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 associated 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 correspond to changes in stream classification. Lotic ecological sites incorporate Rosgen stream classification (Rosgen 1994) to identify the channel morphology and stream succession scenarios. 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 third and fourth order or streams in moderately sloping (1 to 4 percent), narrow, alluvial fill valleys in mountains and on dissected lava plateaus. Drainage area is typically between 8,000 and 25,000 acres. Stream potential is a Rosgen C or Bc channel type. Streams typically have perennial flow, but may have intermittent sections during late summer and fall. Valley bottom width ranges from 75 to 300 feet. Bank full channel widths range from 20 to 75 feet, with mean depths between 0.5 and 2 feet. Channel morphology is dominated by moderately-entrenched, single-thread Rosgen Bc type channels (Rosgen 2006). Valley slopes are typically less than 4 percent, but may range up to 10 percent. Channel gradients are less than 3 percent. Steeper bedrock sections can occur within this ecological site. There are five community components laterally associated with this ecological site. Starting from the stream they are: Gravel bar, Floodplain-frequently flooded, Floodplain-occasionally flooded, Terrace, and Terrace with moist meadow. The gravel bar component occurs in the active channel and is associated with poorly developed soils, which are subject to frequent flooding and reworking. The gravel bar component (CC1) is vegetated by pioneer forbs, of which the majority are invasive, non-native species. The frequently flooded, floodplain component (CC2) occurs within the active flood zone, with greater than 50% chance of flooding in any given year. Depending upon duration of stability, the soils may be poorly developed or have a thick A horizon from accumulation of organic matter and fine sediments. The plant community is dominated by white alder (Alnus rhombifolia), water birch (Betula occidentalis), black cottonwood (Populus balsamifera ssp. trichocarpa), and willows (Salix sp.). The occasionally flooded, floodplain component (CC3) occurs between the historic 2 and 50-year floodplain. Black cottonwood, black hawthorn (Crataegus douglasii), and other shrubs are present. These floodplain soils (CC2 and CC3) have developed in recent alluvium from basalt. 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. Species dependent on a shallow water table or flooding, such as white alder and black cottonwood, 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. Black hawthorn, ponderosa pine (Pinus ponderosa), and common snowberry (Symphoricarpos albus) are common. Community component 5 (CC5) is a moist meadow community situated on the terrace. It is supported by subsurface water from seeps. Vegetation is variable, but is dominated by graminoids and forbs.

Disturbance Factors:
This ecological site is developed based on the main channel of Isquulkpte Creek and sections within Buckaroo Creek. These streams are tributaries of the Umatilla River in northeast Oregon, and are within the boundaries of the Confederated Tribes of the Umatilla Indian Reservation (CTUIR). The treaty between the US government and the CTUIR was signed in 1855; this designated the reservation and began the settlement of tribal people in this area. The valleys were farmed and horses grazed the hillslopes. Additional incentives for land allotments drew more Indian and non-Indian settlers. Land use intensified, and cattle and sheep grazing increased (CTUIR 2014). Highest stocking rates occurred during 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 head of cattle (BIA and CTUIR 2007). Today, cattle and feral horses graze in the uplands and in riparian corridors. Intensive grazing caused a decline in vegetative cover on the steep hillslopes from foraging and hoof trampling (BIA and CTUIR 2007). The exposed and disturbed soils are highly susceptible to water and wind erosion. Sheet, rill and gully erosion transported sediments to the streams, especially during extreme rain events. Grazing along the stream channels can impact and alter riparian vegetation by selective herbivory and physical trampling of the stream banks, resulting in a decline in bank stability from the loss of root structure and increase in bare soil. Exposed, overgrazed hillslopes and riparian areas are then poorly structured for large flood events. Large floods events occurred in 1881-1882, 1947-1948, and 1964-1965, with smaller floods in 1997 and 2011(U.S. Geological Survey 2015). Large flood events erode the hillslopes and unstable banks, which can leave deep sediment deposits in channels and on 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. These streams are showing signs of past down-cutting to reach grade equilibrium, and the stream sections are dominated by transport reaches.

