Experimental design
These data are part of the "Ecosystem responses to changes in
inter-annual precipitation variability” study conducted in
Exclosure 4 of Pasture 13 on the Jornada Experimental Range (JER)
in Dona Ana County, southern New Mexico, USA. The study is
designed to assess the effect of interannual variability in
precipitation on average aboveground net primary productivity
(ANPP) in Chihuahuan Desert grasslands. It began in 2009 and has
five treatments: 1) ambient precipitation, 2) alternating +50% and
-50% precipitation, 3) alternating -50% and +50% precipitation, 4)
alternating + 80% and -80% precipitation, and 5) alternating -80%
and +80% precipitation. Ambient precipitation plots serve as
controls and have no water manipulation. Rainout shelters are used
to exclude 50% and 80% precipitation and an irrigation system is
used to add 50% and 80% of natural PPT (Gherardi and Sala 2013).
The +50% variability, in even years, receives one half of ambient
PPT by installing rainout shelters and, in odd years, receives
150% of ambient PPT via experimental watering. The +80%
variability treatment alternates years of +80% with years of -80%.
For the alternating treatments, annual changeover takes place
during the third week of May. At the end of the study period, each
treatment will have received the same relative amount, but one
treatment received a natural PPT each year while the other
treatments experienced sequences of dry and wet years resulting in
different interannual variability. We use ten replicates per
treatment for a total of 50 plots.
Data collection and biomass calculation
Vegetation cover is measured in the fall at peak biomass (between
September 17th and October 5th) in 50 2.5m x 2.5m plots. There are
three parallel permanent cover lines per plot, each of 250 cm
length, and 60 cm apart, with ends permanently marked by rebar.
Green interception is recorded per species for all plants present
to a 1cm interval. Existing regression equations are used to
obtain an estimate of biomass by species. ANPP was calculated from
plant cover following (Flombaum and Sala 2007) methodology but
specific allometric calibrations were run for this study for each
plant functional type.
Related data and publications
An earlier version of this dataset on EDI contains 2009-2011 data
for this experiment. Those data are being re-reviewed for
inclusion in a future version of this dataset.
For further information and results see:
Gherardi, Laureano A., and Osvaldo E. Sala. "Enhanced
precipitation variability decreases grass-and increases
shrub-productivity." Proceedings of the National Academy of
Sciences 112, no. 41 (2015): 12735-12740.
Gherardi, Laureano A., and Osvaldo E. Sala. "Enhanced
interannual precipitation variability increases plant functional
diversity that in turn ameliorates negative impact on
productivity." Ecology Letters 18, no. 12 (2015): 1293-1300.
Gherardi, Laureano A., and Osvaldo E. Sala. "Automated
rainfall manipulation system: a reliable and inexpensive tool for
ecologists." Ecosphere 4, no. 2 (2013): 1-10.
Flombaum, P., and O. E. Sala. "A non-destructive and rapid
method to estimate biomass and aboveground net primary production
in arid environments." Journal of Arid Environments 69, no. 2
(2007): 352-358.
