native plant area management zone. In addition to this, the plan recommends enhancing site conditions to increase natural regeneration and considering the effects of wind in the forest rehabilitation plans (NPS & Presidio Trust, 2001).
Lastly, management actions should focus on maintaining the historic character of the forest as much as possible. Specifically, significant efforts will be dedicated towards preserving the life of old historic trees as much as possible though intensive tree care. When these tress die, new plantings will not take their place since this would change the aesthetic of the area, rather the dead trees will be removed from the sight and the remaining stand will maintain its historic character (NPS & Presidio Trust, 2001). Other considerations of the vegetation management plan that focus on the historic management zone include: substituting historically planted species (replacement for pest resistance and replacement for height modification), developing site-specific rehabilitation for historic forest stands, maintaining vistas and historic views, recycling plant material and market wood, developing multi-agency cooperative agreements, and evaluating cost effectiveness. More information on these topics can be found at (pp 56-63).
3. Landscape Vegetation Management Zone
Objectives: maximize sustainable practices in the development of landscape vegetation projects; retain historic landscapes and historic plants to the extent possible; document and map historic and existing landscape plantings; identify and maintain historic landmark trees; and treat hazardous tree conditions.
Background and Existing Conditions: Landscape vegetation in the Presidio was planted during periods of historically significant development and consisted of ornamental plantings that played a significant role in the functional evolution of developed sites. The vegetation management plan further separates landscape vegetation into a number of different categories based on their design intent, function and location. These areas include: open space and play fields, landscape screens (separation between public use and residential spaces), road corridors, coastal fortifications and landscaped areas around buildings. Proposed Management Actions, will apply to all categories (NPS & Presidio Trust, 2001).
Recommendations (proposed management actions): The plan suggests rehabilitation of the landscape vegetation at the Presidio, while preserving its historical and cultural character. The following key management actions are proposed.
First, promoting the longevity of exiting plant materials, while propagating Presidio plant stock from historic plant stock, is encouraged. In addition to this, minimizing the impacts of landscape vegetation on adjacent native plant communities and selection of appropriate plants as replacement species is recommended. The selection of plants used in replanting activities should be done based on their suitability to the site (site characterized by a Mediterranean climate with dry summers, and frequent fog and wind). Plants that are pest-resistant, drought tolerant, water efficient and adapted to the site’s microclimate are preferred (NPS & Presidio Trust, 2001).
Second, the plan suggests minimizing the use of chemical fertilizers, pesticides, and herbicides, while maximizing the use of natural functions. Integrated past management, composting and mulching are encouraged. In addition to this, the plan also suggests minimizing the export of waste materials by maximizing the reuse of existing landscape materials (NPS & Presidio Trust, 2001).
Third, surveying, mapping and identifying the existing landscape vegetation helps in determining its historical significance and designing appropriate management practices. Identifying plant species that have historic value, such as plants planted prior to 1946 or have commemorative value is essential in designing effective management techniques for the landscape vegetation management zone. Retaining and maintaining exiting historic landscape species is seen as a key priority. Promoting landscape vegetation health, longevity, and appearance should be supported by adequate management actions such as weeding, pruning, mulching, mowing, pest management, irrigation, and fertilization (NPS & Presidio Trust, 2001).
Soil Erosion and Fire Management:
Two other important considerations discussed in the management plant address proposed management actions for soil erosion control and fire risk management. Given that Presidios’ native soils have been altered due to construction, vegetation planting, and other natural and anthropogenic disturbances (increased foot traffic), large areas are currently covered by soils with high erosion potential. Management actions that result in changes in drainage patterns and/or surface disturbance should consider possible erosion effects. Efforts should be dedicated towards minimizing and controlling runoff by reducing compaction and increasing water filtration (NPS & Presidio Trust, 2001). Suggested management interventions include corrective actions such as: redirecting foot traffic, stabilizing soil and replanting, removing fill, restoring and revegetating sites, repairing gullying and contracting retaining walls and boardwalks (NPS & Presidio Trust, 2001).
Managing fuel loads to reduce fire risk is also an important consideration of the vegetation management plan, particularly due to an increased number of visitors in recent years. Historically, fire management policy has focused on adopting fire suppression measures by removing downed woody vegetation and hazardous fuel accumulations. Due to its wet and humid climate, fire potential is generally low, however during the late summer and early fall months, the easterly winds create an above-normal fire danger (NPS & Presidio Trust, 2001). In addition to this, fire hazard increases due to the presence of a large number of eucalyptus stands that have high fuel loadings and oil content, factors that can contribute to the development of intense fires if leaves, branches, and bark accumulate on site.
Monitoring and Management Techniques
The detailed vegetation management plan prepared for the Presidio is focuses on maintaining a rich tapestry of natural and historic landscapes. Preservation of the Presidio’s cultural, natural, scenic and recreational resources for public use is the overarching goal that directs management actions (Final Environmental Impact Statement- Presidio Trust Management Plan, 2002). The plan provides valuable information and insight by creating a framework for managing a mature landscape that represents an area of unique cultural and historic value, and area designated as a national landmark. Identifying and categorizing different vegetation types into vegetation management zones, is an important first step, since each region has a unique set of landscape characteristics and requirements, and a distinct set of management objectives and challenges. Other issues pertaining to soil erosion control and fire management are also important considerations.
The key management recommendations part of the vegetation management plan are the following:
- Maintain a range of ages from seedlings to dead trees and snags.
- Promote stand regeneration.
- Promote native vegetation and enhance species diversity.
- Develop native species buffer areas.
- Develop a variety of densities within the forest.
- Develop a multi-layer forest structure.
- Create canopy openings to allow light to reach the forest floor.
- Constant, systematic monitoring is important.
- Surveying and mapping are important steps in determining appropriate management actions.
- Minimize the use of chemical fertilizers, pesticides, and herbicides.
- Maintain fuel loads to reduce fire risk.
- Implement erosion control measures.
- Revegetate disturbed weedy habitat with historic forest or native vegetation.
- Identify, document, and map historic and existing landscape plantings and plant
species. - Identify and treat hazardous tree conditions, and identify and maintain heritage landmark trees.