Would you say that the main reason trees are tall is to get away from predators that graze on grasses and plants that are lower to the ground - or would you say that trees get taller to get more light?

Is this true/false (one or the other), or is this multiple choice with an "all of the above" option?

__________________
Numbers are not case sensitive. (me)

I think it's natural for organisms to grow into more complex beings. The only limiting factor is the environment and auto-life support. If they couldn't get the nutrients they needed up to the leaves they would stop growing.


Just look at humans, we are much taller than even 100 years ago. Environmental reasons were the cause: nutrition and health. Now we have better health care for fetuses and children, plus with better diets we can grow taller and stronger. Another concern might be hormones and steroids, we eat they whether we like it or not in our food. We want tomatoes to grow so we add things to make them grow - then we eat the tomatoes.


Anyone remember the Gilligan's Island episode where they found the fruits and vegetables grown with radiation?

__________________
"I will do my best to understand and explain the universe from big to small without invoking miracles, unrepeatable events, or divine intervention. In place of those things I will use observations, mathematics, and science."


-Cross
My travel blog

Some of my Astrophotography


Those that lack education have a hard time understanding its value. - Cross

Light.
Depends on environment though, in a tropical rain forest it's a mad clamour between competing trees to dominate the canopy. Where as in african savanna there is pressure to gain a height above the reach of grazing animals, but then lateral growth tends to occur.
Of course mighty forests of mosses & ferns grew back in the carboniferous period, long before trees as we now know them evolved. Hence I reckon the selection pressure for very tall plants existed before there were large terrestrial herbivours.

Edit: Dudes!
might have wondered into an area of my expertise here though to be fair (now Biosci comes & puts me straight with current thinking in paeleoecology )

Thats ture Cinderman,
we all know that trees need light to grow and to live, So they get taller and taller to grab more light at higher levels of the ground, which means, if there was a tree that reached moon, It would have Tons of light!
Thats why the trees are getting tall and tall...Or maybe not?

__________________
Ahhh am the evil forces of sun!

Evolutionary advantage. Trees in forests have to compete with each other for light. Trees that grew upward had an advantage over trees that grew outward, and so were more likely to survive to reproduce. Staying above grazers would also be an advantage.

__________________
In Fallout 3, 'happiness' is a warm junkyard dog and a loaded gun. It's mostly the loaded gun.
- Moose's one-line review.

"your going to regret that one. You are now a colonoscope...
- Chrissy, corrupting PraedSt's wish.

You could also give a percentage. I think it's probably 10% getting away from predators and 90% getting above other trees in order to get more light, but I wanted to see what other people thought.

The reason I think that predators are less important is that growing tall doesn't really get you away from them. As you evolve taller, there will always be elephants that evolve bigger to knock you down, and giraffes that evolve longer necks to keep eating you.

Now admittedly, there comes a point where even an elephant can't knock you down and even a giraffe can't get to you - but that *cannot* be a driver for evolution. The 5 meter tall trees don't have a master plan, "come on guys, let's keep growing so that in 100 million years these elephants can't knock us down."

So that leads me to believe that the real driver for tree height is getting to the light.

Also, getting taller doesn't get you away from climbing predators like monkeys or do anything to help with insects.

It's mostly for light; light is the main limiting factor in most forests. (In places where the main limiting factor is something else, like water or soil fertility, you normally don't get a forest.) I was a forester for several years before quitting that profession, and we can see this easily in how drastic a forest's reaction is when you alter the light environment. The main purpose for a common forestry practice we call "thinning", which is cutting some trees down but not others, is to let more light in so the ones that are left behind after the cutting will speed up their growth. After logging or fire, you can expect a sudden intense burst of growth at the ground level, of plants that couldn't grow before because of the light. (It can get nearly impassable in a few years; but several more years later, it starts to thin out because light competition, and to some extent soilspace competition, has started killing some of them.) Some seedlings such as oaks sprout, die if it's shady, and sprout again next year, over and over, waiting for the year there's enough light for them to grow. The wide open spaces you can walk in without hitting any plants under a thick park-like canopy of trees are because the shade is so dark. One of the first few most basic and important things you have to know about any tree species before you can manage it is its "shade tolerance", which varies between species. Shade-killing or stunting the growth of the other plants that share soilspace with a tree's own roots also gives that tree exclusive access to that soil's water and nutrients so it doesn't have to compete (or not so much) with others' roots in the same area. (Some trees like sugar maple and black walnut even secrete a toxin into the soil for that purpose.)

