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Shrub Steppe of the Columbia Basin: Our Natural Heritage

I was recently invited to put together a presentation about the biodiversity of the Columbia Basin for a regional conference about shrub steppe. Unfortunately, the conference was canceled. Rather than let the presentation sit idle on my computer, I thought I’d post it here as it seemed to be a relevant sequel to my previous post about shrub steppe. So, here it is…

The Columbia Basin’s shrub steppe contributes important and unique diversity to our regional natural heritage. In this presentation, I hope to inspire you with the subtle beauty and diversity of this landscape and highlight some of the conservation issues associated with preserving it for future generations.

I will first define what our ‘natural heritage’ is, discuss the concept of shrub steppe as this term can be used in a very broad or very specific manner, and then will provide a quick tour of the variety of ecological systems found in the Columbia Basin. Finally, I will conclude with a few slides about some of conservation issues surrounding shrub steppe.

Our Natural heritage consists of the diversity of natural features occurring in Washington State. The Washington Natural Heritage Program focuses on Washington’s biodiversity and this element of our natural heritage is what I will focus on in this presentation.

Biodiversity can be described as the genetic, species, and ecosystem diversity that results from the unique combinations of climate, geology, soils, and biological interactions that occur on the landscape.

The Washington Natural Heritage Program takes a fine filter/coarse filter approach to conserving biodiversity. The assumption is that if we focus on protecting rare species (fine filter) and rare and high-quality examples of common ecosystems (coarse filter) we’ll be able to effectively conserve Washington’s full suite of biodiversity. To achieve this goal, our primary objectives are to inventory the locations of these conservation targets, maintain a database of those locations, and provide and utilize those data to affect conservation actions.

Photo Credit: Rex Crawford, Washington Natural Heritage Program

What is shrub steppe? Depending on your perspective, shrub steppe can be defined numerous ways. Some use shrub steppe to describe a landscape. For example, the Columbia Plateau Ecoregion and Columbia Basin (a physiographic region within the Columbia Plateau Ecoregion) are often referred to as shrub steppe. From a rancher’s perspective, shrub steppe may be just another name for a rangeland--a place where livestock can thrive. Ecologists, always in search of technical terms, might choose to use standardized classification names such as “Inter-Mountain Basins Big Sagebrush Steppe Ecological System” when referencing shrub steppe. Generally speaking, shrub steppe is a grassland with shrubs.

When we talk about shrub steppe as a specific ecosystem, we are referring to those sites where shrubs (typically sagebrush) occur over a layer of bunchgrasses such as bluebunch wheatgrass and Idaho fescue. Historically, it is thought that, on average, shrub cover was probably around 10% as periodic fires kept sagebrush from becoming more dense. However, fire suppression and the introduction of grazing is though to have increased shrub cover in many areas.

We can also refer to shrub steppe as a landscape unit…in our case, the Columbia Plateau Ecoregion. A dry climate in this ecoregion has resulted in the dominance of non-forested vegetation. Most of this vegetation is comprised of the specific shrub steppe ecosystem I just described; however, there is a great deal of variation associated with shrub steppe as there are a host of other small habitats embedded within this matrix of sagebrush. 

In addition, shrub steppe is not limited to the Columbia Plateau and is actually a major vegetation type throughout the Intermountain West. But, here we’ll focus on the Columbia Plateau or, when possible, even more specifically on the Columbia Basin which is mostly limited to Washington and small portions of Idaho and Oregon.

For the moment, let us focus on shrub steppe as a landscape…the Columbia Plateau Ecoregion. Despite what may appear to some as a monotonous landscape, there is much diversity in the Ecoregion. There at least 239 plant and animal species in this area which are considered to be globally vulnerable—in other words, they are threatened with extinction. There are also 450 plant associations found throughout the Ecoregion. These plant associations reflect a myriad of habitats distributed across the region. 

The shrub steppe of the Columbia Basin can be categorized into different vegetation types, based on the dominant plants found in each area. These include:

• Shrub steppe, shown here in the green, which is mostly dominated by sagebrush and bunchgrasses such as bluebunch wheatgrass (Pseudoroegneria spicata) and Idaho fescue (Festuca idahoensis)
• Palouse prairie, shown here in the blue, which is dominated by Idaho fescue and bluebunch wheatgrass.
• Canyon grasslands, shown here in pink, which are dominated by bluebunch wheatgrass and Sandberg’s bluegrass (Poa secunda); and
• Klickitat meadow steppe, shown here in brown, which is similar to Palouse Prairie, but has slightly different species composition and environmental setting.
  
  

This slide shows an elevation model of the Basin, with the various colors showing variation in elevation. Starting from near the center of the Basin near Richland, you can see that there is a gradual rise in elevation as you move the north and east. This rise in elevation, and distance away from the rain shadow cast by the Cascade Mountains, results in a gradual increase in moisture. Thus, although the Basin appears to be a monotonous swath of sagebrush (and orchards and wheat fields) there are very discrete changes relative to this moisture gradient. We can take the map I just showed in the previous slide and further divide the Basin’s vegetation types based on this moisture gradient.

