The cyanolichen dripzone hypothesis revisited: a first report with new insights from eastern North America

Abstract Twenty-five years ago, the dripzone hypothesis, whereby the proximity of understorey conifer branches to the crown of dominant Populus trees significantly increased the diversity and abundance of cyanolichens on these conifers, was first described from western North America. Here, we report a similar phenomenon from eastern North America on conifers under the dripzone of yellow birch and aspen trees. We present field observations of this pattern as well as a quantitative analysis of three humid boreal forests from the Island of Newfoundland. For the latter, we examined epiphytic lichen composition on branches of balsam fir within and immediately outside the dripzone of yellow birch trees. The dripzone effect was strong and spatially restricted to the area under the canopy of yellow birch, as well as aspens, on wet sites in humid forests, with significantly more cyanolichens on balsam fir branches under the yellow birch and aspen canopies. Genera of cyanolichens predominantly found under the dripzone included Fuscopannaria , Leptogium , Lobaria , Lobarina , Neproma , Pannaria , Parmeliella , Pectenia , Pseudocyphellaria and Ricasolia , and included the COSEWIC listed Pectenia plumbea. We suggest here that the canopy of broadleaf phorophytes not only shape the cyanolichen community on understorey conifers by chemical enrichment of the throughfall, but also probably from enrichment by cyanolichens within their own canopy, which also contribute abundant cyanolichen propagules.