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significant difference in mitotic index between the genetic groups was found once in March when
mitotic index in wild stand and seed orchard trees was 1.4% and mitotic index in top-cross trees
was 0.9%. There were no significant differences in mitotic index at any other times during the
year. Date of bud burst and rates of shoot extension were related to levels of cold hardiness in the
three groups of seedlings. The stage of bud burst in May was significantly correlated with levels
of hardiness found earlier in March and April. Trees that completed shoot extension earlier in the
season were significantly more hardy in autumn. Top-cross trees may extend their growing
season later into the fall, thereby gaining a height advantage over wild stand seedlings. These topcross
families do not have an increased mid to late autumn frost damage risk, and in fact may
have reduced risk of critical spring frost damage due to delayed deacclimation.
584. Stinson, S.D. 1999. 50 years of low thinning in second growth Douglas-fir. Forestry-Chronicle
75(3): 401-405.
Keywords: thinning
growth
yield
wood quality
Abstract: Results are presented from four of the Port Blakely XT series of thinning trials,
established during 1948-58 in naturally regenerated Douglas fir [Pseudotsuga menziesii] stands in
western Washington. Three trials were designed to evaluate the effects of repeated low thinning
and extended rotations, while the fourth compared the effects of different levels of removal on
standing volume and wood quality. Periodic and mean annual increment trends were examined in
all trials. Results indicated the extension of culmination of mean annual increment in response to
low thinning, combined with extended rotations. Thinned plots in 2 trials had increased stem size
and total harvested volume. Extended rotations and low thinning increased the quantity of
structural log grades when compared with stands harvested on shorter rotations.
585. Stjernberg, E.I. 1997. Mechanical shock during transportation: effects on seedling performance.
New-Forests 13(1/3): 401-420.
Keywords: nursery operations
tree physiology
tree/stand health
growth
Abstract: A study was carried out to monitor shocks to seedling planting stock during
transport from nursery to the planting site in normal commercial reforestation operations. Size
and exact time of mechanical shocks were measured by a recorder placed inside seedling boxes.
Seedling shipments by refrigerated semi-trailer, 5-t truck, pickup truck, small trailer and allterrain
vehicles were monitored in Alberta and British Columbia. Number of shocks, peak
acceleration and average drop height were tabulated for travel on both paved and gravel roads.
Twenty-two trials involving 7 conifer species (Douglas fir, Pseudotsuga menziesii; western
hemlock [Tsuga heterophylla]; western red cedar [Thuja plicata]; amabilis fir [Abies amabilis];
white spruce, Picea glauca; lodgepole pine, Pinus contorta; Engelmann spruce, Picea
engelmannii) were established at nurseries and field locations covering several ecological zones
in both provinces. Frozen-stored, cool-stored, and freshly lifted seedlings were used in the trials.
Seedlings were given 2 mechanical stress treatments by dropping them 30 times from 0.5 or 1 m
height. Control seedlings were not dropped. Treatments were applied to nursery-trial seedlings
not exposed to normal handling and transport, and to field-trial seedlings after transport to the