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

摘要

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.