Land Cover Trends Project

Columbia Plateau Ecoregion Summary

By Benjamin M. Sleeter 1

Click to see available downloads for this ecoregion

map of  Central Basin and Range ecoregion<

Figure 1. The Columbia Plateau Ecoregion sample blocks overlay the USGS 2001 National Land Cover Database. Click to enlarge.

 

Ecoregion Description

 

Located in eastern Washington and north Oregon, the Columbia Plateau is characterized by sagebrush steppe and grasslands with extensive areas of dryland farming and irrigated agriculture. The ecoregion, which is approximately 90,059 km2, is surrounded on all sides by mountainous regions; the Cascades, Eastern Cascades, Slopes and Foothills, and North Cascades to the west, the Blue Mountains to the south, and the Northern Rockies to the east (Fig. 1). The climate is Mediterranean, with cool wet winters and hot dry summers.

 

The ecoregion was formed by Miocene-aged (17 million to 6 million years ago) flood basalts that covered an area approximately 200,000 km2 in what is currently central and eastern Washington, northern Oregon and western Idaho (Hooper, 1982). The other significant processes that shaped the Columbia Plateau were the great Missoula floods caused by the failure of glacial dams that blocked Montana’s glacial Lake Missoula 10-15 thousand years ago. Massive amounts of water rushing westward from the eastern end of Lake Pend Oreille transformed a dendritic preglacial drainage pattern into the Channeled Scablands of today (Bretz, 1969; Smith, 2006). The great floods resulted in the loss of loess soils that covered much of the region except in areas not in the path of flood waters or with high enough elevations, such as the fertile Palouse region in eastern Washington. These areas spared from the flood waters would later be utilized to grow vast quantities of grain.

 

Since European settlement in the mid-19th century, the region has been heavily utilized for agricultural production. Much of the Columbia Plateau is utilized for dryland winter wheat production with the typical pattern of cultivation being winter-wheat followed by summer-fallow. Soil moisture is accumulated over the winter with most growth occurring in the spring and harvest in summer. The hot and dry summer climate is ideal for maturation of dryland grains and cereals but without irrigation little else can flourish (Schillinger and Papendick, 2008). The Columbia Basin Project began in the 1930’s with the construction of Grand Coulee Dam, originally designed to provide irrigation to the region’s farmers. World War II resulted in the project shifting focus to providing hydro-electric power and the irrigation component was not added until the 1950s. Presently water from the Columbia Basin Project irrigates approximately 670,000 acres of crops valued at over $600 million annually (BOR, 2009).

 

Development of the Columbia Basin is generally rural with only a few major urban areas (Fig. 2). Population growth was slow in the 1980s with an increase of only 4.9 percent. During the 1990s the ecoregion population increased by 20 percent to just under one million people (table 1). 

 

Results

We estimate that 9.0 percent of the Columbia Plateau changed at least one time between 1973 and 2000 (table 2). Compared to other ecoregions, change in the Columbia Plateau can be considered modest (Fig. 3). Of the 9.0 percent change, 2.2 percent changed in more than one time interval, mostly a result of farmland cycling in and out of production. Changes to ecoregion land cover were not spread evenly over the 27-year study period. As is the case in many other agricultural regions, the period between 1986 and 1992 experienced the highest amount of change owing largely to the conversion of marginal agricultural lands to grasslands/shrublands. The average annual rate of change during this period was 0.7 percent while the other three periods experienced rates nearly half that amount (table 3, Figure 4).

