Coquille Subbasin Working Atlas - p6
Vegetation and Land Cover
Page 6: Vegetation and Land Cover
Vegetative cover and land use can be mapped in numerous ways. Systems for classifying vegetation types vary considerably depending on the needs of potential users and resources available in the mapping process. Due to the high degree of variability among different classification systems it is often difficult to combine vegetation maps from different sources. Maps of broad land use and vegetative types are developed from interpretation of aerial photography or satellite imagery and are useful for general purposes. Detailed maps with multiple vegetation classes require extensive field work, particularly where forest tree sizes or age classes are classified. The accuracy of these types of data can only be determined by independent assessments that compare map types to actual field observations. Three general vegetation and land cover maps are presented in this atlas. The accuracy of these thematic data are not quantified. While more detailed vegetation data does exist for the Coquille, none is available across the entire subbasin.
Land use and land cover
The land cover data show on the Land Use and Land Cover map is the 1979 USGS land use/land cover GIS data layer. Land use and land cover (LULC) data were derived from thematic overlays registered to 1:250,000-scale base maps. The LULC data provides broad information on urban or built up land, agricultural land, rangeland, forest land, water, wetlands, barren land, tundra, and perennial snow or ice. While the land use patterns shown in this USGS data layer are generally considered to be accurate, more detailed vegetation information is provided in the GAP analysis data.
As indicated by Figure 11, the vast majority of the Coquille basin is forested, with agriculture, rangeland, and urban areas making up the remainder of the basin. The lower Coquille subdivision is the most diverse area of the subbasin in terms of land use activities, although over 76% of this area is still in forest cover. Most of the agricultural activity occurs along the main fork of the Coquille from the area surrounding the city of Coquille to the city of Bandon. Over 15% of the lower Coquille subdivision is classified as agricultural land. Other small agricultural areas are located along various tributaries within the other subdivisions. Most of the rangeland within the subbasin occurs along the South Fork of the Coquille between Myrtle Point and Powers, although rangeland makes up little more than 4% of the land base in that subdivision. Residential and other urban areas are clustered around the main towns of the subbasin; Bandon, Coquille, Myrtle Point, and Powers. Nearly five percent of the Lower Coquille subdivision is classified in urban land uses. Table 5 lists total area by subdivision and broad cover type. Table 7 lists total area by land use type for the entire Coquille subbasin.
|Table 5: Acres by Major Land Use and Land Cover Class by Subdivision|
|Subdivision||Agricultural||Rangeland||Forest||Urban or Built-up||Other|
|Table 7: Acres by Land Use and Land Cover Class|
|Land Use||Acres||% of Total|
|Evergreen Forest Land||604,827||-|
|Cropland and Pasture||34,742||-|
|Other Agricultural Land||578||-|
|Shrub and Brush Rangeland||55||-|
|Urban and Built-up Land||—||1.4%|
|Commercial and Service||953||-|
|Mixed Urban or Built-up||521||-|
|Other Urban or Built-up||567||-|
|Streams and Canals||1,036||-|
|Sandy Areas other than Beaches||267||-|
|Area Undefined by Coding||4||-|
The Land Use and Land Cover map also indicates the locations of mining sites by type. Mine location data is based on the Mineral Information Layer for Oregon Counties (MILOC) database from the Department of Geology and Mineral Industries (DOGAMI) (Gray, 1994). Although mine locations are indicated, the level of activity is not. Many of the mining sites shown may not be active.
The Vegetative Cover Types and Precipitation Zones map shows large-scale vegetation patterns within the Coquille Basin. The vegetation data used in this map is based on data developed by the Oregon GAP Analysis Program, a cooperative effort between the Oregon Fish and Wildlife Service the Oregon Natural Heritage Program and the Idaho Cooperative Fish and Wildlife Research Unit (Kagan and Caicco, 1992). Actual vegetation was mapped as vegetation complexes or groups of vegetation types through visual interpretation of 1988 satellite imagery. Landsat Multi-Spectral Scanner (MSS) false-color infrared positive prints were visually photo-interpreted at a scale of 1:250,000 to identify boundaries of different vegetation cover types. The nominal minimum mapping unit is 320 acres, and the average polygon size for the statewide coverage is 8,141 acres. The median polygon size is somewhat smaller, on the order of a few thousand acres. No independent assessment is available to verify the accuracy of this data.
|Table 8: Acres by Vegetation Cover Type based on GAP Analysis Data by Subdivision|
|Cover Type||Coquille||East Fork||Middle Fork||North Fork||South Fork||Total|
|Bigleaf Maple-Red Alder-Douglas Fir Forests||10,336||35,442||66,933||52,848||3,374||168,934|
|Brushfields — Recent Clearcuts and Fires||3,463||—||14,802||7,039||4,356||29,659|
|Douglas Fir Forests||8,612||49,830||94,358||35,958||61,045||249,804|
|Oregon White Oak-California Oak Woodland||—||—||448||—||19,801||20,249|
|Oregon White Oak-Douglas Fir Woodlands||—||—||6,363||—||—||6,363|
|Rural Pasture with Remnant Bottomlands||20,852||—||330||3,349||4,474||29,005|
|Sitka Spruce-Western Hemlock Forest||63,824||—||—||—||27,549||91,374|
|Urban and Industrial Areas||—||—||—||154||204||358|
|Tufted Hairgrass Meadows||—||—||4,827||—||—||4,827|
|White Fir-Douglas Fir-Incense Cedar Forests||—||—||5,040||—||53,414||58,454|
The Coquille subbasin is dominated by a variety of forest complexes. The Douglas fir type is the most common, covering approximately 38 percent of the entire subbasin. Sitka Spruce and Western Hemlock Forests are prevalent along the lower and western portions of the subbasin and make up nearly 60 percent of the lower Coquille subdivision. Over 65 percent of the South Fork subdivision in the southern portion of the subbasin is comprised of Douglas fir and a complex of White Fir, Douglas Fir and Incense Cedar. The Bigleaf Maple — Red Alder — Douglas Fir complex covers approximately 25 percent of the Coquille subbasin, but this vegetation type is most prevalent in the East Fork and North Fork subdivisions where it covers 42 percent and 53 percent of the total area, respectively.
