61

Chapter 3

Chapter 3 – Factors Influencing

Ecosystem Integrity

Ecosystems are not defined so much by the objects they contain as by

the processes that regulate them.

 — Christensen et al. 1989

Key Questions

• What are the primary natural

processes and human activities that

drive change in the composition,

structure, and extent of southern

California mountain and foothill

ecosystems?

• How are those processes and

activities currently affecting the

landscape and what can be

determined regarding the natural

range of variability?

• What current trends are apparent and

what threats or opportunities are

presented by them?

This chapter considers the primary processes and activities that modify ecological

communities in the mountains and foothills.

These include (1) natural disturbance processes such as fire, flood, drought, and

outbreaks of insects or disease; (2) human uses

of the land for development, resources, and

recreation; and (3) the spread (often unintentionally) of new elements such as air pollution

and non-native plants and animals.

Each of these “change agents” acts upon

the landscape and modifies its character. To

persist over time, plant and animal species

must continually be able to survive, reproduce,

or recolonize as the landscape changes. Thus

the disturbance processes that shape local ecosystems are as important to understand as the

physical components of those ecosystems.

Since disturbance and climatic variability

are inherent components of natural systems,

all species have adaptations to survive in a

changing world. Yet, their ability to respond

to change is not limitless and some organisms

are clearly more adaptable than others. In general, the complete assemblage of native plants

and animals is most likely to be maintained

when environmental conditions remain within

their natural historic range. Thus we need to

develop an understanding of what the historic

or natural ranges of variability are for various

ecological processes. These serve as the reference conditions to which present day

conditions can be compared. The closer current conditions are to reference conditions, the

greater our confidence that all the ecological

components will continue to persist (for detailed description of the “reference variability”

concept see Manley et al. 1995). This is the

basis for the “coarse-filter” approach to conservation described in chapter 2.

In our analysis, we first asked the assessment task group to identify and describe the

key interactions between landscape elements

and the change agents (e.g., ecological processes or human activities) currently shaping

them. Then we examined those interactions,

using the best available information on reference conditions to assess how today’s dynamics

compare with the historic range of variability.

Of particular interest is how the current management of natural processes (e.g., fire

suppression or streamflow regulation) has affected the species and habitats that evolved

under the influence of those processes.

The element/process interactions identified by the assessment task group are

summarized in the following sections. A separate matrix was developed for each of the six

large-scale vegetation mosaics described in
62

chapter 2. The matrices were used to clarify

the effects of different activities and prioritize

those having the biggest impact on species

conservation and ecosystem integrity. We believe this information will be useful when the

time comes to formally describe desired conditions and management priorities. What

follows is a description of the primary change

agents and how they influence ecosystems.

The Influence of Fire

Experience has taught us that we cannot

prevent fire. In my opinion, it is better to

have a fire every year, which burns off a ...

small area, than to go several years ... and

have a big one denuding the whole watershed

at once.

 — William Mulholland, 1908

Fire is a primary agent of change in vegetation patterns across the southern California

landscape. The distribution, composition, and

structure of almost all plant communities in

this region are influenced by fire, and as the

quote above illustrates, prominent southern

Californians have long recognized its importance and offered opinions on how it should

be managed.

The significance of fire in shaping southern California wildlands is reflected in a large

body of scientific research on the subject. It is

not by coincidence that the Forest Service research station in southern California is the

Forest Fire Laboratory and, as the name implies, is largely devoted to fire research. Yet,

even with the extensive scientific attention

given this subject there are widely divergent

opinions among researchers regarding historic

patterns of fire frequency, size, and intensity

(Zedler 1995). This uncertainty can largely be

attributed to the inherent difficulties associated with studying a phenomenon that affects

large areas, recurs sporadically over time intervals that range from a few years to several

hundred, and whose individual events vary

widely in extent and severity.

Fire history information provides valuable

insights, but the sources suffer from being (1)

anecdotal (e.g., accounts of a few early inhabitants); (2) incomplete and less reliable the

further back in time you go (e.g., official

records of past fires); or (3) based on indirect

information that is subject to varying interpretations (e.g., fire scar analyses, vegetation

patterns observed in old aerial photographs,

and patterns observed in nearby areas where

fire suppression is less of a factor). Unfortunately, this body of evidence does not provide

clear, unequivocal answers; thus, there will always be different interpretations of how things

used to be.

In this assessment we examined various

theories and supporting evidence on how

today’s fire regime may differ from historic

conditions and what is relevant about those

changes. We focused primarily on factors influencing the persistence of native ecological

communities and how today’s conditions compare with what is known about the natural

range of variability. In this section we present

some of the local fire history data, describe

key concerns, and try to identify where there

is strong scientific consensus and where there

is not.

Has the Fire Regime Changed?

There is little argument that the fire regime in southern California has changed as

human populations have grown and fire suppression practices have become increasingly

effective. Even assuming that Native Americans actively burned, there are many more

ignitions today with the combination of human- and lightning-caused starts, and those

ignitions are more concentrated along the interface between urban development and

wildlands. However, most of those ignitions

are quickly suppressed unless conditions are

conducive for rapid fire spread. Most acres now

burn in human-caused fires (Davis and

Michaelsen 1995; Conard and Weise 1998),

presumably because these fires can arise at any

time and thus have the greatest chance of igniting vegetation during key periods when

conditions are prime for fire spread (e.g., during extended heat waves or when “Santa Ana”
63

Chapter 3

or “sundowner” conditions bring high temperatures, ultra-low humidity, and high winds).

It is reported that 10 percent of the fires

in southern California wildlands account for

over 75 percent of the area burned (Strauss et

al. 1989; Keeley et al. 1999). Thus, most areas currently burn in large fires. It is unclear

whether this is a natural, historic pattern or

an artifact of fire suppression. Keeley et al.

(1999) analyzed fire history records and found

that this pattern dates back to at least 1910.

However, we have no way of knowing if it was

the pattern prior to the arrival of Europeans.

Most of the vegetation that burns in southern California is chaparral, which is well

known for its tendency to go from being difficult to burn under moderate conditions to

exploding into a fire storm under extreme conditions (P.H. Zedler, Univ. of Wisconsin, in

litt. 1998). Thus, chaparral has characteristics

that make it naturally susceptible to large fires.

However, it also seems evident that fires in

today’s environment are able to grow significantly in size only when weather and fuel

moisture conditions are severe enough to limit

the effectiveness of suppression actions. A resulting hypothesis is that active suppression

has changed the fire regime such that fires are

now less frequent but likely to be larger in size

and more severe in intensity.

Support for this hypothesis is found in

comparisons of fire patterns in southern California with those in northern Baja California,

Mexico, where fires are generally not suppressed (Minnich 1983; Chou et al. 1993).

In a detailed comparison of 1920 to 1970 fire

patterns in San Diego County and northern

Baja based on examination of aerial photographs, Minnich (1989) found a similar

number of acres burned, but the fires in San

Diego County were significantly fewer and

larger. The vegetation patterns on each side of

the border were strikingly different, with chaparral habitats in northern Baja exhibiting a

much more diverse and fine-grained age-class

mosaic (Minnich 1989). Minnich attributed

this difference primarily to fire suppression north

of the border and lack of suppression south of it.

Studies looking solely at southern California fire history records do not support the

hypothesis that fires have become fewer and

larger. Using fire perimeter maps that extend

back roughly ninety years, Conard and Weise

(1998), Weise et al. (in press), and Keeley et

al. (1999) did not find statistically significant

increases in average fire size over the recorded

time period. Keeley et al. (1999) also found

that most southern California counties have

had a statistically significant increase in the

number of reported fires per decade. These

authors conclude that large fires, usually

fanned by fall Santa Ana weather conditions,

have always been a dominant component of

southern California’s fire regime and this has

not been changed by fire suppression activities. Moritz (1997) came to a similar

conclusion in a statistical analysis of Los Padres National Forest fire history data, but he

did detect a significant decline in the frequency

of small fires. It is suggested that suppresson

may actually be helping maintain something

approximating the historic fire regime by neutralizing the large increase in human-caused

ignitions (Conard and Weise 1998; Keeley et

al. 1999).

It is likely that these differing findings and

interpretations each have some merit. It is undoubtedly true that large fires occurred

historically; there is evidence of such fires in

old charcoal deposits (Byrne et al. 1977), and

the combination of extensive chaparral vegetation and extreme southern California

weather conditions is conducive to such

events. It also seems highly probable that fire

suppression has helped offset the impact of a

large increase in the number of fire ignitions.

But there is also compelling evidence that suppression effectively narrows the range of

conditions under which fires are allowed to

consume vegetation and that the direction of

this narrowing is likely to result in an increase

in the proportion of high-severity fires. Demonstrating such a change is difficult because

there is little quantitative information on the

severity or intensity of historic fires.
64

Fire Issues in Foothill Habitats

There are two primary concerns regarding the current fire regime’s effect on foothill

habitats. First, overly frequent fires in coastal

sage and buckwheat scrub can result in the

degradation of these habitat types. Short intervals between fires (i.e., less than ten years)

can lead to pronounced declines in shrub cover

and concurrent increases in herbaceous cover,

particularly non-native annual grasses

(O’Leary 1990; Zedler et al. 1983). This tends

to be a self-perpetuating shift, because dense

annual grass cover hinders shrub re-establishment (Minnich and Dezzani 1998) and

increases the habitat’s flammability, making it

more prone to frequent fires (D’Antonio and

Vitousek 1992). Degradation of coastal sage

and buckwheat scrub has been widespread

in the “front country” foothills where fires

along the urban interface have been frequent

(table 3.2).

There is particular concern about the degradation of coastal sage scrub because its extent

has already declined by almost 80 percent due

to development in the coastal basins and it is

the primary habitat for the California gnatcatcher and other imperiled species (Westman

1981; Davis et al. 1994; Beyers and Wirtz

Historically, fires appear to have burned

under a wide range of environmental conditions, exhibiting erratic smolder-and-run

behavior patterns as weather and fuel conditions changed. Unsuppressed, some fires

would continue for months until extinguished

by rain or lack of fuel. The landscape would

experience smoldering burns, punctuated often by short-duration, high-intensity

afternoon runs and occasionally by large conflagrations (Minnich 1987b; Minnich 1988).

Today (and for at least the last fifty years),

smoldering fires are actively suppressed and

most are quickly extinguished, thereby significantly reducing opportunities for

short-duration runs. Thus, by effectively reducing the other burn patterns, suppression

has seemingly increased the likelihood that

when an area burns, it will do so in a relatively fast-moving, high-severity fire.

There does not appear to be much change

in the average return interval of chaparral fires.

There is general consensus among experts that

(1) natural fire-return intervals in chaparral

were probably in the range of fifty to eighty

years and (2) current fire-return patterns in

chaparral appear to be either within or near

this range across most of the landscape

(Minnich 1995; Zedler 1995; Conard and

Weise 1998). Fire frequency appears to have

significantly increased only in ignition-prone

areas near the urban interface, usually where

there are high proportions of scrub (i.e., thinstemmed, semi-woody shrubs) and grass

vegetation that facilitate rapid fire spread (fig

3.1).

It is in montane conifer forests where the

disappearence of smolder-and-run fires appears to have markedly decreased fire

frequency. Fire-scar studies suggest that understory fires were historically common in

conifer forests, with average return intervals

of fifteen to thirty years (McBride and Lavin

1976). However, over the last seventy years,

fires have been rare in southern California

montane conifer forests, particularly in interior forest habitats away from the chaparral

interface (fig 3.1). This is probably due to a

high level of suppression effectiveness in the

conifer belt. Ignitions in the forest are not

prone to rapid fire spread and thus are quickly

extinguished. In addition, firefighters have

been largely effective at keeping fires that come

up out of the chaparral from moving into the

montane conifer forest interior.

It is important to understand how the fire

regime has changed and how those changes

are affecting ecological communities. Yet, in

densely populated southern California there

is little likelihood that we can adopt a policy

where wildfires are allowed to smolder and run

at will. There are too many lives, structures,

and resources that would be put at risk by such

a strategy. Consequently, we are better served

by focusing our attention on specific key issues pertaining to fire’s effect on the biota

(table 3.1) and exploring the range of options

available for addressing those specific issues.
65

Chapter 3

Figure 3.1. Fire frequency patterns. Shows the number of times that different areas have burned over the

last century. Areas shown in white have no recorded incidence of fire. This is based on our fire history

database (see the “Information Sources” section of chapter 1 for more information on the fire data).

1997). Coastal sage is restricted to low elevations (below 3,000 feet) and most of it occurs

near the urban interface. The pervasive increase in non-native grass cover has increased

the flammability of this vegetation type, such

that it is often capable of reburning one or

two years after a fire. Given these characteristics, increased management effort will

probably be needed to keep coastal sage from

burning at overly frequent intervals.

Existing management direction in southern California Forest Plans calls for

short-rotation burning to frequently rejuvenate coastal sage scrub habitats (e.g.,

seventeen-year rotations on the Cleveland

National Forest and twelve-year rotations on

the Angeles National Forest) (Cleveland NF

1986; Angeles NF 1987). The information

presented above suggests that a different management approach, which emphasizes

retention of older stands of coastal scrub, may

be necessary to achieve desired conditions

(table 3.3).

The second concern in the foothills is the

tendency for very large fires (e.g., 10,000 acres

or larger) in chaparral-dominated habitats.

There have been a number of these large fires,
66

particularly in the Los Padres National Forest, over the last several decades. Whether a

change from historic conditions or not, a high

incidence of large burns substantially reduces

the structural diversity of chaparral and scrub

habitats and causes high amounts of erosion

and stream siltation. Large chaparral fires also

have the propensity to be self-perpetuating,

since they create a continuous block of singleage vegetation that becomes ready to burn

again at the same time.

An issue that is not of particular concern

is the potential for chaparral stand senescence

or decadence due to the long-term absence of

fire. Formerly believed to be a problem, long

fire-free intervals (i.e., seventy to one hundred

years) have been found in recent studies not

to be detrimental to chaparral shrubs (Keeley

1986; Zedler 1995). Many species, in fact,

continue to produce new stems and even seedlings during long fire-free intervals (Lloret and

Zedler 1991; Keeley 1992). The potential for

negative effects associated with overly frequent

Table 3.1. Key ecological issues that are influenced by the current fire regime.

Key Issues

Habitats/Species

Most Affected

Effects Associated

with Current Fire Regime

Current Trends and

Areas Most Affected

Overly frequent

habitat disturbance,

leading to a shift in

composition and

structure of plant

communities.

Overly infrequent

habitat disturbance,

leading to a shift in

composition and

structure of plant

communities.

Coastal sage scrub.

Bigcone Douglas-fir

forests.

Possibly pinyon-juniper

woodlands.

• Fires spread rapidly in coastal

scrub and an abundance of

ignitions along the urban

interface can lead to frequent

reburns.

• Chaparral fires are

increasingly carrying into

bigcone Douglas-fir stands,

which are very slow to recover

from stand-replacing fires. It is

unclear if the situation is being

caused by increased fire

intensity or frequency or both.

• Coastal scrub in the

foothills is being converted

to annual grassland in

many areas.

• Extent of bigcone Douglasfir has declined by 18% in

San Bernardino Mts. since

1930s and is declining

elsewhere too.

• Recent large fires in

pinyon-juniper woodlands

may be related to increased

grass cover in desert-side

areas.

Mixed conifer forest.

Ponderosa pine

forest.

Fires have been effectively

suppressed in montane conifer

forests, essentially eliminating

understory burns that

historically occurred in these

forests. This increases the risk

of stand-replacing crown fires,

although such an event has yet

to occur in this region.

• Mesic forests have had

substantial increases in the

number of small diameter,

understory trees.

• White fir and incense-cedar

have increased in

abundance; ponderosa pine

and black oak have

decreased.

fire appears to be a much greater threat to

chaparral and scrub habitats.

Fire Issues in Lower Montane

Habitats

Recent fire frequencies in lower montane

habitats are similar to patterns in the foothills

(table 3.4). This reflects the dominant influence of chaparral in both the foothills and

lower montane region. Studies suggest that

most chaparral plant communities are adapted

to considerable variability in fire frequency and

are not believed to be adversely affected by

current return intervals (Keeley 1986; Zedler

1995).

