Mount Sutro Open Space Reserve

Questions and Answers

During the 2009 – 2010 Mount Sutro Open Space Reserve community planning process, which included two community walking tours, participants asked questions on a variety of issues related to the proposed demonstration projects and other management actions for the Mount Sutro Open Space Reserve (the Reserve). This Q&A replaces and updates those published in December 2009 and April 2011.

This Q & A is not designed to be exhaustive.  Rather, it is a supplement and a complement to the Mount Sutro web page, and to reports, summaries, and other documents that can be found here.

Introduction

UCSF is planning for four demonstration projects in the Mount Sutro Open Space Reserve.  These demonstration projects will illustrate the effectiveness of different management techniques and will aid in deciding which techniques will be applied to the remainder of the Reserve.

Before the work is done in the demonstration project areas, UCSF must follow the California Environmental Quality Act (CEQA) and assess the environmental impact of the planned actions.  Work on the Environmental Impact Report (EIR) began in early 2011 and a scoping meeting was held on January 8, 2011.  At this meeting, community members had an opportunity to provide input on the approach UCSF is taking on the EIR analysis and on environmental topics to be analyzed in the EIR.

UCSF has a strong commitment to maintaining the Reserve as a safe, ecologically sustainable resource that can be enjoyed by neighbors and visitors, and well as the UCSF community.

Overview

What is the Mount Sutro Open Space Reserve? 

What is the history of the Reserve?

Why is management of the Reserve important?

Management of the Reserve

Where are we in the process of studying what management actions will be taken in the Reserve?

What is the purpose of CEQA?

When will the EIR be done and demonstration project implementation begin? 

Where are the demonstration projects?  

How will wildlife be impacted?

When the demonstration projects are complete, what will be the process for management action in the rest of the Reserve?

How many of the trees will be left in the demonstration project areas? 

How will the understory in the forest be managed?

Will herbicides be used in the Reserve?

After you implement the management actions, will Mount Sutro still look like a forest from my house? 

Will removing trees from Mount Sutro compromise the stability of slopes and lead to soil erosion?

Why is it necessary to remove or kill the entire tree, including the stump?

When trees are removed from the site, how will UCSF carry them off of Mount Sutro? In other words, will surrounding neighborhoods be impacted by truck traffic or noise associated with this effort?

Will the large, downed trees and chipped material left in the forest create a fire hazard?

Won’t the cut vines create a fire hazard?

Once the thinning and clearing activities take place, how often will it be necessary to trim limbs, clear additional brush and conduct other maintenance?

Would other types of trees be better on Mount Sutro and why?

The Current Environment on Mount Sutro

What are the characteristics of Southern Australia Tasmanian blue gum (including age, size and natural environment (including trees/acre in healthy forest)?

Why do trees in the Mount Sutro forest keep reproducing but do not grow large and healthy? 

Why do the native plants at the Rotary Meadow on the summit look dead? 

Fire Risk and other Hazards on Mount Sutro

Why would this forest burn at all with fog drip, dampness and greenery?

How will fog-drip and remaining trees be affected by the proposed demonstration projects?

Why is it significant that Mount Sutro has relatively dry soil?

How does Mount Sutro’s topography contribute to the fire hazard?

Why are structurally weak trees more of a fire hazard?

Why are multi-stemmed trees hazardous?

How will the changes being implemented in the demonstration project areas minimize the risk of fire if applied to the entire Reserve? 

Are the homes surrounding Mount Sutro in danger from potential fire?

Can UCSF clarify the specific locations of wind direction and potential fire hazards on Mount Sutro in future documents?

Will the activities proposed in the demonstration projects areas increase fire risk and, therefore, the Fire Insurance Rating on Crestmont Drive?

 

Overview

 

What is the Mount Sutro Open Space Reserve? 

The Reserve is a 61-acrea part of the largely undeveloped Sutro Forest located within UCSF’s Parnassus Heights campus site at the center of San Francisco.  It is surround by the UCSF campus, UCSF’s hospital, research, educational and support structures to the north/northwest, and by urban residential neighborhoods to the south, east and west.  The entire Sutro Forest is not within the Reserve; the Interior Greenbelt area, owned by the City and County of San Francisco, is adjacent to the east side of the Reserve.  The Reserve is designated as permanent open space by The Regents of the University of California, is open to the public, and serves as a point of respite and recreation, not only for UCSF, but also for the greater community.

