Begun in winter 2006, this long-term study at the Sevilleta LTER examines how heightened winter precipitation, N addition, and warmer nighttime temperatures affect above-ground biomass production (ANPP) in a mixed desert-grassland. Net primary production is a fundamental ecological variable that quantifies rates of carbon consumption and fixation. Estimates of NPP are important in understanding energy flow at a community level as well as spatial and temporal responses to a range of ecological processes. While measures of both below- and above-ground biomass are important in estimating total NPP, this study focuses on above-ground net primary production (ANPP). Above-ground net primary production is the change in plant biomass, including loss to death and decomposition, over a given period of time. Volumetric measurements are made using vegetation data from permanent plots (SEV176, "Warming-El Nino-Nitrogen Deposition Experiment (WENNDEx): Net Primary Production Quadrat Data") and regressions correlating species biomass and volume constructed using seasonal harvest weights from SEV157, "Net Primary Productivity (NPP) Weight Data."
Derivation of Biomass and NPP:
Data from SEV176 and SEV157 are used to calculate seasonal and annual production of each species in each quadrat for a given year. Allometric equations derived from harvested samples of each species for each season are applied to the measured cover, height, and count of each species in each quadrat. This provides seasonal biomass for spring and and fall.
Seasonal NPP is derived by subtracting the previous season's biomass from the biomass for the current season. For example, spring NPP is calculated by subtracting the winter weight from the spring weight for each species in a given quadrat. Negative differences are considered to be 0. Likewise, fall production is computed by subtracting spring biomass from fall biomass. Annual biomass is taken as the sum of spring and fall NPP.
August 2009 Burn:
On August 4, 2009, a lightning-initiated fire began on the Sevilleta National Wildlife Refuge. By August 5, 2009, the fire had reached the Warming site, which was burned extensively though not entirely. Approximately 50% of plots burned on August 5 and those plots which did not burn were burned within three weeks by US Fish and Wildlife. Thus, the condition of all plots at the Warming site was comparable by early September 2009.
02/06/09 (YX) Metadata created and compiled for 2006, 2007, 2008 data. From 2007, winter measurements are no longer taken.
Other researchers involved with collecting samples/data: Chandra Tucker (CAT: 04/2014-present), Megan McClung (MAM: 04/2013-present), Stephanie Baker (SRB; 09/2010-present), John Mulhouse (JMM; 08/2010-06/2013), Amaris Swann (ALS; 08/2008-01/2013), Maya Kapoor (MLK; 08/2003-01/2005, 05/2010-03/2011), Terri Koontz (TLK; 02/2000-08/2003, 08/2006-08/2010), Yang Xia (YX; 01/2005-03/2010), Karen Wetherill (KRW; 02/2000-08/2009); Michell Thomey (MLT; 09/2005-08/2008).