Riparian Bryophytes of the H. J. Andrews Experimental Forest in the Western Cascades, Oregon

Abstract

The knowledge of the distribution and habitat demands for bryophytes in the Pacific Northwest is scarce, and few published quantitative accounts of the flora are present. The present paper includes habitat description, elevational range, substrate preference, and frequency estimates for more than 130 riparian mosses and liverworts found in old-growth Pseudotsuga-Tsuga forests of the H. J. Andrews Experimental Forest, Oregon. The data are based on 360 samples distributed among 42 sites covering 1st to 5th order streams and 420 to 1250 m. TWINSPAN analysis resulted in 6 sample groups, representing samples from different elevations, geomorphic surfaces, and stream sizes. The most common mosses are Eurhynchium oreganum, Isothecium stoloniferum, Hypnum circinale, and Dicranum fuscescens. Among the hepatics Scapania bolanderi, Cephalozia lunulifolia, and Porella navicularis are the most abundant species. Most species are rare at both site and sample plot level, and this is especially true for acrocarps where more than one-third of the observed species occurred in only one or two sites or/and samples. Four of the occurring species (i.e., Antitrichia curtipendula, Buxbaumia piperi, Douinia ovata, and Ptilidium californicum) are listed for special management and/or regional surveys. Bryophytes constitute an important and conspicuous component of old-growth forests in the Pacific Northwest (Lesica et al. 1991; McCune 1993; Schofield 1988); however, few studies on the abundance and distribution of mosses and liverworts have been conducted. The epiphytic flora, composed of bryophytes and lichens, of old-growth Douglas-fir has been shown to be species rich and influences nutrient dynamics and overall production in old-growth stands (Pike et al. 1975, 1977). Besides these studies, however, there has been until now no published account of factors influencing the distribution of individual species within old-growth forests (see however Peck et al. 1995; Schofield 1976). Dispite this lack of study, many bryophytes are considered to be dependent of old-growth conditions (FEMAT 1993; Soderstrom 1988). Thus, effective management of the bryophyte flora, which is an important forest product of the region (Peck 1990; Schlosser et al. 1992) and a significant part of forest biodiversity, is constrained by lack of knowledge. Riparian zones are thought of as key elements in the forested landscape, and preservation of these is a major goal of forest management (FEMAT 1993). Of the mosses and liverworts considered as vulnerable in the Pacific Northwest (USDA 1994), many occur in riparian areas. This association is dependent on many factors, but the occurrence of a wide range of different substrates, disturbance patterns, and a moist microclimate are important contributors to the diversity in these zones (Glime & Vitt 1987; Vitt et al. 1986). The present paper reports habitats and frequencies of species found in riparian areas of old-growth Pseudotsuga-Tsuga forests in the western Cascades of Oregon. A general treatment of the bryophyte community patterns will be published elsewhere.