Paul J. Hanson
28 February 2018
Empirical and modeling approaches were used to assess the response of lichens as an indicator species for change.
The Spruce and Peatland Responses Under Changing Environments (SPRUCE) environmental manipulation experiment funded by the U.S. Department of Energy (DOE) were used to study productivity and community composition of arboreal lichens (those living on tree branches) in a warmer future environment.
Changing patterns of warming and drying are likely to decrease or reverse tree-based lichen growth at its southern range margins. Negative carbon balances among persisting individuals could commit these epiphytes to local extinction. These findings illuminate fundamental processes underlying local extinctions of epiphytes and suggest broader consequences for range shrinkage if dispersal and recruitment rates cannot keep pace.
Changing climates are expected to affect the abundance and distribution of global vegetation, especially plants and lichens with an epiphytic lifestyle and direct exposure to atmospheric variation. The study of epiphytes could improve understanding of biological responses to climatic changes, but only if the conditions that elicit physiological performance changes are clearly defined. The team evaluated individual growth performance of the epiphytic lichen Evernia mesomorpha, an iconic boreal forest indicator species, in the first year of a decade-long experiment featuring whole-ecosystem warming and drying. Field experimental enclosures were located near the southern edge of the species’ range.
Mean annual biomass growth of Evernia significantly declined 6 percentage points for every +1°C of experimental warming after accounting for interactions with atmospheric drying. Mean annual biomass growth was 14% in ambient treatments, 2% in unheated control treatments, and –9% to –19% (decreases) in energy-added treatments ranging from +2.25 to +9.00°C above ambient temperatures. Warming-induced biomass losses among persistent individuals were suggestive evidence of an extinction debt that could precede further local mortality events.
Changing patterns of warming and drying would decrease or reverse Evernia growth at its southern range margins, with potential consequences for the maintenance of local and regional populations. Negative carbon balances among persisting individuals could physiologically commit these epiphytes to local extinction. These findings illuminate the processes underlying local extinctions of epiphytes and suggest broader consequences for range shrinkage if dispersal and recruitment rates cannot keep pace.
BER Program Manager
Terrestrial Ecosystem Science, SC-23.1
Paul J. Hanson
Environmental Sciences Division, Oak Ridge National Laboratory
Oak Ridge, TN 37831
This material is based on work supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science. Oak Ridge National Laboratory (ORNL) is managed by UT Battelle, LLC, for DOE under contract DEAC05-00OR22725. The SPRUCE experiment is a collaborative research effort between ORNL and the U.S. Department of Agriculture Forest Service.
Smith, R.J., P.R. Nelson, S. Jovan, P.J. Hanson, and B. McCune. "Novel climates reverse carbon uptake of atmospherically dependent epiphytes: climatic constraints on the iconic boreal forest lichen Evernia mesomorpha." American Journal of Botany 105(2), 266–274 (2018). [DOI:10.1002/ajb2.1022]