<http://geology.csupomona.edu/janourse/SGMmapping.htm>
<http://www.corbamtb.com/issues/Misc/Images/SanGabAltC.jpg>
Southern and Central Coast Province Areas.<http://www.fs.fed.us/r5/rsl/clearinghouse/aa-download.shtml>
<http://www.freqofnature.com/frequencies/usgov/usda/images/usfs_r5_map_angeles.jpg>
The San Gabriel Mountains are a transverse (East-West) mountain range located in northern Los Angeles County and western San Bernardino County, between the Mojave Desert and the Los Angeles Basin, with the San Andreas Fault forming the northern border of the range. Much of the area of the mountains lies within the Angeles National Forest, a national park administered by the United States Department of Agriculture Forest Service. According to the Forest Service's website, the Angeles National Forest was established by Executive Order in 1892 and consists of over 650,000 acres. In addition, there are five wilderness areas within the Angeles National Forest: San Gabriel Wilderness (36,000+ acres), Cucamonga Wilderness (1964 - 1/3 of 12,781 acres in Angeles; rest in San Bernardino National Forest), Sheep Mountain Wilderness (1984 – 44,000 acres), Magic Mountain Wilderness (2009 – 12,282 acres), and Pleasant View Ridge Wilderness (2009 - 26,757 acres). There is also the San Dimas Experimental Forest which was established in 1933 to study the hydrology of semi-arid steep terrain. The Angeles National Forest's most obvious use to people is recreation, which can be good in allowing the conservation of natural habitats, but which also has its downsides.
The San Gabriel Mountains are home to the Nelson's bighorn sheep, a sensitive species. This sheep population makes up the largest bighorn sheep population in California. However, this population is declining. According to Bleich et al in their article "Fire History in a Chaparral Ecosystem: Implications for Conservation of a Native Ungulate," the population of bighorn sheep in the San Gabriel Mountains has decreased from 740 in 1980 to 63 in 2002. This decrease in the sheep population is thought to be linked to succession of chaparral vegetation due to fire suppression. According to Bleich et al, this is due to the fact that increased height of chaparral plants limits visibility for the sheep and makes them more susceptible to being hunted by mountain lions. In addition, Bleich et al state that "infrequent but high-intensity fires increase forage quality in the short term and, in the SGM, improve habitat suitability for mountain sheep for about 15 yr... [and that] densely vegetated areas are avoided... [Thus,] availability and quality of forage, in addition to visual openness, [are] factors affecting selection of burned areas by mountain sheep" (575-6).
This decline in the bighorn sheep population is also addressed in a publication by the Forest Service (Chapter 6: Game and Other High-Interest Species), in which it is stated that "census data collected since the early 1980s suggest that the San Gabriel Mountains’ bighorn sheep population has declined substantially over the last twenty years" (325). In addition, the publication also goes on to state that the "decline of sheep in the San Gabriel Mountains [is due] to lack of recent fires, resulting in habitat succession that has altered the abundance of suitable sheep habitat and enhanced the vulnerability of sheep to mountain lion predation" (326). In addition to fire suppression, another problem facing the bighorn sheep is the presence of humans in their ecosystem. According to the publication by the Forest Service, "Bighorn sheep are considered sensitive to the presence of humans, particularly high levels of human activity in their line of sight, and may abandon habitat due to human encroachment" (326). In addition, the publication states that "increased human use in the Baldy Notch area, particularly summer use concentrated around the Mount Baldy Ski Area base facility, has caused sheep to avoid areas that were previously utilized" (326).
This decline in the bighorn sheep population is also addressed in a publication by the Forest Service (Chapter 6: Game and Other High-Interest Species), in which it is stated that "census data collected since the early 1980s suggest that the San Gabriel Mountains’ bighorn sheep population has declined substantially over the last twenty years" (325). In addition, the publication also goes on to state that the "decline of sheep in the San Gabriel Mountains [is due] to lack of recent fires, resulting in habitat succession that has altered the abundance of suitable sheep habitat and enhanced the vulnerability of sheep to mountain lion predation" (326). In addition to fire suppression, another problem facing the bighorn sheep is the presence of humans in their ecosystem. According to the publication by the Forest Service, "Bighorn sheep are considered sensitive to the presence of humans, particularly high levels of human activity in their line of sight, and may abandon habitat due to human encroachment" (326). In addition, the publication states that "increased human use in the Baldy Notch area, particularly summer use concentrated around the Mount Baldy Ski Area base facility, has caused sheep to avoid areas that were previously utilized" (326).
Another benefit to humans that the San Gabriel Mountains, in conjunction with the Angeles National Forest, provides is water. The large human population of the Los Angeles Basin requires a lot of water, and while much of this water now comes from the Colorado River or the California Aqueduct, the San Gabriel Mountain watershed is still an important source of Los Angeles' water. The primary source of this water is the San Gabriel River. For reasons of flood control as well as water usage, the San Gabriel River is dammed twice along its course in the San Gabriel Mountains. These dams are the San Gabriel and Morris Dams (pictured below). The river is then dammed again as it leaves the mountains at the Santa Fe Dam. Obviously, such dams are never benign as they inhibit the flow of sediment and nutrients, as well as inhibit the migration of fish species.
San Gabriel River Flood Control.<http://earthobservatory.nasa.gov/IOTD/view.php?id=5215>
The likely prospect for the San Gabriel Mountains is that they will continue to be protected within the Angeles National Forest and its wilderness areas. We did not find any information in our research that would cause us to conclude otherwise. We feel that the mountains are deemed too important by Angelenos and others for their natural beauty and for the services they provide to become significantly degraded. However, there are some things that could be done better to ensure the stability of the ecosystem.
(Bleich et al)
(Bleich et al)
(Bleich et al)
(Bleich et al)
(Bleich et al)
(Bleich et al)
Aside from continuing to ensure the preservation of the ecosystem through the Angeles National Forest, the most important thing that can be done to improve the situation is to allow for the natural fire patterns to return. Bleich et al espouse this sentiment in regards to the bighorn sheep population when they state that the "use of prescribed fire to simulate a more natural fire regime, and thereby to enhance availability and suitability of habitat, should receive serious consideration by land managers" (578). Another thing that can be done to improve the ecosystem is to further limit human activity in sensitive areas, such as the Baldy Notch. This is especially important in the case of the bighorn sheep, as mentioned above. If these things are done, then the ecosystem will flourish and will be able to continue to be enjoyed by future generations for years to come.Works Cited
Bleich et al. Fire History in a Chaparral Ecosystem: Implications for Conservation of a Native Ungulate. Rangeland Ecology & Management, 61(6):571-579. 2008. Society for Range Management.
Angeles National Forest. August 3, 2009. USDA Forest Service - Staff Office. <http://www.fs.usda.gov/main/angeles/home>
“San Dimas Experimental Forest.” US Forest Service – Experimental Forests. August 28, 2008. USDA Forest Service – Staff Office. < http://www.fs.fed.us/psw/ef/san_dimas/>
“Lakes and Reservoirs of Los Angeles County.” LA Almanac. <http://www.laalmanac.com/geography/ge02.htm>
