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Ecological site XA232X01Y200

Boreal Scrub Loamy Flood Plain Low

Last updated: 5/11/2020
Accessed: 11/14/2024

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General information

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

MLRA notes

Major Land Resource Area (MLRA): 232X–Yukon Flats Lowlands

The Yukon Flats Lowlands MLRA is an expansive basin characterized by numerous levels of flood plains and terraces that are separated by minimal breaks in elevation. This MLRA is in Interior Alaska and is adjacent to the middle reaches of the Yukon River. Numerous tributaries of the Yukon River are within the Yukon Flats Lowlands MLRA. The largest are Beaver Creek, Birch Creek, Black River, Chandalar River, Christian River, Dall River, Hadweenzic River, Hodzana River, Porcupine River, and Sheenjek River. The MLRA has two distinct regions—lowlands and marginal uplands. The lowlands have minimal local relief and are approximately 9,000 square miles in size (Williams 1962). Landforms associated with the lowlands are flood plains and stream terraces. The marginal uplands consist of rolling and dissected plains that are a transitional area between the lowlands and adjacent mountain systems. The marginal uplands are approximately 4,700 square miles in size (Williams 1962).

This MLRA is bounded by the Yukon-Tanana Plateau to the south, Hodzana Highlands to the west, Porcupine Plateau to the east, and southern foothills of the Brooks Range to the north (Williams 1962). These surrounding hills and mountains partially isolate the Yukon Flats Lowlands MLRA from weather systems affecting other MLRAs of Interior Alaska. As a result, temperatures are generally warmer in summer and colder in winter than is characteristic in other areas at comparable latitude. There is a moisture and temperature gradient in which the lowlands region tends to be drier and colder and the surrounding marginal uplands region tends to be moister and warmer (PRISM Climate Group 2006).

The Yukon Flats Lowlands MLRA is mostly undeveloped lands that are sparsely populated and not accessible by a road system. A number of villages, including Beaver, Birch Creek, Chalkyitsik, Circle, Fort Yukon, Stevens Village, and Venetie, are adjacent to the Yukon River or one of its major tributaries. The largest village is Fort Yukon, which according to the 2010 U.S. Census has 583 residents that are dominantly Gwich’in Alaska Natives.

LRU notes

Alaska has no officially recognized LRU. However, there appear to be two distinct LRU in the Yukon Flats Lowlands MLRA. These LRU are thought to have differing climatic regimes, landforms, and soil types (STATSGO and Jorgensen and Meidinger 2015). The two LRU were previously discussed in the MLRA notes section above and are termed the lowlands LRU and the marginal uplands LRU.

This ecological site is associated with the lowlands LRU.

Classification relationships

Yukon Flats Lowlands MLRA.

Ecological site concept

This ecological site is associated with the low flood plain of major tributaries in the Yukon Flats Lowlands MLRA. In this MLRA, the flood plains of major tributaries have been divided into having low, middle, and/or high positions. When compared to the middle and high flood plain, the low flood plain has more frequent and longer duration flood events. Flooding occurs frequently (greater then 50 times in 100 years) for long durations of time (between 7 and 30 days). Associated soils are considered poorly drained. The reference state supports four plant communities related to flooding.

Reference plant community 1.1 is characterized as closed tall scrub (greater than 75 percent shrub cover; Viereck et al. 1992) primarily composed of a mixture of willow (Salix spp.) and alder (Alder spp.). Commonly observed species include feltleaf willow (Salix alaxensis), littletree willow (Salix arbusculoides), Bebb willow (Salix bebbiana), thinleaf alder (Alnus incana ssp. tenuifolia), Siberian alder (Alnus viridis ssp. fruticosa), prickly rose (Rosa acicularis), redosier dogwood (Cornus sericea), and field horsetail (Equisetum arvense). The soil surface is primarily covered with herbaceous litter and woody debris, but large patches of exposed bare soil were observed (as much as 80 percent of plot).