Rexford Daubenmire, in his classic study of shrub steppe in the Columbia Basin, categorized the shrub steppe landscape into different vegetation zones, based on the dominant plants found in each area. These zones essentially represent the moisture gradient I just discussed.

So, what I previously described as shrub steppe (shown here in the green, orange, and pink) can be subdivided into even finer vegetation zones, each representing slightly different ecological conditions. For example, in the center of the basin, which is the hottest and driest portion, Basin Big Sagebrush (Artemisia tridentata subsp. tridentata), Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis), and bluebunch wheatgrass are the dominant species. As one moves further north and east, Idaho fescue increases in dominance resulting in a Big Sagebrush/fescue zone (orange) and in even moister environments, a three-tip sagebrush (Artemisia tripartita)/fescue zone. 

The Palouse Prairie can be split up in a similar manner. The western portion of the Palouse is slightly drier and consists of an open, bluebunch wheatgrass-fescue grassland (or steppe). As you move east, the grassland becomes closed (very dense) and is dominated by fescue, rose, snowberry, and a high diversity of forbs. 

In summary, the shrub steppe, as a landscape, is much more diverse than might first come to mind. In fact, the diversity of ecological types is much greater than shown here as even this map is a broad explanation of the diversity of habitats found in the Basin.

Photo Credit: Rex Crawford (bottom three), Washington Natural Heritage Program

Ecologist can focus ecological classification at a variety of spatial scales. For example, the previous few slides classified the shrub steppe landscape at a very coarse scale (e.g. from a basin-wide perspective). We could also zoom in much finer and divide the landscape into much smaller, yet very discrete units. This slide shows different spatial scales (vertical gradient) at which the Washington Natural Heritage Program classifies ecological communities. Although we mostly use a vegetation-based classification system, in this presentation I will only focus on what we call an Ecological System classification, which was developed by NatureServe. Ecological Systems are essentially repeatable patterns of species which occur in similar environments. In other words, this classification scheme considers both vegetation and environmental factors such as soils, climate, geology, and disturbance regimes. This slide shows the different scales at which we can split up the Shrub Steppe landscape into various ecological types or habitats.

The vegetation zones I showed previously are similar to what the Ecological System classification refers to as a Matrix Ecological System. So, the shrub steppe shown in the light green in the previous slide is what we would call the Inter-mountain Basins Big Sagebrush Steppe. Other Ecological Systems occur at smaller spatial scales such as the Columbia Plateau scablands, riparian areas or vernal pools. 

This is a list of all the Ecological Systems types which occur in the Columbia Basin. As you can see, the Basin isn’t just “sagebrush”; it supports a large variety of ecological systems. For the next few slides, I am going to give you a quick photographic tour of many of these systems (as well as some rare species which they support) in order to provide a sense of the diversity of our natural heritage in the Columbia Basin.

We’ll start with the ecological systems which characterize what we think of “shrub steppe” habitat. In other words, these reflect “shrub steppe” as a specific ecosystem.

The Inter-Mountain Basins Big Sagebrush Steppe Ecological System is one of the matrix types in the Basin. It covers a vast area of the Columbia Plateau. This system is characterized by Basin and Wyoming Big Sagebrush with an understory dominated by bluebunch wheatgrass. This is an example from Washington Department of Natural Resource’s Two Steppe Natural Area Preserve.

This is the Columbia Plateau Low Sagebrush Steppe Ecological System. It is typically found on mountain ridges and flanks on shallow soils. Low sagebrush (Artemisia arbuscula) is dominant along with Idaho fescue, bluebunch wheatgrass, and Sandberg’s bluegrass. Within the Columbia Basin, this type is mostly limited to the southwest portion in the Yakima Folds area.

The Columbia Plateau Scabland Shrubland Ecological System is locally referred to as scabland or lithosol communities. These sites have very shallow soils with exposed rock and gravel being very common. Common species include stiff sage (Artemisia rigida), along with numerous dwarf-shrub buckwheats (Eriogonum ssp.), balsamroot (Balsamorhiza ssp.), and Sandberg’s bluegrass. These small patch sites are very common in the Basin. 

At higher elevations, within the forested zones, mountain sagebrush (Artemisia tridentata subsp. vaseyana) can dominate open flats, ridges, and slopes. Higher moisture at this elevation can result in a species rich understory of both grasses and forbs. This system is mostly found outside the Columbia Plateau Ecoregion, but represents a high-elevation expression of shrub steppe.

The following couple of slides show a few of the rare plants found in these shrub steppe habitats. As a matter of fact, there are nearly 50 rare plants which occur in these shrub steppe and grassland habitats.

This particular plant is Piper’s daisy and is considered to be globally vulnerable. It is listed by Washington Natural Heritage Program as a State Sensitive Species, is endemic to the Columbia Basin, and is mostly found in the Inter-Mountain Basins Big Sagebrush Steppe Ecological System.

