Land Cover Trends Project

North Cascades Ecoregion Summary

By Tamara S. Wilson 1

Click to see available downloads for this ecoregion

map of North Cascades Ecoregion

Figure 1. The North Cascades ecoregion and surrounding ecoregions. Land-use/land-cover data from the 1992 National Land Cover Dataset (Vogelmann and others, 2001) and the 32 randomly selected 100 km2 sample blocks used to create estimates of change for the entire ecoregion.

Ecoregion Description

 

            The North Cascades ecoregion (as defined by Omernik, 1987; Environmental Protection Agency, 1999) covers approximately 30,300 km2 of predominantly steep, mountainous terrain - home to peaks rising over 10,000 feet carved by valleys dropping below 500 feet (fig. 1).  The United States (U.S.) portion of the ecoregion (presented here) falls within north-central Washington, however the ecoregion extends north of the U.S. border into British Columbia. This topographically unique, geographically isolated region has been shaped by glacial processes and deeply incised drainage canyons from subsequent runoff.  Beautiful alpine scenery dominates the ecoregion, which includes several national forests, parks, and wilderness areas such as the North Cascades National Park, the Mount Baker National Forest, Snoqualmie National Forest, Okanogan National Forest, Wenatchee National Forest, and the Pasayten, Glacier Peak, Alpine, and Henry M. Jackson Wilderness areas (fig 2). 

            Climate in the North Cascades ecoregion is remarkably varied.  From fall to spring most of the upper elevation areas are blanketed in snow.  Strong weather systems from the Pacific Ocean pass over the mountain peaks making this region one of the snowiest on earth (National Park Service, 2009).  The western portion of the North Cascades receives, on average, 76 more inches (193 cm) of rain per year and 407 more inches (1,034 cm) of snow than the eastern portion of the range (National Park Service, 2009).  These conditions create the lush, evergreen forests here.  Conditions are markedly drier on the eastern edge of the ecoregion, where dense forests give way to more grasses and shrubland (fig. 1).  Harnessing the annual snowmelt are large-scale dam operations and hydroelectric power plants (e.g. - Ross Lake - 12,000 acres, Diablo Lake - 910 acres, Baker Lake ~3,600 acres, and the enormous Lake Chelan > 61,000 acres – 3rd deepest lake in the U.S. at 1,500 feet, fig. 1, 6). 

            The ecoregion is sparsely populated, with the largest towns represented by Darrington (population 1,347) and Leavenworth (population, 2,269) (Census Bureau, 2007).  Most major cities fall outside of the ecoregion boundary (e.g. Seattle, Tacoma, Everett, Bellingham, and Wenatchee, fig. 3).  Agriculture is evident along low-lying valley bottoms and consisted of irrigated pastureland, alfalfa, wheat, some corn, and other feed crops in the west, as well as apple and pear orchards along the ecoregion’s eastern flank.

            The North Cascades ecoregion supports a diverse range of forests, including some of the oldest and richest tracts of forests remaining in the United States.  At lower elevations and along the western flank of the Cascades these forests are comprised of western red cedar (Thuja plicata), Douglas fir (Pseudotsuga menziesii), western hemlock (Tsuga heterophylla), red alder (Alnus rubra), and big leaf maple (Acer macrophyllum) (fig. 4).  Upslope rise lodgepole pine (Pinus contorta), ponderosa pine (Pinus ponderosa), Pacific silver fir (Abies amabilis), Engelmann spruce (Picea engelmannii), western larch (Larix occidentalis), and whitebark pine (Pinus albicaulis).  (National Park Service, 2007, Washington Biodiversity Office, 2009).

            Late 20th century land cover change in the North Cascades was predominantly associated with timber harvesting via clear-cut logging (fig. 5).  Large scale forestry operations were established where access was the least daunting and harvest delivery options were most efficient.  Timber harvesting occurs to a greater extent on private rather than public lands and along the ecoregion periphery at lower elevations (fig. 3).  According to the National Park Service, widespread logging in this area was not logistically possible in the 19th century, given the rugged terrain, lack of reliable transportation, and availability of more accessible stands elsewhere in the region (National Park Service, 1999).  In the late 1800’s to early 1900’s, mills did operate along the Stehekin Valley, upstream of Lake Chelan, processing logs for eventual use as shipping boxes for apples (National Park Service, 2009).  Selective harvesting of Western red cedar was also allowed along the Skagit River in the early 20th century – in what is today the Mt. Baker Snoqualmie National Forest – but was halted by the early 1920’s (National Park Service, 1999). 

