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Land and Watershed Management
Genetic and Silvicultural Foundations for Management
Oak Root Research
Although much of our oak research is occurring aboveground, we are also interested in what happens below ground because understanding the morphology (size and distribution) of oak roots may help us understand tree responses to environmental factors or to management activities. For example:
We conducted a study in 2003 to document the root morphology of Oregon white oak growing on the rocky soils common in the south Puget Sound area (our oak were growing on the Spanaway series). In this study we used an Air-Spade® (http://www.air-spade.com/index.html) to excavate the root systems of oaks ranging in above-ground diameter from 1 to 57 cm.
Most of the oaks had a central taproot, but the size, taper, and orientation of the taproot varied widely among trees. The majority of the lateral roots were located within 40 cm of the surface where the soil contained fewer rocks, was finer in texture, and thus, had greater water-holding capacity than deeper soil layers. The vertical penetration of roots was partially to totally restricted by an extremely gravelly soil horizon that began at a depth of approximately 70 to 80 cm. Very few roots penetrated beyond a depth of 150 cm. Thus, the oaks we studied were competing for water with shallow-rooted trees, shrubs, and herbaceous vegetation. They were likely drawing little water from deeper soil horizons.
For views of roots of some other species of western oaks, see
roots of a large oak with a decaying Douglas-fir stump in the foreground.
The oak taproot tapers off rapidly around a depth of one meter (scale
in photo is a meter stick). Most of the large lateral roots are near the
surface of the soil where the texture is finer and more soil water is
roots of a 25-year old oak tree. The taproot turns sharply about 80 cm
below ground and then grows horizontally, likely in response to a rocky
Often, oaks were relatively young sprouts from older, sometimes well-developed
root systems. When the aboveground part of an oak is killed by fire, the
roots can survive and sprout new stems.
USDA Forest Service - GenSilv Team