Ecological dynamics

Scale and stream classification system:
Lotic ecological sites describe portions of valley sections with similar reaches, defined by slope, valley width, Strahler stream order, and similar associated fluvial landforms and vegetation. Lotic ecological sites are tied to the scale of the NRCS soil survey. The Umatilla County Soil Survey for this area was mapped at Order 3, with map unit size ranging from 1.6 to 16 hectares (Soil Survey Division Staff 1993). The closest equivalent scale for stream classification is the valley segment, which ranges from 0.1 to 10,000 hectares (Montgomery and Buffington 1993). Soil surveys may have different map units for a valley section, based on slope classes and changes in composition of soil components, which often corresponds to changes in stream classification. Lotic ecological sites incorporate Rosgen stream classification (Rosgen 1994) to identify the channel morphology and the stream succession scenarios. The stream succession scenarios are used to develop state-and-transition models based on morphological changes of stream channels over time.

Site concept:
This riparian complex occurs on Strahler fifth order or greater streams, in gently sloping, wide, alluvium filled, valleys. Drainage area is between 90,000 and 150,000 acres, and the watershed is composed of mountains and lava plateaus. Stream gradients are typically 0.5 to 0.9 percent, but may be up to 2 percent. Valley bottom width ranges from 400 to 1,600 feet, with floodplain widths typically between 150 and 820 feet. Bank full channel widths range from 35 to 95 feet, with average depths between 1.5 and 3.0 feet. Channel morphology alternates between reaches of moderately-entrenched, single-thread Rosgen C type channels and reaches of braided Rosgen D type channels (Rosgen 2006). Reaches with transitional G or F type morphology rarely occur. There are four community components laterally associated with this ecological site. Starting from the stream they are: Gravel bar-frequently flooded, Floodplain-occasionally flooded, Floodplain step-rarely flooded, and Stream Terrace-rarely flooded. The gravel bar component occurs in the active channel and is associated with poorly-developed soils, which are subject to frequent flooding and reworking. This component is vegetated by pioneer forb species, of which the majority are invasive, and non-native. The floodplain components (CC2 and CC3) occur within the flood zone. Depending upon duration of stability, these components may have young soils or more developed soils with a thick A horizon from organic matter accumulation. Black cottonwood (Populus balsamifera ssp. trichocarpa) and black hawthorn (Crataegus douglasii) dominate, with a variety of associated species. The original floodplain components may become abandoned in the altered entrenched states. The floodplain becomes abandoned when the channel is cut deeper and becomes larger, which lowers the water table and reduces flooding frequency onto the floodplain. Plant species that are dependent on a shallow water table or flooding, such as black cottonwood and white alder (Alnus rhombifolia), may become decadent and decline over time. The fourth community component exists on stream terraces typically above the 50-year flood prone area. The water table is only above 60 inches for a short period in spring. This community is often altered for cultivation or pasture. Remnant native species include black hawthorn, western chokecherry (Prunus virginiana), and basin wildrye (Leymus cinereus).

Disturbance Factors:
This ecological site is developed based on lower McKay Creek within the boundaries of the Confederated Tribes of the Umatilla Indian Reservation (CTUIR). It may be used in the future for similar areas outside of the CTUIR boundary, so disturbances are discussed in generality, rather than from specific locations. After the 1855 Treaty between the US government and the CTUIR, tribal people were moved to the reservation. People farmed the valleys and horses grazed the hillslopes. Additional incentives to secure land allotments drew more Indian and non-Indian settlers. Land use intensified, and cattle and sheep grazing increased (CTUIR 2014). Highest stocking rates occurred from the 1880s to the 1920s. The tribes possessed 20,000 horses and 3,000 cattle by 1890, and non-Indian settlers and travelers brought several thousand additional cattle (BIA and CTUIR 2007). Today, grazing by cattle and feral horses still occurs in these riparian corridors. In the upper watershed the U.S. Forest Service logged conifer forests in the early 1900s, but logging has declined in recent years. Past logging practices and unplanned road building have decreased soil stability and caused increased susceptibility to erosion when affected by flooding or fire (Colombaroli and Gavin 2010). In the lower watershed historic, overgrazing caused a decline in vegetative cover on the steep hillslopes from foraging and hoof trampling (BIA and CTUIR 2007). The exposed and disturbed soils became highly susceptible to water and wind erosion. Sheet, rill, and gully erosion transported sediments to the streams, especially during extreme rain events. Historic grazing along the stream channels impacted and altered riparian vegetation by selective herbivory and physical trampling of the stream banks. This resulted in a decline in bank stability due to the loss of root structure and an increase in exposed, bare soil. The exposed hillslopes and riparian areas were poorly structured for large flood events. Large flood events occurred in 1881-1882, 1947-1948, and 1964-1965, with smaller floods in 1997 and 2011 (USGS 2015). Large flood events erode the hillslopes and unstable banks, which can leave deep sediment deposits in channels and floodplains. Although this is a natural process, the scale of sedimentation may be increased by anthropogenic disturbances. These large flood events are the primary drivers of dramatic changes in stream morphology. In this area, the valley bottom may be cultivated, used for pasture, or developed as residential areas. It is difficult to determine the reference stream conditions and channel morphology, due to these complex interactions of natural and anthropogenic disturbances. Based on channel evolution models, valley type, and valley slope, the reference condition for this stream should be a meandering C type channel, but D type channels may also be a natural feature in certain reaches or after depositional flood events.

