Are epiphytic lichens in young forests limited by local dispersal?

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Abstract
We investigated whether dispersal limitation is an important factor for the low abundance of epiphytic lichens in young boreal forests. The number of lichen thalli on branch sections of Pinus sylvestris was counted in five second-growth stands (35-78 years old) at increasing distances (10 m, 50 m, and 100 m) from adjacent old-growth stands (122-298 years old) presumed to function as propagule sources. The number of thalli displayed a pronounced decrease with increasing distance from the old growth in both foliose and pendulous fruticose lichens. The effect of distance was statistically significant in five out of six groups of lichens. The number of thalli at 100 m constituted 22% (Parmelia sulcata) to 61% (Vulpicida pinastri) of the number found near the forest edge (10 m). In the two most abundant groups, Bryoria (fruticose) and Hypogymnia (foliose), there was close to 50% reduction in thallus numbers. The thallus size distribution of both Bryoria and Hypogymnia was strongly skewed towards small thalli but the shape of the distributions was only marginally affected by distance to the old growth stands. Our data strongly suggest that both foliose and fruticose lichens are apparently limited by local dispersal in young boreal forests and that old-growth stands function as a source of lichen propagules. Consequently, efforts to enhance abundance of epiphytic lichens in managed boreal forests should include retention and creation of old stands throughout the landscape.