What is the history of the Reserve?

Although the land within the Reserve is considered a forest today, the area has evolved over time.  From the 1800s when it was a hill covered primarily with native grasses, wildflower and shrubs to a celebration of Arbor Day in 1886 when Adolph Sutro began planting it with blue gum eucalyptus, Monterey pine, Monterey cypress and possibly other species, Mount Sutro has been part of a constantly changing and adapting land.  Parts of Mount Sutro were even logged in the 1930s and 1940s, with the major parts of the forest as it is today growing within the last sixty years.

Some have incorrectly referred to the Reserve as an “old growth” forest or a cloud forest.  The term “old growth” is normally reserved for late successional stage or “climax” forest types. It is reserved for native species and ecosystems. Old growth is commonly restricted to uncut, virgin forest with very little human-caused disturbance. Generally, old growth must be greater than 200 years or more, depending on the life expectancy of the species.  Old growth is generally composed of trees that are large for the species and for the site (Helms, J. A. Dictionary of Forestry, 1998, Society of American Foresters). Old growth forests must be substantial in size, hundreds of acres, to contain the elements of old growth.

Just as Sutro Forest is not “old growth”, neither is it a “cloud forest”.  The moderate temperatures of San Francisco are neither tropical nor sub-tropical, which is the climate where cloud forests exist.  Even with the dense fog that often blankets the Reserve, the area is comparatively dry due to the characteristics of the eucalyptus.  Eucalyptus pulls water from the soil, tying up the moisture in its roots.

Why is management of the Reserve important?

Managing the Reserve is important to keep it safe, healthy, aesthetically pleasing and usable.  Although not frequent, wildfires have occurred in the past.  Neighbors, along with the San Francisco Fire Department, recall a fire that occurred in the City’s Interior Greenbelt adjacent to the Reserve.  With the development around Mount Sutro, there is more opportunity for a structure fire, or a fire started by a barbecue or child.  The homeless who often camp on the hill also pose a risk, as do power lines.  Several factors would affect the behavior of a fire including steep slopes, ascending drainages, south facing slopes, fuel type and the health of the plants on the hill.  The San Francisco Fire Department also has very poor access to the hill; no trails lead down to areas that fire engines could easily access.  Nor does the Department have the right equipment to fight a wildland fire.  Significant assets at risk include structures, habitat, air quality and water quality.

In 2008, the City and County of San Francisco developed a citywide wildfire hazard map as part of its Hazard Mitigation Plan.  Red and orange areas indicate a high to very high fire hazard severity.  A majority of Mount Sutro falls into these categories.   This Plan was approved by the Board of Supervisors and is the official Hazard Mitigation Plan for the City. Every county is required to have a FEMA approved Hazard and Vulnerability Plan in order to be eligible for any FEMA disaster reimbursement in event of a declared disaster.   The following paragraph is quoted from the plan, which is being monitored, evaluated and updated within a 5-year cycle (through 2013):

 “The City and County of San Francisco (the City) has developed this Hazard Mitigation Plan (hereinafter referred to as the 2008 HMP) to assess risks posed by natural and human-caused hazards and to develop a mitigation strategy for reducing the City’s risks. The City has prepared the 2008 HMP in accordance with the requirements of the Disaster Mitigation Act of 2000 (DMA 2000). The Department of Emergency Management (DEM), Division of Emergency Services, has coordinated the preparation of the 2008 HMP in cooperation with other city agencies and departments. The 2008 HMP replaces the HMP prepared by the City in 2005.”]

Management of the Reserve

Where are we in the process of studying what management actions will be taken in the Reserve?

Four demonstration projects, totaling less than 7.5 acres, are proposed for implementation in the Reserve, and an EIR is being prepared to determine what the impacts of these demonstration projects might be if they are implemented in the entire Reserve.  Evaluation criteria and principles have been developed to guide the evaluation process, which will take place one month after implementation for visual impacts and one year after implementation for re-growth control and new plant survival.

What is the purpose of CEQA?

The purpose of CEQA is to inform governmental decision-makers and the public about potential significant environmental effects of proposed activities and to identify ways to avoid or reduce significant impacts by requiring feasible mitigation measures or alternatives.  CEQA documents are informational only, rather than being an approval process for the project.

