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Understanding Land Part III Our American Land Mapping Ecoregions To Manage Land
Robert G. Baiiey, geographer, Land Management Planning Staff, Forest Service
Knowing how the biological and Mapping Ecoregions physical components of land Ecosystem regionalization is the delin- are integrated to form ecosystems is eation of large units of land according basic to understanding its productive to the ecological relationships among value. This integration can be evaluated neighboring ecosystems. Á boundary is with precision for small parcels of placed around groups of related eco- forested or agricultural land called systems that show similarities in both sites. However, strategic planning of appearance and structure. They are large areas calls for grouping the sites influenced by the same climate and into ecosystem regions or ecoregions. soil conditions. Groups of spatially This requires differentiating between related ecosystems can be considered spatial patterns of sites. an ecosystem of higher order and is usually larger—a macroecosystem. Ecoregions often differ in size and Ecoregions' Value to can be ranked by levels of detail  Management hierarchy of boundaries enables scien- Ecoregions are useful to land tists to view the Nation's environment managers in two ways. First, a map with greater and greater resolution as of such regions suggests the area to they move down the map scale. All which the knowledge gained in components of an ecosystem are not studing the ecosystem behavior can be equally signiflcant at defining eco- applied. Second, they provide a geo- regions in the hierarchy. graphical framework for identifying other similar areas from which similar responses may be expected and similar Climatic Factors management policies applied. This Climatic factors determine the boun- facilitates a regional rather than site- daries of ecoregions to a considerable by-site approach to planning land use. extent. The most important of these The need for environmental inven- factors is the climatic regime, deñned tories and analysis is correspondingly as day by day and seasonal fluxes of reduced. energy and moisture. As these change,
82 Understanding land Our American Land
so do kinds and patterns of dominant Sites to consider in regional delinea- plants and animals, as well as the tion should be reasonably uniform sets kinds of soils. The most important of uplands, with well-drained surface, consideration in identifying ecoregions moderate surface-slope, and well- is to recognize significant differences developed soils. In this way, the land- in climate by looking for the following: form differences are screened out, 1. The series of ecosystem regions leaving the biologically effective should express the changing nature of climate as the main variable between the climate over large areas. Unfor- regions. These sites are typical of the tunately, climate changes within short ecoclimatic zones and are referred to distances because of variations in local as zonal ecosystems; the others are landform features and the vegetation azonal. that develops on them. So it is 4. Where ecosystems cover large necessary to look for a climate that areas, in a fairly uniform way, map- hierarchically lies just above the local ping is not difficult. Simplifying moun- modifying irregularities of landform tainous ecosystems into regions on the and vegetation. These macroclimates other hand presents problems. One are shown on maps of broad climatic approach is to look at these as a regions. They outline ecoclimatic sequence of altitudinal zones. Each zones within which are groups of part of a mountain range with the related ecosystems of importance to same sequence is a distinct ecological the climatologist in determining unit. These units correlate with the ecoregion boundaries. Other visible distribution of the lowland climatic and tangible expressions of climate zone within which the range is such as vegetation are also used to located. locate boundaries. 5. The mosaic of ecosystems found 2. The composition of the vegeta- in major transitional zones (ecotones) tion of the ecosystem region changes also should be delineated as separate with time in sequence from pioneer regions. vegetation through intermediate steps 6. The boundaries of ecoregions to the most stable climax state. The can be located best by studying spatial climax plants are used to characterize coincidences, patterning and relation- regions because they are more site- ships of climate, vegetation, soil, and specific than pioneer types, which landform. may occur over a wider range of con- Useful scales for mapping ecosystem ditions. Each ecoregion comprises both regions may be from 1:30,000,000 to the climax communities and all succes- about 1:3,000,000. sional stages within its geographic area including freshwater communities. A National Map 3. Landform (with its geologic sub- A mapping project was begun by the strate, surface slope, and relief) Forest Service in 1976 with the sup- modifies macroclimate to local climate. port of the U.S. Fish and Wildlife
Mapping Ecoregions To Manage Land 83 Our American Land
A variety of ecosystems form this region of sand dune, rocl(, and stirubland sites in tlie Col- orado Plateau, a highland in the semiarid steppe zone. (John S. Shelton)
