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Table 2 Description of abiotic and biotic predictor variables used in ponderosa pine seedling establishment and seedling density models, using field data that were collected in high-severity burn patches in ten fires across Arizona and New Mexico, USA, in 2018 and 2019. Topographic variables were derived from 30 m resolution digital elevation models (DEM). Climate variables were calculated from 4 km resolution TerraClimate data (Abatzoglou et al. 2018)

From: Moisture and vegetation cover limit ponderosa pine regeneration in high-severity burn patches in the southwestern US

Variable name Description Units
Field measurements
 Time since fire Difference between fire year and year when field measurements took place. years
 Conifer seedling density Count of all conifer species. stems ha−1
 Seedling height Height of seedlings >15 cm tall measured in six height classes. m
 Canopy cover Area of canopy measured for each seedling (averaged in a 15 m radius subplot). m2
 Shrubs Percent cover of woody understory vegetation on 30 m transects using line-intercept method (four transects averaged). percent
 Gambel oak cover Percent cover on 30 m transects using line-intercept method (four transects averaged) percent
 Grass and forb cover Ocular estimates of percent cover of grasses and forbs within 1 m2 quadrats (eight quadrats averaged) percent
 Elevation Elevation at plot center with a global positioning system unit. m
 Slope Slope from clinometer. percent
 Aspect Aspect from compass. degrees
 Distance to nearest tree Distance to nearest living mature ponderosa pine measured from plot center with laser rangefinder. meters
 Edge or core Binary variable representing either core or edge plot. unitless
 Post-fire canopy cover Image classification of percent canopy cover of post-fire mature conifers using 4-band 60 cm National Agriculture Imagery Program imagery within 60 to 300 m radii circular plots from plot center (sensu Rodman et al. 2020b). percent
Topographic
 Abs-aspect Absolute value of 180° minus aspect of plot. degrees
 Slope cosine Cosine (aspect)*slope (Stage 1976). Higher values represent steep northern aspects. radians*percent slope
 Slope sine Sine (aspect)*slope (Stage 1976). Higher values represent steep eastern aspects. radians*percent slope
 Northness cos*aspect. Values range from −1 to 1 with positive values indicating more northern aspects. radians
 Eastness sine*aspect. Values range from −1 to 1 with negative values indicating more eastern aspects. radians
 Curvature Describes shape of the slope. Positive values indicate convex slopes while negative values represent concave slopes (drainages). unitless (0.01z)
Climate
 AET 30-yr average Actual evaportranspiration. 30-year average (1981 to 2010) of monthly AET values. AET is the amount of water used (evoptranspired) given water availability. Higher numbers represent higher site productivity. mm
 AET 3-yr post-fire 3-year post-fire average of monthly AET values. mm
 CWD 30-yr average Climate water deficit. 30-year average (1981 to 2010) of monthly CWD values. CWD is a measure of drought and is the evaporative demand of a site minus the amount actually evpotranspired. Higher numbers indicate higher drought stress on a site, since it is not meeting its evaporative demand. mm
 CWD 3-yr post-fire 3-year post-fire average of monthly CWD values. mm
 PPT 30-yr average 30-year average (1981 to 2010) of monthly precipitation values. mm
 PPT 3-yr post-fire 3-year post-fire average of monthly precipitation values. mm
 PPT 1-yr post-fire 1-year post-fire annual mean of monthly precipitation values. mm