Extracts from 'DEAD or ALIVE'
[Richardson, IBK (1995), Dead or Alive?
Is it really that simple? Arb. J., 19 (4): 395-400]
A few comments on trees:
“Assessing the ‘Dead or Alive’ status of a tree is rarely a problem, especially in the summer
months. In the winter, dead buds on the twigs shrivel; bark begins to degenerate and eventually
the twigs dry and snap easily. Later, twigs and branches fall, and the only pitfall then is
whether it is the whole tree or only a part which is dead - a stag-headed oak is an all too
frequent example of an obviously partly dead tree, [this] being evident in winter as well as
in summer.
One hazard relates to the deciduous conifers - larch (Larix), swamp cypress (Taxodium) and dawn
redwood (Metasequoia). Winter visits to the vulnerable can result in large fees being paid for
felling perfectly healthy ‘dead’ specimens.
Stumps (and their associated root systems) are not always clearly dead or alive. It is only the
appearance of sucker growth which will provide visual evidence of a living system.
Invisibly, an apparently inactive root system can sometimes have switched allegiance by natural
root grafting to a similar, nearby tree.”
And some comments on roots: [Important - First read the relevant content on Subsidiary Information on Roots]
“Healthy roots have their bark firmly attached; the
wood is usually moist and pale (although a few have colour characteristics).
Decaying
roots have frayed, detached or missing bark; the wood may be dark or
softened…;
they may smell - either musty or much worse…. On site, such features
often provide the basis for a reliable assessment of status.”
* * *
“The freshness of the sample is relevant. Ideally roots should be tested
within a day or two of excavation. If there is likely to be a delay they should
be stored dry, not in water (mistakenly thought ‘to keep them alive’).
Neither should they be kept with damp soil in a plastic bag [especially in a
warm office!]. Even the use of a bubble-pack envelope for transit can influence
the test result. In such damp conditions microbes can access the starch, while
under dry conditions they are relatively inactive and will scarcely invade the
specimen. All root samples are kept for [six] years, and from time to time it
is necessary to test an old sample for its status. Because the roots are stored
dry (in paper envelopes) the test will reflect starch levels present when the
specimens were first received, often years previously.”
* * *
“Very thin, or immature roots around 0.5mm in diameter and less, can have
little potential to store starch; their tissues may not show much differentiation...
Also, the fact that the root is so thin makes it more accessible to microbes,
so that it is readily invaded and therefore decays faster. The absence of any
starch in such a root does not provide any useful information; it could have
been very recently alive, or lost its limited amount of starch within days of
excavation.
A root system will often total many hundreds of kilometres in length….
Most of these roots are very thin and short-lived, so it can safely be said that
even the healthiest of trees will bear many dead roots; a ‘dead’ sample
may not be representative of the root system as a whole. [And by the way, most
new root growth takes place from April to September inclusive; and Poplar roots
have been measured as growing 5cm in a day!]
A further hazard with the iodine test is that other organic substances, in addition
to starch, react by colour changes that may be taken for starch reactions - for
example fungal products and spores often present in a decaying root.”
