Research Branch

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Western Hemlock: A Manual for Tree Improvement Seed Production

Author(s) or contact(s): J.E. Webber
Source: Research Branch
Subject: Seeds and Pollen
Series: Working Paper
Other details:  Published 2000. Hardcopy is available.


The Forest Genetics Council has laid out objectives for western hemlock seedling requirements up to the year 2007. These objectives include goals for both the number of seedlings and their genetic worth. The only current practical options for meeting these objectives are seed production and a limited amount of bulking through rooted cuttings. Rooted cuttings technology is more costly and relatively new. Performance of seedlings from cuttings remains largely untested although cuttings/seedlings comparisons are in place. For the near future, seed production will be our prime source of reforestation propagules. This manual compiles information from the Ministry of Forests research program as well as other allied programs to make recommendations for seed orchard production of high genetic gain seed lots.
With our current operational seed production capabilities, meeting requirements for numbers of seedlings will be a relatively straightforward task. Meeting goals for genetic worth is more problematic, and will require innovation in two directions:
-developing technologies based on what we have learned, and
-vigorously integrating these technologies into existing and future seed orchards.

Western hemlock lends itself easily to the first of these innovations because it is one our easiest conifer species to manage. The species (1) grafts well, (2) has crowns that are easily pruned for management as well as seed and pollen cone development, (3) is among the easiest species in which to induce flowering, (4) produces pollen that is relatively easy to handle and stores well for at least 3 years, and (5) does not suffer from severe competing pollen clouds (contamination) arising from stands surrounding most western hemlock seed orchards in British Columbia.
This manual includes research summaries for cone induction and crown management and actual research results for pollen management techniques that include:
-evaluation of pollen storage methods,
- comparison of germination techniques,
- development of three pollen viability tests,
- the relationships between viability tests and field fertility, and
-supplemental pollination (SP).

Our research has enabled us to formulate technologies that can be used in existing seed orchards and indicates directions for new orchards. However, our most severe limitation to developing technologies for producing seed of the highest genetic worth is determining supplemental pollination efficacy. At this time if we use pollen from quality lots of known breeding value we cannot accurately predict how much of the applied pollen will end up as seed.
A major unknown in this process is the effect of competing pollen. We need to complete trials under various pollen loads to develop supplemental pollination techniques that work for western hemlock. When these pollination techniques are considered in conjunction with management techniques already developed, we will be able to design orchard systems that will help us meet our target goals for high genetic worth seed lots. In the meantime, if we vigorously utilize recently developed techniques in existing orchards, significant gains in genetic worth are possible.

Working Paper 44 (part 1) (1001 KB)

Working Paper 44 (part 2) (637 KB)

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Updated July 24, 2015