When will the EIR be done and demonstration project implementation begin? 

A draft EIR is expected be published in the fall of 2011.  This schedule has been revised because we will be conducting more analysis in response to community feedback.  There will then be a 45-day public comment period that will include a public hearing.  Comments may be submitted in writing (U.S. Mail or email) anytime during the comment period or verbally at the hearing.  Comments will be responded to in writing, and the Draft EIR will then be revised as necessary, with the final EIR being certified by the decision-making body as determined by the UC Board of Regents.  The decision-making body will certify the EIR if it finds the EIR to be adequate.  The decision-making body will then determine whether to approve the project, and if approved, the demonstration projects will be implemented.  In order to accommodate the bird-nesting season, we expect the demonstration projects to be implemented as soon as August 2012.

Where are the demonstration projects?  

UCSF worked hand-in-hand with neighbors to design the four demonstration projects with different characteristics to allow for study and evaluation of the varying management techniques.  Demonstration project characteristics include tree spacing; amount of undergrowth removal; re-growth control strategies; native plant restoration and view corridor development. 

Demonstration Project 1 is a three-acre area located along the South Ridge of Mount Sutro.  It was selected because of the variable field conditions, good accessibility, high wildfire risk and proximity to residential areas in the event of a wildfire, and because thinning is expected to have very little visibility from off-site.

Demonstration Project 2 is a two-acre demonstration project near Edgewood Avenue and was selected to minimize fire hazards around UCSF buildings and adjacent residences, and to evaluate potential increases in noise, light and wind on concerned neighbors.

Demonstration Project 3 was requested by community members to serve two purposes: to restore an existing native grass area and to create a view of the City from the north side of the summit of Mount Sutro.

Demonstration Project 4 is a two-acre bowl on the eastern side of Mount Sutro.  Tree spacing in this area would be an average of 60 feet to allow more sunlight to penetrate the forest floor in support of native plant growth, greater biodiversity and wildlife habitat.

In addition, UCSF has identified a 2-acre area of the Reserve to serve as a space in the forest for “hands-off” management.  Maintenance will be performed to remove and prune hazardous trees near homes and trails for the safety of residents and visitors and to keep trails clear.  This area would exist for the one-year duration of the demonstration project time frame.

Maps of the locations of the demonstration projects and details on their purpose and evaluation criteria can be found in the Mount Sutro Open Space Reserve Community Planning Process Summary located on UCSF’s website.

How will wildlife be impacted?

As a forest management project, the proposed activities may impact biological resources, including plants, wildlife and wildlife habitat.  UCSF has retained the services of a biological resource team that will assess and document existing conditions and evaluate the impacts of the proposed project on biological resources relevant to significant criteria outlined.  These topics will be outlined in the EIR.

It is UCSF’s hope that creating a more diverse and healthy forest will increase the wildlife diversity of the Reserve.

When the demonstration projects are complete, what will be the process for management action in the rest of the Reserve?

UCSF and neighbors will evaluate the demonstration projects using evaluation criteria developed in the 2010 community process.  Vegetation management activities for the remainder of the forest will be based on these evaluation results.  In the meantime, activities that are exempt from CEQA will continue in the Reserve.  These activities including pruning, shrub and weed removal, trail maintenance and improvements, hazardous tree removal, maintenance and plantings at Rotary Meadow, and installation of accessory structures such as trail markers.

How many of the trees will be left in the demonstration project areas?  

It is UCSF’s intention that the Reserve retain the look of a forested mountain following tree thinning because many trees will remain. As described in the community planning process summary [link to summary], UCSF is committed to tree spacing that will allow healthy trees to flourish, thus retaining a dense forested appearance.

 

Desired tree spacing varies for the four demonstration project areas.  For Demonstration Projects 1 and 2, the desired spacing is an overall average of thirty feet, with some places already having that desired spacing.  In Demonstration Project 3, very few trees would need to be removed to prevent shade on the grassy area and to provide a view.  A sixty-foot average is the goal for Demonstration Project 4.

 

How will the understory in the forest be managed?

