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.

Life of an Oak Part 2: from acorn to sprout

These charred branches are evidence of ground fires in this Oak Savanna.

Fire and the Young Oak
Just prior to and after winter, oak woodlands historically experienced another form of harsh natural selection.  Just when life appears to be as hard as it gets, fire enters the picture.  In the fall before snow fall and early spring after snow melt, the ground is covered with a large supply of flammable dead vegetation.  Oak trees themselves contribute significantly to this fuel with their crunchy leaves covering the ground.  This dead vegetation historically has supported low intensity ground fires across the prairies and bordering oak savannas and woodlands.  Amazingly, most oaks are highly adapted to this type of fire, and anywhere you find fire disturbance you will typically find oaks.  Native Americans and many early European settlers throughout the eastern United States liberally utilized fire for a number of purposes.  In-fact, prior to any European impact Native Americans utilized fire so frequently and on such a large scale that essentially none of the Eastern or Midwestern landscape can be considered without human disturbance.  The general attitude seems to have been when in doubt, burn it.  The thinking went something like this: I want an open forest, lets burn this area.  I want more berry and fruit production here, lets burn it.  I want to create a fire break for the village, lets burn the area surrounding the village.  It would be easier to gather nuts or wild ground bird eggs if there wasn't so much vegetation, lets burn it so we can find these easier.  Prairie and forest floor fires had the added benefit of cooking the eggs also, making them ready to eat.  I want to create better habitat for game animals, burn it.  We need to herd some animals to make the hunting easier, lets round them up by burning them out.  Lets clear the land so we can plant a garden, better burn it.  There are too many snakes and ticks in this area, lets burn it.  And the list goes on.  Scientists have found that fire returned to areas anywhere from every two to 11 years.  Most of this burning was human started for the purpose of benefiting the landscape.  Very few of these fires were "natural" lightning started fires.

A recently burned oak savanna in Eastern Iowa.

Fire was amazingly effective in accomplishing all kinds of positive effects on the prairies, woodlands,and savannas; and oaks always followed right behind these fires.  As fire goes, so goes the oak, or any other tree for that mater.  While most trees are killed by fire, many upland oaks greatly benefit from ground fires.  Shortly after fall fires, Bluejays will begin caching acorns from nearby forests in newly burned areas.  Even if caches are made just before an area burns, low intensity ground fires cause very little harm to these acorns being they are protected underground.  Insect predators, such as Acorn Moths and weevils, are nearly eliminated in burn areas, greatly increasing acorn viability.  Fires also clear thick overhead vegetation, decrease surface soil moisture, and kill seeds deposited on the surface.  This allows for the full sun oaks require for establishment as well as lack of competition they thrive on.  Other tree seedlings typically require higher soil surface moisture for establishment or are killed by fire while oak acorns are safely buried just under the surface, and have access to soil moisture.  Even with very little soil moisture, the large acorn seed is capable of sprouting and sending out a thick strong taproot to search for moisture.  Very few plant seeds have this ability to germinate and survive such low moisture conditions.

This young oak tree has four stems coming from one original stem that was burned in a fire during a previous year.  The four stems showing in this picture were killed by a surface fire this fall but the root remains alive and will sprout next spring.

Sprouting
The cache is an ideal acorn hiding spot where they can snugly wait the winter out.  A few acorns, such as those from White Oaks, will sprout within weeks of falling of the tree in the fall and occasionally even sprouting on the tree.  This gives them a head start come spring and helps them avoid seed predators.  Bluejays or squirrels returning to a cache for a dinner of White Oak acorns, will likely be very disappointed when they find unappetizing sprouting acorns.  Most acorns however wait for snow melt and spring temperatures before germination, requiring exposure to cold before they are even able to germinate.  Once germination starts the seedling immediately puts all its energy into producing a thick taproot that can grow to six inches or more before any greenery sprouts above ground.  Establishing a healthy root system helps ensure the longevity of the plant as well as prepares it for future fires.  When fire does burn through an area, established seedlings may be top killed but thick healthy roots remain safe underground and can quickly sprout new stems.  In general, the thicker and larger a root system the more likely it will survive a top killing fire.  Quick recovery and growth after fire allows oak seedlings to out compete other plants, ensuring survival.

Fall in an eastern oak woodland.

Life of an Oak Part 1: life as an acorn

A White and Red Oak forest in Eastern Iowa.

This is the first of a four part series on the life cycle of oak trees in the eastern upland deciduous forest.

