Forest Plan Implementation
Procedures and Tools
Conducting Cumulative Effects Analyses
The first step in conducting a cumulative effects analysis for a project, is to define a cumulative effects study area. This study area is normally larger than the project area and depends on the size of the project area. Often it will follow watershed, value comparison unit (VCU), or biogeographic province boundaries and should include adjacent non-NFS lands.
Next, the existing level of harvest and road development should be determined for both NFS and non-NFS lands within the cumulative effects study area. Tongass GIS library layers should be used for NFS lands and the "nonnfs_veg" and "non_nf_rds" layers should be used for non-NFS lands.
The third step is to forecast the amount of additional harvest and road construction that will occur in the reasonably foreseeable future, including the harvest and road construction included in the project. For NFS lands, the Forest-wide logging system and transportation analysis (LSTA) can be used to estimate additional harvest and additional road construction within a study area. The estimation of future harvest on non-NFS lands should be made by examining the amount of POG remaining on these lands and making reasonable assumptions regarding the percentage of that POG that would be harvested in the future, giving consideration to the ownership of these lands. Future road construction also should be estimated by examining the existing distribution of roads and the non-NFS road density in the study area, considering the additional estimated harvest, and making reasonable assumptions regarding the increase in road density that would be required to complete the additional harvest. In general, estimates should be conservatively high.
In order to estimate cumulative harvest, combined total harvest acres should be computed. In addition, the effect of cumulative harvest should be calculated by expressing the harvest as a percent of the original productive old growth (POG). The original POG can be estimated by adding all past harvest to the existing POG. Refer to the cumulative effects analysis in the Biodiversity section of the 2008 Forest Plan Amendment Final EIS (pages 3-198 to 3-218) for examples of this approach. Tables of these percentages are presented by biogeographic province in this section.
In order to estimate cumulative road construction, combined total road miles should be computed. In addition, cumulative road densities should be calculated for NFS lands, non-NFS lands, and for all lands combined. Road densities should be estimated by VCU for watershed and fish evaluations and by WAA for wildlife evaluations. Refer to the cumulative effects analysis in the Fish section (pages 3-90 to 3-94) of the 2008 Forest Plan Amendment Final EIS for an example of using this approach by VCUs, and refer to the Wildlife section (3-292 to 3-298) of the 2008 Forest Plan Amendment Final EIS for an example of using this approach by WAA.