Service's National Wetland Inventory. sections that differ in the floristic It delineates successively smaller composition of the climax plant for- ecoregions within larger regions on an mation. Highland provinces and sec- ecoclimatic basis. At each successive tions are distinguished where, as a level, a different aspect of the climate result of the influence of altitude, the and vegetation is assigned prime climatic regime differs substantially importance in the placing of map from adjacent lowlands to cause com- boundaries. plex vertical climate-vegetation-soil zonation. How To Understand Map The hierarchical system begins with Four ecological levels defined by their the country's 3.3 million square miles climate and vegetation are shown. The divided into four domains: Polar (15 broadest levels or domains are based percent of the U.S. land area). Humid on observable differences developed Temperate (53 percent). Dry (31 per- largely because of prevailing climatic cent), and Humid Tropical (less than conditions. Domains are broken down 1/2 percent). These subdivide into 12 further into divisions based on domi- divisions, in total containing 30 nant climax plant formation, and provinces, in turn containing 45 these geographically subdivide into sections. provinces. Provinces subdivide into This map presents twice the detail
84 Understanding Land Our American Land
of previous maps of ecological regions. agriculture, and effectiveness of best Using existing maps of climate, vegeta- management practices in protecting tion, soil, and landform as source fisheries can be applied to similar sites material, it delineates ecosections in with each region. the United States encompassing more The map provides an integrated than 4,300 square miles. geographical framework for use by At the province level, however, the Federal and State agencies throughout more comprehensive ecological descrip- the country. It has been adopted by tions are found. Land-surface form, Federal agencies. National programs climate, soils, vegetation, and fauna and studies using it include the are listed, along with the total land National Wetlands Inventory, Acid area and general geographic location. Precipitation Trends Network, Manage- Sections within each province are ment of Transmission Line Right-of- listed by name and also indicated by Way for Fish and Wildlife, Water number of the ecoregion map. For Resources Evaluation of Non-point example, the redwood forests of Silvicultural Sources, and Habitat northern California are in the Humid Suitability Index Models. The Forest Temperate Domain, of the Marine Service has used the map in assess- Highlands Division, of the Pacific ments of forest and range lands Forest Province, in the Redwood required by the 1980 Resources Plan- Forest Section. ning Act and in the Roadless Area Review and Evaluation (RARE IÍ) Pro- Use gram. The National Oceanic and This map can be used for applying Atmospheric Administration has incor- ecological and land-use information porated the ecoregion code into its within ecoregions. Because the map is national environmental data base. The ecologically based, any ecological data map has been expanded to include the and information can be safely applied rest of North America. It also has to similar sites within the region, e.g., been proposed as a model from which silvicultural practices, estimates of to create a world ecoregions map to forest yields, and seed use. Experiences serve as a reporting structure for concerning land use such as terrain information about global resources and sensitivity to acid rain, suitability for environment.
Mapping Ecoregions To Manage Land 85 Our American Land
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Explanation of Line Symbols
/M/■.•>.'•-A- Domain Boundary ' fa-'-,I -I I Highlands Division Boundary
AiOets Equai Area ProiectK>n Province Boundary SCALE 1 7.500000
Section Boundary 300 400 500 600 700 KILOMETERS
Territories Exhibiting Altitudinal Zonation and Having the Climatic Regime Indicated by the Color and Symbol
M — Mountains P — Plateau A — Altiplano
86 Understanding Land Our American Land
EiqpiiMialkm of niniterlc ccKies on part of iim Eoomglons Map ûl the UiiHiMl StalM
2000 Hmm TEMPEBATE DOMAIN 2400 Marine C^lsion
M2410 Pacific FcH^esI ProvlrK:e M2412 l^e^wood For^ Section M2413 Cedar-Hemlock4>CRigia$-fir Forest Section Ma414 Cali^rnia Mixed Evergreen Forest Section
2i^K) Meditermr^an Division 2810 Ciátfomia Grasland Province
Nighiands'^ M2Ä10 Sierran Forest Province ms^^ Caiifornia Ch^^^arrai Province
»K» DRY IKMflAIN 31CK) SerniaM S^p^P^ Dtvlsbn 3130 Intermoimlain Sa^p^tKush Province 3131 Sagc^rush^Whealgrasa Section 31i^ tahcmtan Saltbrush-6reasewood S^tion 31^ Great Saain Sagebrush Section 3134 Bonne\^ile SaMru$h«Gre^ewood Section 31^ PcHiderosa Shrub Forest
31^ Me)acsani HigWands Shrub Steppe Province
HlgMaruis' P3l^ (^<»^«lo Plateau Province P3131 Juniper>Rn]^:m Woodtsünd ^ Sagebrush-Sattbrush Mosaic P3132 Grama-Gatfeta ^^^ -^ Juniper-Pinycm Woodland Mosaic
A3140 WycHning Ba^ Provim^ A3142 S^^ebrush-Whea^rass ^OIICHI
^00 Md Desert Division 3:^S!0 American Desert (Mc^ve
Mapping Ecoregions To Manage Land 87