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 to change is not limitless and some organisms • What are the primary natural processes and human activities that are clearly more adaptable than others. In gen- drive change in the composition, eral, the complete assemblage of native plants structure, and extent of southern and animals is most likely to be maintained California mountain and foothill when environmental conditions remain within ecosystems? their natural historic range. Thus we need to develop an understanding of what the historic • How are those processes and or natural ranges of variability are for various activities currently affecting the ecological processes. These serve as the refer- landscape and what can be ence conditions to which present day determined regarding the natural range of variability? conditions can be compared. The closer cur- rent conditions are to reference conditions, the • What current trends are apparent and greater our confidence that all the ecological what threats or opportunities are components will continue to persist (for de- presented by them? tailed description of the “reference variability” This chapter considers the primary pro- concept see Manley et al. 1995). This is the cesses and activities that modify ecological basis for the “coarse-filter” approach to con- communities in the mountains and foothills. servation described in chapter 2. These include (1) natural disturbance pro- In our analysis, we first asked the assess- cesses such as fire, flood, drought, and ment task group to identify and describe the outbreaks of insects or disease; (2) human uses key interactions between landscape elements of the land for development, resources, and and the change agents (e.g., ecological pro- recreation; and (3) the spread (often uninten- cesses or human activities) currently shaping tionally) of new elements such as air pollution them. Then we examined those interactions, and non-native plants and animals. using the best available information on refer- Each of these “change agents” acts upon ence conditions to assess how today’s dynamics the landscape and modifies its character. To compare with the historic range of variability. persist over time, plant and animal species Of particular interest is how the current man- must continually be able to survive, reproduce, agement of natural processes (e.g., fire or recolonize as the landscape changes. Thus suppression or streamflow regulation) has af- the disturbance processes that shape local eco- fected the species and habitats that evolved systems are as important to understand as the under the influence of those processes. physical components of those ecosystems. The element/process interactions identi- Since disturbance and climatic variability fied by the assessment task group are are inherent components of natural systems, summarized in the following sections. A sepa- all species have adaptations to survive in a rate matrix was developed for each of the six changing world. Yet, their ability to respond large-scale vegetation mosaics described in 61 chapter 2. The matrices were used to clarify anecdotal (e.g., accounts of a few early inhab- the effects of different activities and prioritize itants); (2) incomplete and less reliable the those having the biggest impact on species further back in time you go (e.g., official conservation and ecosystem integrity. We be- records of past fires); or (3) based on indirect lieve this information will be useful when the information that is subject to varying inter- time comes to formally describe desired con- pretations (e.g., fire scar analyses, vegetation ditions and management priorities. What patterns observed in old aerial photographs, follows is a description of the primary change and patterns observed in nearby areas where agents and how they influence ecosystems. fire suppression is less of a factor). Unfortu- nately, this body of evidence does not provide The Influence of Fire clear, unequivocal answers; thus, there will al- ways be different interpretations of how things Experience has taught us that we cannot used to be. prevent fire. In my opinion, it is better to In this assessment we examined various have a fire every year, which burns off a ... theories and supporting evidence on how small area, than to go several years ... and today’s fire regime may differ from historic have a big one denuding the whole watershed conditions and what is relevant about those at once. changes. We focused primarily on factors in- — William Mulholland, 1908 fluencing the persistence of native ecological Fire is a primary agent of change in veg- communities and how today’s conditions com- etation patterns across the southern California pare with what is known about the natural landscape. The distribution, composition, and range of variability. In this section we present structure of almost all plant communities in some of the local fire history data, describe this region are influenced by fire, and as the key concerns, and try to identify where there quote above illustrates, prominent southern is strong scientific consensus and where there Californians have long recognized its impor- is not. tance and offered opinions on how it should be managed. Has the Fire Regime Changed? The significance of fire in shaping south- There is little argument that the fire re- ern California wildlands is reflected in a large gime in southern California has changed as body of scientific research on the subject. It is human populations have grown and fire sup- not by coincidence that the Forest Service re- pression practices have become increasingly search station in southern California is the effective. Even assuming that Native Ameri- Forest Fire Laboratory and, as the name im- cans actively burned, there are many more plies, is largely devoted to fire research. Yet, ignitions today with the combination of hu- even with the extensive scientific attention man- and lightning-caused starts, and those given this subject there are widely divergent ignitions are more concentrated along the in- opinions among researchers regarding historic terface between urban development and patterns of fire frequency, size, and intensity wildlands. However, most of those ignitions (Zedler 1995). This uncertainty can largely be are quickly suppressed unless conditions are attributed to the inherent difficulties associ- conducive for rapid fire spread. Most acres now ated with studying a phenomenon that affects burn in human-caused fires (Davis and large areas, recurs sporadically over time in- Michaelsen 1995; Conard and Weise 1998), tervals that range from a few years to several presumably because these fires can arise at any hundred, and whose individual events vary time and thus have the greatest chance of ig- widely in extent and severity. niting vegetation during key periods when Fire history information provides valuable conditions are prime for fire spread (e.g., dur- insights, but the sources suffer from being (1) ing extended heat waves or when “Santa Ana”

62 Chapter 3 or “sundowner” conditions bring high tem- Studies looking solely at southern Califor- peratures, ultra-low humidity, and high winds). nia fire history records do not support the It is reported that 10 percent of the fires hypothesis that fires have become fewer and in southern California wildlands account for larger. Using fire perimeter maps that extend over 75 percent of the area burned (Strauss et back roughly ninety years, Conard and Weise al. 1989; Keeley et al. 1999). Thus, most ar- (1998), Weise et al. (in press), and Keeley et eas currently burn in large fires. It is unclear al. (1999) did not find statistically significant whether this is a natural, historic pattern or increases in average fire size over the recorded an artifact of fire suppression. Keeley et al. time period. Keeley et al. (1999) also found (1999) analyzed fire history records and found that most southern California counties have that this pattern dates back to at least 1910. had a statistically significant increase in the However, we have no way of knowing if it was number of reported fires per decade. These the pattern prior to the arrival of Europeans. authors conclude that large fires, usually Most of the vegetation that burns in south- fanned by fall Santa Ana weather conditions, ern California is chaparral, which is well have always been a dominant component of known for its tendency to go from being dif- southern California’s fire regime and this has ficult to burn under moderate conditions to not been changed by fire suppression activi- exploding into a fire storm under extreme con- ties. Moritz (1997) came to a similar ditions (P.H. Zedler, Univ. of Wisconsin, in conclusion in a statistical analysis of Los Pa- litt. 1998). Thus, chaparral has characteristics dres National Forest fire history data, but he that make it naturally susceptible to large fires. did detect a significant decline in the frequency However, it also seems evident that fires in of small fires. It is suggested that suppresson today’s environment are able to grow signifi- may actually be helping maintain something cantly in size only when weather and fuel approximating the historic fire regime by neu- moisture conditions are severe enough to limit tralizing the large increase in human-caused the effectiveness of suppression actions. A re- ignitions (Conard and Weise 1998; Keeley et sulting hypothesis is that active suppression al. 1999). has changed the fire regime such that fires are It is likely that these differing findings and now less frequent but likely to be larger in size interpretations each have some merit. It is un- and more severe in intensity. doubtedly true that large fires occurred Support for this hypothesis is found in historically; there is evidence of such fires in comparisons of fire patterns in southern Cali- old charcoal deposits (Byrne et al. 1977), and fornia with those in northern Baja California, the combination of extensive chaparral veg- Mexico, where fires are generally not sup- etation and extreme southern California pressed (Minnich 1983; Chou et al. 1993). weather conditions is conducive to such In a detailed comparison of 1920 to 1970 fire events. It also seems highly probable that fire patterns in San Diego County and northern suppression has helped offset the impact of a Baja based on examination of aerial photo- large increase in the number of fire ignitions. graphs, Minnich (1989) found a similar But there is also compelling evidence that sup- number of acres burned, but the fires in San pression effectively narrows the range of Diego County were significantly fewer and conditions under which fires are allowed to larger. The vegetation patterns on each side of consume vegetation and that the direction of the border were strikingly different, with chap- this narrowing is likely to result in an increase arral habitats in northern Baja exhibiting a in the proportion of high-severity fires. Dem- much more diverse and fine-grained age-class onstrating such a change is difficult because mosaic (Minnich 1989). Minnich attributed there is little quantitative information on the this difference primarily to fire suppression north severity or intensity of historic fires. of the border and lack of suppression south of it.

63 Historically, fires appear to have burned high level of suppression effectiveness in the under a wide range of environmental condi- conifer belt. Ignitions in the forest are not tions, exhibiting erratic smolder-and-run prone to rapid fire spread and thus are quickly behavior patterns as weather and fuel condi- extinguished. In addition, firefighters have tions changed. Unsuppressed, some fires been largely effective at keeping fires that come would continue for months until extinguished up out of the chaparral from moving into the by rain or lack of fuel. The landscape would montane conifer forest interior. experience smoldering burns, punctuated of- It is important to understand how the fire ten by short-duration, high-intensity regime has changed and how those changes afternoon runs and occasionally by large con- are affecting ecological communities. Yet, in flagrations (Minnich 1987b; Minnich 1988). densely populated southern California there Today (and for at least the last fifty years), is little likelihood that we can adopt a policy smoldering fires are actively suppressed and where wildfires are allowed to smolder and run most are quickly extinguished, thereby signifi- at will. There are too many lives, structures, cantly reducing opportunities for and resources that would be put at risk by such short-duration runs. Thus, by effectively re- a strategy. Consequently, we are better served ducing the other burn patterns, suppression by focusing our attention on specific key is- has seemingly increased the likelihood that sues pertaining to fire’s effect on the biota when an area burns, it will do so in a rela- (table 3.1) and exploring the range of options tively fast-moving, high-severity fire. available for addressing those specific issues. There does not appear to be much change in the average return interval of chaparral fires. Fire Issues in Foothill Habitats There is general consensus among experts that There are two primary concerns regard- (1) natural fire-return intervals in chaparral ing the current fire regime’s effect on foothill were probably in the range of fifty to eighty habitats. First, overly frequent fires in coastal years and (2) current fire-return patterns in sage and buckwheat scrub can result in the chaparral appear to be either within or near degradation of these habitat types. Short in- this range across most of the landscape tervals between fires (i.e., less than ten years) (Minnich 1995; Zedler 1995; Conard and can lead to pronounced declines in shrub cover Weise 1998). Fire frequency appears to have and concurrent increases in herbaceous cover, significantly increased only in ignition-prone particularly non-native annual grasses areas near the urban interface, usually where (O’Leary 1990; Zedler et al. 1983). This tends there are high proportions of scrub (i.e., thin- to be a self-perpetuating shift, because dense stemmed, semi-woody shrubs) and grass annual grass cover hinders shrub re-establish- vegetation that facilitate rapid fire spread (fig ment (Minnich and Dezzani 1998) and 3.1). increases the habitat’s flammability, making it It is in montane conifer forests where the more prone to frequent fires (D’Antonio and disappearence of smolder-and-run fires ap- Vitousek 1992). Degradation of coastal sage pears to have markedly decreased fire and buckwheat scrub has been widespread frequency. Fire-scar studies suggest that un- in the “front country” foothills where fires derstory fires were historically common in along the urban interface have been frequent conifer forests, with average return intervals (table 3.2). of fifteen to thirty years (McBride and Lavin There is particular concern about the deg- 1976). However, over the last seventy years, radation of coastal sage scrub because its extent fires have been rare in southern California has already declined by almost 80 percent due montane conifer forests, particularly in inte- to development in the coastal basins and it is rior forest habitats away from the chaparral the primary habitat for the California gnat- interface (fig 3.1). This is probably due to a catcher and other imperiled species (Westman 1981; Davis et al. 1994; Beyers and Wirtz 64 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 eleva- seventeen-year rotations on the Cleveland tions (below 3,000 feet) and most of it occurs National Forest and twelve-year rotations on near the urban interface. The pervasive in- the Angeles National Forest) (Cleveland NF crease in non-native grass cover has increased 1986; Angeles NF 1987). The information the flammability of this vegetation type, such presented above suggests that a different man- that it is often capable of reburning one or agement approach, which emphasizes two years after a fire. Given these characteris- retention of older stands of coastal scrub, may tics, increased management effort will be necessary to achieve desired conditions probably be needed to keep coastal sage from (table 3.3). burning at overly frequent intervals. The second concern in the foothills is the Existing management direction in south- tendency for very large fires (e.g., 10,000 acres ern California Forest Plans calls for or larger) in chaparral-dominated habitats. short-rotation burning to frequently rejuve- There have been a number of these large fires, nate coastal sage scrub habitats (e.g., 65 Table 3.1. Key ecological issues that are influenced by the current fire regime.

Habitats/Species Effects Associated Current Trends and Key Issues Most Affected with Current Fire Regime Areas Most Affected

Overly frequent Coastal sage scrub. ¥ Fires spread rapidly in coastal ¥ Coastal scrub in the habitat disturbance, Bigcone Douglas-fir scrub and an abundance of foothills is being converted leading to a shift in forests. ignitions along the urban to annual grassland in composition and Possibly pinyon-juniper interface can lead to frequent many areas. structure of plant woodlands. reburns. ¥ Extent of bigcone Douglas- communities. ¥ Chaparral fires are fir has declined by 18% in increasingly carrying into San Bernardino Mts. since bigcone Douglas-fir stands, 1930s and is declining which are very slow to recover elsewhere too. from stand-replacing fires. It is ¥ Recent large fires in unclear if the situation is being pinyon-juniper woodlands caused by increased fire may be related to increased intensity or frequency or both. grass cover in desert-side areas.