The primary fire issue in lower montane

habitats is the apparent loss of bigcone Douglasfir in stand-replacing wildfires. This problem has

not been thoroughly studied; thus, there is uncertainty about the amount of loss incurred and

the reasons for it. Minnich (1999) states that

stand-replacement fires in the San Bernardino

Mountains have resulted in a net decline of 6,016
67

Chapter 3

Values are the percent

 of area meeting the

 described condition

(a) Number of Fires

0 Fires 27% 17% 17% 16% 8% 14% 19% 26% 48% 25%

1 Fire occurrence 38% 33% 42% 35% 22% 43% 43% 41% 40% 39%

2 Fires 22% 27% 26% 24% 41% 26% 25% 21% 9% 22%

3 or more fires 13% 23% 15% 25% 29% 17% 13% 12% 3% 14%

(b) Year of Last Fire

1-19 years ago 16% 48% 37% 47% 26% 35% 22% 45% 10% 28%

20-39 years ago 26% 25% 17% 22% 54% 29% 17% 3% 16% 20%

40-59 years ago 20% 7% 3% 8% 6% 6% 23% 8% 19% 14%

60-90+ years ago 11% 3% 26% 7% 6% 16% 19% 18% 7% 13%

No recorded fires 27% 17% 17% 16% 8% 14% 19% 26% 48% 25%

540,499 229,344 62,297 72,200 156,603 208,903 637,922 468,623 162,586 2,538,976

Cleveland NF Los Padres NF San Bernardino NF Angeles NF

San

Diego

 Ranges

Santa

Ana

Mts

San

Jacinto

Mts

San

Bernardino Mts

San

Gabriel

Mts

Castaic

Ranges

S. Los

Padres

Ranges

S. Santa

Lucia

Rng

N. Santa

Lucia

Rng

Entire

Foothill

Zone

Acres of Foothill

Habitat

Table 3.2. A look at recorded fire history patterns in foothill habitats by mountain range. (a) Shows the

percentage of the foothill landscape that has burned 0, 1, 2, or 3-plus times over approximately the last

eighty years. (b) Shows the percentage of the foothill landscape by categories of time elapsed since the last fire.

Coastal Sage Scrub: Fire-free intervals of

sufficient length (twenty-five years or more) to

allow this vegetation type to reach structural

maturity and remain there for an extended period

of time. This would promote increased shrub cover

and provide higher quality habitat for at-risk

species associated with coastal sage scrub (e.g.,

California gnatcatcher).

Table 3.3. Desired conditions for managing fire in

foothill habitats of special concern.

acres of bigcone Douglas-fir or 18 percent of what

was present in 1938.

Fires seldom start in bigcone Douglas-fir

stands but rather carry into them from the

surrounding chaparral (fig. 3.2). Thus, chaparral fire dynamics strongly influence how

these forest patches are affected by fire. Their

distribution in deep canyons and on steep

north-facing slopes helps limit exposure to fire.

A possible explanation for the recent frequency

of stand-replacing fires in bigcone Douglasfir stands is an increase in the number of

high-intensity chaparral fires, which are more

likely to carry into forest patches. There is not

adequate fire-intensity data to determine if this

is indeed the case. It is considered plausible

because of the current tendency for fires to

escape rapid control only when conditions are

severe, and because urban interface ignitions

may result in more base-of-the-mountain fires

that are prone to high-intensity runs up steep

lower montane slopes.

One thing for certain is that bigcone Douglas-fir forests have been slow to recover from

crown fires and many stands do not appear to

be recovering at all (Minnich 1978). Chaparral invades these sites and for many decades

the new community will be more likely to

reburn than the old one—until live oaks again

attain tree stature and shade out the shrubs.

Bigcone Douglas-firs are particularly slow to
68

Values are the percent

 of area meeting the

 described condition

(a) Number of Fires

0 Fires 34% 24% 34% 18% 6% 30% 23% 4% 7% 19%

1 Fire occurrence 48% 56% 49% 40% 35% 52% 44% 7% 53% 44%

2 Fires 16% 16% 14% 30% 38% 17% 26% 68% 35% 28%

3 or more fires 2% 4% 3% 12% 21% 1% 7% 21% 5% 9%

(b) Year of Last Fire

1-19 years ago 15% 52% 11% 18% 21% 9% 21% 90% 19% 20%

20-39 years ago 13% 4% 19% 35% 40% 31% 17% 66% 30%

40-59 years ago 27% 17% 10% 23% 17% 14% 2% 3% 11%

60-90+ years ago 11% 3% 26% 6% 16% 16% 37% 6% 5% 20%

No recorded fires 34% 24% 34% 18% 6% 30% 23% 4% 7% 19%

Fire Issues in Montane Conifer

Habitats

The widespread and prolonged absence

of fire is a concern in montane conifer forests

(table 3.6). Fire-scar studies suggest that moderate intensity fires (i.e., hot enough to scar

but not kill most mature trees) historically

occurred every fifteen to thirty years (McBride

and Lavin 1976). However, over the last ninety

years understory fires have been virtually

eliminated from large areas, particularly in

interior forest areas. The result is denser stands

and a dramatic increase in the number of understory trees (Minnich et al. 1995). The

concern is that this increase in stand density

and fuel loading makes the forests more susceptible to large, stand-replacing crown fires

(table 3.7).

Using data on precipitation, elevation,

slope, stand density, and fire history, we developed a model to predictively map areas at

risk to stand densification. Almost 30 percent

Cleveland NF Los Padres NF San Bernardino NF Angeles NF

San

Diego

 Ranges

Santa

Ana

Mts

San

Jacinto

Mts

San

Bernardino Mts

San

Gabriel

Mts

Castaic

Ranges

S. Los

Padres

Ranges

S. Santa

Lucia

Rng

N. Santa

Lucia

Rng

Table 3.4. A look at recorded fire history patterns in lower montane habitats by mountain range. (a) Shows

the percentage of the lower montane landscape that has burned 0, 1, 2, or 3-plus times over approximately

the last 90 years. (b) Shows the percentage of the lower montane landscape by categories of time elapsed

since the last fire.

Acres of Lower

Montane Habitat

Entire

Lower

Montane

179,071 22,711 112,443 151,113 281,590 128,016 550,298 31,954 255,971 1,713,167

return when there are no surviving seed trees

nearby (Weatherspoon et al. 1992).

Coulter pine forests also occur mainly in

lower montane areas but do not appear to be

as adversely affected by the current fire regime.

Coulter pine regenerates extremely well after

fire (Vale 1979; Borchert 1985), but it requires

fire-free intervals of approximately sixty to seventy-five years for adequate seed crops to

develop (table 3.5). Thus, Coulter pine can

be negatively affected by frequent reburns or

by extremely long intervals without fire. This

may be a problem in localized areas (M.

Borchert, Los Padres NF, pers. comm.), but

overall fire frequency in lower montane landscapes does not appear to be outside the

historic range of variability.
69

Chapter 3

(108,500 acres) of mixed conifer and pine

stands in the assessment area were predicted

to be experiencing this problem (see fig. 2.17

in chapter 2).

Over the last fifty years, there have been

very few “forest” fires in southern California’s

montane conifer region. Those that have occurred were either (1) driven primarily by steep

Figure 3.2 Bigcone Douglas-fir stands are at risk in high-intensity fires. This stand is located west of

Coldbrook Campground on the Angeles National Forest. RICHARD HAWKINS

Bigcone Douglas-Fir/Canyon Live Oak: Minimal

occurrence of high-severity crown fires in these

forest stands. This is needed to maintain or

increase the distribution and extent of this forest

type which has recently been declining.

Coulter Pine: Fire return intervals of

approximately 60 to 75 years are desired in this

forest type, which requires fire for regeneration. At

maturity, stands should be fairly open (40% to 60%

canopy closure) with trees reaching 20 inches

diameter at breast height (dbh).

Table 3.5. Desired conditions for managing fire in

lower montane habitats of special concern.

terrain and extreme winds (e.g., the 1980

Thunder Fire in the San Gabriel Mountains)

(R. Hawkins, Cleveland NF, pers. comm.); or

(2) took place in forest stands that were surrounded and interspersed with mature

chaparral that facilitated the spread of highintensity fires into them (e.g., the 1950

Conejos and 1970 Laguna fires in the

Cuyamaca and Laguna mountains, the 1970

Bear Fire in the San Bernardino Mountains).

There seem to be few instances where the severity of these fires was attributed primarily

to increased fuel loads in overcrowded forests.

However, events in other areas give cause

for concern. On the Boise National Forest in

Idaho, many years of near-complete fire exclusion came to an abrupt end when a series

of intense crown fires from 1986 to 1995 consumed 45 percent of the area’s ponderosa pine

forest (Weiland 1996). The severity of these

fires was attributed to excessive fuel loading

resulting from the prolonged absence of fire.

Similar large and unusually intense standreplacing wildfires have occurred in recent
70

Values are the percent

 of area meeting the

 described condition

(a) Number of Fires

0 Fires 45% 56% 78% 53% 32% 71% 66%

1 Fire occurrence 47% 31% 20% 31% 40% 27% 27%

2 Fires 8% 12% 2% 13% 27% 2% 6%

3 or more fires 1% 3% 1% 1%

(b) Year of Last Fire

1-19 years ago 12% 13% 21% 3% 2% 7%

20-39 years ago 5% 4% 7% 5% 36% 2% 5%

40-59 years ago 24% 18% 9% 12% 7% 4% 11%

60-90+ years ago 14% 9% 6% 9% 22% 21% 11%

No recorded fires 45% 56% 78% 53% 32% 71% 66%

49,467 0 55,749 202,112 105,681 1,748 96,544 0 0 511,301

Cleveland NF Los Padres NF San Bernardino NF Angeles NF

San

Diego

 Ranges

Santa

Ana

Mts

San

Jacinto

Mts

San

Bernardino Mts

San

Gabriel

Mts

Castaic

Ranges

S. Los

Padres

Ranges

S. Santa

Lucia

Rng

N. Santa

Lucia

Rng

Entire

Montane

Conifer

Acres of Montane

Conifer Habitat

Table 3.6. A look at recorded fire history patterns in montane conifer habitats by mountain range. (a) Shows

the percentage of the montane conifer landscape that has burned 0, 1, 2, or 3-plus times over approximately

the last ninety years. (b) Shows the percentage of the montane conifer landscape by categories of time

elapsed since the last fire.

Fire Issues in Desert-Montane

Habitats

Fires have historically been infrequent in

sparsely vegetated desert-side habitats and, for

the most part, this continues to be the case

(table 3.8). Proximity to urbanized areas apyears in the Sierra Nevada and the mountains

of northern Arizona.

At higher elevations, subalpine forests

dominated by lodgepole pine (Pinus contorta)

typically do not carry fire well. In a study of

fire patterns in lodgepole pine forests of the

San Jacinto Mountains, lightning-caused fires

occurred every few years but were typically

small (less than 20 acres) and of low intensity

(Sheppard and Lassoie 1998). This fire regime

appears to be within the natural range of variability and not substantially influenced by fire

suppression activities.

pears to be a significant factor in historic fire

frequencies. A high occurrence of multiple fires

on the desert side of the San Jacinto Mountains (table 3.8) appears to be concentrated in

the vicinity of Beaumont and Palm Springs

(fig. 3.1). The most remote desert-montane areas (i.e., the southern Los Padres ranges around

Mount Pinos and the extreme northeastern corner of the San Bernardino Mountains) have had

very little fire history (fig. 3.1).

Vegetation type is also a factor in firereturn intervals, with fires being more frequent

in desert chaparral and scrub than in pinyonjuniper woodlands. The sparse understories

and open canopies typical of pinyon-juniper

woodlands translate into long fire-free periods. A study of these woodlands in the San

Bernardino Mountains estimated that the average fire-return interval was 480 years

(Wangler and Minnich 1996). The authors

concluded that twentieth-century fire suppression has had little effect on this vegetation type.
71

Chapter 3

Forest stands with understory species ratios

that are similar to the current overstory

species composition. The emphasis is on

arresting encroachment of shade-tolerant white fir

and incense-cedar and providing opportunities for

pine and black oak regeneration.

Landscape patterns that are resilient to large

crown fires. Forest thickening and fuel continuity

problems must be addressed at a landscape scale

(e.g., watersheds) to avoid large stand-replacing

fires. Understory fires (or thinning) should occur in

each forest stand at twenty to forty year intervals.

Some overstory kill during these events (2% to 4%

of the stand) is desirable to create small openings

for pine and oak regeneration. Under existing

conditions, heavy fuels create a high potential for

forest fires that kill a much larger fraction of the

overstory.

A continuous and well distributed supply of

large trees. Large trees are both highly

characteristic of pre-suppression forests and vital

to many wildlife species. They have declined in

number over the last fifty years and are threatened

further by stand thickening and crown fire risk.

Table 3.7. Desired conditions for managing or

mimicking fire regimes in montane conifer forests.

Fire Management Considerations

Options for managing fire or mimicking

its ecological function fall into three general

categories: (1) prescribed burning where a fire

is intentionally set under controlled conditions; (2) fuels treatments where vegetation is

manually or mechanically cut to reduce fire

hazard or mimick an effect that fire would

have; and (3) wildfire suppression strategies,

which include confine-and-contain approaches where an unplanned or natural

ignition is allowed to burn within a predefined

containment area. The potential opportunities and barriers associated with these

approaches are summarized in table 3.10.

The defensible fuel profile is a fuels treatment option that is being considered

throughout the western United States for reducing crown-fire hazards in conifer forests.

A defensible fuel profile zone (DFPZ) is defined by Olson (1993) as a “low-density,

low-fuel zone averaging 0.4 km (0.25 mi.) in

width, located mostly along roads and designed to support suppression activities.”

DFPZs can be likened to shaded fuel breaks,

only on a larger scale. The focus of DFPZs is

to break up fuel continuity over landscapes. A

network of DFPZs is expected to do several

things: (1) reduce wildfire severity in treated

areas; (2) create broad zones where suppression efforts can be conducted safely and

effectively; (3) effectively break up continuity

of fuels; and 4) become anchor lines for further areawide fuel treatments.

According to Weatherspoon and Skinner

(1996) and Olson (1993), DFPZs should be

placed primarily on ridges and upper south

and west slopes. Where possible they should

also coincide with existing roads to simplify

construction and maintenance and to facilitate their use by suppression forces. This

treatment will result in a fairly open stand,

which is dominated by large trees of firetolerant species. Post-treatment canopy closure

is recommended to be no more than 40 percent. One of the key features of this is the

general openness and discontinuity of crown

fuels (horizontal and vertical) to produce a very

However, Wangler and Minnich’s (1996)

study looked at fire patterns up to 1983. Since

that time, there have been several large fires in

pinyon-juniper woodlands on the north end

of the San Bernardino Mountains. This has

led to speculation that increases in nonnative grass cover (e.g., cheatgrass), combined

with increased ignition sources associated with

the rapidly growing human populations just

north of the mountains (i.e., Hesperia, Apple

Valley, and Victorville) could be facilitating

fire spread in these woodlands. The hypothesis is that this problem would only be present

after particularly wet winters, when grass cover

reaches its peak. This issue needs further study.

Pinyon woodlands are extremely slow to regenerate; thus, an acceleration in fire return

intervals would be of concern (table 3.9).
72

Values are the percent

 of area meeting the

 described condition

(a) Number of Fires

0 Fires 56% 32% 61% 43% 60% 83% 65%

1 Fire occurrence 38% 35% 28% 50% 35% 13% 26%

2 Fires 5% 20% 9% 6% 5% 4% 7%

3 or more fires 1% 14% 2% 1% 2%

(b) Year of Last Fire

1-19 years ago 8% 50% 22% 15% 12% 6% 15%

20-39 years ago 6% 1% 11% 17% 7% <1% 4%

40-59 years ago 29% 17% 4% 24% 4% 3% 11%

60-90+ years ago 1% 2% 1% 17% 8% 5%

No recorded fires 56% 32% 61% 43% 60% 83% 65%

78,406 0 110,135 134,468 88,560 61,092 418,145 0 0 1,713,167

Table 3.8. A look at recorded fire history patterns in desert-montane habitats by mountain range. (a) Shows

the percentage of the desert-montane landscape that has burned 0, 1, 2, or 3-plus times over approximately

the last ninety years. (b) Shows the percentage of the desert-montane landscape by categories of time

elapsed since the last fire.

Pinyon-Juniper Woodlands: Long fire-free

intervals (one hundred to three hundred years) to

allow this vegetation type to reach structural

maturity and remain there for an extended period

of time. Pinyon-juniper woodlands recover very

slowly from crown fires.

Table 3.9. Desired conditions for managing fire in

desert montane habitats of special concern.

Cleveland NF Los Padres NF San Bernardino NF Angeles NF

San

Diego

 Ranges

Santa

Ana

Mts

San

Jacinto

Mts

San

Bernardino Mts

San

Gabriel

Mts

Castaic

Ranges

S. Los

Padres

Ranges

S. Santa

Lucia

Rng

N. Santa

Lucia

Rng

Entire

Desert

Side

Acres of DesertSide Habitat

The Influence of Water:

Hydrology, Regulation, and

Withdrawal

The flow of water, both on the land surface and underneath it, is a powerful force in

shaping landscape patterns and ecological

communities (Dunne and Leopold 1978). The

dynamics of streamflows and the proximity

of groundwater largely determine the extent

and character of riparian, wetland, and aquatic

habitats. Seasonality, volume, duration, and

year-to-year variability of streamflows all

greatly influence the structure and composition of ecological communities found in the

channel and floodplain. Groundwater fluctuations have a similar effect on communities

associated with springs, seeps, and ephemeral

water bodies.

