Songbird surveys were conducted for the third consecutive year in Weyerhaeuser?s South Island Timberlands to evaluate the effects of variable-retention (VR) harvesting methods on avian species richness, species diversity, and relative abundance. Our preliminary results had indicated that variable-retention cut blocks retained all of the avian species detected in the controls, but generally had lower species diversity, lower abundance of all-species combined, and lower relative abundance of individual species that depend on mature forests. Our preliminary results had also suggested that group blocks were more similar than dispersed or mixed blocks to control sites. Much of our preliminary results were based on data from only 2001. The low availability of variable-retention blocks in 2000 limited our sample size to only 10 VR blocks that year, and this was insufficient to simultaneously analyse the effects of variable-retention method and retention level. A third year of songbird surveys was needed to reduce the sampling error and to provide allowance for interannual variation. In 2002, we also initiated songbird surveys in 4 more clearcuts. In addition to retrospective sampling of operational VR blocks, we conducted songbird surveys in 3 active experimental sites: the Tsitika, Stillwater, and Port McNeill. The Tsitika site, in TFL 39 Block 2 of the North Island Timberlands, was established as an experimental unit to assess 3 levels of group retention treatments (10%, 20%, and 30%) in relation to clearcut harvesting and an undisturbed, old growth control. The 2002 surveys represented the Year 1 post-treatment assessment of bird abundances at this site, which had been harvested in June 2001. Pre-treatment data for this site was collected in May 2001. The Stillwater site, located on the Sunshine Coast, was established to assess 3 levels of dispersed retention treatments (5%, 10%, and 30%) in relation to the clearcut and old growth controls. The 2002 surveys also represented the Year 1 post-treatment assessment of bird abundances for this site, but pre-treatment data was not collected. The Port McNeill site was established as an experimental unit for group-size comparisons. It was scheduled to be harvested in either winter 2002-03 or winter 2003-04. The 2002 surveys therefore represented the pre-treatment assessment for this site. Songbird surveys were also conducted in 2 benchmark sites that had been identified by Weyerhaeuser on the South Island Timberlands. Collecting benchmark data was not one of the initial study objectives, but was opportunistically conducted when favourable weather conditions compressed the amount of time needed to survey the operational and active experimental sites. Our specific objectives for 2002 were to: 1) evaluate the effects of the VR method (dispersed, grouped, and mixed) and retention level on avian species richness, species diversity, and relative abundance of individual bird species, using retrospective sampling of operational VR sites; 2) conduct the first year post-treatment assessment of Tsitika and Stillwater active experimental sites, and conduct the pre-treatment assessment of the Port McNeill site; and; 3) collect benchmark data at control sites identified by Weyerhaeuser.
Chan-McLeod, Ann, Bunnell, Fred L.. 2003. Effects of variable-retention harvest techniques on bird communities in coastal British Columbia: 2002-2003 annual progress report. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2003MR059