|Abstract or Summary
- The effects of winter plant moisture stress (P145) on bare-root 2+0 Douglas-fir (Pseudotsuga menziesii (Mirb.) Frañco) seedlings during nursery lifting and processing were studied. Seedlings were undercut at Ca. 4, 12, and 20 atm PMS during mid-February. Half of the seedlings undercut at 12 and 20 atm were not moistened after lifting (dry treated), the remaining seedlings received water sprayed directly on shoots and roots after lifting (wet treated). All seedlings were processed for
field planting within six hours of lifting, and were cold stored for 55 days. Seedlings were planted in contrasting growth environments at two sites near Corvallis, Oregon, in early spring, 1977. Survival and growth were monitored during the first season after seedlings were planted under
heavy and light irrigation, and with and without vegetative competition. The effects of winter PMS were highly associated with severity of the growing site. When moisture was not limiting, as under heavy and light irrigation schedules, treatment differences were small. Under non-irrigated field conditions treatment effects were significant. Wet treated seedlings produced significantly more height growth (9.0 cm
vs 8.0 cm), and new foliage growth (5.70 gin vs 4.77 gin) than dry treated seedlings when grown free of vegetative competition. Survival without competition was excellent for all treatments ranging from 9% to 98%.
On a site dominated by grass competition wet treated seedlings had higher survival (43% vs 23%), more height growth prior to mortality (7.6 cm vs 6.6 cm), and more new foliage growth (3.59 gin vs 3.07 gin).
Seedlings which had early dates of bud burst survived better than those with late dates. Wet treated seedlings maintained better than average survival for later periods of bud burst than dry treated seedlings. The level of PMS at the time of undercutting had no effect on survival or growth when seedlings were moistened after lifting. However, dry treated seedlings undercut at 12 atm had better growth than those undercut at 20 atm when planted with competition. PHS of lifted seedlings increases to a level governed by atmospheric demands unless shoots and roots are protected from drying. Increased
survival and growth can be expected over a wide range of site conditions by maintaining PMS at 5 atm or lower during nursery processing. Reduced survival and growth of dry treated seedlings are most likely the results of poor root vigor caused by desiccation of tissues after exposure to
high levels of PMS. Modification of nursery procedures to reduce the risks of exposure are discussed. The severe effect of grass competition on first year survival and growth of Douglas-fir seedlings is re-emphasized. Survival with competition
was 36% compared to 96% without competition. Seedlings which survived the effects of competition were significantly smaller in diameter, weighed less, and produced less height growth and new foliage than seedlings grown free of competition. A model relating site severity to the expression of treatment differences is presented. The implications of measuring treatment effects on surviving seedlings are discussed.