Southern California is an arid region where

the human demand for fresh water greatly exceeds the natural supply. Consequently, all of

low probability of sustained crown fire.

Conard and Weise (1998) propose similar fuel

management zones in southern California

chaparral habitats.
73

Chapter 3

Table 3.10. Summary of the opportunities and barriers associated with the primary management tools

available for restoring or mimicking the role of fire on the landscape.

Prescribed Burning Fuel Treatments Wildfire “Confine & Contain”

Opportunities

Treatment

Potential

(acres per year)

Effectiveness in

and around

Developed Areas

Institutional

Barriers to

Implementation

• Understory burns to thin

forest stands.

• Chaparral burning to

manage fire frequency

and intensity.

• Selective timber harvests

to thin the forest understory.

• Fuel breaks or defensible

fuel profiles to increase

ability to control wildfires.

Confine and contain

strategies allow unplanned

ignitions occurring under

desirable conditions to burn

within defined containment

boundaries.

Moderate. Considerable

preparatory work is often

required. Most efficient in

areas far removed from

buildings.

Low. High cost per unit

area; requires accessible

locations.

Moderate. Low cost per unit

area, but is feasible only in

remote areas where life or

property is not at risk.

Moderate. Only very low

intensity fires can usually be

prescribed near developed

areas.

High. Can be done in areas

where burning is too risky.

Not an option near

developed areas; The risk

of property damage is too

high.

Environmental

Barriers to

Implementation

• Complexities of keeping

fire on the wildland side of

the urban/wildland

interface.

• In forests, high fuel

buildups now make it

difficult to underburn in

many stands.

• Air quality regulations limit

when burning can be

done.

• Forest thinning is not cost

effective on steep slopes

or in areas that lack road

access.

• Fuel breaks require

maintenance and can have

environmental impacts.

• Inadequate funding.

Need authority to use

suppression money to

fund this work.

• Lack of institutional

incentives to burn.

• Liability risks are a major

disincentive to burning.

• Lack of viable commercial

markets for small-diameter

trees.

• Inadequate funding. Need

authority to use suppression

money to fund fuels

reduction work.

• Need change in Forest

Plan direction

• Requires change in

attitudes towards

suppression — immediate

control is not always the

desired objective.

• Liability risks

• Limited to areas where the

risk to life and property are

very low.

• Air quality considerations

may also limit this option.

the major streams that originate in the mountains contain dams or diversions at some point

along them. In addition, many small streams

and springs are dammed or diverted, both for

water supply and flood control. Subsurface

waters are also heavily tapped. Yet this still does

not come close to meeting the needs of the

region’s human population, so large quantities of water are imported into the area from

northern California and the Colorado River.

The result is a dramatic reduction in the

extent and distribution of native freshwater

habitats in this region. Faber et al. (1989) estimate that 95 to 97 percent of riparian habitat in southern California floodplain areas has

been eliminated. In addition, much of what

remains must function under a highly modified hydrologic regime with upstream dams

regulating streamflows. Clearly no other landscape feature has been so drastically altered by

human activities as has freshwater habitat.

The presence of dams and diversions on

most of the region’s major streams (fig. 3.3)

has greatly altered aquatic and riparian

habitats and reduced the capability of these
74

The Effect of Dams and Water

Release Regimes

Dams destroy riparian habitat directly by

inundation, but their greater effect (in terms

Figure 3.3. The locations of dams and diversions on central and south coast streams. Notice that the

majority are concentrated in the foothills below 3,000 feet.

of miles of habitat degraded) is downstream.

By retaining all or part of flood flows, or modifying the shape of the discharge curve, dams

tend to rob the drainage below of the hydraulic forces necessary to maintain a natural form.

Sweet (1992) illustrates the downstream

effect of dams by comparing the Santa Ynez

River below Gibraltar Dam (completed in

1921) with Piru Creek below Pyramid Dam

(completed in 1973). Most of the regulated

streams within the assessment area resemble

one of these two downstream patterns:

After 70 years, the affected section

of the Santa Ynez River is characterized

by a near-total lack of sand and fine

habitats to support native species (table 3.11).

However, the importance of these structures

in preserving domestic water supplies and controlling downstream flooding ensure that

most, if not all, are here to stay. Recognizing

that their continued presence is necessary,

there are important factors in the operation

of major dams and diversions that significantly

affect native habitats and species.
75

Chapter 3

Table 3.11. Key ecological issues that are influenced by water storage, control, and withdrawal.

gravel, and by a succession of very deep

scour pools floored with boulders and

mud. There are no sandy levees, only

cobble bars, and several oak terraces are

being eroded as the channel moves laterally. Little if any arroyo toad habitat

remains in the first 4 stream miles below the dam, and only marginal habitat

below this as a consequence of the scarcity and small size of tributary canyons

which can supply the sediment and flood

discharge needed to maintain the system.... Gibraltar Dam appears to have

rendered the entirety of the downstream

length of the Santa Ynez river on the

LPNF uninhabitable for arroyo toads.

Pyramid Dam has been affecting

lower Piru Creek for less than 20 years,

and presents a somewhat different picture. As on the Santa Ynez River the sand

deposits are disappearing from the segment between Frenchman Flat and the

dam, and the creek has acquired a deep

and boulder-filled channel. Unlike the

Santa Ynez, large tributaries join Piru

Creek within a few miles below Pyramid Dam and restore part of its sediment

load. There is a second difference in that

Pyramid Dam releases 10-25 cfs

throughout the summer and early fall,

resulting in the development of a very

dense riparian corridor which is protected from flood scouring. This

vegetation effectively channelizes the

creek, and has transformed it into a habitat quite unsuitable for most native aquatic

and riparian species. (Sweet 1992, pg 154)

Key Issues

Habitats/Species

Most Affected

Effects Associated

with Water Storage,

Control and Withdrawal

Current Trends and

Areas Most Affected

Streams downstream of

reservoirs tend to be most

affected.

Declines in habitat

capability caused by

major changes in the

volume, duration,

timing, and variability

of stream flows.

Establishment and

spread of invasive,

non-native species.

Reductions in

surface water flows.

Aquatic and riparian

habitats below dams

and diversions.

Dams and diversions

dramatically alter flow regimes.

Water releases below dams, if

they occur at all, tend to be

either “high volume, short

duration,” or “continuous low

volume,” neither of which

resemble historic patterns.

Downstream transport of

sediment is also curtailed by

dams, resulting in channel

downcutting over time.

Most large streams have

been dammed or diverted

for many years and will

remain so. Efforts are

ongoing in some areas to

establish release schedules

that more closely mimic

historic flow regimes.

Aquatic and

riparian species.

Reservoirs, both large and

small, tend to be dominated by

non-native flora and fauna.

These serve as points of spread

into nearby native habitats.

• Wet meadows

• Aquatic and riparian

habitats

Withdrawals of sub-surface

water (i.e., spring- and groundwater extraction) can lower the

water table and reduce

availability at the surface.

The popularity of bottled

mountain spring water is

leading to an increase in

extractions, particularly on

private lands in the

mountains.
76

The Influence of Invasive,

Non-Native Species

The spread of non-native species that displace, prey upon, or otherwise harm native

species is a major problem in both aquatic and

terrestrial habitats. Alternately referred to as

“exotic,” “alien,” or “non-indigenous” species,

the alarming consequences of their invasion

on the capability of habitats to support native

species is becoming increasingly recognized

(Dudley and Collins 1995; Quammen 1998).

Survival and reproductive success are greatly

affected by predation and competition for limited resources (e.g., food and breeding sites).

Introductions of new species, particularly

highly successful or predatory ones, can dramatically decrease the ability of some native

species to survive and reproduce in what otherwise would be suitable habitat (table 3.12).

In a statewide survey of non-indigenous

species, Dudley and Collins (1995) concluded

that the South Coast Bioregion was particularly hard hit, with more non-native species

than any other California bioregion. To better

The historic flow pattern in southern California streams reflects the region’s climate of

long, dry summers and short, wet winters.

Thus, flows would peak in the winter and early

spring and decline dramatically in the summer months, where in many cases they would

dry up in the uppermost and lowermost

reaches (Faber et al. 1989). The high variability of runoff and precipitation in southern

California also produced large flood events,

which periodically scoured channels and redistributed sediment.

There is little ability to recreate large flood

events, and the sediment transport that comes

with them, below existing dams (fig. 3.4). Yet

in some drainages, rather minor changes in

the management of water releases could greatly

improve habitat capability for species of concern. On Piru Creek, spring and summer

discharges from Pyramid Lake used to fluctuate on a daily or weekly basis from zero to 150

cubic feet per second (cfs) and arroyo toad

clutches and larvae were often stranded or

swept away. In 1992, a shift to constant releases during the spring/summer period

resulted in a large increase in larval arroyo toad

survivorship (Sweet 1993).

Similar changes would be beneficial in

other drainages within the assessment area.

The resource management agencies should

pursue opportunities to work with water and

flood control agencies to address flow release

issues (timing, duration, and volume of water

Figure 3.4. Sutherland Dam on Santa Ysabel Creek

in the Cleveland National Forest is typical of

impoundments in the assessment area. Water from

Sutherland is released downstream only in high

rainfall years when the lake level rises to the spillway

height. GENA CALCARONE

The timing and duration of water releases

from reservoirs can greatly influence downstream habitats. Large, sudden releases of

water, particularly in the summer months, can

quickly scour away a whole year’s reproductive effort for native species such as arroyo

toad, red-legged frog, pond turtle, and California newt. Conversely, low-level year-round

flow regimes facilitate the spread of exotic

predators (e.g., bullfrogs, sunfish, bass, bluegill, catfish, and Asian clams) into downstream

areas that historically would have gone dry in

late summer (Sweet 1992). Neither of these

water release schedules is similar to historic

flow conditions.

releases) on a site-specific basis. In particular,

efforts should be made to limit the practice of

rapid, large changes in the volume of spring

and summer water releases.
77

Chapter 3

Table 3.12. Key ecological issues that are affected by the spread of invasive, non-native species.

document the extent of this problem in the

assessment area, we developed a database that

compiles occurrences of the most problematic,

non-native species by stream or watershed.

Many of these species are associated with riparian habitats and thus their presence or

absence on individual streams is important to

consider when assessing overall habitat capability. The database (displayed in appendix C)

provides a good snapshot of what is currently

known about the distribution of exotic pest

species. However, it does not allow us to conclusively say where they do not occur; areas

may lack observations of these species simply

because thorough surveys have not been conducted. Also, in most areas where we know an

exotic species is present, we lack accurate information on the extent of the infestation.

These are important information needs.

Key Issues

Habitats/Species

Most Affected

Effects Associated

with the Spread of NonNative Species

Current Trends and

Areas Most Affected

Shifts in composition

and structure of plant

communities.

Declines in survival

rates of native

animals that breed

in aquatic habitats.

Declines in

reproductive success

of native animals

Shifts in composition

of invertebrate fauna.

• Riparian habitats

• Grasslands

• Coastal scrub

• Arundo, tamarisk, and other

successful non-natives can

dramatically alter the

composition and structure of

riparian habitats.

• Non-native grasses and forbs

have come to dominate many

grassland and coastal scrub

habitats, displacing native

species.

Arundo is spreading rapidly

in many low-elevation

streams. Efforts to control or

eradicate it are ongoing in

several areas and have

been successful, but where

uncontrolled it is increasing.

Tamarisk is present in many

foothill streams, but does not

seem to be spreading

rapidly in most of them,

particularly if stream channel

is rocky.

• Red-legged frog

• Yellow-legged

frogs (mtn & fthill)

• Arroyo toad

• Santa Ana sucker

• SA speckled dace

Predation and competition by

aquatic non-natives (bullfrogs,

African clawed frogs, bass,

sunfish, bluegill, brown trout,

bullhead, and crayfish) can

cause steep declines in survival

rates.

• Least Bell’s vireo

• Willow flycatcher

• Riparian birds

• CA gnatcatcher

• Native fish and

amphibians

• Purple martins

• Cowbirds parasitize the nests

of many bird species

• Non-native frogs and fish

consume egg masses and

young of native amphibians

and fish

• European starlings displace

native cavity nesters

• Aggressive cowbird control

across so. CA has helped

increase Bell’s vireo

numbers

• Most native fish and

amphibians are declining

• Aquatic non-native species

are well established in

many streams; those below

reservoirs are particularly

prone to infestation.

• Some targeted control

efforts have recently been

initiated

• Coast horned lizard

• Habitats along the

urban interface

Argentine ants and red

imported fire ants displace

native ants and other

invertebrates in areas near the

urban or agricultural interface.

Native ants are the primary

food of coast horned lizards

and arroyo toad.

Argentine ants appear to be

spreading, particularly in

habitat fragments and in

riparian areas. Red

imported fire ants have just

appeared in southern CA,

so it is too early to say how

far and fast they will spread.
78

Non-Native Forest Pathogens

The pitch canker fungus, Fusarium

subglutinans ssp. pini (also called Fusarium

circinatum), is established in native and planted

Monterey, knobcone, and bishop pines from

Mendocino County south. This fungal pathogen is native to the southeast United States.

Although there appears to be some natural resistance in the Monterey pine population (gene

pool), it is predicted that 25 percent of the

Monterey pines in infested stands will be killed

by the fungus. Because the disease is new to

the West Coast it is not known how many

other pine species will be similarly affected.

Several pine species and Douglas-fir are capable

of being infected by the fungus (Dallara et al.

1995), but it may be rare for some of these

species to develop the disease. Pines native to

southern California which may be at risk include bishop pine (Pinus muricata), Coulter

pine (P. coulteri), gray or foothill pine (P.

sabiniana), knobcone pine (P. attenuata),

Monterey-knobcone cross, ponderosa pine (P.

ponderosa), lodgepole pine (P. contorta), and

Torrey pine (P. torreyana) (Dallara et al. 1995).

Even with resistant genes, re-establishing a forest is an expensive and slow process, and

survival of other plant, wildlife, and microbial species dependent on the affected conifers

could be threatened by the disease.

Unfortunately, pitch canker is probably

only the first of many exotic pests of native

trees which will profoundly affect southern

California forests. Despite restrictions on importation of raw wood products, increasing

trade and movement of people have increased

the probability of the inadvertent or deliberate introduction of pest species. One pathogen

expected to appear soon in southern California forests is white pine blister rust

(Cronartium ribicola), which affects sugar pine.

Invasive, Non-Native Plants

Over one thousand non-native plants have

become naturalized in California wildlands

since the late 1700s when European settlement

began (Randall et al. 1998). Some of these

plants have caused little impact, while others

are both invasive and damaging to natural ecosystems. The California Exotic Pest Plant

Council (CalEPPC 1996) has developed a list

of seventy-six exotic plants known to be invading native ecosystems and plant

communities. These species can cause ecologic

and economic damage by changing the natural processes associated with succession,

nutrient cycling, hydrology, substrate stability, soil chemistry, or the frequency and

intensity of wildfires (Randall et al. 1998;

D’Antonio and Haubensak 1998). Many of

these species outcompete native plants,

thereby changing the composition and structure of ecological communities and sometimes

reducing the quality of forage and cover for

wildlife. Non-native plants can also hybridize

with related native species [e.g., the nonnative dandelion (Taraxacum officinale) is hybridizing with California dandelion (T.

californicum) in montane meadows].

Probably because many non-native plants

first became established in coastal areas of

California (i.e., in and around ports, missions,

and early settlements), their numbers tend to

decline with increasing elevation and increasing distance from the coast. A relatively low

number of exotic plants (approximately

twenty-five) have invaded the desert areas of

southeastern California (Kemp and Brooks

1998). High levels of disturbance and habitat

modification tend to favor a non-native flora.

For example, powerline right-of-ways that run

through intact vegetation in southern California have been shown to be points-of-entry

for several exotic species, including black mustard (Brassica nigra) and ripgut brome (Bromus

diandrus) (D’Antonio and Haubensak 1998).

In addition, hydrologic changes to streams

brought on by dams and diversions appear to

reduce the ability of native riparian plants to

survive, creating conditions that promote the

establishment of exotic species.

