Tongass National Forest Soils

This digital soil survey information is used by soil scientists, hydrologists, ecologists, planners and other land managers to locate, compare, and select suitable areas for major kinds of land uses; to identify areas that need more intensive investigations; and to evaluate various management alternatives and predict the effects of the particular alternative on the land. Other intended uses of the soil survey include, but are not limited to, providing federal, state, and private organizations with resource information as it relates to activities such as power transmission right-of-way, coastal zone management, forest land management plans, mineral and energy exploration and development, and site suitability for buildings and dwellings. Tongass National Forest soil scientists began mapping soils in the early 1960s. By 1992 mapping was largely completed for approximately 10 million acres of the forest. During mapping, polylines were created using tones and textures on aerial photographs and field-verification. Soil map units were digitized from polygons drawn on 1:31,680 scale Mylar maps. Polygons on aerial photos were traced onto Mylar overlay sheets using a rapidiograph pen, which is accurate to .035 inches of the source data. Polygons were digitized to .001 inches of their location of the digitizing source (Mylar overlay). Accounting for the possibility of cumulative errors during transfer and digitizing, positional accuracy may vary by ± 250 feet. More recent inventories like Yakutat and South Kruzof were pre-mapped using on-screen digitizing with orthophotos and contours as base maps. Historically, the forest was divided into three soil survey areas-Stikine, Chatham, and Ketchikan. These areas are indicated in the FOREST field of the attribute table as follows: 2 = Stikine, 3 = Chatham, 5 = Ketchikan. By the end of the 1990s the digital soil inventory for the three survey areas on the forest were aggregated into one feature class. Beginning in the late 2000s an effort was made to move the soil inventory to Web Soil Survey (WSS). Each survey area was correlated separately. Updates to line work have occurred since 2010 to include areas not previously mapped. In 2020 a fourth area, the Yakutat Forelands was incorporated in WSS and the forest-wide feature class updated with that information. Line work for the southern half of Kruzof Island is included in this feature class but is currently in the correlation process and is not yet available on WSS. The update in 2020 also used all available line work from WSS to make the forest-wide dataset consistent with the data on WSS. Stikine Area (FOREST = 2): All lands within the Stikine Administrative Area have been mapped. This includes all federal, state, and private lands, including wilderness. The soil is mapped at different intensities across the area based on their Land Use Designations (LUDs) in the Tongass Land Management Plan, USDA-FS, 1979. Generally, areas designated for intensive land use (LUD III) are mapped at larger scales (Order 3 level, 1:15,840), while other areas designated for low intensity land use (LUD I&II) are mapped at smaller scales (Order 4 level, 1:31,680). Some areas that are currently LUD I&II were mapped to Order 3 prior to designation. All of the Stikine Area is mapped to an Order 3 level with the exception of the following, which were mapped to Order 4: the Stikine-LeConte Wilderness Area (Farm and Dry Islands are mapped to Order 3), Anan Creek area, and mainland areas designated for semi-remote recreation use. For exact locations, see Preliminary Soil Resource Inventory Report, Stikine Area. Order 3 surveys were mapped on 1:15,840 scale aerial photos. This resulted in map delineations no smaller than approximately 3 acres, ranging up to several hundred acres. The map units in the Order 3 survey area are composed of soil associations, some consociations and some complexes. The Order 4 surveys were mapped on 1:31,680 scale high-altitude infrared aerial photographs. This resulted in map units no smaller than approximately 10 acres and ranged as high as 500 acres in size. The map units in the Order 4 survey area are composed of phases of soil families, or subgroups. Design of initial mapping units in the Stikine area was strongly influenced by soil-vegetation relationships. This is referred to as the "Soil Ecosystem" type of mapping units, which are defined based on natural vegetation types, corresponding soil properties and associated landform types. Map units were also broken out by slope class. Chatham Area (FOREST = 3): The Chatham Area soil survey covers approximately 4.5 million acres of the Tongass National Forest. The inventory occurred in two stages and was done at two levels of detail. An Order 3 survey was conducted from 1981 to 1984, and an Order 4 survey was conducted from 1987 to 1989. Wilderness areas, national monuments, ANILCA additions, state, private and native lands were not mapped. The Order 3 survey is composed primarily of areas referred to as "Land Use Designations (LUDs) III and IV in the Tongass Land Management Plan, USDA-FS, 1979. LUD III were managed for a combination of uses, including recreation and some timber harvest. LUD IV were allocated to intensive resource use and development opportunities, primarily timber harvest and mining. Both LUD III and IV