Photo Credit: John Gamon, Washington Natural Heritage Program

The Columbia milk-vetch is found in a variety of shrub steppe habitats (shrub steppe, lithosols, etc.) but is restricted to a 5 X 25 mile area along the western side of the Columbia River in Yakima, Kittitas, and Benton counties. It is considered to be a State Threatened species, is on the U.S. Fish & Wildlife Service’s Species of Concern list and occurs in a variety of shrub steppe habitats. 

Photo Credits: Washington Department of Fish and Wildlife

These are a few of the sagebrush-obligate vertebrate species that are struggling due to the loss of shrub steppe habitat. There are many other species that have been impacted by this habitat loss but I’m just going to mention a few things about these critters. 

The Sage Grouse has experienced a large decline due to conversion of shrub steppe to agriculture and degradation of remaining habitat and fragmentation. The Washington Department of Fish and Wildlife estimates that there are less than 1,000 grouse remaining in Washington, occupying only 8-10% of historic habitat. The Sage Grouse is considered a State Threatened species. 

The Sage Sparrow commonly nests within or beneath sagebrush and is closely tied to shrub steppe habitats. It is considered a Candidate for State listing as it is also sensitive to many of the same threats experienced by the Sage Grouse.

The Pygmy rabbit is a Federal and State Endangered species and as of 2003, there was less than 30 of these critters left in Washington. They typically are found in dense stands of big sagebrush growing in deep, loose soils. The deep soils are critical to them being able to burrow for cover and possibly nesting. 

The next group of ecological systems we’ll explore is the Palouse Prairie and related grasslands found in the Basin.

As its name suggests, the Columbia Basin Palouse Prairie occurs in the Palouse region of southeast Washington and adjacent areas in Idaho. Historically, it was characterized by rolling topography composed of loess hills and plains over basalt bedrock. The Palouse prairie is located along the cooler and moister eastern rim of the Basin, getting anywhere from 15-30 inches of rain/year. Species diversity is relatively high due to having more moisture and slightly cooler climate than other parts of the Basin. The Palouse prairie was once an extensive grassland that has been almost completely lost from the landscape. Most remnants of this grassland are located on steep and rocky sites or are small and isolated sites that do not function at the same scale this grassland once did. 

Photo Credit: Washington Natural Heritage Program

This is the Columbia Basin Foothill and Canyon Dry Grassland Ecological System. It is mostly found in the canyons and steep slopes of the Snake River drainage in southeast Washington. Bluebunch wheatgrass and Sandberg’s bluegrass are common, especially on south-facing slopes while Bluebunch wheatgrass and Idaho fescue are also common, especially on the north slopes. These grasslands differ from others in that they are located on different landforms, have shallow soils, and have lower moisture and thus lower species diversity than grasslands such as the Palouse Prairie. 

Outside of the Palouse region, yet within cooler and moisture portions of the Basin, the Northern Rocky Mountain Lower Montane, Foothill, and Valley Grassland can be found. This particular example is a site in the northern portion of the Basin where three-tip sagebrush, Idaho fescue, and a rich diversity of herbaceous species dominate. 

Photo Credit: Chris Chappell, Washington Natural Heritage Program

Scattered mostly throughout the central part of the Columbia Basin, are Columbia Plateau Steppe and Grasslands. These extensive grasslands occur on sites which experience frequent fire or a fire of sufficient size which precludes sagebrush from gaining a foothold. In other words, these grasslands are maintained by fire. This grassland type is probably most abundant near the Hanford area.

Photo Credit: John Gamon, Washington Natural Heritage Program

The following couple of slides show a few of the rare plants found in these grassland habitats. As mentioned previously, there are nearly 50 rare plants which occur in these shrub steppe and grassland habitats. Thus, this is just a small taste of the rare plants which occur in these habitats.

The first species is the Palouse Goldenweed. The Washington Natural Heritage Program considers is to be State Threatened and U.S. Fish and Wildlife Service consider it to be a Species of Concern. This plant is endemic to the Palouse prairie. 

Photo Credit: John Gamon & Reid Schuller, Washington Natural Heritage Program

Jessica’s aster is a State Endangered species and considered a Species of Concern by U.S. Fish and Wildlife Service. It is also endemic to the Palouse region and occurs in Palouse prairie and forest/grassland transition areas. 

One of the more interesting critters unique to the Palouse prairie is the Giant Palouse earthworm. Little is known about the Giant Palouse earthworm. But, it is believed to grow up to 1 m (~3 ft) in length. However, contemporary specimens have only been observed up to about half that length. As with many of the other species in the Basin, it suffers from habitat destruction. Since the original sighting of this species in 1897, the worm has rarely been seen, with the most recent observation being in 2005 when a Washington State University graduate student found one near Palouse, Washington.

