Modelling: biological productivity, structural resistance, reproductive model

[Marcus B-T]

OK; we all know that trees are basically a balance between biological productivity (the building blocks); Structural stability (the frame work) and reproductive development (continuing the species). But at some point in the trees life it all breaks down and this is what we ulitmatey want to know. Also, if we manage a tree we want to know how to balance these aspects, i.e. we don't want to promote one to the detriment of others.

 

Now the problem is that this is a complex relationship and this is where the opinion and argument comes in.

 

So it strikes me that a model of the system in some way will help the process.

 

Now I could just write one publish it and let everyone prop up the bed with it.

 

Or we could start a thread, i.e. this one and I can produce the model in real time and you can all review it as we go along. So here is the starting point.

 

 

The canopy area intercepts light and uses the enegy to convert water and CO2 into photosynthates (building blocks). These are then distributed to various parts of the tree based on a thing called sink strength (relative demand for photsynthates). This determines what grows at what rate.

 

 

Ok who's next where does it go from here?

[Tony Croft aka hamadryad]

Well, after the above mentioned portion of the equation, maintaining the "structure" i would think is pretty important, as without maintanence of said structure it cant compete and will fail, so designation of avaliable resources....

 

But how do we determine what triggers alocation of those resources to optimisation as apposed to seed production or reserve storage?

[Marcus B-T]

A few requests if you want to post on this thread. By all means give opinion, this is how we get the ideas that are 'outside the box' but if you can back things up with a reference all the better.

 

OK model version one. Based on a large number of plant models but the books of Kozlowski, Pallardy and Kramer are as good as any.

 

 

Incident light energy (I) is inetercepted by the Photosynthetic Area (A)

 

This gives rise to net amout of photosynthate (P) some of this is used up in respiration © and so what is left over (P') can be thought of as the dry mass (well nearly all, there is the nutients to add in as well) of the tree and is divided between biological structure (B) and includes the leaf area and vascular system so A is actually related to B. P' is also divide into storage molecules (S) which intially we can put transport sugars like glucose and sucrose into as a temporary transient storage pool. Finally P' also can be used for reproductive organs ®.

 

So initially P' = B+S+R

 

Over time part of B will loose its function and become a structural pool (M) so that overall Net photsynthate P' =B+S+R+M

 

This is not a static system, the storage pool can be used in either B or R, and also there is a movement from P' to B to M.

 

These are described as fluxes so that they can in theory go in either direction, e.g. the mass can flow from S (storage) to B (biological) but also back to S.

 

Before we go any further, we can already see some intereting relationships. First you can only have mechanical structure if you have biological structure i.e. M relies heavily on B, but also it all relies on A for the interception of I (radiation).

 

Also the balance between the four pools of P' is also important.

 

 

 

Back to the fluxes if we use b to describe the fluxes of B; s for S, m for M etc.

 

we can call the flux of P' to B bP', and the flux of storage molecules to B bS etc this allows us to do two things.

 

Firstly the fluxes are over time so we can introduce development of the plant over time so that at any point.

 

dB/dt which is the rate of change in B with time is equal to bP' + bS - bM -bO

 

dR/dt (the rate of change in Reproductive material) is rP' + rS - rO

 

The term O is introduced as the loss of material during shedding, abscision or sencence. O for organic. We can add include decay as part of the O pool later.

 

As we can see the relationship becomes complex but at the center is P'. The less P' we have the less of everything. Also trees can divert P' to B without necessarily compromising the production of M.

 

The last thing to point out is the relationship between A and B which can be described as A = aB where a is an area density ratio of the part of B that goes into the production of A . The relationship between I, A and P' is not described yet.

 

So to conclude so far reducing A will reduce P' and therefore B,S,R and M these can feedback to further reduce A since A also changes with time and the elements of A (the leaves) have a finite lifespan.

 

So dA/dt = a dB/dt

 

and if dB/dt is reduced then A is reduced.

 

And if dB/dt is reduced then M is reduced.

[Tony Croft aka hamadryad]

A few requests if you want to post on this thread. By all means give opinion, this is how we get the ideas that are 'outside the box' but if you can back things up with a reference all the better..

 

Unlike you marcus i dont have the training to be so perdantic, i had come on board as noone else was entering your thread to discuss the subject, call my entry to it both curiosity, and moral support for a man who has a lot to offer, if a little strange in delivery!

 

its way too late for this post of yours, i will be back on it tommorow with a fresh mind, but do pull your head out your butt, this is arbtalk not "nerds R us":lol:

 

No reference reqiured!

