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Title: Vegetation productivity responds to sub-annual climate conditions across semiarid biomes

item BARNES, M.L. - University Of Arizona
item Moran, Mary
item Scott, Russell - Russ
item KOLB, T.E. - Northern Arizona University
item Ponce Campos, Guillermo
item MOORE, D.J.P. - University Of Arizona
item ROSS, M.A. - University Of Arizona
item MITRA, B. - University Of Arkansas
item DORE, S. - Northern Arizona University

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2015
Publication Date: 5/27/2016
Citation: Barnes, M., Moran, M.S., Scott, R.L., Kolb, T., Ponce Campos, G.E., Moore, D., Ross, M., Mitra, B., Dore, S. 2016. Vegetation productivity responds to sub-annual climate conditions across semiarid biomes. Ecosphere. 7(5):e01339.

Interpretive Summary: In the early 21st century, the American Southwest has been experiencing a prolonged, unprecedented drought characterized by reduced precipitation and high temperatures that exacerbate the effects of the drought on plants. In our study, we explored the relationship between plant growth and climate in grasslands, shrublands, and forests in the Southwestern United States (SW). We used a combination of satellite data and ground measurements to determine the vegetation response to changing climate conditions across SW vegetation types. We found that each vegetation type was sensitive to a different climatic period, where forest growth was most sensitive to near-year-long conditions whereas grasslands and shrublands were responsive to the more immediate summer climate. Further, vegetation growth was closely linked to both precipitation and temperature, rather than just precipitation alone. In this study, we successfully determined the vegetation response to predicted future climate conditions across the Southwestern United States.

Technical Abstract: In the Southwestern United States (SW), 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 plant functional types (forests, shrublands, and grasslands) would have different relative sensitivities to both climate drivers (precipitation and temperature) and legacy effects (previous-year’s production). We tested this hypothesis at eight Ameriflux sites in various Southwest biomes using NASA MODIS Enhanced Vegetation Index (EVI) as a surrogate for above-ground net primary production (ANPP). The Standardized Precipitation Evapotranspiration Index (SPEI) was tested to examine the impact of combined precipitation and temperature on Southwest ecosystems. Results showed that in forests, ANPP was best predicted by SPEI computed over the period from January to July. In shrublands and grasslands, ANPP was best predicted by monsoon season (July to September) SPEI, with little effect of the previous year’s ANPP. 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 monsoon precipitation and constrained by high daily maximum temperatures during the monsoon season. In grasslands, there was a negative relationship between temperature and GEP early in the monsoon season, but no relationship later in the monsoon season. 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 across biomes in the Southwestern United States.