Tucked inside the matrix of Columbia Basin shrub steppe and grasslands are numerous smaller habitats such as wetlands, riparian areas, vernal pools, cliffs, and sand dunes. Although small in size, these habitats are an important part of the Basin’s natural heritage. The following couple of slides introduce just a few of these types. 

Photo Credit: Rex Crawford, Washington Natural Heritage Program

The Columbia Basin Foothill Riparian Woodland and Shrubland is found below lower treeline and mostly along the Columbia River and along some of its major tributaries. Cottonwood (Populus trichocarpa), hawthorn (Craetaegus ssp.), alder (Alnus ssp.), and willows (Salix ssp.) are common dominate species. Water management (diversions, irrigation, dams, etc.) and heavy grazing have both reduced the extent of this type and degraded remaining examples. The structural diversity of the vegetation provides important habitat for a variety of creatures. 

Scattered through the Basin, but concentrated in the northern and eastern section, are small, seasonally wet depressions called Columbia Plateau Vernal Pools. Rain and snowmelt fill the pools in winter and spring, and impervious underlying basalt bedrock or clay keeps the pools wet until mid-summer when they completely dry out, as shown here. This unique hydrological regime results in a specialized environment where species specifically adapted to the ephemeral nature of these wetlands thrive. Because of this harsh and unpredictable environment, 63% of the plants found in these wetlands are annual species. In addition, the unique nature of these pools supports about 12 rare plants.

These pools are very similar to those found in California which have received far more conservation attention than those in Washington. Research funded by The Nature Conservancy increased our understanding of the types of plants found in these wetlands but there is still much more work needed to be done in order to understand the biological importance of these pools.

Pothole Ponds Photo Credit: Rex Crawford, Washington Natural Heritage Program

Numerous other wetland types occur in the Basin and all provide important habitat for wildlife. Wetland Ecological Systems such as the North American Arid Freshwater Marsh, Northern Columbia Plateau Basalt Pothole Ponds, and Inter-Mountain Basins Playa & Alkaline Closed Depressions can be found in the Basin.

Photo Credit: Washington Natural Heritage Program

The Inter-Mountain Basins Active and Stabilized Dunes Ecological System is found throughout the Basin although it has been reduced about 75% from its historical extent. The Washington Natural Heritage Program recently conducted a conservation assessment of sand dunes in the Basin and found that these sites support a unique array of rare species and plant communities and have become an important conservation target.

Another small but important habitat in the Basin are the Inter-Mountain Basins Cliffs and Canyons. This Ecological System can have sparse vegetation occurring on steep cliff faces and unstable scree and talus slopes, as shown here. Serviceberry (Amelanchier alnifolia), netleaf hackberry (Celtis reticulata), and sumac (Rhus glabra) are common shrubs found in these areas. Cliffs and canyons provide habitat for reptiles, birds, and other small critters.

Now that we have had an opportunity to enjoy a few photos and hopefully gain an appreciation of shrub steppe biodiversity, I thought I’d turn to the somber conservation issues facing the Columbian Basin’s shrub steppe. 

The contemporary distribution of shrub steppe vegetation types has changed drastically from its historical extent. Originally, over 10 million acres were covered by a sea of sagebrush and bunchgrasses but the onset of development and agriculture has eliminated over 50% of the original coverage. Not only has the absolute loss been great, but you can see in this slide that the remaining shrub steppe is highly fragmented. And, as of 1995, only 1% of the original extent was protected as some form of Natural Area.

Photo Credit: from Washington Natural Heritage Program 2007 Plan

These are the ‘Natural Area’ sites which comprise the ~1% of shrub steppe with protection status. These sites are managed specifically for their natural heritage values. Designation and ownership of these sites ranges from State Natural Area Preserves, Washington State University Biological Study Areas, Federal Research Natural Areas and Areas of Critical Environmental Concern, and private preserves (for example, The Nature Conservancy).

There are many other areas which contribute some form of protection of shrub steppe. For example, the Yakima Training Center, Hanford Reach National Monument, State and Federal Wildlife Areas, etc. are all important areas for shrub steppe conservation. However, because these areas manage for multiple land uses, the Washington Natural Heritage Program does not consider these sites as ‘protected’ due to the fact that some of these land uses can have detrimental effects on biodiversity. Nonetheless, some of these sites support the largest and most intact shrub steppe landscapes in the Basin. 

To highlight these land use differences, I wanted to quickly review this generalized, conceptual model of what happens to the ecological integrity of shrub steppe with a given land use. Sites managed for biodiversity conservation will focus management activities to maintain shrub steppe condition within the bounds of its historic range of variability. Historic range of variability refers to the range of climatic, disturbances, and compositional changes that these ecosystems evolved with. In some cases, the historic range of variability may have included human-induced disturbances such as deliberate fire management. However, most contemporary human-induced disturbances occur at are novel experiences for many ecosystems. The types, intensity, and duration of land use of the contemporary landscape is mostly outside the bounds of an ecosystem’s historic range of variability. Thus, these land uses can often have detrimental effects on ecological integrity. 

