Executive Summary

1.  Overview

Introduction

NATURAL AREAS PROGRAM

NAP Background and  Goals

Objectives

Definitions

2. Management Approach

Goals

Values

Strategies

3. Setting

Biology

Vegetation

Wildlife

Landuse History

4. IPM

5. General Recommendation

Vegetation

Birds

Mammals

Soils, Erosion, and Public Use

6.Site Specific Recommendations

7. Monitoring

Issue GR-10: Many of the Natural Areas are covered with networks of informal trails. Often these trails go directly up and down slope with no steps, water bars, or other erosion control features.

Erosion problems have been caused by excessive foot traffic that wears away the trails' vegetation.

Recommendation GR-10a: Natural Areas shall be monitored on a routine basis for the development of new informal trails. As these are found, they shall be evaluated for their impact to the Natural Area. Those that impact sensitive species or sensitive habitats or that contribute to erosional problems shall be closed (see Recommendation GR-10b). Trails that serve a direct function (e.g., access from parking to picnic areas) and have limited environmental impacts shall be formalized. This includes actions to clearly delineate and stabilize the trails as required to support human use.  

Recommendation GR-10b.- Most existing informal trails with the Natural Areas shall be closed to prevent further erosion of the slopes and removal of vegetation (see details in Sections 6. 1 through 6.2 1). Prevent public access to these trails with brush barriers (or fencing if necessary) and signage. Install appropriate biotechnical erosion control measures (coir rolls or matting combined with native vegetation) and/or water bars to prevent further erosion. If relocation of the trails is infeasible, measures shall be taken to minimize erosion (water bars, steps, trail delineation, etc.). Some of these measures are currently underway at different Natural Areas, but they need to be continued and expanded. Tank Hill is a Natural Area where erosion control measures were well designed and properly installed, and it serves as an example to be followed for other locations:

 •    The stairway from Belgrave Avenue is curved to conform to the shape of the hill and the risers are tied back into the face of the hill to prevent erosion around the ends. The treads are broad enough to allow some infiltration to occur, thereby reducing the flow of water along the stairway.

Issue GR-11: Most of the Natural Areas occupy sites characterized by steep, erosion-prone slopes. Many of these locations exist as parks today because building homes or streets on such steep hillsides was considered infeasible. The soils in the steepest portions of these hillsides tend to be thin, sandy, and rocky, with limited vegetative cover. This combination of factors (steep slopes, thin soils, sparse vegetation) makes the areas highly susceptible to erosion from wind, rain, and trampling. The effects of wind and rain are increased when trampling removes the sparse vegetation and disturbs the unstable soils. Even when other factors are equal, the severity of erosion is directly related to the level of uncontrolled public use, including the creation of informal trails with little regard to slope, substrate, or vegetation: the greater the uncontrolled use of the site, the more severe the erosion of the steep hillsides.

Recommendation GR-11a: To promote general soil stability on steep slopes, areas of unusually thin vegetation cover shall be revegetated. Native species shall be planted to simulate the diversity, cover, and density of adjacent habitat or reference plots in similar habitats at other parks (Appendix B).

Recommendation GR-11b: To reduce the deleterious effects of trampling in unstable areas, formal use areas, including designated trails, shall be created at locations that are sufficiently stable to withstand the pressure of public use (see Recommendations GR-10a and 10b). To the extent feasible, formal use areas shall be outside the Critical Areas.

Recommendation GR-11c: Work that involves exposure of large areas of soil shall be completed during the dry season whenever possible. If this is not feasible, or if extensive areas of soil remain exposed after work is completed, revegetation or erosion control measures shall be implemented to control movement of soil from work sites during storms. An example of a temporary method of reducing downslope erosion is to install a row of abutting, securely anchored straw bales as required on work area slopes. These bales would be removed once areas were revegetated.

Issue GR-12- There is little public awareness about native ecosystems and their importance to humans as well as native plant and animal species. However, because of the wealth of resources, ease of access, and diverse locations, the Significant Natural Resource Areas provide abundant ecological educational opportunities.

Recommendation GR-12a: The SFRPD shall continue to network with local schools and research institutions to provide environmental education resources and opportunities for school children in San Francisco. Additionally, SFRPD shall continue to identify research projects and funding opportunities for on-going research.

Recommendation GR-12b: SFRPD shall develop signage appropriate for installation within Natural Areas that explains the importance of the natural resources, ecosystem functions, management activities and goals, and public involvement contacts.