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Canada Yew: Not a traditional forest product
A new, non-traditional forest product industry has been gradually creeping east from the Maritimes into Ontario. Recently there has been increased interest from several biopharmaceutical companies seeking to harvest Canada yew (also known as ground hemlock) from private woodlots in Ontario. The potential of this new, non-traditional forest product centres on a natural substance derived from yew that has been proven useful in the fight against cancer.
Aboriginal people have used Canada yew (Taxus canadensis) for medicinal purposes for generations. However, the recent discovery that this shrub contains compounds (e.g., paclitaxel) in its leaves and bark that can be used to make anticancer drugs has sparked new interest. Paclitaxel, also referred to as taxol 1, is a taxane that prevents the growth of cancer cells and has become a cornerstone in cancer therapy.
In 2003, taxane products registered worldwide sales in the amount of $4.2 billion US. With sales expected to continue to climb, there are concerns that if not managed correctly, the increased interest in harvesting Canada yew may affect the sustainability of this species.
Characteristics
Canada yew or ground hemlock prefers to grow in the shaded understory of upland tolerant hardwood forests and in moister mixed hardwood/conifer forests. However, it will also grow in more open spaces such as plantations. It is a low-spreading evergreen shrub that seldom exceeds 2 m in height. The needles are flat (1 to 2.5 cm in length and 1 to 3 mm in width), with a distinct point and are arranged in a spiral fashion around the branch. The upper surface of the needle is dark green; the underside is a paler green colour.
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This photo illustrates the flat needles and flat-appearing branches of Canada yew.4
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The needles and seed of the Canada yew are considered poisonous. However, the fleshy red berry is edible and is sweet tasting. The Canada yew is an important source of food for wildlife such as deer and moose.
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In 1999 researchers at Natural Resources Canada, Canadian Forest Service (Fredericton) and the PEI Department of Agriculture and Forestry developed the first set of harvesting guidelines for Canada yew for use in Atlantic Canada. Since this time, new knowledge and information about this species has been gained, and the guidelines were revised in April 2002.
While harvesting guidelines have not yet been developed specifically for Ontario, forest researchers say the guidelines developed for Atlantic Canada (below) can be followed by landowners in Ontario.
Minimum standards for harvesting ground hemlock (revised April 2002) 3
If you are considering harvesting yew foliage to sell, you should take a moment to read the following background information.
These guidelines have been developed using results from pruning trials conducted in Atlantic Canada by staff from the Provincial Department of Agriculture and Forestry on PEI and the Canadian Forest Service, and by collaborators in Quebec. These guidelines represent the fifth version since the first draft was released in May 1999. The number of revisions reflects efforts to incorporate new knowledge and information as soon as it has become available.
Members of the Eastern Canadian Ground Hemlock Working Group 2 support the use of these guidelines as the minimum standard for harvesting.
I. When to harvest?
Although harvesting can be done throughout the year, there are several factors to consider that affect the quality of the material, the costs of harvesting, and equally importantly, how the plants will respond. Taxane yields are generally higher in dormant than in actively growing shoots. If your purchase arrangement is based on a sliding scale (e.g., higher selling price for higher taxane content) then the recommended time to harvest will likely be from late August to March/April when the plants are dormant. From December to March snow cover will usually prevent you from harvesting. In the early spring access to harvest sites may be limited by road conditions.
II. What trees to harvest?
Only harvest branches from plants (stems) that are 1 metre (36 inches) or more in height. This minimum plant size is recommended to help ensure that plants have a minimum vigour prior to harvest. Adopting the minimum size increases the likelihood that heavily browsed or recently harvested plants would be excluded.