Much of the understory in the Reserve looks green on top but is dead underneath, creating a fire hazard.  The amount of understory to be removed varies in each project area.  Please see Chapter 4 of the Mount Sutro Open Space Reserve Community Planning Process Summary for details.  In some cases, most of the undergrowth will be removed, excluding natives and some islands of brush for wildlife maintenance, to mitigate this hazard.  As with tree spacing, the visual effects of understory removal will be evaluated in the demonstration project areas before applying to the rest of the Reserve.

Will herbicides be used in the Reserve?

UCSF will restrict the use of herbicides to one acre in Demonstration Project 1 (i.e. 1 of 61 total Reserve acres).  After cutting, targeted spot-application methods will be used on eucalyptus stumps, vine, blackberry and broom stems, and on poison oak base, root collar, or stumps.  Results of herbicides on this single acre and other re-growth control methods used in the remainder of the demonstration project areas will be compared and evaluated before developing a policy for the remainder of the Reserve.

After you implement the management actions, will Mount Sutro still look like a forest from my house? 

Mount Sutro will retain the look of a forested mountain because many trees will remain after thinning and the trees will become healthier. The canopy and number of leaves produced per tree will increase in those areas where the forest is thinned, thus creating areas that appear more dense. Further, on slopes in the project areas, the green covering will remain visually the same because of the healthier canopy and because the trees are staggered up the slopes, one above the other, like a step-ladder with a continuous visible canopy.

Will removing trees from Mount Sutro compromise the stability of slopes and lead to soil erosion?

The slopes will remain stable during and after the proposed work because the root systems which provide the tree contribution to the soil mantle anchorage and horizontal cohesion will not be destroyed and will persist in the soil for a number of years. The trees that will remain on the slopes in the demonstration project areas will be on average 30 or 60 feet apart. This means the roots of each tree need only extend approximately 15 or 30 feet respectively to overlap the root system of the neighboring trees. These radii are not very great, and the trees certainly currently exceed that extension.  The root matrix of the eucalyptus trees is grafted together, creating strong, horizontal soil cohesion and adherence of the soil mantel to the underlying rock substrate. Over time, die-back of removed tree roots will occur, but preserved trees will greatly expand their root systems and there will still be an adequate number of trees with healthy roots to provide slope stability.

Why is it necessary to remove or kill the entire tree, including the stump?

Stumps of trees are not dead, and if left in the ground or untreated, they can grow a number of shoots and end up growing in more thickly than when originally cut. Also, a second growth multiple stem condition would occur by preserving the cut stumps.  The fuels generated by cut stumps, if the stumps are not killed, are closer to the ground and will create fuel ladders to the canopies of the trees.

When trees are removed from the site, how will UCSF carry them off of Mount Sutro? In other words, will surrounding neighborhoods be impacted by truck traffic or noise associated with this effort?

The plan is to masticate all trees with diameters that are generally less than 12-14 inches and to spread the chips around on the ground.  Only larger trees will be felled, stripped of all branches and leaves and the logs left on the ground. If it is determined that some logs should be removed, UCSF will consult with neighbors and minimize any noise and traffic impacts.

Will the large, downed trees and chipped material left in the forest create a fire hazard?

Just like when lighting a campfire or a fire in a fireplace, a flame next to a log will not light. Those fuels are considered unavailable because they are greater than 10,000 hour fuels in terms of fuel classes: it would take 10,000 hours for them to dry out enough to catch fire because of how dense they are.  Therefore, fallen trunks can remain in the forest and not pose a fire hazard.

Chipped material will also be very dense.  Like mulch, it will protect and retain soil moisture for living plants; so chipped material provides a higher moisture content and lower flammability.  In addition, air cannot mix with dense material to fuel a fire, so the chipped area will have a potential flame length of less than a foot and a fire would be very slow moving.  Chipped material will be moist and not oxygenated because it is very good at collecting and trapping overnight moisture in addition to drawing up and retaining moisture from the water table.  The lower part of the chip layer will remain moist throughout the day.  Chips are used on firebreaks to raise the soil moisture content of plants left in the firebreak and also to suppress weeds.

Won’t the cut vines create a fire hazard?