CalEPPC’s Exotic Pest Plants of Greatest

Ecological Concern list (1996) is divided into

several categories based on level of invasiveness

and distribution. The non-native plants considered to be of particular concern in our assessment

area are addressed individually below.
79

Chapter 3

Arundo or Giant Reed (Arundo donax)

Arundo is a large, perennial grass that has

become widespread in many states (Dudley

1998). It was intentionally introduced to California in the 1820s in the Los Angeles area as

an erosion-control agent in drainage canals

(Robbins et al. 1951; Bell 1999). It forms

dense thickets primarily in riparian areas but

also in places that receive runoff (e.g., roadsides) or where there is a shallow water table

(fig. 3.5).

Within the assessment area arundo occurs

in foothill areas, primarily along large streams

but also in other areas where there is pooled

water. It reaches peak abundance downstream

of the assessment area along major rivers in

the coastal basins. The Ventura, Santa Clara,

Santa Ana, Santa Margarita, San Luis Rey, and

San Diego river systems are particularly infested. Arundo has generally not spread into

the mountains or up the steep, narrow canyons that characterize lower montane areas. It

apparently is restricted to low elevations (primarily below 2,000 feet according to Hickman

1993) and requires well developed soils to

become established. We have documented the

presence of arundo in fifty drainages within

the assessment area.

We briefly describe the effects of arundo

here, but see Bell (1999) for a thorough review of arundo’s impacts in southern

California streams. Arundo tends to have a

competitive advantage in riparian areas where

there is a modified hydrologic regime. It has

rapid growth rates; in a comparison between

arundo and two willow species (Salix goodingii

and S. laevigata), arundo grew 2.1 to 4.9 times

faster (Rieger and Kreager 1989). Arundo can

reportedly reach heights of 8 to 13 feet in less

than one growing season. This rapid growth

is sustained by the consumption of prodigious

amounts of water—as much as 2,000 liters per

meter of standing arundo (Iverson 1994)—

and causes a decline in the availability of

surface water.

Once established, the reed often forms

monocultural stands that physically inhibit the

growth of other plant species. These stands

provide neither food nor cover for most native species of wildlife (Bell 1999; Reiger and

Kreager 1989). Only a small number of bird

species have been observed using arundo for

nest sites and dramatic reductions (50 percent

or more) in the abundance and diversity of

invertebrates were documented in arundo

thickets compared with those found in native

willow/cottonwood vegetation (Dudley

1998). Arundo also provides less shade in riparian areas when compared to native

vegetation, causing increased water temperatures and lower oxygen concentrations, which

in turn negatively affect fish and other aquatic

animals (Kan 1998).

Arundo thickets are highly flammable and

known to carry wildfire up and down riparian corridors (Scott 1994; D’Antonio and

Haubensak 1998). In recent years there have

been a significant number of fires fueled by

arundo in the Prado Dam area and along the

Santa Ana River (J. Wright, Riverside County

Fire Dept., pers. comm.). The most recent

occurred in 1998 when an intense wildfire

threatened to burn homes in the Santa Ana

River drainage. Firefighting in arundo thickets is proving to be a significant drain on fire

management resources (J. Wright, Riverside

County Fire Dept., pers. comm.; R. Hawkins,

Cleveland NF, pers. comm.).

A number of private and public organizations (including the U.S. Forest Service) have

formed alliances (Team Arundo) to coordinate

Figure 3.5. Arundo donax forms dense thickets like

this one along Santa Ysabel Creek in San Pasqual

Valley, San Diego County. GENA CALCARONE
80

Tamarisk or Salt Cedar (Tamarix spp.)

Tamarisk is widely distributed in southern California, in both coastal and desert-side

drainages. There are at least four different species of tamarisk invading native riparian

habitat in the assessment area: Tamarix

chinensis, T. gallica, T. parviflora, and T.

ramosissima.

Tamarisk has the ability to uptake large

quantities of water from the soil, effectively

lowering the water table and reducing the

amount of available surface water. One mature tree can reportedly absorb upwards of 200

gallons of water per day (Johnson 1987). In

some areas, tamarisk has reduced or eliminated

water supplies for bighorn sheep, pupfish, salamanders, and desert palm groves (Johnson

1987).

Tamarisk also provides poor forage and

nesting sites for wildlife. The scale-like leaves

are unpalatable to grazers and, in one study

done by Bertin Anderson and Robert Ohmart

of Arizona State University, birds were shown

to favor native riparian vegetation over tamarisk at a ratio of approximately 38:1 (Johnson

1987). Tamarisk is often called salt cedar because it exudes salts from its leaves. These salts

accumulate in the soil, making the area less

hospitable to native plants.

Tamarisk appears to be most successful in

drainages with unnatural or reduced flow regimes, such as those containing dams or

diversions (D’Antonio and Haubensak 1998).

Robert Ohmart of the Center for Environmental Studies at Arizona State University

believes that tamarisk is not displacing cottonwoods but actually replacing them in areas

now incapable of supporting a native riparian

vegetation.

Because the species is sometimes planted

as an ornamental on private lands, invasions

into riparian habitat are likely to continue. The

tree produces enormous quantities of seed

which are dispersed by wind and water

(Schierenbeck et al. 1998; Johnson 1987).

Tamarisk is documented in at least sixty

drainages in the assessment area. It appears to

spread most aggressively in foothill and desert

streams with deep alluvial channels (e.g., arroyos). It occurs in a number of lower montane

drainages as well, but seems to spread slowly

in narrow bedrock channels.

Brooms

Three weedy species of European broom

have become naturalized in California. These

plants are members of the legume family that

were introduced into the state as ornamentals

and have since escaped into native habitats.

Now well established in our study area, these

shrubs have proven to be very difficult and

expensive to eradicate.

Of the three brooms, French broom

(Genista monspessulana) is the most widespread. It ranges from northern California

south to San Diego County and east to San

Bernardino County (McClintock 1985). In

the assessment area, it is reported below 1,700

feet in the Santa Lucia Ranges, southern Los

Padres region, and San Diego region. It has

been found in coastal scrub, grasslands, oak

woodlands, and the understory of Santa Lucia

fir forests. The Jepson Manual reports the species to be toxic to both humans and livestock

(Hickman 1993).

Scotch broom (Cytisus scoparius) occurs

primarily in northern and central California

(including Monterey County) where it grows

up to 3,300 feet (McClintock 1985). Occurrences are also reported further south, in the

interior valleys of Los Angeles, San Bernardino, Riverside, and Orange counties. The

species is not as aggressive as French broom;

however, it is beginning to invade chaparral

and lower montane habitats in the San Bernardino Mountains (E. Allen, UC Riverside,

in litt. 1998).

Spanish broom (Spartium junceum) is distributed from northern California to San

Diego County but is less widespread than the

efforts in controlling the spread of this

species. Considerable progress has been made

in the refinement of techniques for effective

arundo eradication (Lawson 1998; Nickerman

1999).
81

Chapter 3

other brooms. In the assessment area it is most

prevalent below 2,000 feet in the Santa Lucia

Ranges, southern Los Padres region, Castaic

region, and the interior valleys of Los Angeles, San Bernardino, Riverside, and Orange

counties. This species primarily occupies disturbed areas and is not as invasive in native

habitats (McClintock 1985).

Knapweeds and Star Thistle

(Centaurea spp.)

The genus Centaurea contains many invasive weeds including yellow star-thistle (C.

solstitialis) and spotted knapweed (C.

maculosa). Yellow star-thistle is one of the most

pervasive weeds in California, occupying pastures, roadsides, and disturbed grasslands or

woodlands below approximately 4,300 feet.

The Jepson Manual reports yellow star-thistle

as cumulatively toxic to horses (Hickman

1993).

Spotted knapweed is widespread in California, occurring in disturbed areas up to

6,600 feet (Hickman 1993). The biennial species is reported in the assessment area in the

southern Peninsular Ranges. Its early spring

growth makes spotted knapweed very competitive for soil moisture and nutrients. The

species tends to thrive under agricultural conditions and is listed as a “noxious weed” by

both state and federal governments.

Mediterranean Grasses

Grasses account for the greatest number

(181) of non-native plants in California. Over

40 percent of grasses in the state are exotic

and now dominate vast areas of California’s

grasslands and savannas (Randall et al. 1998).

Some of these grasses have become especially

problematic, outcompeting native perennial

bunchgrasses and hardwood seedlings. The

most widespread grasses are the Mediterranean

annuals, which include the oats, bromes, and

barleys. They are well established in the assessment area and it is unlikely they could ever

be eradicated on a broad scale.

All oat species are non-native. Three occur in the assessment area: slender wild oat

(Avena barbata), wild oat (A. fatua), and cultivated oat (A. sativa). All three are highly

successful in disturbed areas.

Red brome (Bromus madritensis ssp.

rubens) is known to carry fire in areas below

approximately 3,200 feet in the San Bernardino and San Jacinto mountains (R. Minnich,

UC Riverside, pers. comm.). Red brome, oats,

barley (Hordeum spp.), and foxtail fescue

(Vulpia myuros) have invaded coastal sage

scrub and chamise chaparral in many areas.

These invasions have led to increased fire frequencies and type conversion of

shrub-dominated habitats to grassland

(Minnich and Dezzani 1998).

The primary distribution of red brome

occurs east of the assessment area in the

Mojave and Sonoran deserts, where it has the

ability to invade intact native habitats. Red

brome is also prevalent in the Cuyama Valley

(J. O’Hare, Angeles NF, pers, comm.). The

grass spreads rapidly in wet years, and studies

have indicated that repeated fires fueled by

this grass have occurred in places where fire

was previously rare (D’Antonio and

Haubensak 1998; Kemp and Brooks 1998).

While fires fueled by red brome are periodic

(depending on rainfall patterns), their cumulative effect over time is expected to alter native

vegetation.

Cheatgrass (Bromus tectorum) is distributed primarily in the Great Basin, Mojave

Desert, and Sonoran Desert. However, it is

also found within the assessment area, primarily on desert-facing slopes around Mount

Pinos and in the San Gabriel, San Bernardino,

San Jacinto, and Laguna mountains. It has invaded a variety of mainly arid habitats,

including pinyon-juniper woodlands, yellow

pine and mixed conifer forests, montane chaparral, and pebble plains (M. Lardner, San

Bernardino NF, pers. comm.).

Like red brome, cheatgrass has the ability to

invade pristine habitats. However, occurrences

of cheatgrass in the assessment area are sparser

and distributed at higher elevations than red

brome. Where abundant, cheatgrass is known

to cause increased fire frequencies (D’Antonio
82

Invasive, Non-Native Animals

The introduction and spread of invasive

non-native animals have been particularly

prevalent in riparian and aquatic habitats.

These infestations often coincide with habitat disturbance, making it difficult to separate

the influence of one from the other. For example, introduced fish and amphibians tend

to thrive in highly modified habitats, conand Haubensak 1998), but there is little evidence

to suggest that this is currently a problem in the

assessment area (R. Minnich, UC Riverside,

pers. comm.).

Ripgut brome is distributed widely in the

assessment area. It forms a dense understory

in open ponderosa pine forest near Lake Gregory, west of Lake Arrowhead in the San

Bernardino Mountains. At this location the

grass poses a fire threat and appears to be inhibiting conifer recruitment (R. Minnich, UC

Riverside, pers. comm.).

Pampas Grasses

Two species of pampas grass have been

introduced in California. Cortaderia selloana,

native to Argentina and southern Brazil, seldom spreads from where it is planted. It often

is cultivated as a lawn ornamental in warmer

areas. In the past, it was planted by the Soil

Conservation Service for supplemental dryland pasture in Ventura and Los Angeles

counties (Hitchcock and Chase 1971).

Andean pampas grass (Cortaderia jubata),

native to Bolivia, Peru, and Ecuador, is very

invasive. It was originally introduced for landscaping and by the 1960s was spreading into

intact native ecosystems (e.g., redwood forest) in coastal areas of California (Kerbavaz

1985). Now considered a major weed, the species is very difficult to eradicate. In the

assessment area, Andean pampas grass is especially problematic along the coast of

Monterey County, where it frequently occupies road cuts, cliff habitat, and hillsides. The

species is susceptible to frost, however, and

may remain naturally restricted to milder climates near the coast.

founding habitat degradation with the exotic

predators as the primary source of native amphibian declines. However, observations of

successful breeding activity by native amphibians in extremely modified breeding sites that

were free of exotics supports the interpretation that the exotic species themselves are an

important problem (Fisher and Shaffer 1996;

Kiesecker and Blaustein 1997).

Table 3.13 lists the principal non-native

animals that are considered to be a problem

in southern California. The ones considered

to be most problematic within the assessment

area are described below.

Bullfrog (Rana catesbeiana)

Bullfrogs are strongly implicated in the

decline of many native amphibians and aquatic

reptiles (Schwalbe and Rosen 1988; Jennings

and Hayes 1994). First introduced into California in 1896 (Jennings and Hayes 1985),

they have progressively spread over much of

the state and today occur in most suitable

streams and water bodies west of the Sierra

Nevada Mountains and southern deserts

(Stebbins 1972). They are an effective predator of amphibians and aquatic reptiles,

including California red-legged frogs (Bury

and Luckenbach 1976; Hayes and Jennings

1986), arroyo toads (Sweet 1992), western

pond turtles (Holland 1994) (fig 3.6), and

two-striped garter snakes (Sweet 1992). Recently in San Mateo Creek, a single bullfrog was

found to have three adult arroyo toads in its stomach (P. Griffith, UC San Diego, pers. comm.).

Bullfrogs have a competitive advantage over

native frogs and toads because of their large size,

generalized food habits, extended breeding season which allows for production of two large

clutches each year, and larvae that are less palatable to predatory fish (Kruse and Francis 1977;

Bury and Whelan 1984). They also tolerate elevated water temperatures better than native

frogs, which is often advantageous in humanmodified habitats (Jennings 1988). Bullfrogs are

able to occupy a wide variety of aquatic habitats,

from coastal estuaries to mountain waters at elevations over 5,000 feet (e.g., Doane Pond on

Palomar Mountain).
Table 3.13. Some of the non-native animals occurring in southern California wildlands with an

assessment of the level of threat they pose (modified slightly from Dudley and Collins 1995).

Threat level category definitions: 1 = Serious, documented threat to sensitive species or ecosystems;

2 = Moderate threat to native species or ecosystems; 3 = Benign, low risk; 4 = Potential threat,

but impacts not well documented. Species with multiple threat levels are considered a threat in

some areas, but not a problem in other areas.

Invertebrates Threat Level

 Mollusca

Potamocorbula amurensis Asian clam 1

 Arthropoda

Apis mellifera scutellata Africanized honey-bee 4

Apis mellifera ssp. European honey-bee 3

Forficula auricularia European earwig 3

Linepithema humile Argentine ant 2

Solenopsis invicta red imported fire ant 4

Procambarus clarkii Louisiana crayfish 2

Reptiles and Amphibians

Chelydra serpentina snapping turtle 4

Chrysemys picta, C. scripta red-eared slider, painted turtle 4

Rana catesbeiana bullfrog 1

Xenopus laevis African clawed frog 1

Fish

 Centrarchidae

Lepomis spp. green sunfish, bluegill, pumpkinseed 1

Micropterus spp largemouth and smallmouth bass 1

 Cyprinidae (minnows and carps)

Carrasius auratus goldfish 2

Cyprinella lutrensis red shiner 1

Cyprinus carpio carp 2

Pimephales promelas fathead minnow 2

 Ictaluridae (catfish)

Ameiurus (Ictalurus) melas black bullhead 1

Ictalurus punctatus channel catfish 3

 Percichthyidae

Morone saxitilis striped bass 1,3

 Poeciliidae

Gambusia affinis mosquitofish 1

 Salmonidae

Oncorhynchus mykiss rainbow trout (stocked pops.) 1,3

Salmo trutta German brown trout 1

Mammals

Castor canadensis beaver 1,3

Didelphus virginiana opossum 3,4

Equus cabullus feral horse 2

Equus asinus feral burro 2

Rattus rattus, R. norvehicus black rat, Norway rat 1

Sus scrofa European boar, feral pig 1

Vulpes fulva red fox 1

Felis domesticus feral cats 2

Birds

Bubulcus ibis cattle egret 3

Meleagris gallopavo wild turkey 4

Molothrus ater brown-headed cowbird 1

Sternus vulgaris European starling 1
84

African Clawed Frog (Xenopus laevis)

African clawed frogs are currently not as

widespread as bullfrogs (eleven known occurrences in the assessment area), but they are a

potent predator of native fish and amphibians.

Concerns about their consumption of the endangered unarmored threespine stickleback

fish have led to eradication efforts on the Santa

Clara River in Soledad Canyon (Dick 1988).

Although trapable, African clawed frogs are

difficult to eradicate because they are highly

aquatic and resistent to chemical toxins such

as rotenone (Dick 1988).

