Feb

4

Vic Queries About Tree Growth

February 4, 2007 |

Vic Queries:

There are only a few people I know who know more about trees than Bill Craft does. He's a forester and things like the laws of uniform stress are second nature to him. I feel like sitting on a log with him and asking such questions as

1. Why do the canopies of trees tend to grow to the same height in a stand?
1a. Is there such a thing as hubris in trees and is it dangerous the way it is in markets?

2. Why do trees decide to have a single trunk rather than several?

3. What are the strategies that determine the horizontal versus the vertical growth of trees?

4. What predictions can be made from the distribution of different species of trees at a time as to the ultimate succession and climax community?

5. When does the growth of a tree decelerate relative to its mortality, i.e. the risk return of a tree?

6. Is there a systematic difference in subsequent expectations of growth between the tree strategists that spend their time developing a trunk resistant to disease and attack from flora and fauna and those that just shoot way up with attention to getting to the sun as fast as possible without regard to the buffets of time?

7. Are the relative occupancy levels of various size trees in a forest predictive of movements between them, eg. if there is a relative clustering of numbers of trees of 100 feet and 25 feet tall, does that imply that there will be a growth in the numbers of trees with a height of 50 feet?

8. What is the relative success of trees at each size range in a stand?

9. How does the shape of leaves determine the success of a tree?

I could go on with many child-like questions and I might be able to answer similar questions if they were directed to the defunct game of hard ball squash, but I believe that thinking in such areas might lead to good insights into markets, over and above the natural drift.

Bill Craft replies:

Generally trees/plants, whether woody or herbaceous, grow as a response to light stimulation and the subsequent internal chemistry/clock/aspect/elevation/latitude etc. Thank the sun for all our biomass, hydrocarbons and friends.

1. Why do the canopies of trees tend to grow to the same height in a stand?
1a. Is there such a thing as hubris in trees and is it dangerous the way it is in markets?

Canopies of stands (similar soil/site/age/population) tend toward the same height as a response to this demand for energy. Genetics and position in a stand determine what individual will be dominant or codominant in the group. Being in a dominant position, a stem forms a large Wolfy crown able to utilize energy and transfer it to diameter growth at a faster rate.

But this exposes the dominant stem to more risk, breakage, lightning, ice storms and such. Therefore, the majority of thriving individuals in a stand are co-dominant, in a less risky position, swapping, by chance, growth for support from neighbors/cohorts.

2.Why do trees decide to have a single trunk rather than several?

Tree species have varying responses to gravity and utilization of sunlight. Generally, the softwoods grow straight and tall (excludes understory Hemlock et al) and the ones that are more shade (uses less light if need be) tolerant, such as oak/hickory/beech, have larger spreading crowns. They are programmed to respond within certain bounds of energy and competition. Multiple limbs form the crown, which is in a lower position, chemically, from the dominant top bud/buds, and is called apical dominance.

When the controlling bud is lost, dominance is transferred resulting in more crown or several stems. Pines that have poor apical dominance will have multiple stems or ramicorn branches. An example is the white pines' response to bud damage. In hardwood forests, a Coppice method can used to regenerate a stand. Harvest the stem, and multiple fast growth (already have a root system) leaders appear.

3. What are the strategies that determine the horizontal versus the vertical growth of trees?

It depends on the need for light, how crowded the stand is, and the level of competition (they all do better with some stress/competition). This results in better form, better wood, better yield and so on.

4. What predictions can be made from the distribution of different species of trees at a time as to the ultimate succession and climax community?

If undisturbed, stands tend toward species' compositions most capable of reproducing under the canopy in lower light. Here, if one sees similar species in the canopy and understory, you possibly reached the late successional stages. Most things are not undisturbed, so some things are guesswork, swags if you will. I always wonder what the vocally enamored mean by old growth? Where would the discussion be if we still have Castanea Dentata? Now there's a big burr under the saddle! Many species react differently to location and types of competition. At Yellowstone, there is the lodge pole pine, armed with its serotinous cones, and the stands reproduce with response to full sun and bare mineral soil. In other areas, lodge poles act differently. (Please read under Associated Forest Cover. Ya gotta know in what ecosystem you stand.)