III. How much to harvest?
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Harvest the terminal shoot and the two or three most vigorous lateral shoots closest to the top of the plant (see Figure 1). |
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Remove up to three years of growth. On a moderately “vigorous’” branch/plant, current year growth will be approximately 7 to 10 cm. Therefore harvesting three years of growth will typically produce a branch with a total length of 20 to 25 cm. |
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Figure 1 Examples of how much foliage to remove from a given plant stem. NOTE: the amount to be cut = a maximum of 3 years of growth will vary between 15 and 25 cm length. All cuts should be made immediately above the lateral branches. These lateral branches should become “invigorated” in response to the removal of the terminal portion of the branch as occurs in hedges.3
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| 3. |
In ground hemlock, the shoots typically stay green for up to three years. Do not make cuts into the brown woody stem below the third year (see Figure 2). Following pruning, new buds and the shoots that are produced from these buds form close to the cut surface. For plants that are heavily pruned, (e.g., removal of 4 to 6 years of growth) new shoots usually take longer to form. Although there may initially be a large number of new shoots, they typically are very weak and grow very slowly. Measurements from research plots show that when more than three years of growth is removed, new or replacement growth is less than what was previously predicted. |
In ground hemlock, the shoots typically stay green for up to three years. Do not make cuts into the brown woody stem below the third year (see Figure 2). Following pruning, new buds and the shoots that are produced from these buds form close to the cut surface. For plants that are heavily pruned, (e.g., removal of 4 to 6 years of growth) new shoots usually take longer to form. Although there may initially be a large number of new shoots, they typically are very weak and grow very slowly. Measurements from research plots show that when more than three years of growth is removed, new or replacement growth is less than what was previously predicted. |
| IV. How to harvest? |
| 1. |
Use hand pruners. Do not break or tear branches. |
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Regardless of how much you are removing (up to the maximum of 3 years of growth), try to make your cut just above side branches (see Figure 1). This will allow for the lateral branches just below the cut to grow out and replace the removed shoot. Furthermore, new shoots may originate from the tissue located at the nodes and the regrowth from the pruned branch will therefore be quicker and likely more vigorous. |
| 3. |
Leave every fifth stem unpruned.
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Do not reharvest a site for at least 4 years (= number of years of growth removed +1). Note: In previous harvest guidelines, it was recommended to leave at least one stem in every clump intact. This method is still valid. However, identifying individual clumps can be very difficult where Taxus is particularly dense. Therefore leaving at least 1 in 5 stems should be practicable and accomplish the same goal.
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Figure 2. Close-up illustrating how to quickly identify the age of a branch. Cuts should be made close to the base of “3” (= 3-year-old wood) and not into the part of the stem marked “4”.3 |
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Selling Canada yew
Selling ground hemlock or Canada yew is similar to selling standing timber. You have the option of undertaking the harvest yourself or you can make arrangements to sell the harvesting rights to a contractor.
Should you choose to sell the rights to a contractor you will have to do some homework to ensure the harvesting activities are conducted in a sustainable manner and that your assets (woodlot) are protected. Here are some important questions to ask a contractor.
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Is the contractor (and workers) trained in sustainable harvesting techniques? As a minimum standard, they should carry out their harvesting activities consistent to the guidelines noted above. |
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Does the contractor (and/or subcontractors) carry workers’ compensation and liability insurance? Will they provide you with certificates substantiating coverage? |
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Does the contractor (and/or subcontractors) carry workers’ compensation and liability insurance? Will they provide you with certificates substantiating coverage?
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Is the contractor on the job site (daily) to supervise workers? Does the contractor subcontract any of the work out? |
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How will payment be made? Will partial payment be made at the start of operations, or will full payment be made after the harvest has been competed? |
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What type of vehicles will be used in the woodlot to collect the clippings (e.g., ATVs, 4x4 vehicle, etc.)? |
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Who will be responsible for damages should they occur (to roads, fences, gates, etc.)? |
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Does the contractor have good references (check a minimum of two to three references)? |
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Will the contractor provide a written agreement outlining the conditions of the sale (including a map delineating the area to be harvested)?
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Buyers of Canada yew
The following biopharmaceutical companies have recently expressed an interest in purchasing Canada yew in Ontario:
Chatham Biotex Limited: Telephone (506) 854-7253 or visit their Web site at <www.chathambiotec.com> for a list of buyers in Ontario.
Bioxel Pharma: Telephone (418) 654-9666. Web site < www.bioxelpharma.com>.
Footnotes
1 Taxol and paclitaxel are the same. Taxol is actually the trade name for Bristol-Myers Squibb's preparation while paclitaxel is the chemical name. However, the name taxol is by far the most commonly used name when referring to paclitaxel.
2 The Eastern Canadian Ground Hemlock Working Group is comprised of representatives from the federal government, the provincial governments of Quebec, New Brunswick, Prince Edward Island, Nova Scotia and Newfoundland, ENGO and the private sector.
Acknowledgements & Illustration Credits
3 Extracted from Ground Hemlock Harvesting Guidelines Developed jointly by NRCan, Canadian Forest Service, Fredericton, and the PEI Dept. Agriculture and Forestry, April 2002
4 Bill Cook, Michigan State University, UGA 1218072, <www.forestryimages.org>
This article appeared in the Fall/Winter 2004 (Volume 37) edition of the S&W Report the newsletter of the Ontario Woodlot Association.
© Ontario Woodlot Association
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