African clawed frogs tend to become established in ponds and spread from there. The

planting of mosquitofish by vector-control

agencies may be contributing to their spread

due to the presence of clawed frog larvae in

several mosquitofish source ponds in San Diego County (R. Fisher, USGS Biological

Resources Division, pers. comm.).

Predatory Warm-Water Fish

(Centrarchids, Ictalurids, Cyprinids)

Green sunfish (Lepomis cyanellus), bluegill

(Lepomis macrochirus), largemouth bass

(Micropterus salmoides), black bullheads

(Ameiurus melas), fathead minnows

(Pimephales promelas), carp (Cyprinus carpio),

and red shiners (Cyprinella lutrensis) have been

widely planted into south coast reservoirs and

streams as sport fish or as bait for sport fish

(Dudley and Collins 1995). These are hardy

fish that thrive in warm waters of lakes, ponds,

and low-elevation streams. They all prey on

one or more life stages (i.e., eggs, larvae,

metamorphs or adults) of native amphibians

and fish.

Native frogs are often absent from aquatic

habitats where benthos-disturbing ictalurid

(bullheads) and centrarchid (sunfish, bass) fish

are introduced (Hayes and Jennings 1986).

ing present in fifty-three drainages within the

assessment area. Of those fifty-three occupied

drainages, forty-three (81 percent) are also

known to be occupied by predatory fish (primarily sunfish, bass, and bullheads).

Figure 3.6. Non-native bullfrogs prey on many native

amphibians and reptiles, including western pond

turtles. ROBERT H. GOODMAN JR.

The effect of bullfrogs on red-legged frogs

has been particularly well documented. Hayes

and Jennings (1988) found that California redlegged frogs were still present at 81 percent

(n=70) of sites lacking introduced bullfrogs

and no longer present at all sites (n=10) where

bullfrogs were established. Using field enclosure experiments, Kiesecker and Blaustein

(1998) found an 84 percent survival rate of

red-legged frog metamorphs when bullfrogs

were absent; the survival rate was only 27 percent when adult bullfrogs were present.

The work of Kiesecker and Blaustein

(1998) suggests an increased negative effect

when bullfrogs occur in combination with

predatory fish. Survival rates of red-legged frog

tadpoles averaged 89 percent when occurring

alone or in the presence of only bullfrog tadpoles or only smallmouth bass. However, the

survival rate decreased to 47 percent when

bullfrog tadpoles and smallmouth bass were

both present. Apparently, red-legged frog tadpoles respond to the presence of bullfrog

tadpoles by retreating to deeper waters and reducing their activity levels. This can be

effective at reducing competition. But when

smallmouth bass (or other predatory fish) are

present in the deeper water, they prey extensively on the tadpoles (Kiesecker and Blaustein

1998). This phenomenon probably affects the

survival of other amphibians as well.

Our database of species occurrences by

watershed and drainage shows bullfrogs be-
85

Chapter 3

This is caused by high levels of predation on

frog eggs and tadpoles, particularly when tadpoles and predatory fish are crowded into small

pools during periods of interrupted surface

flow during the driest parts of the year

(Jennings 1988). This pattern of interrupted

surface flow is common in many streams

within the assessment area.

Red shiners and fathead minnows are effective predators on the eggs of native fish. Red

shiner predation is believed to be a primary

factor in the disappearence of Santa Ana speckled dace from Big Tujunga Creek (Moyle et

al. 1995).

One or more of these warm-water fish are

known to be present in eighty-one streams

within the assessment area. As described in the

section on bullfrogs, the impact of these predatory fish appears to be exacerbated when

bullfrogs are also present (Kiesecker and

Blaustein 1998). They are known to co-occur in

forty-three steams within the assessment area.

German Brown Trout (Salmo trutta)

As with many of the warm-water fish,

brown trout have been introduced into mountain streams in southern California as a sport

fish. They tend to be more predatory on native fish and amphibians than rainbow trout,

and thus are considered more of a problem.

The extirpation of Santa Ana suckers from the

upper Santa Ana River has been attributed to

brown trout predation (Moyle et al. 1995).

Although brown trout have historically

been stocked into many streams, they have not

persisted in most locations. Currently, they are

documented as present in only three assessment area streams: upper Little Rock Creek,

Bear Creek, and the upper Santa Ana River.

Crayfish (Procambarus clarkii)

Non-native crayfish are commonly sold as

live bait and have been widely introduced into

streams, lakes, and ponds. Crayfish are omnivorous and thus consume aquatic plants,

algae, invertebrates, amphibian eggs, and fish

eggs (Hobbs et al. 1989). In laboratory and

field experiments, Gamradt and Kats (1996)

found that crayfish were effective predators of

California newt (Taricha torosa) egg masses and

larvae, inflicting mortality rates of greater than

80 percent.

In natural habitat within the Santa Monica

Mountains of southern California, newts were

absent from all streams where crayfish were

present (Gamradt and Kats 1996). In one instance where crayfish were washed out of a

stream by winter floods, newts were back

breeding in the stream the next summer.

Crayfish have been documented in fortythree streams within the assessment area.

Mosquitofish (Gambusia affinis)

Mosquitofish are distributed freely by

county vector-control personnel (Gamradt

and Kats 1996) and thus have been introduced

into a large number of aquatic habitats. Once

believed to be an environmentally benign biological agent for mosquito control, studies have

since determined that they can cause considerable ecological impact (Dudley and Collins

1995). Mosquitofish prey on amphibian eggs

and hatchlings (Grubb 1972; Gamradt and

Kats 1996) and are capable of dramatically

altering aquatic community structure

(Hurlbert et al. 1972).

In the Santa Monica Mountains, Gamradt

and Kats (1996) found that California newts

were present in all eight streams where

mosquitofish and crayfish were absent, but

newts were absent from all four streams that

contained either of these two exotics.

Our database shows that mosquitofish are

present in forty-seven drainages within the assessment area. This is likely to be a substantial

undercount, however, since mosquitofish are

often taken for granted and not recorded in

fish surveys.

Brown-Headed Cowbird

(Molothrus ater)

Brown-headed cowbirds are brood parasites that lay their eggs in the nests of other

“host” birds, particularly those that build

open-cup nests (fig 3.7). Because many hosts

raise cowbird young instead of their own,
86

Figure 3.7. Speckled brown-headed cowbird eggs

in a least Bell’s vireo nest. The cowbird hatchlings

will be fed and raised by the adult vireos as if they

were their own offspring. USFWS

birds forage on insects attracted by the livestock concentrations and on the hay and grain

that are supplied to such areas (Rothstein et

al. 1980). They are capable of traveling considerable distances between foraging sites and

breeding areas. In the San Luis Rey River Valley in San Diego County, Nickel (1992) found

radio-tagged male cowbirds travelling as much

as 5.4 miles (9 kilometers) from foraging to

breeding sites. Females traveled a maximum

of 2.1 miles (3.5 kilometers) (Nickel 1992).

Cowbirds occur throughout the assessment area but are especially numerous in the

foothills where riparian woodlands are in close

proximity to grass or agricultural lands. Riparian woodlands support a rich diversity of

nesting birds from which the cowbirds select

hosts (Unitt 1984). Densities of cowbirds are

much lower in montane coniferous forests

(Verner and Ritter 1983) and desert-montane

habitats where high-quality foraging habitat

is scarce.

Many birds are parasitized by cowbirds in

southern California, including threatened and

endangered species such as the least Bell’s vireo,

southwestern willow flycatcher, and California gnatcatcher. One of the primary recovery

actions for the least Bell’s vireo has been the

widespread trapping of cowbirds near known

vireo populations (Beezley and Rieger 1987).

These trapping efforts have been highly successful in some areas.

On the Santa Margarita River within the

Camp Pendleton Marine Corps Base, the rate

of cowbird parasitism on least Bell’s vireo nests

was at 47 percent in 1983 when the base began an intensive cowbird trapping program.

With annual trapping, by 1990 the brood

parasitism rate had dropped to less than 1 percent (Griffith and Griffith, in press). The

population of Bell’s vireos on the Santa

Margarita River rose from 60 pairs in 1983 to

319 pairs in 1993 (Griffith and Griffith 1995).

Since the initiation of annual cowbird removal

programs, similarly dramatic population increases have occurred on the Tijuana and San

Luis Rey rivers and in the Prado Basin (Kus

1995; Kus 1996; Pike and Hays 1997).

Brown-headed cowbirds are native to

North America but prior to European settlement were largely confined to short-grass

prairies in the middle of the continent

(Mayfield 1965). Cowbirds feed by walking

on the ground in areas of short grass and bare

ground. They originally followed the herds of

bison present in the prairies and are likely to

have used scattered trees and riparian woodlands within prairie areas for nest searching

(Robinson et al. 1995).

European settlement was beneficial to

cowbirds and enabled them to expand their

range both westward and eastward. Irrigated

agriculture, livestock grazing, and urbanization all facilitated the spread of cowbirds and

they were well established in coastal southern

California by the 1920s (Rothstein 1994).

In southern California, cowbirds reach

their highest densities near dairies, stables, and

other areas where livestock are concentrated

and provided with supplemental food. Cowbrood parasitism can substantially reduce host

breeding productivity. High levels of brood parasitism can threaten some host populations; thus,

cowbirds have been implicated in the decline of

many North American birds (reviewed in

Robinson et al. 1995).
87

Chapter 3

European Starling (Sturnus vulgaris)

European starlings cause ecological problems because of their sheer abundance and

their ability to outcompete native birds for nest

sites in tree cavities. Starlings have benefited

from human habitat modifications, irrigated

agriculture in particular (Ehrlich et al. 1988).

First introduced in New York City in

1890, starlings were first documented in California in the 1940s (Jewett 1942). Populations

in southern California apparently exploded in

the 1960s. San Diego Christmas Bird Counts

during the 1960s show the following pattern

in starling numbers: 153 in 1963, 974 in 1964,

1500 in 1965, 4,448 in 1968, and 7,928 in

1969 (Unitt 1984).

The purple martin is a native bird whose

decline in southern California has been largely

attributed to competition for nest sites from

starlings (Garrett and Dunn 1981). Western

bluebirds have also been significantly affected.

Argentine Ants (Linepithema humile)

Argentine ants are abundant in many areas of human habitation, particularly where

there is irrigated landscaping. They have spread

into wildland habitats from developed areas

and thus are primarily a problem near the urban interface and in areas fragmented by

development.

Suarez et al. (1998) studied Argentine ant

invasions in habitat fragments of various sizes

in urbanized coastal San Diego County. Argentine ants were found in each fragment, but

activity was correlated with proximity to the

urban edge and the amount of exotic vegetation. Activity was always high within 320 feet

(100 meters) of an urban edge.

Areas invaded by Argentine ants had fewer

native ant species than uninvaded areas. Species most frequently absent in areas occupied

by Argentine ants were army ants

(Neivamyrmex spp.) and harvester ants (genera Messor and Pogonomyrmex) (Suarez et al.

1998). Studies elsewhere have documented similar declines in the abundance of native ant

species in areas where the Argentine ant has

become established (Ward 1987; Holway 1995).

Ants and other invertebrates are fundamental components of many ecological

communities and large shifts in abundance

and species composition are likely to have significant effects on other species. Harvester ants

are an important food source for the coast

horned lizard. These lizards appear to be declining in natural habitat fragments in

southern California. This decline may be related to the influence of Argentine ants on

harvester ants.

Red Imported Fire Ants

(Solenopsis invicta)

Red imported fire ants have only recently

invaded southern California. They were first

discovered in November 1998 at a nursery and

golf course in Orange County (CDFA 1998;

Schoch 1999). Since that time, colonies have

been discovered in San Diego, Los Angeles,

Riverside, and Kern counties (CDFA 1999).

The ant is now thought to have been present

in the region for five to seven years (anonymous 1999).

The red imported fire ant is native to the

Pantanal region of Brazil, Paraguay, and Argentina, and is thought to have been

accidentally introduced multiple times to

Mobile, Alabama, between 1933 and 1945

(Buren et al. 1974; Greenberg et al. 1999).

Concerns about its arrival in southern California stem from the well-documented damage

caused by infestations of red imported fire ants

in twelve southeastern states. In that region,

the ant has invaded residential areas and some

natural habitats. It aggressively stings when disturbed and thus is considered to be a major

nuisance pest in developed areas.

From an ecological standpoint, the threat

posed by imported fire ants is similar to that

of the Argentine ant, although perhaps greater

in magnitude. Like the Argentine ant, the red

imported fire ant readily invades disturbed

areas around human habitation. It requires

moisture and cannot survive cold temperatures

(Vinson and Greenberg 1986). Thus, occupation of wildlands is expected to be limited

to lower elevation riparian zones or irrigated
88

areas adjacent to urban areas. However, red

imported fire ants have recently invaded areas

of west Texas formerly thought to be too dry

for the species, and there is evidence that this

represents a heritable adaptation (Mackay and

Fagerlund 1997; Li and Heinz 1998; Phillips

et al. 1996). Thus, there is potential for the

ants to eventually occupy portions of California previously thought to be too dry. At a

minimum, they pose a threat to the integrity

of any habitats that lie along the urban-wildland interface, particularly small wildland

patches that are largely surrounded by development or irrigated land.

Similar to the Argentine ant, red imported

fire ants have greatly reduced the abundance

of native ants and other invertebrates in portions of the southeastern United States (Porter

and Savignano 1990; Morris and Steigman

1993). Yet, they have the additional impact

of being an aggressive predator of vertebrate

nests and young, commonly swarming the

nests of ground-nesting birds, mammals, and

reptiles (Hill 1969; Mount et al. 1981;

Ridlehuber 1982; Drees 1994; Allen et al.

1995).

Management Considerations for

Exotic Species Control

Exotic species are widespread and most are

difficult to eradicate even from small areas.

The potential is high for control efforts to be

ineffective if they are not carefully planned and

sustained. Consequently, management activities to control exotics should (1) have clearly

defined and achievable objectives, (2) be sustained over time, and (3) be monitored in an

adaptive management framework to ensure

objectives are being met and the most effective techniques are being used.

To succeed, exotic species control efforts

probably need to be narrowly targeted to specific key areas where both the circumstances

for control are favorable and the potential for

recovery of rare habitats or species is high.

Examples of successful, targeted control efforts

currently ongoing within the assessment area

include:

• Arundo removal to restore high-quality,

low-elevation riparian habitat along San

Francisquito Creek and Elizabeth Lake

Canyon in the Angeles National Forest

and along the Santa Margarita River in

San Diego County;

• Brown-headed cowbird trapping to

control nest parasitism on the

southwestern willow flycatcher and least

Bell’s vireo along the San Luis Rey River

in the Cleveland National Forest;

• Bullfrog control to improve arroyo toad

and red-legged frog survivorship along

portions of Sespe Creek in the Los

Padres National Forest; and

• Mediterranean grass control through the

careful timing of prescribed fire to

increase the abundance of native grasses

and forbs and improve Engelmann oak

regeneration on the Santa Rosa Plateau

Reserve in Riverside County.

Another important management consideration is how best to minimize or prevent

additional introductions of undesirable, nonnative species. This is a difficult task, since

introductions can occur in a multitude of ways

that are usually difficult to anticipate and prevent. However, some feasible preventative

measures include (1) close coordination with

CDFG representatives on planned introductions and stockings; and (2) careful screening

of seed mixes or plantings used for erosion

control, landscaping of recreation facilities,

and habitat restoration projects.

The Influence of Native

Insect and Disease Outbreaks

Vegetation is continually preyed upon by

indigenous insects and pathogens. Most of the

time these organisms remain at levels where

they do not cause rapid, large-scale changes

in the structure or composition of plant communities. Yet certain conditions can trigger

major insect or disease outbreaks that result

in substantial plant mortality. The specific

insects and diseases prone to damaging outbreaks are often described as pest species.
89

Chapter 3

Historically, pests of forest trees have received more attention than those of other

native plants, perhaps because of the economic

value of the commodity affected and the highly

visible nature of concentrated tree mortality.

Native insect herbivores and pathogens of forest trees perform important functions in

natural ecosystems, killing decadent trees, creating dead and down woody habitat for other

species, recycling nutrients, and creating gaps

for regeneration (Pronos et al. 1999). However, these pests also increase fuel loading,

contributing to fire hazards in forests. The following discussion concerns the major forest

pests (in terms of numbers of trees damaged

or killed) in southern California.

The pests discussed below are not inclusive; there are many other insects and

pathogens of importance in southern California forests. Of particular interest here are those

pest species whose populations have greatly

increased as a result of twentieth-century management activities, particularly tree removal

and changes in natural fire regimes.

