00745nas a2200241 4500008004100000245009500041210006900136100002000205700001700225700002400242700001500266700001800281700001700299700001500316700001500331700001900346700001100365700001800376700001200394700001600406700001600422856006500438 2021 eng d00aIs a drought a drought in grasslands? Productivity responses to different types of drought0 adrought a drought in grasslands Productivity responses to differ1 aCarroll, C.J.W.1 aSlette, I.J.1 aGriffin-Nolan, R.J.1 aBaur, L.E.1 aHoffman, A.M.1 aDenton, E.M.1 aGray, J.E.1 aPost, A.K.1 aJohnston, M.K.1 aYu, Q.1 aCollins, S.L.1 aLuo, Y.1 aSmith, M.D.1 aKnapp, A.K. uhttps://link.springer.com/article/10.1007/s00442-020-04793-802332nas a2200265 4500008004100000245008400041210006900125300001400194490000700208520155900215100002001774700002001794700002401814700001701838700001701855700001301872700001701885700001301902700001801915700001801933700001201951700001301963700001601976856007401992 2018 eng d00aA reality check for climate change experiments: Do they reflect the real world?0 areality check for climate change experiments Do they reflect the a2145-21510 v993 a

Experiments are widely used in ecology, particularly for assessing global change impacts on ecosystem function. However, results from experiments often are inconsistent with observations made under natural conditions, suggesting the need for rigorous comparisons of experimental and observational studies. We conducted such a “reality check” for a grassland ecosystem by compiling results from nine independently conducted climate change experiments. Each experiment manipulated growing season precipitation (GSP) and measured responses in aboveground net primary production (ANPP). We compared results from experiments with long‐term (33‐yr) annual precipitation and ANPP records to ask if collectively (n = 44 experiment‐years) experiments yielded estimates of ANPP, rain‐use efficiency (RUE, grams per square meter ANPP per mm precipitation), and the relationship between GSP and ANPP comparable to observations. We found that mean ANPP and RUE from experiments did not deviate from observations. Experiments and observational data also yielded similar functional relationships between ANPP and GSP, but only within the range of historically observed GSP. Fewer experiments imposed extreme levels of GSP (outside the observed 33‐yr record), but when these were included, they altered the GSP–ANPP relationship. This result underscores the need for more experiments imposing extreme precipitation levels to resolve how forecast changes in climate regimes will affect ecosystem function in the future.

1 aKnapp, Alan, K.1 aCarroll, C.J.W.1 aGriffin-Nolan, R.J.1 aSlette, I.J.1 aChavez, F.A.1 aBaur, L.1 aFelton, A.J.1 aGray, J.1 aHoffman, A.M.1 aLemoine, N.P.1 aMao, W.1 aPost, A.1 aSmith, M.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecy.247403239nas a2200313 4500008004100000245011900041210006900160300001400229490000700243520231400250100002002564700001702584700001402601700002002615700002402635700001602659700001702675700002402692700001702716700001602733700001502749700001902764700001502783700001502798700001702813700001702830700001602847856006202863 2017 eng d00aPushing precipitation to the extremes in distributed experiments: recommendations for simulating wet and dry years0 aPushing precipitation to the extremes in distributed experiments a1774-17820 v233 a

Intensification of the global hydrological cycle, ranging from larger individual precipitation events to more extreme multiyear droughts, has the potential to cause widespread alterations in ecosystem structure and function. With evidence that the incidence of extreme precipitation years (defined statistically from historical precipitation records) is increasing, there is a clear need to identify ecosystems that are most vulnerable to these changes and understand why some ecosystems are more sensitive to extremes than others. To date, opportunistic studies of naturally occurring extreme precipitation years, combined with results from a relatively small number of experiments, have provided limited mechanistic understanding of differences in ecosystem sensitivity, suggesting that new approaches are needed. Coordinated distributed experiments (CDEs) arrayed across multiple ecosystem types and focused on water can enhance our understanding of differential ecosystem sensitivity to precipitation extremes, but there are many design challenges to overcome (e.g., cost, comparability, standardization). Here, we evaluate contemporary experimental approaches for manipulating precipitation under field conditions to inform the design of ‘Drought-Net’, a relatively low-cost CDE that simulates extreme precipitation years. A common method for imposing both dry and wet years is to alter each ambient precipitation event. We endorse this approach for imposing extreme precipitation years because it simultaneously alters other precipitation characteristics (i.e., event size) consistent with natural precipitation patterns. However, we do not advocate applying identical treatment levels at all sites – a common approach to standardization in CDEs. This is because precipitation variability varies >fivefold globally resulting in a wide range of ecosystem-specific thresholds for defining extreme precipitation years. For CDEs focused on precipitation extremes, treatments should be based on each site's past climatic characteristics. This approach, though not often used by ecologists, allows ecological responses to be directly compared across disparate ecosystems and climates, facilitating process-level understanding of ecosystem sensitivity to precipitation extremes.

1 aKnapp, Alan, K.1 aAvolio, M.L.1 aBeier, C.1 aCarroll, C.J.W.1 aCollins, Scott., L.1 aDukes, J.S.1 aFraser, L.H.1 aGriffin-Nolan, R.J.1 aHoover, D.L.1 aJentsch, A.1 aLoik, M.E.1 aPhillips, R.P.1 aPost, A.K.1 aSala, O.E.1 aSlette, I.J.1 aYahdjian, L.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1350402530nas a2200241 4500008004100000245008400041210006900125300001300194490000800207520176300215653001901978653002501997653003402022653001802056653002302074100002002097700002002117700001702137700002802154700002402182700001602206856006602222 2015 eng d00aDifferential sensitivity to regional-scale drought in six central US grasslands0 aDifferential sensitivity to regionalscale drought in six central a949 -9570 v1773 a

Terrestrial ecosystems often vary dramatically in their responses to drought, but the reasons for this are unclear. With climate change forecasts for more frequent and extensive drought in the future, a more complete understanding of the mechanisms that determine differential ecosystem sensitivity to drought is needed. In 2012, the Central US experienced the fourth largest drought in a century, with a regional-scale 40 % reduction in growing season precipitation affecting ecosystems ranging from desert grassland to mesic tallgrass prairie. This provided an opportunity to assess ecosystem sensitivity to a drought of common magnitude in six native grasslands. We tested the prediction that drought sensitivity is inversely related to mean annual precipitation (MAP) by quantifying reductions in aboveground net primary production (ANPP). Long-term ANPP data available for each site (mean length = 16 years) were used as a baseline for calculating reductions in ANPP, and drought sensitivity was estimated as the reduction in ANPP per millimeter reduction in precipitation. Arid grasslands were the most sensitive to drought, but drought responses and sensitivity varied by more than twofold among the six grasslands, despite all sites experiencing 40 % reductions in growing season precipitation. Although drought sensitivity generally decreased with increasing MAP as predicted, there was evidence that the identity and traits of the dominant species, as well as plant functional diversity, influenced sensitivity. A more comprehensive understanding of the mechanisms leading to differences in drought sensitivity will require multi-site manipulative experiments designed to assess both biotic and abiotic determinants of ecosystem sensitivity.

10aClimate change10aFunctional diversity10aLong-term ecological research10aPrecipitation10aPrimary production1 aKnapp, Alan, K.1 aCarroll, C.J.W.1 aDenton, E.M.1 aLa Pierre, Kimberly, J.1 aCollins, Scott., L.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-015-3233-6