Tree Growth Issues for Further Study

New Factors that Foresters Need Help Resolving:

Items missing in previous response studies:

  1. An attempt to understand the observations from a tree physiology perspective:

    1. The mechanisms within the tree that were affected by the treatments:

      1. Height Growth: We saw that the small pine saplings in wind shadows had almost double the leader length of those found on more exposed sites. Shaking of the leader has been shown to shorten height growth by 50% in tulip poplar and red oak.

      2. Diameter Growth: Diameter growth is stimulated by bending of the stem during the growing season as long as there is sugar available for cellulose production. One can tell when diameter growth has been shut down for more than a week by trying to peel the bark from the stem in areas where growth is expected.

      3. Root Sugar Situation: Tree system balance often determines whether the foliage of the tree is able to produce sugar. The crown needs water for the leaf stomates to remain open during periods of high evaporative potential. Stem bending stimulates the use of sugar from the phloem if it is available. Sugar must reach the roots in order for new root growth into areas with excess water, and sugar must be available in the root tips for water to flow into the root hairs to be pumped up the xylem to the crown. If the crown is unable to produce sugar beyond the stem growth needs the crown becomes dehydrated and sugar production stops.

    2. Site characteristics that control the length of time in which cell division (diameter growth) can occur:

      1. Soil Aeration: Adequate soil aeration is essential for root respiration to occur. Well aerated soils generally have higher rates of soil water movement from places of high water content to dryer areas.

      2. Soil Compaction or Cementation: Very dense compacted areas are common in glaciated soils, as are thin layers of clay layers or chemically cemented regions. Any one of which can seal off water movement from one soil region to another.

      3. Soil Water Availability: The normal midsummer condition for convex topography is for soils to be at the wilting point. Normal rains are not sufficient to do more than rehydrate the stem. Exceptional periods of extended rain fall may allow sugar production to begin again, but this is very rare. Sites with good soil aeration and access to the ground water table or continuous water inflow from above may allow continued sugar production by trees with limited crown size. On the other hand there may also be sites with a steady water supply that can maintain superior growth only when there is continuous water removal by trees with large crowns. Removal of overstory trees in such a situation could result in death of residuals from waterlogging.

  2. Incorporation of value production into the setup of the tests:

    1. Evolution of our rural society from a rural agricultural ethic to that of a prudent investor has been governed more by the appreciation in land value than to sustainable production for the long term.

      1. Exit strategies are often planned in advance.

      2. Short term performance is expected and

      3. Biological basis of understanding is missing

      4. In fact there is no basis for proactive measures in our current financial system since trees have no regular debt service capability
    2. Tree value is difficult to assess

      1. Foresters never get to test their impressions of how value is developed within the tree

      2. Tests of new techniques are good times to test a variety of assumptions

      3. Local portable mills provide opportunity to take trees apart in ways that would be difficult or impossible at larger mills

      4. Local mill based lumber yards offer outlets for short high quality material.

    3. Markets Dictate Pruning Lengths:

    4. Markets Dictate Minimum Log Lengths:

    5. Land value and taxation must be factored into prudent investor analysis

Tree Physiological Principles Provide the Basis for Development of Tests:

  1. Normal Silvicultural Rules of Thumb;

    1. Hierarchy of sugar allocation:

      1. Highest priority for sugar allocation is the last to be eliminated before a tree dies

        1. In white pine the formation of terminal buds and next season stem elongation are directly linked to the vigor of the tree, and are the last to stop before death.

        2. Height growth is a very strongly controlled parameter because the allocation of very small amounts of energy for bud primordial formation may commit the tree to large sugar outlays for future tem strengthening throughout the length of the main stem.

      2. Diameter growth is a relatively low priority use of energy and is constantly minimized when ever sugar is in short supply.

      3. Root growth is dependent on excess sugar beyond that called for by cambial region cells. This excess sugar is left in the phloem and flows down the stem phloem eventually arriving at the roots.

      4. Stand structure acts to control (reduce or increase) the possible activity of cambial region cells by modifying the amount of bending that is possible in the main stem during the growing season. Stand structure also affects the rate of water useand availability to residual trees.

        1. Cambial activity depends on the supply of sugar for cellulose production and energy for all cell functions. Cell division is possible only after a cell has elongated beyond a minimum amount. Bending of the stem helps to elongate (by stretching) the very weak recently divided cells so that they can quickly attain the required minimum length for division. This is only possible I the cell wall building blocks are available in the right place when the cell is stretched either by water pressure or by stem bending.

        2. Water availability for maintenance of leaf turgor pressure (keeping stomates open) allows photosynthesis to occur. Conversely, limited water shuts down photosynthesis regardless of other conditions Thus thinning of tall stands may increase evapo-transpiration (adding to water demand), and at the same time limit the amount of sugar available to the roots because of upper stem bending causing mot of the sugar being withdrawn from the phloem for new cell growth.

        3. Modifications of stand structure to enhance small tree growth before the development of a tall weak stem have the best chance of keeping the whole tree in balance with the available water. Thinning at appropriate periods can redistribute limited water among fewer fast growing occupants of the site. Careful analysis of what is happening may be necessary to determine just what the limiting factor is in the developing stand.

Subpages (1): Pine Simulations
Alan Page,
Feb 21, 2011, 8:25 AM