In the southwest United States, the current prolonged warm drought is similar to the predicted future climate change scenarios for the region. This study aimed to determine patterns in vegetation response to the early 21st century drought across multiple biomes. We hypothesized that different biomes (forests, shrublands, and grasslands) would have different relative sensitivities to both climate drivers (precipitation and temperature) and legacy effects (previous-year's productivity). We tested this hypothesis at eight Ameriflux sites in various Southwest biomes using NASA Moderate-resolution Imaging Spectroradiometer Enhanced Vegetation Index (EVI) from 2001 to 2013. All sites experienced prolonged dry conditions during the study period. The impact of combined precipitation and temperature on Southwest ecosystems at both annual and sub-annual timescales was tested using Standardized Precipitation Evapotranspiration Index (SPEI). All biomes studied had critical sub-annual climate periods during which precipitation and temperature influenced production. In forests, annual peak greenness (EVImax) was best predicted by 9-month SPEI calculated in July (i.e., January-July). In shrublands and grasslands, EVImax was best predicted by SPEI in July through September, with little effect of the previous year's EVImax. Daily gross ecosystem production (GEP) derived from flux tower data yielded further insights into the complex interplay between precipitation and temperature. In forests, GEP was driven by cool-season precipitation and constrained by warm-season maximum temperature. GEP in both shrublands and grasslands was driven by summer precipitation and constrained by high daily summer maximum temperatures. In grasslands, there was a negative relationship between temperature and GEP in July, but no relationship in August and September. Consideration of sub-annual climate conditions and the inclusion of the effect of temperature on the water balance allowed us to generalize the functional responses of vegetation to predicted future climate conditions. We conclude that across biomes, drought conditions during critical sub-annual climate periods could have a strong negative impact on vegetation production in the southwestern United States.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/616989 |
| Date | 05 1900 |
| Creators | Barnes, Mallory L., Moran, M. Susan, Scott, Russell L., Kolb, Thomas E., Ponce-Campos, Guillermo E., Moore, David J. P., Ross, Morgan A., Mitra, Bhaskar, Dore, Sabina |
| Contributors | Univ Arizona, Sch Nat Resources & Environm, School of Natural Resources and the Environment; University of Arizona; Tucson Arizona 85719 USA, United States Department of Agriculture, Agricultural Research Service; Southwest Watershed Research Center; Tucson Arizona 85719 USA, United States Department of Agriculture, Agricultural Research Service; Southwest Watershed Research Center; Tucson Arizona 85719 USA, School of Forestry; Northern Arizona University; Flagstaff Arizona 86001 USA, United States Department of Agriculture, Agricultural Research Service; Southwest Watershed Research Center; Tucson Arizona 85719 USA, School of Natural Resources and the Environment; University of Arizona; Tucson Arizona 85719 USA, School of Natural Resources and the Environment; University of Arizona; Tucson Arizona 85719 USA, School of Natural Resources and the Environment; University of Arizona; Tucson Arizona 85719 USA, School of Forestry; Northern Arizona University; Flagstaff Arizona 86001 USA |
| Publisher | WILEY-BLACKWELL |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | Article |
| Rights | Copyright: © 2016 Barnes et al. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
| Relation | http://doi.wiley.com/10.1002/ecs2.1339 |
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