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Seedling ecology of Garry oaks in British Columbia and dispersal of Garry oak acorns by Steller’s jays

University of British Columbia

Garry oak (Quercus garryand) ecosystems are endangered in southern British Columbia and their management requires approaches that ensure adequate oak regeneration. Garry oak acorns are dispersed in B.C. primarily by Steller's Jays (Cyanocitta stelleri) and therefore regeneration must be considered within the context of where and how acorns are dispersed by jays. I planted acorns at different depths and in different habitats to examine factors influencing survival of acorns and seedlings. Depending on habitat type, predators removed 53-100 % of acorns that were planted on the surface but 10-92 % of acorns buried in ground cover or soil. Predation on buried acorns was extremely high in all habitats with sparse herb, dense shrub, and moderate to high tree cover. Of the acorns that were not predated, > 83 % of buried acorns produced seedlings, but, perhaps because of desiccation, only < 60% of acorns on the surface produced seedlings in most habitats. In most habitats, > 65 % of first-year seedlings survived to their second year. Some habitats that had high seedling emergence had relatively low seedling survival and vice versa. Many seedlings died from desiccation in habitats with thin soil on a south-facing slope. I observed caching of acorns by Steller's Jays to investigate the role of the jays in dispersal of Garry oaks. Steller's Jays cached acorns between a few centimetres to at least 600 m from harvesting locations, and probably transported some acorns more than 1 km. Almost all cached acorns were hidden within ground cover or soil. Steller's Jays preferred to cache acorns in habitats with extensive tree and shrub cover but sparse herb cover. Jays cached approximately one half of their acorns in these habitats, where seedling establishment is low because of high rates of acorn predation and sapling recruitment is likely poor because of shade from dense trees and shrubs. However, half of their acorns were cached in other habitats, some of which provide conditions favourable for oak regeneration. Conservation of Garry oak ecosystems in B.C. must include retention of ecological processes and management at both the stand and landscape levels.

Thesis/Dissertation

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2009-05-23

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http://hdl.handle.net/2429/8085

Forestry

University of British Columbia

UBCV

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