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.
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. Diversity indices are derived according to: 1) Tuomisto, H.
2011. Commentary: do we have a consistent terminology for species
diversity? Yes, if we choose to use it. Oecologia 167:903-911 and 2)
Tuomisto, H. 2012. An updated consumer’s guide to evenness and related
indices. Oikos 121:1203-1218. Species richness is calculated counting
the number of species with cover greater than zero.
