Effect of plant date on subsequent seedling field performance

Graduation date: 2008Douglas-fir (Psudotsuga menziesii (Mirb.) Franco) seedlings were outplanted\ud on eight dates (every three weeks from mid-August 2005 through mid-January 2006).\ud On each plant date, seedlings from a conventional dormancy (CONV) induction\ud treatment, including moisture and nutrient stress, and a shortened daylength (SD)\ud treatment were outplanted on three western Oregon sites ranging from the moist\ud coastal region (365 m above sea level, 315-355 cm annual precipitation) to the drier\ud valley fringe (275 m above sea level, 100-150 cm annual precipitation). SD treated\ud seedlings initiated primordial development earlier than CONV treated seedlings and\ud tended to have a lower shoot:root ratio due to larger stem diameter and root biomass.\ud On all three sites, seedlings planted on the first three plant dates (August-September)\ud had more root growth shortly after planting and greater seasonal height and stem\ud diameter growth after the first season than those planted on the later 5 dates (October-\ud January). On two of the three sites, seedlings from the CONV dormancy induction\ud treatment grew more in height and stem diameter than SD treated seedlings regardless\ud of planting date. On the wet coastal site seedlings planted on the earliest date (August)grew on average 20 cm more than seedlings planted on the latest date (January) and\ud averaged more than 2 mm in stem diameter growth when measured at the end of the\ud first growing season. Also on this site seedlings treated with CONV averaged almost 4\ud cm more in height growth and more than 1 mm in stem diameter growth than\ud seedlings treated with SD.\ud Soil moisture and temperature were monitored throughout the study period.\ud Soil moisture was above 20% (volumetric water content, soil core method) on all sites\ud at the time of planting and was not deemed a limiting factor when modeled with\ud seedling field performance. However, soil temperature at the time of planting was\ud found to have a significant influence, which is attributed to its effect on early root\ud egress. Seedlings planted into warm soils (>15ºC, first three plant dates) averaged\ud more height growth and stem diameter growth compared with seedlings planted in\ud cooler soils (