Macroclimate drives growth of hair lichens in boreal forest canopies

1.  Epiphytic lichens are important biodiversity components of forest canopies worldwide, significantly contributing to ecosystem function. The relative growth rate (RGR), a measure of fitness, drives population dynamics and shapes lichens’ large-scale distributions. In a climate change scenario, we need to know how external (macro- and microclimate, and nitrogen deposition), and internal factors (cortical pigments, chlorophyll and specimen size) affect RGR in these ecologically important canopy organisms. 2.  We used dominant pendulous (hair) lichens widely distributed across the boreal biome to test the hypothesis that precipitation drives RGR of pale (Alectoria sarmentosa, Usnea dasopoga) and dark species (Bryoria fuscescens) to a different extent across a large-scale gradient from continental to oceanic climates (precipitation: 450-2600 mm) in Scandinavia (60-64° N, 5-19° E). After transplanting lichens to lower branches of Picea abies in nine boreal forest sites for one year, we...