(Arboricultural-styled) 'Fact of the Day'

[Kveldssanger]

23/12/15. Fact #105.

 

These last few days have been a little tumultuous, so pardon the lack of posts.

 

A short and snappy fact here, though nonetheless awesome. A Ganoderma applanatum sporophore of a large size can release up to 30,000,000,000 (30 billion) spores per day, or 5,000,000,000,000 (five trillion) per year (from late spring to early autumn). It is suggested that such a profuse outpouring of spores into the atmosphere is necessary for the continuation of the species (as the odds of a spore germinating on a suitable substrate are low).

 

Source: Stamets, P. (2005) Mycelium Running. China: Ten Speed Press.

[Kveldssanger]

24/12/15. Fact #106.

 

Xylem conductivity is not constant. Conductivity will vary depending upon leaf water potential, and the associated effects of cavitation in the water column that is being (principally) pulled through the xylem.

 

In fresh xylem of the current growth year, the transition between a fully-functioning xylem and a highly embolised one is very short - only small changes in water potential may mark the difference between the two. If left un-checked, any such embolism at an undesirable water potential may lead to "runaway embolism" (as in, the xylem rapidly becomes wholly lacking in function).

 

Because "runaway embolism" is not to be desired, plants will invest heavily into producing cavitation-resistant xylem tissue. Varying significantly between species and individuals however (photosynthetic rates, genetics, environment, etc), the quality of the xylem from an embolism-resistant perspective depends upon the amount of carbon invested in producing effective walls and membranes for the xylem conduits. Increased resistance to cavitation also means the xylem vessels have reduced hydraulic conductivity (they cannot transport as much water per hour).

 

Because of the above (demanding) factors associated with producing robust xylems, many plants will lurk at the threshold of what is 'safe' - as in, hydraulic conductivity will be at a level very close to the 'tipping point' that would induce cavitation, so to maintain maximum efficiency. Therefore, stomatal regulation of minimum leaf water potential is crucial to maintaining this fragile hydraulic 'optimum' of the xylem.

 

Source: Franks, P. & Brodribb, T. (2005) Stomatal control and water transport in the xylem. In Holbrook, N. & Zwieniecki, M. (eds.) Vascular Transport in Plants. USA: Elsevier.

[Kveldssanger]

I shall be horifically festive and post a fact tomorrow, so for all of you here who are relying on me posting a fact so to not have your Christmas ruined, fret not.

[Kveldssanger]

When people buy you tree books as presents you know you talk about trees too much.

 

[Gary Prentice]

Surprised that anyone can find a book you haven't already got/read .

 

Merry Christmas

[Kveldssanger]

Hah! There are plenty. Got my eyes on a few books from Summerfield - Rethinking Ancient Woodlands being one of them. In time...

[Mark J]

Merry Christmas! Plenty of food for thought in these pages.

[Kveldssanger]

25/12/15. Fact #107.

 

The response of a tree - in terms of cambial growth - to insect defoliation will vary greatly, with some variables including insect species, tree species, tree vigour, and defoliating extent. For example, one single defoliation event upon a gymnosperm may kill it, though defoliation of a similar extent upon an angiosperm or deciduous gymnosperm will likely not lead to death. This is because they can rapidly replace foliage lost (and they do this every year as the seasons change, by default). However, two severe defoliation events within a single year may well kill angiosperms and deciduous gymnosperms, as may a single extensive defoliation event not necessarily kill a coniferous gymnosperm - different species of Pinus will vary in their ability to withstand huge losses in foliage, for instance.

 

Defoliator species will also play a role in the effects of defoliation upon cambial growth. Some insects only gradually remove foliage whereas others do so rapidly, and some insects may only feast upon the latest year's worth of growth and others older growth. There really are a huge amount of variables.

 

To give an example, we can look at Choristoneura fumiferana (eastern spruce budworm) and see how it will consume only the newest year's foliage. This consumption strategy leads to cambial growth remaining largely unimpacted at the base of the tree during the first year of defoliation, whilst the cambial growth in the crown is greatly impacted. This reduction is cambial growth is principally down to the reduction in supply of carbohydrates, though other drivers also exist (such as a drop in the supply of hormonal growth regulators).

 

In fact, insect defoliation effects will typically manifest within the crown first-and-foremost (perhaps for obvious reasons). At times, there may be a lag period of a few years before the radial growth in the lower trunk is negatively impacted by insect defoliation

 

The timing of defoliation also determines how cambial growth will be affected. In early summer, before shoots have fully extended, defoliation is more likely to kill gymnosperms, though by mid summer (once shoots have fully extended from the buds) defoliation is less impactful. In Pinus echinata, for example, early summer defoliation lead to a drop in radial growth during the current growing season and a subsequent recovery of radial growth within the following growing season, whilst late summer defoliation lead instead to a reduction in cambial growth in the following year (growth in the same season was not impacted). This is because most of the radial increment had already been laid down by late summer.

 

Source: Kozlowski, T. (1971) Growth and Development of Trees - Volume II: Cambial Growth, Root Growth, and Reproductive Growth. USA: Academic Press.

[Kveldssanger]

Merry Christmas! Plenty of food for thought in these pages.

 

Almost as good as a turkey roast, eh!

[Kveldssanger]

27/12/15. Fact #108.

 

We often see parasitic fungi (such as honey fungus) as bad - perhaps because they kill prized ornamental trees, reduce the (financial) productivity of a forest, or make trees more of a hazard to human existence. More intrinsically however, parasitic fungi are good, and in fact are crucial to the healthy existence of an ecosystem.

 

The author of this source asserts that parasitic fungi filter-out weak specimens and, at times, entire weakened ecosystems. This enables for stronger individuals (and groups of plants) to come in and take the place of the (now dead or dying) weaker ones. Without this constant destruction and renewal, and alongside the recycling of all the nutrients and minerals contained within the decaying weakened individuals, ecosystems would cease to function as they must.

 

In artificial environments this concept may not apply as robustly, though even when we are looking at ornamental trees that are struggling, what can we assert as a result of their host role for parasitic fungi? Probably many things, including poor genetic stock of the individual (a nursery / breeding issue), and improper planting of species (an individual of the wrong species planted in the wrong place; thus causing it to be weak), to name two.

 

Source: Stamets, P. (2005) Mycelium Running. China: Ten Speed Press.