Overly infrequent Mixed conifer forest. Fires have been effectively ¥ Mesic forests have had habitat disturbance, Ponderosa pine suppressed in montane conifer substantial increases in the leading to a shift in forest. forests, essentially eliminating number of small diameter, composition and understory burns that understory trees. structure of plant historically occurred in these ¥ White fir and incense-cedar communities. forests. This increases the risk have increased in of stand-replacing crown fires, abundance; ponderosa pine although such an event has yet and black oak have to occur in this region. decreased.

particularly in the Los Padres National For- fire appears to be a much greater threat to est, over the last several decades. Whether a chaparral and scrub habitats. change from historic conditions or not, a high incidence of large burns substantially reduces Fire Issues in Lower Montane the structural diversity of chaparral and scrub Habitats habitats and causes high amounts of erosion Recent fire frequencies in lower montane and stream siltation. Large chaparral fires also habitats are similar to patterns in the foothills have the propensity to be self-perpetuating, (table 3.4). This reflects the dominant influ- since they create a continuous block of single- ence of chaparral in both the foothills and age vegetation that becomes ready to burn lower montane region. Studies suggest that again at the same time. most chaparral plant communities are adapted An issue that is not of particular concern to considerable variability in fire frequency and is the potential for chaparral stand senescence are not believed to be adversely affected by or decadence due to the long-term absence of current return intervals (Keeley 1986; Zedler fire. Formerly believed to be a problem, long 1995). fire-free intervals (i.e., seventy to one hundred The primary fire issue in lower montane years) have been found in recent studies not habitats is the apparent loss of bigcone Douglas- to be detrimental to chaparral shrubs (Keeley fir in stand-replacing wildfires. This problem has 1986; Zedler 1995). Many species, in fact, not been thoroughly studied; thus, there is un- continue to produce new stems and even seed- certainty about the amount of loss incurred and lings during long fire-free intervals (Lloret and the reasons for it. Minnich (1999) states that Zedler 1991; Keeley 1992). The potential for stand-replacement fires in the San Bernardino negative effects associated with overly frequent Mountains have resulted in a net decline of 6,016

66 Chapter 3

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.

Cleveland NFSan Bernardino NF Angeles NF Los Padres NF Values are the percent Entire of area meeting the San Santa San San San Castaic S. Los S. Santa N. Santa Foothill described condition Diego Ana Jacinto Bernar- Gabriel Ranges Padres Lucia Lucia Ranges Mts Mts dino Mts Mts Ranges Rng Rng Zone

(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%

Acres of Foothill 540,499 229,344 62,297 72,200 156,603 208,903 637,922 468,623 162,586 2,538,976 Habitat acres of bigcone Douglas-fir or 18 percent of what One thing for certain is that bigcone Dou- was present in 1938. glas-fir forests have been slow to recover from Fires seldom start in bigcone Douglas-fir crown fires and many stands do not appear to stands but rather carry into them from the be recovering at all (Minnich 1978). Chapar- surrounding chaparral (fig. 3.2). Thus, chap- ral invades these sites and for many decades arral fire dynamics strongly influence how the new community will be more likely to these forest patches are affected by fire. Their reburn than the old one—until live oaks again distribution in deep canyons and on steep attain tree stature and shade out the shrubs. north-facing slopes helps limit exposure to fire. Bigcone Douglas-firs are particularly slow to A possible explanation for the recent frequency of stand-replacing fires in bigcone Douglas- fir stands is an increase in the number of Table 3.3. Desired conditions for managing fire in high-intensity chaparral fires, which are more foothill habitats of special concern. likely to carry into forest patches. There is not adequate fire-intensity data to determine if this Coastal Sage Scrub: Fire-free intervals of is indeed the case. It is considered plausible sufficient length (twenty-five years or more) to because of the current tendency for fires to allow this vegetation type to reach structural escape rapid control only when conditions are maturity and remain there for an extended period severe, and because urban interface ignitions of time. This would promote increased shrub cover may result in more base-of-the-mountain fires and provide higher quality habitat for at-risk that are prone to high-intensity runs up steep species associated with coastal sage scrub (e.g., lower montane slopes. California gnatcatcher).

67 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.

Cleveland NFSan Bernardino NF Angeles NF Los Padres NF Values are the percent Entire of area meeting the San Santa San San San Castaic S. Los S. Santa N. Santa Lower described condition Diego Ana Jacinto Bernar- Gabriel Ranges Padres Lucia Lucia Montane Ranges Mts Mts dino Mts Mts Ranges Rng Rng

(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%

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

return when there are no surviving seed trees Fire Issues in Montane Conifer nearby (Weatherspoon et al. 1992). Habitats Coulter pine forests also occur mainly in The widespread and prolonged absence lower montane areas but do not appear to be of fire is a concern in montane conifer forests as adversely affected by the current fire regime. (table 3.6). Fire-scar studies suggest that mod- Coulter pine regenerates extremely well after erate intensity fires (i.e., hot enough to scar fire (Vale 1979; Borchert 1985), but it requires but not kill most mature trees) historically fire-free intervals of approximately sixty to sev- occurred every fifteen to thirty years (McBride enty-five years for adequate seed crops to and Lavin 1976). However, over the last ninety develop (table 3.5). Thus, Coulter pine can years understory fires have been virtually be negatively affected by frequent reburns or eliminated from large areas, particularly in by extremely long intervals without fire. This interior forest areas. The result is denser stands may be a problem in localized areas (M. and a dramatic increase in the number of un- Borchert, Los Padres NF, pers. comm.), but derstory trees (Minnich et al. 1995). The overall fire frequency in lower montane land- concern is that this increase in stand density scapes does not appear to be outside the and fuel loading makes the forests more sus- historic range of variability. ceptible to large, stand-replacing crown fires (table 3.7). Using data on precipitation, elevation, slope, stand density, and fire history, we de- veloped a model to predictively map areas at risk to stand densification. Almost 30 percent

68 Chapter 3

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

(108,500 acres) of mixed conifer and pine terrain and extreme winds (e.g., the 1980 stands in the assessment area were predicted Thunder Fire in the San Gabriel Mountains) to be experiencing this problem (see fig. 2.17 (R. Hawkins, Cleveland NF, pers. comm.); or in chapter 2). (2) took place in forest stands that were sur- Over the last fifty years, there have been rounded and interspersed with mature very few “forest” fires in southern California’s chaparral that facilitated the spread of high- montane conifer region. Those that have oc- intensity fires into them (e.g., the 1950 curred were either (1) driven primarily by steep Conejos and 1970 Laguna fires in the Cuyamaca and Laguna mountains, the 1970 Table 3.5. Desired conditions for managing fire in Bear Fire in the San Bernardino Mountains). lower montane habitats of special concern. There seem to be few instances where the se- verity of these fires was attributed primarily Bigcone Douglas-Fir/Canyon Live Oak: Minimal to increased fuel loads in overcrowded forests. occurrence of high-severity crown fires in these However, events in other areas give cause forest stands. This is needed to maintain or for concern. On the Boise National Forest in increase the distribution and extent of this forest Idaho, many years of near-complete fire ex- type which has recently been declining. clusion came to an abrupt end when a series of intense crown fires from 1986 to 1995 con- Coulter Pine: Fire return intervals of sumed 45 percent of the area’s ponderosa pine approximately 60 to 75 years are desired in this forest (Weiland 1996). The severity of these forest type, which requires fire for regeneration. At fires was attributed to excessive fuel loading maturity, stands should be fairly open (40% to 60% resulting from the prolonged absence of fire. canopy closure) with trees reaching 20 inches Similar large and unusually intense stand- diameter at breast height (dbh). replacing wildfires have occurred in recent

69 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. Cleveland NFSan Bernardino NF Angeles NF Los Padres NF Values are the percent Entire of area meeting the San Santa San San San Castaic S. Los S. Santa N. Santa Montane described condition Diego Ana Jacinto Bernar- Gabriel Ranges Padres Lucia Lucia Conifer Ranges Mts Mts dino Mts Mts Ranges Rng Rng

(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%

Acres of Montane 49,467 0 55,749 202,112 105,681 1,748 96,544 0 0 511,301 Conifer Habitat

years in the Sierra Nevada and the mountains pears to be a significant factor in historic fire of northern Arizona. frequencies. A high occurrence of multiple fires At higher elevations, subalpine forests on the desert side of the San Jacinto Moun- dominated by lodgepole pine (Pinus contorta) tains (table 3.8) appears to be concentrated in typically do not carry fire well. In a study of the vicinity of Beaumont and Palm Springs fire patterns in lodgepole pine forests of the (fig. 3.1). The most remote desert-montane ar- San Jacinto Mountains, lightning-caused fires eas (i.e., the southern Los Padres ranges around occurred every few years but were typically Mount Pinos and the extreme northeastern cor- small (less than 20 acres) and of low intensity ner of the San Bernardino Mountains) have had (Sheppard and Lassoie 1998). This fire regime very little fire history (fig. 3.1). appears to be within the natural range of vari- Vegetation type is also a factor in fire- ability and not substantially influenced by fire return intervals, with fires being more frequent suppression activities. in desert chaparral and scrub than in pinyon- juniper woodlands. The sparse understories and open canopies typical of pinyon-juniper woodlands translate into long fire-free peri- Fire Issues in Desert-Montane ods. A study of these woodlands in the San Habitats Bernardino Mountains estimated that the av- Fires have historically been infrequent in erage fire-return interval was 480 years sparsely vegetated desert-side habitats and, for (Wangler and Minnich 1996). The authors the most part, this continues to be the case concluded that twentieth-century fire suppres- (table 3.8). Proximity to urbanized areas ap- sion has had little effect on this vegetation type.

70 Chapter 3

Table 3.7. Desired conditions for managing or Fire Management Considerations mimicking fire regimes in montane conifer forests. Options for managing fire or mimicking its ecological function fall into three general Forest stands with understory species ratios categories: (1) prescribed burning where a fire that are similar to the current overstory is intentionally set under controlled condi- species composition. The emphasis is on tions; (2) fuels treatments where vegetation is arresting encroachment of shade-tolerant white fir manually or mechanically cut to reduce fire and incense-cedar and providing opportunities for hazard or mimick an effect that fire would pine and black oak regeneration. have; and (3) wildfire suppression strategies, which include confine-and-contain ap- Landscape patterns that are resilient to large proaches where an unplanned or natural crown fires. Forest thickening and fuel continuity ignition is allowed to burn within a predefined problems must be addressed at a landscape scale containment area. The potential opportuni- (e.g., watersheds) to avoid large stand-replacing ties and barriers associated with these fires. Understory fires (or thinning) should occur in approaches are summarized in table 3.10. each forest stand at twenty to forty year intervals. The defensible fuel profile is a fuels treat- Some overstory kill during these events (2% to 4% ment option that is being considered of the stand) is desirable to create small openings throughout the western United States for re- for pine and oak regeneration. Under existing ducing crown-fire hazards in conifer forests. conditions, heavy fuels create a high potential for forest fires that kill a much larger fraction of the A defensible fuel profile zone (DFPZ) is de- overstory. fined by Olson (1993) as a “low-density, low-fuel zone averaging 0.4 km (0.25 mi.) in A continuous and well distributed supply of width, located mostly along roads and de- large trees. Large trees are both highly signed to support suppression activities.” characteristic of pre-suppression forests and vital DFPZs can be likened to shaded fuel breaks, to many wildlife species. They have declined in only on a larger scale. The focus of DFPZs is number over the last fifty years and are threatened to break up fuel continuity over landscapes. A further by stand thickening and crown fire risk. network of DFPZs is expected to do several things: (1) reduce wildfire severity in treated areas; (2) create broad zones where suppres- However, Wangler and Minnich’s (1996) sion efforts can be conducted safely and study looked at fire patterns up to 1983. Since effectively; (3) effectively break up continuity that time, there have been several large fires in of fuels; and 4) become anchor lines for fur- pinyon-juniper woodlands on the north end ther areawide fuel treatments. of the San Bernardino Mountains. This has According to Weatherspoon and Skinner led to speculation that increases in non- (1996) and Olson (1993), DFPZs should be native grass cover (e.g., cheatgrass), combined placed primarily on ridges and upper south with increased ignition sources associated with and west slopes. Where possible they should the rapidly growing human populations just also coincide with existing roads to simplify north of the mountains (i.e., Hesperia, Apple construction and maintenance and to facili- Valley, and Victorville) could be facilitating tate their use by suppression forces. This fire spread in these woodlands. The hypoth- treatment will result in a fairly open stand, esis is that this problem would only be present which is dominated by large trees of fire- after particularly wet winters, when grass cover tolerant species. Post-treatment canopy closure reaches its peak. This issue needs further study. is recommended to be no more than 40 per- Pinyon woodlands are extremely slow to re- cent. One of the key features of this is the generate; thus, an acceleration in fire return general openness and discontinuity of crown intervals would be of concern (table 3.9). fuels (horizontal and vertical) to produce a very

71 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.

Cleveland NFSan Bernardino NF Angeles NF Los Padres NF Values are the percent Entire of area meeting the San Santa San San San Castaic S. Los S. Santa N. Santa Desert described condition Diego Ana Jacinto Bernar- Gabriel Ranges Padres Lucia Lucia Side Ranges Mts Mts dino Mts Mts Ranges Rng Rng

(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%

Acres of Desert- 78,406 0 110,135 134,468 88,560 61,092 418,145 0 0 1,713,167 Side Habitat

low probability of sustained crown fire. The Influence of Water: Conard and Weise (1998) propose similar fuel Hydrology, Regulation, and management zones in southern California Withdrawal chaparral habitats. The flow of water, both on the land sur- face 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 Table 3.9. Desired conditions for managing fire in greatly influence the structure and composi- desert montane habitats of special concern. tion of ecological communities found in the Pinyon-Juniper Woodlands: Long fire-free channel and floodplain. Groundwater fluctua- intervals (one hundred to three hundred years) to tions have a similar effect on communities allow this vegetation type to reach structural associated with springs, seeps, and ephemeral maturity and remain there for an extended period water bodies. of time. Pinyon-juniper woodlands recover very Southern California is an arid region where slowly from crown fires. the human demand for fresh water greatly ex- ceeds the natural supply. Consequently, all of

72 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 ¥ Understory burns to thin ¥ Selective timber harvests Confine and contain forest stands. to thin the forest understory. strategies allow unplanned ¥ Chaparral burning to ¥ Fuel breaks or defensible ignitions occurring under manage fire frequency fuel profiles to increase desirable conditions to burn and intensity. ability to control wildfires. within defined containment boundaries.

Treatment Moderate. Considerable Low. High cost per unit Moderate. Low cost per unit Potential preparatory work is often area; requires accessible area, but is feasible only in (acres per year) required. Most efficient in locations. remote areas where life or areas far removed from property is not at risk. buildings.

Effectiveness in Moderate. Only very low High. Can be done in areas Not an option near and around intensity fires can usually be where burning is too risky. developed areas; The risk Developed Areas prescribed near developed of property damage is too areas. high.

Environmental ¥ Complexities of keeping ¥ Forest thinning is not cost ¥ Limited to areas where the Barriers to fire on the wildland side of effective on steep slopes risk to life and property are Implementation the urban/wildland or in areas that lack road very low. interface. access. ¥ Air quality considerations ¥ In forests, high fuel ¥ Fuel breaks require may also limit this option. buildups now make it maintenance and can have difficult to underburn in environmental impacts. many stands. ¥ Air quality regulations limit when burning can be done.

