REMNANT TREES AND CANOPY LICHEN COMMUNITIES IN WESTERN OREGON: A RETROSPECTIVE APPROACH

Abstract

The “New Forestry” practice of green-tree retention is becoming an important management tool for publicly owned lands, yet few data exist to demonstrate that this tool can succeed at enhancing biodiversity. We addressed this issue by using a retrospective approach to compare canopy lichen litter in adjacent, paired stands of rotation age (55–120 yr): one with and one without old-growth (>300 yr) remnant trees. We sampled three functional groups of lichens in 17 stands in western Oregon: alectorioid lichens, cyanolichens, and green-algal foliose lichens. Thirteen stands were low elevation (520–850 m) and four were mid-elevation (1220–1340 m). Biomass of cyanolichen and green-algal foliose lichen litter was greater in low-elevation sites, whereas alectorioid lichen litter biomass was greater in mid-elevation sites. Cyanolichens were absent from all mid-elevation sites. Biomass of alectorioid lichen and cyanolichen litter was greater in low-elevation sites with remnant trees than in those without remnant trees by 86% and 233%, respectively. The biomass of green-algal foliose lichen litter was 80% greater in mid-elevation sites without remnant trees than in those with remnant trees. Total lichen litter biomass was slightly, but not significantly, greater in stands with remnant trees at both low elevations (by 23%; ∼370 kg/ha standing biomass in remnant stands) and mid elevations (by 12%; ∼470 kg/ha standing biomass). Cyanolichen litter biomass was positively related to the number of remnant trees present; alectorioid and green-algal lichen litter biomass were negatively correlated with the density of trees in the regeneration cohort. Because retaining live remnant trees will differentially affect these three functional groups of macrolichens, managers must be clear as to their objectives before using green-tree retention as a tool to enhance biodiversity.