Managing a site for occasional, light, or selective grazing may result in the ecological system being in some form of an ‘alternative steady state’. These sites maintain many of the species you’d expect in an ecosystem functioning within its historic range of variability, but they may be missing some species sensitive to anthropogenic disturbances or suffer from slight changes in ecological processes. Severe or prolonged grazing could greatly simplify the system. Typically, only native weedy species or nonnative and invasive species occur at these sites. In addition, many of the key ecological processes have been altered or even eliminated. For example, overgrazing may destroy the cryptogamic crust found in many shrub steppe ecological systems. These soil crusts (a combination of algae, lichens, and mosses) are important for many ecosystem functions such as encouraging infiltration of precipitation, preventing soil erosion, and nutrient cycling. These crusts can also serve as a barrier to many aggressive nonnative species such as cheatgrass (Bromus tectorum). When these crusts are trampled and broken a part, bare soil is exposed and cheatgrass and other invasive annual species are able to establish. Even further degradation could force the ecosystem to a tipping point where it becomes something entirely different. An example would be a former shrub steppe site that is now completely dominated by nonnative annual grasslands, such as cheat grass. Of course, land conversion results in the direct loss of the ecological system.

Photo Credit: Rex Crawford (top right), Washington Natural Heritage Program

Here is a photographic interpretation of the previous slide. In the top left corner, is an example of an intact shrub steppe site where vegetation is within the historic range of variability (HRV). Sagebrush and bunchgrasses are dominant along with a diversity of forbs and intact cryptogamic crust on the soil surface.

The photo in the upper right is an example of a site that has experienced some light grazing. Most of the native bunchgrasses are not very tolerant of grazing, thus they begin to decline with continued grazing. As you can see in this photo, there is much more space between bunchgrass than in the site functioning within HRV. The cryptogamic crust has been impacted but is still functioning. However, overall species composition is pretty similar to the HRV site. Restoration of these sites is often just a matter of removing or suspending current land use.

In the lower right is a simplified site that has been degraded due to overgrazing. Bunchgrasses have declined dramatically, but shrubs are still present. The cryptogamic crust has mostly been eliminated and much of the ground cover consists of cheatgrass. These changes have altered any ecological processes. Restoring such a site requires much more effort and the likelihood of getting back to the HRV is increasingly low.

The photo in the lower left shows a site that has crossed a threshold into a new type--in this case an annual grassland. Shrubs and bunchgrasses are pretty much gone and species composition consists almost entirely of nonnative or weedy native species. Restoration of these is extremely difficult and costly.

This is, of course, a simplistic model and the relationship between each of these states does not always follow in this linear order. The intensity and duration of each type of land use have a different impact on shrub steppe. 

Despite all those photos of nice shrub steppe I showed earlier, most of the shrub steppe in the Columbia Basin is functioning outside the HRV state. Thus, not only have we lost a over half of the historical extent of shrub steppe, but the remaining shrub steppe is not always in the ecological condition we’d prefer, at least from a conservation point of view. 

For example, In the early 1980’s, the Washington Rangeland Committee and Washington Conservation Commission conducted an assessment of the ecological condition of Washington’s rangelands. In this study, condition was rated as the similarity of vegetation composition to “natural, undisturbed plant communities”. The results were disturbing. The study found that, of the remaining shrub steppe on the landscape, only about 11% was comparable to historical conditions while nearly 40% was in poor condition. In summary, as of 1984, nearly 70% of remaining shrub steppe is in fair to poor condition. The ecological condition of shrub steppe has likely not improved since then.

Due to direct loss and degradation of remaining shrub steppe stemming from a variety of land uses, sagebrush habitats are among the most imperiled ecosystems in North America. The impact on biodiversity is not evenly distributed across the different habitat types found in the shrub steppe landscape. For example, of those sites in Washington which have been converted to agriculture, 75% occur on loamy soil sites whereas <15% of shallow soil sites have been converted. These sites support different types of shrub steppe and associated critters. In addition, the remaining shrub steppe now occurs in a matrix of agriculture and is highly fragmented. Such fragmentation disrupts many of the natural ecological processes such as fire and species movement between habitats. Fragmentation has had a detrimental impact on many species, especially birds. Many researchers now think that shrubland and grassland birds are declining faster than any other group of species in North America.

Because of the dramatic loss and continual degradation of shrub steppe in eastern Washington, the Washington Department of Natural Resource’s Natural Heritage Program has initiated an inventory and assessment of the conservation value of shrub steppe remaining on State Trust lands. For the past 3 years, the Washington Natural Heritage Program has been conducting field work to determine:

• what kinds of ecological systems occur on Trust lands
• their current ecological condition
• whether or not they support any rare species
• whether they serve as critical wildlife habitat, and
• whether they serve as an important ecological corridor.

To date, we have collected data from about 75 % of the DNR Trust Lands we are targeting in eastern WA. Depending on funding, we hope to finish the assessment in the next few years.

