future of forests 1 Flashcards
(25 cards)
what is a tree
in 2015 there was 430 000 people per person
angiosperm (flowering plants with protected seeds)
gymnosperm (woody, perennial see-producing plants)
conifers (cone-bearing woody, seeded plants)
requires tree rings, trunk and crown of foliage
sometimes hight dependent: no distinct taxonomic group
ecological vs taxamonic group
types of forest
tropical
temperate
boreal
sub-tropical
Northern
deforestation in Europe
used to be 84% forest coverage, now 34%
this occurred over the last 2000 years
for wood, beef, soy, palm oil
ecosystem services provided by forests
temperature regulation
shelter for organisms
carbon sequestration
soil stability
nutrient cycles
recreational purposes
tree rings
width of tree ring indicates carbon storage
tree ring is predominantly old xylem
contains bark, phloem, vascular cambium and xylem in middle
xylem
under negative pressure
thickening prevents collapse: lignin, annular rings
role of cambium in tree ring size
cambium grown outwards each year
determines tree ring size
growth rate depends on water and other available nutrients
therefore, ring size can indicate tree health in that year
how does water move through the xylem
lower pressure in cell walls of leaves
creates negative pressure
pulls water up the xylem
root pressure: transport of water
less important for water movement up tree
osmotic pressure generated in roots
moves water up xylem
caused by accumulation of solutes in the stele
casparian strip is involved by separating cortex and steel
casparian strip has lignified parts of radial walls which enables stele to generate pressure (only happens at night, when stomata are closed)
transpiration: movement of water
evaporative pull of water up the tree
involves capillary action
generates the negative pressure but doesn’t itself move water
guttation
xylem sap forced out due to root pressure
cohesion tension theory
evaporation: creates negative pressure
cohesion: water molecules stick together due to H bonds, forms a continuous water column
adhesion: water molecules stick to xylem wall
tension: evaporation causes tension pulling water up
root pressure: pushes water into xylem (less significant)
cell wall composition
cellulose microfibrils embedded in a pectin jelly
role of transpiration in water molecules moving in plant
evaporation
pulls up water molecules by surface tension
continuous column of water
stomata
regulate how much CO2 goes in and water goes out
stomata tends to close at night
some different, e.g. C4 and CAM minimise time where stomata are open
photosynthesis/transpiration compromise is crucial to surviving climate change due to inc Co2 and dec water
effect of drought on tree rings
drought so stomata close
to prevent water loss
less CO2 absorbed
less carbon fixed
smaller tree rings
too much transpiration
water column breaks
xylem cavitation (embolism) stops transport
no backflow into soil
experiment to show cavitation of xylem
loss of conductivity in xylem positively corelated with water potential increases
water column snap
role of root pressure in drought
root pressure can “blow out” the water vapour embolism
at night when stomata is shut the root pressure can flush out embolism
cavitation noise
cavitation makes a click
can be measured by microphone
during the day the most clicks heard
more wind/more transpiration/more cavitation/more clicks
loss of conductivity varies between species
some plants are more drought tolerant
narrow xylem vessels are less likely to cavitate under negative pressure and low water potential
narrow xylem is less transport efficient
xyelm vessels can reduce size in summer
bordered pits
pores between xylem vessels
prevent the spread of gas embolism
gymnosperm bordered pits
taurus is whole between xylem vessels
isolates the cavitation event to one xylem
angiosperm bordered pits
size of “valve” prevents air passing through to neighbouring vessels
