Tree Biology

Today I took a master naturalist class on tree biology.  We started out with the definition of a tree.  The definition is not so easy. Tall plant with a single trunk?  What is tall?  400 feet is tall and most trees don't get that high.  And a single trunk? Well, aspen are a kind of tree but under the ground they can share a single root and the same DNA.  If you clear cut an aspen forest they will grow right back up again in quick order because they use the same roots.  Trees have fruit? Yes, deciduous trees have fruits.  Some have large fruits like apples and others have smaller fruit like the maple helicopter seeds or round basswood seeds.  What do trees eat?  Although they came move 100 gallons of water from their roots out of their stomata on their leaves, they don't actually eat the water.  They don't eat fertilizer.  Since 49% of the tree is carbon ad 50% is hydrogen and oxygen and less than 1% is nitrogen and other trace minerals, the best way to feed a tree is to walk up to it and breath on it.  Expel your breath against the trunk or the leaves or the branches.  Blow on a tree. Trees eat air.  Trees feed on air.  From massive coastal redwoods to gnarly oaks to sinewy bamboo air is what feeds them.  From bark to phloem trees are amazing organisms.  Take two trees. Plant one in a park.  Plant the other tree on a boulevard between the street and the sidewalk.  Which tree will grow faster?  I would think the tree in the park with plenty of room and fresh air and soil that is permeable and not compacted by traffic would grow faster.  I am wrong.  The tree on the boulevard grows faster.  The water on the sidewalk can't be absorbed into the concrete so it runs off right onto the roots of the tree.  The tree in the park doesn't get as much water right onto the roots so it grows slower.  The tree in the park lives longer but grows at a slower pace.  Some trees have male and female sexual organs on the same branch.  Some trees have male branches and female branches.  Some trees, like ginkgo, have male trees and female trees.  Most trees have the pith in the center of the trunk.  So if you take a slice of the tree you will see concentric circles indicating growth years radiating outward from the pith out to the bark.  But if a tree grows on a slope or a tree is growing crooked to reach for the sun out of the shade of a neighboring tree, the pith will be at one end or the other towards the bark. Or maybe wind pushes a tree to lean to one side.  For whatever reason the tree is growing at an angle, a deciduous tree will put the extra wood to balance itself out on top of the pith.  So a tree leaning to the right will have the pith closer to the right side of the trunk. A coniferous tree will put the extra wood on the other side so a tree leaning to the right with have the pith closer to the left side of the trunk.  How crazy is that? Two kinds of trees choosing the opposite coping method?  Trees are just amazing.  The picture above shows an acacia tree growing out in the savanna on the Masai Mara grasslands.  I took this photo ten years ago.  I arrived on this spot in a truck and I could barely make out the track where our truck traveled. I looked around and as far as my eyes could see I saw nothing human.  Of course I saw my fellow passengers and our truck but other than that I saw no houses, no roads, no planes, no towers, no telephone lines, no structures of any kind and it was a very cool experience. I turned in circles and enjoyed the lack of human impact. I loved these acacia trees. I loved the shade they provided on these grass lands. I loved the hills.  I loved the slopes.  I loved the wildness.  I loved the wilderness.  A forest of acacia trees would not have been as cool as being here on this day seeing an occasional acacia tree on the savanna.  I'm not saying acacia trees are my favorite.  I also love oaks and maples and conifers.  I am not a fan of buck thorn or other invasive species but bamboo in the right place are quite lovely.  I get excited to see palm trees because I know I am in a warm place but actually palm trees are more like a grass than a tree.  Olive trees are cool.  Cork oaks are also cool because you can strip them of their bark and the bark will grow back again.  The bark on eucalyptus trees if fascinating. If you come near one of the oaks in my yard with a chain saw I will knock you flat.  If you use that chain saw on the amur maples?  I would pay you to do it. So I guess I really can not say I have a favorite tree.  Like people, the diversity is fascinating.  I love the diversity of trees.