Beavers were abundant in these watersheds prior to 1840. The fur trade was a major industry in Oregon in the early 1800s, and beaver were highly desired for their thick, smooth pelts. From 1820 to 1830, the Hudson Bay Company initiated a practice of exterminating beaver from areas south and east of the Columbia River to eliminate competition. This purposeful, detrimental practice, along with other trapping, caused a severe decline in beaver populations by 1825 and a near extinction of beaver by 1900 (Harrison 2009). Since the 1900s, there has been a gradual increase in beaver populations. Beavers are present in these streams today, but have few well developed dams. Beaver dams create ponds, which slow water flow and raise surface flow. Beaver dams, raise water tables and allow for more frequent flooding onto floodplains. A higher water table and increased flooding can change species composition to wetland obligate species, and increases growth rates and abundance of existing riparian vegetation. Below the beaver dam, stream flow may be reduced for short to long durations. Beaver can be detrimental to vegetation if the vegetation does not produce forage fast enough for beaver consumption. Although beavers are a natural part of the ecology for these streams, beaver dams may have detrimental impacts on developed landscapes by eroding or flooding railroads, roads, and other structures built adjacent to streams. Some agencies are attempting to reintroduce or enhance existing beaver dams to improve habitat for steelhead. Initial results have shown an increase in density and survival rates of young steelhead (Pollock, Jordan et al. , Pollock, Beechie et al. 2007).

In addition to land use disturbance, physical barriers and alterations from railroad and road development in flood plains or at stream crossings have confined or redirected stream channel flow, causing changes in channel gradient, sinuosity, and morphology. An earthen dam at McKay Reservoir is a migration barrier for summer steelhead (Oncorhynchus mykiss). The Oregon Department of Fish and Wildlife listed McKay dam as Group 1, in the top 10 priority list for restoring fish passage (Loffink 2013).

Invasive weeds and non-native species are a concern for this ecological site. Non-native forbs common on the gravel bars include lesser burdock (Arctium minus), annual ragweed (Ambrosia artemisiifolia), chicory (Cichorium intybus), Fuller’s teasel (Dipsacus fullonum), Jerusalem oak goosefoot (Dysphania botrys), common St. Johnswort (Hypericum perforatum), sweetclover (Melilotus officinalis), Scotch cottonthistle (Onopordum acanthium), narrowleaf plantain (Plantago lanceolata), sulphur cinquefoil (Potentilla recta), curly dock (Rumex crispus), and common mullein (Verbascum thapus). Himalayan blackberry (Rubus armeniacus) is common on the floodplains and terraces and can create dense, impenetrable thickets, which outcompete native species. Non-native grasses, such as tall oatgrass (Arrhenatherum elatius), ripgut brome (Bromus diandrus), cheatgrass (Bromus tectorum), bulbous bluegrass (Poa bulbosa), medusahead (Taeniatherum caput-medusae), intermediate wheatgrass (Thinopyrum intermedium), tall wheatgrass (Thinopyrum ponticum), North Africa grass (Ventenata dubia), and fescue (Vulpia sp.) dominate the upper terraces.

Information regarding the historical fire regime on the Colombia plateau or in associated riparian areas is limited. Fires may be less common today than historically due to fire suppression and barriers, such as road, croplands, and residential areas. The shrubs associated with this ecological site are adapted to fire. They have the ability to re-sprout from the root crown or from rhizomes after being top-killed by fire. Shrubs which re-sprout after fire include black hawthorn, western chokecherry, Woods’ rose (Rosa woodsii), and common snowberry (Symphoricarpos albus), Saskatoon serviceberry (Amelanchier alnifolia), Lewis’ mock orange (Philadelphus lewisii), and the non-native Himalayan blackberry (Rubus armeniacus). Native bunchgrasses, such as Idaho fescue (Festuca idahoensis), bluebunch wheatgrass (Pseudoroegneria spicata), and basin wildrye may have been reduced on this site due to overgrazing, erosion, and exclusion of low intensity fires. The presence of cheatgrass in the area poses a threat for this site to transition to an altered, non-native, grassland state. Cheatgrass increases flammability and fire frequency. Frequent burns can eliminate shrub cover. Black cottonwood is injured by fire, but can also re-sprout from the root crown, and may regenerate well from seed in the freshly exposed soil if there is sufficient moisture (Steinberg 2001). White alder is often killed by severe fire, and reestablishes poorly from seed or by sprouting from the root crown. It may take decades for white alder to reestablish (Fryer 2014). In the absence of fire, dense development of mid-canopy layers may occur. Upland cycles are not included in the state and transition model for this riparian complex, due to the complexity of the model that would be needed to consistently incorporate these concepts.

