Unified Ecoregions of Alaska
G. Nowacki (USFS), P. Spencer (NPS), T. Brock (USFS),
M. Fleming (USGS) and Torre Jorgenson (ABRI)
Unified Ecoregions of Alaska portrays major ecosystems of the state of Alaska and neighboring portions of Canada and Russia. The word "Unified" in the title refers to the interdisciplinary, interagency, and international effort to derive this broad-scale ecosystem map. The Ecoregions, as portrayed on this dataset, are large ecosystems primarily defined by climate and topography, with refinements from vegetation patterns, lithology, and surficial deposits. A total of thirty-two ecoregion units were mapped representing the major ecosystems of Alaska. Ecoregions were mapped in their entirety, with some spanning international boundaries to include portions of Canada and Russia. This dataset is provided with linked compilation tables of environmental variables and a feature linked “Users Guide” that includes representative photographs and detailed community descriptions. A two-sided wall map is also available through USGS at: http://mapping.usgs.gov/esic/esic_index.html
Several attempts have been made over the past 50 years to map large ecosystems in Alaska. The first approximation was by L.A. Spetzman, who interpreted terrain and vegetation from black and white air photos to evaluate the feasibility of military vehicular movement during the Cold War. In 1973, these data were reinterpreted by vegetation types, and published as "Major Ecosystems of Alaska" (LUPC 1973). This map was further refined and published in Alaska Regional Profiles (Selkregg 1974-1976). The U.S. space program and the advent of earth imaging satellites in the early 1970's helped changed our perception of our lands with respect to a global context.
Throughout the 1980's, remotely sensed data and the growing understanding of ecosystem processes provided impetus for mapping global ecosystems. Various mapping philosophies and derivative maps were published throughout the last twenty years of the twentieth century. Different ecological classification and mapping systems employed at this time resulted in two separate maps for Alaska (Gallant et al. 1995, Nowacki and Brock 1995). Unfortunately, having multiple maps depicting Alaskan ecoregions was awkward and confusing for users and impeded interagency communication. Recognizing this, and concurrent with national efforts to rectify this problem (McMahon et al. 2001.), we have used an interdisciplinary group of environmental scientists and managers to unify ecoregion boundaries to benefit users and facilitate interagency work.
The burgeoning fields of remote sensing data analysis and GIS provided new datasets and analysis tools for Alaska during the 1990's. The first statewide vegetation map since Spetzman's 1950 effort was developed (Fleming 1996). Digital topographic data and various statewide images became available. Long-term weather records were interpreted as climatic data (Fleming et al 2000). Other datasets were digitized for use in GIS analysis, including permafrost (Ferrians 1965), soils (Reiger et al 1979), surficial (Karlstrom et al 164) and bedrock geology (Beikman 1980) , previous ecosystem maps (Nowacki and Brock 1995, Gallant et al 1995), and hydrography. Concurrently, several agencies and non-profit organizations in Alaska began to develop their own ecosystem maps for various applications.
Field and resource specialists representing a variety of organizations assembled in Anchorage in April 1999 to evaluate ecoregion maps with the benefit of updated resource layers. The degree of similarity between the two core maps was substantial. Coincident lines/units encapsulating equivalent features were identified and used in the new map. During this process, line placement was refined using many of the recently developed data. Delineation criteria ultimately included climate, physiography, vegetation, geology/surficial deposits and glaciation. Several map versions were generated over a period of one year incorporating suggestions received from various ecologists, biologists, soil scientists and geologists from across the state and adjacent Canadian lands. In areas where data were lacking or pattern changes on the land were indistinct, the advice of local experts was used extensively for line placement. The final dataset represents the combined wisdom of 40-50 scientists from many disciplines with hundreds of years of experience in Alaska and nearby country. It closely matches with Canadian mapping along our mutual borders (Smith et al 2001, Demarchi et al 2000).
Ecoregions are nested together to form eight groups that possess similar ecological character (patterns and processes). However, when attempting to fit these groups into a classification hierarchy, it became readily apparent that a dichotomous framework could not convey the spatial arrangement of these groups. Rather, ecosystems in Alaska are spread out along three major bioclimatic gradients, which are represented by the factors of vegetation (forested to non-forested), climate (temperature and precipitation), and disturbance regime. The corners of the triangle represent polar, boreal, and maritime regimes. These bioclimatic regimes grade from one to another across the state, forming the space within the triangle. When eight broad groups of ecoregions are arrayed along the spatial gradients within a triangle (or tri-archy, rather than a dichotomous hierarchy), clear patterns emerge which accurately reflect distinct climatic-vegetation relationships. This spatial projection allows the natural associations among ecoregion groups to be displayed as they occur on the land without loss of information (i.e., retains the spatial interrelations of the groups). This display is intuitive, flexible and fosters interagency use by allowing people to understand and conveniently place these groups and component ecoregions into classifications or frameworks of their choice.
Data Analyses for Ecoregion Descriptions
Various environmental variables were tabulated for each ecoregion, and the top five values for each parameter listed in the accompanying table. The variables used are: lithology
as grouped by D. Brew (1999), soils, surficial geology, surficial geology type and landcover .
Annual cycles of average temperature and precipitation are graphed for each ecoregion, which are grouped into the eight groups portrayed on the tri-archy. Each climograph line represents the monthly averages for temperature and precipitation of a given ecoregion. The groupings of ecoregions show similarities of climate, with subtle changes due to latitude, proximity to oceans, and mountains. Points along each climograph represent monthly temperature and precipitation averages. Each line begins with January (1) and sweeps up to warmer summer temperatures (6, 7, 8) and greater precipitation, then reverts to winter conditions (12). The Arctic Tundra group shows a pattern of low temperature and precipitation, reflecting the harsh polar desert system near the Beaufort Sea. The Bering Tundra group is slightly warmer in winter months, with more rain during summers; a function of cold maritime conditions of the Bering Sea. The Intermontane Boreal ecoregions all have similar climate patterns with large temperature variation but low precipitation throughout the year. The Coastal Rainforest group shows warmer temperatures and high, variable precipitation caused by moderating influences of the Pacific Ocean.
A surface roughness dataset was calculated for the area as a function of terrain relief/unit area. The points on the graph plot the average surface roughness against average elevation for each ecoregion. Thus ecoregion 1 (Beaufort Coastal Plain) is flat and low elevation. Ecoregion 23 (Copper River Basin) is also flat, but at higher elevations. The Wrangell Mountains ecoregion (24) is the most rugged area of the state.
A total of 32 ecoregions were delineated within the state of Alaska. Ecoregions were mapped in their entirety and spanned international boundaries where necessary (Russia and Canada). Each ecoregion is described according to its major ecological and geomorphic processes, associated vegetation patterns, dominant wildlife, geologic features and major climatic parameters. Tables and graphs are presented showing prominent patterns of landcover, soils, lithology, surficial geologic materials, dominant geomorphic processes, temperature/precipation regime and surface roughness. Photographs of representative landscapes are shown for each ecoregion.
This map, associated GIS dataset, climate data and Users Guide provide resource managers a valuable tool for understanding the resources they manage. The interagency and interdisciplinary approach has resulted in a unified dataset that provides a consistent basis for analysis throughout the Alaska region regardless of managing agency.
This important GIS layer also provides a useful stratification tool for future research since flora and fauna species distribution is strongly related to ecosystems. The online User Guide provides detailed narrative descriptions of vegetation communities, disturbance regimes, physiography and climate provides an exceptional “Virtual Ecological Tour” of Alaska’s National Parks.