Root Diseases

Foremost among the root diseases in

southern California is annosus root disease of

pine, caused by a strain of Heterobasidion

annosum. This fungus colonizes freshly cut,

untreated conifer stumps and grows down

through the woody tissue and into the roots,

where it may survive saprophytically for up to

fifty years. Live pines and other susceptible

woody plants become infected when their

roots contact infected roots in the soil. The

fungus may kill the pines directly or debilitate them to the point where they are readily

colonized and killed by bark beetles or other

woodboring insects (Smith 1993). Annosus

root disease has significantly reduced vegetative cover in some recreation sites, particularly

since the openings created by the disease cannot be replanted with pines. Infection by this

pathogen can be prevented by treating freshly

cut stumps with borate (Sporax®)(Graham

1970; Smith 1970). Tree removal in southern

California forests, particularly in the years

prior to the mid-1970s, when borate treatment

became common, is thought to be responsible

for the widespread occurence of annosus root

disease centers. This disease is particularly

common in the Jeffrey pine forests of Laguna

Mountain and to the northeast of Big Bear

Lake in the San Bernardino Mountains where

western juniper is also affected, and in the

mixed conifer forests of the San Bernardino

and San Gabriel mountains, as well as in other

forested lands in the Transverse and Peninsular ranges.

Another strain of H. annosum causes a

root, butt, and heart rot of true fir. The fungus enters the wood through logging and other

injuries, fire scars, broken tops, and freshly cut

stumps (Scharpf and Goheen 1993). In firs

this disease causes a general decline rather than

rapid mortality, and is found in mixed conifer

forests throughout the Transverse and Peninsular ranges.

Black stain root disease, caused by

Leptographium wageneri, causes extensive mortality in one species of single leaf pinyon pine

(P. monophylla) in portions of the San Bernardino Mountains, but not elsewhere in

southern California. In the San Bernardino

Mountains, 8,000 acres are reported to be affected. The disease has not been reported from

two southern California endemics, P.

californiarum ssp. californiarum, a lower elevation single leaf pinyon, and P. quadrifolia, Parry

pinyon. Spread is through root contact and

most likely, though not adquately investigated,

through the activities of root-feeding insects.

Trees infected with black stain are often attacked and killed by the pinyon pine engraver,

Ips confusus (see below), although the disease

alone often kills trees. This disease is second

only to stand-replacing fires as a mortality

agent in pinyon. It is not known if management activities have affected the incidence of

the disease (Merrill et al. 1992).

Armillaria root disease, caused by

Armillaria mellea, can build up on dead or

dying native oaks and attack and kill young

conifers nearby. In southern California this

fungus does not cause extensive mortality but

can be a problem when large oaks are removed
90

from a site and conifers are planted. The newly

killed oak stumps provide a large food base,

allowing the fungus to grow rapidly and

overcome nearby conifers.

Dwarf and True (Leafy) Mistletoes

The dwarf mistletoes (Arceuthobium spp.)

are serious parasites of pines in southern California. These mistletoes are both water and

nutrient parasites, and heavily infected trees

are readily killed by bark beetles and other

insects or drought. The most widespread species are the western dwarf mistletoe, A.

campylopodum—which infects ponderosa, Jeffrey, knobcone, and Coulter pine—and sugar

pine dwarf mistletoe, A. californicum, which

infects sugar pine. A. occidentale, which infects

gray (foothill) pine, as well as A. divaricatum,

in pinyon pines, and A. cyanocarpum, in limber pine, also occur in southern California

(Scharpf and Hawksworth 1993). Although

birds can carry dwarf mistletoe seeds on their

feet and feathers, infection most often occurs as

a result of the forceful ejection of seeds from the

female plant. Thus, susceptible understory trees

can be infected by mistletoe in the overstory.

Management of dwarf mistletoes can be

accomplished by removing diseased overstory,

isolation of susceptible understory from diseased overstory trees by distance or the use of

buffers (nonhost trees planted between the infected and uninfected trees), and pruning or

removal of infected trees (Scharpf et al. 1988).

The latter method is used in southern California campgrounds and other high-use

recreation sites where the value of individual

trees can justify treatment costs. Dwarf mistletoe is a good example of an organism which

should not be considered a pest where infection, dieback, and some tree mortality do not

interfere with management objectives. The

mistletoe plants support their own herbivores,

and the witches’ brooms, dead limbs, and dead

trees that result from mistletoe infections create habitat for other species.

It is not known if fire suppression and

other management activities in the twentieth

century have changed the relative abundance

of dwarf mistletoes. Stand-replacing fires can

eliminate local populations as the host trees

are able to return to sites more rapidly than

their mistletoe parasites. Spotty fires can leave

infested overstory trees which both regenerate the stand and reinfect it. Heavily infested

stands may contain more fuels because of the

accumulation of dead witches’ brooms and

trees, and fires in them may turn into conflagrations. Smoke may inhibit dwarf mistletoe

seed germination, depending on length of exposure (all reviewed by Hawksworth and Wiens

1996). It is likely that prior to the arrival of Europeans in southern California, dwarf mistletoes

were abundant, at least in patches.

True mistletoes, Phoradendron spp., infect

hardwoods, white fir, incense-cedar, and junipers in southern California. Unlike dwarf

mistletoes, these species photosynthesize and

are primarily water parasites and thus are far

less damaging to their hosts. The berries are

eaten by birds, which then disperse the seeds.

True mistletoes can be serious pests where individual trees are of high value, such as in

campgrounds. Heavily infected trees have reduced growth rates, are weakened, and are

sometimes killed outright. Weakened trees

may be attacked and killed by insects or may

succumb in times of drought. There is no evidence that general management activities have

increased the frequency of infection by these

species, except perhaps in the case of white

fir, where fire suppression is thought to have

increased the occurrence of the host and thus,

too, of the parasite. Mistletoe infections in

white fir contribute, with annosus root and

butt rot, to general decline of trees, leading to

topkill or whole tree mortality when insects

(particularly bark beetles and roundheaded

borers) attack.

Bark Beetles

Beetles in the family Scolytidae are best

known for delivering the “coup de grâce” to

conifers stressed by disease, drought, or other

factors. When populations of some species

build up during droughts, even vigorously

growing trees may be successfully attacked and

killed. Two genera are primarily responsible
91

Chapter 3

tack. Thus proper sanitation is believed to be

essential to the management of these beetles

(Furniss and Carolin 1977).

Scolytus ventralis, the fir engraver, is the

most commonly found bark beetle in white

fir. This nonaggressive scolytid may kill patches

of the phloem, which may heal over; tops of

trees; and whole trees; depending upon the

size of the trees and the relative level of stress

to the trees from pathogens and other agents

(Furniss and Carolin 1977).

Preventing losses to bark beetles requires

keeping stressors—such as root disease and

dwarf mistletoe—at low levels. Thinning to

reduce stocking density should be used to reduce the risk of drought stress, but shortages

of personnel and Timber Stand Improvement

(TSI) dollars have reduced the number of acres

thinned in recent years. Forest Pest Management pest prevention and suppression dollars

can be used, when available, to thin stands at

risk of bark beetle-caused mortality, and to

suppress dwarf mistletoe and other pests.

Round and Flatheaded Borers

Round and flatheaded beetles are sometimes

important mortality agents. Two species are of

particular importance in southern California, the

California flatheaded borer, Melanophila

californica (Buprestidae), and the roundheaded

fir borer, Tetropium abietis (Cerambycidae). M.

californica infests and kills mature to decadent

trees and is usually found in dying trees in the

largest diameter classes, e.g., the large old Jeffrey

pines which were once common on Laguna

Mountain in San Diego County. T. abietis is a

common mortality agent of white fir stressed by

other pests, drought, or poor growing conditions (Pronos et al. 1999). Other cerambycids

and buprestids feed in dead and dying trees,

returning nutrients to the soil and serving

themselves as food for birds. These insects are

sometimes considered pests because their feeding decreases the value of lumber (Furniss and

Carolin 1977). Fire suppression is thought to

have increased the proportion of white fir in

stands that were formerly primarily pine, increasing the abundance of T. abietis and other

pests on the off-site firs.

for pine mortality in southern California,

Dendroctonus and Ips. The former includes

species such as the western pine beetle, D.

brevicomis, which has several generations per

year and can build up rapidly in stressed trees.

This species has been associated with widespread Coulter pine mortality on the western

slopes of the San Jacinto Mountains and portions of Palomar Mountain in the early 1990s

(Merrill, pers. obs.; Merrill 1991), as well as

historically in Lost Valley and the northern

slope of Hot Springs Mountain in San Diego

County (Hall 1958). Other species in the genus—including the Jeffrey and mountain pine

beetles, D. jeffreyi and D. ponderosae, respectively—have one generation per year. Like D.

brevicomis, these species can attack and kill

otherwise vigorous trees when beetle populations are high. In southern California these

beetles are most often found in Jeffrey pine

(D. jeffreyi), and ponderosa and sugar pines

(D. ponderosae). For unknown reasons both

species have patchy distributions among the

mountains of the Transverse and Peninsular

ranges in southern and Baja California. D.

valens, the red turpentine beetle, infests freshly

cut stumps and roots and lower bole of living

trees, particularly those damaged by fire or

root disease. This species rarely causes tree

mortality but does contribute to the decline

of trees which are then attacked by more aggressive species (Furniss and Carolin 1977).

Ips species are commonly called engraver

beetles for their habit of feeding on (engraving) the cambial surface of the xylem as well

as the phloem of pines. These beetles are usually not considered as aggressive as

Dendroctonus spp., although they are responsible

for much tree mortality, particularly of pinyon

pines with black stain root disease (the pinyon

ips, I. confusus) and smaller diameter trees or

portions of trees. For example, I. paraconfusus

and I. pini commonly kill tops of large pines. I.

emarginatus can kill Jeffrey, ponderosa, sugar, and

lodgepole pine in southern California. All of

these species of Ips have several generations per

year. Ips beetle populations may build up in slash

to levels where small diameter trees and tops of

mature trees in the vicinity are at risk for at-
92

Figure 3.8. An aerial view of ski area developments

near Big Bear Lake on the San Bernardino National

Forest. JOHN STEPHENSON

The Influence of Recreation

Activities

Public lands in the southern California

mountains and foothills are popular outdoor

recreation areas. Recreation is the principal

land use activity in the region’s state and

county parks and it is also the most common

activity in the national forests. With a rapidly

growing urban population nearby, the number of recreationists visiting the assessment area

is steadily increasing. Some go in search of

calm and serenity, while others pursue adventure, excitement, or simply escape from the

urban environment. Activities that fall into the

category of outdoor recreation include, although are by no means limited to, camping,

picnicking, driving, hiking, site-seeing, wildlife viewing, hunting, fishing, target shooting,

off-highway vehicle (OHV) driving, horseback

riding, mountain bike riding, skiing, and

mountain climbing.

The land management agencies do a variety of things to accommodate and enhance

these outdoor recreation experiences. A vast

network of roads and trails is maintained. Picnic areas and campgrounds (both developed

and remote) are established and maintained.

Information centers and interpretive programs

are provided. Through special use permits, sites

are leased to private entities for downhill ski

area developments (fig. 3.8), organizational

youth camps, recreation residences, and shooting ranges. Habitat improvement projects are

undertaken to enhance game and sport fish

populations, and the California Department

of Fish and Game stocks many lakes and

streams with catchable fish. These developments and services are popular and there is a

steady demand for improvements and additions.

While some level of recreation activity

occurs almost everywhere, the vast majority is

concentrated in a relatively small number of

popular areas (fig 3.9). These areas are often

associated with developed facilities and easily

accessible by road. Developed sites provide a

measure of environmental protection by keeping impacts localized and by providing facilities such as toilets and trash cans. However,

concentration of activity also tends to cause

ecological impacts (Boyle and Samson 1985).

Frequent traffic in an area causes reductions

in vegetative cover, with the rate of reduction

being highly influenced by the type of activity (e.g., motorized vehicle or horse traffic

reduces ground cover more rapidly than foot

traffic)(Liddle 1997). Concentrated human

activity is also more likely to cause incidental

animal mortality (e.g., trampling of nests or egg

masses) and can cause disturbance-sensitive

species to avoid areas that would otherwise by

suitable habitat (e.g., bighorn sheep).

Localized impacts from recreation activities can be relatively benign. Problems arise

when high-use recreation areas overlap with

sensitive habitats or rare species populations

(table 3.14). In southern California, the potential for overlap is heightened by the fact

that areas rich in rare habitats and species—

riparian areas, montane meadows, and conifer forests—also tend to be popular locations

for recreationists. In some of these areas, normally harmless activities become serious

threats because of the extreme rarity or vulnerability of a species occurring in the vicinity.
93

Chapter 3

Figure 3.9. Developed recreation sites and other areas that receive concentrated recreation use in the

assessment area.

et al. 1988; Gutzwiller 1991; Knight and

Gutzwiller 1995; Liddle 1997). Making matters worse is the lack of scientific studies on

the ecological effects of recreation activities in

the southern California mountains and foothills. All of the local information we could

find on this subject was based on anecdotal

observations. There is a real need for formal

scientific studies to assess the effects of recreation activities on rare species and habitats and

to evaluate the efficacy of management actions

currently being taken to avoid or mitigate

those effects.

For example, people walking in a creek is a

normally harmless activity, but at certain times

of the year in the few remaining areas where

arroyo toads or mountain yellow-legged frogs

still occur, it can greatly affect the survival of

these imperiled species (Jennings 1998; Sweet

1992).

Our scientific understanding of the effects

of recreation activities on wildlife is rudimentary at best (Knight and Cole 1995).

Numerous studies on the ecological effects of

recreation have been conducted, but the

knowledge gained is disparate and seldom

definitive (see reviews in Boyle and Sampson

1985; Hammitt and Cole 1987; Pomerantz
94

Human activities in and around these sites

(e.g., driving, biking, walking through the

stream, and picking up animals) are reportedly causing significant adult mortality and

declines in reproductive success (Sweet 1992;

USFWS 1998a). Similar adverse effects resulting from recreational activity have been

reported for pond turtles (Holland 1991), redlegged frogs (Jennings and Hayes 1994), and

mountain yellow-legged frogs (Jennings

1995a, 1998).

Management efforts to avoid or mitigate

these impacts include seasonal closures of some

roads and recreation areas and restrictions on

vehicle access in some areas (e.g., walk-in

campgrounds). Most of these measures have

Table 3.14. Key ecological issues that are influenced by recreation activities.

Many of the anecdotal reports of negative

recreation impacts pertain to riparian and

aquatic habitats. Foothill river corridors are

cool, pleasant places that are often only a short

drive from urban areas. They attract

recreationists in large numbers (fig. 3.10), and

over the years that demand has been accommodated through the establishment of

campgrounds and picnic areas in popular areas. Only recently has it been recognized that

many of these same areas are also important

habitats for imperiled species.

Developed recreation sites are particularly

prevalent near low-gradient stream and terrace habitats occupied by the endangered

arroyo toad (Sweet 1992; USFWS 1998a).

Key Issues

Habitats/Species

Most Affected

Effects Associated

with Recreational Activities

Current Trends and

Areas Most Affected

Declines in condition

of sensitive habitats

or direct mortality

of rare species.

Indirect impacts to

disturbance-sensitive

species.

• Riparian habitat

• Arroyo toad

• Meadows

• Pebble plains

• Alpine plants

• Reductions in vegetative cover

are common in areas that

receive frequent recreation use

• Direct mortality occurs

primarily from vehicular traffic,

but also is caused by trampling,

pollution, or harassment (e.g.,

capturing or plinking slow

moving animals)

• Impacts are localized but can

be significant; the level of

impact is strongly related to the

amount of use an area receives

• Facilities operated by private

entities under special use

permit (e.g., ski areas,

organizational camps,

recreation residences) are

sometimes located in sensitive

habitats or near rare species.

• Recreation use is believed

to be increasing in most

areas; there is a high

demand for additional

recreation facilities

• Popular recreation areas

that also contain many rare

species include Laguna

Mtn., Big Bear Valley,

Holcomb Valley, San

Gabriel River, Little Rock

Ck, Big Tujunga Ck, Sespe

Ck, and Santa Ynez River

• Popular trails to the

summits of Mt. San

Gorgonio, Mt. San Jacinto,

Mt. San Antonio (Baldy) and

Mt. Baden-Powell cause

some impacts to alpine

habitats

• Bighorn sheep

• Mule deer

fawning habitat

(meadows)

• Bat roosts

(abandoned

mines and

buildings

• Bighorn sheep are extremely

sensitive to human activity and

move to avoid it; this has

caused them to retreat from

some of their most suitable

habitat areas.

• Mule deer will avoid suitable

fawning habitat if there is a lot

of human activity

• Bats will abandon roost sites if

there is a a high level of human

activity

• Bighorn sheep are being

affected in the eastern San

Jacinto Mts near Palm

Springs and in the San

Gabriel Mts in Lytle Creek

and around Mt. Baldy

• Some of the best fawning

habitat in the upper Santa

Ana River watershed is

avoided by deer due to high

levels of recreation use

(Nicholson 1995)
95

Chapter 3

only recently been instituted. Much could be

learned by careful monitoring of their effectiveness, both in terms of controlling

recreationists and reducing impacts to the target species.

