Epiphytic lichens along gradients in topography and stand structure in western Oregon, USA

Abstract

Epiphytic macrolichen communities were compared among forest stand types in the Blue River watershed of western Oregon. Stand types were defined by stand structure, according to age classes of the younger tree cohort and remnant tree retention. Remnant trees were those in an older cohort that remained following a stand disturbance that initiated tree regeneration, such as a timber harvest or natural forest fire. Stands were located in upland and riparian forests of two vascular plant series (western hemlock and true fir). Presence and abundance of all epiphytic macrolichen species were sampled in a 0.4 ha circular plot in 117 stands. Nonmetric multidimensional scaling (NMS) ordination revealed that the strongest differences in lichen community composition were related to elevation, which was correlated with vascular plant series. Cyanolichens were largely limited to lower elevation forests (470 – 950 m) of the western hemlock series, while matrix lichens and forage lichens with green-algal photobionts dominated high elevation stands (950 – 1470 m) of the true fir series. Lichen communities differed with stand age. In even-aged young stands, lichen communities were species poor and lichen community composition differed from all other stand types. In general, macrolichen species richness varied little among stand types. However, cyanolichen species were most diverse in old-growth and mature stands at lower elevations. Lichen communities in young stands (< 20 yr) with remnants differed from those in even-aged young forests in both plant series. As a stand develops, the presence of remnant trees may accelerate the development of the lichen community towards those found in older stands. We infer that remnant trees serve as refugia for lichens through a disturbance and provide lichen inoculum to younger trees. Hardwood patches were hotspots for lichen diversity, particularly cyanolichens that are infrequent on conifers. Hardwood patches were most prevalent along perennial streams. To maintain and enhance lichen communities at a landscape level, forest managers must consider the importance of features such as late-successional stands, remnant trees, hardwoods, and riparian areas to lichen communities. These features are especially important to retain in or near regenerating forests to promote colonization by dispersal-limited lichens.