Design, treatments, and vegetation measurements
This study was conducted on the Jornada Experimental Range (JER)
from 1938-2001 and is described in detail in Havstad et al. 1999.
The study area is located on a bajada slope where typic Paleorthid
soils have formed on an old alluvial fan. Vegetation is dominated
by creosotebush, with honey mesquite (Prosopis glandulosa) and
tarbush (Flourensia cernua) also present. Sixteen plots (21.3 m x
21.3 m) were established in 1938 in four rows of four plots per
row with a buffer zone of 7.6 m between plots. All plots were
sampled prior to treatment applications. Each plot was divided
into east and west halves and 14 randomly located 10.65 m line
intercept transects, running north to south, were sampled for
shrub canopy cover and perennial grass basal cover in each
half-plot using the line intercept method (see Herrick et
al. 2005). Grasses were measured for basal cover, and all other
species were measured for canopy cover. The 28 transects are not
marked; they are randomly relocated for each remeasurement.
Vegetation was measured using vertical line point intercepts in
1938, 1947, 1956, 1960, 1967, 1989, 1995, and 2001 for Gravelly
Ridges and 1939, 1947, 1960, 1967, and 2001 for Dona Ana and
Parker Tank.
Treatments were factorially applied, yielding a control plot,
single factor plots, and plots with varying degrees of
combinations of factors. Original treatments applied to these 16
plots in 1939 were clearing (hand removal of shrubs severed at
ground surface), furrowing (shallow, hand raked furrows designed
to trap surface water), seeding (broadcast application of seeds of
native perennials), and lagomorph exclusion. Only the lagomorph
exclusion and shrub removal treatments were continued in later
years. Poultry netting with a 2.5 cm mesh buried about 15 cm in
the ground and extending above-ground about 75 cm was used to
exclude lagomorphs. Shrubs (not including suffrutescents) have
been removed from the cleared plots immediately following all
resampling periods listed above. Seeded species were black grama,
spike dropseed, mesa dropseed (Sporobolus flexuosus), and fourwing
saltbush (Atriplex canescens). All treatments were applied after
the initial vegetation measurements were recorded in 1938, except
that the lagomorph exclusion fences were constructed in 1939.
Livestock were excluded from the study area in 1938, and the site
has not been grazed by livestock at any time during the study
period.
Treatments are indicated in the included data file using the
description in Havstad et al. 1999.
References
Havstad, K.M., R.P. Gibbens, C.A. Knorr, and L.W. Murray, (1999).
"Long-term influences of shrub removal and lagomorph
exclusion on Chihuahuan Desert vegetation dynamics." Journal
of Arid Environments 42: 155-166.
https://doi.org/10.1006/jare.1999.0516
Herrick, J. E., J. W. Van Zee, K. M. Havstad, L. M. Burkett, and
W. G. Whitford, (2005). "Monitoring manual for grassland,
shrubland and savanna ecosystems, Volume I." US Department of
Agriculture-Agriculture Research Service, Jornada Experimental
Range, Las Cruces, New Mexico.