Plant-eating animals could be a part of it, but they're a minor threat in most cases. Most ecosystems have lots of green plant mass and relatively not so many animals to eat them, as you can tell by looking and seeing all the plants that are surviving, so the odds of any one plant getting attacked are fairly low. And the worst animals in this regard are often insects, which height doesn't get you away from anyway. Plus, to get away from land animals, you don't need to be many times taller than they are; you just need anything greater than the top of their reach. And there were ferns up to 30 feet tall before there were animals that could reach much more than a few inches.

Tree size/height also has some other potential uses...

Large size means many leaves, which means much photosynthesis, which means large amounts of whatever stuff you want to make with those resources. And large size means greater capacity to store it for later. This is part of the answer to a question my sister asked me once during a drought, about why the grass was dead but the trees were green.

Another part of the answer to my sister's question: bigger root system means more chance to reach water in the soil where you couldn't reach otherwise, both vertically and horizontally.

A sort of a subset of the "light issue", with some embellishments, is the shelter effect. Under a tree, or especially a full canopy of trees, the light's lower intensity means there's less (nearly no) risk of getting scorched by too much sunlight, air movement is inhibited, and radiative cooling at night is blocked just as much as sunlight is in the day. So the temperature fluctuates less and the humidity's higher and fluctuates less. Some plants, such as firs and red maples, can handle photosynthesis alright in the shade but are vulnerable to scorching, extreme temperature/humidity changes, and/or dryness when they're seedlings, so the older trees above are protecting them. (Those trees get tougher when they're older.) My guess is that this is what the ancient giant ferns were going for; modern ferns dry out easily and stay where they're sheltered from sunlight and low humidity.

Bulk also allows a single plant to create a large number of seed-bearing sites (cones and fruits), instead of just whatever can fit on a small plant, thus producing more seeds. For trees whose seeds are scattered on the air, being tall gives the seeds more exposure to wind and a longer "flight path" to fall. For trees that use animal dispersal and live in a fairly open environment (savannah), being taller than the surrounding grass and shrubs might improve the dispersal of their scents or their visibility to the animals in question.

Most "forest fires" don't burn whole trees up like you see on TV; they start at ground level and usually stay there, burning up fallen twigs and leaves and killing only small plants. The more intense a fire gets, the greater the height it can reach and do its damage at, so the taller a tree is, the less likely it is to suffer fire damage.

A subcategory of pine, a group of species called yellow pines, thrives in soils with a lower pH than most plants can handle, and pine needles on the ground tend to reduce the soil's pH. So the more needles they produce and drop, the more they can influence the environment to their benefit. And large size means they can produce more needles than they could if they were small.

I grew up in a yellow pine forrest. Yellow Pine was the floors, walls, and ceilings in the house my dad built. Later extensions used white pine and several oaks, but the original part is still 100% yellow pine.


man, I haven't talked to my dad in a while, maybe I should call him.

__________________
"I will do my best to understand and explain the universe from big to small without invoking miracles, unrepeatable events, or divine intervention. In place of those things I will use observations, mathematics, and science."


-Cross
My travel blog

Some of my Astrophotography


Those that lack education have a hard time understanding its value. - Cross

Careful though, tofu. You're right that evolution doesn't have a master plan. It's not a situation that trees grow to get away from it all. It's that trees that have grown have, for several reasons, a statistically greater chance at perpetuating their genes.