Beavers were abundant in these watersheds prior to 1840. The fur trade was a major industry in Oregon in the early 1800s, when beavers were avidly exploited for their thick, smooth pelts. From 1820 to 1830, the Hudson Bay Company initiated a practice of exterminating beavers 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 this species by 1900 (Harrison 2009). Since the 1900s there has been a gradual increase in beaver populations, however, beavers are still uncommon in these streams today. Beaver dams create ponds, which slow water flow and raise surface flow. Beaver ponds also raise water tables and cause more frequent flooding onto floodplains. A higher water table and increased flooding can change plant species composition to wetland obligate species, and will also increase 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.

Invasive weeds are a concern for this ecological site. Himalayan blackberry (Rubus armeniacus) is common, and can create dense impenetrable thickets that crowd out native species. Invasive forbs such as bull thistle (Cirsium vulgare), gypsyflower (Cynoglossum officinale), Queen Anne's lace (Daucus carota), Fuller's teasel (Dipsacus fullonum), common viper's bugloss (Echium vulgare), common St. Johnswort (Hypericum perforatum), catnip (Nepeta cataria), yellow salsify (Tragopogon dubius), moth mullein (Vebascum blatteria), and common mullein (Verbascum thapsus) were recorded on this ecological site. Non-native grasses recorded in plots are tall oatgrass (Arrhenatherrum elatius), orchardgrass (Dactylis glomerata) and medusahead (Taeniatherum caput-medusae).

Fire was historically an important natural disturbance in these riparian areas and adjacent ponderosa pine forests. Ponderosa pine forests typically have fire regimes dominated by frequent, low intensity understory burns. Ponderosa pine forests and shrublands are typical on north facing slopes and grasslands are typical on the south facing slopes above the valley floor. Fires initiated on the hillslopes may burn down into the riparian areas due to wind or fuel conditions. A study in the Blue Mountains, south of this ecological site, indicate that historic fire regimes in riparian areas are closely associated with the fire regime of the surrounding upslope vegetation. The mean fire return interval (MFRI) for the riparian plots near Dugout, OR was between 13-14 years, one year longer than the upslope forest. The riparian plots near Baker, OR had a MRFI of 13-36 years, while paired upland plots have 10 to 20 year MFRI (Olson 2000). With fire suppression since the 1900’s the structure, density, and extent of the riparian forest and upland ponderosa pine forest has changed. Documentation is limited on historic riparian forest structure, but with frequent understory burns, a more open herbaceous and grass dominated understory would be favored. 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 (Prunus virginiana), Woods’ rose (Rosa woodsii), and common snowberry, oceanspray (Holodiscus discolor), mallow ninebark (Physocarpus malvaceus), Lewis’ mock orange (Philadelphus lewisii), and the non-native Himalayan blackberry. Repeated fire may reduce 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. The present structure of 95% of the riparian forest in the Dugout area is prone to severe crown fires under 90th percentile fire conditions, so fuel reduction is necessary prior to implementing prescribed burns (Olson 2000). The combination of altered hydrologic conditions (lower water tables, and less flood activity on floodplains) and fire suppression has allowed succession to continue with ponderosa pine forests becoming dominant on abandoned floodplains and terraces. When the floodplain and terraces become dry and disconnected from flooding events, these areas are more influenced by upland disturbance processes such as fire, lack of fire, and forest pathogens. 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 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 within 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 of a scale to be described in 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 slightly-entrenched C and B type channel complex. A C type channel is a slightly entrenched, single thread 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. 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 erosion potential. The channels on this site support gravel and cobble (C4 and C3) reaches, which have very high erosion potentials 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 incision, bank erosion, or aggradation. This can shift a C type channel to a Bc, 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.

Bc type channels have the channel morphology of a B type channel, but have less than 2 percent channel gradients characteristic of C type channels. B type channels have 2 to 4 percent channel gradients and are naturally moderately entrenched, with entrenchment ratios between 1.4 and 2.2. B type channels are often in colluvial valleys or narrow moderately sloping alluvial valleys (Rosgen 1994). The Bc type channel can be a prolonged entrenched phase of a C type channel, caused by channel straightening and incision. Bc type channels may develop naturally where slopes range between 1.5 to 3 percent.

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 Bc type channel.

Climate change
Climate records for the Pacific 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 (EPA 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; for example, 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.