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

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  R  2 = x  R  2 = 0.83). Biomass on dead trees showed a similar but weaker pattern (x  R  2 = 0.45); including  Abies grandis  as an indicator variable substantially improved the model (x  R  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.

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