 

Unles of course you would prefer my chav replies remain unentered:lol:

[Marcus B-T]

Keep following all wil become clear. Also you are a fine one to talk having posted the stuff on FS' book.

 

 

Read the last two bits! and think about what it tells us.

 

 

"So dA/dt = a dB/dt

 

and if dB/dt is reduced then A is reduced.

 

And if dB/dt is reduced then M is reduced. "

 

Also if A is reduced then dB/dt is reduced!!

 

dB/dt is biological growth rate

dA/dt (approximates to leaf area growth rate)

A (approximates to leaf area)

M is mechanically structural wood

[Tony Croft aka hamadryad]

Keep following all wil become clear. Also you are a fine one to talk having posted the stuff on FS' book.

 

 

Read the last two bits! and think about what it tells us.

 

 

"So dA/dt = a dB/dt

 

and if dB/dt is reduced then A is reduced.

 

And if dB/dt is reduced then M is reduced. "

 

Also if A is reduced then dB/dt is reduced!!

 

dB/dt is biological growth rate

dA/dt (approximates to leaf area growth rate)

A (approximates to leaf area)

M is mechanically structural wood

 

Im with you thus far, but for FS book? what is that!

[Tony Croft aka hamadryad]

Took me a while! FMWR Shwarze, THAT book! lol yes fair remark too! lol

 

You could have stuck your head in and returned the moral support on that one!

 

Why dont you re start the merip stuff in here marcus, im talking on arbtalk, id like to know what the "meripilus netwrok" was all about and where you all got to on this, david spoke of it a few times but i never saw it. Something im well interested in.

[Marcus B-T]

I didn't get involved on that link because I don't have that particular book though I have many of his others. Funny you should mention the network. A long story but to cut it short, I had the web address taken from me and this caused all sorts of problems with sponsors and other things, but I have recently got round these so it will rise phoenix like from the ashes this week.

 

Regarding the Merip postings, this posting will address the issue so keep watching.

 

So back to the thread.

 

We now have a situation where if you reduce the photsynthetic area A you potentially reduce the size of the biological pool and therefore, eventually the amount of structural wood.

 

Now then, we hit a first critical point. Supposing you have a tree that is deemed to be structurally unsound and the recommendation is some kind of reduction. Then if the redcution is too severe then A will be reduced to an extent that the contribution to the biological pool B is significantly reduced and so then the contirbution to the mechancal pool M is significantly reduced. Not only that but the further contributions back to A may be reduced. If this last one happens then the tree is effectively in a downward spiral, because it is nolonger self supporting.

[Tony Croft aka hamadryad]

 

Now then, we hit a first critical point. Supposing you have a tree that is deemed to be structurally unsound and the recommendation is some kind of reduction. Then if the redcution is too severe then A will be reduced to an extent that the contribution to the biological pool B is significantly reduced and so then the contirbution to the mechancal pool M is significantly reduced. Not only that but the further contributions back to A may be reduced. If this last one happens then the tree is effectively in a downward spiral, because it is nolonger self supporting.

 

yes yes, and this goes along with my recent thoughts regarding reduction and less than 100% vitality and vigour, ive been witnessing a few reductions going down hill of late, and this would have been drasticly exadurated by the stress from drought this summer which was severe in herts and bucks.

 

One of the critical errors a lot of climbers make is cutting out internal growth, it makes the climb easier, but doesnt help the tree in any way, in fact it has a very negative impact on carb distributions. This is the same principle as over lifting etc, freed trees etc with long transport distances, it just isnt optimal and the tree has to work harder.

 

you have my atention:thumbup1:

[Marcus B-T]

OK the storage pool.

 

The most interesting work on this has been carried out on a relatively narrow number of species and also mostly with younger trees, (look up the work of Abod and Webster from the 1990's) or the WRC work on willow and poplar published in the Arb Journal or some of the French work on London Plane. So there has to be note of caution here.

 

The first thing is that storage pools are transient, i.e. carbon will go in an out of pools depending on seasons and stress. Also they are all over the tree so there are very small pools in leaves and larger ones in roots and shoots.

 

With the simple model we have so far you can see that if you reduce leaf area then you put extra dependency on storage pools to make up the difference.

If the tree is under strain (either seasonally demand on stored resources, or impossed due to environmental, biological or physical stresses) then resources will be low and there will be a greater effect on the biology of the tree.

 

Therefore leaf area reduction should be in tune with the activity of storage pools and the environment.