 

Agricultural lands comprised approximately 48.8 percent of the ecoregion in 1973. By 1986 agriculture had increased an estimated 1,475 km2 to make up 50.4 percent of the ecoregion. Between 1986 and 1992, we estimate a net decline of 1,531 km2 of agriculture, composing approximately 48.7 percent of the ecoregion. By 2000, agriculture had once again increased to account for 49.4 percent of the ecoregion (table 4). The Conservation Reserve Program (CRP), a federal policy to encourage land owners to convert marginal farmlands to native vegetation, played an important role in the Columbia Plateau. With the onset of the program, the ecoregion reversed the trend of increasing agricultural land use, and by 1997 enrollment in the CRP program totaled 3,311 km2 (U.S. Department of Agriculture, 1999). Expiration of 10-year CRP contracts in the late 1990’s contributed to 0.6 percent of the ecoregion converting back into agricultural use by 2000. During our study period dryland wheat farming experienced a sharp decline while other areas of agriculture intensified with the addition of new irrigated lands. Historical wheat, irrigated cropland, and CRP enrollments are summarized in figure 5.

 

Trends in grasslands/shrublands mirrored those of the agricultural class. Grasslands/shrublands comprised 41.0 percent of the ecoregion in 1973 and 39.9 percent in 2000, a net loss of 973 km2. Developed land covers accounted for a very small proportion of the ecoregion (~1.0 percent); we estimate a net increase of approximately 284 km2 over the 27-year period. All other land cover classes remained relatively stable (table 4).

 

As expected, the most common land-cover conversions were between the agriculture and grasslands/shrublands classes. In all time intervals these were the two most common conversions. In three of the four intervals increases in agriculture from grasslands/shrublands outpaced losses. The exception was between 1986 and 1992 when 2,342 km2 changed from agriculture to grasslands/shrublands and only 886 km2 converted from grasslands/shrublands to agriculture. Other conversions of note were grasslands/shrublands to non-mechanical disturbance (fire) and agriculture to developed (table 5).

 

Discussion

Irrigation technology, infrastructure development, federal conservation efforts, and population growth all acted as drivers of change on Columbia Plateau land cover. In the 1960s and 1970s the spread of center pivot irrigation technology enhanced the ability to bring marginal lands into production. Also occurring during the same period was the expansion and utilization of water delivery infrastructure from the Columbia Basin Project which was planned to irrigate over 1 million acres of marginal lands. Our estimates indicate that this period resulted in the highest rate of change from sagebrush steppe to new agriculture, with an addition of an average of 290 km2 per year between 1973 and 1980.

 

While new lands were being added to the Columbia Plateau’s agriculture mosaic in each time period, in only one period, 1986 to1992, were these additions outpaced by the reversion back to natural vegetative conditions. At least partially responsible was the federal CRP program which provided economic incentives to local farmers to enter into land conservation contracts. Resulting from this program were large amounts of marginal farmland being taken out of production; a pattern observed across the country. In the western U.S., CRP had its most significant impact in the Columbia Plateau Ecoregion (figure 6). Our estimates reveal this period experienced the only net decline in agricultural land cover during the 27-year land-cover study.

 

Regional population growth has also had an impact on regional land-cover change. While developed land covers accounted for approximately 1 percent of the total ecoregion area, there was a measured increase in developed lands of approximately 32 percent between 1973 and 2000. Demand for new housing and infrastructure to support an additional 200,000 people resulted in the conversion of a relatively small amount of agricultural land, and to a lesser extent grasslands/shrublands, to new developed uses.


References

 

Bretz, J. H., 1969, The Lake Missoula floods and the channeled scabland, Journal of Geology, Vol. 77, p. 505-543. [need a copy of article]

 

Hooper, P. R., 1982, The Columbia River basalts, Science, Vol. 215, No. 4539, pp. 1463-1468.

 

Schillinger, W. F., R. I. Papendick, 2008, Then and Now: 125 years of dryland wheat farming in the inland Pacific Northwest, Agronomy Journal, Vol. 100, pp. 166-182.

 

Smith, L. N., 2006, Stratigraphic evidence for multiple drainings of glacial Lake Missoula along the Clark Fork River, Montana, USA, Quaternary Research, Vol. 66, pp. 311-322.

 

Geolytics, 2005, Planners Package Plus, PO Box 10 East Brunswick, NJ 08816.

 

U.S. Bureau of Reclamation, http://www.usbr.gov/pn/project/columbia_index.html#, last accessed 16 July, 2009.

