Overview and study location
This study was conducted in 1997 as part of the Jornada Basin LTER
program. The primary 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. In addition to plant responses, animal community responses
were also observed
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 experiment took place from June through
August 1997. The site contained 6 blocks, each containing 8
treatments. The treatments consisted of plots of land (25m x25m)
which had been altered by removing plant types in a systematic
fashion. Species were removed based on plant functional group and
species dominance within the community.
Treatments and bird observations
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. Plants were removed by cutting at
the soil surface (no soil disturbance or herbicide application).
Birds were observed in each plot for periods of 35 minutes with a
10 minute acclimation period prior to the start of the observation
period. The acclimation period was meant to allow time for birds
to settle and to orient the observer. Observations started at
sunrise and ended between and 8:30 and 9:00 am. In all cases,
observer movement was coordinated so as not to disturb other
observers.
Four observers participated each day, each observing a total of
four plots. They watched (using binoculars) their assigned plot
from a step ladder at the corner of the plot in order to get a
better view of the entire plot. Also, in order to help the
observers distinguish between adjacent plots, markers were placed
around the perimeter of the plots. These markers were put in place
the day before and then promptly taken down so that ecosystem
function was not disrupted. An attempt was made to choose and
place the markers so as not to frighten or attract the birds in
any way. The following data were recorded in each plot: species
type, time spent in plot, type of vegetation utilized, presence of
a pair or family group, and behavior. Behaviors recorded included
perching, singing, calling, foraging on the ground, foraging in
the vegetation, nesting , and preening. Birds that simply flew
over the plot or that landed on the plot boundaries were not
counted.
There were four replications over the course of ten weeks. The
replications were done according to a predetermined schedule which
was developed in such a manner so as to reduce sampling error as
much as possible. In order to do this, the following were avoided:
replications of the same plot at the same time of day, replicating
all of the 6 similar treatments on the same day, and having the
same observer do more than one of the replications of a single
plot.
Variable descriptions
The column "spp_list" in the data file contains codes
for bird species or groups. The additional file
"JRN121006_biodiversity_bird_codes.csv" contains the
definition of these codes as common names or group names of the
species.
Time1 is the total time in seconds that any bird spent in a
particular plot. Time1 is different from Time2 in that if a family
group was present, the young were not counted as individuals,
(since they were probably just following their parent and not
choosing that plot for any reason). For Time2, these young were
counted as separate individuals. This is also true of pairs of
birds. For Time1, they were counted as 1 total, and for Time2,
they were counted as separate individuals.
Additional Files
An additional metadata file - bdbrdsur.dsd.txt - from the earlier
Jornada information management system is included and may contain
useful metadata.
