Size hierarchy in conifer seedbeds. I. Time of emergence

Abstract

Studies conducted at two pine nurseries in the South and one in the West empirically related the genesis of seedling size hierarchies to time of emergence (TOE). Pinus taeda seeds were operationally sown at the southern nurseries in late April and P. ponderosa in late July at the western nursery. Germinated seedlings were tagged with color-coded plastic rings (20 turn dia.) every other day until germination was complete. Emergence was complete in 16–20 days. Growth response to TOE effects was determined 8 and 15 months, respectively, after sowing.

Results were strikingly similar across nurseries; TOE strongly influenced germinant mortality and shoot biomass decreased 3.5% per day elapsed from initial emergence. That is, seedlings emerging 10 days after emergence began were 35% smaller at harvest than those emerging first. Late germinants accounted for significantly more culls among harvested seedlings than early germinants. Also, TOE accountend for more than 80% of variation in harvest biomass. Findings suggest that the germination period should not exceed 5 days. Response models are proposed to elucidate TOE effects in nursery operations.