Table 1 Topographic variables used in site selection for 2016 sampling on the Tripod Complex fires in the Okanogan-Wenatchee National Forest, Washington, USA, and as candidate predictor variables. All variables were computed at 100 m resolution from a digital elevation model (DEM)

Elevation

Elevation above sea level in meters

National Elevation Dataset (http://nationalmap.usgs.gov)

Slope

Slope angle in degrees

Computed from DEM with ArcGIS v10.4 Spatial Analyst (ESRI, Redlands, California, USA.)

Heat Load Index (HLI)

Unitless index that accounts for slope, aspect, latitude, and potential direct incident radiation. Smaller values correspond to less heat loading and larger values correspond to more heat loading.

Computed from DEM using the Geomorphometry and Gradient Metric ArcGIS Toolbox v2.0 (Evans et al. 2014)

Topographic Position Index (TPI)

Unitless index that expresses relative ridge or valley position by comparing the elevation of each cell in a DEM to the mean elevation of a specified neighborhood (here, 1000 m) around that cell. More negative values correspond to valleys and more positive values correspond to ridges.

Computed from DEM using the Land Facet Corridor Designer ArcGIS Toolbox (Jenness et al. 2013)

Topographic Wetness Index (TWI)

Steady-state wetness index that expresses flow-accumulation as a function of both slope and upstream contributing area, thus reflecting potential site moisture balance. Smaller TWI values correspond to less potential moisture, larger TWI values correspond to more potential moisture.

Computed from DEM using the Geomorphometry and Gradient Metric ArcGIS Toolbox v2.0 (Evans et al. 2014)