[neilep (OP)]

Wocha Peeps,

I love Trees...trees are great...love to listen to the wind rustling through them. Parking my backside against them and breaking wind is not so evocative though ! []

This would be a good one for Andrew if he still frequents the site.

I know tree rings are an excellent way to determine the age of a tree (or the age of a tree when it was cut down etc)..

........but...can someone please explain the actual process behind the creation of the actual ring itself [?] what is it [?] what is the reaction that is happening [?]


THANK YOU

Men are the same as women, just inside out !

[crandles]

In temperate regions, in late spring/summer there is lots of growth due to length of day, level of light and area of leaves. This leads to a wide band of light coloured wood being grown. In autumn there is less growth (again depending on length of day, level of light and area of green leaves) which leads to a narrow band of dark coloured wood.

[neilep (OP)]

THANK YOU Crandles,

So it's the level of light that determines the shade of the ring ! !

(the penny drops )

I suppose it's obvious now when you think about it.

cheers

Men are the same as women, just inside out !

[ROBERT]

quote:Originally posted by neilep

Wocha Peeps,

I love Trees...trees are great..

I know tree rings are an excellent way to determine the age of a tree (or the age of a tree when it was cut down etc)..

The shape of their luvverly leaves is useful to climatologists:-

" Leaf Shapes and Climate Clues
Want to know what the temperature was when the dinosaurs were clomping around? The answer all lies in the shape of the leaves.

It has long been known that vegetation and climate are closely related. For example, rain forests grow in areas of high rainfall, while deserts and grasslands are formed in areas of low rainfall. Is it possible to take this any further and predict what the climate might have been like in the past by looking at fossilized trees and plants?

In 1910 two explorers, Bailey and Sinnott, happened to notice that the shapes of leaves on the plants and trees appeared to be closely related to the climate of the area. The most noticeable trait was that trees that grew in warm places had large leaves with smooth edges, while trees that grew in cold places tended to have smaller leaves with very serrated edges.

All this was almost forgotten about until in the late 70s a researcher from the US, Jack Wolfe, thought perhaps fossilized leaves could reveal more about the climate that they grew in if their shapes were compared to leaves growing today. He set about collecting thousands of leaves from all over the United States and Canada and carefully measuring and recording various aspects of their shape. Alongside this data he also recorded the average weather conditions from the last thirty years for each area. All the hard work really appeared to pay off and using sophisticated statistical analysis programs he was able to compare the shapes of leaves from fossil leaf assemblages to present day leaves and come up with average temperature and rainfall values that the fossil leaves once grew in.

For example he predicted that the average temperature 90 Million years ago in Northeastern Russia was 9¼C warmer than it is today. Such data is very useful to climate modelers, as it is important to test climate models by ensuring they can accurately reproduce past climates. If a climate model can model the past then it is going to be far more trustworthy at predicting the climate of the future. Until the method of using leaf shape to predict climate was developed, estimates for ancient weather conditions in continental interiors (such as Siberia) were very poor. "
http://www.ravilious.net/kate/publications/NERCnews.html

[neilep (OP)]

That is fascinating stuff Robert.

Now then...because I am such a lazy bi-ped and can not be arsed to click the link, do we know why are the leaves large and smooth in warm climes and that in cooler climes they are smaller and serrated ?

I am interested particularly in the smooth against serrated aspect.

Men are the same as women, just inside out !

[ROBERT]

quote:Originally posted by neilep

That is fascinating stuff Robert.

Now then...because I am such a lazy bi-ped and can not be arsed to click the link, do we know why are the leaves large and smooth in warm climes and that in cooler climes they are smaller and serrated ?

I am interested particularly in the smooth against serrated aspect.

Don’t know, (not a botanist), but my guess is that:-

The cool climate trees need to maximize their exposure to sunlight.
The angle of the leaf to the sun makes a great difference to the amount of energy absorbed,
 (it is proportional to the cosine of the incident angle of the sun's rays to the leaf surface).
The serrations on the edge of a leaf cause turbulence in the air flowing over it, causing the leaf to flap more than a smooth edged leaf.
When a leaf flaps its orientation to the sun changes randomly, this will increase the time the leaf is at the optimum angle to the sun as it moves across the sky, compared with a static non-flapping leaf.
So flapping increases the amount of solar energy absorbed, (using free wind power), serrations increase turbulence and flapping.