           

Contemporary Land-Cover Change (1973 to 2000)

            Between 1973 and 2000, the areal extent of land-use/land-cover (LU/LC) change in the North Cascades was 10.7 percent, or approximately 3,269 km2 of area changed (table 1).  The North Cascades experienced a modest amount of change compared to other western ecoregions, although the rate was substantially lower than other forested ecoregions in the Pacific Northwest (fig. 7).  The footprint of change can be interpreted as the area that experienced LU/LC change during at least one of the four multi-year periods within the 27-year study period.  Overall, an estimated 1,333 km2 of land experienced change in at least one of the time periods, 1,425 km2 changed during two time periods, 483 km2 changed during three periods, and less than 30 km2 of sampled land area changed during all four time periods (table 1). 

            The average annual rate of LU/LC change in the North Cascades from 1973 to 2000 was 0.7 percent (212.7 km2) of change each year in the 27-year study period (table 2).  This measurement is a cumulative average of the annual average change values for each time period reported.  A steady rate of change is observed between the first two time intervals (0.6 percent), peaking at 0.9 percent during the 1986-1992 period and dropping again to 0.7 percent between 1992 and 2000 (table 2).  Figure 8 shows the percent change by time interval, normalized to annual rates for all western ecoregions.

            Our analysis reveals that in 2000, the North Cascades was dominated by forest (70.3 percent), grassland/shrubland (17.6 percent), natural barren (5.2 percent), snow/ice (2.6 percent), and mechanical disturbance (2.0 percent; table 3).  Only 0.6 percent of the land area was developed and 1.1 percent devoted to agriculture.  The remaining five LU/LC classes comprise less than 1 percent of the remaining ecoregion area (table 3).  From 1973 to 2000, the LU/LC classes experiencing net change in relation to total ecoregion area include net losses overall of forest cover (-1.3 percent; -385 km2) and mechanically disturbed lands (-0.4 percent; -121 km2) and net gains in grassland/shrubland (1.7 percent; 507 km2). 

            Post-classification of our results allowed for the identification of “from class - to class” LU/LC transitions and ranking of these conversions according to their magnitude.  In the North Cascades ecoregion, more than 97 percent of all land-cover conversions between 1973 and 2000 were related to timber harvesting (forest to mechanical disturbance) and successional regrowth (i.e. transition from mechanical disturbance to grassland or forest and transition of grassland to forest, table 4).  Overall, an estimated 2,320 km2 of forested lands were mechanically disturbed (table 4), equating to approximately 7.6 percent of the total ecoregion area.  Of particular note was the doubling of timber harvest rates during the 1986 to 1992 time interval and the subsequent sharp decline in forest cutting post-1992 (table 4).  This pattern is mirrored in other forest-dominated ecoregions of the western U.S. (e.g. Klamath Mountains, Coast Range, Sierra Nevada).

 

Discussion 

            The timber industry has had a dominant influence on LU/LC change in the North Cascades ecoregion.  However, external drivers such as federal endangered species protection and international timber markets have helped dictate the amount and type of forest harvesting during the study period.  Public lands dominate in the North Cascades and are subject to federal regulation (fig. 3).  In 1984, the Washington State Wilderness Act set aside more than a million acres of new wilderness area (Washington Biodiversity Office, 2009).  In 1990, the northern spotted owl was listed as “threatened” under the Endangered Species Act and new habitat protection measures outlined by the Northwest Forest Plan in 1994 set harvesting limits on lands administered by the Forest Service and the Bureau of Land Management.  Timber yields were set at 25 percent of the 1980’s baseline, a drop to only 1 billion board feet of allowable harvest (USDA and USDI, 1994).  In fact, timber harvesting restrictions imposed by endangered species protection led to a 30 percent decline in overall timber volume from 1980’s levels (Daniels, 2005).  This, coupled with reductions in global timber demand, also influenced the decline in logging activity since 1992 (Warren, 1999; Daniels, 2005).  Changes in the Japanese housing industry and the economic collapse in Asia significantly reduced demand for lumber in the 1990’s, along with greater competition from southern U.S. and Canadian forest products (Daniels, 2005).  Overall, the near doubling of forest cutting between 1986 and 1992 in the North Cascades was a region-wide phenomena, driven by international market demand and reined in by the regulation on public lands.   