Organizational camps, recreation areas,

and public campgrounds are numerous in conifer forests and montane meadows (e.g.,

Laguna Mountain, Cuyamaca, Idyllwild,

Barton Flats, Big Bear/Holcomb Valley,

Lake Arrowhead, Big Pines, Crystal Lake,

Mount Pinos/Cuddy Valley, and Pine

Mountain). The facilities and interpretive

programs provided in these areas offer important opportunities for young people from

southern California’s cities to learn about the

natural environment. The organizational

camps in particular tend to have strong environmental education programs and are

conscientious about minimizing human impacts. However, in some areas these facilities

overlap with highly sensitive ecological areas

and can cause declines in habitat capability.

Figure 3.10. Recreation use in and along the San Gabriel River, Angeles National Forest. ROBERT

GOODMAN JR

Sensitive plants are particularly common in

montane meadows and, in dense conifer forests, some recreation facilities are in close

proximity to spotted owl nest sites. Nicholson

(1995) reported that mule deer largely avoided

areas regularly occupied by humans (e.g.,

campgrounds and summer cabins), to the extent that they did not utilize meadow habitats

that would otherwise be high quality foraging

and fawning areas.
96

Table 3.15. Key ecological issues that are influenced by the presence or density of roads.

Key Issues

Habitats/Species

Most Affected

Effects Associated

with Roads

Current Trends and

Areas Most Affected

Declines in survival

and recruitment rates

of some species.

Illegal collecting or

poaching of animals.

Barriers to animal

dispersal.

Declines in condition

of sensitive habitats.

• Riparian habitats

• Arroyo toad

• Spadefoot toad

Animal mortality caused by

vehicle traffic on roads can be

substantial. Stream crossings

and roads adjacent to riparian

habitats pose particular

concerns for slow-moving

species (e.g. toads, frogs).

Roads on stream terraces

and crossings in lowgradient foothill and desert

streams are affecting the

endangered arroyo toad.

Seasonal closures and

modifications to crossings

are being done to reduce

impacts.

• Mtn. kingsnakes

• Rosy boas

• Pond turtles

• CA newts

• Mule deer

Can cause substantial declines

in species abundance in

heavily collected areas. Roads

facilitate this activity because

collecting is almost invariably

done along or near them.

Mountain lions Busy highways (particularly

interstate highways) can be

very difficult for some animals

to cross, and may be resulting

in population fragmentation.

Interstates 8 and 15 cross

the Cleveland NF; I-10 and I15 separate portions of the

San Bernardino NF; I-5 runs

between the Angeles and

Los Padres NFs.

It is difficult to determine

trends in this activity.

• Pebble plains

• Riparian habitats

• Illegal or unauthorized

activities are more likely to

occur in roaded areas and

are difficult to prevent; this

includes pollution, vandalism,

driving in unauthorized areas.

• Increased flow of sediment

into streams

There is little new road

construction on public lands

and some problem roads

are being obliterated.

The Influence of Roads

Roads are the primary means by which

people access the outdoors. Thus, the amount

of human use in a area is highly correlated

with an area’s road accessibility. There are many

benefits to having areas accessible by road: it

improves firefighting effectiveness, increases

opportunities for habitat management work,

and provides basic access to the public lands.

However, the presence of roads also leads to

impacts associated with vehicular traffic and

increased human use (table 3.15).

Roads in and adjacent to riparian areas can

cause substantial impacts. Roads located on

stream terraces, or that frequently cross

streams, can be a major source of mortality to

slow-moving animals such as the arroyo toad.

These nocturnal toads actually move onto dirt

roads at night to feed and many individuals can

be killed by a few vehicles (USFWS 1998a). This

is a particular problem in and around campgrounds that are located on stream terraces near

arroyo toad breeding habitat (Sweet 1992). Similar problems of high mortality rates where a road

runs close to breeding habitat have been observed

for the spadefoot toad (E. Ervin, San Diego State

University, pers. comm.).
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Chapter 3

The increased flow of sediment into

streams is one of the most commonly cited

environmental effects of unpaved roads. Roads

reportedly contribute more sediment to

streams than any other land management activity (Gibbons and Salo 1973; Lee et al.

1997). Old roads that were not designed using current “Best Management Practices”

(BMP) standards often have the greatest environmental impact, particularly if located in

steep terrain (fig 3.11). Sediment production

from logging roads in steep terrain in Idaho

was 770 times higher than in undisturbed areas; approximately 71 percent of the increased

sediment production was due to mass erosion

and 29 percent was due to surface erosion

(Megahan and Kidd 1972). Increases in mass

erosion due to plugged culverts and fill slope

failures are especially common on abandoned

or unmaintained roads (Weaver et al. 1987).

Figure 3.11. Gully erosion caused by runoff from a

culvert on Gator Road, Laguna Mountain, Cleveland

National Forest. Restoration efforts have since been

implemented and the area is recovering. DEVEREE

VOLGARINO

Roads tend to cross streams in low-gradient reaches where the current slows.

Unfortunately, those areas are also where sandy

pools form, the primarily breeding habitat for

arroyo toads. Vehicle traffic on roads that cross

through, or adjacent to, breeding pools cause

mortality of eggs and juvenile toads. Efforts

are underway in several areas, particularly on

the Los Padres and Cleveland national forests

where this problem is most common, to

modify stream crossings to reduce impacts to

arroyo toads.

Unlawful activities tend to be a chronic

problem in some road-accessible areas. Illegal

collecting of reptiles, unauthorized woodcutting, illegal OHV activity, poaching,

vandalism, and dumping of hazardous materials: all of these are difficult law enforcement

issues that occur almost exclusively along or

near roads. Non-native species introductions

(both purposeful and inadvertent ones) also

occur predominately in areas that are accessible by road. All of these things cause

significant declines in habitat capability in localized areas. The inherent difficulty in

preventing these impacts from occurring in

roaded areas is a compelling reason for maintaining some areas in a roadless condition.

As part of our watershed-scale analysis we

looked at “roadedness” in several different

ways. First, we identified all existing roadless

areas that are larger than 1,000 acres (fig 3.12).

Second, we looked separately at each watershed, calculating the percentage of the

watershed that falls within 250 meters of an

active road (table 3.16). Not surprisingly,

many of these “least-roaded” watersheds also

show up in table 2.15 (chapter 2) in the list

of drainages that have high potential for

maintaining aquatic ecological integrity due

to low land use intensity and low numbers

of exotic species.
Figure 3.12. Roadless areas of 1,000 acres or more are shaded. The black lines outline the boundaries of

formally designated roadless areas (i.e., designated wilderness areas or areas specified as unroaded in the

Forest Plan).
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Chapter 3

Table 3.16. The fifteen least-roaded watersheds in the assessment area based on the percent of

the watershed that lies within 250 meters of an existing road.

Sisquoc River (above Cuyama confl.) So. Los Padres 10% 87%

Big Sur River No. Santa Lucia 11% 84%

Upper Sespe Ck (above Timber Ck) So. Los Padres 14% 96%

Upper San Gabriel R. (East Fork) San Gabriel Mts 12% 98%

West Fk, San Gabriel R. San Gabriel Mts 16%

Little Rock Creek San Gabriel Mts 15% 97%

Santa Cruz Creek So. Los Padres 14% 72%

Upper Ventura River So. Los Padres 14% 94%

Little Sur River No. Santa Lucia 17% 56%

Up. Arroyo Grande (above Lopez Res.) So. Santa Lucia 18%

Up. Santa Ynez (above Gibraltar Res.) So. Los Padres 18% 98%

Lower Sespe Ck (below Timber Ck) So. Los Padres 19% 84%

Castaic Creek Castaic Ranges 20% 93%

Palm Canyon San Jacinto Mts 20% 30%

Deep Canyon San Jacinto Mts 21% 37%

Percent of

watershed that

lies within 250

meters of a road

Percent

public

land in

watershed

Mountain Range

Watershed Subarea

○○○○○ ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○○○○○○○

The Influence of Timber and

Fuelwood Harvest

Most of the land base suitable for commercial timber harvest in southern California

is within the San Bernardino National Forest.

An active timber program was sustained on

that forest from the late 1940s (post World

War II) through the mid-1980s (fig 3.13).

Harvest levels peaked in the 1960s, with 27.4

million board feet (MMBF) harvested on the

San Bernardino National Forest in 1963 alone

(McKelvey and Johnston 1992). Volume data

from the California Department of Forestry

and Fire Protection (1947 to 1978) and the

California State Board of Equalization (1979

to 1990) for San Bernardino and Los Angeles

counties show that 362.3 MMBF of timber

were removed from those counties between

1947 and 1990 (McKelvey and Johnston

1992). Some of that would have come from

the San Gabriel Mountains within the Angeles National Forest, but most was from the

more densely forested San Bernardino Mountains.

Figure 3.13. Logging intensity in San Bernardino

and Los Angeles counties, 1947 to 1990. Most of

this timber came off the San Bernardino National

Forest (from McKelvey and Johnston 1992).

Some commercial timber harvesting was

done in the Cleveland and Los Padres national

forests during peak years in the 1960s and

1970s, but it was short lived. The small

volumes produced in these areas were not sufficient to support viable sawmill operations; Millions of Board Feet (scaled)

0

5

10

15

20

25

30

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990

Year
100

The Influence of Livestock

Grazing

Livestock grazing has been a traditional

activity on both public and private land in the

southern California mountains and foothills

since at least the early 1800s (Lockmann

1981). When assessing the effect of this activity on ecosystems and species, it is important

to distinguish the impact of historic grazing

from that which can be attributed to grazing

levels occurring today. Abusive grazing practices in the late 1800s and early 1900s caused

environmental changes that are orders of magnitude greater than anything seen in recent

times.

Livestock numbers reached their peak in

this region from approximately 1860 to 1900,

when sheep grazing was in its heyday. Use was

particularly high in the montane meadows of

the San Bernardino and San Jacinto mountains; it is reported that 30,000 sheep were

herded into Big Bear Valley in the late 1860s

(Lockmann 1981). There are numerous accounts of extensive devegetation and erosion

damage occurring during this period

(Lockmann 1981; Minnich 1988) and, although sheep grazing was discontinued in the

mountains in the early 1900s, the damage

done was evident long afterwards (Pillsbury

1933).

Table 3.17. Key ecological issues that are influenced by fuelwood harvesting.

Key Issues

Habitats/Species

Most Affected

Effects Associated

with Fuelwood Harvest

Activities

Current Trends and

Areas Most Affected

Retention and

recruitment of large

diameter trees, snags

(standing dead trees),

and downed logs.

Increases in smalldiameter trees in

the forest understory.

Cavity nesters, snagdependent species.

Large snags that are

reachable by roads can be

difficult to retain because of

unauthorized cutting.

The same is true of large

downed logs.

Snag retention

requirements in existing

Forest Plans are adequate,

but enforcement is difficult

in popular woodcutting

areas.

Mesic mixed conifer

forests.

If fuelwood demand can be met

through harvesting small trees,

this activity could help control

the problem.

Problem is most acute in the

western San Bernardino

Mtns. but is occurring in

many montane conifer

areas.

thus, timber had to be trucked long distances

to the nearest mill. This same problem ultimately affected the San Bernardino National

Forest timber program when dropping harvest levels in the late 1970s led to closure of

the last mill in the area.

For the past decade (much longer in some

areas), small timber programs on the southern forests have focused on (1) forest health

issues (e.g., treatment of insect and disease

centers, understory thinning, and fuels reduction); (2) administering individual permits to

accommodate local demand for fuelwood; and

(3) identifying and removing hazard trees.

Small-scale salvage operations to remove trees

killed by wildfire or bark beetles are also occasionally done.

When evaluating the influence of timber

harvesting on southern California ecosystems,

we must separately consider historic effects

from current effects. Past timber harvesting,

particularly in the San Bernardino and San

Jacinto mountains, has probably resulted in a

substantial reduction in the number of large

trees, with ponderosa and Jeffrey pines incurring the greatest reductions. It may also have

contributed to the increased dominance of

white fir.
101

Chapter 3

Figure 3.14. Livestock grazing at Hudson Ranch adjacent to the Los Padres National Forest. Brush

Mountain can be seen in the background. DAVE CLENDENON

Since 1900, cattle have been the principal

livestock animal on southern California rangelands. Grazing can occur year-round in foothill

savannas and grasslands and during the summer months in montane meadows and forests

(fig. 3.14). Over the years there has been a

gradual decline in the intensity and extent of

cattle grazing in this region. Once the dominant use of meadows in the San Bernardino

and San Jacinto mountains, grazing has been

greatly reduced in these ranges as ranching in

the surrounding valleys has declined and other

land use activities, particularly recreation, have

received greater emphasis.

Today, grazing within the assessment area

is concentrated in and adjacent to the Los Padres National Forest and, to a lesser extent, in

the San Diego County foothills within and

adjacent to the Cleveland National Forest

(table 3.18) (fig. 3.15). Rangelands in these

areas are predominantly oak savannas, grasslands, montane meadows, and openings in

chaparral and scrub.

Ecological changes most commonly attributed to overgrazing by cattle involve declines

in the condition of riparian, oak woodland,

grassland, and meadow habitats. More specifically, livestock grazing has been implicated in

reduced tree regeneration, substantial reductions in vegetative cover, streambank

destablization, water quality degradation, and

the spread of non-native weeds (table 3.19).

A comprehensive review of studies assessing the impact of livestock on California

ecosystems, with particular emphasis on the

Sierra Nevada, was recently conducted by a

group of scientists with expertise in California rangeland issues (see Allen-Diaz et al.

1999). Their findings suggest that despite the

many studies of grazing and its impact on ecosystems, there are still far more questions than

answers regarding this issue. There appears to

be a scarcity of studies which quantify the effects of different grazing intensities,

frequencies, and seasons of use. Instead most

studies simply compare the impacts of heavy
Figure 3.15. Locations of current grazing allotments on national forest system lands within the assessment

area.

Table 3.18. Shows acres of national forest system land that are within grazing allotments, by mountain range

and over the entire assessment area. Also, the percentage of all national forest system lands that are within

these allotments. Some of the allotments are not currently being used.

Cleveland NF Los Padres NF San Bernardino NF Angeles NF

San

Diego

 Ranges

Santa

Ana

Mts

San

Jacinto

Mts

San

Bernardino Mts

San

Gabriel

Mts

Castaic

Ranges

S. Los

Padres

Ranges

S. Santa

Lucia

Rng

N. Santa

Lucia

Rng

Acres 129,147 5,017 76,917 94,968 0 22,344 560,619 184,202 51,898 1,133,456

Percent of National 45% 4% 39% 24% 11% 44% 99% 59% 32%

Forest System Land

Area within Forest

Service Grazing

Allotments

Entire

Assessment

Area
103

Chapter 3

Table 3.19. Key ecological issues that are influenced by livestock grazing activities.

Key Issues

Habitats/Species

Most Affected

Effects Associated with

Livestock Grazing Activities

Current Trends and

Areas Most Affected

Declines in condition

of sensitive habitats

or direct mortality

of rare species.

Lack of oak

regeneration.

Spread of invasive

non-native species

e.g., brown-headed

cowbirds, star thistle,

Mediterranean

grasses) .

Fuels reduction.

• Riparian habitat

• Meadows

Grazing in riparian areas can

cause increased sediment yield,

stream-bank degradation,

reductions in vegetative cover,

and direct mortality of rare

species.

• Impacts have been reduced

substantially in recent years

due to excluding livestock

from some riparian areas

and improved management

of stocking rates and

season of use in other

areas

• Entrenched downcuts

caused by past overgrazing

still remain in some

meadows

• Blue oak woodlands

• Engelmann oak

woodlands

Grazing can negatively affect

oak regeneration through

seedling removal and soil

compaction.

Recent studies have shown

that livestock grazing

contributes to this problem

but is not the sole or even the

primary cause in most areas.

• Riparian habitat

• Grasslands

• Oak woodlands

• Least Bell’s vireo

• Willow flycatcher

• CA gnatcatcher

• Studies suggest that grazing

attracts cowbirds, but its

influence varies based on other

surrounding land uses

• Overgrazing can facilitate

spread of star thistle and other

weeds

Grazing historically was a

major factor in the spread of

undesirable plants, but the

continued spread of those

plants today is often

triggered by other factors.

Nonspecific. Grazing can be used as a tool for

fuels reduction in grasslands and

on fire breaks.

