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)
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 |