             


map of Northen Cascades

Figure 1. The North Cascades ecoregion and surrounding ecoregions. Land-use/land-cover data from the 1992 National Land Cover Dataset (Vogelmann and others, 2001) and the 32 randomly selected 100 km2 sample blocks used to create estimates of change for the entire ecoregion.


 

See caption

Figure 2.  Federal land ownership and cumulative land-use/land-cover change (percent block area) from 1973 to 2000 in the North Cascades. 

 


See caption

Figure 3.  North Cascades ecoregion in Washington with major metropolitan areas and roadways.  The 32 – 100 km2 sample blocks are labeled. 


 

See caption

Figure 4.  Lush riparian forest and undergrowth within the Mount Baker-Snoqualmie

National Forest, Washington.     


 

 

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Figure 5.  Clear-cut logging and regrowth in the North Cascades ecoregion, Washington.


 

 

See caption

Figure 6.  Man-made reservoir of Diablo Lake, along the North Cascades Highway within the North Cascades National Park, Washington.

 


See caption

Figure 7. 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 8. Change by time interval normalized to annual rates. Red bar represents the North Cascades Ecoregion, gray bars represent other

western ecoregions.

 

 

Table 1.  Overall spatial change in the North Cascades as expressed in both percentage of ecoregion and ecoregion area that experienced detectable change during the 1973 to 2000 study period. 

 

 

 

 

85% Confidence Interval

 

 

 

 

 

 

% of Ecoregion

+/- (%)

Lower Bound

Upper Bound

Standard Error

Relative Error

Ecoregion Area (Km2)

+/- (km2)

1973-2000

All Change

10.7%

3.6%

7.1%

14.4%

2.5%

22.9%

3269.5

1107.2

1 Change

4.4%

1.4%

3.0%

5.8%

0.9%

21.1%

1333.6

415.8

2 Changes

4.7%

1.8%

2.9%

6.5%

1.2%

26.1%

1425.8

549.8

3 Changes

1.6%

0.7%

0.9%

2.3%

0.5%

31.5%

483.5

224.7

4 Changes

0.1%

0.1%

0.0%

0.1%

0.0%

46.0%

26.6

18.0

 

Table 2. Overall change in the North Cascades ecoregion per time interval in percent stratum (top) and km2 (bottom).

Period

Total Change (%)

Margin Of Error

(+/- ,%)

Lower Bound (%)

Upper Bound (%)

Standard Error (%)

Relative Error (%)

Average Annual Rate (%)

1973-1980

4.0

1.9

2.1

5.9

1.3

32.1

0.6

1980-1986

3.5

1.5

2.0

5.0

1.0

28.3

0.6

1986-1992

5.7

2.2

3.5

7.8

1.5

25.8

0.9

1992-2000

5.6

2.0

3.5

7.6

1.4

24.6

0.7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Period

Total Change (km2)

Margin of Error

(+/- km2)

Lower Bound (km2)

Upper Bound (km2)

Standard Error (km2)

Relative Error (%)

Average Annual Rate (km2)

1973-1980

1225

581

644

1805

393

32.1

175

1980-1986

1065

444

621

1510

301

28.3

178

1986-1992

1724

656

1069

2380

444

25.8

287

1992-2000

1689

614

1076

2303

416

24.6

211

 


 

 

Table 3. Land cover trends in the North Cascades ecoregion.  Percentages and amounts of each land cover class for each of the five mapped dates and associated margins of error (ME).

 

 

Water

Developed

Mech. Dist.

