Figure 5
From: Thermodynamic basis for the demarcation of Arctic and alpine treelines
Feasibility analysis demonstrating annual net loss of CO\(_2\)flux for the United States Rocky Mountains alpine simulated forest counterfactual scenario due to increased snowpack and shortened growing seasons. (a) 2009 daily timeseries of modeled snow depth (blue) and leaf CO\(_2\) flux—the averaged daily photosynthetic CO\(_2\) uptake (orange solid line) and above-ground autotrophic respiration (orange dotted line)—for the United States Rocky Mountains scenarios. For the alpine simulated forest, cooler temperatures near the earth’s surface result in faster accumulation of snow and less snowmelt throughout the winter, extending the time needed to melt the snow. Thus, the simulated forest exhibits compounding snow depth and an abbreviated summer season without snowpack, leading to shortened photosynthesis periods compared to the alpine fellfield scenario (top panel). (b) Modeled average annual net leaf CO\(_2\) flux over the entire study period (IT, 2 years; CA, 3 years; US, 6 years). Positive flux corresponds to net leaf uptake (i.e., photosynthesis minus above-ground autotrophic respiration). Error bars indicate the range of annual net leaf CO\(_2\) flux for all years of the study period. Simulated forests for the two alpine sites (orange; US-Tr & IT-Tr) experience decreases in net CO\(_2\) flux compared to the other scenarios. Further, the US-Tr scenario exhibits overall losses in CO\(_2\) year to year, creating unsustainable mass balance for biomass productivity and indicating that the counterfactual is infeasible.