Hiking though the cathedral like upland forest normally gives us no impression of the journey those trees took to where they are today.  Towering trees give the impression of quiet permanence, as though they have always been there and always will.  This path operates on a different time frame from what we do, years or perhaps seasons as apposed to our hour and minutes.  Very very few people actually are privileged and patient enough to observe this process, let alone live long enough.  The journey from seed, to seedling, to sapling is not survived by many.  It is a long, difficult journey back to the canopy.  Each tree species has a particular preferred route from the ground to the canopy programmed into their DNA.  Any deviations from this DNA program prove fatal for the vast majority of seeds, seedlings, and saplings.  Even when everything follows pre-programmed genetic pathways, the vast majority do not survive, falling to predators or the abundance of natural hazards filling the woods.  But slowly and surely, some do survive, and some do produce seed to start the whole cycle over again.

Pin Oak leaves and acorn.

The Mighty Oak and Vulnerable Acorn
Mighty oaks are revered in every culture they are found as symbols of strength, royalty, high rank, endurance, and even deity.  It is easy to see why when gazing upon a mature oak tree, and it is easy to forget this oak was once an acorn among thousands or millions of similar acorns.  Life as an acorn is quite simple, growing on the mother oak for a year or two, depending on the species, and then making the short quick journey from mother to ground.  This fall is quick and easy but the return is long and difficult, exceedingly few survive.  Once on the ground the acorn finds itself in a rather non-ideal location under its mothers canopy.  Shade from the mother plant can limit growth of young oaks and competition of roots between the plants can end up hurting both mother and child, but primarily child.  So what's an acorn to do?  It can't roll itself to another location and its too heavy blow in the wind.  At the same time often 90 or more percent of these acorns will become infected by insects, bacteria, or fungi, causing them to rot long before they ever have the chance to germinate.  On top of that, deer, turkey, chipmunks, squirrels, and birds of all types literally flock to oak trees each fall, gorging themselves on calorie rich acorns in preparation for winter.  From a practical standpoint none survive this magnet like attraction to acorns.  Literally, searching a forest floor the following spring or even a few months after the initial fall, likely not a single viable acorn will be found.  The food source is simply too valuable for wildlife to leave alone.

The Blessing and Curse of Predators
But with the curse of wildlife gorging themselves comes deliverance.  While deer and turkey consume acorns as soon as they find them, this is not true of all wildlife.  Chipmunks, squirrels, and certain types of birds gather and hide huge numbers of acorns in caches to get them through winter.  Squirrel and oaks seem to be particularly fond of each other.  Squirrels sneak around under oak trees hiding from predators, searching out acorns.  Often acorns hidden under foliage are the first to be gathered.  Foliage that hides acorns also hides squirrels from hawks flying overhead, thus oddly, hidden acorns are not hidden at all from seed loving rodents.   But as squirrels eat they also gather and hide many acorns by burying then in secret locations for winter feasting.  Oddly, Red Oaks appear to encourage both eating and caching of acorns by squirrels at the same time.  Top portions of Red Oak acorns are sweeter while bottom portions have higher proportions of bitter tannins.  Squirrels will bite in, eat the top portions, but leave the bottom behind.  Interestingly, these bottom portions contains the embryo, and even without a top portion the seed can easily germinate and grow, so both oak and squirrel have their nut and eat it too.  Cached acorns are often buried in location away from trees and in open areas ideal for oak seedling growth.  The often forgotten caches later germinate, potentially growing into trees.

Bluejay, picture from allaboutbirds.org

Acorn Snobs
Bluejays and oaks also have a particularly close relationship.  These loud and aggressive birds are like snobbish connoisseurs of the acorn world.  Nothing gets in the way of a Bluejays acorns, and if something does the bird lets it be known loud and clear.  Depending on their mood, nothing is too big for the Bluejay to squawk at or try and chase off.  These birds are quite opinionated, and quite entertaining to watch, as long as you are not the one they are squawking opinions at.  Jays are excessively efficient at what they are designed to do, which is gather and cache large seeds.  Jays have the ability of gather nearly all acorns fallen from a tree within days, without the help of other wildlife.  And true to their connoisseur title, only the best, most viable acorns are gathered.  Jays examine, peck, shake, and weigh acorns in their beaks.  Acorns meeting their high standards are then stored temporarily in their expandable esophagus.  Several acorns can be stored this way and transported quickly to distant locations for caching.

The Bluejay cache is the ideal location for acorns.  High quality seed, buried in the dirt, hidden from predators, in areas away from other trees, like any master gardener would do it.  Most caches will be relocated by the jay and eaten during winter, but many will be forgotten or simply not used.  Some oaks such as the white, prevent their acorns from being eaten by germinating within days of being cached.  Others survive the winter hoping they are lost or not needed by the jay to get through the winter.  Come spring however, the acorns readily germinate, potentially expanding the oak forest.  Very few acorns actually get to the stage of germination, and of the few that do germinate most don't continue much past seedling stage.  Life as an acorn is passive and easy, if survived.  No real work is ever done by the seed.  But with germination begins the work as the tiny oak begins its climb back to the canopy.