Institutional ¥ Inadequate funding. ¥ Lack of viable commercial ¥ Need change in Forest Barriers to Need authority to use markets for small-diameter Plan direction Implementation suppression money to trees. ¥ Requires change in fund this work. ¥ Inadequate funding. Need attitudes towards ¥ Lack of institutional authority to use suppression suppression — immediate incentives to burn. money to fund fuels control is not always the ¥ Liability risks are a major reduction work. desired objective. disincentive to burning. ¥ Liability risks the major streams that originate in the moun- timate that 95 to 97 percent of riparian habi- tains contain dams or diversions at some point tat in southern California floodplain areas has along them. In addition, many small streams been eliminated. In addition, much of what and springs are dammed or diverted, both for remains must function under a highly modi- water supply and flood control. Subsurface fied hydrologic regime with upstream dams waters are also heavily tapped. Yet this still does regulating streamflows. Clearly no other land- not come close to meeting the needs of the scape feature has been so drastically altered by region’s human population, so large quanti- human activities as has freshwater habitat. ties of water are imported into the area from The presence of dams and diversions on northern California and the Colorado River. most of the region’s major streams (fig. 3.3) The result is a dramatic reduction in the has greatly altered aquatic and riparian extent and distribution of native freshwater habitats and reduced the capability of these habitats in this region. Faber et al. (1989) es- 73 habitats to support native species (table 3.11). of miles of habitat degraded) is downstream. However, the importance of these structures By retaining all or part of flood flows, or modi- in preserving domestic water supplies and con- fying the shape of the discharge curve, dams trolling downstream flooding ensure that tend to rob the drainage below of the hydrau- most, if not all, are here to stay. Recognizing lic forces necessary to maintain a natural form. that their continued presence is necessary, Sweet (1992) illustrates the downstream there are important factors in the operation effect of dams by comparing the Santa Ynez of major dams and diversions that significantly River below Gibraltar Dam (completed in affect native habitats and species. 1921) with Piru Creek below Pyramid Dam (completed in 1973). Most of the regulated streams within the assessment area resemble The Effect of Dams and Water one of these two downstream patterns: Release Regimes After 70 years, the affected section Dams destroy riparian habitat directly by of the Santa Ynez River is characterized inundation, but their greater effect (in terms by a near-total lack of sand and fine

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.

74 Chapter 3

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

Effects Associated Habitats/Species with Water Storage, Current Trends and Key Issues Most Affected Control and Withdrawal Areas Most Affected

Declines in habitat Aquatic and riparian Dams and diversions Most large streams have capability caused by habitats below dams dramatically alter flow regimes. been dammed or diverted major changes in the and diversions. Water releases below dams, if for many years and will volume, duration, they occur at all, tend to be remain so. Efforts are timing, and variability either “high volume, short ongoing in some areas to of stream flows. duration,” or “continuous low establish release schedules volume,” neither of which that more closely mimic resemble historic patterns. historic flow regimes. Downstream transport of sediment is also curtailed by dams, resulting in channel downcutting over time.

Establishment and Aquatic and Reservoirs, both large and Streams downstream of spread of invasive, riparian species. small, tend to be dominated by reservoirs tend to be most non-native species. non-native flora and fauna. affected. These serve as points of spread into nearby native habitats.

Reductions in ¥ Wet meadows Withdrawals of sub-surface The popularity of bottled surface water flows. ¥ Aquatic and riparian water (i.e., spring- and ground- mountain spring water is habitats water extraction) can lower the leading to an increase in water table and reduce extractions, particularly on availability at the surface. private lands in the mountains.

gravel, and by a succession of very deep ture. As on the Santa Ynez River the sand scour pools floored with boulders and deposits are disappearing from the seg- mud. There are no sandy levees, only ment between Frenchman Flat and the cobble bars, and several oak terraces are dam, and the creek has acquired a deep being eroded as the channel moves lat- and boulder-filled channel. Unlike the erally. Little if any arroyo toad habitat Santa Ynez, large tributaries join Piru remains in the first 4 stream miles be- Creek within a few miles below Pyra- low the dam, and only marginal habitat mid Dam and restore part of its sediment below this as a consequence of the scar- load. There is a second difference in that city and small size of tributary canyons Pyramid Dam releases 10-25 cfs which can supply the sediment and flood throughout the summer and early fall, discharge needed to maintain the sys- resulting in the development of a very tem.... Gibraltar Dam appears to have dense riparian corridor which is pro- rendered the entirety of the downstream tected from flood scouring. This length of the Santa Ynez river on the vegetation effectively channelizes the LPNF uninhabitable for arroyo toads. creek, and has transformed it into a habi- Pyramid Dam has been affecting tat quite unsuitable for most native aquatic lower Piru Creek for less than 20 years, and riparian species. (Sweet 1992, pg 154) and presents a somewhat different pic- 75 The timing and duration of water releases releases) on a site-specific basis. In particular, from reservoirs can greatly influence down- efforts should be made to limit the practice of stream habitats. Large, sudden releases of rapid, large changes in the volume of spring water, particularly in the summer months, can and summer water releases. quickly scour away a whole year’s reproduc- tive effort for native species such as arroyo toad, red-legged frog, pond turtle, and Cali- The Influence of Invasive, fornia newt. Conversely, low-level year-round Non-Native Species flow regimes facilitate the spread of exotic predators (e.g., bullfrogs, sunfish, bass, blue- The spread of non-native species that dis- gill, catfish, and Asian clams) into downstream place, prey upon, or otherwise harm native areas that historically would have gone dry in species is a major problem in both aquatic and late summer (Sweet 1992). Neither of these terrestrial habitats. Alternately referred to as water release schedules is similar to historic “exotic,” “alien,” or “non-indigenous” species, flow conditions. the alarming consequences of their invasion The historic flow pattern in southern Cali- on the capability of habitats to support native fornia streams reflects the region’s climate of species is becoming increasingly recognized long, dry summers and short, wet winters. (Dudley and Collins 1995; Quammen 1998). Thus, flows would peak in the winter and early Survival and reproductive success are greatly spring and decline dramatically in the sum- affected by predation and competition for lim- mer months, where in many cases they would ited resources (e.g., food and breeding sites). dry up in the uppermost and lowermost Introductions of new species, particularly reaches (Faber et al. 1989). The high variabil- highly successful or predatory ones, can dra- ity of runoff and precipitation in southern matically decrease the ability of some native California also produced large flood events, species to survive and reproduce in what oth- which periodically scoured channels and re- erwise would be suitable habitat (table 3.12). distributed sediment. In a statewide survey of non-indigenous There is little ability to recreate large flood species, Dudley and Collins (1995) concluded events, and the sediment transport that comes that the South Coast Bioregion was particu- with them, below existing dams (fig. 3.4). Yet larly hard hit, with more non-native species in some drainages, rather minor changes in than any other California bioregion. To better the management of water releases could greatly improve habitat capability for species of con- Figure 3.4. Sutherland Dam on Santa Ysabel Creek cern. On Piru Creek, spring and summer in the Cleveland National Forest is typical of discharges from Pyramid Lake used to fluctu- impoundments in the assessment area. Water from ate on a daily or weekly basis from zero to 150 Sutherland is released downstream only in high cubic feet per second (cfs) and arroyo toad rainfall years when the lake level rises to the spillway clutches and larvae were often stranded or height. GENA CALCARONE swept away. In 1992, a shift to constant re- leases 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

76 Chapter 3

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

Effects Associated Habitats/Species with the Spread of Non- Current Trends and Key Issues Most Affected Native Species Areas Most Affected

Shifts in composition ¥ Riparian habitats ¥ Arundo, tamarisk, and other Arundo is spreading rapidly and structure of plant ¥ Grasslands successful non-natives can in many low-elevation communities. ¥ Coastal scrub dramatically alter the streams. Efforts to control or composition and structure of eradicate it are ongoing in riparian habitats. several areas and have ¥ Non-native grasses and forbs been successful, but where have come to dominate many uncontrolled it is increasing. grassland and coastal scrub Tamarisk is present in many habitats, displacing native foothill streams, but does not species. seem to be spreading rapidly in most of them, particularly if stream channel is rocky.

Declines in survival ¥ Red-legged frog Predation and competition by ¥ Aquatic non-native species rates of native ¥ Yellow-legged aquatic non-natives (bullfrogs, are well established in animals that breed frogs (mtn & fthill) African clawed frogs, bass, many streams; those below in aquatic habitats. ¥ Arroyo toad sunfish, bluegill, brown trout, reservoirs are particularly ¥ Santa Ana sucker bullhead, and crayfish) can prone to infestation. ¥ SA speckled dace cause steep declines in survival ¥ Some targeted control rates. efforts have recently been initiated

Declines in ¥ Least Bell’s vireo ¥ Cowbirds parasitize the nests ¥ Aggressive cowbird control reproductive success ¥ Willow flycatcher of many bird species across so. CA has helped of native animals ¥ Riparian birds ¥ Non-native frogs and fish increase Bell’s vireo ¥ CA gnatcatcher consume egg masses and numbers ¥ Native fish and young of native amphibians ¥ Most native fish and amphibians and fish amphibians are declining ¥ Purple martins ¥ European starlings displace native cavity nesters

