iii. Flashcards
sapwood
living xylem, typically from the most-recent few years of the tree’s growth.
living xylem
transports water from the soil up to the leaves
the more leaves that a tree has …
the more sapwood it needs to get water to them
The xylem in
sapwood is ____ and so ____
living; requires energy from maintenance respiration to keep it alive
heartwood
older, dead xylem that had been sapwood when it was first created
waterproof because of being filled with secondary substances
when the tree turned old sapwood into heartwood
the sapwood had its nutrient
reserves removed, and had secondary substances added that reduce the chance of it
decaying.
secondary substances
tyloses, resins and dyes
tyloses
deformed cells that fill vessels
a tree does not need …
heartwood to be able to survive, because it is no longer functional
hollow trees can
stand up fine as long as they are in closed-forests
that protect them from high winds
Hollow trees growing in the open …
are more prone being blown down
the hollows in hollow tree-trunks concentrate the wind and that increases the chance they will be blown over
annual tree-rings are typically much clearer in the
heartwood than they are in the
sapwood
photosynthate
chemical energy created from photosynthesis
trees typically allocate the photosynthate in the following ranking of abundance, from
most to least
maintenance respiration
producing leaves and fine roots
flower and seed production
primary growth
secondary growth
maintenance respiration
the greatest amount of photosynthate is used to keep
existing tissues alive
respiration increases as …
temperature increases
producing leaves and fine roots …
to enable continued photosynthesis,
by replacing leaves that fall off seasonally
flower and seed production …
to enable continued survival of a tree’s genes
In years
when many seeds are produced …
trees have lower primary and secondary growth, due
to the energy put into making the seeds
primary growth
elongation of terminal and lateral shoots and woody roots to enable a tree to compete with its neighbors for light and water
secondary growth
new wood to conduct water
trees growing vigorously in high quality habitat …
… have so much photosynthate that
maintenance respiration only takes up 25% of photosynthate, leaving 75% for growth
trees in low quality habitat …
may need 75% of photosynthate for maintenance
respiration and only have 25% left for growth
in very low quality habitats …
the photosynthate may go to maintenance respiration, leaving no energy to grow at all,
which results in those trees having missing rings over their whole surface
sudden reduction in crown size …
can occur from people pruning leaves and branches from the tree
naturally by animals browsing (e.g. spruce budworm feed on needles and buds) or wind disturbance
a sudden loss of >50% of the leaves typically results
in the tree dying
the tree will survive if it
can …
quickly “abandon” (i.e. kill) much of the now unneeded xylem tissue, by removing the nutrients from the xylem and adding resins or tyloses to them
how can trees survive
coppicing and pollarding?
they have their upper stem portions removed during winter when the plant is dormant and has stored most of its nutrients in the trunk and roots
trees must be first coppiced or pollarded when they are young and have a small diameter, and regularly coppiced or pollarded after that, to ensure that the trunk does not have a large amount of sapwood that would have a high maintenance respiration
tree growth efficiency
the volume of wood grown per year per area of land on which the trees are grown
as a tree ages …
its functional live crown stays the same size and thus so does its gross photosynthesis but, because the total tree size is
larger its respiration increases, and thus its net rate of photosynthesis decreases
the tree growth efficiency for trees with strong apical control is highest …
for young trees when they are narrowly-spaced
for old trees when they are more widely spaced
the tree growth efficiency for trees with weak apical control is highest …
for young trees if they are narrowly-spaced
for old trees when they are widely- spaced
stability of decurrent tree stems
will be rapidly twisted by the wind which will cause it to split in half vertically (if hollow, growing in the open, and subject to high wind)
stability of excurrent tree stems
if DBH is 1% of less of it’s height - will have much weight concentrated over a narrow based and may, as a result of
that weight, buckle, breaking horizontally several feet above the ground.
dense stands of trees may support each other during wind because
their roots will be entwined and their crowns will be leaning on each other
when trees are killed by disturbance or logging …
the environment for the remaining trees changes due to the loss of shading of their sides: the tree’s environment will change in terms of heat, moisture, light, and wind
side-shade temperature increases
increased soil temperature increases nutrient availability in cold climates because the warmer temperatures increase the activity of bacteria and fungi in the soil
side-shade moisture
the air typically becomes drier because there are no longer so many leaves transpiring moisture into the air
side-shade brightness
thin shade-leaves may not be able to handle the sunlight and may thus die
sun-scald
may develop on a tree released from side-shade
the sunlight might be strong enough to heat the dormant tree up enough to cause a part of the lateral meristem to become active; If the sunshine suddenly disappears, the temperature of the lateral meristem will suddenly drop, the tissues will
freeze, and that part of the lateral meristem will die leaving a crack or a scar
if the tree was small when released (ages A or B)
it will grow to look like an open-growth tree, with its crown beginning low to the ground
