The base of the arrow is the value of V in the control plots and the tip of the arrow is its value in the manipulated plots. The cases A through E pose a mix of declining opportunity and increasing challenge for scaling. To apply this conceptual framework to montane meadows, Harte and colleagues have set up field sites and climate manipulations along an elevational gradient spanning a horizontal distance of 12 km and an elevational range of 350 m. As in the illustration, monitoring and climate manipulation are carried out at 3 sites along the gradient . Preliminary results suggest that the timing of the flowering cycle of plants along the gradient resembles cases A and C, depending on the individual species.
Soil carbon exemplifies a more interesting situation.
Indeed, grass biomass and soil carbon correlate strongly across a range of scales from quadrats within plots, to plots within elevational sites, and across elevational sites. But graminoid biomass is unresponsive to warming, indicating that the long-term controls over soil carbon may bear little relation to the factors influencing soil carbon response to manipulated climate. The latter appears to be most responsive to forb biomass. Harte concludes that natural climate gradient analyses may not serve as a valid substitute for manipulation experiments in predicting how soil carbon will respond to global warming. Thus determination of the magnitude and even sign of this carbon-mediated ecological feedback to climate change will require further application of manipulation experiments.