Long-term Effects of Changes in Climate Effects of changes in climate on the functioning of arid and semiarid ecosystems.

LTER, several other networks and now NEON measure net primary production, plant species composition and precipitation for decades in arid and semiarid ecosystems. However, scientists cannot predict the future functioning of these ecosystems under climate change because it is impossible to extrapolate patterns emerging from observations and correlations beyond their original range. Only experimentation allows us to establish cause-effect relationships that can be used to predict the future functioning of arid ecosystems under novel climatic conditions. In addition, it is now clear to scientists that is impossible to predict responses to long-term directional changes based on short-term trends. In deserts of the American Southwest, as in many arid-semiarid regions globally, precipitation amount and its variability are expected to change as a result of climate change.

The objectives of this long-term study are: (1) to assess the effects of directional and prolonged changes in precipitation amount and variability on population, community and ecosystem processes; (2) to elucidate the mechanisms behind those changes, and finally (3) to predict the future state of drylands functioning under novel climate conditions.

To address these objectives, we build upon two extant experiments located in a Desert Grassland at the Jornada LTER (NM): (a) manipulation of rainfall amount (80% reduced PPT, ambient, 80% increased), and (b) manipulation of rainfall variability (control, enhanced variability by 50% and 80%). Long-term manipulations of precipitation amount will be accomplished using rainout shelters coupled with irrigation systems. Manipulations of precipitation variability is conducted by flipping drought and irrigation treatments from year to year in the same plots. Response variables monitored during the last 10 years will continue to be measured; aboveground net primary production by species, plant species cover, richness, diversity, composition and belowground productivity are measured annually to disentangle endogenous mechanisms at population, community and ecosystem levels.

Fig. 2 (from Gherardi et al. 2015. PNAS). Effects of inter-annual precipitation coefficient of variation on aboveground net primary production (ANPP). Six-year mean ANPP as a function of precipitation coefficient of variation for the six-year period for (a) total, (b) dominant grass, (c) shrub and (d) rare species ANPP. Points indicate mean values (+/- SE) for each treatment (N=10). Black: control, red: +/-50%, blue: +/-80%.


Gherardi, L., and O.E. Sala. 2015. Enhanced precipitation variability decreases grass- and increases shrub-productivity. Proceedings of National Academy of Sciences 112 (41): 12735-12740. doi: 10.1073/pnas.1506433112 PDF

Sala, O. E., L. Gherardi, and D. P. C. Peters. 2015. Enhanced Precipitation Variability Effects on Water Losses and Ecosystem Functioning: Differential Response of Arid and Mesic Regions. Climatic Change (2015) 131:213–227. doi: 10.1007/s10584-015-1389-z. PDF

Reichmann, L. G. and O. E. Sala. 2014. Differential sensitivities of grassland structural components to changes in precipitation mediate productivity response in a desert ecosystem. Functional Ecology doi: 10.1111/1365-2435. PDF