Soil properties and climate drive ponderosa pine seedling presence in the southwestern USA

Abstract

Abstract A continual improvement of our understanding about factors that influence tree regeneration is needed to inform landscape-scale restoration efforts across the western USA. This is increasingly important because changing climate and disturbance regimes will influence where restoration efforts should be implemented across landscapes. In this study, we used Forest Inventory and Analysis (FIA) data to model ponderosa pine (Pinus ponderosa C. Lawson var. scopulorum Engelm.) seedling presence across FIA plots in Arizona and New Mexico, USA. Additionally, we analyzed archived soil samples from FIA plots for percent clay, silt, and sand; samples were collected from the upper 20\xa0cm of the mineral soil. Soil particle size is correlated with soil parent material, which has been shown to influence ponderosa pine regeneration. We used structural equation modeling to determine the relative importance of direct and indirect factors affecting ponderosa pine seedling presence. For the 0–10\xa0cm depth increment of the mineral soil, soils with high inorganic C (carbonate) concentrations, a low percentage of coarse fragments (>2 mm) in the mineral soil, a low percentage of sand in the fine fractions (