Mining

Barren

Forest

Grass/Shrub

Agriculture

Wetlands

Snow/Ice

 

%

ME (+/-)

%

ME (+/-)

%

ME (+/-)

%

ME (+/-)

%

ME (+/-)

%

ME (+/-)

%

ME (+/-)

%

ME (+/-)

%

ME (+/-)

%

ME (+/-)

1973

0.3

0.1

0.5

0.5

2.4

1.3

0.0

0.0

5.1

1.7

71.6

5.2

16.0

4.5

1.2

0.9

0.2

0.1

2.6

1.5

1980

0.3

0.1

0.5

0.5

1.4

0.7

0.0

0.0

5.2

1.7

71.7

5.2

16.9

4.4

1.1

0.9

0.2

0.1

2.6

1.5

1986

0.3

0.1

0.5

0.5

1.4

0.6

0.0

0.0

5.2

1.7

71.3

5.2

17.2

4.3

1.1

0.9

0.2

0.1

2.6

1.5

1992

0.3

0.1

0.6

0.5

2.9

1.1

0.0

0.0

5.2

1.8

70.5

5.1

16.6

4.4

1.1

0.9

0.2

0.1

2.6

1.5

2000

0.3

0.1

0.6

0.5

2.0

0.9

0.0

0.0

5.2

1.8

70.3

5.1

17.6

4.3

1.1

0.9

0.2

0.1

2.6

1.5

Gross Change

0.0

0.0

0.0

0.0

6.0

2.1

0.0

0.0

0.1

0.1

6.6

2.6

4.6

2.0

0.1

0.2

0.0

0.0

0.1

0.1

Net Change

0.0

0.0

0.0

0.0

-0.4

1.2

0.0

0.0

0.1

0.1

-1.3

1.6

1.7

0.7

0.0

0.1

0.0

0.0

329044.6

-329044.6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Water

Developed

Mech. Dist.

Mining

Barren

Forest

Grass/Shrub

Agriculture

Wetlands

Snow/Ice

 

km2

ME (+/-)

km2

ME (+/-)

km2

ME (+/-)

Km2

ME (+/-)

km2

ME (+/-)

km2

ME (+/-)

km2

ME (+/-)

km2

ME (+/-)

km2

ME (+/-)

km2

ME (+/-)

1973

85

36

165

139

733

399

7

8

1566

529

21781

1571

4856

1356

361

266

66

31

801

464

1980

92

43

166

139

425

211

9

9

1572

532

21813

1568

5139

1324

343

263

66

31

795

459

1986

92

42

166

139

434

176

6

4

1573

531

21705

1569

5248

1323

338

261

65

30

795

459

1992

94

43

169

139

886

332

4

3

1582

533

21432

1553

5057

1343

339

261

66

31

792

456

2000

95

45

169

139

612

265

4

3

1588

537

21396

1564

5362

1305

347

264

64

29

783

450

Gross Change

13

13

4

4

1836

625

7

8

30

20

1999

777

1407

618

39

47

5

6

18

17

Net Change

10

12

4

4

-121

368

-3

8

22

17

-385

493

507

216

-14

28

-2

3

100099719

-100099719


 

Table 4. Common land cover conversions in the North Cascades ecoregion.  Top five land-cover conversions in area changed and associated margin of error and standard error for change estimates, and as a percentage of all changes within the ecoregion 

 

Period

From class

To class

Area Changed (km2)

Std. Error (km2)

85% CI +/- (km2)

% of ecoregion

% of all changes

1973-1980

Forest

Mechanically disturbed

420

143

211

1.4%

34.3%

 

Mechanically disturbed

Forest

412

218

322

1.4%

33.7%

 

Mechanically disturbed

Grassland/Shrubland

309

130

192

1.0%

25.2%

 

Wetland

Wetland

66

21

31

0.2%

5.4%

 

Grassland/Shrubland

Forest

46

24

36

0.1%

3.7%

 

Other

Other

-28

n/a

n/a

-0.1%

-2.3%

 

 

 

 

 

 

 

 

1980-1986

Forest

Mechanically disturbed

415

119

176

1.4%

39.0%

 

Mechanically disturbed

Grassland/Shrubland

314

126

186

1.0%

29.5%

 