Associated sites

XA232X01Y209	Boreal Tussock Loamy Frozen Terraces This ecological site occurs on stream terraces in the lowlands region of the Yukon Flats Lowlands MLRA. Soils commonly have permafrost at moderate depth (20 to 40 inches) and pond frequently for very long durations. The reference plant community is characterized as open low mixed shrub-sedge tussock bog (Viereck et al. 1992).
XA232X01Y202	Boreal Forest Loamy Flood Plain Middle This ecological site occurs on the middle flood plain of major tributaries in the Yukon Flats Lowlands MLRA. Flooding occurs occasionally (5 to 50 times in 100 years) for long durations of time (between 7 and 30 days). The reference plant community is characterized as a closed deciduous forest (60-100 percent cover; Viereck et al. 1992) primarily composed of mature balsam poplar (Populus balsamifera).
XA232X01Y221	Boreal Forest Loamy Terraces This ecological site is associated with well drained soils on the treads of stream terraces in the Yukon Flats Lowlands MLRA. Flooding frequency ranges from rare to none. The reference plant community is characterized as an open needleleaf forest (25 to 60 percent cover) primarily composed of mature white spruce (Picea glauca).
XA232X01Y205	Boreal Grass Loamy Flood Plain Depressions This ecological site is associated with depressions on flood plains in the Yukon Flats Lowlands MLRA. The reference state plant communities are associated with soils that both pond and flood. Ponding occurs occasionally (5 to 50 times in 100 years) for brief durations of time (between 2 and 7 days). Flooding occurs occasionally for brief durations of time. The reference plant community is characterized as open tall scrub (Viereck et al. 1992) and is primarily composed of willow (Salix spp.).
XA232X01Y204	Boreal Forest Loamy Flood Plain High This ecological site occurs on the high flood plain of major tributaries in the Yukon Flats Lowlands MLRA. Flooding occurs occasionally (5 to 50 times in 100 years) for brief durations of time (between 2 and 7 days). The reference plant community is characterized as an open needleleaf forest (25 to 60 percent cover) primarily composed of mature white spruce (Picea glauca).
XA232X01Y218	Boreal Woodland Loamy Frozen Terraces This ecological site is associated with wet soils on the tread of stream terraces in Yukon Flats Lowlands MLRA. Soils generally have permafrost at moderate depth (20 to 40 inches) and pond occasionally for long durations of time. The reference plant community is characterized as a needleleaf woodland (10 to 25 percent cover; Viereck et al. 1992) composed of black spruce (Picea mariana) and white spruce (Picea glauca).
XA232X01Y250	Boreal Woodland Gravelly Terraces Dry This ecological site is associated with somewhat excessively drained soils on the tread of gravelly stream terraces in Yukon Flats Lowlands MLRA. Gravelly horizons occur at very shallow depth (0 to 10 inches). The reference plant community is characterized as a needleleaf woodland (10 to 25 percent cover; Viereck et al. 1992) composed primarily of mature white spruce (Picea glauca).
XA232X01Y206	Boreal Scrub Loamy Frozen Flood Plain Depressions This ecological site is associated with depressions on flood plains in the Yukon Flats Lowlands MLRA. The reference state plant communities are associated with soils that both pond and flood. Ponding occurs frequently (greater than 50 times in 100 years) for long durations of time (between 7 and 30 days). Flooding occurs occasionally (5 to 50 times in 100 years) for brief durations of time (between 2 and 7 days). The reference plant community is characterized as mesic graminoid herbaceous (Viereck et al. 1992) and is primarily composed of bluejoint (Calamagrostis canadensis).

Similar sites

XA232X01Y206	Boreal Scrub Loamy Frozen Flood Plain Depressions XA232X01Y206 occurs on the edges of flood plain depressions and is commonly associated with permafrost. This shrubby ecological site has similar similar reference state plant communities.
XA232X01Y223	Boreal Scrub Loamy Frozen Terrace Depressions XA232X01Y223 occurs on the edges of terrace depressions and is commonly associated with permafrost. This shrubby ecological site has similar similar reference state plant communities.
XA232X01Y280	Boreal Scrub Loamy Flood Plain Wet XA232X01Y280 is associated with the flood plain of minor tributaries and is associated with wetter soils. These differences in landform position, disturbance regime, and soil type result in similar, but unique, plant community phases for each ecological site.