There are many other shrub steppe conservation efforts occurring in the Basin. To more effectively and efficiently formulate and implement conservation strategies for shrub steppe, these efforts need to be coordinated. Such a broad-scale partnership should consider the following objectives in order to effectively protect the Columbia Basin’s natural heritage:

• rare & high quality examples of ecological systems
• rare species
• ecological corridors
• wildlife habitat
• ecological services

I’ll conclude with a quote from one of our eminent grassland ecologists, John Weaver, and one of the first to study Washington’s shrub steppe. I really like this quote because it reminds us that our natural heritage is not easily replaced. If we are to maintain the natural heritage of the Columbia Basin’s shrub steppe landscape, we need to conserve, whether through protection or compatible land uses, as much of the remnant high-quality shrub steppe while we still can and restore those sites that are currently in fair or poor condition.

Note: Unless otherwise noted, photos are my own.

Technorati Tags: shrub steppe,sagebrush steppe,Washington,natural history,ecological classification

High Creek Fen: A Pocket of Unique Beauty & Diversity in the Southern Rocky Mountains

Descending Kenosha Pass and driving south toward Fairplay on U.S. Hwy. 285, South Park's expansive, high montane grassland fills the view out the windshield. This short, sparsely vegetated grassland is dominated by Festuca arizonica (Arizona fescue) and Muhlenbergia filiculmis (slimstem muhly) and covers much of South Park's 900 square mile (50x35 miles) valley floor. Walt Whitman noted from Kenosha Pass: "...South Park stretches fifty miles before me. Mountainous chains and peaks in every variety of perspective, every hue of vista, fringe the view, in nearer, or middle, or far-dim distance, or fade on the horizon."  The view out the windshield is immense and intimidating, yet welcoming. Sometimes it is necessary to overwhelm our spatial sense and temporal perspective in order to feel the intricacies of the Natural world—to feel apart of something as opposed to its oppressor. 

South Park grassland in foreground. Spruce trees in background are growing in High Creek Fen.

South Park is one of four, large intermountain basins scattered north and south in Colorado’s Southern Rocky Mountains. South Park is about 80 miles southwest of Denver and the “Park” itself is delimited by the valley floor grassland contrasting with the forested slopes of the surrounding mountain ranges: the Mosquito Range to the west, the Park Range to the north, Tarryall Mountains and Puma Hills to the east, and the Black and Thirtynine Mile mountains to the south. Although much of South Park's valley floor is above 9,000 feet in elevation, this intermountain park only gets about 13 inches of rain each year due to the generally dry climate of the region exasperated by the imposing rainshadows of the surrounding mountains.

Location of South Park in Colorado.

High Creek fen is located at the blue maker. South Park is delimited
by the tan color to the north, south, and east of the marker.

After pulling out of Fairplay and driving south on Hwy. 285 a few miles, a strange cluster of spruce trees appears to the east of the highway.  The trees are completely out of place amidst the short-grass steppe of South Park's valley floor.  Taking a left turn off the highway and heading down a two-track, dirt road, High Creek Fen emerges from the high montane steppe revealing an immense area of wet ground.  Hummocks, pools, rivulets, and a creek; spruce trees, willows, bog birch, bulrushes, sedges, cottongrass, and aquatic plants all blanket the area.

 High Creek Fen in background

Although early botanical explorers had visited the site, it is a bit astonishing that the significance of High Creek Fen as a refugia for glacial relicts and haven for rare critters went unnoticed until 1990 when Dr. David Cooper recognized the unique character and biodiversity significance of this ecological Eden. What Dr. Cooper had stumbled upon is what many North American ecologists consider to be one of the rarest wetland types on the continent—a calcareous or extremely rich fen. Extremely rich fens differ from other fens due to the unique chemical quality of the groundwater that supports their existence—a preponderance of calcium, magnesium, and other nutrients which create a very basic (i.e. high pH) environment. There is some confusion in the scientific literature as to whether extremely rich and calcareous are synonymous terms. From what I can tell, calcareous is a subset of extremely rich, since other types of bedrock than limestone can result in high cation concentrations in groundwater (e.g. marine shale). Extremely rich fens are only found where groundwater is in contact with calcareous bedrock, such as limestone and dolomite, or other types of bedrock rich in cations. South Park is one of those places. Numerous extremely rich fens occur in the northern and western portion of South Park and High Creek Fen is one of the largest, most intact, floristically rich, and ecologically diverse extremely rich fens in Colorado.  It harbors more rare plants (14) than any other wetland in the state.  Because of its importance to global and regional biodiversity, the Nature Conservancy purchased the property and now manages it to preserve its unique biological character.

High Creek Fen's ecological diversity, uniqueness, and abundance of rare plants make it one of the most significant sites of biodiversity in the Southern Rocky Mountains.