Shifts in composition ¥ Coast horned lizard Argentine ants and red Argentine ants appear to be of invertebrate fauna. ¥ Habitats along the imported fire ants displace spreading, particularly in urban interface native ants and other habitat fragments and in invertebrates in areas near the riparian areas. Red urban or agricultural interface. imported fire ants have just Native ants are the primary appeared in southern CA, food of coast horned lizards so it is too early to say how and arroyo toad. far and fast they will spread. document the extent of this problem in the known about the distribution of exotic pest assessment area, we developed a database that species. However, it does not allow us to con- compiles occurrences of the most problematic, clusively say where they do not occur; areas non-native species by stream or watershed. may lack observations of these species simply Many of these species are associated with ri- because thorough surveys have not been con- parian habitats and thus their presence or ducted. Also, in most areas where we know an absence on individual streams is important to exotic species is present, we lack accurate in- consider when assessing overall habitat capa- formation on the extent of the infestation. bility. The database (displayed in appendix C) These are important information needs. provides a good snapshot of what is currently 77 Non-Native Forest Pathogens are both invasive and damaging to natural eco- The pitch canker fungus, Fusarium systems. The California Exotic Pest Plant subglutinans ssp. pini (also called Fusarium Council (CalEPPC 1996) has developed a list circinatum), is established in native and planted of seventy-six exotic plants known to be in- Monterey, knobcone, and bishop pines from vading native ecosystems and plant Mendocino County south. This fungal patho- communities. These species can cause ecologic gen is native to the southeast United States. and economic damage by changing the natu- Although there appears to be some natural re- ral processes associated with succession, sistance in the Monterey pine population (gene nutrient cycling, hydrology, substrate stabil- pool), it is predicted that 25 percent of the ity, soil chemistry, or the frequency and Monterey pines in infested stands will be killed intensity of wildfires (Randall et al. 1998; by the fungus. Because the disease is new to D’Antonio and Haubensak 1998). Many of the West Coast it is not known how many these species outcompete native plants, other pine species will be similarly affected. thereby changing the composition and struc- Several pine species and Douglas-fir are capable ture of ecological communities and sometimes of being infected by the fungus (Dallara et al. reducing the quality of forage and cover for 1995), but it may be rare for some of these wildlife. Non-native plants can also hybridize species to develop the disease. Pines native to with related native species [e.g., the non- southern California which may be at risk in- native dandelion (Taraxacum officinale) is hy- clude bishop pine (Pinus muricata), Coulter bridizing with California dandelion (T. pine (P. coulteri), gray or foothill pine (P. californicum) in montane meadows]. sabiniana), knobcone pine (P. attenuata), Probably because many non-native plants Monterey-knobcone cross, ponderosa pine (P. first became established in coastal areas of ponderosa), lodgepole pine (P. contorta), and California (i.e., in and around ports, missions, Torrey pine (P. torreyana) (Dallara et al. 1995). and early settlements), their numbers tend to Even with resistant genes, re-establishing a for- decline with increasing elevation and increas- est is an expensive and slow process, and ing distance from the coast. A relatively low survival of other plant, wildlife, and micro- number of exotic plants (approximately bial species dependent on the affected conifers twenty-five) have invaded the desert areas of could be threatened by the disease. southeastern California (Kemp and Brooks Unfortunately, pitch canker is probably 1998). High levels of disturbance and habitat only the first of many exotic pests of native modification tend to favor a non-native flora. trees which will profoundly affect southern For example, powerline right-of-ways that run California forests. Despite restrictions on im- through intact vegetation in southern Cali- portation of raw wood products, increasing fornia have been shown to be points-of-entry trade and movement of people have increased for several exotic species, including black mus- the probability of the inadvertent or deliber- tard (Brassica nigra) and ripgut brome (Bromus ate introduction of pest species. One pathogen diandrus) (D’Antonio and Haubensak 1998). expected to appear soon in southern Califor- In addition, hydrologic changes to streams nia forests is white pine blister rust brought on by dams and diversions appear to (Cronartium ribicola), which affects sugar pine. reduce the ability of native riparian plants to survive, creating conditions that promote the Invasive, Non-Native Plants establishment of exotic species. Over one thousand non-native plants have CalEPPC’s Exotic Pest Plants of Greatest become naturalized in California wildlands Ecological Concern list (1996) is divided into since the late 1700s when European settlement several categories based on level of invasiveness began (Randall et al. 1998). Some of these and distribution. The non-native plants consid- plants have caused little impact, while others ered to be of particular concern in our assessment area are addressed individually below. 78 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 Cali- fornia 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., road- sides) or where there is a shallow water table (fig. 3.5). Within the assessment area arundo occurs Figure 3.5. Arundo donax forms dense thickets like in foothill areas, primarily along large streams this one along Santa Ysabel Creek in San Pasqual but also in other areas where there is pooled Valley, San Diego County. GENA CALCARONE water. It reaches peak abundance downstream of the assessment area along major rivers in provide neither food nor cover for most na- the coastal basins. The Ventura, Santa Clara, tive species of wildlife (Bell 1999; Reiger and Santa Ana, Santa Margarita, San Luis Rey, and Kreager 1989). Only a small number of bird San Diego river systems are particularly in- species have been observed using arundo for fested. Arundo has generally not spread into nest sites and dramatic reductions (50 percent the mountains or up the steep, narrow can- or more) in the abundance and diversity of yons that characterize lower montane areas. It invertebrates were documented in arundo apparently is restricted to low elevations (pri- thickets compared with those found in native marily below 2,000 feet according to Hickman willow/cottonwood vegetation (Dudley 1993) and requires well developed soils to 1998). Arundo also provides less shade in ri- become established. We have documented the parian areas when compared to native presence of arundo in fifty drainages within vegetation, causing increased water tempera- the assessment area. tures and lower oxygen concentrations, which We briefly describe the effects of arundo in turn negatively affect fish and other aquatic here, but see Bell (1999) for a thorough re- animals (Kan 1998). view of arundo’s impacts in southern Arundo thickets are highly flammable and California streams. Arundo tends to have a known to carry wildfire up and down ripar- competitive advantage in riparian areas where ian corridors (Scott 1994; D’Antonio and there is a modified hydrologic regime. It has Haubensak 1998). In recent years there have rapid growth rates; in a comparison between been a significant number of fires fueled by arundo and two willow species (Salix goodingii arundo in the Prado Dam area and along the and S. laevigata), arundo grew 2.1 to 4.9 times Santa Ana River (J. Wright, Riverside County faster (Rieger and Kreager 1989). Arundo can Fire Dept., pers. comm.). The most recent reportedly reach heights of 8 to 13 feet in less occurred in 1998 when an intense wildfire than one growing season. This rapid growth threatened to burn homes in the Santa Ana is sustained by the consumption of prodigious River drainage. Firefighting in arundo thick- amounts of water—as much as 2,000 liters per ets is proving to be a significant drain on fire meter of standing arundo (Iverson 1994)— management resources (J. Wright, Riverside and causes a decline in the availability of County Fire Dept., pers. comm.; R. Hawkins, surface water. Cleveland NF, pers. comm.). Once established, the reed often forms A number of private and public organiza- monocultural stands that physically inhibit the tions (including the U.S. Forest Service) have growth of other plant species. These stands formed alliances (Team Arundo) to coordinate 79 efforts in controlling the spread of this tree produces enormous quantities of seed species. Considerable progress has been made which are dispersed by wind and water in the refinement of techniques for effective (Schierenbeck et al. 1998; Johnson 1987). arundo eradication (Lawson 1998; Nickerman Tamarisk is documented in at least sixty 1999). drainages in the assessment area. It appears to spread most aggressively in foothill and desert Tamarisk or Salt Cedar (Tamarix spp.) streams with deep alluvial channels (e.g., ar- Tamarisk is widely distributed in south- royos). It occurs in a number of lower montane ern California, in both coastal and desert-side drainages as well, but seems to spread slowly drainages. There are at least four different spe- in narrow bedrock channels. cies of tamarisk invading native riparian habitat in the assessment area: Tamarix Brooms chinensis, T. gallica, T. parviflora, and T. Three weedy species of European broom ramosissima. have become naturalized in California. These Tamarisk has the ability to uptake large plants are members of the legume family that quantities of water from the soil, effectively were introduced into the state as ornamentals lowering the water table and reducing the and have since escaped into native habitats. amount of available surface water. One ma- Now well established in our study area, these ture tree can reportedly absorb upwards of 200 shrubs have proven to be very difficult and gallons of water per day (Johnson 1987). In expensive to eradicate. some areas, tamarisk has reduced or eliminated Of the three brooms, French broom water supplies for bighorn sheep, pupfish, sala- (Genista monspessulana) is the most wide- manders, and desert palm groves (Johnson spread. It ranges from northern California 1987). south to San Diego County and east to San Tamarisk also provides poor forage and Bernardino County (McClintock 1985). In nesting sites for wildlife. The scale-like leaves the assessment area, it is reported below 1,700 are unpalatable to grazers and, in one study feet in the Santa Lucia Ranges, southern Los done by Bertin Anderson and Robert Ohmart Padres region, and San Diego region. It has of Arizona State University, birds were shown been found in coastal scrub, grasslands, oak to favor native riparian vegetation over tama- woodlands, and the understory of Santa Lucia risk at a ratio of approximately 38:1 (Johnson fir forests. The Jepson Manual reports the spe- 1987). Tamarisk is often called salt cedar be- cies to be toxic to both humans and livestock cause it exudes salts from its leaves. These salts (Hickman 1993). accumulate in the soil, making the area less Scotch broom (Cytisus scoparius) occurs hospitable to native plants. primarily in northern and central California Tamarisk appears to be most successful in (including Monterey County) where it grows drainages with unnatural or reduced flow re- up to 3,300 feet (McClintock 1985). Occur- gimes, such as those containing dams or rences are also reported further south, in the diversions (D’Antonio and Haubensak 1998). interior valleys of Los Angeles, San Bernar- Robert Ohmart of the Center for Environ- dino, Riverside, and Orange counties. The mental Studies at Arizona State University species is not as aggressive as French broom; believes that tamarisk is not displacing cot- however, it is beginning to invade chaparral tonwoods but actually replacing them in areas and lower montane habitats in the San Ber- now incapable of supporting a native riparian nardino Mountains (E. Allen, UC Riverside, vegetation. in litt. 1998). Because the species is sometimes planted Spanish broom (Spartium junceum) is dis- as an ornamental on private lands, invasions tributed from northern California to San into riparian habitat are likely to continue. The Diego County but is less widespread than the

80 Chapter 3 other brooms. In the assessment area it is most (Avena barbata), wild oat (A. fatua), and cul- prevalent below 2,000 feet in the Santa Lucia tivated oat (A. sativa). All three are highly Ranges, southern Los Padres region, Castaic successful in disturbed areas. region, and the interior valleys of Los Ange- Red brome (Bromus madritensis ssp. les, San Bernardino, Riverside, and Orange rubens) is known to carry fire in areas below counties. This species primarily occupies dis- approximately 3,200 feet in the San Bernar- turbed areas and is not as invasive in native dino and San Jacinto mountains (R. Minnich, habitats (McClintock 1985). UC Riverside, pers. comm.). Red brome, oats, barley (Hordeum spp.), and foxtail fescue Knapweeds and Star Thistle (Vulpia myuros) have invaded coastal sage (Centaurea spp.) scrub and chamise chaparral in many areas. The genus Centaurea contains many in- These invasions have led to increased fire fre- vasive weeds including yellow star-thistle (C. quencies and type conversion of solstitialis) and spotted knapweed (C. shrub-dominated habitats to grassland maculosa). Yellow star-thistle is one of the most (Minnich and Dezzani 1998). pervasive weeds in California, occupying pas- The primary distribution of red brome tures, roadsides, and disturbed grasslands or occurs east of the assessment area in the woodlands below approximately 4,300 feet. Mojave and Sonoran deserts, where it has the The Jepson Manual reports yellow star-thistle ability to invade intact native habitats. Red as cumulatively toxic to horses (Hickman brome is also prevalent in the Cuyama Valley 1993). (J. O’Hare, Angeles NF, pers, comm.). The Spotted knapweed is widespread in Cali- grass spreads rapidly in wet years, and studies fornia, occurring in disturbed areas up to have indicated that repeated fires fueled by 6,600 feet (Hickman 1993). The biennial spe- this grass have occurred in places where fire cies is reported in the assessment area in the was previously rare (D’Antonio and southern Peninsular Ranges. Its early spring Haubensak 1998; Kemp and Brooks 1998). growth makes spotted knapweed very com- While fires fueled by red brome are periodic petitive for soil moisture and nutrients. The (depending on rainfall patterns), their cumu- species tends to thrive under agricultural con- lative effect over time is expected to alter native ditions and is listed as a “noxious weed” by vegetation. both state and federal governments. Cheatgrass (Bromus tectorum) is distrib- uted primarily in the Great Basin, Mojave Mediterranean Grasses Desert, and Sonoran Desert. However, it is Grasses account for the greatest number also found within the assessment area, prima- (181) of non-native plants in California. Over rily on desert-facing slopes around Mount 40 percent of grasses in the state are exotic Pinos and in the San Gabriel, San Bernardino, and now dominate vast areas of California’s San Jacinto, and Laguna mountains. It has in- grasslands and savannas (Randall et al. 1998). vaded a variety of mainly arid habitats, Some of these grasses have become especially including pinyon-juniper woodlands, yellow problematic, outcompeting native perennial pine and mixed conifer forests, montane chap- bunchgrasses and hardwood seedlings. The arral, and pebble plains (M. Lardner, San most widespread grasses are the Mediterranean Bernardino NF, pers. comm.). annuals, which include the oats, bromes, and Like red brome, cheatgrass has the ability to barleys. They are well established in the as- invade pristine habitats. However, occurrences sessment area and it is unlikely they could ever of cheatgrass in the assessment area are sparser be eradicated on a broad scale. and distributed at higher elevations than red All oat species are non-native. Three oc- brome. Where abundant, cheatgrass is known cur in the assessment area: slender wild oat to cause increased fire frequencies (D’Antonio

81 and Haubensak 1998), but there is little evidence founding habitat degradation with the exotic to suggest that this is currently a problem in the predators as the primary source of native am- assessment area (R. Minnich, UC Riverside, phibian declines. However, observations of pers. comm.). successful breeding activity by native amphib- Ripgut brome is distributed widely in the ians in extremely modified breeding sites that assessment area. It forms a dense understory were free of exotics supports the interpreta- in open ponderosa pine forest near Lake Gre- tion that the exotic species themselves are an gory, west of Lake Arrowhead in the San important problem (Fisher and Shaffer 1996; Bernardino Mountains. At this location the Kiesecker and Blaustein 1997). grass poses a fire threat and appears to be in- Table 3.13 lists the principal non-native hibiting conifer recruitment (R. Minnich, UC animals that are considered to be a problem Riverside, pers. comm.). in southern California. The ones considered to be most problematic within the assessment Pampas Grasses area are described below. Two species of pampas grass have been introduced in California. Cortaderia selloana, Bullfrog (Rana catesbeiana) native to Argentina and southern Brazil, sel- Bullfrogs are strongly implicated in the dom spreads from where it is planted. It often decline of many native amphibians and aquatic is cultivated as a lawn ornamental in warmer reptiles (Schwalbe and Rosen 1988; Jennings areas. In the past, it was planted by the Soil and Hayes 1994). First introduced into Cali- Conservation Service for supplemental dry- fornia in 1896 (Jennings and Hayes 1985), land pasture in Ventura and Los Angeles they have progressively spread over much of counties (Hitchcock and Chase 1971). the state and today occur in most suitable Andean pampas grass (Cortaderia jubata), streams and water bodies west of the Sierra native to Bolivia, Peru, and Ecuador, is very Nevada Mountains and southern deserts invasive. It was originally introduced for land- (Stebbins 1972). They are an effective preda- scaping and by the 1960s was spreading into tor of amphibians and aquatic reptiles, intact native ecosystems (e.g., redwood for- including California red-legged frogs (Bury est) in coastal areas of California (Kerbavaz and Luckenbach 1976; Hayes and Jennings 1985). Now considered a major weed, the spe- 1986), arroyo toads (Sweet 1992), western cies is very difficult to eradicate. In the pond turtles (Holland 1994) (fig 3.6), and assessment area, Andean pampas grass is es- two-striped garter snakes (Sweet 1992). Re- pecially problematic along the coast of cently in San Mateo Creek, a single bullfrog was Monterey County, where it frequently occu- found to have three adult arroyo toads in its stom- pies road cuts, cliff habitat, and hillsides. The ach (P. Griffith, UC San Diego, pers. comm.). species is susceptible to frost, however, and Bullfrogs have a competitive advantage over may remain naturally restricted to milder cli- native frogs and toads because of their large size, mates near the coast. generalized food habits, extended breeding sea- son which allows for production of two large Invasive, Non-Native Animals clutches each year, and larvae that are less palat- The introduction and spread of invasive able to predatory fish (Kruse and Francis 1977; non-native animals have been particularly Bury and Whelan 1984). They also tolerate el- prevalent in riparian and aquatic habitats. evated water temperatures better than native These infestations often coincide with habi- frogs, which is often advantageous in human- tat disturbance, making it difficult to separate modified habitats (Jennings 1988). Bullfrogs are the influence of one from the other. For ex- able to occupy a wide variety of aquatic habitats, ample, introduced fish and amphibians tend from coastal estuaries to mountain waters at el- to thrive in highly modified habitats, con- evations over 5,000 feet (e.g., Doane Pond on Palomar Mountain). 82 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 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 (pri- marily sunfish, bass, and bullheads).