XA232X01Y206

Boreal Scrub Loamy Frozen Flood Plain Depressions

XA232X01Y206 occurs on the edges of flood plain depressions and is commonly associated with permafrost. This shrubby ecological site has similar similar reference state plant communities.

XA232X01Y223

Boreal Scrub Loamy Frozen Terrace Depressions

XA232X01Y223 occurs on the edges of terrace depressions and is commonly associated with permafrost. This shrubby ecological site has similar similar reference state plant communities.

XA232X01Y280

Boreal Scrub Loamy Flood Plain Wet

XA232X01Y280 is associated with the flood plain of minor tributaries and is associated with wetter soils. These differences in landform position, disturbance regime, and soil type result in similar, but unique, plant community phases for each ecological site.

Table 1. Dominant plant species

Tree	Not specified
Shrub	(1) Salix alaxensis (2) Alnus incana ssp. tenuifolia
Herbaceous	(1) Equisetum arvense

Legacy ID

R232XY200AK

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Physiographic features

This ecological site and its associated plant communities occur throughout the Yukon Flats Lowlands MLRA. Given the large spatial extent, the site is associated with two soil components. The differences in site characteristics among these soils are discussed in this section.

Soils associated with rivers that are currently or have previously been glacially fed have different characteristics than those associated with nonglacial rivers. For instance, glacial rivers that flow out of the southern foothills of the Brooks Range created large gravelly stream terraces north of the Yukon River (e.g. Sheenjek River). The soils on these stream terraces and adjacent flood plains tend to have a sandy and gravelly substrata. Nonglacial rivers that flow out of the Yukon-Tanana Plateau (e.g., Birch Creek) formed numerous terrace levels south of the Yukon River. The soils on these flood plain and terrace levels have a loamy substrata (Typic Cryaquents, frequently flooded soils).

Each soil type originally had a correspondingly unique ecological site. After more fieldwork and data analysis, it was determined that these two soil types appear to support plant communities that have similar kinds and amounts of vegetation in the reference state. As a result, the soil components were all correlated into one ecological site.

Table 2. Representative physiographic features

Landforms	(1) Alluvial plain > Flood plain
Flooding duration	Long (7 to 30 days)
Flooding frequency	Frequent
Ponding frequency	None
Elevation	300 – 1,000 ft
Slope	3%
Aspect	W, NW, N, NE, E, SE, S, SW

Climatic features

Short, warm summers and long, very cold winters characterize the subarctic continental climate of the area. The surrounding hills and mountains of this MLRA partially isolate it from weather systems affecting other interior lowlands. As a result, temperatures are generally warmer in summer and colder in winter than is characteristic in other areas of comparable latitude. The average annual temperature ranges from about 20 to 25 degrees F (-7 to -4 degrees C). The freeze-free period averages 70 to 120 days. The temperature usually remains above freezing from early June through late August. The average annual precipitation ranges from about 6 inches (150 millimeters) in the central basin to 15 inches (380 millimeters) along the boundary with the surrounding highlands. The maximum precipitation occurs in late summer, mainly as a result of thunderstorms. The average annual snowfall is about 45 to 55 inches (115 to 140 centimeters) (USDA, NRCS 2006).

All of the tabular data below was calculated from the PRISM dataset (1971-2000) and is specific to the Lowlands LRU in the Yukon Flats Lowlands MLRA.

Table 3. Representative climatic features

Frost-free period (characteristic range)	45-97 days
Freeze-free period (characteristic range)	70-120 days
Precipitation total (characteristic range)	8-13 in
Frost-free period (average)	75 days
Freeze-free period (average)
Precipitation total (average)	10 in

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Figure 1. Monthly precipitation range

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Figure 2. Monthly minimum temperature range

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Figure 3. Monthly maximum temperature range

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Figure 4. Monthly average minimum and maximum temperature

Influencing water features

During the early growing season (May and June), a water table commonly occurs at very shallow depths in the soil profile (between 0 and 10 inches). This time period is when rivers typically have peak volume in the Yukon Flats Lowlands , which directly impacts the water table in the soil profile. During the early growing season, overland flooding occurs frequently (greater then 50 times in 100 years) for long durations of time (between 7 and 30 days). After the early growing season, the water drains from these soils. During the rest of the growing season, a water table is typically no longer observed in the soil profile (60+ inches). The typical depth to the water table was determined through field observation and by the presence of redoximorphic features in the soil profile.

