The practical application of two dormancy induction trials on douglas-fir and western hemlock container seedlings
Creators: name: Wickman, Marise
Publisher: name: University of British Columbia
Year: 2010

description: Two dormancy induction trials were conducted in a private container nursery in Saanichton, British Columbia. The first study examined the effects of photoperiod induced dormancy on morphology, root growth and field performance of fall planted western hemlock (Tsuga heterophyl_1ji (Raf.)Sarg.) and Douglas-fir (Pseudotsuga menzi_esv[ (Mirb.) Franco) seedlings. Various periods of eight hour days, ranging from two to eight weeks, were applied throughout July and August 1983. Outplanting was done in late September. Survival and growth were assessed one year later. The second project investigated the effectiveness of short days, varying levels of moisture stress and a combination of both as dormancy induction techniques for Douglas-fir seedlings. The short day treatment was four weeks of eight hour days. Four levels of predawn moisture stress were: -5, -10, -15 and -25 bars. These classes respectively corresponded to control, light, medium and severe moisture stress levels. Short days and moisture stress were also combined whereby the four week period of short days followed the moisture stress treatments. These induction treatments were applied in July and August 1984. All seedlings were lifted in January 1985 and placed into cold storage for five weeks until March 1985. Morphology, root growth capacity, frost hardiness and dormancy intensity were assessed in January. Root growth capacity and dormancy intensity were again measured in March. In Study I, short days quickly initiated homogeneous budset in both species in approximately three weeks. The average height increment after treatment initiation was 3.7 cm in Douglas-fir and 4.2 cm in western hemlock. Short days reduced shoot dry weight and height. Caliper and root dry weight were unaffected. In September a surge in root growth occurred in hemlock seedlings treated with six or eight weeks of short days. The importance of early budset to allow increased root growth prior to a fall lift was demonstrated. Root growth capacity was similar among all treatments for both species. The planting survival of western hemlock seedlings increased with increasing weeks of short days. Control plants had 76% survival while the eight week regime had 91%. Survival was similar for all treated Douglas-fir seedlings. It ranged from 89% in the two week interval to 98% in the four week regime. One year height increment was significantly greater in the six and eight week short day treatments for both species. For hemlock, it ranged from 6.1 cm in the control plants to 10.4 cm in the six week trees. Douglas-fir height increment ranged from 6.4 cm for the control interval to 8.6 cm in the eight week regime. The six and eight week photoregimes produced the best quality hemlock seedlings for this study. Four weeks of short days appeared adequate for Douglas-fir. In Study II short days effectively initiated and maintained budset in Douglas-fir seedlings in four weeks. After six weeks from treatment initiation, a light to severe moisture stress was as effective in controlling height growth. A natural photoperiod with no moisture stress was least effective. In a comparison of all treatment combinations, only the control plants under a natural photoperiod were significantly larger in all morphological properties. Short days, moisture stress or a combination of both had similar effects on reducing height, caliper, shoot dry weight and root dry weight. Unstressed seedlings in a natural daylength had the highest value of root growth capacity. All other treatment combinations had significantly lower root growth capacity. Only the severe stress under a natural photoperiod significantly reduced root growth capacity compared to any other treatment. Short days accelerated bud burst in the January and March dormancy intensity tests. Frost hardiness was similar among all treatments. Selection of a regime which controlled height growth while maintaining seedling quality was not clearcut. A short photoperiod with no moisture stress was most effective in initiating budset. However, few morphological and physiological differences were evident between short day plants and light and medium stressed seedlings.