Siskiyou Ecological Province

 

 

Location

The Siskiyou Ecological Province in Oregon encompasses a very small area in the southwest corner of Klamath County, most of Jackson County, the southern portion of Douglas County, all of Josephine County, and the mountainous eastern portion of Curry County. It extends about 100 air miles east to west and about 75 air miles north to south in Oregon. Siskiyou Province covers about 3.7 million acres in Oregon and extends into California.

Description

Siskiyou Province in Oregon is influenced by the mild climate of northern California. Physiographically, the portion of the province in Oregon encompasses nearly the entire Rogue River drainage system, including its tributaries, the Illinois and Applegate rivers. The lower Rogue River—about 15 riverbank miles upriver from Gold Beach—is in the normal coastal fog zone and, therefore, in Coast Province. Headwaters of the Rogue River above about 4,000 feet elevation in northeastern Jackson County are in Cascade and Mazama provinces. However, tributaries to the Rogue below about 4,000 feet elevation in eastern Jackson County are in Siskiyou Province.

The South Umpqua River drainage in southern Douglas County is in Siskiyou Province upriver from the Highway I-5 bridge over the river, which is about 4 miles northwest of Myrtle Creek community.

A small portion of Siskiyou Province in southwestern Klamath and southeastern Jackson counties is drained south by Klamath River which flows into California. A small area of Siskiyou Province in southeastern Curry County is drained to the south by Smith River.

Siskiyou Province in Oregon includes extensive mountainous areas of the Klamath and Siskiyou mountains and the western slopes of the Cascade Mountains in which dendritic drainage patterns are seen in steep terrain (Fig. 37). Geomorphic features include granitic, serpentine, schist, volcanic, sedimentary, and intrusive igneous rocks. Valleys of the Rogue, Illinois, and Applegate rivers and their major tributaries consist of flood plains, terraces, alluvial fans, and low hills which formed through geologic erosion and extensive deposition of alluvial outwash and colluvium from surrounding mountains.^{59, 61} Rocks of Klamath Mountains are considered to be much older than those in any other part of western Oregon, and the area probably contains the oldest geologic formations in the state.⁹

Figure 37: A mosaic of wedgeleaf ceanothus, Oregon white oak, and grassy openings typifies the nonforested portions of Siskiyou Province, Oregon

The highest elevation in Siskiyou Province in Oregon is Mt. Ashland at 7,533 feet, which is about 7 air miles south of the city of Ashland in Jackson County. Other high promontories in the province in Oregon include Whiskey Peak, 6,497 feet, in the headwaters of Applegate River, and Chinquapin Mountain, 6,155 feet, Soda Mountain, 6,135 feet, and Table Mountain, 6,125 feet, all east of Ashland. Most of the mountain promontories in the province in Oregon are about 5,000 feet elevation or less.

The lowest elevation in Siskiyou Province in Oregon is on the Rogue River about 15 riverbank miles upriver from Gold Beach. In this vicinity there is a series of sharp bends in the river and upland topography that, based on hillside vegetation, apparently diminish the effects of the normal coast fog zone penetration farther upstream. This elevation is less than 100 feet.

Soils

The geomorphology of soils typifying Siskiyou Province in Oregon involves a wide variety of parent materials ranging from geologically recent alluviums in valleys to what is thought to be the oldest geologic formations in the state. This is further complicated by the presence within the province of the lower western slopes of Cascade Mountains in southeastern Douglas and eastern Jackson counties, of the Siskiyou Mountains in southern Josephine County, and of the Klamath Mountains in Josephine and Curry counties, each of which is significantly different from the others.

Soil parent materials in Siskiyou Province can be grouped into six general categories: soils formed in materials weathered from igneous rocks; sedimentary, sandstone, and siltstone rocks; altered sedimentary and igneous rocks; granitic rocks; serpentine rocks; and schist rocks.^{56, 61, 91, 95} Each of these six categories includes a distinct group of soil series which may vary according to location within the province (Table 32).

