Impacts on the Carbon Cycle of Warming and Species Removal in Montane Ecosystems

Abstract:

In terrestrial ecosystems, the majority of carbon (C) available for atmospheric exchange resides in the soil and the atmosphere-soil C exchange is regulated directly by climate and indirectly plant and soil communities. Shifts in plant community and trait composition can lead to dramatic alterations in ecosystem function and the indirect effects of climate change, through effects on plant communities and traits, can have a larger impact on C dynamics than the direct effects of climate. The effects of changing composition can be especially pronounced if the loss of dominant species and their associated traits occurs. Here, we present data from the Warming and species Removal in Mountains (WaRM) network, which for the past 5+ years has manipulated the interactive effects of warming (by open top chambers) and species interactions (by dominant species removal) at high and low elevations in 10 mountain regions globally. We measure plant community composition, soil respiration, net ecosystem carbon exchange (GPP, ER), soil carbon, soil moisture, soil and air temperature, as well as a suite of plant traits in each plot at each site. We have three overarching predictions: (1) Across treatments, higher temperatures, more plant biomass and higher leaf area at low elevation sites relative to the high elevation sites will result in a greater net CO2 sink at the lower elevations. (2) Both GPP and ER will be stimulated by short-term experimental warming, but ER will be more stimulated than GPP and dominant plant species removal will reduce GPP more than ER. Hence, both experimental warming and dominant plant species removal will result in a weaker net CO2 sink. (3) Decreases in the net CO2 sink resulting from warming and dominant species removal should be greater at high elevations than at low elevations. We predict this pattern because dominant plant species removal should be most detrimental for neighboring plant cover at the high elevation site. To date, we find that NEE is surprisingly resistant to both warming and dominant plant species removal; however these results depend on the properties of the ecosystems being measured.