Lichen abundance and biodiversity along a chronosequence from young managed stands to ancient forest

Epiphytic lichens constitute a great portion of the vegetational biodiversity ofPacific Northwestern forests. The ecological importance of lichens in late-successionalforests is increasingly appreciated, but little is known about the effect of forestmanagement (e.g., conversion of old growth to young rotational stands) on lichenpopulations. This study compared the species richness and biomass of epiphyticmacrolichens in four forest age classes (40, 70,140 and 510 years after stand replacingdisturbance) in the Tsuga heterophylla-Pseudotsuga menziesii zone of the westernCascades in Oregon. Litterfall plots were used to achieve a broader ecologicalcomparison than has been possible by directly sampling individual trees.
Equal areas of each age class were sampled. Mature and old growth (140 and 510year old) forests had 40 percent more lichen species than young and rotation-aged (40and 70 year old) forests (p=0.03). Several lichen species were found only in oldgrowth, and many others were restricted to forests at least 140 years old. Old growthforests contained 66% of the pooled biomass of all four age classes; the sum of thelichen biomass in old growth and mature stands totaled approximately 90% of thepooled biomass of all age classes. Lichen biomass of old growth stands (4.7 t/ha) wasapproximately 30 times that of young stands (0.2 t/ha), 6 times that of rotation-agestands (0.7 Oa) and 3 times that of mature stands (1.5 t/ha; 0.04>p>0.001). A list ofold growth-associated species is proposed based on biomass and species presence data.
Conversion of old growth forests to young managed stands in the westernCascades has ripple effects in the ecosystem including 30 to 145 fold reductions infixed nitrogen contributed by lichens, four fold reductions in lichen-associated canopy arthropod abundance, and decreases in the availability of traditionally used forage andnesting materials among birds, small mammals and ungulates.
Key words: lichens, ecology, forest management, conservation biology, arthropods.