|CARROLL, CHARLES - COLORADO STATE UNIVERSITY|
|SLETTE, INGRID - COLORADO STATE UNIVERSITY|
|GRIFFIN-NOLAN, ROBERT - SYRACUSE UNIVERSITY|
|BAUR, LAUREN - UNIVERSITY OF NEW MEXICO|
|HOFFMAN, AVA - JOHNS HOPKINS UNIVERSITY|
|GRAY, JESSE - COLORADO STATE UNIVERSITY|
|POST, ALISON - COLORADO STATE UNIVERSITY|
|YU, QIANG - CHINESE ACADEMY OF AGRICULTURAL SCIENCES|
Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2020
Publication Date: 1/8/2021
Citation: Carroll, C., Slette, I.J., Griffin-Nolan, R.J., Baur, L.E., Hoffman, A.M., Denton, E.M., Gray, J.E., Post, A.K., Johnston, M.K., Yu, Q., et al. 2021. Is a drought a drought in grasslands? Productivity responses to different types of drought. Oecologia. 2021. https://doi.org/10.1007/s00442-020-04793-8.
Interpretive Summary: Climate extremes including severe drought (a marked reduction in precipitation) are expected to become more intense in coming years. Understanding how ecosystems respond to this type of disturbance can help us manage for continued resilience of systems. We tested the way two different types of drought of Dust Bowl intensity (66% reduction in precipitation over four years) affected grasslands across the Great Plains of the US. One drought completely blocked all precipitation for a portion of the growing season and the other reduced the size of each rain event. We found that in most cases both droughts caused similar reductions in above and belowground plant growth, but in the few cases where there was a difference the intense shorter drought seemed to hit systems harder. These results were consistent between sites in Colorado, Wyoming and Kansas.
Technical Abstract: Drought, defined as a marked deficiency of precipitation relative to normal, occurs as periods of below-average precipitation or complete failure of precipitation inputs, and can be limited to a single season or prolonged over multiple years. Grasslands are typically quite sensitive to drought, but there can be substantial variability in the magnitude of loss of ecosystem function. We hypothesized that differences in how drought occurs may contribute to this variability. In four native Great Plains grasslands (three C4- and one C3-dominated) spanning a'~'500-mm precipitation gradient, we imposed drought for four consecutive years by (1) reducing each rainfall event by 66% during the growing season (chronic drought) or (2) completely excluding rainfall during a shorter portion of the growing season (intense drought). The drought treatments were similar in magnitude but differed in the following characteristics: event number, event size and length of dry periods. We observed consistent drought-induced reductions (28–37%) in aboveground net primary production (ANPP) only in the C4-dominated grasslands. In general, intense drought reduced ANPP more than chronic drought, with little evidence that drought duration altered this pattern. Conversely, belowground net primary production (BNPP) was reduced by drought in all grasslands (32–64%), with BNPP reductions greater in intense vs. chronic drought treatments in the most mesic grassland. We conclude that grassland productivity responses to drought did not strongly differ between these two types of drought, but when differences existed, intense drought consistently reduced function more than chronic drought.