Leaves in warm, tropical climates have more difficulty in transpiring, compared with “cool” trees, because "warm" leaves exist in a more humid atmosphere. Having a large surface area will increase the rate of transpiration, so could explain why “warm” trees have larger leaves than “cool” trees.

[neilep (OP)]

Fascinating speculation Robert.

one would think that in the cooler climes the need for maximum exposure would also lead to bigger leaves,
but, perhaps the same exposure can be got with a smaller serrated edge using less energy to create a big floppy leaf.

THANK YOU ROBERT.

Men are the same as women, just inside out !

[another_someone]

I suspect we are looking at too few parameters.

So far we have looked at the shape and size of an individual leaf – I would be interested to know about the number of leaves as well.

Could it be that in the tropics we have a few large leaves, while in temperate regions we have many small leaves?

How much is this determined by the temperature of the environment, its humidity, the average amount of daylight, and the latitude?

As you say, in higher latitudes the direction of sunlight is more variable.  I don't believe that leaves fluttering in the wind would actually increase exposure to sunlight – yes, it would guarantee that it is facing towards the sun some of the time, but it would also guarantee that it is facing away from the sun sometimes, and on average the two would probably cancel out.  On the other hand, if the tree has lots of small leaves, each with different orientation, then that would allow it to cover a wider angle in the sky.  It could also help drainage, as the water will easier flow off the leaves (in extreme cases, it could even allow snow to better fall off the leaves).

Fewer but larger leaves can probably function more efficiently, allowing for a more efficient vascular system, and may even be a competitive advantage if it puts other, smaller, trees in the shade – but such few leaves would only cover a small angle across the sky, and so possibly would be useless in higher latitudes where the sun's direction is more variable.

The above is pure speculation.

George

[ROBERT]

Wikipedia has a page on leaf morphology, lovely diagrams, but no explanation for serrations.

http://en.wikipedia.org/wiki/Leaf
I believe "Another Someone" is correct in saying some leaf shapes have evolved to shed water.
 A leaf which retained water on its surface is more prone to rot, and in downpours could create sufficient force to break the leaf from the tree.

[another_someone]

A totally out of the blue idea, but serrations could hold drops of water on their tips, and could this not have a lensing effect for sunlight falling though them (again, more relevant for leaves that are small and densely packed, thus allowing an upper leaf to focus light on a lower leaf).

George

[neilep (OP)]

This is fantastic....and what with George on a mission to count all the leaves means we'll have this one solved in no time []

I would imagine in contrast to some leaves evolving to shed water that some leaves are designed to hold water also!....

What do you think ? is the reason why  some leaves are designed to displace snow ?....Snow is dry !....so it's not going to dampen the leaf !...snow is an insulator and would probably serve as a blanket rather than expose the leaf to a strong wind or a colder atmosphere....Unless, it serves the tree/leaf to be exposed like that !


Men are the same as women, just inside out !

[ROBERT]

quote:Originally posted by neilep

I would imagine in contrast to some leaves evolving to shed water that some leaves are designed to hold water also!....

Like the carniverous pitcher plant, (its specialized leaves provide a drink and a meal []).
http://en.wikipedia.org/wiki/Pitcher_plant
http://en.wikipedia.org/wiki/Image:Pitcher_Plant.jpg

quote:
What do you think ? is the reason why  some leaves are designed to displace snow ?....Snow is dry !....so it's not going to dampen the leaf !...snow is an insulator and would probably serve as a blanket rather than expose the leaf to a strong wind or a colder atmosphere....Unless, it serves the tree/leaf to be exposed like that !

A coating of snow would reduce the amount of sun reaching the leaf,
 no sunlight = no photosynthesis = plant dies.
An accumulation of snow could be heavy enough to snap off leaves and braches.
So a snow shedding shape is an advantage, (tonguetwister [])

[ROBERT]

quote:Originally posted by another_someone

A totally out of the blue idea, but serrations could hold drops of water on their tips, and could this not have a lensing effect for sunlight falling though them (again, more relevant for leaves that are small and densely packed, thus allowing an upper leaf to focus light on a lower leaf).

George

I think you are correct about serrations causing droplets to form.
However any lensing effect would not increase the amount of solar energy reaching the lower leaves,
 (lenses do not create energy).
Some light would be reflected from the sun-side of the droplet-lens rather than transmitted through it to the lower leaf; more energy would have reached the lower leaves if the droplet was absent.

