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Thesis (M.S.)—University of Nebraska—Lincoln, 1965. Department of Horticulture and Forestry.


Copyright 1965, the author. Used by permission.


Tree improvement programs designed to discover and develop strains of trees better adapted to the rigorous climate of the Great Plains are presently being initiated with more planned for the future.

Bur Oak, Quercus macrocarpa, is one of the species selected for investigation because of the large segment of the Great Plains which it naturally occupies, ability to withstand drought, and relative freedom from serious insect and disease attack.

Adaptations to the Great Plains environments through natural selection in the evolutionary development of the species would be expected to result in a large amount of variability throughout the natural range.A reliable estimate of variability must be available before success of improvement procedures can be predicted.Provenance or seed origin studies has been the main technique used to supply this type of information. This procedure involves the growing of material of different origin in a uniform environment.The effects of habitat can be minimized by replication and phenotypes compared directly.

Photoperiod is the most consistent factor in a plant’s environment.European foresters recognized long ago that tree species moved too far north from their origin would fail to go dormant at the proper time and be damaged by frost.They also knew that trees moved too far south would be dwarfed.In the past thirty years there has been an increasing amount of evidence that difference in daylength during the growing season at different latitudes is the main factor governing this phenomenon.Because of the apparent fundamental role in the vegetative growth cycle the photoperiodic response is of primary concern to tree breeders.

The primary objective of this study was to determine the response of bur oak seedlings from different parts of the native range to different photoperiods.Seed for the study was collected from native stands of trees throughout the western part of the native range of the species.Seed lots were also obtained from Indiana and Pennsylvania to compare with the western ones.

Advisor:W. T. Bagley