Effects of Habitat and Landscape Structure on Oregon White Oak (Quercus garryana) Regeneration Across an Urban Gradient

Oregon white oak (Quercus garryana) woodlands are the focus of intensive conservation efforts. However, little is known about regeneration in protected oak stands, particularly in small stands surrounded by residential and commercial development. This study investigates the relationship between habitat and landscape structure and patterns of oak seedling and sapling abundance. Specifically, I ask whether patterns of oak seedling and sapling abundance reflect the habitat preferences of animals that disperse acorns and whether seedling and sapling abundance differ in urban versus non-urban landscapes. I conducted vegetation surveys within 30 oak woodlands with natural understory distributed across a gradient of urban development. I used general linear mixed models to determine relationships between oak seedling and sapling abundance and habitat and landscape features. Seedling and sapling patterns showed different relationships to habitat and landscape structure, suggesting that different factors mediate the transition between each stage. I found that seedlings are most abundant under oak and non-oak forest canopy and least abundant under no forest canopy, possibly reflecting dispersal patterns. I found no relationship between seedling abundance and urban development, but young saplings show a negative relationship with urban development. These results suggest that seed dispersers influence seedling spatial patterns, but that this influence is reduced in later life history stages. Although urban development is not related to seedling production, young sapling abundance was significantly lower in urban landscapes. Improved understanding of how habitat and landscape structure influence forest regeneration processes is needed in order to create effective forest restoration and management plans.


For more articles from the Spring 2011 issue of Northwest Science please refer to the link below:

The Future of Restoration and Management of Prairie-Oak Ecosystems in the Pacific Northwest