Overview and study location
This biodiversity study was conducted from 1997-2002 as part of
the Jornada Basin LTER program. The objective of this study was to
distinguish the differential effects of plant community biomass,
plant community functional groups, and biodiversity within
functional groups to a number of plant community responses. To
make these distinctions, treatments were established by the
selective removal of plant species or of all species of a
functional group within a plot.
Given the long lifespans and difficulty of establishment of desert
perennials, establishment of desired communities from seed or
transplant was impractical. Instead, we established our stands of
varying plant diversity by making appropriate removals of species
or species groups from replicate plots of a diverse Chihuahuan
scrub site. Treatments were established in summer/fall 1995.
Plants were removed by simple cutting at the soil surface (no soil
disturbance or herbicide). For most species, this was effective;
recruits of perennial grasses were removed from the appropriate
plots twice per year, and regrowing shrubs were clipped back as
needed. After 2 years only one perennial grass and two shrubs
required substantial effort for plot maintenance.
The experimental area is a 250 m x 250 m area located on the NMSU
Chihuahuan Desert Rangeland Research Center, immediately northeast
of the intersection of the Summerford powerline road and the road
running along the southern boundary of the Jornada Experimental
Range and the CDRRC. The area was gridded into 25 m x 25 m plots;
because of some existing environmental gradients (the area slopes
to the east, and mesquite abundance varies from north to south) 6
blocks were established and treatments were randomly assigned to
plots within blocks. Plot boundaries are marked with rebar in the
corners and simple steel wire stretched along boundaries; plots
are identified by number and treatment on aluminum tags and on
plastic rebar caps in the southwest corner.
Treatments and sampling design
There are eight treatments: a control (C, no removals); four
functional group removal treatments (PG, perennial grass removed;
S, shrubs removed; SSh, subshrubs removed; Succ, succulents
removed), and three treatments where richness within a functional
group was manipulated. The latter include the simplified treatment
(Simp, where only the single most abundant species of each growth
form remains, while all other species of those growth forms are
removed), the reduced‐Larrea treatment (rL, where the dominant of
each growth form is removed, and minority components remain), and
a second form of the reduced treatment (rP, where Prosopis rather
than Larrea is removed as the shrub dominant).
Treatments were established in summer/fall 1995 by randomly
assigning all 8 treatments to plots within each of 6 blocks in the
experimental area (blocking to allow for spatial heterogeneity in
environment and vegetation). There are therefore 6 replicates of
each of the 8 treatments in 48 total plots. In removal treatments
plants were removed by cutting at the soil surface (no soil
disturbance or herbicide application). All vegetation removed
during treatment application (Fall 1995) was field weighed and dry
weighed for the study and these data, and detailed vegetation
removal methods, are available in EDI dataset
knb-lter-jrn.210121003.
Within each plot, three 1 m x 15 m transects (total area 45 m2)
crossed each 15 m x 15 m central area in the plots: one at the
western-most edge of each area, one 5 m to the east, and the third
10 m to the east of the western boundary. The vegetation transects
were measured once or twice a year to assess the response of the
plant community to the manipulations of species and functional
diversity. Measurements occured every fall at a minimum. When
resources permit and vegetation seems to deserve it, spring
sampling was also carried out (2 x per year).
Detailed transect methods and data
The transects were sampled by the use of meter sticks to frame
individual quadrats (numbered 1-15 within each transect; the
transects are numbered 1 to 3, from west to east in each plot).
Sampling took place twice a year (Spring and Fall) for 5 years
from 1997-2002 (no data was collected in 1998). All plants rooted
within the quadrat (or with more than half of the stem or basal
area rooted within) were measured for maximum diameter, maximum
perpendicular diameter, and height (all to nearest cm). The entire
plant canopy was measured, not just that portion falling within
the quadrat. Plants rooted outside the quadrat, whose canopies may
overlap the quadrat, were not measured. Multiple individuals of
the same dimensions in a single quadrat were given a
"count" (if no count recorded, count = 1). Dead plants
are identified as species (where possible) and recorded as
"condition = dead." High densities of fluffgrass in fall
1997 forced alterations to sampling, such that DAPU was measured
only in odd-numbered quadrats for most of the transects. The
following applies to readings of DAPU (fluffgrass): In Spring 97
all quads read for DAPU). Beginning with Fall 97 only odd numbered
quads measured for DAPU. In Spring and Fall 99 DAPU and all forbs
were read in only odd numbered quads. In Spring and Fall 2000 DAPU
was read in odd numbered quads (forbs were read in all quads). In
Spring 2001 DAPU and all forbs were read in odd numbered quads. In
Fall 2001, all vegetation in every quad was read. In Spring 2002
all vegetation in all quads was read.
This data set consists of the date of collection, plot number,
treatment type, transect number, quadrat number, species codes,
two diameters, height, condition, count, record IDs, and error
codes. Data collection was completed in 2002.
Additional Files
An additional metadata file - bdvegtrn.dsd.txt - from the earlier
Jornada information management system is included and may contain
useful metadata. If there are errors noted in the "ec"
column of the data file, these may be described in the history
files for the project, which are collected in an additional
attached archive (bdvt00f.his.zip).
REFERENCES
Buonopane, Michelle, Laura Foster Huenneke, and Marta Remmenga.
"Community response to removals of plant functional groups
and species from a Chihuahuan Desert shrubland." Oikos 110.1
(2005): 67-80.
