Garry oak
Quercus garryana Dougl.

Introduction

Garry oak is a small- or medium-sized, long-lived tree that grows in both small, open-canopy mono-specific stands and in mixed-species stands. It is most frequent on dry, rich soils. Its deep, extensive root system makes it very wind-firm and helps stabilize steep slopes in watershed areas. Garry oak is drought-resistant, flood-tolerant, and a highly valued ornamental (Burns and Honkala 1990; Howard 2002). Several root and butt rots are damaging Garry oak. With the exception of acorn-feeding insects, insect damage is usually not severe. The grasslands associated with Garry oak provide forage and nesting cover for many birds and animals (Glendenning, 1944; Howard, 2002). Garry oak is considered an endangered species throughout most of its range. It is regenerating poorly and many oak woodlands are being invaded by conifers (Glendenning 1944; Habeck 1961; Howard 2002). Garry oak woodlands are climax forests in the presence of fire, but seral to conifer forests in its absence. In order to increase Garry oak populations, competing conifers have to be removed by burning or other methods (Howard 2002). Garry oak is fire resistant as an older tree, but vulnerable in the early developmental stage. In British Columbia, Garry oak is threatened because its habitat is mostly in areas under rapid urbanization. Sudden death resulting from a Phytophtora disease is a growing problem for oaks in California (DeFrancesco 2001), and may become a problem for British Columbia in the future. The acorns of Garry oak were eaten by some groups of the first peoples (Turner 1995). The wood was used as fuel and for making tools (Turner 1979).

The natural range of Garry oak stretches down along the coast from southeastern Vancouver Island and the Gulf Islands to central California (Little 1971). As such, the majority of the range is in the United States.

Distribution and Protected Areas – from Hamann et.al. 2005

Conservation Status Summary – from Chourmouzis et.al. 2009

No in situ conservation concerns were identified for this species.

Reproduction

Garry oak is wind pollinated, monoecious and self-incompatible (Burns and Honkala 1990; Howard 2002). Seed crops are heavy but irregular; two to three years apart (Banerjee et al. 2001). Acorn predation is high and mast fruiting may be an evolved strategy keeping predator populations low (Fuchs 1998). Steller’s jays (Cyanocitta stelleri) are the primary dispersers of Garry oak acorns in British Columbia (Fuchs 1998). Garry oak needs exposed mineral soil for regeneration. It will also re-sprout from dormant buds on cut stumps and from roots (Taylor and Boss 1975). The relative contribution of vegetative regeneration methods to within-stand recruitment is not well understood (Agee 1993). Oak regeneration is a common problem around the world, and the contributing factors vary by species, location and year. Some of the most damaging insects to acorns are introduced rather than endemic pests (Fuchs 1998).

Genetic structure

Garry oak hybridizes with four other oak species in California (Tucker 1980) but not in British Columbia, where it is the only oak species. The oak populations of Washington, though disjunct and scattered, have similar chemical and morphological characteristics for foliage (Taylor and Boss 1975). Voeks (1981) thought that current oak distributions reflect periodic occupancy of refugia. Hebda et al. (2000) found that current oak distributions largely reflect movements in response to climate change. Edwards et al. (2000) gathered isozyme data across the range of Garry oak and found considerable genetic variation. Ritland et al. (submitted) performed a detailed analysis of these data, finding values of 0.17 for expected heterozygosity and 1.84 for the number of alleles per locus, about one half of the values found for other white oak species, indicating close adaptation. Inbreeding was very low. Populations clustered in two groups: Washington – Oregon and Vancouver Island – Gulf Islands. The difference between the northern and the southern group, however, is not very large. Two mainland BC populations appear to have anthropogenic origins, being quite different and genetically more depauperate.

Resource management and seed transfer

Populations of Vancouver Island and the Gulf Islands are closely related, and transfer of genetic material would not alter the current genetic structure (Ritland et al. submitted).