The data in Table 32 reflect the fact that soils derived from igneous materials in Siskiyou Province in Oregon have been mapped only in Jackson County. Based on field studies, these soils were mapped primarily in eastern Jackson County where the line of demarcation lies between Siskiyou and Cascade and Klamath provinces, both with extensive igneous formations. Soils derived from sedimentary, sandstone, and siltstone rocks have been mapped in Jackson and Curry counties. Soils derived from altered sedimentary and igneous materials have been mapped in Douglas, Jackson, Josephine, and Curry counties; these parent materials exist over a major portion of Siskiyou Province in Oregon. Soils derived from granitic rock have been mapped in Jackson and Josephine counties. Granitic parent materials appear as low as about 800 feet (Siskiyou soil series) to about 7,000 feet elevation (Crannier soil series), both in Josephine County. Soils derived from serpentine materials have been mapped in Josephine and Curry counties. These soils are very high in magnesium and very low in calcium, which limits plant growth and results in the growth of specific plant species that apparently can tolerate this radical imbalance of soil nutrients.

In general, the soils of Siskiyou Province in Oregon are clayey, especially in the subsoils. Soil formed in materials weathered from granitic rock, however, are loamy and sandy. These factors have significant impact on erodibility, potential natural vegetation cover, and responses to management strategies.

 

Climate

The climate of Siskiyou Province in Oregon is the most diverse of all the ecological provinces in Oregon. Dramatic climatic gradients are common. One such gradient extends from the normal coastal fog zone, where average minimum January temperatures are about 40°F and average annual precipitation is about 80 inches, eastward over the crest of Klamath Mountains where precipitation exceeds 125 inches annually, to interior valleys such as at Medford where average minimum January temperatures are about 27°F and average annual precipitation is about 20 inches. A less dramatic gradient occurs north to south, from the mild, moist southern Willamette Valley to the warm dry climate of northern California.

Such regional climatic gradients are further complicated by mountainous topography of the Cascade, Siskiyou, and Klamath mountains within the province which produce a wide variety of local climatic gradients such as between Ashland at 1,750 feet elevation and Mt. Ashland at 7,503 feet elevation just 7 air miles south of Ashland.

A precipitation map⁵³ shows the highest average annual precipitation in Siskiyou Province in Oregon is about 160 inches. This is on the crest of Klamath Mountains about 10 air miles west of Cave Junction and about 30 air miles inland from the Pacific Ocean. This high country, about 4,000 to 4,500 feet elevation, is a portion of a precipitation zone receiving over 125 inches annually. The zone extends about 45 air miles, from near the California border north to about 10 miles east of Illahe, which is on Rogue River.

According to this precipitation map, Mt. Ashland, the highest promontory in Siskiyou Province in Oregon, receives about 65 inches average annual precipitation. The major portion of Siskiyou Province in Oregon receives between 20 and 50 inches average annual precipitation.

 

Vegetation

The Siskiyou Province in Oregon is defined in terms of vegetation as generally that area in southwestern Oregon that is affected by the warm climate of northern California to the extent that certain plant species common in California grow there but only rarely, if at all, in other Oregon ecological provinces. These species include wedgeleaf ceanothus, whiteleaf and hoary manzanita, boxleaf silktassel, California buckthorn, California-laurel, California black oak, Sadler oak, canyon live oak, huckleberry oak, tanoak, Jeffrey and knobcone pine, Port-Orford-cedar, and Brewer spruce.

Pacific madrone, which also occurs to a minor degree in Willamette Province to the north, is abundant and ubiquitous, except in high-elevation, cold-climate conditions, in conifer forest plant communities throughout most of Siskiyou Province in Oregon. Madrone is especially abundant as a shrub on disturbed forested areas.

Golden chinkapin, Pacific madrone, tanoak, California-laurel, and canyon live oak are species that are shrubs in arid effective environments or in snow zones but are trees in warm, moist effective environments such as north-facing exposures.

Madrone, tanoak, and canyon live oak are examples of Siskiyou shrubs that readily sprout after being injured by cutting or burning, thereby becoming significantly competitive with other plant species and causing severe restrictions in resource management strategies. In lower elevations of central and eastern portions of Siskiyou Province in Oregon, poison-oak, wedgeleaf ceanothus, whiteleaf manzanita, and a wide variety of other shrub species dominate disturbed plant communities. There is a very wide variety of shrub species within Siskiyou Province, especially on forested sites.

Changes in vegetation that are related to higher elevations begin at about 3,000 feet; the snow zone begins at about 4,000 feet. Plant species generally associated with snow zones include Douglas-fir, white fir, sugar pine, and Brewer spruce, with understory species such as prince’s-pine, Sadler oak, common snowberry, and Cascade Oregon-grape. Above about 5,000 feet elevation the colder climate is signalled by a dominance of white fir, Shasta red fir, and mountain hemlock.