areas required the greater detail of an Order 3 survey. The Order 4 survey is composed primarily of LUD II. LUD II areas were allocated to roadless area management. The lower intensity management of LUD II justified a less detailed Order 4 survey. For exact locations, see Chatham Area Ecological Unit Inventory User Guide, figure 1. The inventory area was pre-mapped on either color aerial photographs at a scale of 1:15,840 (Order 3) or high altitude, color infrared aerial photographs at a scale of 1:63,360 (Order 4). South Kruzof soil survey covers about 60,795 acres of the Tongass National Forest. It represents the soils on the young Mount Edgecumbe volcanic field. The area was initially mapped during the 1981 to 1984 Order 3 Chatham soil survey. A second effort to gather more data began in 1994 but was not completed at that time. The effort to map South Kruzof restarted during 2009 and was completed in 2011. It was mapped digitally at a scale of 1:31,680 on 1998 2-meter black and white Digital Ortho Quads. The Yakutat soil survey covers about 487,758 acres of the Tongass, primarily on the Yakutat Forelands. This survey was also started during the 1981 to 1984 Order 3 soil survey. Additional data was collected in 1987, 1989, 1991, 1992, and 1993. The Yakutat survey was picked up again in 2009 and completed in 2013, although the mountainous areas are still unmapped. Yakutat was mapped digitally at a scale of 1:31,680 on 2008 Color 1 meter Digital Ortho Quarter Quads. The NRCS completed correlation on the Yakutat mapping area in 2020 but has not completed correlation of South Kruzof. The Chatham inventory was strongly influenced by soil-landform relationships. Additionally, vegetation, geology, and soils information was used to stratify the landscape into natural integral units that reflect ecological processes. Map units were also broken out by slope classes. The mapping criteria are based on features that may be either directly observed or inferred from natural landscape and vegetative features viewed on an aerial photograph. The intent of the mapping is to delineate integral ecological units that provide information required to achieve National Forest System management objectives. The Yakutat SMUs are nested in the landtype associations (LTAs) that were mapped in Landtype Associations of the Yakutat Foreland by Michael Shephard and Terry Brock (Technical Publication No. R10-TP-109, 2002). These LTAs were generalized for the soil survey. Ketchikan Area (FOREST = 5): The Ketchikan soil survey area covers approximately 3 million acres. It includes all of the area previously known as the Ketchikan Administrative Area except the following: Misty Fjords National Monument Wilderness and non-wilderness areas, the South Prince of Wales area and large tracts of federal (Bureau of Land Management), state, private borough and municipal lands. These unmapped lands are found on Cleveland Peninsula, Revillagigedo Island, Sukkwan Island, Long Island, Dall Island and Prince of Wales Island. Areas within the Ketchikan Area Soil Survey are mapped at different levels of intensity. Those designated as moderate and intensive development under the 1997 Tongass Land Management Plan (1997 TLMP) Revision, are mapped at an Order 3 level. Most wilderness areas were not included in the soil survey, although some areas now designated as wilderness and National Monument or 'Mostly Natural Setting' were mapped prior to those designations. These areas include: outside islands (Noyes, Lulu and Baker), Mt Calder/Mt. Holbrook Area, Salmon Bay, Coronation Island, Maurelle Islands, Warren Island, and the Karta River. Some other lands identified in the 1997 TLMP Revision under Wilderness and National Monument and 'Mostly Natural' settings were mapped at an Order 4 level. These areas include: Duke, Hotspur and Cat Islands, Cleveland Peninsula (North of Yes Bay), Bell Island, area east of Naha Bay, and area north of Cholmondeley Sound. For exact locations, see Ketchikan Area Soil Survey User Guide, Tongass N.F., p. 13. The Order 3 surveys were mapped on 1:15,840 or 1:40,000 aerial photos. This resulted in map delineations no smaller than approximately 3 acres ranging up to several hundred acres. The Order 3 survey areas are composed approximately of one-third each of map units of soil consociations, associations and complexes. The Order 4 surveys were mapped on 1:15,840 colored aerial photographs. This resulted in map delineations no smaller than approximately 10 acres and ranging as high as 500 acres in size. The map units are composed of phases of series, soil families, or subgroups. The criteria used to delineate map units on the Ketchikan soil survey area were based on natural vegetation, soils, and landforms. Pre-mapping on 15,840 field sheets established the preliminary map unit delineations by separating vegetative patterns (crown size, crown closure, color, and texture) and landforms. Map units were also broken out by slope classes. Northern Prince of Wales survey area map units had no documentation explaining the criteria used to delineate map units, but a review of map unit descriptions and photos indicate the mapping criteria used a combination of soils, landforms and natural vegetation, with an emphasis on soils. Field sheets indicate a stronger soil-landform relationship than a soil-natural vegetation relationship.