5. When does the growth of a tree decelerate relative to its mortality, i.e. the risk return of a tree?

This is measured using stand tables, age expectancy (there are economic and biologic rotation ages), projected growth rates (Hello CO2,) and mortality. In an economic setting, when one drops below a growth rate relative to standard density, it is time to thin or regenerate. Try to thin prior to or at the asymptote to prevent slowing. Boot leather says to thin when you have less than 25% live crown ratio. Sophisticated thinning/harvesting Max IRR etc. programs have been developed. Another reason to shorten the rotation is the replacement with better 'genetics,' which is in fact a great plan. These have more genetic diversity than the original local seed sources. What's the next hot stock?

6. Is there a systematic difference in subsequent expectations of growth between the tree strategists that spend their time developing a trunk resistant to disease and attack from flora and fauna and those that just shoot way up with attention to getting to the sun as fast as possible without regard to the buffets of time?

Yes, the genetic 'diversity' of i.e. Loblolly I am planting is great. Genetic material from many sources, prodegeny tests (takes time). Increases of 10 to 15% growth without soil amendments i.e. same site, better form, more compact crowns (use less space, more efficient user of sunlight), less repeating spiral grain (as pines grow away from gravity they twist, see one hit by lightning with the barber pole effect), and disease resistance. Insect resistance from being more thrifty can repeal attacks. Older seeds were from localized sources. Less genetic diversity is due to deforestation for crops. One interesting note is: In my duties, when trying to prepare a harvest with seed tree for regeneration, I have to cut it, and it is hard to find stems with abundant cones that are straight, not as limby, low disease etc. Better to replant now. The cone response is one of/to stress, just like pruning an apple/peach tree to get the max amount of blooms. The geneticists are always working, holding those few/precious sought after seeds that will benefit us all.

7. Are the relative occupancy levels of various size trees in a forest predictive of movements between them, eg. if there is a relative clustering of numbers of trees of 100 feet and 25 feet tall, does that imply that there will be a growth in numbers of trees of height 50 feet tall?

Yes, in similar stands and between species, if not too old and if mixed, the shorter ones are more shade tolerant. If the height differences are different as a 'group' then that group is a stand. We try not to get the stands too small. Edge effect takes over and can reduce expectation, i.e. A planting of Loblolly fails (rarely), do not interplant the surviving with newer seedlings. This means losing on year's growth. This edge effect is remarkable even at very young ages and one will not know this until 12 to 15 years out when this interaction causes lower growth.

If the stand is mixed, Loblolly and some sweetgum (ubiquitous here), then by measuring relative growth rates and the density and prices of the material, there is an argument for growing the hardwood for pull or pallet. Hey money is money. (Density = Basal area, described in square feet or meters, which is the sum of all the cross sectional areas of the stump if the stems were cut off at 4.5 feet (dbh) expressed on an acre or HA basis. It describes stems/acre and 'thickness' or diameter relative to age.)

8. What is the relative success of trees at each size range in a stand?

In a stand, the bigger get bigger, and the small bonzai die out, which equals increased mortality. The larger are more 'successful' per value and survival, and also take up more canopy. Live Oaks can deploy enough taninc acid within the drip line to stop most competition. They have to capture (harvest) that growth or it will be lost to mortality.

9. How does the shape of leaves determine the success of a tree ?

Wider leaves are bigger solar panels, mostly deciduous here, and they are generally more shade tolerant and love better ground. They only last a season, and they need rest.

Long needle Conifers shed the ice and snow and whistle in the wind. They are generally more shade intolerant but they are able to survive in poorer spots.

Surviving in poorer spots is a good strategy.


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