DOI: 10.5061/dryad.dc863
title: Data from: Thermal segregation drives patterns of alder and willow expansion in a montane ecosystem subject to climate warming

description: 1.Tall-shrub expansion into low-statured communities, a hallmark of recent
 vegetative change across tundra ecosystems, involves three major genera:
 Alnus, Betula, and Salix. Which genus expands most into tundra landscapes
 will determine ecosystem properties. 2.We show that Alnus and Salix shrubs
 segregate thermal space (elevation x insolation) and colonize tundra
 landscapes differently in response to climate warming, thereby replacing
 different tundra types. 3.Vegetative change estimated from repeat
 photography should account for hill-slope. Methodologically, slope
 determines surface area estimated from orthophotos as projected pixel area
 times secant of pixel slope. Ecologically, the change in
 thermally-responsive vegetative area is sensitive to terrain steepness,
 scaling as the cosecant of hill-slope, so that studies should expect more
 shrub expansion in areas of shallow slopes than steep slopes. 4.Repeat
 aerial photography in Alaska's Chugach Mountains from 1972-2012
 orthorectified on high-resolution lidar DEM indicated tall Salix was rare
 in 1972 and colonized warmer slopes by 2012. Tall Alnus colonized steeper,
 cooler slopes both by 2012 and by 1972. Salix and forest colonized similar
 thermal space. Colonization probability for both shrub genera was
 maximized at intermediate elevations. 5.Alnus colonization adjacent to
 dwarf-shrub tundra was twenty-times as likely as Salix colonization. Salix
 colonization adjacent to low-shrub/herbaceous tundra was three-times as
 likely as Alnus colonization. Replacement of dwarf-shrub tundra by Alnus
 and of low-shrub/herbaceous communities by Salix will affect herbivores
 and soil properties. 6.Good agreement between observations of plant
 functional type and multinomial predictions in a thermal space defined by
 elevation and insolation suggested that these two variables were
 sufficient for forecast modeling. Spatially explicit, climate-driven GLM
 multinomial and random forest classification models in available thermal
 space forecast surface areas of forest, Alnus, Salix, and tundra over a
 range of warming, modeled as upward shifted isotherms, including expected
 IPCC scenarios. Both modeling approaches indicated that shrubs may respond
 non-linearly to warming. 7.Synthesis The provision of taxon-specific
 coefficients for climate-driven, spatially-explicit models using high
 resolution digital elevation models is necessary for accurately
 forecasting vegetative change due to climate warming in montane and arctic
 regions.
description: Elevation, slope,
 aspect, and vegetation classes for 1972 and 2012Three sub-areas covering
 a total projected area of about 14 ha in the western Chugach Mountains of
 southcentral Alaska were digitized and attributed by vegetation class for
 1972 and 2012 from a series of orthophotos. A 1m pixel digital elevation
 model provided elevation, slope, and aspect (DEM variables). This file
 contains the DEM attributes and vegetation classification for each 1m
 pixel.FullData.csv2000 random points for statistical modeling2000 random points across the three study sub-areas were selected for statistical modeling in binomial generalized linear mixed models. These points have digital elevation model (DEM) variables (elevation, slope, aspect, potential insolation in four seasons) and vegetation classifications for 1972 and 2012.SamplePoints.csvSoil pit moisture dataSoil pits with location and moisture content. This file has the location data for temperature data loggers listed in the file Soil Temperature data file.SoilSampleData.csvSoil Temperature DataSoil temperatures at 15 cm for up to one year. The samples were blocked by location for up to three vegetation classes (alder, willow, and tundra) but unbalanced.SoilTemperatures.csvNeighborCommunitiesNeighborCommunities is an ArcMap version 10.4.1 shapefile of line-features (SpatialLinesDataFrame in R) with four attributes giving the “Sub_area” of the study area, the length in km (“length_km”) of the line-feature, the functional class of the new, tall woody vegetation (“NewTWV”), and the bounding vegetation outside the polygon on a given poygon edge (“BoundVeg”). Projection is UTM zone6 with datum of WGS84. Please see NeighborCommunities_README.rtf for further details.VegClassVegClass is an ArcMap version 10.4.1 shapefile of polygon-features (SpatialPolygonsDataFramein R) with four attributes giving the “Subarea” of the study area, the area in ha (“area_ha”) of the polygon-feature, the functional class of the polygon in 1972 (“Veg1972”), and the functional class of the polygon in 2012 (“Veg2012”). Projection is UTM zone6 with datum of WGS84. Please see VegClass_README.rtf for further details.