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NATURAL HISTORY

of the

Klamath-Siskiyou bioregion 

Every place has a story...

The mixed conifer plant community in my bioregion is a part of the 10-million-acre bioregion commonly referred to as the Klamath-Siskiyous (KS).  Its boundaries are defined on the east by the Coast Range running north-south along Oregon’s west coast, the west by the Cascade Mountains running north-south close to Oregon’s center, and the south by the Siskiyou Crest Mountains running east-west through northern California and southern Oregon.  The Siskiyous, actually a sub range of the Klamath Mountains, act as a land bridge between the Coastal Range and the Cascades. 

It is home to 3,500 plant species, 281 of which are endemic, including 35 species of conifers making it the most diverse temperate forest in the world.   The elevations of the Siskiyou Crest range from sea level to its highest peak, Mt. Ashland, at 7,533 ft.  It is the complex and poorly understood geologic history of the Siskiyous that has provided for such a biodiversity to exist. The geology of the KS is a result of thousands of years of pressure and movement between oceanic and continental plates.  This is unlike the Cascades that were built through violent volcanic activity. Some 300 to 160 million years ago, the collision of the Continental and Pacific plate resulted in the emergence of an island that would become the KS Mountains, which later would join the Klamath Mountains (North Mountain Park Nature Center, 2013). Species of animals and plants began to colonize at this time, but unlike most of North America this island was spared periods of glaciation. 

The Rogue River Valley is born

37 million years ago, another series of tectonic activities took place, giving rise eventually to the Cascade Mountains and the Oregon Coastal Range. The emergence of these mountains created a land locked lake in the area that would later become the Rogue River Valley. This began the catchment of sediment that would later become the fertile soil that makes this area the agricultural center it is today (Watson, 1909).   The water that filled this lake would slowly carve its way to the ocean, eventually creating the Rogue River Valley of current times.  

A changing climate

Throughout the next 13 million years, conditions in the region slowly moved from sub-tropical to the more “Mediterranean climate” of today, frequently fluctuating between warm and cold periods and even glaciation (Todt, 1990). The connection of the Siskiyous with other landforms, its unique soil composition, coupled with the fluctuations in temperate, created a rhythm of species advancement and retreat.  During times of warmer or cooler climactic conditions, successive migrations would occur from areas north, south, east, and west of the Siskiyou Mountains (Todt, 1990).  Species like the Pacific silver fir would move in from the north during cold moist spells, while the white Manzanita from the south would move in during periods of dry warmth (Todt, 1990).  When conditions would change, once accommodated species would recede, often leaving small isolated patches in distinct micro-climates found throughout the Siskiyous even today.  The pollen and fossil records from this time show evidence that the area once supported a temperate forest including species like the dawn redwood, magnolia, hickory, beech, and gingko.  As conditions changed to become cooler and drier, deciduous hardwoods either retreated to the southeast of North America where the summer rain they required was still available, were limited locally to riparian zones, or became extinct from the North American continent entirely, such as the dawn redwood now of China (Wallace, 1983). It is also believed that the Siskiyous provided refuge for many species during periods of glaciation; the Siskiyous relatively untouched by glaciers become yet again an island, this time, in a sea of ice (Ruediger, 2013).

It is currently believed that near the end of these periods of glaciation, 14,000 to 12,000 years ago, began the first inhabitation of the Pacific Northwest by humans (Jenkins, 2014).  They are thought to have traveled via the Bering Strait in small groups, hunting large game like the mammoth, camel, and three-toed horse (Sutton, 1973).  These early people were highly nomadic.  During this time the climate of southwest Oregon was undergoing a dramatic and consistent shift from a cooler climate to the Mediterranean climate we know today of hot dry summers and cool wet winters. This caused a great expansion in the range of species adapted to warmer and drier conditions (Todt, 1990).  This includes much of the chaparral plant community such as madrone, white oak, Manzanita, ceanothus, buckbrush, California coffeeberry, and yerba santa.  All of these species are now iconic plants of this bioregion.  Fire played an important role in sculpting this landscape.  With the increased frequency of fires due to drier conditions, many species evolved fire related adaptations and distribution patterns (Ruediger, 2013).