The presence of such a large wetland in such a dry landscape is curious. High Creek is a meager stream and surely not large enough to wet such a large area. As a matter of fact, there is often no surface water in the channel before it enters High Creek Fen. It is not entirely clear why this is the case, but some researchers believe it may be (1) due to upstream diversions for agricultural use, or (2) due to the fact that as High Creek flows out of the mountains it 'loses' its flow to the underlying gravels and permeable limestone where it becomes groundwater, or (3) due to evaporation of the creek's meager flow prior to reaching High Creek Fen. Likely, all three factors may be at play. Regardless, High Creek Fen is wet…very wet.  What keeps such a large place, in such a dry climate, so soggy? Groundwater, and lots of it. The Nature Conservancy has conducted hydrogeologic studies of the site and believes that groundwater feeding High Creek Fen emerges from two major types of aquifers: a shallow aquifer associated with surficial glacial and alluvial (i.e. stream) deposits and a regional aquifer associated with the Leadville limestone formation. Discharge from these aquifers occurs throughout a variety of orifices—cobble beds, pools, springs, and floating mats. Groundwater discharge from gravel and cobble beds, outwash from past glaciation, can be seasonal or permanent. Cobble beds typically serve as the ‘headwaters’ of numerous rivulets which end up coalescenceing into larger channels and then proceed to sneak their way through the fen. These channels also pick up slow moving groundwater emerging from other sources such as springs, pools, and quagmires or floating mats.  All of this water eventually gets channeled back into our old friend, High Creek, which abruptly leaves the fen in the southeast corner with much more volume that when it entered the fen. 

Aerial view of High Creek Fen showing extent of wet ground and exit of High Creek in the southeast portion of the fen. Sodic flats (white areas) can also been seen near the mouth of the fen. (Google Maps)

High Creek in the central portion of High Creek Fen (the grayish shrub is Salix candida, a rare willow in Colorado restricted to calcareous fens.)

So where does all this groundwater come from? The shallow aquifer is likely supported by seasonal precipitation and streamflow in High Creek. The more stable and deeper aquifer is associated with limestone bedrock that was formed during the late Cambrian period when South Park was inundated by a series of advancing and retreating seas.  Sediments in this sea were deposited and over time converted to limestone and dolomite deposits found underneath South Park’s valley floor. These deposits were also uplifted and subsequently eroded by glaciers and streams when the Mosquito Range pushed upward. Thousands of years of snowmelt have found its way into these relatively porous bedrock formations forming a regional aquifer. Each year, as snowmelt rushes down the numerous creeks flowing out of the Mosquito Range, both the shallow and deep aquifer are recharged. Another important contributing factor to High Creek Fen’s unique quality is the interaction of its geological past and contemporary hydrology.  During the Pleistocene, mountain glaciers and their associated meltwaters tore apart the uplifted limestone and dolomite bedrock and deposited large quantities of sediment, gravel, and cobbles, derived from these calcareous formations, out into South Park’s valley floor.  Groundwater associated with the shallow aquifer comes into contact with this glacial outwash and, along with groundwater associated with the Leadville limestone aquifer (which emerges as springs throughout the site), is rich with dissolved calcium and magnesium.  These waters are the reason High Creek Fens supports such unique vegetation patterns, rare plants, mosses and invertebrates.

Possible groundwater flow of shallow and deep aquifers originating in the Mosquito Range and flowing southeast toward High Creek Fen (in red).

As you walk through the fen, the ecological effects of all this emerging groundwater are very apparent. The groundwater presents itself to the surface in a variety of ways. Already discussed above were the cobble beds, which support vegetation typical of gravel bars and small, spring-fed creeks.  Groundwater also emerges from springs in flat areas to form pools, water tracks, and sedge lawns. Some have referred to the shallow pools as quagmires due to their unstable, soft marly peat soils. Similar areas with a sturdier substrate are called floating mats. Floating mats are places where a thick mat of sedges sits on top of strong upwelling groundwater. Walking on these areas is like tromping across a waterbed. Serving as very shallow, linear aquatic corridors between individual quagmires and floating mats are water tracks. Quagmire, floating mats, and water tracks support similar types of vegetation dominated by Eleocharis quinqueflora (few-flowered spikerush), Triglochin spp. (arrowgrass), and Utricularia spp. (bladderwort). Eriophorum spp. (cottongrass) is often found growing along the edges of quagmires and on floating mats. Sedge lawns are dominated by Carex aquatilis (water sedge) and Carex simulata (analogue sedge).

 Quagmires and floating mats.

Sedge lawn spreading out from a spring.

Hummocky areas consists of both hummock and hollow topography. Small hummocks are covered by Kobresia simpliciuscula (simple bog sedge) and Trichophorum pumilum (little bulrush) while slightly taller and drier hummocks are capped with Kobresia myosuroides and Thalictrum alpinum (alpine meadowrue). Both vegetation types are considered to be globally rare with examples only known to occur in South Park, Convict Creek Basin in California (latter type), and Swamp Lake in Wyoming (former type). Hollows are the low troughs between hummocks.  Hollows support similar vegetation as found in water tracks.

Tall hummocks dominated by Kobresia myosuroides and Thalictrum alpinum.

