Global change and arctic ecosystems: is lichen decline a function of increases in vascular plant biomass?

Abstract

1 Macrolichens are important for the functioning and biodiversity of cold northern ecosystems and their reindeer-based cultures and economies. 2 We hypothesized that, in climatically milder parts of the Arctic, where ecosystems have relatively dense plant canopies, climate warming and/or increased nutrient availability leads to decline in macrolichen abundance as a function of increased abundance of vascular plants. In more open high-arctic or arctic-alpine plant communities such a relationship should be absent. To test this, we synthesized cross-continental arctic vegetation data from ecosystem manipulation experiments simulating mostly warming and increased nutrient availability, and compared these with similar data from natural environmental gradients. 3 Regressions between abundance or biomass of macrolichens and vascular plants were consistently negative across the subarctic and mid-arctic experimental studies. Such a pattern did not emerge in the coldest high-arctic or arctic-alpine sites. The slopes of the negative regressions increased across 10 sites as the climate became milder (as indicated by a simple climatic index) or the vegetation denser (greater site above-ground biomass). 4 Seven natural vegetation gradients in the lower-altitude sub-and mid-arctic zone confirmed the patterns seen in the experimental studies, showing consistent negative relationships between abundance of macrolichens and vascular plants. 5 We conclude that the data supported the hypothesis. Macrolichens in climatically milder arctic ecosystems may decline if and where global changes cause vascular plants to increase in abundance. 6 However, a refining of our findings is needed, for instance by integrating other abiotic and biotic effects such as reindeer grazing feedback on the balance between vascular plants and lichens.

Subalpine-nival gradient of species richness for vascular plants, bryophytes and lichens in the Swiss Inner Alps

“…The low mean annual temperatures (or degree days) of alpine environments result in lower potential evapotranspiration and higher moisture, which are favourable conditions for these species (Grau et al 2007). Their small sizes allow them to benefit from the warmer substrate (Körner 2003), and the decreasing vascular plant cover reduces competition (Cornelissen et al 2001). All of these conditions result in a higher richness of cryptogam species than vascular plants on the highest summits (Grau et al 2007).…”

Plant community responses to 5 years of simulated climate change in meadow and heath ecosystems at a subarctic-alpine site

“…Lichens increased under C and showed a similar trend of increase in response to T in the heath. Macro lichens, such as in milder arctic and subarctic sites, may decrease in response to experimental change under diVerent environments when plant vegetation cover is more closed or at maximum coverage, or as the biomass of vascular plants increases (Cornelissen et al 2001). The biomass of lichens was shown to decline to fertiliser additions in both Alaska and northern Sweden (Van Wijk et al 2003).…”

Experimental climate warming decreases photosynthetic efficiency of lichens in an arid South African ecosystem

“…Diminished cover of lichens and mosses have been reported from standardized warming experiments at 11 locations across the tundra biome (Cornelissen et al 2001;Walker et al 2006). Also, new and increased occurrences of sub-tropical epiphytic lichen species have been observed in the Netherlands between 1980(Van Herk et al 2002Aptroot and Van Herk 2007).…”