The Influence of Epiphytic Lichens on the Nutrient Cycling of a Blue Oak Woodland1

We evaluated the importance of epiphytic lichens in the nutrient cycling of a blue oak (Quercus douglasii) woodland in California. Each oak tree contained an average of 3.8 kg lichen biomass, totaling 590 kg per ha. For comparison, oak leaf biomass was 958 kg per ha. We compared tree growth, volume and composition of throughfall (rainfall falling though the tree canopy), litterfall, and soil nutrients under 20 trees from which we removed the lichens to 20 control trees. The removal of lichens had no effect on the growth of the oak trees, but it did influence nutrient cycling fluxes significantly. We calculated an enhanced atmospheric deposition for nitrogen of 2.85 kg/ha/yr and for phosphorus of 0.15 kg/ha/yr. This is caused by the presence of epiphytic lichens in the canopy where they act as an intercepting surface, enhancing dry deposition into the tree canopy. Thus, epiphytes can significantly influence nutrient fluxes in blue oak woodlands. This also supports the hypothesis that the tree canopy influences atmospheric deposition and that this, in turn, contributes to the observed “canopy effect” on the understory productivity in oak savannas. A large part of the California landscape is made up of oak woodlands, and in the past 20 years considerable research has focused on understanding the functioning of these ecosystems. Most of these studies have focused on the dominant growth forms in these ecosystems, and consequently, there is abundant evidence that oak trees and the annual grass understory both influence energy, water, and nutrient balances (Callaway and others 1991, Gordon and Rice 1992, Holland 1973, Huenneke and Mooney 1989, Jackson and others 1990, McNaughton 1968, Mooney and others 1986). However, one understudied group is the epiphytic community, which can make up a substantial part of the aboveground biomass in oak woodlands (Boucher and Nash 1990, Callaway and Nadkarni 1991). Epiphytes are known to affect ecosystem processes in various forest ecosystems (Knops and others 1996, Lang and others 1980, Nadkarni 1986, Pike 1978). In this study, we examine whether epiphytes are a significant part of California oak woodlands. Lichens are the dominant taxonomic group of epiphytes present in Californian oak woodlands, and Ramalina menziesii (lace lichen) is the most conspicuous lichen in the coastal foothill oak woodlands (Larson and others 1985, Rundel 1974) and is considered the unofficial State lichen of California (Hale and Cole 1988). Ramalina menziesii occurs along the coast from Baja California to southern Alaska. It is very sensitive to air pollution (Boonpragob and Nash 1991, Sigal and Nash 1983) and is especially abundant in areas with frequent fog (Larson and others 1985). This is partly because lichens do not tap into the vascular system of their host trees, but they depend entirely on rainfall, dew, fog, and atmospheric water vapor (Matthes-Sears and Nash 1986). Study Area and Methods This research was conducted at the Hastings Natural History Reservation, which is a field station of the University of California at Berkeley. Hastings is located in the Santa Lucia Mountains in the central coast of California (Carmel Valley, Monterey County) approximately 20 km east of the Pacific Ocean and 42 km 1An abbreviated version of this paper was presented at the Symposium on Oak Woodlands: Ecology, Management and Urban Interface Issues, March 19-22, 1996, San Luis Obispo, Calif. 2Research Director, Cedar Creek LTER, University of Minnesota, Department of Ecology, Evolution and Behavior, 1987 Upper Buford Circle, St. Paul, MN 55108. 3Professor, Department of Botany, Arizona State University, Tempe, AZ 85287 4Professor, Departments of Botany and Geology, Duke University, Durham, NC 27708