Another "out of the blue idea":-
Serrated leaves flap more than smooth leaves, flapping leaves could shed insects which parisitize the tree.
 Imagine being a caterpillar on a flapping leaf, it would be like a bucking-bronco ride, (I said bucking []).

[neilep (OP)]

quote:Originally posted by ROBERT



A coating of snow would reduce the amount of sun reaching the leaf,
 no sunlight = no photosynthesis = plant dies.
An accumulation of snow could be heavy enough to snap off leaves and braches.
So a snow shedding shape is an advantage, (tonguetwister [])

I think the snow would have to be pretty damn thick to not let any light in at all and by the time it even approached that thickness it would have slid off, or the leaf/ branch would given way to release it!...but I see your point and agree with it.

Men are the same as women, just inside out !

[crandles]

quote:I think you are correct about serrations causing droplets to form.
However any lensing effect would not increase the amount of solar energy reaching the lower leaves,
(lenses do not create energy).

Many trees like diffuse light. This gets difficult to analyse and I am certainly not an expert. My suggestion is: If it is hot there will be more water droplets in the atmosphere and the light may be diffuse enough for the tree. If it is cold there will be less water droplets in the atmosphere so there may be insufficient diffuse light so creating the need for the tree to collect and keep water droplets to create enough diffuse light.

[ROBERT]

I’d like to refine my guess (above) about the role of flapping leaves to increase solar efficiency.

I was incorrect to suggest that flapping would increase the quantity of solar energy absorbed by the leaf.
 “Another Someone” is correct when he said:-

quote:Originally posted by another_someone

 I don't believe that leaves fluttering in the wind would actually increase exposure to sunlight – yes, it would guarantee that it is facing towards the sun some of the time, but it would also guarantee that it is facing away from the sun sometimes, and on average the two would probably cancel out.

George

Here is a graph comparing the solar energy absorbed by static and flapping leaves during one day,
note: the values have been averaged over each hour.



The area under the red and green graphs is the same: both static and flapping leaves absorb the same amount of energy in a day. However, if averaged every hour, the energy absorbed by flapping leaves is constant from sunrise to sunset, as the constantly changing orientation of the leaf makes the position of the sun irrelevant. Whereas the energy absorbed by the static leaf varies considerably as the sun moves across the sky.

If energy is being supplied at a constant level then photochemistry will be better able to utilize the solar energy absorbed by the leaf for photosynthesis, (greater solar efficiency).

-------------------------------------------------------------------

Here is an analogy of the comparison between static and flapping leaves,
(where: factory = leaf, electricity = solar energy , batteries = photosynthesis).

Imagine two factories whose purpose is to charge batteries from the mains electricity supply.

Factory “C” has a constant electricity supply of 70units/hour.

Factory “V” has an electricity supply which varies throughout the day from 0 to 100units/hour.

Both factories can only receive the same total amount of electrical energy each day.

Factory “C” need only have enough equipment and workers to utilize all the 70units/day power supply, all its equipment and workers would be constantly employed, (maximum efficiency).

Factory “V” must have more workers and equipment than “C” to take advantage when the power supply exceeded 70units/hour. All the workers and equipment in factory “V” would not be constantly employed, (not efficient).

If factory “V” was limited to the same amount of workers and equipment as factory “C” then factory “C” would produce more batteries per day. Factory “V” would be underperforming “C” when its power supply was below 70units/hour, and would not be able to take advantage when its power supply could exceed 70units/hour.

[another_someone]

quote:Originally posted by ROBERT
Here is an analogy of the comparison between static and flapping leaves,
(where: factory = leaf, electricity = solar energy , batteries = photosynthesis).

Imagine two factories whose purpose is to charge batteries from the mains electricity supply.

Factory “C” has a constant electricity supply of 70units/hour.

Factory “V” has an electricity supply which varies throughout the day from 0 to 100units/hour.

Both factories can only receive the same total amount of electrical energy each day.

Factory “C” need only have enough equipment and workers to utilize all the 70units/day power supply, all its equipment and workers would be constantly employed, (maximum efficiency).

Factory “V” must have more workers and equipment than “C” to take advantage when the power supply exceeded 70units/hour. All the workers and equipment in factory “V” would not be constantly employed, (not efficient).