Soil features

Correlated soil components for Yukon Flats Area, Alaska (AK685): Typic Cryaquents, frequently flooded.

Figure 5. Typical soil profile of Typic cryaquents (frequently flooded) soil component.

Table 4. Representative soil features

Parent material	(1) Alluvium
Family particle size	(1) Coarse-loamy over sandy or sandy-skeletal (2) Coarse-loamy
Drainage class	Poorly drained
Soil depth	80 in

Ecological dynamics

Flooding

All major tributaries within the Yukon Flats Lowlands have low, middle, and/or high flood plain ecological sites. These flood plain ecological sites represent major breaks in the flood regime (i.e. flood frequency and flood duration) and dominant vegetative type on associated tributaries. The low flood plain ecological site is thought to flood frequently (>50 times in 100 years) for long durations of time (7 to 30 days) and supports a willow dominant reference plant community (community 1.1). The middle flood plain ecological site is thought to flood occasionally (5 to 50 times in 100 years) for long durations of time and supports a balsam poplar dominant reference plant community. The high flood plain ecological site is thought to flood occasionally for brief durations of time (2 to 7 days) and supports a white spruce (Picea glauca) dominant reference plant community.

The shift of vegetative type from willow to white spruce dominance represents riparian primary succession along major tributaries in the Yukon Flats Lowlands MLRA. On other Interior Alaska flood plains, this successional process is thought to take between 200 and 300 years (Chapin et al. 2006). The flood regime, growth traits of vegetation, biotic competition, and a slew of other factors contribute to the dynamic nature of boreal flood plain succession. For more detailed information on boreal flood plain succession and successional drivers, refer to Walker et al. (1986) and Chapin et al. (2006).

Field work indicates that certain sampled communities within the reference state flood more frequently and/or severely then other communities. As flooding frequency and duration decreases, willow and alder cover increases. Given this observation, more frequently flooded plant communities were incorporated into the reference state (community 1.2, 1.3, and 1.4). These plant communities likely represent the successional transition from river wash to the reference plant community 1.1.

Other Observations

Community 1.3 and 1.4 are both considered pioneering phases of flood plain succession. Community 1.3 is associated with wetter soil conditions and community 1.4 with drier soil conditions. Regardless of these differences, both plant communities are believed to transition to community 1.2.

Animal use (browsing and grazing) of this ecological site primarily consists of slight moose browse on willow, which was common in each community phase. A browse severity rating of slight on willow is defined as a majority of individual plants having no signs of browsing.

State and transition model

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

Ecosystem states

1. Reference State

State 1 submodel, plant communities

1.1. Feltleaf willow-thinleaf alder / field horsetail

1.2. Feltleaf willow-sandbar willow / field horsetail

1.3. Feltleaf willow-sandbar willow / field horsetail-water horsetail

1.4. Balsam poplar / arctic aster-alpine sweetvetch

State 1
Reference State

Figure 6. The Yukon River flood plain. This ecological site occurs on the flood plains of large tributaries in the Yukon Flats Lowlands MLRA.

The reference state has four associated plant communities. These communities are grouped by the structure and dominance of the vegetation (e.g., coniferous trees, deciduous trees, shrubs, and forbs) and their ecological function and stability. Plant communities in the reference state appear to be largely controlled by the influences of flooding. As flooding becomes less frequent and lasts for shorter durations of time, balsam poplar and white spruce gain dominance and the ecological site shifts to the middle or high flood plain. This report provides baseline vegetation inventory data for the ecological site. More data collection is needed to provide further information about existing plant communities and the disturbance regimes that would result in transitions from one community or state to another. The common and scientific plant names are from the USDA PLANTS database. All community phases in this report are characterized using the Alaska Vegetation Classification (Viereck et al. 1992).

Community 1.1
Feltleaf willow-thinleaf alder / field horsetail

Figure 7. Typical plant community associated with community 1.1.

Figure 8. Canopy cover table for community 1.1.

