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Sitka spruce has been an under-utilized tree species for reforestation purposes on the coast due to its susceptibility to attack and damage by the terminal weevil, Pissodes strobi.
Sitka spruce is a valuable, fast growing tree species and is a preferred species for reforestation on many west coast sites. It is particularly useful on sites prone to brush competition and browsing by deer and elk. Meeting stand diversity objectives can also be served by planting more Sitka spruce. Current stocking standards recommend limiting Sitka spruce planting in moderate to high weevil hazard sites. Weevil hazard estimates by biogeoclimatic variant have been developed and are correlated to biogeoclimatic zone variants. This information can be found within the pest risk tables of A Field Guide for Site Identification and Interpretation for the Vancouver Forest Region (page 229) and the Spruce Weevil and Western Spruce Budworm Forest Health Stand Establishment Decision Aids http://www.forrex.org/publications/jem/ISS38/vol7_no3_art6.pdf. Over 30 years of research by provincial, federal and university researchers has uncovered some valuable and heritable natural resistance to the weevil. Populations and individual trees that demonstrate low susceptibility to the spruce weevil have been identified. Seed collections have been made from these naturally resistant stands (class B+ seed) and highly resistant individuals are now included in seed orchards (class A seed). Class B+ seed is currently available and the highly resistant class A seed is ramping up production with the goal of providing seed for 3 million plantables annually by 2012. With the availability of this resistant planting stock, higher stocking levels of Sitka spruce can now be utilized. Three series comprising the F1 breeding program for weevil resistance are now fully established. Parents were designated by their phenotypic resistance to the weevil and their source (mainly Haney or Big Qualicum). Some susceptible parents were also used for controls. The trials were established in the Adam River drainage of North Vancouver Island, Jordan River, South Vancouver Island, as well as on the Queen Charlotte Islands/Haida Gwaii. Selection and breeding work continues but our focus in the future for the breeding program will be to identify parents for specific traits. They will still be field assessed for resistance after weevil augmentation but a more detailed microscopic evaluation is being undertaken in order to classify parents according to putative mechanisms. This is particularly valuable for constitutive resistance mechanisms such as sclereid cells or constitutive resin canals. We are working to extend these techniques to look at some of the inducible mechanisms, particularly traumatic resin canal production. In the past we have relied on the Canadian Forestry Service for entomology expertise and technical support for this program. With changing directions, we expect to rely more on universities, although Dr. René Alfaro, CFS still provides essential input. Ongoing trial assessments for weevil attack have continued, including the hazard assessment trials, which were established to test resistance over a variety of ecological and potential weevil hazard areas. The main objective is to refine deployment guidelines. This exercise will be carried out with the Coast Regional entomologist and silviculturists. Besides the work with weevil resistance, there are two other key research programs. The Queen Charlotte Island/Haida Gwaii program allows us to assess Sitka spruce growth free from weevil attack and supports the Seed Orchard program. Our major difficulty has been in getting free-growing conditions in this area that suffers heavily from deer browse - a good deal of our maintenance effort is on browse protection. The transition program is in northwest B.C. in the area where Sitka naturally hybridizes with white spruce. It is designed mainly to test seed transferability in a very environmentally heterogeneous area with pressures from both frost and weevil. Major recent articles published include: King, J.N. and R.I. Alfaro. 2009. Developing Sitka spruce populations for resistance to the white pine weevil: Summary of research and breeding program. B.C. Min. For. Range, Res. Br., Victoria, B.C. Tech. Rep. 050. King J.N. and Alfaro R.I. 2004. Breeding for resistance to a shoot weevil of Sitka spruce in British Columbia, Canada. In: Carson, M.J., C. Walter eds. Plantation Forest Biotechnology for the 21st Century. 2004 Forest Research, New Zealand. King J.N., Alfaro R.I. and C. Cartwright. 2004. Genetic resistance of Sitka spruce (Picea sitchensis) populations to the white pine weevil (Pissodes strobi): distribution of resistance. Forestry 77:269-278.
Ministry Contact: Alvin Yanchuk |
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