If factory “V” was limited to the same amount of workers and equipment as factory “C” then factory “C” would produce more batteries per day. Factory “V” would be underperforming “C” when its power supply was below 70units/hour, and would not be able to take advantage when its power supply could exceed 70units/hour.

A perfectly plausible, but not inevitable, conclusion.

Remaining with your factory analogy, it is true that factory V will need larger premises, and a larger peak work force, but the latter may not necessarily be a problem if there is a ready supply of part time labour and a shortage of full time labour.

It really depends upon whether the leaves work better in burst mode, with good recovery time between bursts, or better at constant output with little recovery (or at least, no recovery during daylight hours).

Ofcourse, one could suggest that a flapping leaf actually is also a form of burst mode, except that the bursts are for a period of tenths or hundredths of a second, rather than for a period of hours.

Without knowing better the characteristics of the process, it is difficult to know which would be the better outcome.

I am not even convinced that the serrated edged will flap more.  I fully accept that the serrations will increase turbulence, but this could actually have the effect of softening the forces the wind applies to the leaf, as the wind will be gradually spilt around the leaf rather than allowing all of the wind pressure to spill around the leaf at once, and hence possibly actually reducing the aerodynamic stresses on the leaf.

Anyone available to do a proper aerodynamic analysis of a leaf (bearing in mind that smaller leaves will have smaller Reynolds numbers, which will alter the aerodynamic behaviour).

George

[another_someone]

quote:Originally posted by ROBERT
Here is an analogy of the comparison between static and flapping leaves,
(where: factory = leaf, electricity = solar energy , batteries = photosynthesis).

Imagine two factories whose purpose is to charge batteries from the mains electricity supply.

Factory “C” has a constant electricity supply of 70units/hour.

Factory “V” has an electricity supply which varies throughout the day from 0 to 100units/hour.

Both factories can only receive the same total amount of electrical energy each day.

Factory “C” need only have enough equipment and workers to utilize all the 70units/day power supply, all its equipment and workers would be constantly employed, (maximum efficiency).

Factory “V” must have more workers and equipment than “C” to take advantage when the power supply exceeded 70units/hour. All the workers and equipment in factory “V” would not be constantly employed, (not efficient).

If factory “V” was limited to the same amount of workers and equipment as factory “C” then factory “C” would produce more batteries per day. Factory “V” would be underperforming “C” when its power supply was below 70units/hour, and would not be able to take advantage when its power supply could exceed 70units/hour.

A perfectly plausible, but not inevitable, conclusion.

Remaining with your factory analogy, it is true that factory V will need larger premises, and a larger peak work force, but the latter may not necessarily be a problem if there is a ready supply of part time labour and a shortage of full time labour.

It really depends upon whether the leaves work better in burst mode, with good recovery time between bursts, or better at constant output with little recovery (or at least, no recovery during daylight hours).

Ofcourse, one could suggest that a flapping leaf actually is also a form of burst mode, except that the bursts are for a period of tenths or hundredths of a second, rather than for a period of hours.

Without knowing better the characteristics of the process, it is difficult to know which would be the better outcome.

I am not even convinced that the serrated edged will flap more.  I fully accept that the serrations will increase turbulence, but this could actually have the effect of softening the forces the wind applies to the leaf, as the wind will be gradually spilt around the leaf rather than allowing all of the wind pressure to spill around the leaf at once, and hence possibly actually reducing the aerodynamic stresses on the leaf.

Anyone available to do a proper aerodynamic analysis of a leaf (bearing in mind that smaller leaves will have smaller Reynolds numbers, which will alter the aerodynamic behaviour).

George

[ROBERT]

quote:Originally posted by another_someone
Anyone available to do a proper aerodynamic analysis of a leaf (bearing in mind that smaller leaves will have smaller Reynolds numbers, which will alter the aerodynamic behaviour).

George

[PDF] Lecture 22, Leaf Boundary Layers and their Resistances and Mass ...File Format: PDF/Adobe Acrobat - View as HTML
lobes and serrations, which can reduce average boundary layer thickness. ... Wind flow over a leaf can be laminar or turbulent. 2. The Reynolds’ number is ...
http://nature.berkeley.edu/biometlab/espm129/pdf/Lecture%2025%20espm%20129.pdf - Similar pages


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importance of leaf serrations and veins in the heat and mass transport process, ... where Re is Reynolds number, defined as Re = W/V, U being the mean wind ...
www.springerlink.com/index/N414MG2477067683.pdf - Similar pages