Garry oak

Garry oak (Qg) - Quercus garryana

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Geographic range and ecological amplitudes 


In British Columbia, Garry oak is a tall shrub to small-sized, less often, medium-sized (<30m ) deciduous broad-leaved tree, at maturity with a broad rounded crown, short, stout, and often forked stem, numerous twisted, gnarled, branches, and dark, grayish-brown, scaly bark, with narrow shallow furrows. Garry oak is not grown for timber production in our province. While Garry oak is not considered an endangered species in B.C., there are several ecological communities on the provincial Red List where Garry oak is a dominant tree species.

For more information about species and ecosystems at-risk in B.C., visit the BC Species and Ecosystem Explorer.

Geographic range 

Geographic element:
Western North American/mainly Pacific and less Cordilleran

Distribution in Western North America:
central and south in the Pacific region; (central) and south in the Cordilleran region

Ecological amplitudes 

Climatic amplitude:

(warm temperate) - cool and warm mesothermal

Orographic amplitude:

submontane - montane

Occurrence in biogeoclimatic zones:

Edaphic amplitude

Garry oak

Range of soil moisture regimes:
very dry - moderately dry - slightly dry – (fresh)

Range of soil nutrient regimes:
(poor) - medium - rich - very rich

Based on field studies, Krajina (1969) concluded that soil melanization is more intensive in Garry oak ecosystems than in coniferous ecosystems. The uppermost, dark gray melanized soil horizon in the Garry oak ecosystems is only slightly acidic, and resembles prairie soils in colour, but with no calcification in the B horizon. Under these conditions there is active nitrification, as indicated by the frequent occurrence of Galium aparine L., Geranium molle L., and Dactylis glomerata L., understory species that require nitrate-N for their growth.

Garry oak appears to require large quantities of calcium, similar to bigleaf maple or black cottonwood, and deposits this element in its bark. This is why some calciphytic bryophytes may inhabit the bark of Garry oak trees.


Tolerance and damaging agents

Root system characteristics

Garry oak has a deep taproot and well-developed lateral roots, thus is very windfirm. Roots are associated with ecto- and endo-mycorrhizae.


Tolerance to Tolerance class Comments
low light M moderately shade-tolerant in warm mesothermal climates
frost L not a concern in cool mesothermal climates
heat H frequent on warm and dry sites
water deficit H frequent on dry and warm sites
water surplus H tolerates flooding and a strongly fluctuating water table
nutrient (mainly N) deficiency M absent in acid, very poor soils; infrequent in poor soils


Damaging agents

Damaging agent Resistance class Comments
snow L snowfall is very low in the CDF zone
wind M high winds will break boles and branches rather than uproot trees


  Risk class  
fire L fire-resistant, except in the early developmental stage
insect L not a serious concern
fungi L not a serious concern (root and butt rots)

Associated tree species and successional role

In British Columbia, Garry oak grows in small, open-canopy stands or mixed-species stands, typically with common douglas, less often with Pacific madrone on warm-aspect, water-deficient sites on southeastern Vancouver Island and the Gulf Islands. It is present in early, mid-, and late stages of secondary succession and can be present as a minor or major component in old-growth stands on a few sites in the CDF zone.


Silvical characteristics

Characteristic Interpretive class Comments
reproduction capacity M reproduces also vegetatively from dormant buds on cut stumps and root collars
seed dissemination capacity L very low
potential for natural regeneration in low light L low light conditions do not exist in Garry oak stands
potential for natural regeneration in the open H providing the presence of exposed mineral soil
potential initial growth rate (<5 years) L varies with soil moisture availability
response of advance regeneration to release na advance regeneration does not develop in the absence of adequate light and seedbeds
self-pruning capacity in dense stands L dense stands are very infrequent
crown spatial requirements H very wide crowns
light conditions beneath closed-canopy, mature stands H associated with well-developed understory vegetation
potential productivity na non-crop species
longevity M occasionally >200 years


Genetics and notes


Though Garry oak populations in Oregon and Washington are disjunct and scattered, the chemical composition and morphological characteristics of their foliage are similar. Genetic differences appear to be minor. Garry oak hybridizes with Quercus dumosa Nutt., Q. douglasii Hook. & Arn., and Q. lobata Née.


Although not grown for timber production, scattered trees and open-canopy Garry oak stands are highly valued scenic assets in wildlands, parks, and urban areas. Feasibility of managing Garry oak stands for truffle production is being investigated. More detailed silvics information is given by:

Stein, W.I. 1990. Quercus garryana. Pp. 650-660 in R.M. Burns and B.H. Honkala (technical coordinators) Silvics of North America, Vol. 2. Agri. Handbook 654, USDA For. Serv., Washington, D.C.