Our seed sources
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.
Seed zone map, Western Red Cedar
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.
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.
Download the DNR seed zones book for more detailed information on tree seed zones for some of the more common tree species in Washington State.