Some fuel breaks are

currently maintained by

livestock grazing.

grazing with no grazing (Blackburn 1984;

Allen-Diaz et al. 1999). There are few solid

scientific assessments of the ecological effects

of management practices that fall in “the great

middle ground” between abusive grazing and

no grazing (Allen-Diaz et al. 1999).

Despite these limitations, some studies are

pertinent to the ecological issues within our

assessment area. The effect of grazing on

riparian habitats and species is of interest because there are many sensitive resources in

riparian areas and they are also a preferred

habitat for cattle (Kie and Boroski 1996).

Overgrazing by cattle was identified as a probable cause of limited cottonwood sapling

establishment along much of the Nacimiento

River in the northern Santa Lucia Range

(Shanfield 1984). Studies on the Blitzen River

in Oregon found dramatic increases in willow flycatcher and yellow warbler populations

when the intensity of year-round cattle grazing was reduced and willow cutting and

spraying were eliminated (Taylor 1986; Taylor and Littlefield 1986). The researchers

hypothesized that the mechanism involved was

that cattle grazing reduced willow nesting

cover for these species.

Several studies have assessed the effect of

livestock grazing on the survival of blue oak

seedlings. The results have been mixed; some

results suggest that grazing reduces blue oak

recruitment while others show no effect (Davis

et al. 1991; Allen-Diaz and Bartolome 1992).

There is general consensus, however, that grazing is just one of many factors that may be

affecting oak seedling survival.

Recent changes in the management of livestock grazing allotments on national forest

system lands have included (1) fencing to
104

exclude cattle from some sensitive riparian and

meadow habitats (figs. 3.16), (2) reductions

in stocking rates, and (3) changes in the season of use, reducing the amount of summer/

fall grazing in favor of a winter/early spring

use regime.

Figure 3.17. A limestone quarry in the San

Bernardino Mountains. DEVEREE VOLGARINO

Ecological impacts from these operations

are localized and present a significant problem mainly in areas where they overlap with

The Influence of Mining

Much of the assessment area is under mining claim, with the notable exception of large

portions of the San Gabriel Mountains, but

commercial mining in the region is not extensive. Most claims are small, individual

operations. The primary hub of mining activity is in the northeastern San Bernardino

Mountains, where high-grade limestone deposits are extracted by several large companies

in open-pit mines and quarries (fig. 3.17).

Smaller limestone mines are also in operation

at the north end of the San Rafael Mountains

Figure 3.16. (Left) Overgrazing of cattle contributed significantly to reduced vegetative cover in the Las

Bancas area of Pine Valley Creek, Cleveland National Forest in 1991. (Right) The same area along Pine Valley

Creek supported dense riparian vegetation two years after cattle were excluded and native willows were

planted. DEVEREE VOLGARINO

and in the Santa Lucia Ranges near Little Sur.

There is also active exploration for oil and gas

reserves occurring in southeastern portions of

the Los Padres National Forest.
105

Chapter 3

Table 3.20. Key ecological issues that are influenced by mining activities.

Key Issues

Habitats/Species

Most Affected

Effects Associated

with Mining Activities

Current Trends and

Areas Most Affected

Habitat degradation

or impacts to TES

species from in-stream

mining operations.

Habitat degradation

or impacts to TES

species from hardrock

mining.

Potential impacts to

habitats or species

from future

development of

existing mining claims.

Aquatic and riparian

habitats/species.

Suction dredging, sand and

gravel mining, and some

prospecting activities can cause

localized habitat degradation

and/or direct mortality to TES

species. Of primary concern is

where such activities overlap

with occurrences of sensitive

habitats or species.

Coordination between FS

and CDFG is occurring to

clarify permit process for

suction dredging and identify

areas for closure. Lowelevation, large-order

streams are most affected.

Suction dredging occurs

frequently on the San

Gabriel River.

Limestone outcrops and

associated endemic

plants.

• High-grade limestone deposits

in the northeastern San

Bernardino Mountains has led

to the development of open-pit

mines in an area where there

are a large number of rare

plants.

• Active mining of tourmaline

and other gemstones primarily

on private lands in the Palomar

Mountain area.

Nonspecific, but

greatest potential is in

desert-montane

habitats.

Much of the assessment area

is under mining claims. There

is potential for commercially

viable deposits of low-grade

gold, gemstones, or oil and

gas.

Currently there are few

active commercial mines

outside of the San

Bernardino Mountains,

limestone region.

• A site-specific conservation

strategy is currently being

developed to address the

San Bernardino Mts

limestone issue.

• Some localized habitat

degradation is resulting from

other hardrock mines, but in

general the assessment

area is not an active mining

region.

sensitive habitats or species (table 3.20). The

most prominent example of such overlap is

the occurrence of an entire assemblage of endemic, rare plants on high-grade limestone

deposits in the San Bernardino Mountains.

A commonplace form of mining in the

region’s larger streams is suction dredging.

Suction dredges utilize high-pressure water

pumps driven by gasoline-powered motors

which create suction in a flexible intake pipe.

A mixture of streambed sediment and water

is vacuumed into the intake pipe and passed

over a sluice box mounted on a floating barge.

Dense particles (including gold) are trapped

in the sluice box. The remainder of the entrained material is discharged into the stream

as “tailings” or “spoils,” which can form large

piles where dredges have remained in one location for a long period (Fredley 1995).

Suction dredging can have a number of

impacts on aquatic habitats: (1) increased water turbidity, (2) disturbance of channel morphology and bottom substrates that serve as

spawning areas for fish, and (3) direct mortality of fish and amphibian eggs and larvae in

the sediment vacuuming process. The significance of these impacts varies by site and

depends largely on the site’s ecological integrity (e.g., naturalness of the hydrologic regime,

other prevailing land uses, presence of rare or

at risk species, and presence of exotic species).

The State of California regulates suction

dredging activities. The Department of Fish

and Game (CDFG) is required to issue permits to suction dredge if it determines that

the operation will not be deleterious to fish.

They can also institute seasonal closures to

reduce impacts. The CDFG is currently conducting a statewide environmental review of

its policy on suction dredging (USFWS 1998a).
106

Figure 3.18. Housing construction in an isolated

area adjacent to the Cleveland National Forest. JOHN

STEPHENSON

The Influence of Air Pollution

Long-term studies to determine the effects

that air pollution is having on forest vegetation have occurred in the San Bernardino

Mountains and, to a lesser extent, in the San

Gabriel Mountains (Miller et al. 1996; Miller

and McBride 1999). Prevailing climatic conditions transport most of the air pollution from

the Los Angeles Basin into these mountains

(Miller et al. 1989). The two depositional

components of air pollution that have the

greatest effect on ecosystems are ozone (reviewed in Miller et al. 1996) and nitrogen

(reviewed in Bytnerowicz and Fenn 1996).

Ozone Deposition

Studies have determined that ponderosa

and Jeffrey pine trees, and to a lesser extent

bigcone Douglas-fir, are experiencing foliage

injury from ozone deposition (Miller et al.

1989; Peterson et al. 1995). Other tree species in the area appear to be considerably more

tolerant of ozone. Chronic ozone injury to

ponderosa pines was first identified in the San

Bernardino Mountains in the 1950s (Miller

et al. 1963). Mortality and damage was highest in the 1970s when ozone concentrations

reached their peak. Ozone concentrations

steadily declined between 1976 and 1991 and

a concurrent reduction in injury to the crowns

of ponderosa and Jeffrey pines was observed

(Miller et al. 1996).

The Influence of Private Land

Development

Development on private lands is steadily

consuming wildland habitats (fig. 3.18) and

reducing connectivity between the natural areas that remain. This trend poses some

significant challenges for conservation of habitats and species on public lands (table 3.21).

In the southern end of the assessment area,

rapid development has the potential to eliminate habitat corridors between the mountain

ranges. These corridors are believed to be important for the movement of some

wide-ranging animals. Mountain lions in particular are vulnerable to declines if individuals

in one mountain range become cut off from

the larger population (Beier 1993).

Development tends to simplify ecological

communities, eliminating some species and

increasing the abundance of others. Species

with wide tolerances and generalized habitat

requirements (common traits of exotic species)

are the ones that typically thrive in developed

areas. In addition, a number of plants commonly used in landscaping are on CalEPPC’s

list of Exotic Pest Plants of Greatest Ecological Concern, including arundo, tamarisk, ice

plant, pampas grass, Russian olive, fountain

grass, and Brazilian pepper tree.

Sand and gravel mining operations occur in

a number of foothill drainages where there are

well-developed alluvial deposits. Most of these

operations are on private lands. Sand and gravel

mines completely alter the drainage channel and

usually result in the creation of deep pools.
107

Chapter 3

Table 3.21. Key ecological issues that are influenced by development on private lands.

Key Issues

Habitats/Species

Most Affected

Effects Associated

with Private Land

Development

Current Trends and

Areas Most Affected

The distribution,

extent, and integrity

of habitats and

species which occur

predominantly on

private lands.

Fragmentation of

animal populations

caused by the loss

of wildland habitat

corridors between

mountain ranges.

Effects associated

with expansion of the

urban–wildland

interface.

Effects associated

with increased urban

infrastructure needs

on public lands.

• Coastal sage scrub

• Engelmann oak

woodland

• Valley oak woodland

• Grassland

• Montane meadow

Development on private land is

reducing the extent of native

habitats and fragmenting those

habitats into disjunct patches.

This increases the significance

of these habitats on public

lands.

Development is occurring

most rapidly in Orange, San

Diego, Riverside, San

Bernardino, Ventura, and

Santa Barbara counties.

Several counties are

developing habitat or

species conservation plans

which attempt to conserve

key areas and provide

corridors to the surrounding

public lands.

Species with large

area requirements

that disperse along

or near the ground

(e.g., mountain

lions).

Buildout on private lands can

eliminate habitat connections

between mountain ranges

unless natural habitat corridors

are designated and protected.

• Peninsular bighorn

sheep

• Many habitats/

species affected by

altered fire regime and

spread of non-natives

• Drives disturbance-intolerant

species away from preferred

habitats

• Increases the risk and

difficulty of using fire as a

management tool

• Contributes to rise in

invasive, non-native species

Urban interface is expanding

rapidly on both the desert

and coastal sides of the San

Gabriel, San Bernardino,

and San Jacinto mountains

and on the coastal side of

San Diego and southern Los

Padres ranges.

Imperiled habitat

connections include: Santa

Ana Mts — Palomar Mtn;

Palomar Mtn —San Jacinto

Mts; San Jacinto Mts — San

Bernardino Mts.

Nonspecific. Power lines, pipelines, water

storage, communication

facilities, highways, landfills,

sewage treatment areas, etc.

can cause localized habitat

degradation and habitat

fragmentation and provide

avenues for the spread of

invasive, non-native species.

Requests for infrastructures

to cross through or be

located in the mountains are

increasing as urban areas

expand.

Pine mortality was highest during extended periods of low precipitation (droughts),

when these trees are most vulnerable to bark

beetles. Trees with chronic ozone injury enter

a period of drought without the reserves required to mount an active defense against bark

beetle attack (Miller et al. 1991).

In the San Bernardino Mountains, there

is a clear west-to-east gradient in both ozone

levels and tree damage. Forests on the western

side of the range are exposed to much higher

levels of ozone and are experiencing the most

damage (Miller et al. 1989). Monitoring of

study sites in the west-side forests over a

fourteen-year period (1974 to 1988) found

that ponderosa and Jeffrey pine are losing basal

area in relation to competing species that are

more tolerant to ozone, namely, white fir,
108

incense-cedar, and black oak (Miller et al.

1996). The accumulation of more stems of

ozone-tolerant species in the understory presents

a fuel ladder situation that jeopardizes the remaining overstory trees in the event of a

catastrophic fire.

Quantitative information on ozone damage is scarce for other mountain ranges within

the assessment area. However, given the location of major pollution sources and prevailing

wind patterns, it appears that areas of high

potential for damage are probably confined

to the eastern San Gabriel and western San

Bernardino mountains (P. Miller, Riverside

Fire Lab, pers. comm. 1997).

Nitrogen Deposition

The effects of nitrogen deposition on local forests and shrublands have not been

studied for as long as ozone and are only beginning to become apparent. High rates of

nitrogen deposition have increased soil fertility and surface litter decomposition rates in

some mixed conifer forests in the San Bernardino Mountains (Fenn 1991b). However,

excessive nitrogen inputs can lead to various

negative effects, including nutrient deficienTable 3.22. Key ecological issues that are influenced by air pollution.

Key Issues

Habitats/Species

Most Affected

Effects Associated

with Air Pollution

Current Trends and

Areas Most Affected

Vigor and longevity

of forest trees,

particularly of those

species most

sensitive to ozone

damage;

ramifications to

structure and

composition of mixed

conifer forests.

Shifts in the structure

and composition of

plant communities

and reduced water

quality related to

excessive nitrogen

inputs.

• Ponderosa and

Jeffrey pine

• Bigcone Douglas-fir

High levels of ozone

deposition is a chronic

condition in some areas and is

known to reduce the vigor of

trees sensitive to it. This leads

to increased mortality and

appears to be contributing to a

shift in tree species

composition.

• Rates of ozone deposition

have declined from 1970s

peaks, but are still some of

the highest in the U.S.

• Western San Bernardino

Mountains and eastern San

Gabriel Mountains are most

affected.

• Coastal sage

scrub

• Mixed conifer

forests

High levels of nitrogen

deposition is a chronic condition

in some areas. Elevated

nitrogen levels in the soil has a

fertilizing effect for some

species, altering community

dynamics. Runoff into streams

and groundwater is elevating

water nitrate concentrations.

Western San Bernardino

Mountains and eastern San

Gabriel Mountains are highly

affected, as are lowland

areas on the coastal side of

the mountains (e.g., western

Riverside and San

Bernardino counties).

cies, soil acidification, altered species composition, decreases in mycorrhizal root symbiosis,

and elevated concentrations of nitrate in soil,

groundwater, and streams (Bytnerowicz and

Fenn 1996; Padgett et al. in press). Recent

studies in Riverside County indicate that high

levels of nitrogen deposition may be contributing to the decline of coastal sage scrub and

its conversion to Mediterranean annual grassland (Allen et al. 1997).

Spatial patterns in levels of nitrogen deposition mirror that described for ozone. Eastern

Los Angeles County and western San Bernardino and Riverside counties receive the highest

concentrations. In the mountains, the coastal

side of the eastern San Gabriel and western

San Bernardino mountains are the most polluted (Bytnerowicz and Fenn 1996). In

montane conifer forests, the fertilizing effect

of nitrogen may be accelerating understory

development of white fir and incense-cedar,

thereby elevating fuel loads and potentially increasing the risk of stand-replacing fires.

Riggan et al. (1985) reported elevated concentrations of particulate nitrate in stream

water emanating from watersheds exposed to

high nitrogen deposition in the San Gabriel
109

Chapter 3

Climate Change

Considerations

The subject of long-term climate change

is really beyond the scope of this report. Research on this topic is generally conducted at

continental or global scales, making it difficult to determine how local landscapes might

be influenced. However, several researchers

have attempted to interpret predictions from

global climate change models in terms of how

southern California ecosystems, and in particularly local fire regimes, might be affected.

Although highly speculative, some of the local climate change predictions described in

those studies are worth describing.

 Davis and Michaelsen (1995) and

Westman and Malanson (1992) simulated the

potential effects of climate change on fire regimes in southern California chaparral

ecosystems. To figure out what those climate

changes would be, they used predictions from

three widely accepted general circulation models (GCMs) that assume a doubling of

atmospheric carbon dioxide (CO2

). Under this

scenario, several changes are predicted with

varying levels of confidence.

The most probable climatic change occurring in the assessment area would be an

increase in average daily maximum and minimum temperatures of 1 degree to 4 degrees

Centigrade. There is more uncertainty associated with precipitation predictions, but the

various GCM results are in general agreement

that winter and spring precipitation should inMountains. Stream water particulate nitrate

concentrations in watersheds heavily influenced by urban air pollution were one to three

orders of magnitude greater than in watersheds

which were not exposed to high concentrations of air pollution. Sharp peaks in

particulate nitrate levels occur during the first

winter storms when the ecosystem is loaded

with nitrogen accumulated during the dry

summer months. Additional information is

needed on the extent of this problem and how

it is affecting aquatic ecosystems.

crease. The three GCMs predicted increases

in precipitation for the months of November

through March of 36, 21, and 21 percent. Predicted increases for March and April were 59,

17, and 27 percent (Davis and Michaelsen

1995).

The fire regime simulations were very sensitive to predicted increases in fire season

temperatures and equally sensitive to large

changes in stand productivity. Total area

burned was predicted to increase and the firerecurrence interval was predicted to significantly

decrease (Davis and Michaelsen 1995).

Westman and Malanson (1992) suggest that

these changes could lead to potentially large

changes in chaparral composition.