DOI: 10.5061/dryad.sxksn033t
title: Spatial patterning of Artemisia tridentata neighborhoods and relative crowding

description: Plants reflect resource use in their spatial patterning. Competition for
 limited resources—such as available soil water in a dryland
 ecosystem—drives establishment, growth, and mortality, resulting in shifts
 of spatial arrangement over time. We characterized the spatial patterning
 of two big sagebrush (Artemisia tridentata subspecies wyomingensis)
 communities in the upper Green River Basin of Wyoming, USA. We mapped big
 sagebrush canopies in two, 100-square meter sites and calculated plant
 neighborhoods as the area closer to a target plant than to any other
 plant. We assumed that neighborhoods were areas in which the target plant
 dominates resource use. We found that plant neighborhoods had strong,
 positive correlations with plant size, indicating that larger
 neighborhoods may access more belowground resources. We also found that
 the relationships between experienced crowding, i.e. Crowding Index (CI)
 by an average neighbor, and neighborhood size, were consistently negative
 regardless of calculation method. We also found that the residuals of a
 regression of target plant biomass and neighborhood area were strongly
 related to the CI calculated via all methods. This means that plants with
 smaller neighborhoods than expected also experience the greatest crowding
 by an average neighbor. These results are consistent with negative density
 dependence and show that greater static crowding predicts smaller
 neighborhoods in two, undisturbed, intermediate-successional big sagebrush
 communities. In the future, similar studies of spatial patterning that
 include interspecific plant-plant interactions will be useful for
 understanding the relationship between spatial patterning and negative
 density dependence.
description: We collected these data in order to characterize the spatial
 patterning of <em>Artemisia tridentata</em> plant communities
 in the upper Green River Basin of Wyoming. During the summer of 2020, we
 measured plant canopies and mapped their coordinates at two, 10 x 10 meter
 sites, and captured aerial imagery of the sites. We manually traced plant
 canopies in ArcMap using both the georeferenced aerial imagery and the
 coordinates collected in the field. We employed Euclidean allocation in
 GIS to assign neighborhood polygons to plants and created a dataset of
 target-plant/neighbor-plant relationships (polygon neighbor analysis) to
 describe the relative crowding experienced by target plants. Additional
 details about the data processing are included in the archived Excel
 document (spatial_patterning_bigsagebrush_RAW_DAC.xlsx).
description: This archive includes an Excel spreadsheet of all raw space
 patterning data, variable descriptions, and some metadata notes about data
 processing. Shapefiles of the neighborhood polygons, plant canopy
 polygons, and neighborhood centroids are included. While we conducted the
 majority of our GIS sampling (the creation of the polygon neighbor
 dataset) in ArcMap, the provided shapefiles are not proprietary so that
 the analysis may be replicated elsewhere (e.g. R). A README file is also
 included.