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BC Conservation Data Centre: Conservation Status Report

Fraxinus latifolia
Oregon ash

Scientific Name: Fraxinus latifolia
English Name: Oregon ash
Provincial Status Summary
Status: SU
Date Status Assigned: April 30, 2023
Date Last Reviewed: April 30, 2023
Reasons: Fraxinus latifolia is found in a small number of native populations and there is a lack of gene flow that exists between them. For this species to decline so significantly from its apparent abundance 4000 years ago suggests there are additonal unknown threats contributing to its decline outside of habitat loss and reproductive isolation. Further research is required to determine if existing populations are successfully reproducing.
Range Extent: E = 5,000-20,000 square km
Range Extent Comments: Fraxinus latifolia occurs over 8374 sq km in BC.
Area of Occupancy (km2): EF = 26-500
Area of Occupancy Comments: Using index of area of occupancy and distribution over 2km by 2km grid cells, this species occupies eleven 4 sq km (44 sq km).
Occurrences & Population
Number of Occurrences: B = 6 - 20
Comments: As of March 2012 the total number of known occurrences is 13. Only 2 of the populations (Macktush Creek Estuary, Port Alberni and Normandy Creek, Saanich) appear to be of native origin. The origin of the other populations existing within the urban interface in Victoria and Duncan was the source of much speculation by Brayshaw and others working on this species. However these populations occur in landscaping and along road margins where they are unlikely to be viable anyway.
Number of Occurrences with Good Viability / Ecological Integrity: B = 1 - 3
Comments: Number of EO's with good viability remains unknown. Most records of this species do not provide details on stand size, sex ratios or levels of regeneration. The Normandy Creek occurrence it the largest but it is unknown whether it is of sufficent size to be capable of long term vaiblity, changes in hydrology may eventually negatively impact this population. Most populations are very small and occur in landscaping and along road margins where they are unlikely to be viable.
Number of Occurrences Appropriately Protected & Managed: A = None
Comments: 3; Two occurrences occur in municipal parks managed by the Capitol Regional District. A third occurrence is protected in Pacific Rim National Park.
Population Size: U = Unknown
Comments: Most of the records have either no population data or are colloquial reports of single trees and thus it is difficult infer the extent of the search effort by the surveyor or the suitability of surrounding habitat. Thus, the described population sizes may be incorrect.
Threats (to population, occurrences, or area affected)
Degree of Threat: Moderate and imminent threat
Comments: [B] Urban expansion and logging are the primary threats in the Cowichan and Alberni Valleys where possible remnant populations may still remain. Some populations are connected to stream courses or near estuaries and thus my be impacted by changes in hydrology and drought years. Fungal and viral pathogens may also pose a potential risk to the health and reproductive success of this species. Herbivory by deer and rabbits (which are currently in rapid population booms) and shading by invasive species (i.e., Phalaris arundinacea) could be seen to likely impact juvenile trees.
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: U = Unknown
Comments: Small incremental increases in the number known populations are likely as search efforts and awarness of rare species expand onto private and First Nation lands. Overall the species lacks occurrences with enough individuals to maintain adequate genetic diversity. At this point it is unclear whether there is any successful recruitment occurring even within the largest of the known populations (Normandy Creek) an area with little suitable habitat left for this process to occur at all. Study is needed to assess any effect of unsuccessful recruitment on population sizes as older individuals senesce and die.
Long-Term Trend: U = Unknown
Comments: Based on sediment cores and pollen analysis (R. Hebda et. al Marine Geology 174: 211-226) it would appear that over a large time scale that wild populations of F. latifolia in British Columbia have been in significant decline. It is unclear whether that decline is the result of broad scale climate change, succession or urban development, or a combination of these factors on southern Vancouver Island. This past decline suggests a trajectory that may be continuing from the present time into the long term.
Other Factors
Intrinsic Vulnerability: A=Highly vulnerable
Comments: Fraxinius latifolia appears to have high intrinsic vulnerability. Small isolated populations are all that remain, possibly now with insufficient connectivity to interbreed. Most occurrences are thought to be limited to single trees or only small groups of trees that may be all of one sex, and these may contribute nothing to the long-term maintenance of F. latifolia in British Columbia.
Environmental Specificity: C=Moderate. Generalist or community with some key requirements scarce.
Comments: In British Columbia Fraxinus latifolia occurs in stream courses, tidally influenced estuaries, lawns and along urban streets. At least among the B.C. occurrences there is a broad range of soil types and moisture regimes occupied. However, in Oregon and Washington, where F. latifolia populations are expansive and numerous in more abundant suitable habitat, occurrences are predictably found in and around wetlands.
Other Rank Considerations: Two additional Fraxinus species F. excelsior and F. pennsylvanica have been introduced into urban and suburban environments where F. latifolia is known to occur. Reports should be verified from collections of leaves, twigs, buds and samaras when possible.
Information Gaps
Research Needs: Studies of reproductive success among existing populations are required to assess short and long term trends for this species. Monitoring the health of existing occurrences for fungal and viral pathogens should also take place at regular intervals to determine if British Columbia populations may be at risk. Additional research may study more closely the role F. latifolia plays in the ecosytems they inhabit and if there are any species that are dependent on F. latifolia for their survival. Elsewhere in its global range, F. latifolia is known to be an important substrate for diverse communities of lichens and bryophytes, some of which are globally rare.
Inventory Needs: Additional surveys of the Discovery Islands, Gulf Islands, Cowichan and Chilliwack Valleys should be done to determine the veracity of informal and historical accounts of this species from those areas.
Protection: With strong threats from urban expansion, timber harvesting and succession every effort should be made to secure protection on properties with any new and especially large occurrences.
Management: Populations of Fraxinus latifolia should be managed to ensure suitable habitat is available for population-sustaining recrutiment of new individuals. Some effort should be made to ensure as much connectivity as possible exists between known populations to maintain the most natural levels of gene flow possible.
Author: Bjork, C. & R. Batten
Date: March 29, 2012
British Columbia Conservation Data Centre. Botany Program. 2000. Database containing records of rare plant collections and observations in the province of British Columbia.
Pellatt, M.G. R.J. Hebda, and R.W. Matthews. 2001. High-resolution Holocene vegetation history and climate from Hole 1034B, ODP leg 169S, Saanich Inlet, Canada. Marine Geology Vol. 174 pages 211-222.

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Suggested Citation:

B.C. Conservation Data Centre. 2012. Conservation Status Report: Fraxinus latifolia. B.C. Minist. of Environment. Available: (accessed Oct 3, 2023).