Elevation gradients, as natural experiments, offer global change researchers the unique ability to understand the coupling of above and below ground properties at macroecological time scales. Along gradients of temperature and nutrient availability major factors governing high altitude plant and microbial community and ecosystem properties can be assessed. The formation of treelines – the threshold where trees can no longer grow large due to cold conditions – is perhaps the most conspicuous incarnation of temperature controls over ecosystem properties. Recently it has been proposed that nutrient limitations resulting from temperature inhibited microbial activity may also contribute to treeline formation in an indirect manner. Understanding such processes has been hampered by research originating from single-site transects or by syntheses using widely divergent methodologies and/or temperature ranges. 

We overcame these limitations by using replicate transects and consistent methods in seven countries from both Northern and Southern hemispheres. I will illustrate how above and below ground ecosystem properties are influenced by declining temperatures both continuously with elevation associated temperature declines and, in many cases, suddenly with the transition from forest to low-statured alpine vegetation. Specifically, declines in soil nitrogen and phosphorus led to declining tree and understory plant root and foliar nutrients; turnover of plant species under colder conditions led to greater nutrient conservative traits including a uniform maintenance of plant N/P ratios; and, various metrics of soil fertility, microbial biomass, and microbial activity similarly declined with increasing elevation. The complexity of some responses suggests predicting how montane plants will respond to global climate change will depend indirectly on the slow rate of treeline expansion and directly on the functional ability of local understory plant communities to respond to changes in nutrient availability and possibly greater stress.

About the speaker: Dr. Jordan Mayor is currently a postdoctoral researcher in David Wardle’s Vegetation & Ecosystem Ecology laboratory group in the Dept. of Forest Ecology & Management at SLU in Sweden. He has previously worked as an NSF international postdoctoral fellow with Ben Turner at the Smithsonian Tropical Research Institute in Panama, as a PhD student with Ted Schuur in boreal forests of Alaska, and as a Master’s student with Terry Henkel in remote monodominant rainforests of Guyana.