In grabbing at all available light, the canopy becomes the dome for the tree's biosphere.  The arch shape giving maximum surface area for light, carbon dioxide absorption, water               etc.  This biosphere cap serves many functions to staking and protecting a tree system's territory.  The canopy and the mulch/Soil Protection work together many ways to keep down competing seedlings by starving them for resources.  This maintains more resources for the trees inside the biosphere.  sometimes even favoring the forest system's own pollen (over foreign pollen's interfered with by the canopy seal), to acclimate a family of trees to the local region more over the generations.
Water Delivery
	We must look at the outermost reach on top and the slant down/trail underneath the canopy as 2 different factors.  Here, the canopy's outermost reach, is also a downward trail for water.  A Smart Canopy delivers water wide, as it's umbrella slants down and stretches.  This puts less water shallow under the canopy and close to the trunk.  This limits growth of competing seedlings close tot he tree.  Also, this draws the roots out wider; thus gives more leveraged strength to the tree's support.  The maximized canopy also  has more transpiration, needing more water, causing the roots to chase water more.  This need gives better rooting, along with the other canopy functions; as part of a system plan.
	The water delivery favoring the extremes of wide and deep, encourages roots reaching towards these extremes for the water source, as it keeps other growths water starved.  The farther the horizontal distance from the trunk for the roots, the more leverage of support the roots gives the tree.  The horizontal reaching roots can't get all their water just out of their reach, so have to chase it deep too.  The deeper roots vertical length, give more strength to grab and "Hold" to soil.  The support comes from the deeper grab at the soil giving greatly more hold at the soil for that root; which is then multiplied by how far the root is from the trunk.  So the farther across reach X deeper reach gives tons more leveraged support, just by proper the water delivery.
	A trimmed canopy, shortens the reach, but also changes the angle of the run of the branches too many times.  The water following down, then would stand more of a chance to delivering in closer to the trunk than even the shortened canopy.  This delivers close, but also, to more developed roots, that can absorb more water before having to chase it so low.  This allows roots to not reach out for more leverage, or deep for more holding power.  Giving a short ball of roots.  People over watering , especially frequently enough to keep grass alive gives similar results, though perhaps with wider root stretch.  The light can come underneath the canopy easier to encourage growth to nutrient competing grasses, seedlings etc.  Especially with the shallower water supply.  In 1 move 2 functions limiting seed competition have been compromised inside the tree territory, underneath the canopy biosphere.  This is really the mighty tree's territory, grass has no place on the feeding grounds.
	Mechanically: The trees in woods will  touch or nearly touch, to support and or restrict movement at the tops; giving leveraged support far from the only connection at the ground.  The leverage of additional support to the roots, is always in terms of distance from stump, the farther the better.  Single trees can't avail themselves to this, so carry weight lower and wider, and eventually reach towards ground; when the reach of the branches would give meaningful leverage, in distance from the only connection to ground (trunk forming pivot).  Also protecting it's ground too.
	Protections of the Biosphere Cap
Light
	The seedlings that do sprout, mostly just absorb trace elements before the elements might be washed away, then die and melt into the mulch bed to feed the tree. Lots of green area for lots of energy absorbtion, storage etc. cuts down on some foreign wind blown seed.  Perhaps gives some purity of local species, as the thick green cap could keep out competing wind blown pollen etc.(?)  As well as mistletoe, moss invasions etc.(?)
Trees Together
	Biologically: Even as a single tree, the tree will eventually try to grow limbs to the ground, that will protect the soil garden.  As above if the branches (trunks) die, they still stand protecting the rest from invasion, by plant, beast, wind etc.!
Single Tree Application
	On the other end of the protection of the tough trunks are the leaves.  The lush growth caps the biosphere, sealing out competition for resources as well as preserving it's own strain purity, acclimating generations to that specific woods conditions quicker with 2 local parents.   The biosphere cap is the first line of defense against seeds to go competing plants, the mulch bed is another barrier, then the quality of light, amount of water etc. are all programmed to keep down competition for resources inside the biosphere territory.
Biosphere Cap
	The extremes leverages of the tops; reaching far before touching each other or the ground, giving more leveraged support at those points to the stump/roots, as well as shading more area of the ground; more leaf surface area too.  So, the light exists less dense in intensity, duration as well as broadness of wavelength spectrum, by the super competitor, trees setting up their territorial biosphere.