Reference plant community 1.1 is characterized as closed tall scrub (Viereck et al. 1992), which is primarily composed of willow and alder. Commonly observed species include feltleaf willow, littletree willow, Bebb willow, thinleaf alder, Siberian alder, prickly rose, redosier dogwood, and field horsetail. The vegetative strata that characterize this community are tall shrubs (greater than 10 feet), medium shrubs (between 3 and 10 feet), and medium forbs (between 4 and 24 inches). The soil surface is primarily covered with herbaceous litter and woody debris, but large patches of exposed bare soil can occur (as much as 80 percent of plot).

Dominant plant species

feltleaf willow (Salix alaxensis), shrub
Bebb willow (Salix bebbiana), shrub
littletree willow (Salix arbusculoides), shrub
thinleaf alder (Alnus incana ssp. tenuifolia), shrub
Siberian alder (Alnus viridis ssp. fruticosa), shrub
prickly rose (Rosa acicularis), shrub
redosier dogwood (Cornus sericea), shrub
reedgrass (Calamagrostis), grass
field horsetail (Equisetum arvense), other herbaceous

Community 1.2
Feltleaf willow-sandbar willow / field horsetail

Figure 9. Typical plant community associated with community 1.2.

Figure 10. Canopy cover table for community 1.2.

Community 1.2 is characterized as open tall scrub (between 25 and 75 percent shrub cover) primarily composed of willow. Commonly observed species include feltleaf willow, sandbar willow (Salix interior), thinleaf alder, prickly rose, redosier dogwood, bluejoint (Calamagrostis canadensis), fireweed (Chamerion angustifolium), and field horsetail. The vegetative strata that characterize this community are medium shrubs (between 3 and 10 feet) and medium forbs (between 4 and 24 inches). The soil surface is primarily covered with herbaceous litter and woody debris, but large patches of exposed bare soil can occur (as much as 70 percent of plot).

Dominant plant species

feltleaf willow (Salix alaxensis), shrub
sandbar willow (Salix interior), shrub
thinleaf alder (Alnus incana ssp. tenuifolia), shrub
prickly rose (Rosa acicularis), shrub
redosier dogwood (Cornus sericea), shrub
bluejoint (Calamagrostis canadensis), grass
fireweed (Chamerion angustifolium), other herbaceous
field horsetail (Equisetum arvense), other herbaceous

Community 1.3
Feltleaf willow-sandbar willow / field horsetail-water horsetail

Figure 11. Typical plant community associated with community 1.3.

Figure 12. Canopy cover table for community 1.3.

Community 1.3 is characterized as open low scrub (between 25 and 75 percent shrub cover). Commonly observed species include feltleaf willow, little tree willow, sandbar willow, bluejoint, water sedge (Carex aquatilis), field horsetail, and water horsetail (Equisetum fluviatile). The vegetative strata that characterize this community are medium forbs (between 4 and 24 inches) and low shrubs (between 8 and 36 inches). Large patches of exposed bare soil commonly occurs (as much as 100 percent of plot).

Dominant plant species

feltleaf willow (Salix alaxensis), shrub
littletree willow (Salix arbusculoides), shrub
sandbar willow (Salix interior), shrub
bluejoint (Calamagrostis canadensis), grass
water sedge (Carex aquatilis), grass
field horsetail (Equisetum arvense), other herbaceous
water horsetail (Equisetum fluviatile), other herbaceous

Community 1.4
Balsam poplar / arctic aster-alpine sweetvetch

Figure 13. Typical plant community associated with community 1.4.

Figure 14. Canopy cover table for community 1.4.

Community 1.4 is sparsely vegetated and is best characterized as mesic forb herbaceous. Commonly observed species include balsam poplar, redosier dogwood, kinnikinnick (Arctostaphylos uva-ursi), wild rye (Elymus spp.), common yarrow (Achillea millefolium), alpine sweetvetch (Hedysarum alpinum), arctic aster (Eurybia sibirica), and Tilesius' wormwood (Artemisia tilesii). The vegetative strata that characterize this community are regenerating trees (less than 15 feet in height), low shrubs (between 8 and 36 inches), and medium forbs (between 4 and 24 inches). Extensive areas with exposed bare soil and surface rock fragments commonly occur (as much as 95 percent of plot).