Experimental design
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 files "csis_treatment_key.csv"
and "Study413_CSIS_Plot_Treatments.pdf".
Lateral photo collection and analysis
In each ConMod plot (ConMod-only and ConMod + Herbicide treatments
only), repeat lateral photos of ten randomly selected microplots
were photographed annually from 2013-2017. Photos were taken
looking laterally across the microplot (parallel to ground, or
side-looking orientation) in four cardinal directions (N, E, S, W)
from a height of approximately 10cm above ground level and 50-cm
away from the ConMod center axis. Photos were taken using a 12.1
megapixel digital camera, resulting in image dimensions of 4,000 x
3,000 pixels. Annual photos were taken in winter (Jan-Feb) from
2013-2016 to try to better distinguish perennial grass from annual
plant biomass. In 2017 the method changed and photos were taken
near peak biomass during the growing season (July-Sept) in order
to better capture and identify living biomass. Images were
archived for later analysis of plant growth and litter
accumulation within the microplots. Lateral photos were
discontinued after 2017 when density and cover of herbaceous
plants made the analysis of litter and soil accumulation difficult
and prone to error.
Lateral photos obtained from ConMods in the same locations as
overhead photos (EDI dataset knb-lter-jrn.210413004) were used to
estimate the redistribution of soil and litter by wind and water
from bare interspaces to ConMods. Lateral imagery from the axis of
ConMod microplots facing in each cardinal direction was used to
estimate the combined vertical accumulation of soil and litter.
The area between the tops and sides of each ConMod’s outer rods
and the top contour of the combined litter and soil surface was
determined (methods described in Peters et al 2020; SigmaScan Pro
5.0: Systat Software, Inc. San Jose, CA USA) using Trace
Measurement Mode with Area and Distance measurement options. Due
to vertical movement of mesh over time, adjustments in the
calculations were performed to correct for shifting reference
points by changing to an area based method from a distance only
method (see the 'cal_dist_cm' data column). This is the raw data
file and provides the calculated area associated with each photo
but not the difference among years. The area is a measure of
displacement above the combined litter/soil, not of the
litter/soil itself. A smaller area above the litter/soil in a
following year indicates litter/soil accumulation. A larger area
indicates litter/soil loss. Comparing the change in area per year
can be used to estimate gain or loss of litter/soil on the
microplot. Data here include photo information, estimated area
above the vertical accumulation of litter/soil, and distance
calibration quality used by SigmaScan to calculate area.
References
Okin, Gregory S., Mariano Moreno-de las Heras, Patricia M. Saco,
Heather L. Throop, Enrique R. Vivoni, Anthony J. Parsons, John
Wainwright, and Debra P. C. Peters. 2015. "Connectivity in
Dryland Landscapes: Shifting Concepts of Spatial
Interactions." Frontiers in Ecology and the Environment 13
(1): 20–27. https://doi.org/10.1890/140163.
Peters, Debra P. C., Gregory S. Okin, Jeffrey E. Herrick, Heather
M. Savoy, John P. Anderson, Stacey L. P. Scroggs, and Junzhe
Zhang. 2020. "Modifying Connectivity to Promote State Change
Reversal: The Importance of Geomorphic Context and Plant–Soil
Feedbacks." Ecology 101 (9): e03069.
https://doi.org/10.1002/ecy.3069.
This method step describes provenance-based metadata as specified in the LTER EML Best Practices.
This provenance metadata does not contain entity specific information.