Grassland/Shrubland

Forest

217

84

124

0.7%

20.4%

 

Mechanically disturbed

Forest

93

50

74

0.3%

8.7%

 

Agriculture

Grassland/Shrubland

9

8

12

0.0%

0.8%

 

Other

Other

17

n/a

n/a

0.1%

1.6%

 

 

 

 

 

 

 

 

1986-1992

Forest

Mechanically disturbed

876

222

328

2.9%

50.8%

 

Grassland/Shrubland

Forest

388

161

237

1.3%

22.5%

 

Mechanically disturbed

Forest

225

84

124

0.7%

13.1%

 

Mechanically disturbed

Grassland/Shrubland

203

58

86

0.7%

11.7%

 

Forest

Barren

7

5

7

0.0%

0.4%

 

Other

Other

26

n/a

n/a

0.1%

1.5%

 

 

 

 

 

 

 

 

1992-2000

Forest

Mechanically disturbed

609

179

264

2.0%

36.0%

 

Mechanically disturbed

Grassland/Shrubland

475

149

220

1.6%

28.1%

 

Mechanically disturbed

Forest

408

176

260

1.3%

24.2%

 

Grassland/Shrubland

Forest

166

54

79

0.5%

9.8%

 

Snow/Ice

Barren

8

6

8

0.0%

0.5%

 

Other

Other

22

n/a

n/a

0.1%

1.3%

 

 

 

 

 

 

 

 

Overall

 

 

 

 

 

 

 

1973-2000

Forest

Mechanically disturbed

2320

598

882

7.6%

40.7%

 

Mechanically disturbed

Grassland/Shrubland

1301

364

537

4.3%

22.8%

 

Mechanically disturbed

Forest

1139

477

703

3.7%

20.0%

 

Grassland/Shrubland

Forest

816

265

391

2.7%

14.3%

 

Agriculture

Grassland/Shrubland

26

25

37

0.1%

0.5%

 

Snow/Ice

Barren

17

11

17

0.1%

0.3%

 

Forest

Barren

12

8

12

0.0%

0.2%

 

Grassland/Shrubland

Mechanically disturbed

9

5

7

0.0%

0.2%

 

Mechanically disturbed

Water

8

7

11

0.0%

0.1%

 

Other

Other

54

n/a

n/a

0.2%

0.9%


References

Daniels, J. M., 2005, The rise and fall of the Pacific Northwest log export market, United States Department of Agriculture, Forest Service, General Technical Report PNW-GTR-624.

 

EPA, 1999, Level III Ecoregions of the Continental United States: U.S. Environmental Protection

Agency, National Health and Environmental Effects Research Laboratory, Corvallis, Oregon, 1 map, scale 1:7,500,000.

 

National Park Service, 1999, [http://www.nps.gov/archive/noca/hrs4-3a.htm, last accessed July 1, 2009].

 

National Park Service, 2007, [http://www.north.cascades.national-park.com/info.htm#bio, last accessed July 1, 2009].

 

National Park Service, 2009, [http://www.nps.gov/NOCA, last accessed July 1, 2009].

 

Omernik, 1987; Omernik, J.M., 1987, Ecoregions of the conterminous United States: Annals of the Association of American Geographers, v. 77, p.118-125.

 

U.S. Census Bureau, 2007, [http://www.census.gov/, last accessed July 1, 2009].

 

USDA and USDI, 1994, Record of decision on management of the habitat for late-successional and old-growth forest related species within the range of the northern spotted owl (Northwest Forest Plan), Portaland, Oregon.

 

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., Wylie, B.K., and van Driel, N., 2001, Completion of the 1990s National Land Cover Data Set for the conterminous United States from Landsat Thematic Mapper data and ancillary data sources: Photogrammetic Engineering and Remote Sensing, v. 67, p. 650-662.

 

Warren, D.D., 1999, Production, prices, employment, and trade in Northwest forest industries, fourth quarter 1997: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Resource Bulletin PNW-RB-230, 130 p.

 

Washington Biodiversity Office, 2009, [http://www.biodiversity.wa.gov/ecoregions/e_cascades/e_cascades.html, last accessed July 1, 2009].

 

 

 

 

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

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