Observations of Douglas-fir, the most dominant and widespread coniferous tree in both Siskiyou and Coast provinces in Oregon, indicate a subtle visual difference in this species according to which province it is in. In the more moist Coast Province, Douglas-fir usually have moss growing on them; in the drier Siskiyou Province, moss is scarce or absent.

Plant communities in southeast Siskiyou Province in Oregon include some species that typify the adjoining Klamath Province and much of eastern Oregon in general. This can be attributed to the southern termination of Cascade Province in this area about 10 air miles north of the California border at about 5,500 feet elevation. This leaves a lower-elevation gap through which plant species such as bitterbrush, birchleaf mountain-mahogany, and western juniper apparently have extended their range from east to west. There is only a mild climatic barrier between Siskiyou and Klamath provinces in the topography traversed by Highway 66 from Klamath Falls to Ashland. Consequently, the transition from one province to the other is a belt: the line of demarcation is a judgment call based primarily on the presence of such Siskiyou Province species as Oregon white oak and wedgeleaf ceanothus.

Vegetation characteristics of Siskiyou Province cited here are based on unpublished field studies.^{36, 37, 39, 51}

Temperature and the amount and timing of precipitation are primary factors in variability of local effective environments. Undoubtedly they also are major influences in the geographical distribution and abundance of certain plant species within Siskiyou Province in Oregon. However, geographic distribution of certain plant species also is somewhat related to the nature of soils formed in materials weathered from various kinds of geological formations.

 

 

Management Implications

Siskiyou Province is the most complex ecological province in Oregon, especially from a resource management standpoint. Diverse geological formations result in an unusually wide variety of soil parent materials, each having inherent features that affect local resource management strategies. The variable climate of the province, which ranges from near-coastal to arid interior valleys to near-alpine, also has great influence on resource management strategies. The situation is further complicated by the diverse assemblage of plants which includes species that are representative of contiguous provinces including the Klamath area of eastern Oregon, the lower western slopes of the Cascade Mountains, the southern portion of the Willamette Valley, the lower southeast slopes of the Coast Range, the coastal fog zone, and, most significant, the warm climate of northern California.

Resource management strategies are also complicated by the topographic pattern of interspersed valleys, low hills, dendritic drainage patterns with steep slopes and very contrasting north and south exposures, and a wide range of elevation patterns (Fig. 38).

Figure 38: Overview of the steep topography, interspersed valleys, contrasting vegetation cover, and the wide variety of elevations that, together, typify much of Siskiyou Province, Oregon

A preponderance of shrubby species in nearly all natural plant communities, typical of Siskiyou Province in Oregon, has strong influence on resource management strategies. Some of these species, such as tanoak and Pacific madrone, are trees under certain, favorable conditions but are aggressive shrubs under other conditions. Furthermore, some Siskiyou shrub species are strongly prolific when damaged by burning, logging, overgrazing, or other activity that damages the shrubs or the site. This results in areas of dense shrubs that hinder most remedial resource management activities designed to obtain natural rehabilitation and growth of desirable plant species.

Not all shrubs in Siskiyou Province have undesirable characteristics. Many forested plant communities include a wide variety of nonaggressive shrubs that help provide the necessary layering in the canopy cover, benefitting watershed quality and tree regeneration. These shrubs also provide nutritious forage important for food and cover for wildlife and domestic livestock. It is noteworthy that cattle accustomed to grazing Siskiyou-type plant communities use an unusual amount of browse in their diets by choice, even when adequate herbaceous forage is readily available.

The extent and pattern of public and private land ownership is another important feature of Siskiyou Province in Oregon that has major implications on resource management strategies. About 75% of Siskiyou Province in Oregon is publicly owned and is administered by the U.S. Forest Service and the Bureau of Land Management. Furthermore, except for the major valley area around Ashland and Medford, nearly all the private lands are in an alternate-section checkerboard pattern with BLM lands. This land pattern further complicates relationships and interdependencies that are basic considerations in resource management strategies.

Broad vegetation characteristics differentiate between Willamette and Siskiyou provinces. For example, uplands below about 1,300 feet in southern Willamette Province are typified by bigleaf maple, Oregon white oak, scotchbroom, and some Pacific madrone. Equivalent uplands in Siskiyou Province are typified by California black oak, wedgeleaf ceanothus, and abundant madrone, which strongly dominates logged or otherwise disturbed forested areas.

