Friday, August 17, 2012

Life of a Maple Tree: Part 1 Seed to Sprout

I'll be starting a new series on the blog about the life cycle of the maple tree, specifically the sugar maple.  This is sort of a follow-up to the series on oaks and hickory trees.  Maples are sort of a logical follow-up to the oak-hickory forest being they are later successional species to the oaks and hickories.
Sugar Maple leave

The life of a maple tree begins with the charismatic "whirlybird" seed which fall like helicopters from the mother maple.  Often masses of these seeds will blow off of mature maples and twirl to the ground on windy fall days.  Technically, these "whirlybird" seeds are called samara, which are simple seeds with a flattened papery wing-like portion.  The whirlybird nature of these seeds helps the wind to carry them a long to new locations, often hundreds of yards away.  Then hopefully, the seed will be able to sprout and develop into a new tree.

Once on the ground, the maple seed prefers moist and undisturbed locations, such as in a maple forest or an oak-hickory forest that has not been disturbed by fire.  This is because the maple seed is not well protected.  While the wing portion of the samara is good for transporting the seed with the wind, it doesn't do much else.  The seed requires a moist area, and is easily killed by damage from trampling animals, dehydration, or heat from fire.  Once on the ground though the seed becomes actively searched out for by numerous small animals such as rabbits, squirrels, and mice.  Predation really isn't too much of a problem though, the maple tree typically produces so many seeds that it overwhelms predators.  Predators have plenty to go around and there are still plenty of seeds left over to germinate and sprout. 
Sugar Maple samara seeds.
If not found by seed predators on the ground, the seed than requires the cold of winter in order for it to germinate.  Without cold, the seed will not germinate.  Many species of trees, such as oaks, have a difficult time establishing themselves in soil covered with a thick layer of leaves.  Oaks therefore require the ground to be disturbed by fire so their acorns can sprout and grow.  The maple however, does not have this problem and prefers undisturbed forest ground cover, often thickly covered with dead leaves.  Once germinated, the root easily penetrates through thick moist layers of leaves from the previous year. 

Another oddity of the maple is that it prefers shade.  The maple does not like competition with other small plants such as grasses and shrubs.  It does to quite well though when growing under the canopy of mature trees that shade-out other plants.  In-fact, maple seeds germinate and grow best where there is 50 percent or more shade.  In these areas tiny maple seeds can sprout by the thousands, often leading to a carpet of young maple trees.  The problem though is, once germinated there is so little light in these areas the trees will not grow very large and growth will be stunted.  Again though, the maple is adapted to this situation, being able to survive, but not grow, in minimal light retirements for many years.  The tiny stunted tree simply waits until older larger trees casting shade on the forest floor die.  Once these larger trees die, the tiny maple tree grows rapidly in the new sunlight. 

During the potentially long period of time that a maple seedling remains a small stunted tree it is important that the forest remains undisturbed.  Fire and drought both will easily kill these seedlings.  Predators, such as deer, also heavily browse on "carpets" of small maple seedlings.  Usually though, plenty of seedlings survive predation with drought and fire being the big killers. 

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