Hydrologic factors:

This ecological site incorporates the longitudinal, lateral, and to some extent the vertical connectivity of the stream. Longitudinally, the stream includes reaches of differing channel morphology. The channel may include reaches that are more confined by bedrock hillslopes, impacted by human alterations, or are less confined with a broad accessible floodplain. The valley bottom is typically wide (300 to 800 feet) throughout. Laterally, there may be braided side channels, active floodplains, and terraces. The variation in the hyporheic zone, and the relationship between surface water and ground water is at too fine a scale for this ecological site. The hyporheic zone associated with these streams has a complex pattern of upwelling and downwelling, which impacts the aquatic community and is important for fish spawning. Areas of downwelling may occur in sediment-laden sections or above steps created by woody debris or bedrock. Upwelling is likely to occur where subsurface flow reenters the stream channel. Upwelling ground water is often cooler and more nutrient-rich, which is preferable for fish spawning and creates a unique habitat for aquatic organisms.

Although historic information is lacking, the valley type and valley slope combined with current conditions indicate the potential for a non-entrenched C and D type channel complex. A C type channel is a slightly entrenched, single meandering channel with a well-defined floodplain. The channel has moderate to high sinuosity with less than two percent channel gradient. These channel types generally have a width to depth ratio greater than 12, which means they are moderately wide and shallow. They are often found in broad valleys with well-developed alluvial floodplains and terraces. These channels typically flood over bank two years out of three. In an un-degraded state, a 50-year flood event should overflow onto the floodplain. C type channels are constantly in the process of transporting and storing sediments from upstream sources or bank erosion. As the particle- size of the channel bottom material decreases, the sediment supply generally increases, as does the erosion potential. The channels on this site support gravel (C4) reaches, which have a very high erosion potential and are very sensitive to disturbance. Vegetation such as white alder and willows exert a very high controlling influence on C type channel dynamics (Rosgen 1994).

C type channels can become unstable due to disturbances that impact stream bank vegetation, change the flow regime, sediment loads, or alter channel morphology. These channels respond quickly to such disturbances, exhibiting channel aggradation, channel incision, and/or bank erosion. This can shift a C type channel to a D, G, or F type channel. Overgrazing and excessive trampling by livestock can reduce streambank stability by reducing the vegetative cover or by physically trampling the banks. Increased sedimentation can fill the channel, thereby causing erosion of streambanks. This results in a wider and shallower channel, which initiates a transition to a D type channel.

D type channels are low slope, braided channels with barren or partially vegetated gravel bars and mid channel islands that are exposed during low flow and are typically flooded at bankfull flows. D channels are typically considered unstable systems that have an excessive sediment load, but may occur at equilibrium in some systems. Factors that may contribute to an increased sediment load are large flood events, excessive hillslope erosion, loss of riparian vegetation, change in flow regime, and channel or floodplain alterations (Leopold and Wolman 1957, Rosgen 1996).

Braided channels develop as sediments deposit in low velocity areas of the stream and form incipient bars. Additional sediments may accumulate behind this initial bar, developing larger and wider gravel bars. As mid-channel bars develop, the divided stream flow is deflected into the outer stream banks, which typically erodes (especially if there is poor root structure on the banks), and the channel becomes wider and shallower over time.

G and F type channels are often temporary or occur in short sections along the stream. G type channels occur as a stream headcuts or downcuts into sediments, creating a deep narrow channel. F type channels typically develop as bank erosion widens the narrow G type channel. In this site, the F type channel will develop into a C or D type channel.

Climate change
Climate records for the Northwest United States show that average annual temperature has increased 1.5 degree F in the last 100 years, and it is predicted to increase by 3 to 10 degrees F in the next century (U.S. Environmental Protection Agency 2013). Precipitation predictions are less clear, but warmer temperatures are expected to cause more winter precipitation to come as rain instead of snow, and cause the reduced snowpack to melt 20 to 40 days earlier in spring (EPA, 2013). The snowpack is currently the primary water source for late spring and summer flows in these streams. A greater proportion of rain and earlier snow melt could increase flood severity and frequency in winter and spring, and reduce flow in summer and fall. The change in timing of flooding could impact the migration and spawning of the anadromous fish that utilize these creeks; in fact, increased flooding in the winter months could flush eggs and young fish from the streams (EPA, 2013). The Meacham Creek USGS station has already shown a significant increase in flow during March (Chang and Jones 2010), likely due to earlier snow melt from warmer temperatures.