Province Demarcation

Siskiyou and Klamath Demarcation

The line of demarcation between Siskiyou and Klamath provinces begins at the Oregon–California border in southwestern Klamath County on the east side of Klamath River. At this point, the line coincides reasonably well with the soils line between Pinehurst, Greystoke, and Bly soil mapping units, which represent Klamath Province, and Skookum–McMullin soil map unit, which represents Siskiyou Province.⁶¹

The line travels up Klamath River about 5 miles and then meanders west to the Jackson–Klamath county line at about 4,000 feet elevation where it goes northwest to pass close by Pinehurst on Highway 66. From the vicinity of Pinehurst, the line runs north up Jenny Creek and intersects the juncture of Siskiyou, Klamath, and Cascade provinces at about 5,000 feet elevation west of Brush Mountain, which is in Cascade Province.

The demarcation line between Siskiyou and Klamath provinces in this area is not based on soil maps. Rather, the line is the approximate boundary between the area vegetated with plant communities that include oak and wedgeleaf ceanothus, which typify Siskiyou Province in this area, and the mixed-pine–mixed-fir plant communities which typify Klamath Province.⁵⁰ However, the Skookum–McMullin and McNull–McMullin soil map units are generally associated with plant communities that include white oak, ponderosa pine, and wedgeleaf ceanothus, which typify Siskiyou Province in this area, and the Pokegma–Woodcock soil map units which are associated with the mixed-pine and mixed-fir forest of Klamath Province in this area.⁶¹ Wedgeleaf ceanothus is a key indicator species of Siskiyou Province arid sites.

Siskiyou and Cascade Demarcation

The line of demarcation between Siskiyou and Cascade provinces wanders north from the vicinity of Brush Mountain at about 5,500 feet elevation to Fish Lake and along the western slopes of Mt. McLoughlin, which is in Cascade Province. The line continues north in the headwaters of Big Butte Creek and its tributaries, on to Rustler Peak, and then northwest to cross Rogue River and Highway 62 about 6 miles below the community of Prospect.

The line in this area is based on forested plant communities dominated by Douglas-fir, grand fir, sugar pine, and ponderosa pine, which represent Siskiyou Province, and forested plant communities dominated by mountain hemlock and true firs, which represent Cascade Province.⁵⁰

From where the line crosses Highway 62 near Prospect, it runs northward around the headwaters of Elk Creek and South Umpqua River at about 4,000 feet elevation. The line turns west around headwaters of tributaries of South Umpqua River, which are in Siskiyou Province, at about 3,500 feet elevation. Consequently, the south- and west-facing slopes along South Umpqua River are in Siskiyou Province. In the vicinity of Tater Hill, the line veers northwest to White Rock at about 3,000 feet elevation and on to Lane Mountain where Siskiyou, Cascade, and Willamette provinces join.

The line between Siskiyou and Cascade provinces in the vicinity of South Umpqua River is based on the presence of western hemlock in Cascade Province forested plant communities and a lack of western hemlock in the more arid forested plant communities of Siskiyou Province. The line is supported in this area by such soil series as Holderman and Keel, which represent Cascade Province,⁹¹ and Lettia, Beal, Acker, Kanid, and Atring series, which represent Siskiyou Province.⁹⁵

Siskiyou and Willamette Demarcation

From the junction of Siskiyou, Cascade, and Willamette provinces on Lane Mountain about 10 air miles east of Roseburg in Douglas County, the line of demarcation between Siskiyou and Willamette provinces goes southwest down the ridge to Brushy Butte and Dodson Mountain to cross South Umpqua River at the Highway I-5 bridge over the river about 4 air miles northwest of Myrtle Creek community.^{36, 95} From the Highway I-5 bridge, the line follows the southern border of bottomlands along South Fork Umpqua River and Olalla Creek at about 600 feet elevation. From there it veers south up the ridge separating drainages flowing west into lower Olalla Creek, in Willamette Province, from drainages flowing north, which are in Siskiyou Province, to Big Baldy Mountain about 4 air miles northwest of Riddle community.

From Big Baldy Mountain the line goes southwest along the ridgetop at about 2,500 feet elevation past Buck Mountain to Table Mountain where it curves north to circle the headwaters of Olalla Creek, which is in Siskiyou Province. The line follows the ridge from Live Oak Mountain southwest to Chipmunk Ridge, which is where the junction of Siskiyou, Willamette, and Coast provinces lies.

