Pinus strobiformis seedling growth in southwestern US mixed conifer forests in managed and non-managed stands

Resources available for tree regeneration growth vary within and between stands. Understanding variation can help land managers choose appropriate sites and management strategies for desired regeneration. We measured southwestern white pine (Pinus strobiformis, SWWP) age, annual height growth, stem diameter, crown widths and lengths, needle lengths and branch morphology to determine geographic variation and effects of different silvicultural treatments on seedling height growth in southwestern US mixed conifer stands. We hypothesized both between- and within-stand variables would be related to mean and recent height growth. Thirty-seven per cent of the variance in mean annual growth (cm yr â '1) was explained; growth increased with Douglas-fir site index and on north-facing slopes, and decreased with increasing ponderosa pine densities and per cent ground cover of litter. Recent 3-year height growth increased with site index and decreased with per cent ground cover of litter, increasing canopy closure and in the presence of a nearby microsite object. Height growth was less near downed-woody debris and next to the base of overstory trees. Land managers can use results by regenerating SWWP (natural or planted) on higher productivity sites and north-facing slopes, and avoiding areas with thick layers of litter/duff or planting in areas with high ponderosa pine seedling densities. Stimulating natural regeneration or outplanting seedlings may be necessary to sustain SWWP with the dual threats of climate change and an invasive pathogen.