Monday, November 14, 2011

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
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.

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