In the demonstration project areas, vines will be removed to a height of ten feet, and this treatment will leave compact and low fuels on the soil surface (ground fuel) and will generate only a flame length of approximately one foot.  Since the dead ends of the vines will be above ten feet, that is a safe distance so the small vines will not catch fire from a wildfire moving along the forest floor. This is the national standard to make them unavailable to ground fuel.  There will be dead material clinging to higher trunks for several years, but to get to the goal of having the lowest possible fire risk on Mount Sutro, we will have wait for a few years during which time the dead vines will decay and fall off.  To have a climber remove dead vines would be prohibitively expensive.

Once the thinning and clearing activities take place, how often will it be necessary to trim limbs, clear additional brush and conduct other maintenance?

Forest maintenance practices in some areas will be intensive the first year but will decrease over subsequent years.

Would other types of trees be better on Mount Sutro and why?

For all the reasons we have discussed about eucalyptus, many other tress are simply less flammable and less of a fire risk, especially native tress like redwood and coast live oak.  Also, a greater diversity of plants, like we see on the Mount Sutro summit in the Rotary Meadow, provides better habitat for a wider variety of animals and insects. Greater diversity also makes a forest more stable from a health perspective; one disease would not infect a significant portion of the overall forest.  In a forest of all oak trees, for example, live oak disease would decimate the entire forest.  In a diverse forest, that would not happen.

The Current Environment on Mount Sutro

What are the characteristics of Southern Australia Tasmanian blue gum (including age, size and natural environment (including trees/acre in healthy forest)?

Blue gum eucalyptus is a rapidly growing evergreen tree native to Australia, but it is widely cultivated and is the most common eucalyptus in California. The trees are typically 100 to 120 feet in height and approximately 3 feet in diameter at maturity.

Blue gum eucalyptus is an extremely competitive and aggressive plant. These trees compete with other plants in several major ways: they grow quickly and spread widely; they have very aggressive roots that tie up all available soil moisture and soil nutrients such as potassium, phosphorus and nitrogen; they are incredible water pumpers, meaning they grab up the available moisture in the soil.  Many other plants, therefore, cannot compete with eucalyptus.

Eucalyptus forests in California tend to be even-aged forests, meaning the trees dominate quickly and mature together. Most animals prefer an uneven aged forest with a higher diversity of plant species for nesting, escape, and food.  Eucalyptus forests are typically a monoculture with very low biodiversity. In Australia, low-intensity regular fires thin out forests. A native, mature eucalyptus forest has more the type of spacing that the demonstration project areas propose to create.

Why do trees in the Mount Sutro forest keep reproducing but do not grow large and healthy? 

Simply put, it’s over-competition: the eucalyptus trees are too dense to be healthy. In Australia, low-intensity fires and other environmental conditions regularly thin out forests.  A native, mature eucalyptus forest typically has the type of spacing that these project areas propose to create.  Current tree spacing on Mount Sutro is very dense.  If the soil is viewed as a plate of food and the amount of air above as growing space, we can imagine there is not enough food for the number of trees feeding off a limited soil volume and, consequently, the trees become sick and stunted when there are too many stems per unit area.  There are not enough nutrients, water or growing space. The competition creates suppressed trees because there is not enough space to be vigorous. 

The oils produced in eucalyptus tree leaves and distributed throughout the tree are natural antibiotics, pesticides and fungicides and help defend the trees from destructive insects and disease, but small trees with small canopies produce little oil for protection, so they can’t recover from injuries and can’t fight off insects and other biotic predators.  In the Mount Sutro Forest, this creates more pest predation, disease, and decay than in a healthy, uncrowded forest.  Because the trees are sick, they produce more seed for the survival of the next generation, simply adding to the problem.

Why do the native plants at the Rotary Meadow on the summit look dead? 

Because they are native plants, their adaptation to a dry summer is to produce seed, dry up and go into dormancy during the mid to late summer.  The phrase “Golden Hills of California” is based on the predominantly dry landscape of native plants that flourish only during the rainy season, spring and early summer, when soil moisture is adequate.  Most native plants are still quite green and have adapted to the summer dry climate in other ways, such as vast root systems that can access more moisture and woody leaves that can stay well displayed and green during the heat of summer.  Simply put, native plants on the Mount Sutro summit are behaving as native plants do.  Diversity on the summit is incredible and far exceeds that of the eucalyptus forest.

Fire Risk and other Hazards on Mount Sutro

Why would this forest burn at all with fog drip, dampness and greenery?