The GAP data were used in conjunction with the ownership data to determine the general pattern of vegetation by owner type. Over 78 percent of the White Fir, Douglas Fir and Incense Cedar complex in the entire Coquille subbasin is found in the Siskiyou National Forest. Most of the Sitka Spruce and Western Hemlock Forest type is on private non-industrial (49 percent) and industrial (44 percent) ownerships. Forty four percent of the Douglas fir type is in private industrial ownerships and another 32 percent is on federal lands managed by the BLM. The brushfields and recent clearcuts and fires in the Coquille are found primarily on private industrial (56 percent) and private non-industrial (24 percent) lands. Thirty-seven percent of the Bigleaf Maple — Red Alder — Douglas Fir complex occurs on land managed by the BLM, 35 percent on private industrial and another 27 percent on non-industrial ownerships.
|Table 9: Acres by Vegetation Cover Type based on GAP Analysis Data|
|Vegetation Cover Type||Acres||%|
|Bigleaf Maple-Red Alder-Douglas Fir Forests||168,934||25.6%|
|Oregon White Oak-California Oak Woodland||20,249||3.1%|
|Oregon White Oak-Douglas Fir Woodlands||6,363||1.0%|
|Sitka Spruce-Western Hemlock Forest||91,374||13.8%|
|Douglas Fir Forests||249,804||37.9%|
|White Fir-Douglas Fir-Incense Cedar Forests||58,454||8.9%|
|Brushfields — Recent Clearcuts and Fires||29,659||4.5%|
|Tufted Hairgrass Meadows||4,827||0.7%|
|Rural Pasture with Remnant Bottomlands||29,005||4.4%|
|Urban and Industrial Areas||358||0.1%|
Forest cover seral stage
The Forest Seral Stage map shows three forest cover seral stage classes — late seral, mid seral, and early seral — along with non-forested, other forest, and water. The data was developed from 1988 Landsat Thematic Mapper (TM) satellite imagery for the Oregon Department of Forestry. The six classes are defined as follows:
Late seral stage: greater than 70% tree crown closure with greater than 10% of total crown closure in trees 21 inches diameter at breast height (dbh) or more, and not more than 75% of total crown closure in hardwoods.
Mid seral stage: greater than 70% tree crown closure with less than 10% of total crown closure in trees 21 inches diameter dbh or more, and not more than 75% of total crown closure in hardwoods.
Early seral stage: greater than 10% and less than 70% tree crown closure and not more than 75% of total crown closure in hardwoods.
Other: less than 10% crown closure of conifers and/or greater than 75% of total crown closure in hardwoods.
Water: open water.
Non-forested: not forestland as determined by 1:250,000 scale USGS landuse coverage.
Table 10 shows acres by seral stage class within each subdivision. Thirty-two percent of the Coquille subbasin is classified as mid seral stage. Another 22 percent is classified as other forest due most likely to a predominance of hardwoods. The lower Coquille subdivision has the lowest percentage of late and mid seral class. One third of the lower Coquille is classed in the other forest category, and another third is non-forest. The Middle Fork subdivision has the highest percentage (60%) of late and mid seral stage forest.
|Table 10: Acres of Seral Stage by Subdivision|
|Seral Stage||Coquille||East Fork||Middle Fork||North Fork||South Fork||Total|
Merging the ownership data with seral stage data highlights variation in the pattern of ownership relative to general forest condition. Figure 12 indicates the distribution of seral class by ownership type. The BLM, which manages 23 percent of the land within the Coquille subbasin, controls 46 percent of the late seral stage class. Private industrial ownerships, which account for 36 percent of the entire subbasin, control forty-six percent of the mid seral stage class lands.
|Table 11: Cover Type as Percentage of total Ownership Type*|
|Bigleaf Maple-Red Alder-Douglas Fir Forests||41.31%||24.50%||23.83%||—|
|Brushfields — Recent Clearcuts and Fires||3.23%||6.95%||3.71%||—|
|Douglas Fir Forests||51.92%||45.72%||21.55%||27.53%|
|Oregon White Oak-California Oak Woodland||0.08%||1.17%||8.92%||—|
|Oregon White Oak-Douglas Fir Woodlands||1.41%||0.35%||1.73%||—|
|Rural Pasture with Remnant Bottomlands||—||0.62%||14.07%||—|
|Sitka Spruce-Western Hemlock Forest||0.67%||16.96%||22.98%||—|
|Tufted Hairgrass Meadows||0.14%||0.01%||2.36%||—|
|Urban and Industrial Areas||—||—||0.18%||—|
|White Fir-Douglas Fir-Incense Cedar Forests||1.23%||3.69%||0.53%||72.47%|
The distribution of land by seral stage class varies considerably within ownership groups. National forest land managed by the USFS is nearly evenly divided among late, mid and early seral classes. One third of BLM land is classified as late and another third as mid seral stage. Twenty-eight percent, however, is in either the other seral or non-forest class. Forty-one percent of private industrial land is in the mid seral stage and 25 percent is in the other seral class. The remaining third of private industrial land is evenly distributed among the late seral, early seral and non-forest classes. Approximately two thirds of all private non-industrial lands are in other seral or non-forest classes. Twenty percent of non-industrial lands are in the mid seral stage class.