 

U.S. Department of Agriculture, 1999, 1997 Census of agriculture—agricultural atlas of the United States v. 2, subject series, part 1: Washington, D.C., U.S. Government Printing Office, 163 p.
Table 1. Columbia Plateau Ecoregion population estimates by state for the 1980, 1990, and 2000 censuses (Geolytics, 2005). Population estimates are calculated using Census tracts that have their centroid within the Columbia Plateau Ecoregion.

Census Year

Population

% Change from Previous Decade

1980

777,166

 

Oregon

90,051

 

Washington

618,055

 

Idaho

69,060

 

 

 

 

1990

814,979

+4.9%

Oregon

90,861

---

Washington

654,062

+5.8%

Idaho

70,056

+1.4%

 

 

 

2000

978,069

+20.0%

Oregon

107,212

+18.0%

Washington

792,260

+21.1%

Idaho

78,597

+12.2%

 

Table 2.  Percentage of the ecoregion that experienced change and associated error

[Most of the sample pixels remained unchanged (91.0 percent), whereas 9.0 percent changed at least once through the study period]

 

 

 

 

 

 

 

 

 

 

 

 

 

Number

Percent

Margin

Lower

Upper

Standard

Relative

of

of

of error

bound

bound

error

error

changes

ecoregion

(+/- %)

(%)

(%)

(%)

(%)

1

6.8

 

2.3

 

4.5

 

9.1

 

1.6

 

23.2

 

2

1.8

 

0.6

 

1.2

 

2.4

 

0.4

 

22.3

 

3

0.4

 

0.2

 

0.2

 

0.5

 

0.1

 

32.0

 

4

0.1

 

0.1

 

0.0

 

0.1

 

0.0

 

73.7

 

Overall spatial change

9.0

 

2.7

 

6.3

 

11.7

 

1.8

 

20.4

 

 

Table 3.  Raw estimates of area and percent change in the ecoregion computed for each of the four time periods and associated error at an 85-percent confidence level

[Estimates of change per period normalized to an annual rate of change for each of the four time periods]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Period

Total change

Margin of error

Lower bound

Upper bound

Standard error

Relative error

Average rate

(% of ecoregion)

(+/- %)

(%)

(%)

(%)

(%)

(% per year)

1973-1980

2.9

 

1.4

 

1.5

 

4.3

 

1.0

 

32.8

 

0.4

 

1980-1986

2.3

 

0.6

 

1.7

 

3.0

 

0.4

 

18.9

 

0.4

 

1986-1992

4.1

 

1.4

 

2.7

 

5.5

 

0.9

 

23.0

 

0.7

 

1992-2000

2.4

 

0.7

 

1.7

 

3.2

 

0.5

 

21.0

 

0.3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Period

Total change

Margin of error

Lower bound

Upper bound

Standard error

Relative error

Average rate

(km2 of ecoregion)

(+/- km2)

(km2)

(km2)

(km2)

(%)

(km2 per year)

1973-1980

2641

 

1275

 

1366

 

3915

 

866

 

32.8

 

377

 

1980-1986

2080

 

579

 

1501

 

2659

 

393

 

18.9

 

347

 

1986-1992

3702

 

1251

 

2451

 

4954

 

850

 

23.0

 

617

 

1992-2000

2174

 

671

 

1504

 

2845

 

456

 

21.0

 

272

 

 


 

Table 4.  Estimated area and associated margins of error for each land cover class between 1973 and 2000

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Water

Developed

Mech dist

Mining

Barren

Forest

Grass/Shrub

Agriculture

Wetlands

Nonmech dist

 

