Changes in forage lichen biomass after insect outbreaks and fuel reduction treatments in the Blue Mountains, Oregon

Bruce McCune, Sarah Jovan, Amanda Hardman

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Abstract

Forage lichens are pendulous, hairlike species eaten by a wide range of mammals. Our overall goal was to estimate losses of Bryoria, a genus of ecologically important forage species, in forests subjected to disease and fuel reduction treatments at Starkey Experimental Forest in the Blue Mountains of northeastern Oregon. Specific objectives were to (1) estimate Bryoria biomass in stands decimated by insects and disease, (2) compare Bryoria biomass in untreated stands with those treated by mechanical fuels reduction and prescribed fire, and (3) estimate the range of pre-insect outbreak Bryoria biomass using historical data. Our general approach was to estimate tree-level Bryoria biomass on a sample of trees, regress estimates against tree size and species using nonparametric multiplicative regression (NPMR), then predict stand-level biomass by applying NPMR to tree size and density data. For live trees, logarithm of dbh was a strong predictor of Bryoria biomass (cross validated 2 = x 2 = 0.83). Biomass on dead trees showed a similar but weaker pattern (x 2 = 0.45); including Abies grandis as an indicator variable substantially improved the model (x 2 = 0.52). Current Bryoria biomass is clearly much lower than the potential biomass for forests of this type. Based on our prediction of pre-outbreak Bryoria biomass and benchmarks from related studies, we conclude that the biomass in intact, mature forests should be about 0.5 – 2.0 T/ha. This means insects and disease caused a loss of about 50-80% of starting Bryoria biomass, and fuel reduction treatments removed roughly another 10%. How long it will take for the biomass to recover is unknown, but we assume that Bryoria recovery will keep pace with structural recovery of the canopy. Even though small, young trees individually supported very low Bryoria biomass, their combined contribution to standing biomass will soon be appreciable due to high regeneration density.

Keywords

Leptogium pseudofurfuraceum; Leptogium tacomae; Leptogium subaridum; epiphyte; California; Oregon; Siskiyou Mountains; Trinity Alps



DOI: http://dx.doi.org/10.2509/naf2008.003.004

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