Ecological dynamics

Scale and stream classification system:
Lotic ecological sites describe portions of valley section 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 mapunit size ranging from 1.6 to 16 hectare (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 mapunits 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 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 alluvial valleys in mountains and dissected lava plateaus. Stream gradients are typically 0.5 to 1 percent, but may be up to 2 percent. Valley bottom width ranges from 300 to 1000 feet, with floodplain widths typically between 300 and 800 feet. Bank full channel widths range from 50 to 150 feet, with mean depths between 1 and 3.5 feet. Channel morphology alternates between reaches of moderately entrenched single-thread Rosgen C type channel 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, Floodplain-frequently flooded, Floodplain-rarely flooded, and Stream Terrace. 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 is vegetated by pioneer forbs, of which the majority are invasive, non-native species. The floodplain components occur within the flood zone, and depending upon duration of stability, may have young soils or more developed soils with a thick A horizon from organic matter accumulation. White alder (Alnus rhombifolia) and black cottonwood (Populus balsamifera ssp. trichocarpa) are the dominant trees, 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. 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 (Crataegus douglasii), ponderosa pine (Pinus ponderosa), and common snowberry (Symphoricarpos albus) are common. Soils are typically loamy-skeletal with thick A horizon development, indicating stability for organic matter accumulation.

Disturbance Factors:
This ecological site is developed based on lower Meacham Creek within the boundaries of the Confederated Tribes of the Umatilla Indian Reservation. It may be used in the future for similar areas outside of the CTUIR boundary, so disturbances are discussed in generality, rather than specific locations. After the1855 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 for land allotments drew more Indian and non-Indian settlers. Land use intensified, and cattle and sheep grazing increased (Confederated Tribes of the Umatilla Indian Reservation 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 heads of cattle (BIA and CTUIR 2007). Today, grazing by cattle and feral horses still occurs in these riparian corridors. In the upper watershed the United States Forest Service logged conifer forests in the early 1900s, but logging has declined in recent years. Past logging practices and unplanned road building has decreased soil stability and caused increased susceptibility to erosion when affected by flooding or fire (Colombaroli and Gavin 2010). In the lower watershed, historic, 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 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 (U.S. Geological Survey 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, it appears that channel aggradation has increased, and braided channels are in the process of transferring excessive sediment. These sediments can be rapidly incised, because the channel tries to regain equilibrium between sediment supply, stream volume, and velocity. 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 uncommon in these streams today. Beaver dams create ponds, which slow water flow and raise surface flow, which raises water tables and allows 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.

Invasive weeds are a concern for this ecological site. Himalayan blackberry (Rubus armeniacus) is common, and can create dense impenetrable thickets, crowding out native species. Invasive forbs such as diffuse knapweed (Centaurea diffusa), spotted knapweed (Centaurea stoebe), gypsyflower (Cynoglossum officinale), common viper's bugloss (Echium vulgare), common St Johnswort (Hypericum perforatum), Dalmatian toadflax (Linaria dalmatica), sweetclover (Melilotus officinalis), catnip (Nepeta cataria), curly dock (Rumex crispus), moth mullein (Vebascum blatteria), and common mullein (Verbascum thapsus) were recorded on this ecological site. Most forbs occur on the gravel bar, but some are on the floodplains and terraces.

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 1900s, 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), Saskatoon serviceberry (Amelanchier alnifolia), white spirea (Spirea betulifolia), mallow ninebark (Physocarpus malvaceus), Lewis’ mock orange (Philadelphus lewisii), and the non-native Himalayan blackberry (Rubus armeniacus). 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 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 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. 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 erosion potential. The channels on this site support gravel (C4) 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 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 bank full 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, forming 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 (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.