%

+/-

%

+/-

%

+/-

%

+/-

%

+/-

%

+/-

%

+/-

%

+/-

%

+/-

%

+/-

1973

0.8

0.4

1.0

0.6

0.0

0.0

0.0

0.0

0.0

0.0

7.6

3.1

41.0

6.4

48.8

7.4

0.9

0.3

0.0

0.0

1980

0.8

0.4

1.1

0.7

0.0

0.1

0.0

0.0

0.0

0.0

7.6

3.0

39.2

6.1

50.4

7.3

0.9

0.3

0.0

0.0

1986

0.8

0.4

1.1

0.7

0.0

0.0

0.0

0.1

0.0

0.0

7.7

3.1

38.9

5.9

50.4

7.1

0.9

0.3

0.1

0.2

1992

0.8

0.4

1.2

0.8

0.0

0.0

0.0

0.0

0.0

0.0

7.6

3.0

40.5

6.1

48.7

7.2

0.9

0.3

0.1

0.2

2000

0.8

0.4

1.3

0.8

0.0

0.0

0.0

0.0

0.0

0.0

7.6

3.0

39.9

6.1

49.4

7.2

0.9

0.3

0.0

0.0

Net Change

0.1

0.1

0.3

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.2

-1.1

2.5

0.6

2.5

0.1

0.1

0.0

0.0

Gross Change

0.1

0.1

0.3

0.2

0.1

0.1

0.1

0.1

0.0

0.0

0.4

0.4

7.6

2.4

7.3

2.4

0.1

0.1

0.5

0.5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Water

Developed

Mech dist

Mining

Barren

Forest

Grass/Shrub

Agriculture

Wetlands

Nonmech dist

 

km2

+/-

km2

+/-

km2

+/-

km2

+/-

km2

+/-

km2

+/-

km2

+/-

km2

+/-

km2

+/-

km2

+/-

1973

680

360

878

580

0

0

7

8

1

1

6836

2754

36943

5742

43946

6674

768

291

0

0

1980

730

390

967

612

41

59

18

18

0

1

6817

2728

35331

5455

45387

6532

768

288

0

0

1986

738

394

1025

647

0

0

40

46

1

2

6894

2779

35068

5350

45421

6435

775

288

96

139

1992

718

387

1095

682

8

9

36

43

1

1

6847

2679

36495

5464

43889

6447

840

291

131

189

2000

740

388

1162

734

5

5

29

28

4

5

6843

2678

35970

5486

44480

6525

826

289

0

0

Net Change

61

71

284

172

5

5

21

25

3

4

7

224

-973

2270

534

2223

58

63

0

0

Gross Change

113

83

284

172

94

118

57

61

5

7

381

325

6881

2166

6561

2144

111

74

455

463

 


 

Table 5.  Leading land cover conversions during each of four time periods

 

 

 

 

 

 

 

 

 

 

 

 

 

Period

From class

To class

Area changed

Margin of error

Standard error

Percent of ecoregion

Percent of all changes

(km2)

(+/- km2)*

(km2)

 

 

1973-1980

Grassland/Shrubland

Agriculture

1954

 

1138

 

773

 

2.2

 

74.0

 

 

Agriculture

Grassland/Shrubland

429

 

300

 

204

 

0.5

 

16.2

 

 

Agriculture

Developed

61

 

50

 

34

 

0.1

 

2.3

 

 

Grassland/Shrubland

Water

51

 

73

 

50

 

0.1

 

1.9

 

 

Forest

Mechanically disturbed

41

 

59

 

40

 

0.0

 

1.5

 

 

Other

Other

105

 

n/a

 

n/a

 

0.1

 

4.0

 

 

 

 

2641

 

 

 

 

 

2.9

 

100.0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1980-1986

Grassland/Shrubland

Agriculture

932

 

359

 

244

 

1.0

 

44.8

 

 

Agriculture

Grassland/Shrubland

822

 

419

 

285

 

0.9

 

39.5

 

 

Grassland/Shrubland

Nonmechanically disturbed

94

 

135

 

92

 

0.1

 

4.5

 

 

Agriculture

Developed

47

 

37

 

25

 

0.1

 

2.3

 

 

Agriculture

Forest

42

 

60

 

41

 

0.0

 

2.0

 

 

Other

Other

144

 

n/a

 

n/a

 

0.2

 

6.9

 

 

 

 

2080

 

 

 

 

 

2.3

 