Another unique area of the fen is toward the outlet. This area is not permanently inundated like the rest of the fen rather is wetted by capillary action of the soil. Evaporation on the soil surface results in the soil ‘pulling’ up moisture from a relatively shallow water table, leaving magnesium and sodium salts to accumulate on the soil surface. This area has much more sodium than the rest of the site and thus has been referred to as the sodic flats. Although you wouldn’t guess it by handling the soil, it is comprised of more than 20% organic matter which makes it an organic soil, or peat. Instead of calciphiles, halophytes such as Poa juncifolia (alkali bluegrass), Phlox sibirica (alpine phlox), and Glaux maritima (sea milkwort) are dominant on these sodic peats.

 

Sodic flats in the southeast corner of High Creek Fen.

As mentioned previously, High  Creek Fen supports an abundance of rare plants. Two species, Ptilagrostis porteri (Porter feathergrass) and Sisyrinchium pallidum (pale blue-eyed grass) are globally rare, both having the majority of their global range in the extremely rich fens of South Park. Ptilagrostis porteri occurs on the top of hummocks while Sisyrinchium pallidum occurs in alkaline wet meadows and occasionally in the fen itself. The remaining 12 plants are considered rare in Colorado but are more common when their global distribution is considered:  Carex livida (Livid sedge) is found in the sedge lawns; Carex scirpoidea (single-spike sedge) grows in wet meadows and on top of taller and slightly drier hummocks; Carex viridula (green sedge) is found in sedge lawns, water tracks, and at the base of hummocks; Eriophorum gracile (slender cottongrass) grow in sedge lawns and near quagmires; Lilium philadelphicum (wood lily) is found growing on the small ‘islands’ of spruce in the shaded understory; Packera pauciflora (few-flowered ragwort) is found in wet meadows; Primula egaliksensis (Greenland primrose) grows on hummocks; Salix candida (hoary willow) is found in sedge lawns and on low hummocks; Salix serissima (autumn willow) is found in sedge lawns and in areas with low hummocks; Trichophorum pumilum (little bulrush) grows on low hummocks; Utricularia ochroleuca (northern bladderwort) is found growing in the shallow waters of the quagmires and water tracks; and Salix myrtillifolia (blueberry willow) is found near springs or strong upwelling groundwater. Salix myrtillifolia was once thought to not occur south of where past continental glaciation occurred and its presence at High Creek Fen indicates the role this fen (and other extremely rich fens in South Park) has played as a refugia for glacial relicts.  Basically, as the climate warmed following Pleistocene glaciation, many arctic and boreal species disappeared from Colorado’s landscape or moved to higher elevations.  High Creek Fen provided a refuge for some of those species, and many still survive here today (e.g. many of the rare plants discussed above) despite their absence throughout the lower 48 states.

 Packera pauciflora, a rare species

 

Salix serissima (bright green shrub) and Salix candida (grayish shrub) with High Creek in foreground.

Salix myrtillifolia in center of photograph.

The rare Utricularia ochroleuca (on left) and common Utricularia macrorhiza (on right).

Salix candida.

Carex viridula.

In addition to the rare plants, researchers have also found rare insects at High Creek Fen. Nine aquatic beetles were collected here that are not known from anywhere else in Colorado, with four of those beetles occurring well south of their known range. An extremely rare caddisfly (Ochrotrichia susanae) was also found and is known from only one other location in the world. A rare moss, Scorpidium scorpoides is also found a High Creek Fen growing in the sluggish waters of quagmires, water tracks, and pools.

Spending the day at High Creek Fen is an easy way to get lost—in time and space. There are very few wetlands, let alone fens, in the Southern Rocky Mountains as large and as diverse as this site. Although I have never been to the true boreal or arctic reaches of the North American continent, when I’m immersed in High Creek Fen’s wilderness I definitely feel as if I’m in those far northern landscapes—and very far from anything I have ever experienced. Time slows to a pace where my thoughts are set free in the present and not burdened by thoughts of future or past events.  No matter how many times I have visited the site, that same feeling returns. Now that I live in Washington State, I am not sure when my next visit to High Creek Fen will be, but I very much look forward to that day. High Creek Fen’s beauty may be hidden in the vast steppe of South Park’s floor but it is not to be missed.

A wise, old, spruce tree keeping a close watch on its beloved home—High Creek Fen.

 

Sources: Sanderson, J. and M. March, 1996. Extreme Rich Fens of South Park, Colorado: Their Distribution, Identification, and Natural Heritage Significance.  Colorado Natural Heritage Program, Colorado State University.

Cooper, D.J. 1996. Water and soil chemistry, floristics, and phytosociology of the extreme rich High Creek fen, in South Park, Colorado, U.S.A. Can. J. Bot. 74:1801-1811.

Johnson, J.B. and D.A. Steingraeber. 2003. The vegetation and ecological gradients of calcareous mires in the South Park valley, Colorado. Can. J. Bot. 81: 201-219.

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