Site: Sevilleta LTER
Skyler Hackley, research technician in the Litvak lab at UNM, inspects the grassland eddy covariance tower on the Sevilleta LTER

There is broad consensus among scientists that the ongoing increase in atmospheric CO2 is changing global climate. The role of ecosystems in regulating atmospheric CO2 depends on the relative balance of gross primary production (GPP, total carbon assimilated by photosynthetic organisms) and ecosystem respiration (Re, total carbon released by respiration). Both GPP and Re respond to fluctuations in temperature and water availability in the soil. As a result, the relative changes of GPP and Re as temperature and water availability change determines ecosystem carbon balance, both during seasonal fluctuations and with directional changes associated with changes in global climate. Understanding ecosystem responses requires long-term large-scale measurements of carbon balance that span the range of regional climate variability. Such measurements can also inform models describing how water and temperature interact to determine carbon balance and these models can be used to predict how carbon balance will change with future climate.

SEV scientists from the University of New Mexico have established a network of flux towers, suites of instruments that measure net ecosystem exchange of carbon (NEE) and water (evapotranspiration – ET) at six sites representing major natural ecosystems across NM. The goal of this long-term measurement network is to understand how NEE responds to variations in temperature and soil water availability in the ecosystems that strongly influence regional carbon balance. NEE increased with elevation, driven by decreasing mean temperature and increasing annual precipitation. Temperature and precipitation response functions indicated that increasing temperatures associated with global change will shift the carbon balance in favor of respiration in all biomes. The likely result will be a net release of carbon from New Mexico ecosystems that may approach 3 Gt statewide by the turn of the century, acting as a positive feedback to increasing atmospheric CO2 concentrations that drive climate change.

This research is important because it provides a regional perspective on the likely effects of climate change using empirically derived functions describing the ecosystems that dominate the region.

Graph for
Change in carbon exchange as a function of increasing mean annual temperature (MAT) for desert grassland (DG), desert shrubland (DS), juniper savanna (JS), pinon-juniper woodland (PJ), ponderosa pine forest (PP) and mixed conifer forest (SC).
The map shows the distribution of these ecosystems across New Mexico.