100.0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1986-1992

Agriculture

Grassland/Shrubland

2342

 

1155

 

785

 

2.6

 

63.3

 

 

Grassland/Shrubland

Agriculture

886

 

469

 

319

 

1.0

 

23.9

 

 

Forest

Nonmechanically disturbed

132

 

189

 

129

 

0.1

 

3.6

 

 

Nonmechanically disturbed

Grassland/Shrubland

96

 

138

 

94

 

0.1

 

2.6

 

 

Grassland/Shrubland

Forest

89

 

76

 

52

 

0.1

 

2.4

 

 

Other

Other

159

 

n/a

 

n/a

 

0.2

 

4.3

 

 

 

 

3702

 

 

 

 

 

4.1

 

100.0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1992-2000

Grassland/Shrubland

Agriculture

1276

 

527

 

358

 

1.4

 

58.7

 

 

Agriculture

Grassland/Shrubland

634

 

313

 

212

 

0.7

 

29.1

 

 

Nonmechanically disturbed

Grassland/Shrubland

131

 

188

 

128

 

0.1

 

6.0

 

 

Agriculture

Developed

49

 

44

 

30

 

0.1

 

2.3

 

 

Grassland/Shrubland

Developed

12

 

8

 

5

 

0.0

 

0.6

 

 

Other

Other

72

 

n/a

 

n/a

 

0.1

 

3.3

 

 

 

 

2174

 

 

 

 

 

2.4

 

100.0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Overall

 

 

 

 

 

 

 

 

 

 

 

 

1973-2000

Grassland/Shrubland

Agriculture

5048

 

2074

 

1409

 

5.6

 

47.6

 

 

Agriculture

Grassland/Shrubland

4226

 

1621

 

1101

 

4.7

 

39.9

 

 

Nonmechanically disturbed

Grassland/Shrubland

226

 

230

 

156

 

0.3

 

2.1

 

 

Agriculture

Developed

211

 

149

 

102

 

0.2

 

2.0

 

 

Forest

Nonmechanically disturbed

134

 

189

 

129

 

0.1

 

1.3

 

 

Other

Other

752

 

n/a

 

n/a

 

0.8

 

7.1

 

 

 

 

10597

 

 

 

 

 

11.8

 

100.0

 

 


 

 

Figures

see Caption

Figure 1. The Columbia Plateau Ecoregion sample blocks overlay the USGS 2001 National Land Cover Database.

 

see Caption

Figure 2. Major cities and rivers in the Columbia Plateau Ecoregion overlay a satellite image of the region.

 

see Captionsee Caption

Figure 3. The overall spatial change in western U.S. ecoregions. Each bar shows the proportion of the ecoregion that experienced change on 1, 2, 3, or 4 dates.

 

see Caption

 

Figure 4. Land-cover change by time interval normalized to average annual rates. The red bar is the Columbia Plateau Ecoregion and the gray bars are other western ecoregion.

 

See caption

Figure 5. Historical trends in irrigated agriculture, dryland wheat, and Conservation Reserve program enrollments summarized by counties with centroid within the Columbia Plateau Ecoregion. Data is from USDA’s Agriculture Census.

 

See caption

Figure 6. Conservation Reserve Program (CRP) enrollments for the year 2000 by county and EPA Level III Ecoregions.

 


Supplemental Photos

See caption

Photo 21-668. Wheat fields near Moro, Oregon.

 

See caption

Photo 397-275. Young orchard planted in the Yakima Valley, Washington.

 

See caption

Photo 411-275. New home construction and orchard near the Naches River and the town of Tieton, Washington.

 

See caption

Photo 303-210. Cut wheat fields and farm buildings outside of Spokane, Washington.

 

See caption

Photo 159-585. Mixed agricultural fields in the Palouse region of the Columbia Plateau, near Johnson, Washington.

 

See caption

Photo 442-405. Corn field near Grange, Washington.

 

[1] U.S. Geological Survey, Western Geographic Science Center, Menlo Park, CA 94025

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