Macrorefugia for North American trees and songbirds

Tree and Songbird Refugia

This page provides links to data that were generated for and presented in Stralberg et al. 2018 (full citation below). These data represent the distribution of potential climatic refugia given projected end-of-century climate conditions. Refugia indices are based on calculations of individual species’ niche-based velocity (biotic velocity), which are derived from species distribution model projections for 324 tree species (McKenney et al. 2011b) and 268 songbird species (Distler et al. 2015). Underlying downscaled climate model projections are from McKenney et al. (2011a). At a species level, the refugia index is based on a negative-exponential distance decay function, which strongly down-weights locations that are far away from currently suitable climate space. For the multi-species index, species with projected increases in suitable niche space are down-weighted. Details are given in Stralberg, D, Carroll, C., Wilsey, C., Pedlar, J., McKenney, D. & Nielsen, S. 2018. "Macrorefugia for North American trees and songbirds: climatic limiting factors and multi-scale topographic influences. Global Ecology and Biogeography. available on request from first author, and read-only version available here).

Fig. 1
Figure 1. Multispecies end-of-century (2071–2100) refugia indices averaged across (a) 324 tree species, (b) 268 songbird species and (c) all species combined, weighted by projected climate-change response. Legend breaks are defined by percentile values. (d) Difference between refugia percentile ranks for trees and songbirds. Radiative forcing values: Representative Concentration Pathway 8.5.


The archives linked below provides results from the study in two alternative zipfile formats. The 7-zip format allows smaller file sizes, but requires the 7-zip software for extraction. 7-zip software is freely available for Windows (link) as well as Mac and Linux systems (link). 

These data have been prepared as part of the AdaptWest project and their development was funded by the Wilburforce Foundation.

Data files
All files, 7-zip format (80MB)
Zipfile: ASCII format
All files, zip format (160MB)
Zipfile: ASCII format
Selected rasters as Databasin map layers

Tree refugia (RCP 8.5, 2080s) Map layer
Bird refugia (RCP 8.5,  2080s) Map layer
Tree and bird refugia (RCP 8.5, 2080s) Map layer

Description of data layers 

Input data used to derive refugia metrics:

The tree distribution models used in the analysis are available here (link).
The songbird distribution models used in the analysis are available upon request from the National Audubon Society (link).

"2050s" refugia layers represent mid-century (2041-2070) conditions at 10-km resolution
"2080s" refugia layers represent end-of-century (2071-2100) conditions at 10-km resolution

Naming of raster data layers:

Trees and Songbirds Combined:
NA_combo_refugia_rankdiffX.tif = difference between tree and bird refugia ranks
NA_combo_refugia_sumX.tif = sum of tree and bird refugia values

NA_songbird_refugia_comboX.tif = average refugia values across all songbird species across all 4 GCMs
NA_songbird_refugia_Z_2071-2100_comboX.tif = average refugia values across all songbird species for GCM Z
Y_songbird_refugia_comboX.tif = average refugia values for songbird species associated with habitat type Y (see bird_lookup.csv)
XX_Z_2071-2100_refugiaX.tif = refugia values for individual songbird species for GCM Z (see bird_lookup.csv)
XX_refugiaX.tif = refugia values for individual songbird species across all 4 GCMs (see bird_lookup.csv)

NA_tree_refugia_comboX.tif = average refugia values across all tree species across all 4 GCMs
YY_refugiaX.tif = refugia values for individual tree species across all 4 GCMs (see tree_lookup.csv)

X = Representative Concentration Pathway (4.5 or 8.5)
Y = Habitat Type (Forest, Open Woodland, Shrub, or Grassland)
XX = Songbird Species Code (see bird_lookup.csv)
YY = Tree Species Code (see tree_lookup.csv)

Projection information

Lambert Azimuthal Equal Area
Datum WGS 1984
Linear Unit Meter 
Angular Unit Degree 
False Easting 0
False Northing 0
Central Meridian -100
Latitude of Origin 45
Cell Size 10000

Distler, T., J. G. Schuetz, J. Velásquez-Tibatá, and G. M. Langham. 2015. Stacked species distribution models and macroecological models provide congruent projections of avian species richness under climate change. Journal of Biogeography 42:976–988.
McKenney, D. W., M. F. Hutchinson, P. Papadopol, K. Lawrence, J. Pedlar, K. Campbell, E. Milewska, R. F. Hopkinson, D. Price, and T. Owen. 2011a. Customized spatial climate models for North America. Bulletin of the American Meteorological Society 92:1611-1622.
McKenney, D. W., J. H. Pedlar, R. B. Rood, and D. Price. 2011b. Revisiting projected shifts in the climate envelopes of North American trees using updated general circulation models. Global Change Biology 17:2720-2730.