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Provenance
(Seed Source)
Provenance refers to the geographical origin of the seed or
cutting used in propagation. It is important since it can have a direct effect
on plant vigor and survivability.
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Western Red Cedar seed zone map |
Plants with a provenance that is similar to the planting site
will often grow better. Tree Seed Zone maps (DNR map) have been published
for use in the forest industry for forest species. Areas of provenance are less
defined for deciduous / hardwood species, for which differing schools of thought
exist.
One states that plants should be propagated from seeds and
cuttings that originate in the same watershed as the planting site. There is
ample evidence that maintaining provenance on this level results in increased
vigor and decreased mortality, but at increased time and money. A minimum lead
time of 3 years is required to acquire the appropriate seeds and grow them to
size. The cost of conducting custom seed collections, propagating and growing
small site-specific lots result in seedlings that are more expensive.
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WSDOT Ecoregions Map |
A less restrictive definition bases a plants provenance upon
ecoregions of the Northwest. Ecoregions are regions with broad environmental
similarities such as temperature and precipitation. There are 7 recognized
ecoregions in Washington (Coastal, Puget Lowland, West Cascades, East Cascades,
Columbia Basin, Blue Mountains, and Northern Rockies). Most plant materials
grown at the PMC follow the ecoregion concept of provenance. It provides plant
materials that are suitably adapted to the general climate of the planting site,
at a reasonable cost, in substantial quantities. It is understood that many
planting projects occur within a time frame far too limited for custom
propagation.
Most of the
seeds, transplants and cuttings used at the PMC are source identified,
meaning that the origin of that material is identified and tracked through
harvest. This information is usually listed on plant availability sheets. The
PMC does its best to ensure that districts and cooperators are receiving the
most genetically suitable plant material possible.
DNR Seed Zones Webpage
- This website has maps and descriptions of the seed zones for some of the more
common tree species.
Page last updated -
08/18/05
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