African Clawed Frog (Xenopus laevis) African clawed frogs are currently not as widespread as bullfrogs (eleven known occur- rences in the assessment area), but they are a Figure 3.6. Non-native bullfrogs prey on many native potent predator of native fish and amphibians. amphibians and reptiles, including western pond Concerns about their consumption of the en- turtles. ROBERT H. GOODMAN JR. dangered unarmored threespine stickleback fish have led to eradication efforts on the Santa The effect of bullfrogs on red-legged frogs Clara River in Soledad Canyon (Dick 1988). has been particularly well documented. Hayes Although trapable, African clawed frogs are and Jennings (1988) found that California red- difficult to eradicate because they are highly legged frogs were still present at 81 percent aquatic and resistent to chemical toxins such (n=70) of sites lacking introduced bullfrogs as rotenone (Dick 1988). and no longer present at all sites (n=10) where African clawed frogs tend to become es- bullfrogs were established. Using field enclo- tablished in ponds and spread from there. The sure experiments, Kiesecker and Blaustein planting of mosquitofish by vector-control (1998) found an 84 percent survival rate of agencies may be contributing to their spread red-legged frog metamorphs when bullfrogs due to the presence of clawed frog larvae in were absent; the survival rate was only 27 per- several mosquitofish source ponds in San Di- cent when adult bullfrogs were present. ego County (R. Fisher, USGS Biological The work of Kiesecker and Blaustein Resources Division, pers. comm.). (1998) suggests an increased negative effect when bullfrogs occur in combination with Predatory Warm-Water Fish predatory fish. Survival rates of red-legged frog (Centrarchids, Ictalurids, Cyprinids) tadpoles averaged 89 percent when occurring Green sunfish (Lepomis cyanellus), bluegill alone or in the presence of only bullfrog tad- (Lepomis macrochirus), largemouth bass poles or only smallmouth bass. However, the (Micropterus salmoides), black bullheads survival rate decreased to 47 percent when (Ameiurus melas), fathead minnows bullfrog tadpoles and smallmouth bass were (Pimephales promelas), carp (Cyprinus carpio), both present. Apparently, red-legged frog tad- and red shiners (Cyprinella lutrensis) have been poles respond to the presence of bullfrog widely planted into south coast reservoirs and tadpoles by retreating to deeper waters and re- streams as sport fish or as bait for sport fish ducing their activity levels. This can be (Dudley and Collins 1995). These are hardy effective at reducing competition. But when fish that thrive in warm waters of lakes, ponds, smallmouth bass (or other predatory fish) are and low-elevation streams. They all prey on present in the deeper water, they prey exten- one or more life stages (i.e., eggs, larvae, sively on the tadpoles (Kiesecker and Blaustein metamorphs or adults) of native amphibians 1998). This phenomenon probably affects the and fish. survival of other amphibians as well. Native frogs are often absent from aquatic Our database of species occurrences by habitats where benthos-disturbing ictalurid watershed and drainage shows bullfrogs be- (bullheads) and centrarchid (sunfish, bass) fish are introduced (Hayes and Jennings 1986). 84 Chapter 3 This is caused by high levels of predation on found that crayfish were effective predators of frog eggs and tadpoles, particularly when tad- California newt (Taricha torosa) egg masses and poles and predatory fish are crowded into small larvae, inflicting mortality rates of greater than pools during periods of interrupted surface 80 percent. flow during the driest parts of the year In natural habitat within the Santa Monica (Jennings 1988). This pattern of interrupted Mountains of southern California, newts were surface flow is common in many streams absent from all streams where crayfish were within the assessment area. present (Gamradt and Kats 1996). In one in- Red shiners and fathead minnows are ef- stance where crayfish were washed out of a fective predators on the eggs of native fish. Red stream by winter floods, newts were back shiner predation is believed to be a primary breeding in the stream the next summer. factor in the disappearence of Santa Ana speck- Crayfish have been documented in forty- led dace from Big Tujunga Creek (Moyle et three streams within the assessment area. al. 1995). One or more of these warm-water fish are Mosquitofish (Gambusia affinis) known to be present in eighty-one streams Mosquitofish are distributed freely by within the assessment area. As described in the county vector-control personnel (Gamradt section on bullfrogs, the impact of these preda- and Kats 1996) and thus have been introduced tory fish appears to be exacerbated when into a large number of aquatic habitats. Once bullfrogs are also present (Kiesecker and believed to be an environmentally benign bio- Blaustein 1998). They are known to co-occur in logical agent for mosquito control, studies have forty-three steams within the assessment area. since determined that they can cause consid- erable ecological impact (Dudley and Collins German Brown Trout (Salmo trutta) 1995). Mosquitofish prey on amphibian eggs As with many of the warm-water fish, and hatchlings (Grubb 1972; Gamradt and brown trout have been introduced into moun- Kats 1996) and are capable of dramatically tain streams in southern California as a sport altering aquatic community structure fish. They tend to be more predatory on na- (Hurlbert et al. 1972). tive fish and amphibians than rainbow trout, In the Santa Monica Mountains, Gamradt and thus are considered more of a problem. and Kats (1996) found that California newts The extirpation of Santa Ana suckers from the were present in all eight streams where upper Santa Ana River has been attributed to mosquitofish and crayfish were absent, but brown trout predation (Moyle et al. 1995). newts were absent from all four streams that Although brown trout have historically contained either of these two exotics. been stocked into many streams, they have not Our database shows that mosquitofish are persisted in most locations. Currently, they are present in forty-seven drainages within the as- documented as present in only three assess- sessment area. This is likely to be a substantial ment area streams: upper Little Rock Creek, undercount, however, since mosquitofish are Bear Creek, and the upper Santa Ana River. often taken for granted and not recorded in fish surveys. Crayfish (Procambarus clarkii) Non-native crayfish are commonly sold as Brown-Headed Cowbird live bait and have been widely introduced into (Molothrus ater) streams, lakes, and ponds. Crayfish are om- Brown-headed cowbirds are brood para- nivorous and thus consume aquatic plants, sites that lay their eggs in the nests of other algae, invertebrates, amphibian eggs, and fish “host” birds, particularly those that build eggs (Hobbs et al. 1989). In laboratory and open-cup nests (fig 3.7). Because many hosts field experiments, Gamradt and Kats (1996) raise cowbird young instead of their own,

85 birds forage on insects attracted by the live- stock concentrations and on the hay and grain that are supplied to such areas (Rothstein et al. 1980). They are capable of traveling con- siderable distances between foraging sites and breeding areas. In the San Luis Rey River Val- ley 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 assess- ment area but are especially numerous in the foothills where riparian woodlands are in close proximity to grass or agricultural lands. Ri- Figure 3.7. Speckled brown-headed cowbird eggs parian woodlands support a rich diversity of in a least Bell’s vireo nest. The cowbird hatchlings nesting birds from which the cowbirds select will be fed and raised by the adult vireos as if they hosts (Unitt 1984). Densities of cowbirds are were their own offspring. USFWS much lower in montane coniferous forests (Verner and Ritter 1983) and desert-montane brood parasitism can substantially reduce host habitats where high-quality foraging habitat breeding productivity. High levels of brood para- is scarce. sitism can threaten some host populations; thus, Many birds are parasitized by cowbirds in cowbirds have been implicated in the decline of southern California, including threatened and many North American birds (reviewed in endangered species such as the least Bell’s vireo, Robinson et al. 1995). southwestern willow flycatcher, and Califor- Brown-headed cowbirds are native to nia gnatcatcher. One of the primary recovery North America but prior to European settle- actions for the least Bell’s vireo has been the ment were largely confined to short-grass widespread trapping of cowbirds near known prairies in the middle of the continent vireo populations (Beezley and Rieger 1987). (Mayfield 1965). Cowbirds feed by walking These trapping efforts have been highly suc- on the ground in areas of short grass and bare cessful in some areas. ground. They originally followed the herds of On the Santa Margarita River within the bison present in the prairies and are likely to Camp Pendleton Marine Corps Base, the rate have used scattered trees and riparian wood- of cowbird parasitism on least Bell’s vireo nests lands within prairie areas for nest searching was at 47 percent in 1983 when the base be- (Robinson et al. 1995). gan an intensive cowbird trapping program. European settlement was beneficial to With annual trapping, by 1990 the brood cowbirds and enabled them to expand their parasitism rate had dropped to less than 1 per- range both westward and eastward. Irrigated cent (Griffith and Griffith, in press). The agriculture, livestock grazing, and urbaniza- population of Bell’s vireos on the Santa tion all facilitated the spread of cowbirds and Margarita River rose from 60 pairs in 1983 to they were well established in coastal southern 319 pairs in 1993 (Griffith and Griffith 1995). California by the 1920s (Rothstein 1994). Since the initiation of annual cowbird removal In southern California, cowbirds reach programs, similarly dramatic population in- their highest densities near dairies, stables, and creases have occurred on the Tijuana and San other areas where livestock are concentrated Luis Rey rivers and in the Prado Basin (Kus and provided with supplemental food. Cow- 1995; Kus 1996; Pike and Hays 1997).

