Monday, November 21, 2011

Life of an Oak Part 3: seedling to canopy

This is part three of a four part series titled "Life of an Oak".

Root Before Shoot
Oak seedlings thrive in recently disturbed areas.  Whether the disturbance was a result of logging, fire, or diseased caused death of larger trees, oaks establish themselves by taking advantage of the lack of competition with other plants and the abundance of sunlight.  Most oaks start off rather slowly compared to other trees.  Willows, birches, aspens, or cottonwoods put most of their energy into quick above ground growth.  However, these trees later suffer the consequences with a shortened lifespan, maybe 100 years, partially due to smaller root systems.  Oaks however are in it for the long-hall, say three to five hundred years in some instances, and order their life strategy accordingly.  Immediately upon germination oaks begin with this long-term view by putting all of their energy into root establishment.  Even after above ground foliage appears on seedlings or saplings, much of their energy goes into root establishment at the expense of above ground growth.  Extensive well established root systems later in life will benefit the oak with strong hard wood, capable of surviving all but the worst ice storms, fires, winds, and droughts.  Faster growing trees with weaker root systems and softer woods, such as cottonwoods, suffer dramatically from these same natural events.  When an oak sends roots out it claims the soil as its own for the long run.

Slow determined growth emphasizing root and long term establishment is an excellent life strategy.  This strategy is not however without consequence.  Slow growth makes oak seedlings easy targets for Whitetail Deer who love to munch on the new sprouts.  Unfortunately, over population of Whitetails in much of the eastern United States has partially resulted in poor establishment of oak seedlings over the past several decades.  Faster growing trees can quickly out grow young oaks and shade them out.  Fortunately, though oaks prefer lots of sunlight, most are fairly tolerant of some shade.  Too much shade will however, kill an oak.  When partially shaded by faster growing trees, oaks don't change life strategies and try to compete by growing faster.  Rather, in tortoise and the hare like fashion, the slow growing oak continues according to plan.  By slowly out growing and out living the faster growing, weaker, and shorter lived tree the oak eventually prevails.  The oak may suffer in the short run due to faster growing trees, but oaks have a long term perspective.  Often, if low intensity ground fires are present, oaks will not need to wait long to overcome other trees.  While other trees may be killed by fire the thick bark of oak insulates from and resists fire.  Even if a young sapling is killed by the fire the roots remain alive underground ready to sprout soon after the fire.  Very few tree species have both the ability to resist flames as well as resprout from roots.
Fire killed oak sapling.  This young trees roots still survive underground and will sprout next spring.
Fire and Resprout
Young oaks can be killed back by fire and resprout many times.  The larger an oak grows the thicker its bark becomes making it increasingly resistant to ground fires.  With time, oaks overcome both competitor trees and fire.  As the oak continues to grow it continues to take advantage of ground fires as they eliminate competing trees and replenish the soil with nutrients.  Once an oak is around five years old it is very likely it will survive to old age, only a fraction of a percent survive even to this age.  At this stage the tree has earned the ground it has slowly but surely taken, as most of the predators, fire, insects, and competing trees have been overcome or will be overcome in a matter of years.  The slow but steady path of growth will continue and the oak tree will become increasingly a landscape landmark.

After twenty or so years, the young acorn sprout makes its way back to the canopy.  The severe struggle against the forces of nature are overcome and the oak enters the next stage of life.

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