Long-term impacts of road disturbance on old-growth coast redwood forests

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College of Forest Resources and Environmental Science


In forest ecosystems, road expansions and other landcover changes create abrupt artificial boundaries that alter the microclimate along the forest edge, potentially impacting growth and physiology of bordering trees. To understand how previous landcover changes and road installations have affected coast redwoods (Sequoia sempervirens), we used dendroecological methods to contrast tree-ring growth patterns and stable isotopes (Δ13C) of redwoods before and after a known disturbance event, the expansion of Highway 101 in the 1950s, that bisected several old-growth stands of Humboldt Redwoods State Park. Increment cores were extracted from redwoods in old-growth stands that bordered the highway and other forest edges (secondary forests and agricultural fields) as well as two control areas. Disturbance detection methods and dendroclimatic modeling were then employed to determine whether the expansion led to growth suppression and elevated water stress. Tree-ring growth data indicated that the construction of Highway 101 disproportionately impacted the growth of trees that were within 30 m of the highway and that these effects were particularly elevated in trees that currently exhibit crown dieback. Similarly, climatic modeling of tree-ring Δ13C data indicated that highway adjacent trees also experienced elevated water stress for several decades following the construction of the highway. By analyzing tree-ring data of redwoods within Humboldt Redwoods State Park, here we provide critical insight to the temporal and spatial implications of the habitat fragmentation and road installation that has been nearly ubiquitous in the redwood distribution since Euro-American settlement.

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Forest Ecology and Management