Our history tells us that the fog zone of the San Francisco Bay region is not immune to catastrophic wildfires. A pre-settlement fire history of Mount Tamalpais in Marin County shows that fires hot enough to scar Redwood trees occurred approximately every 25 years, so fires were not uncommon.  More recently, the Bay Area coastal zone has suffered a number of catastrophic fires.

In the Oakland Tunnel Fire in October 1991, one of the major fuels was the blue gum eucalyptus, the same species present on Mount Sutro.  The 1995 Vision Fire in Inverness occurred in a dense fog zone very much like that of Mount Sutro, and that fire consumed 14,000 acres.  During the fire’s peak, when Santa Ana-type winds blew from the north to the northeast, it ran at 1,000 acres per hour.  In 2008 in Santa Cruz, a fire started along Highway 1and quickly moved from grass to blue gum eucalyptus.  The fire exploded and moved up hills, destroying many homes and causing firefighters to flee.

A running, high-intensity flame front relies only on relatively small fuels in two fuel classes: one-hour fuels and ten-hour fuels that can dry out within those short periods of hot, dry wind. A running fire takes advantage of fuels up to approximately the size of a thumb, or one inch in diameter.  One-hour and ten-hour fuels are labeled as such because the internal moisture and temperature of plants adjust to weather conditions in just one to ten hours, a very short time frame. On those dates when the Tunnel, Vision and Santa Cruz fires burned, an ignition adjacent to Mount Sutro could have had the same result.  A good example of a large window of opportunity for fire occurred last summer.  In July 2008, when there were fires all over California, especially near Chico, we had almost two weeks of weather where Mount Sutro could have burned with high intensity.

How will fog-drip and remaining trees be affected by the proposed demonstration projects?

The proposed demonstration projects propose to reduce the number of trees taking moisture from soil so, in reducing the number of trees, they would also reduce the fog drip. Reduction of fog drip does not increase fire hazard because fog drip only moistens surface soil and does not replenish the internal moisture content of the living trees or understory very well. Dampness and green appearance disguise the internal conditions of the plants. The Mount Sutro undergrowth has a dense, dead sub-canopy under the leafy green surface.

Why is it significant that Mount Sutro has relatively dry soil?

Drier soils provide less moisture for living vegetation to access, which means the internal moisture content of that vegetation is relatively low and more susceptible to burning. Drier soils also mean that understory fuels on the ground recover less moisture overnight. Blue gum eucalyptus produces an abundance of down and dead branches, twigs, bark strips and leaves.

How does Mount Sutro’s topography contribute to the fire hazard?

Steep slopes such as those on Mount Sutro contribute to the rapid uphill spread of fire because the treetops act as a stair step or fire ladder.  In addition, fire creates a blast of air and extensive flame lengths, parallel with slope, that preheat unburned fuels ahead of the flame front so fire spreads more rapidly and more intensely under trees as it moves up the slope, creating even more of a fire hazard.

On a typical “fire day”, which progresses in general from 10 am to 5 pm, as the sun rises in the southern sky, it begins heating the southeast slope of hills.  The air starts moving up the slope and, like a chimney, warm air rises.  As the sun moves across the southern sky from east to west, the temperature increases, creating more energy and greater movement of air up the slope, even in the absence of fire.  From 2pm to 5 pm, southwestern slopes are the worst for fire behavior, because the air moves rapidly and fuels are at their driest.  South slopes focus more energy per unit area, much like a flashlight focused on a wall, which makes things more flammable.

Why are structurally weak trees more of a fire hazard?

From a structural perspective, hazardous trees are a huge problem on Mount Sutro.  Many trees are over-mature for an urban environment.  Blue gum eucalyptus can live many years, but in California the threes are over-mature at 80 years. In an urban environment with pollutants and stresses that they do not experience in a native forest, and especially the over dense forest on Mount Sutro, the stress and aging is greatly increased. Just like with people, stress ages a tree more quickly. Over-mature forests in poor condition produce trees that are more likely to fall in windstorms.  In addition, trees with structural defects are more likely to fail, which creates several impacts including adding to the amount of small fuel on the ground within easy reach of a fire.  During a fire, defective trees are more likely to fail and inhibit emergency response, evacuation and fire suppression activities blocking roads, paths, driveways, and simply the access to the fire, even within the forest itself.