The line between Siskiyou and Willamette provinces, which is about 70 miles long, is not always clear-cut in terms of soil or vegetational differences. Both provinces have arid, warm climatic conditions though Siskiyou is relatively more arid and warmer than Willamette Province. The line was selected by using data shown on the 1993 Preliminary General Soil Map, Douglas County, Oregon⁹⁵ which covers the area where these two provinces join. The line was drawn between upland soils that have been mapped definitely within Willamette Province to the north and upland soils that have been mapped in other areas definitely within Siskiyou Province. Upland soils definitely associated with Willamette Province include Oakland, Sutherlin, Nonpariel, Philomath, and Dixonville series. Upland soils definitely associated with Siskiyou Province include Speaker, Josephine, Lettia, and Beal series.

Broad vegetation characteristics differentiate between Willamette and Siskiyou provinces. For example, uplands below about 1,300 feet elevation in southern Willamette Province are typified by the common occurrence of bigleaf maple, Oregon white oak, scotchbroom, and some Pacific madrone. Equivalent uplands in Siskiyou Province are typified by California black oak, wedgeleaf ceanothus, and abundant madrone, which strongly dominates logged or otherwise disturbed forested areas.

Siskiyou and Coast Demarcation

From the junction of Willamette, Siskiyou, and Coast provinces in the vicinity of Chipmunk Ridge in southwestern Douglas County, the line of demarcation between Siskiyou and Coast provinces goes south at about 3,000 feet elevation to Dutchman Butte. It follows Hayes Ridge southwesterly and south to Ninemile Mountain and continues southwesterly at about 3,000 feet elevation to north of Kelsey Peak in northeastern Curry County. From there, the line wanders west to Big Meadows vicinity and then north, west, and southwest at about 3,000 feet elevation around the upper Mule Creek watershed. It follows Panther Ridge southwesterly at about 2,000 feet elevation close to the Coos–Curry county line.

From this point, the line extends south along the east slopes of Ophir Mountain and Brushy Mountain at about 2,000 feet elevation. In the vicinity of Lake of the Woods Mountain the line goes southwest to Soldier Camp Mountain, Second Prairie Mountain, and First Prairie Mountain while decreasing in elevation from about 2,000 feet at Soldier Camp Mountain to about 1,200 feet in the vicinity of Lobster Hill just north of Rogue River.⁵¹

The line in northeastern and north-central Curry County is based primarily on the elevation at which western hemlock is a common component of forested uplands in Coast Province, compared to the common appearance of tanoak, madrone, and other plant species that signify warmer and drier conditions typifying the western part of Siskiyou Province. The line also is indicated by the general presence of such forested soils as Preacher, Bohannon, Digger, and Umpcoos, which typify Coast Province, 60and the soil series Atring, Kanid, Acker, Beekman, Pollard, and Vermisa, which typify Siskiyou Province in this vicinity.⁵⁶

In the vicinity of Lobster Hill, the line intersects the upper boundary of the normal coastal fog zone at about 1,200 feet elevation. This upper boundary coincides with the line of demarcation between provinces from this area south to the Oregon–California border. Several sharp bends in Rogue River near Lobster Hill apparently hinder the upper boundary of the normal fog zone from extending farther upriver. The line of demarcation, therefore, crosses Rogue River between Lobster Hill and Skookumhouse Butte.

The line—the upper boundary of the coastal fog zone—continues at about 1,200 feet elevation around the headwaters of Quosatana Creek and west around Kimball Hill. The line goes southwest, somewhat parallel to Rogue River, and then south at about 1,200 feet elevation. It winds up and around the headwaters of Hunter Creek, then west of Sundown Mountain, up and around headwaters of Pistol River and its tributaries, of Chetco River and its tributaries, and of Winchuck River and its tributaries at about 1,200 feet elevation.⁵¹ It crosses from Oregon into California about 8 air miles east of the Pacific Ocean.

From the vicinity east of Lobster Creek, which is a tributary of Rogue River, and south to the Oregon–California border, thedemarcation line is based on the presence of Sitka spruce, red alder, Douglas-fir, western hemlock, and other species that typify the cool, moist fog zone coastal climate as compared to the common occurrence of tanoak, Pacific madrone, and related species that signify the warmer, drier conditions typifying Siskiyou Province. This line also is indicated by the general presence of such soils as Bosland, Floras, Millicoma, and Reedsport, which typify Coast Province in this area, and Fritsland, Bravo, Mislatnah, and Pollard soil series which typify Siskiyou Province in this area.⁵⁶