An estimation procedure of habitat impacts of highways as a general guide for an initial route selection

Imanishi, J. and Morimoto, Y. 2002. An estimation procedure of habitat impacts of highways as a general guide for an initial route selection. Proceedings for the 5th International Landscape Architectural Symposium of China, Japan and Korea, 2002, Beijing, China. 100-107.

Abstract

It is essential to estimate and avoid the impacts of large structures on ecosystems from an early planning stage. Although detailed and long-termed data collection is desirable, conducting such intensive surveys at a number of locations during the initial stage of highway route selection is not realistic. Conventional ecological assessment methods essentially have positive values; however, a holistic point of view for biodiversity protection is currently missing. With these concerns in mind, we carried out research on the procedure to estimate the relative impacts of highway alternative routes on habitats as a general guide for initial route selections. The estimation procedure that embodied a holistic approach incorporated habitat dependency indices (HDIs) of species groups that were hypothetically established from landscape ecological studies. The procedural steps are 1) delineate a study area, 2) prepare an existing land cover layer, 3) determine species groups for the habitat impact assessment, 4) define the levels of habitat values for each species group (a habitat value matrix), 5) assign a number (0 to 1) to each level of the habitat values, 6) produce the habitat impact layer of each species group, 7) calculate the habitat dependency index (HDI) of each species group, 8) determine a road-effect width, 9) multiply the number on the habitat impact layer by the HDI of each species group, 10) sum up the weighted habitat impacts within the road-effect zone for all the species groups, 11) repeat steps 5 to 10 and analyze sensitivities of the 2 parameters: the assigned habitat values at the step 5 and the road-effect width at the step 8 and 12) interpret the output. We conducted a case study along US highway 93 in the Flathead Reservation, Montana, U.S.A. to observe the resourcefulness of the results derived from the proposed procedure in relation to the sensitivity of the parameters. The consistency in the rank of the routes indicated that the estimation method can potentially be used as a general guide for a highway planning. The effects of the parameters were deemed relatively small. The effects of the sets of the habitat value numbers were to operate HDIs with the numbers of grid cells and to change the degree of agreement for a longer route. The general effect of the widths of road-effect zone was to increase or decrease the difference of the estimated habitat impacts of 2 routes. Narrower buffer zones created the greater difference. The use of landscape ecological species groups has the merit of the holistic approach of the procedure. The complementary use of the estimation procedure will enhance the conventional approach that relies on rarity, typicality and ecological rank of species. Further research with actual field data was necessary to examine the detailed characteristics of the habitat impact estimation procedure.

Key words: A Habitat Impact Estimation Procedure; Highways; Habitat Dependency Index (HDI); Ecological Impact Assessment; Geographic Information System (GIS)