Why are multi-stemmed trees hazardous?

Multi-stemmed, first-growth trees tend to have leaning trunks, unbalanced canopies away from one another, and weak acute angle crotches. Second-growth, multi-trunk trees share a parent stump that eventually dies and decays.  These trees have unbalanced root systems and often have decay. They are inherently weak and lopsided, prone to failure and therefore hazardous, especially when located within falling distance of trails, roads, parking lots and buildings.  When one tree fails it increases the failure potential of the surrounding trees because their root systems are disturbed and the remaining trees are subjected to winds that they are not accustomed to.

How will the changes being implemented in the demonstration project areas minimize the risk of fire if applied to the entire Reserve?

Since eucalyptus is the dominant tree on Mount Sutro, it is important to understand the factors that make it far more of a fire hazard than other species. Blue gum eucalyptus produces more twiggy leaf and bark debris on the ground than any other species in California, and those twigs, branches, bark and leaves form a lofty, well-aerated, high energy fuel bed.  On top of that, quite often, all the downed and dead material form a foundation for other things like blackberry to grow and that adds to the depth and quantity of fuel in that fuel bed.  Blackberry, like a lot of other vine species, typically has a dead sub-canopy.  This means that under the green portion there are a lot of dead vines that have been shaded out by new growth, so the sub-canopy of dead material is often greater in quantity than new material. On Mount Sutro, the problem is that poison oak, blackberry and other vine species grow on top of eucalyptus debris, adding to the amount of fuel on ground. When ground fuel burns, it preheats the canopy, drives off what water might be left, and makes the canopy that much more vulnerable to a high intensity crown fire.  The trees can torch with flame lengths well over 100 feet.

The architecture and self-laddering of the eucalyptus fuels on Mount Sutro are an extreme hazard.  Ground fuels, shrub layers, vines, young trees, low branches, etc. create a ladder for a fire to climb up trees and ignite their canopies, which is a far more difficult fire to suppress.  Eucalyptus, with its loose bark that accumulates in the crotches and on branches, even in the absence of ground fuel, means a fire can climb to the canopy of the tree.

Fires in a treated forest creep along the ground at a rate of feet per hour versus 1,000 acres per hour, like the 1995 Vision Fire in Inverness, because there is less available fuel and the fire is therefore less intense. In a treated eucalyptus forest, most of the fire-prone fuels are isolated high above the potential flame front and simply inaccessible to potential fire; canopies burn more easily when they are preheated by ground fuels and conducted upward by fire ladders, as discussed above. Finally, if there are fewer trees per unit area, they all will have a higher internal moisture content and therefore are more difficult to ignite.

Are the homes surrounding Mount Sutro in danger from potential fire?

Most homes in an urban wildfire are ignited not by the flame front, but by embers that precede the flame front, embers that can lodge in tiny spaces in the covering of buildings.  Wind is generated by both the weather conditions and by the fire itself, creating powerful winds that blow on trapped embers like we might blow on kindling to ignite a campfire.

Blue gum eucalyptus is infamous for ember and firebrand production. It holds the world’s record for sending a firebrand downwind of a main fire and starting a spot fire well beyond the confines of the main fire.  Firebrands may continue to burn many kilometers beyond a main fire.  Wildfires create updrafts that lift large quantities of burning fuel downwind that may be deposited on homes.  With the developed urban wildfire interface so close to the forest, not only are homes highly vulnerable, but also medical research and clinical facilities at UCSF’s Parnassus campus, including the UCSF Medical Center and UCSF Children’s Hospital.

Can UCSF clarify the specific locations of wind direction and potential fire hazards on Mount Sutro in future documents?

As discussed above, severe fire weather occurs for a limited period every year.  The frequency and extent of severe fire weather, typically hot, dry winds out of the north to east can be determined from local fire weather records. UCSF will retain a professional forestry firm to perform this specific analysis.

Will the activities proposed in the demonstration projects areas increase fire risk and, therefore, the Fire Insurance Rating on Crestmont Drive?

The goal of UCSF is to reduce, not increase, fire risk on Mount Sutro.  Because the City and County of San Francisco has already identified parts of Mount Sutro as either a “high” or “very high” fire risk, the work to be done on the location will have the result of reducing that fire risk.

Mount Sutro Open Space Reserve Q & A [PDF]