Pacific Inland Resources (PIR, A Division of West Fraser Mills Ltd.) initiated a pilot project in 1999 to address where an upper elevation operability line should be placed for forest planning and modeling in the Bulkley Timber Supply Area (TSA). During the 1999 pilot project, an ecotone was recognized between mid-elevation Engelmann Spruce Subalpine Fir Zone (ESSF) forests of relatively average productivity, to a zone that was characterized as low productivity (Trowbridge 2000). In continuation of the pilot project in 2000 and 2001 (Trowbridge 2001, Trowbridge 2002), we proposed to: 1. define a new biogeoclimatic unit and site classification that would identify this ecotone (and ecosystems) of low forest productivity, and; 2. have this biogeoclimatic unit be considered as an option for establishing a biological/elevational limit to industrial forestry operations . At that time, this ecotone was termed ESSF Upper Forest phase (ESSFu), and primarily reflected productivity restraints due to harsh climate and sensitive environments through plant species composition and structure. All reporting and mapping in this study applied that terminology up to April, 2002. Provincial biogeoclimatic correlation recommended treating all similar high elevation ESSF transition zones in the Province as woodland subzones (ESSFw) (Trowbridge et al. 2002). The terminology in this current report is consistent with that latest recommendation. R. Trowbridge.
Trowbridge, Rick, Boreal Research and Development Ltd.. 2003. ESSF high elevation subzone mapping in the Bulkley Timber Supply Area: Progress Report 2003. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2003MR189