86 Chapter 3

European Starling (Sturnus vulgaris) Ants and other invertebrates are funda- European starlings cause ecological prob- mental components of many ecological lems because of their sheer abundance and communities and large shifts in abundance their ability to outcompete native birds for nest and species composition are likely to have sig- sites in tree cavities. Starlings have benefited nificant effects on other species. Harvester ants from human habitat modifications, irrigated are an important food source for the coast agriculture in particular (Ehrlich et al. 1988). horned lizard. These lizards appear to be de- First introduced in New York City in clining in natural habitat fragments in 1890, starlings were first documented in Cali- southern California. This decline may be re- fornia in the 1940s (Jewett 1942). Populations lated to the influence of Argentine ants on in southern California apparently exploded in harvester ants. the 1960s. San Diego Christmas Bird Counts during the 1960s show the following pattern Red Imported Fire Ants in starling numbers: 153 in 1963, 974 in 1964, (Solenopsis invicta) 1500 in 1965, 4,448 in 1968, and 7,928 in Red imported fire ants have only recently 1969 (Unitt 1984). invaded southern California. They were first The purple martin is a native bird whose discovered in November 1998 at a nursery and decline in southern California has been largely golf course in Orange County (CDFA 1998; attributed to competition for nest sites from Schoch 1999). Since that time, colonies have starlings (Garrett and Dunn 1981). Western been discovered in San Diego, Los Angeles, bluebirds have also been significantly affected. Riverside, and Kern counties (CDFA 1999). The ant is now thought to have been present Argentine Ants (Linepithema humile) in the region for five to seven years (anony- Argentine ants are abundant in many ar- mous 1999). eas of human habitation, particularly where The red imported fire ant is native to the there is irrigated landscaping. They have spread Pantanal region of Brazil, Paraguay, and Ar- into wildland habitats from developed areas gentina, and is thought to have been and thus are primarily a problem near the ur- accidentally introduced multiple times to ban interface and in areas fragmented by Mobile, Alabama, between 1933 and 1945 development. (Buren et al. 1974; Greenberg et al. 1999). Suarez et al. (1998) studied Argentine ant Concerns about its arrival in southern Cali- invasions in habitat fragments of various sizes fornia stem from the well-documented damage in urbanized coastal San Diego County. Ar- caused by infestations of red imported fire ants gentine ants were found in each fragment, but in twelve southeastern states. In that region, activity was correlated with proximity to the the ant has invaded residential areas and some urban edge and the amount of exotic vegeta- natural habitats. It aggressively stings when dis- tion. Activity was always high within 320 feet turbed and thus is considered to be a major (100 meters) of an urban edge. nuisance pest in developed areas. Areas invaded by Argentine ants had fewer From an ecological standpoint, the threat native ant species than uninvaded areas. Spe- posed by imported fire ants is similar to that cies most frequently absent in areas occupied of the Argentine ant, although perhaps greater by Argentine ants were army ants in magnitude. Like the Argentine ant, the red (Neivamyrmex spp.) and harvester ants (gen- imported fire ant readily invades disturbed era Messor and Pogonomyrmex) (Suarez et al. areas around human habitation. It requires 1998). Studies elsewhere have documented simi- moisture and cannot survive cold temperatures lar declines in the abundance of native ant (Vinson and Greenberg 1986). Thus, occu- species in areas where the Argentine ant has pation of wildlands is expected to be limited become established (Ward 1987; Holway 1995). to lower elevation riparian zones or irrigated 87 areas adjacent to urban areas. However, red • Arundo removal to restore high-quality, imported fire ants have recently invaded areas low-elevation riparian habitat along San of west Texas formerly thought to be too dry Francisquito Creek and Elizabeth Lake for the species, and there is evidence that this Canyon in the Angeles National Forest represents a heritable adaptation (Mackay and and along the Santa Margarita River in Fagerlund 1997; Li and Heinz 1998; Phillips San Diego County; et al. 1996). Thus, there is potential for the • Brown-headed cowbird trapping to ants to eventually occupy portions of Califor- control nest parasitism on the nia previously thought to be too dry. At a southwestern willow flycatcher and least minimum, they pose a threat to the integrity Bell’s vireo along the San Luis Rey River of any habitats that lie along the urban-wild- in the Cleveland National Forest; land interface, particularly small wildland • Bullfrog control to improve arroyo toad patches that are largely surrounded by devel- and red-legged frog survivorship along opment or irrigated land. portions of Sespe Creek in the Los Similar to the Argentine ant, red imported Padres National Forest; and fire ants have greatly reduced the abundance • Mediterranean grass control through the of native ants and other invertebrates in por- careful timing of prescribed fire to tions of the southeastern United States (Porter increase the abundance of native grasses and Savignano 1990; Morris and Steigman and forbs and improve Engelmann oak 1993). Yet, they have the additional impact regeneration on the Santa Rosa Plateau of being an aggressive predator of vertebrate Reserve in Riverside County. nests and young, commonly swarming the nests of ground-nesting birds, mammals, and Another important management consid- reptiles (Hill 1969; Mount et al. 1981; eration is how best to minimize or prevent Ridlehuber 1982; Drees 1994; Allen et al. additional introductions of undesirable, non- 1995). native species. This is a difficult task, since introductions can occur in a multitude of ways Management Considerations for that are usually difficult to anticipate and pre- Exotic Species Control vent. However, some feasible preventative Exotic species are widespread and most are measures include (1) close coordination with difficult to eradicate even from small areas. CDFG representatives on planned introduc- The potential is high for control efforts to be tions and stockings; and (2) careful screening ineffective if they are not carefully planned and of seed mixes or plantings used for erosion sustained. Consequently, management activi- control, landscaping of recreation facilities, ties to control exotics should (1) have clearly and habitat restoration projects. defined and achievable objectives, (2) be sus- tained over time, and (3) be monitored in an The Influence of Native adaptive management framework to ensure objectives are being met and the most effec- Insect and Disease Outbreaks tive techniques are being used. Vegetation is continually preyed upon by To succeed, exotic species control efforts indigenous insects and pathogens. Most of the probably need to be narrowly targeted to spe- time these organisms remain at levels where cific key areas where both the circumstances they do not cause rapid, large-scale changes for control are favorable and the potential for in the structure or composition of plant com- recovery of rare habitats or species is high. munities. Yet certain conditions can trigger Examples of successful, targeted control efforts major insect or disease outbreaks that result currently ongoing within the assessment area in substantial plant mortality. The specific include: insects and diseases prone to damaging out- breaks are often described as pest species. 88 Chapter 3 Historically, pests of forest trees have re- became common, is thought to be responsible ceived more attention than those of other for the widespread occurence of annosus root native plants, perhaps because of the economic disease centers. This disease is particularly value of the commodity affected and the highly common in the Jeffrey pine forests of Laguna visible nature of concentrated tree mortality. Mountain and to the northeast of Big Bear Native insect herbivores and pathogens of for- Lake in the San Bernardino Mountains where est trees perform important functions in western juniper is also affected, and in the natural ecosystems, killing decadent trees, cre- mixed conifer forests of the San Bernardino ating dead and down woody habitat for other and San Gabriel mountains, as well as in other species, recycling nutrients, and creating gaps forested lands in the Transverse and Peninsu- for regeneration (Pronos et al. 1999). How- lar ranges. ever, these pests also increase fuel loading, Another strain of H. annosum causes a contributing to fire hazards in forests. The fol- root, butt, and heart rot of true fir. The fun- lowing discussion concerns the major forest gus enters the wood through logging and other pests (in terms of numbers of trees damaged injuries, fire scars, broken tops, and freshly cut or killed) in southern California. stumps (Scharpf and Goheen 1993). In firs The pests discussed below are not inclu- this disease causes a general decline rather than sive; there are many other insects and rapid mortality, and is found in mixed conifer pathogens of importance in southern Califor- forests throughout the Transverse and Penin- nia forests. Of particular interest here are those sular ranges. pest species whose populations have greatly Black stain root disease, caused by increased as a result of twentieth-century man- Leptographium wageneri, causes extensive mor- agement activities, particularly tree removal tality in one species of single leaf pinyon pine and changes in natural fire regimes. (P. monophylla) in portions of the San Bernar- dino Mountains, but not elsewhere in Root Diseases southern California. In the San Bernardino Foremost among the root diseases in Mountains, 8,000 acres are reported to be af- southern California is annosus root disease of fected. The disease has not been reported from pine, caused by a strain of Heterobasidion two southern California endemics, P. annosum. This fungus colonizes freshly cut, californiarum ssp. californiarum, a lower eleva- untreated conifer stumps and grows down tion single leaf pinyon, and P. quadrifolia, Parry through the woody tissue and into the roots, pinyon. Spread is through root contact and where it may survive saprophytically for up to most likely, though not adquately investigated, fifty years. Live pines and other susceptible through the activities of root-feeding insects. woody plants become infected when their Trees infected with black stain are often at- roots contact infected roots in the soil. The tacked and killed by the pinyon pine engraver, fungus may kill the pines directly or debili- Ips confusus (see below), although the disease tate them to the point where they are readily alone often kills trees. This disease is second colonized and killed by bark beetles or other only to stand-replacing fires as a mortality woodboring insects (Smith 1993). Annosus agent in pinyon. It is not known if manage- root disease has significantly reduced vegeta- ment activities have affected the incidence of tive cover in some recreation sites, particularly the disease (Merrill et al. 1992). since the openings created by the disease can- Armillaria root disease, caused by not be replanted with pines. Infection by this Armillaria mellea, can build up on dead or pathogen can be prevented by treating freshly dying native oaks and attack and kill young cut stumps with borate (Sporax®)(Graham conifers nearby. In southern California this 1970; Smith 1970). Tree removal in southern fungus does not cause extensive mortality but California forests, particularly in the years can be a problem when large oaks are removed prior to the mid-1970s, when borate treatment 89 from a site and conifers are planted. The newly of dwarf mistletoes. Stand-replacing fires can killed oak stumps provide a large food base, eliminate local populations as the host trees allowing the fungus to grow rapidly and are able to return to sites more rapidly than overcome nearby conifers. their mistletoe parasites. Spotty fires can leave infested overstory trees which both regener- Dwarf and True (Leafy) Mistletoes ate the stand and reinfect it. Heavily infested The dwarf mistletoes (Arceuthobium spp.) stands may contain more fuels because of the are serious parasites of pines in southern Cali- accumulation of dead witches’ brooms and fornia. These mistletoes are both water and trees, and fires in them may turn into confla- nutrient parasites, and heavily infected trees grations. Smoke may inhibit dwarf mistletoe are readily killed by bark beetles and other seed germination, depending on length of expo- insects or drought. The most widespread spe- sure (all reviewed by Hawksworth and Wiens cies are the western dwarf mistletoe, A. 1996). It is likely that prior to the arrival of Eu- campylopodum—which infects ponderosa, Jef- ropeans in southern California, dwarf mistletoes frey, knobcone, and Coulter pine—and sugar were abundant, at least in patches. pine dwarf mistletoe, A. californicum, which True mistletoes, Phoradendron spp., infect infects sugar pine. A. occidentale, which infects hardwoods, white fir, incense-cedar, and ju- gray (foothill) pine, as well as A. divaricatum, nipers in southern California. Unlike dwarf in pinyon pines, and A. cyanocarpum, in lim- mistletoes, these species photosynthesize and ber pine, also occur in southern California are primarily water parasites and thus are far (Scharpf and Hawksworth 1993). Although less damaging to their hosts. The berries are birds can carry dwarf mistletoe seeds on their eaten by birds, which then disperse the seeds. feet and feathers, infection most often occurs as True mistletoes can be serious pests where in- a result of the forceful ejection of seeds from the dividual trees are of high value, such as in female plant. Thus, susceptible understory trees campgrounds. Heavily infected trees have re- can be infected by mistletoe in the overstory. duced growth rates, are weakened, and are Management of dwarf mistletoes can be sometimes killed outright. Weakened trees accomplished by removing diseased overstory, may be attacked and killed by insects or may isolation of susceptible understory from dis- succumb in times of drought. There is no evi- eased overstory trees by distance or the use of dence that general management activities have buffers (nonhost trees planted between the in- increased the frequency of infection by these fected and uninfected trees), and pruning or species, except perhaps in the case of white removal of infected trees (Scharpf et al. 1988). fir, where fire suppression is thought to have The latter method is used in southern Cali- increased the occurrence of the host and thus, fornia campgrounds and other high-use too, of the parasite. Mistletoe infections in recreation sites where the value of individual white fir contribute, with annosus root and trees can justify treatment costs. Dwarf mistle- butt rot, to general decline of trees, leading to toe is a good example of an organism which topkill or whole tree mortality when insects should not be considered a pest where infec- (particularly bark beetles and roundheaded tion, dieback, and some tree mortality do not borers) attack. interfere with management objectives. The mistletoe plants support their own herbivores, Bark Beetles and the witches’ brooms, dead limbs, and dead Beetles in the family Scolytidae are best trees that result from mistletoe infections cre- known for delivering the “coup de grâce” to ate habitat for other species. conifers stressed by disease, drought, or other It is not known if fire suppression and factors. When populations of some species other management activities in the twentieth build up during droughts, even vigorously century have changed the relative abundance growing trees may be successfully attacked and killed. Two genera are primarily responsible 90 Chapter 3 for pine mortality in southern California, tack. Thus proper sanitation is believed to be Dendroctonus and Ips. The former includes essential to the management of these beetles species such as the western pine beetle, D. (Furniss and Carolin 1977). brevicomis, which has several generations per Scolytus ventralis, the fir engraver, is the year and can build up rapidly in stressed trees. most commonly found bark beetle in white This species has been associated with wide- fir. This nonaggressive scolytid may kill patches spread Coulter pine mortality on the western of the phloem, which may heal over; tops of slopes of the San Jacinto Mountains and por- trees; and whole trees; depending upon the tions of Palomar Mountain in the early 1990s size of the trees and the relative level of stress (Merrill, pers. obs.; Merrill 1991), as well as to the trees from pathogens and other agents historically in Lost Valley and the northern (Furniss and Carolin 1977). slope of Hot Springs Mountain in San Diego Preventing losses to bark beetles requires County (Hall 1958). Other species in the ge- keeping stressors—such as root disease and nus—including the Jeffrey and mountain pine dwarf mistletoe—at low levels. Thinning to beetles, D. jeffreyi and D. ponderosae, respec- reduce stocking density should be used to re- tively—have one generation per year. Like D. duce the risk of drought stress, but shortages brevicomis, these species can attack and kill of personnel and Timber Stand Improvement otherwise vigorous trees when beetle popula- (TSI) dollars have reduced the number of acres tions are high. In southern California these thinned in recent years. Forest Pest Manage- beetles are most often found in Jeffrey pine ment pest prevention and suppression dollars (D. jeffreyi), and ponderosa and sugar pines can be used, when available, to thin stands at (D. ponderosae). For unknown reasons both risk of bark beetle-caused mortality, and to species have patchy distributions among the suppress dwarf mistletoe and other pests. mountains of the Transverse and Peninsular ranges in southern and Baja California. D. Round and Flatheaded Borers valens, the red turpentine beetle, infests freshly Round and flatheaded beetles are sometimes cut stumps and roots and lower bole of living important mortality agents. Two species are of trees, particularly those damaged by fire or particular importance in southern California, the root disease. This species rarely causes tree California flatheaded borer, Melanophila mortality but does contribute to the decline californica (Buprestidae), and the roundheaded of trees which are then attacked by more ag- fir borer, Tetropium abietis (Cerambycidae). M. gressive species (Furniss and Carolin 1977). californica infests and kills mature to decadent Ips species are commonly called engraver trees and is usually found in dying trees in the beetles for their habit of feeding on (engrav- largest diameter classes, e.g., the large old Jeffrey ing) the cambial surface of the xylem as well pines which were once common on Laguna as the phloem of pines. These beetles are usu- Mountain in San Diego County. T. abietis is a ally not considered as aggressive as common mortality agent of white fir stressed by Dendroctonus spp., although they are responsible other pests, drought, or poor growing condi- for much tree mortality, particularly of pinyon tions (Pronos et al. 1999). Other cerambycids pines with black stain root disease (the pinyon and buprestids feed in dead and dying trees, ips, I. confusus) and smaller diameter trees or returning nutrients to the soil and serving portions of trees. For example, I. paraconfusus themselves as food for birds. These insects are and I. pini commonly kill tops of large pines. I. sometimes considered pests because their feed- emarginatus can kill Jeffrey, ponderosa, sugar, and ing decreases the value of lumber (Furniss and lodgepole pine in southern California. All of Carolin 1977). Fire suppression is thought to these species of Ips have several generations per have increased the proportion of white fir in year. Ips beetle populations may build up in slash stands that were formerly primarily pine, in- to levels where small diameter trees and tops of creasing the abundance of T. abietis and other mature trees in the vicinity are at risk for at- pests on the off-site firs. 91 The Influence of Recreation ing impacts localized and by providing facili- Activities ties such as toilets and trash cans. However, concentration of activity also tends to cause Public lands in the southern California ecological impacts (Boyle and Samson 1985). mountains and foothills are popular outdoor Frequent traffic in an area causes reductions recreation areas. Recreation is the principal in vegetative cover, with the rate of reduction land use activity in the region’s state and being highly influenced by the type of activ- county parks and it is also the most common ity (e.g., motorized vehicle or horse traffic activity in the national forests. With a rapidly reduces ground cover more rapidly than foot growing urban population nearby, the num- traffic)(Liddle 1997). Concentrated human ber of recreationists visiting the assessment area activity is also more likely to cause incidental is steadily increasing. Some go in search of animal mortality (e.g., trampling of nests or egg calm and serenity, while others pursue adven- masses) and can cause disturbance-sensitive ture, excitement, or simply escape from the species to avoid areas that would otherwise by urban environment. Activities that fall into the suitable habitat (e.g., bighorn sheep). category of outdoor recreation include, al- Localized impacts from recreation activi- though are by no means limited to, camping, ties can be relatively benign. Problems arise picnicking, driving, hiking, site-seeing, wild- when high-use recreation areas overlap with life viewing, hunting, fishing, target shooting, sensitive habitats or rare species populations off-highway vehicle (OHV) driving, horseback (table 3.14). In southern California, the po- riding, mountain bike riding, skiing, and tential for overlap is heightened by the fact mountain climbing. that areas rich in rare habitats and species— The land management agencies do a vari- riparian areas, montane meadows, and coni- ety of things to accommodate and enhance fer forests—also tend to be popular locations these outdoor recreation experiences. A vast for recreationists. In some of these areas, nor- network of roads and trails is maintained. Pic- mally harmless activities become serious nic areas and campgrounds (both developed threats because of the extreme rarity or vul- and remote) are established and maintained. nerability of a species occurring in the vicinity. Information centers and interpretive programs are provided. Through special use permits, sites Figure 3.8. An aerial view of ski area developments are leased to private entities for downhill ski near Big Bear Lake on the San Bernardino National area developments (fig. 3.8), organizational Forest. JOHN STEPHENSON youth camps, recreation residences, and shoot- ing 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 develop- ments and services are popular and there is a steady demand for improvements and addi- tions. 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 keep-

92 Chapter 3

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

For example, people walking in a creek is a et al. 1988; Gutzwiller 1991; Knight and normally harmless activity, but at certain times Gutzwiller 1995; Liddle 1997). Making mat- of the year in the few remaining areas where ters worse is the lack of scientific studies on arroyo toads or mountain yellow-legged frogs the ecological effects of recreation activities in still occur, it can greatly affect the survival of the southern California mountains and foot- these imperiled species (Jennings 1998; Sweet hills. All of the local information we could 1992). find on this subject was based on anecdotal Our scientific understanding of the effects observations. There is a real need for formal of recreation activities on wildlife is rudimen- scientific studies to assess the effects of recre- tary at best (Knight and Cole 1995). ation activities on rare species and habitats and Numerous studies on the ecological effects of to evaluate the efficacy of management actions recreation have been conducted, but the currently being taken to avoid or mitigate knowledge gained is disparate and seldom those effects. definitive (see reviews in Boyle and Sampson 1985; Hammitt and Cole 1987; Pomerantz 93 Table 3.14. Key ecological issues that are influenced by recreation activities.

