High Desert & Great Basin. Part 2

24 Aug

“Cataclysmic transformations such as moving continents, lava inundations, freezing Ice Ages, and apocalyptic floods exterminated entire plant and animal communities while successive new life forms adapted. Relative to these expansive epochs, human life spans seem but mere seconds in duration. This myopic snapshot of our current familiar environment with its modern species can foster an inaccurate perception of unchanging surroundings. But the fossil records tell us otherwise.” – Alan St. John, author of Oregon’s Dry Side.

Climate change is not a stranger to the Pacific Northwest. With two mountain ranges that run north and south, modern residents and visitors can experience the coastal fog or cool and temperate summers and winters in Oregon’s Willamette River valley between the Coastal and Cascade mountain ranges. On the east side of the higher peaks of the Cascades, and in the rainshadow of these same mountains, lies central and eastern Oregon. Here, springtime is later, summers more hot and dry, and winters cold and snowy. Yet a common denominator throughout the state is water, just in varying volumes and persistence. Water is not a stranger to even the most arid regions of modern Oregon.

Not only did Oregon’s terrain change and shift numerous times, so did the climate. Fossils from eastern and central Oregon, especially from the John Day River area, reveal the climatic conditions and the flora and fauna that lived in the area beginning 55 million years ago (mya). After a long period (~10 my) following global decimation by a planet-wide catastrophe in the Paleocene , life began to repopulate the entire continent. The Pacific Northwest became a lush subtropical region dominated by forests. Small mammals that survived in small pockets during the catastrophe began diversifying into a multitude of forms.

Conditions shifted again, possibly due to another global catastrophe,  some 34 mya to a cooler and drier temperate climate. Grasslands replaced subtropical forests and animals more suited to grazing dominated, as did their predators. This cooling trend continued on into the Pleistocene and culminated in the Ice Age.

Climate in the Pacific Northwest shifted again 10-12 thousand years ago back to more temperate conditions. The ecosystems we see now are the results of this shift. This long and active changing geological and climatic history has left its marks on the land and the life that lives on it.

Harney Lake in early August.

Northern Great Basin

The Great Basin’s northern region lies in Southeastern Oregon between the dramatic upthrusts of fault blocks and in sunken basins. Surrounded by miles of dry steppe vegetation zones are many ancient inland seas and lakes. What was once teeming with wading animals, lush tropical trees,and ancient birds are now sun-scorched basins. These dessicated lakebeds with alkaline and sandy soils are the only true deserts of Oregon.

Because the term ‘desert’ is a wide classification of regions that have an annual moisture deficit, such areas can be further categorized as semi-arid or arid. A semi-arid region is a climatic area that receives precipitation less than the combined potential of evapo-transpiration (combination of transpiration via plants and evaporation*), although not extremely. An arid region has a severe lack of available water and where the evapo-transpiration rate significantly exceeds annual precipitation to the extent that normal growth and function of all life is impaired or limited.

Although most of central and eastern Oregon is considered semi-arid, a ‘true’ desert is an area where vegetation is exceedingly sparse and rainfall is also very rare and infrequent. Interspersed amongst the semi-arid steppe lands of the northern Great Basin are isolated lakebeds (playas) that lie within double rainshadows. Precipitation is usually less frequent due to the barriers of the Cascade mountains to the west and tall block fault mountains to the east. Some of these playas may be simply expanses of sand or cracked alkali-encrusted soil, or they may hold seasonal water.

Thriving Watersheds

As the climate warmed, melting glaciers of the Ice Age formed giant pluvial lakes covering much of the Great Basin while rivers carved deep canyons and gorges. Temporary connections between rivers and the lakes may have permitted fish to migrate from the rivers. But, as the climate warmed, the inland lakes dwindled or dried completely. Many of these reservoirs became shallow lakes with feeder streams and fish populations were trapped, where some evolved into unique species.

Most of these basins are closed systems that retain water with no outlfow to external bodies of water. Instead, precipitation draining from higher ranges seasonally feed marshes and playas where they may be seasonally or permanently wet depending on annual evaporation and the presence of springs.

Seasonal and annual water levels depend on a variety  of factors: winter snow pack, rate of snow melt, cycles of drought and rains, and summer temperatures. Typically, water in drainage basins either flows out into larger water bodies or diffuses through permeable rock. However, water in many of the playas in the Great Basin leaves only by evaporation and seepage. Thus the bottom of such basins become salt lakes or salt pan.

Buena Vista marshlands of Malheur National Wildlife Refuge.

Harney Basin: High Desert and Wetlands

At the most northeast corner of the Great Basin region and in Oregon is Harney Basin. Covering 1,490 square miles, it is the watershed of Malheur and Harney Lakes. Both are not true lakes, but playas once divided by a sand dune. Before the sand dune was breached by settlers in the early 1900’s, the Malheur Lake was a freshwater lake, while Harney Lake was saline-alkaline.

The basin receives an average of 6 inches of rain per year, but the surrounding mountains may have 15 inches of precipitation. Both playas receive water from streams originating within the basin in the surrounding mountains, including the Silvies River from the north and the Donner und Blitzen River (often called the Blitzen River) from the south. The watershed of the latter river is the Steens Mountain, which stretches some 50 miles north to south and attains an elevation of 9,733 feet at the summit.

The Harney Basin is considered a part of the larger High Desert Wetlands ecoregion, which consists of high desert lakes and surrounding wetlands. These marshes and seasonal reservoirs provide critical habitat for nesting and migratory birds as well as associated upland birds and mammals. Both Harney and Malheur lakes cycle between open water in wetter years and marshes in drier years. The wetlands around Malheur Lake and the Blitzen River form a wetlands oasis in the basin and has served as habitat for many migratory bird species since before human presence in the Basin.

Malheur Lake and most of the Blitzen River valley are now included in and managed by Malheur National Wildlife Refuge. Each year as many as 320 species of birds and 58 species of mammals can be found in the refuge. Among these, Malheur serves as a Pacific Flyway stop for the Northern Pintail duck and Tundra Swan, Lesser and Greater Sandhill Crane, Snow Goose and Ross’ Goose. Ducks, grebes, pelicans, terns, and trumpeter swans are drawn to the numerous ponds, marshes and lakes. Many raptors, including Peregrine falcons, also call the Refuge home.

This juxtaposition of high desert and watershed with its rich wildlife is indeed a jewel and gem. And one I am grateful to experience this summer.

“Unaccustomed to the desert, we may literally overlook what is directly in front of us. A true irony: not being able to see the desert for lack of trees.” – Alan St. John, author of Oregon’s Dry Side.

 

* Potential evapo-transpiration is the amount of water that would be evaporated and transpired if there was sufficient water available.

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