Contrasting Fundamental and Realized Ecological Niches with Epiphytic Lichen Transplants in an Old-Growth Pseudotsuga Forest

Abstract

Three lichen transplant experiments examined the effect of height in the canopy on the growth rates of four lichen species, using the Wind River Canopy Crane in an old-growth Pseudotsuga-Tsuga forest in the Cascade Range of southern Washington. A total of 40 to 100 transplants were used for each species, and growth was measured over a one-year period. We then compared the vertical profiles of growth rates to the vertical profiles of natural abundance. The vertical pattern of abundance of Letharia vulpina more or less corresponded with the vertical pattern in growth rates. The other two species for which we had vertical profiles in both abundance (realized niche) and growth of transplants (fundamental niche) showed some potentially important discrepancies between the two niche spaces. Usnea peaked in abundance at the highest levels in the canopy, but appeared to reach a maximum growth rate at about 30 m. The treetop environment is evidently ideal for Usnea, and its capacity for rapid growth suggests that it is a vigorous competitor. Lobaria oregana peaked in abundance at 25–30 m, while its growth rates were maximal considerably higher in the canopy, at 40–45 m. We must conclude that some aspect of establishment or competition has a pronounced negative effect on L. oregana above about 35 m in the 65-m-high canopy. Further experiments are needed to test the hypotheses that these cyanolichens fail in the upper canopy because of competition, or that they fail by an inability to tolerate rare microclimatic extremes, such as low temperatures.