Habitats/Species Effects Associated Current Trends and Key Issues Most Affected with Recreational Activities Areas Most Affected

Declines in condition ¥ Riparian habitat ¥ Reductions in vegetative cover ¥ Recreation use is believed of sensitive habitats ¥ Arroyo toad are common in areas that to be increasing in most or direct mortality ¥ Meadows receive frequent recreation use areas; there is a high of rare species. ¥ Pebble plains ¥ Direct mortality occurs demand for additional ¥ Alpine plants primarily from vehicular traffic, recreation facilities but also is caused by trampling, ¥ Popular recreation areas pollution, or harassment (e.g., that also contain many rare capturing or plinking slow species include Laguna moving animals) Mtn., Big Bear Valley, ¥ Impacts are localized but can Holcomb Valley, San be significant; the level of Gabriel River, Little Rock impact is strongly related to the Ck, Big Tujunga Ck, Sespe amount of use an area receives Ck, and Santa Ynez River ¥ Facilities operated by private ¥ Popular trails to the entities under special use summits of Mt. San permit (e.g., ski areas, Gorgonio, Mt. San Jacinto, organizational camps, Mt. San Antonio (Baldy) and recreation residences) are Mt. Baden-Powell cause sometimes located in sensitive some impacts to alpine habitats or near rare species. habitats

Indirect impacts to ¥ Bighorn sheep ¥ Bighorn sheep are extremely ¥ Bighorn sheep are being disturbance-sensitive ¥ Mule deer sensitive to human activity and affected in the eastern San species. fawning habitat move to avoid it; this has Jacinto Mts near Palm (meadows) caused them to retreat from Springs and in the San ¥ Bat roosts some of their most suitable Gabriel Mts in Lytle Creek (abandoned habitat areas. and around Mt. Baldy mines and ¥ Mule deer will avoid suitable ¥ Some of the best fawning buildings fawning habitat if there is a lot habitat in the upper Santa of human activity Ana River watershed is ¥ Bats will abandon roost sites if avoided by deer due to high there is a a high level of human levels of recreation use activity (Nicholson 1995)

Many of the anecdotal reports of negative Human activities in and around these sites recreation impacts pertain to riparian and (e.g., driving, biking, walking through the aquatic habitats. Foothill river corridors are stream, and picking up animals) are report- cool, pleasant places that are often only a short edly causing significant adult mortality and drive from urban areas. They attract declines in reproductive success (Sweet 1992; recreationists in large numbers (fig. 3.10), and USFWS 1998a). Similar adverse effects result- over the years that demand has been accom- ing from recreational activity have been modated through the establishment of reported for pond turtles (Holland 1991), red- campgrounds and picnic areas in popular ar- legged frogs (Jennings and Hayes 1994), and eas. Only recently has it been recognized that mountain yellow-legged frogs (Jennings many of these same areas are also important 1995a, 1998). habitats for imperiled species. Management efforts to avoid or mitigate Developed recreation sites are particularly these impacts include seasonal closures of some prevalent near low-gradient stream and ter- roads and recreation areas and restrictions on race habitats occupied by the endangered vehicle access in some areas (e.g., walk-in arroyo toad (Sweet 1992; USFWS 1998a). campgrounds). Most of these measures have

94 Chapter 3 only recently been instituted. Much could be Sensitive plants are particularly common in learned by careful monitoring of their effec- montane meadows and, in dense conifer for- tiveness, both in terms of controlling ests, some recreation facilities are in close recreationists and reducing impacts to the tar- proximity to spotted owl nest sites. Nicholson get species. (1995) reported that mule deer largely avoided Organizational camps, recreation areas, areas regularly occupied by humans (e.g., and public campgrounds are numerous in co- campgrounds and summer cabins), to the ex- nifer forests and montane meadows (e.g., tent that they did not utilize meadow habitats Laguna Mountain, Cuyamaca, Idyllwild, that would otherwise be high quality foraging Barton Flats, Big Bear/Holcomb Valley, and fawning areas. Lake Arrowhead, Big Pines, Crystal Lake, Mount Pinos/Cuddy Valley, and Pine Mountain). The facilities and interpretive programs provided in these areas offer impor- tant opportunities for young people from southern California’s cities to learn about the natural environment. The organizational camps in particular tend to have strong envi- ronmental education programs and are conscientious about minimizing human im- pacts. 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

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

Habitats/Species Effects Associated Current Trends and Key Issues Most Affected with Roads Areas Most Affected

Declines in survival ¥ Riparian habitats Animal mortality caused by Roads on stream terraces and recruitment rates ¥ Arroyo toad vehicle traffic on roads can be and crossings in low- of some species. ¥ Spadefoot toad substantial. Stream crossings gradient foothill and desert and roads adjacent to riparian streams are affecting the habitats pose particular endangered arroyo toad. concerns for slow-moving Seasonal closures and species (e.g. toads, frogs). modifications to crossings are being done to reduce impacts.

Illegal collecting or ¥ Mtn. kingsnakes Can cause substantial declines It is difficult to determine poaching of animals. ¥ Rosy boas in species abundance in trends in this activity. ¥ Pond turtles heavily collected areas. Roads ¥ CA newts facilitate this activity because ¥ Mule deer collecting is almost invariably done along or near them.

Barriers to animal Mountain lions Busy highways (particularly Interstates 8 and 15 cross dispersal. interstate highways) can be the Cleveland NF; I-10 and I- very difficult for some animals 15 separate portions of the to cross, and may be resulting San Bernardino NF; I-5 runs in population fragmentation. between the Angeles and Los Padres NFs.

Declines in condition ¥ Pebble plains ¥ Illegal or unauthorized There is little new road of sensitive habitats. ¥ Riparian habitats activities are more likely to construction on public lands occur in roaded areas and and some problem roads are difficult to prevent; this are being obliterated. includes pollution, vandalism, driving in unauthorized areas. ¥ Increased flow of sediment into streams

The Influence of Roads

Roads are the primary means by which stream terraces, or that frequently cross people access the outdoors. Thus, the amount streams, can be a major source of mortality to of human use in a area is highly correlated slow-moving animals such as the arroyo toad. with an area’s road accessibility. There are many These nocturnal toads actually move onto dirt benefits to having areas accessible by road: it roads at night to feed and many individuals can improves firefighting effectiveness, increases be killed by a few vehicles (USFWS 1998a). This opportunities for habitat management work, is a particular problem in and around camp- and provides basic access to the public lands. grounds that are located on stream terraces near However, the presence of roads also leads to arroyo toad breeding habitat (Sweet 1992). Simi- impacts associated with vehicular traffic and lar problems of high mortality rates where a road increased human use (table 3.15). runs close to breeding habitat have been observed Roads in and adjacent to riparian areas can for the spadefoot toad (E. Ervin, San Diego State cause substantial impacts. Roads located on University, pers. comm.). 96 Chapter 3 Roads tend to cross streams in low-gradi- ent 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 Figure 3.11. Gully erosion caused by runoff from a problem in some road-accessible areas. Illegal culvert on Gator Road, Laguna Mountain, Cleveland collecting of reptiles, unauthorized woodcut- National Forest. Restoration efforts have since been implemented and the area is recovering. DEVEREE ting, illegal OHV activity, poaching, VOLGARINO vandalism, and dumping of hazardous mate- rials: all of these are difficult law enforcement issues that occur almost exclusively along or As part of our watershed-scale analysis we near roads. Non-native species introductions looked at “roadedness” in several different (both purposeful and inadvertent ones) also ways. First, we identified all existing roadless occur predominately in areas that are acces- areas that are larger than 1,000 acres (fig 3.12). sible by road. All of these things cause Second, we looked separately at each water- significant declines in habitat capability in lo- shed, calculating the percentage of the calized areas. The inherent difficulty in watershed that falls within 250 meters of an preventing these impacts from occurring in active road (table 3.16). Not surprisingly, roaded areas is a compelling reason for main- many of these “least-roaded” watersheds also taining some areas in a roadless condition. show up in table 2.15 (chapter 2) in the list The increased flow of sediment into of drainages that have high potential for streams is one of the most commonly cited maintaining aquatic ecological integrity due environmental effects of unpaved roads. Roads to low land use intensity and low numbers reportedly contribute more sediment to of exotic species. streams than any other land management ac- tivity (Gibbons and Salo 1973; Lee et al. 1997). Old roads that were not designed us- ing current “Best Management Practices” (BMP) standards often have the greatest en- vironmental 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 ar- eas; 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).

97 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). 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. Percent of Percent watershed that public Mountain Range lies within 250 land in Watershed Subarea meters of a road watershed

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%

The Influence of Timber and Some commercial timber harvesting was Fuelwood Harvest done in the Cleveland and Los Padres national Most of the land base suitable for com- forests during peak years in the 1960s and mercial timber harvest in southern California 1970s, but it was short lived. The small is within the San Bernardino National Forest. volumes produced in these areas were not suf- An active timber program was sustained on ficient to support viable sawmill operations; that forest from the late 1940s (post World War II) through the mid-1980s (fig 3.13). 30 Harvest levels peaked in the 1960s, with 27.4 million board feet (MMBF) harvested on the 25 San Bernardino National Forest in 1963 alone 20 (McKelvey and Johnston 1992). Volume data from the California Department of Forestry 15

and Fire Protection (1947 to 1978) and the 10 California State Board of Equalization (1979 to 1990) for San Bernardino and Los Angeles 5 Millions of Board Feet (scaled) counties show that 362.3 MMBF of timber 0 were removed from those counties between 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1947 and 1990 (McKelvey and Johnston Year 1992). Some of that would have come from Figure 3.13. Logging intensity in San Bernardino the San Gabriel Mountains within the Ange- and Los Angeles counties, 1947 to 1990. Most of les National Forest, but most was from the this timber came off the San Bernardino National more densely forested San Bernardino Moun- Forest (from McKelvey and Johnston 1992). tains.

99 thus, timber had to be trucked long distances The Influence of Livestock to the nearest mill. This same problem ulti- Grazing mately affected the San Bernardino National Forest timber program when dropping har- Livestock grazing has been a traditional vest levels in the late 1970s led to closure of activity on both public and private land in the the last mill in the area. southern California mountains and foothills For the past decade (much longer in some since at least the early 1800s (Lockmann areas), small timber programs on the south- 1981). When assessing the effect of this activ- ern forests have focused on (1) forest health ity on ecosystems and species, it is important issues (e.g., treatment of insect and disease to distinguish the impact of historic grazing centers, understory thinning, and fuels reduc- from that which can be attributed to grazing tion); (2) administering individual permits to levels occurring today. Abusive grazing prac- accommodate local demand for fuelwood; and tices in the late 1800s and early 1900s caused (3) identifying and removing hazard trees. environmental changes that are orders of mag- Small-scale salvage operations to remove trees nitude greater than anything seen in recent killed by wildfire or bark beetles are also occa- times. sionally done. Livestock numbers reached their peak in When evaluating the influence of timber this region from approximately 1860 to 1900, harvesting on southern California ecosystems, when sheep grazing was in its heyday. Use was we must separately consider historic effects particularly high in the montane meadows of from current effects. Past timber harvesting, the San Bernardino and San Jacinto moun- particularly in the San Bernardino and San tains; it is reported that 30,000 sheep were Jacinto mountains, has probably resulted in a herded into Big Bear Valley in the late 1860s substantial reduction in the number of large (Lockmann 1981). There are numerous ac- trees, with ponderosa and Jeffrey pines incur- counts of extensive devegetation and erosion ring the greatest reductions. It may also have damage occurring during this period contributed to the increased dominance of (Lockmann 1981; Minnich 1988) and, al- white fir. though 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.

Effects Associated Habitats/Species with Fuelwood Harvest Current Trends and Key Issues Most Affected Activities Areas Most Affected

Retention and Cavity nesters, snag- Large snags that are Snag retention recruitment of large dependent species. reachable by roads can be requirements in existing diameter trees, snags difficult to retain because of Forest Plans are adequate, (standing dead trees), unauthorized cutting. but enforcement is difficult and downed logs. The same is true of large in popular woodcutting downed logs. areas.

Increases in small- Mesic mixed conifer If fuelwood demand can be met Problem is most acute in the diameter trees in forests. through harvesting small trees, western San Bernardino the forest understory. this activity could help control Mtns. but is occurring in the problem. many montane conifer areas.

100 Chapter 3 Since 1900, cattle have been the principal Ecological changes most commonly attrib- livestock animal on southern California range- uted to overgrazing by cattle involve declines lands. Grazing can occur year-round in foothill in the condition of riparian, oak woodland, savannas and grasslands and during the sum- grassland, and meadow habitats. More specifi- mer months in montane meadows and forests cally, livestock grazing has been implicated in (fig. 3.14). Over the years there has been a reduced tree regeneration, substantial reduc- gradual decline in the intensity and extent of tions in vegetative cover, streambank cattle grazing in this region. Once the domi- destablization, water quality degradation, and nant use of meadows in the San Bernardino the spread of non-native weeds (table 3.19). and San Jacinto mountains, grazing has been A comprehensive review of studies assess- greatly reduced in these ranges as ranching in ing the impact of livestock on California the surrounding valleys has declined and other ecosystems, with particular emphasis on the land use activities, particularly recreation, have Sierra Nevada, was recently conducted by a received greater emphasis. group of scientists with expertise in Califor- Today, grazing within the assessment area nia rangeland issues (see Allen-Diaz et al. is concentrated in and adjacent to the Los Pa- 1999). Their findings suggest that despite the dres National Forest and, to a lesser extent, in many studies of grazing and its impact on eco- the San Diego County foothills within and systems, there are still far more questions than adjacent to the Cleveland National Forest answers regarding this issue. There appears to (table 3.18) (fig. 3.15). Rangelands in these be a scarcity of studies which quantify the ef- areas are predominantly oak savannas, grass- fects of different grazing intensities, lands, montane meadows, and openings in frequencies, and seasons of use. Instead most chaparral and scrub. studies simply compare the impacts of heavy

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

101 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 NFSan Bernardino NF Angeles NF Los Padres NF Area within Forest Entire Assess- Service Grazing San Santa San San San Castaic S. Los S. Santa N. Santa ment Allotments Diego Ana Jacinto Bernar- Gabriel Ranges Padres Lucia Lucia Ranges Mts Mts dino Mts Mts Ranges Rng Rng Area

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

Figure 3.15. Locations of current grazing allotments on national forest system lands within the assessment area. Chapter 3

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

Habitats/Species Effects Associated with Current Trends and Key Issues Most Affected Livestock Grazing Activities Areas Most Affected

Declines in condition ¥ Riparian habitat Grazing in riparian areas can ¥ Impacts have been reduced of sensitive habitats ¥ Meadows cause increased sediment yield, substantially in recent years or direct mortality stream-bank degradation, due to excluding livestock of rare species. reductions in vegetative cover, from some riparian areas and direct mortality of rare and improved management species. of stocking rates and season of use in other areas ¥ Entrenched downcuts caused by past overgrazing still remain in some meadows

Lack of oak ¥ Blue oak woodlands Grazing can negatively affect Recent studies have shown regeneration. ¥ Engelmann oak oak regeneration through that livestock grazing woodlands seedling removal and soil contributes to this problem compaction. but is not the sole or even the primary cause in most areas.