If growing upward has a genetic component, then there's a greater probability of these genes being passed along, but over many generations. The effect of evolutionary pressure is really only meaningful over a population over a very large number of generations. Individual trees really don't come into it.

__________________
In Fallout 3, 'happiness' is a warm junkyard dog and a loaded gun. It's mostly the loaded gun.
- Moose's one-line review.

"your going to regret that one. You are now a colonoscope...
- Chrissy, corrupting PraedSt's wish.

Delvo, well said.

__________________
In Fallout 3, 'happiness' is a warm junkyard dog and a loaded gun. It's mostly the loaded gun.
- Moose's one-line review.

"your going to regret that one. You are now a colonoscope...
- Chrissy, corrupting PraedSt's wish.

The common interpretation is to get a share of light, but light is only one trait on which selection operates. For those plants that didn't develop the ability to grow tall, other adaptations are needed. There are many, many species that live in the understorey and do not get tall, yet they grow and reproduce very well. These will have developed other adaptations to their environment, and obviously, the ability to survive and reproduce in low light conditions (look closely though, many will be occuping gaps that receive slightly more light than the surrounding area - lucky for the seed that fell there). There is no adaptation that comes free of costs to the plant. For tall species, strong physical structures are required, and there is the risk in many environments of their lives being cut short by wind, ice or snow damage. And height is apparently not a favoured trait in dry zones.

For shorter species, being browsed is one of the risks. But the ability to readily regenerate browsed structures and produce viable seed would be a characteristic of some of these species, and having numerous individuals in the same space occupied by one large tree would be another advantage to such a species as a whole. Some individuals will survive to reproduce, and that's all that really matters to the species.

And of course, none of the species evolves in isolation. So while one species is doing it's thing, another species may by chance develop a trait that is advantageous relative to the environment created by the other species.

Don't you mean the one where they almost got off the island, until Gilligan goofed it up?

__________________
Don of Borg - Cool, Calm, Collective.

"Within the next generation I believe that the world's leaders will discover that infant conditioning and narco-hypnosis are more efficient, as instruments of government, than clubs and prisons, and that the lust for power can be just as completely satisfied by suggesting people into loving their servitude as by flogging them and kicking them into obedience." -- Aldous Huxley

Or how about the Friends episode that starts off with a lot of incredibly predictable and insipid sexual inuendo and then ends up being some sort of moronic morality lesson on what it means to be friends?

__________________
Don of Borg - Cool, Calm, Collective.

"Within the next generation I believe that the world's leaders will discover that infant conditioning and narco-hypnosis are more efficient, as instruments of government, than clubs and prisons, and that the lust for power can be just as completely satisfied by suggesting people into loving their servitude as by flogging them and kicking them into obedience." -- Aldous Huxley

I can't remember a Friends episode that did not go like that

__________________
PW -- Plant Whisperer

__________________
SeanF

"Ask to understand, but don't challenge unless you have the knowledge."--NEOWatcher

The contents of this post are ©2008 by SeanF and may not be copied or retransmitted in any form without the express written consent of SeanF

It used to be all the trees were the same height, just a few feet. They all cooperated with each other and each had an equal share of light.

Then one day one tree decided it was better than the other trees and grew a foot higher than the rest. Not wanting to be left in the shade, the trees around this taller tree grew two feet higher. Soon this tendency spread to the rest of the forest and there was no stopping the trees until some got so tall they fell over and rotted.

This is the story of the origin of the first tall trees, whose Linnaean name was Arbor gatesi.

__________________
A person's name, or a mark representing it, as signed personally or by deputy, as in subscribing a letter or other document.

that's the one

__________________
"I will do my best to understand and explain the universe from big to small without invoking miracles, unrepeatable events, or divine intervention. In place of those things I will use observations, mathematics, and science."


-Cross
My travel blog

Some of my Astrophotography


Those that lack education have a hard time understanding its value. - Cross

Maksutov wrote:

And it happened Just So.

__________________
The Devil offered me power. I told him I preferred aperture.