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.
This study was designed as a complement data from plant cover
measurements taken along vegetation transects that are found in
EDI dataset knb-lter-jrn.210121001. It is a pilot program to
examine the feasibility of measuring individuals from selected
species to determine their response to removal of competing
vegetation.
Individual sampling methods and data
Ten randomly selected individuals of eight plant species were
measured in each plot. The species of interest were the two most
dominant species in each of four classes: shrubs (Larrea
tridentata and Flourensia cernua), sub-shrubs (Xanthocephalum
microcephalum and Zinnia acerosa), succulents (Yucca baccata and
Opuntia violacea), and perennial grasses (Muhlenberiga Porteri and
Dasyochloa pulchella). All forty-eight experimental plots were
surveyed; the plots were divided into six blocks of eight plots
each. Each section contained a control plot and seven plots that
had received a specific removal treatment as described above.
For all but one species, the plants to be measured were selected
from a random number table after first performing a rough count to
determine the number of individuals in the plot. To select a plant
for measurement, a field crew member would hold the numbers to be
sampled while another member of the team counted off the plants
while walking around the plot. When a plant to be measured was
called the counting paused for the individual plant to be
measured.
Dasyochloa pulchella was extremely abundant in most plots. For
this species the plot was subdivided into 25 5-meter square
subplots. The subplot to be sampled was then selected from the
random number table and the individual plant within th eplot was
chosen by one member of the team turning their back to the subplot
and flipping a coin over their shoulder while the other member of
the team watched to see where the coin fell, the nearest plant was
then measured.
Three measurements were taken on each selected plant: first the
longest diameter of the canopy, followed by the longest
perpendicular diameter of the canopy, and the height from the
highest part of the canopy to the ground immediately below. These
three variables are recorded in the data table for this dataset
(diam1, diam2, height). If no species are present it is indicated
by "0" in the two diameter and height fields. If less
than 10 individuals were present in the plot then only the
measured individuals are shown in the data table.
Additional Files
An additional metadata file - bdpltres.dsd.txt - from the earlier
Jornada information management system is included and may contain
useful metadata.
REFERENCES
For more information on the study (not necessarily these data) see
the article:
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.
