Cross-Scale Interaction Study methods
For the data table in this data package, the air dry weight, in
grams, of the dust sample in each collector is calculated from the
mass of the sample and the bag minus the average mass of all bags
used during the collection ( (Bag + Sample) - Avg_Bag_Wt ). Data
collection flags and observations impacting the quality of these
sample weights are indicated in the "qwt" and
"comment" columns of the data table. More study
information can be found in attached files - see "Additional
documents" below.
Experimental design and data collection
The experimental design for the Cross-Scale Interactions study
(CSIs) consists of 15 - 1 ha blocks spatially distributed across
the study area selected to have similar total percentage
vegetation cover within a block, but to vary in the proportion of
perennial grass and mesquite cover among blocks. At each block
location, four 15 x 25 meter experimental plots were identified
with similar percentage grass and shrub cover. Within an
experimental plot was a buffer area, an 8 x 8 meter treatment or
control subplot (the "focal patch"), and 8 x 8 meter
upwind and downwind subplots. Each experimental plot was arrayed
perpendicular lengthwise to the dominant southwest to northeast
wind direction, and was placed > 15 meters away from the other
experimental plots to minimize between-plot treatment effects.
Excluding the buffer zones, the distance between focal patches and
subplots in different experimental plots ranges from > 20 to
~40 meters.
Each experimental plot within a block was randomly assigned to one
of four connectivity treatments: (1) plant scale where all
mesquite plants within and surrounding the focal patch were killed
in place with herbicide to modify competitive interactions between
woody plants and recovery of perennial grasses and other
herbaceous plants with no direct effects on horizontal transport
by wind and water, (2) patch scale where Connectivity Modifiers
(ConMods, Okin et al. 2015) were located in bare soil interspaces
between plants in the focal patch to reduce gap size and to modify
transport of water, soil, nutrients, litter, and herbaceous seeds,
(3) both patch- and plant-scale manipulations were conducted in
each focal patch, and (4) no manipulations [controls]. Block and
plot selection were completed in June 2012 followed by the
characterization of initial vegetation cover in all plots in June
2013 when treatments were initiated.
Assignment of treatments to experimental plots (by block) is
described in the attached file "csis_treatment_key.csv".
There are two BSNE (aeolian dust collector) stands per
experimental plot positioned at the edge of the upwind and
downwind 8m x 8m buffers. Each stand has 3 collectors positioned
at heights of 10 cm, 30 cm, and 50 cm, and all collector openings
face the prevailing wind direction. Upwind BSNEs collected the
amount of dust entering the plot, and the downwind BSNEs collected
the amount of dust moving off the plot. These collectors estimate
the effectiveness of the plot surface (including Conmods and
mesquite shrubs) in obstructing wind blown dust. It is important
the BSNEs are fixed in an orientation that points across the full
length of the plot.
The Conmod BSNEs are collected quarterly in February, May, August,
and November. They are collected in the last week of the month,
or, if not able, in the first week of the next month.
Additional documents
The guidelines and procedures for BSNE collection, maintenance,
and sample/data processing can be found in the file
"CSIS_BSNE-protocol.pdf" provided in this data package.
There is also a key to experimental treatments applied by block
and plot in the file
"Study413_CSIS_Plot_Treatments.pdf".