CDRRC growing season aridity and grazing season vegetation biomass data

Growing season aridity and livestock grazing seasonality can
influence biomass production of perennial grasses in dryland
systems. For this study, we used a long-term dataset (1967-2004) to
investigate the independent and joint effects of growing season
aridity (De Martonne aridity index calculated for the months of June
through September) and grazing season (yearlong continuous, fall,
winter/spring, or summer season grazing) on the mean annual biomass
(kg per hectare) of the perennial grasses Bouteloua eriopoda (black
grama), Aristida spp. (threeawn), and Sporobolus spp. (dropseed) in
a southwestern United States Chihuahuan Desert rangeland system.
Biomass data were collected from 78 permanent sampling transects
that were within one mile (1609.34 m) distance to water. Over the
37-year study period, total perennial grass biomass decreased as
growing season aridity increased, but the extent of this
relationship depended upon season of grazing and specific grass
taxon. Aridity-related decreases in total perennial grass biomass
were most severe in the summer and fall summer seasonal grazing
pastures, primarily due to inherently low black grama levels. Our
findings indicate that over time, summer and fall grazing can
potentially exacerbate the negative effects of increasing aridity on
perennial grass biomass.