Spread of invasive ¥ Riparian habitat ¥ Studies suggest that grazing Grazing historically was a non-native species ¥ Grasslands attracts cowbirds, but its major factor in the spread of e.g., brown-headed ¥ Oak woodlands influence varies based on other undesirable plants, but the cowbirds, star thistle, • Least Bell’s vireo surrounding land uses continued spread of those Mediterranean ¥ Willow flycatcher ¥ Overgrazing can facilitate plants today is often grasses) . ¥ CA gnatcatcher spread of star thistle and other triggered by other factors. weeds

Fuels reduction. Nonspecific. Grazing can be used as a tool for Some fuel breaks are fuels reduction in grasslands and currently maintained by on fire breaks. livestock grazing. grazing with no grazing (Blackburn 1984; when the intensity of year-round cattle graz- Allen-Diaz et al. 1999). There are few solid ing was reduced and willow cutting and scientific assessments of the ecological effects spraying were eliminated (Taylor 1986; Tay- of management practices that fall in “the great lor and Littlefield 1986). The researchers middle ground” between abusive grazing and hypothesized that the mechanism involved was no grazing (Allen-Diaz et al. 1999). that cattle grazing reduced willow nesting Despite these limitations, some studies are cover for these species. pertinent to the ecological issues within our Several studies have assessed the effect of assessment area. The effect of grazing on livestock grazing on the survival of blue oak riparian habitats and species is of interest be- seedlings. The results have been mixed; some cause there are many sensitive resources in results suggest that grazing reduces blue oak riparian areas and they are also a preferred recruitment while others show no effect (Davis habitat for cattle (Kie and Boroski 1996). et al. 1991; Allen-Diaz and Bartolome 1992). Overgrazing by cattle was identified as a prob- There is general consensus, however, that graz- able cause of limited cottonwood sapling ing is just one of many factors that may be establishment along much of the Nacimiento affecting oak seedling survival. River in the northern Santa Lucia Range Recent changes in the management of live- (Shanfield 1984). Studies on the Blitzen River stock grazing allotments on national forest in Oregon found dramatic increases in wil- system lands have included (1) fencing to low flycatcher and yellow warbler populations 103 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

exclude cattle from some sensitive riparian and and in the Santa Lucia Ranges near Little Sur. meadow habitats (figs. 3.16), (2) reductions There is also active exploration for oil and gas in stocking rates, and (3) changes in the sea- reserves occurring in southeastern portions of son of use, reducing the amount of summer/ the Los Padres National Forest. fall grazing in favor of a winter/early spring Ecological impacts from these operations use regime. are localized and present a significant prob- lem mainly in areas where they overlap with The Influence of Mining Figure 3.17. A limestone quarry in the San Much of the assessment area is under min- Bernardino Mountains. DEVEREE VOLGARINO ing claim, with the notable exception of large portions of the San Gabriel Mountains, but commercial mining in the region is not ex- tensive. Most claims are small, individual operations. The primary hub of mining activ- ity is in the northeastern San Bernardino Mountains, where high-grade limestone de- posits 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 104 Chapter 3

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

Habitats/Species Effects Associated Current Trends and Key Issues Most Affected with Mining Activities Areas Most Affected

Habitat degradation Aquatic and riparian Suction dredging, sand and Coordination between FS or impacts to TES habitats/species. gravel mining, and some and CDFG is occurring to species from in-stream prospecting activities can cause clarify permit process for mining operations. localized habitat degradation suction dredging and identify and/or direct mortality to TES areas for closure. Low- species. Of primary concern is elevation, large-order where such activities overlap streams are most affected. with occurrences of sensitive Suction dredging occurs habitats or species. frequently on the San Gabriel River.

Habitat degradation Limestone outcrops and ¥ High-grade limestone deposits ¥ A site-specific conservation or impacts to TES associated endemic in the northeastern San strategy is currently being species from hardrock plants. Bernardino Mountains has led developed to address the mining. to the development of open-pit San Bernardino Mts mines in an area where there limestone issue. are a large number of rare ¥ Some localized habitat plants. degradation is resulting from ¥ Active mining of tourmaline other hardrock mines, but in and other gemstones primarily general the assessment on private lands in the Palomar area is not an active mining Mountain area. region.

Potential impacts to Nonspecific, but Much of the assessment area Currently there are few habitats or species greatest potential is in is under mining claims. There active commercial mines from future desert-montane is potential for commercially outside of the San development of habitats. viable deposits of low-grade Bernardino Mountains, existing mining claims. gold, gemstones, or oil and limestone region. gas. sensitive habitats or species (table 3.20). The ter turbidity, (2) disturbance of channel mor- most prominent example of such overlap is phology and bottom substrates that serve as the occurrence of an entire assemblage of en- spawning areas for fish, and (3) direct mortal- demic, rare plants on high-grade limestone ity of fish and amphibian eggs and larvae in deposits in the San Bernardino Mountains. the sediment vacuuming process. The signifi- A commonplace form of mining in the cance of these impacts varies by site and region’s larger streams is suction dredging. depends largely on the site’s ecological integ- Suction dredges utilize high-pressure water rity (e.g., naturalness of the hydrologic regime, pumps driven by gasoline-powered motors other prevailing land uses, presence of rare or which create suction in a flexible intake pipe. at risk species, and presence of exotic species). A mixture of streambed sediment and water The State of California regulates suction is vacuumed into the intake pipe and passed dredging activities. The Department of Fish over a sluice box mounted on a floating barge. and Game (CDFG) is required to issue per- Dense particles (including gold) are trapped mits to suction dredge if it determines that in the sluice box. The remainder of the en- the operation will not be deleterious to fish. trained material is discharged into the stream They can also institute seasonal closures to as “tailings” or “spoils,” which can form large reduce impacts. The CDFG is currently con- piles where dredges have remained in one lo- ducting a statewide environmental review of cation for a long period (Fredley 1995). its policy on suction dredging (USFWS 1998a). Suction dredging can have a number of impacts on aquatic habitats: (1) increased wa- 105 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.

The Influence of Private Land Development

Development on private lands is steadily consuming wildland habitats (fig. 3.18) and Figure 3.18. Housing construction in an isolated area adjacent to the Cleveland National Forest. JOHN reducing connectivity between the natural ar- STEPHENSON eas that remain. This trend poses some significant challenges for conservation of habi- tats and species on public lands (table 3.21). The Influence of Air Pollution In the southern end of the assessment area, rapid development has the potential to elimi- Long-term studies to determine the effects nate habitat corridors between the mountain that air pollution is having on forest vegeta- ranges. These corridors are believed to be im- tion have occurred in the San Bernardino portant for the movement of some Mountains and, to a lesser extent, in the San wide-ranging animals. Mountain lions in par- Gabriel Mountains (Miller et al. 1996; Miller ticular are vulnerable to declines if individuals and McBride 1999). Prevailing climatic con- in one mountain range become cut off from ditions transport most of the air pollution from the larger population (Beier 1993). the Los Angeles Basin into these mountains Development tends to simplify ecological (Miller et al. 1989). The two depositional communities, eliminating some species and components of air pollution that have the increasing the abundance of others. Species greatest effect on ecosystems are ozone (re- with wide tolerances and generalized habitat viewed in Miller et al. 1996) and nitrogen requirements (common traits of exotic species) (reviewed in Bytnerowicz and Fenn 1996). are the ones that typically thrive in developed areas. In addition, a number of plants com- Ozone Deposition monly used in landscaping are on CalEPPC’s Studies have determined that ponderosa list of Exotic Pest Plants of Greatest Ecologi- and Jeffrey pine trees, and to a lesser extent cal Concern, including arundo, tamarisk, ice bigcone Douglas-fir, are experiencing foliage plant, pampas grass, Russian olive, fountain injury from ozone deposition (Miller et al. grass, and Brazilian pepper tree. 1989; Peterson et al. 1995). Other tree spe- cies 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 high- est 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). 106 Chapter 3

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

Effects Associated Habitats/Species with Private Land Current Trends and Key Issues Most Affected Development Areas Most Affected

The distribution, ¥ Coastal sage scrub Development on private land is Development is occurring extent, and integrity ¥ Engelmann oak reducing the extent of native most rapidly in Orange, San of habitats and woodland habitats and fragmenting those Diego, Riverside, San species which occur ¥ Valley oak woodland habitats into disjunct patches. Bernardino, Ventura, and predominantly on ¥ Grassland This increases the significance Santa Barbara counties. private lands. ¥ Montane meadow of these habitats on public Several counties are lands. developing habitat or species conservation plans which attempt to conserve key areas and provide corridors to the surrounding public lands.

Fragmentation of Species with large Buildout on private lands can Imperiled habitat animal populations area requirements eliminate habitat connections connections include: Santa caused by the loss that disperse along between mountain ranges Ana Mts — Palomar Mtn; of wildland habitat or near the ground unless natural habitat corridors Palomar Mtn —San Jacinto corridors between (e.g., mountain are designated and protected. Mts; San Jacinto Mts — San mountain ranges. lions). Bernardino Mts.

Effects associated ¥ Peninsular bighorn ¥ Drives disturbance-intolerant Urban interface is expanding with expansion of the sheep species away from preferred rapidly on both the desert urbanÐwildland ¥ Many habitats/ habitats and coastal sides of the San interface. species affected by ¥ Increases the risk and Gabriel, San Bernardino, altered fire regime and difficulty of using fire as a and San Jacinto mountains spread of non-natives management tool and on the coastal side of ¥ Contributes to rise in San Diego and southern Los invasive, non-native species Padres ranges.

Effects associated Nonspecific. Power lines, pipelines, water Requests for infrastructures with increased urban storage, communication to cross through or be infrastructure needs facilities, highways, landfills, located in the mountains are on public lands. sewage treatment areas, etc. increasing as urban areas can cause localized habitat expand. degradation and habitat fragmentation and provide avenues for the spread of invasive, non-native species.

Pine mortality was highest during ex- levels and tree damage. Forests on the western tended periods of low precipitation (droughts), side of the range are exposed to much higher when these trees are most vulnerable to bark levels of ozone and are experiencing the most beetles. Trees with chronic ozone injury enter damage (Miller et al. 1989). Monitoring of a period of drought without the reserves re- study sites in the west-side forests over a quired to mount an active defense against bark fourteen-year period (1974 to 1988) found beetle attack (Miller et al. 1991). that ponderosa and Jeffrey pine are losing basal In the San Bernardino Mountains, there area in relation to competing species that are is a clear west-to-east gradient in both ozone more tolerant to ozone, namely, white fir, 107 Table 3.22. Key ecological issues that are influenced by air pollution.

Habitats/Species Effects Associated Current Trends and Key Issues Most Affected with Air Pollution Areas Most Affected

Vigor and longevity ¥ Ponderosa and High levels of ozone ¥ Rates of ozone deposition of forest trees, Jeffrey pine deposition is a chronic have declined from 1970s particularly of those ¥ Bigcone Douglas-fir condition in some areas and is peaks, but are still some of species most known to reduce the vigor of the highest in the U.S. sensitive to ozone trees sensitive to it. This leads ¥ Western San Bernardino damage; to increased mortality and Mountains and eastern San ramifications to appears to be contributing to a Gabriel Mountains are most structure and shift in tree species affected. composition of mixed composition. conifer forests.

Shifts in the structure ¥ Coastal sage High levels of nitrogen Western San Bernardino and composition of scrub deposition is a chronic condition Mountains and eastern San plant communities ¥ Mixed conifer in some areas. Elevated Gabriel Mountains are highly and reduced water forests nitrogen levels in the soil has a affected, as are lowland quality related to fertilizing effect for some areas on the coastal side of excessive nitrogen species, altering community the mountains (e.g., western inputs. dynamics. Runoff into streams Riverside and San and groundwater is elevating Bernardino counties). water nitrate concentrations.

incense-cedar, and black oak (Miller et al. cies, soil acidification, altered species compo- 1996). The accumulation of more stems of sition, decreases in mycorrhizal root symbiosis, ozone-tolerant species in the understory presents and elevated concentrations of nitrate in soil, a fuel ladder situation that jeopardizes the re- groundwater, and streams (Bytnerowicz and maining overstory trees in the event of a Fenn 1996; Padgett et al. in press). Recent catastrophic fire. studies in Riverside County indicate that high Quantitative information on ozone dam- levels of nitrogen deposition may be contrib- age is scarce for other mountain ranges within uting to the decline of coastal sage scrub and the assessment area. However, given the loca- its conversion to Mediterranean annual grass- tion of major pollution sources and prevailing land (Allen et al. 1997). wind patterns, it appears that areas of high Spatial patterns in levels of nitrogen depo- potential for damage are probably confined sition mirror that described for ozone. Eastern to the eastern San Gabriel and western San Los Angeles County and western San Bernar- Bernardino mountains (P. Miller, Riverside dino and Riverside counties receive the highest Fire Lab, pers. comm. 1997). concentrations. In the mountains, the coastal side of the eastern San Gabriel and western Nitrogen Deposition San Bernardino mountains are the most pol- The effects of nitrogen deposition on lo- luted (Bytnerowicz and Fenn 1996). In cal forests and shrublands have not been montane conifer forests, the fertilizing effect studied for as long as ozone and are only be- of nitrogen may be accelerating understory ginning to become apparent. High rates of development of white fir and incense-cedar, nitrogen deposition have increased soil fertil- thereby elevating fuel loads and potentially in- ity and surface litter decomposition rates in creasing the risk of stand-replacing fires. some mixed conifer forests in the San Bernar- Riggan et al. (1985) reported elevated con- dino Mountains (Fenn 1991b). However, centrations of particulate nitrate in stream excessive nitrogen inputs can lead to various water emanating from watersheds exposed to negative effects, including nutrient deficien- high nitrogen deposition in the San Gabriel 108 Chapter 3 Mountains. Stream water particulate nitrate crease. The three GCMs predicted increases concentrations in watersheds heavily influ- in precipitation for the months of November enced by urban air pollution were one to three through March of 36, 21, and 21 percent. Pre- orders of magnitude greater than in watersheds dicted increases for March and April were 59, which were not exposed to high concentra- 17, and 27 percent (Davis and Michaelsen tions of air pollution. Sharp peaks in 1995). particulate nitrate levels occur during the first The fire regime simulations were very sen- winter storms when the ecosystem is loaded sitive to predicted increases in fire season with nitrogen accumulated during the dry temperatures and equally sensitive to large summer months. Additional information is changes in stand productivity. Total area needed on the extent of this problem and how burned was predicted to increase and the fire- it is affecting aquatic ecosystems. recurrence interval was predicted to significantly decrease (Davis and Michaelsen 1995). Westman and Malanson (1992) suggest that Climate Change these changes could lead to potentially large Considerations changes in chaparral composition. The subject of long-term climate change is really beyond the scope of this report. Re- search on this topic is generally conducted at continental or global scales, making it diffi- cult 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 par- ticularly local fire regimes, might be affected. Although highly speculative, some of the lo- cal 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 re- gimes in southern California chaparral ecosystems. To figure out what those climate changes would be, they used predictions from three widely accepted general circulation mod- els (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 occur- ring in the assessment area would be an increase in average daily maximum and mini- mum temperatures of 1 degree to 4 degrees Centigrade. There is more uncertainty associ- ated with precipitation predictions, but the various GCM results are in general agreement that winter and spring precipitation should in- 109