Lecture 6 CM Flashcards
(13 cards)
What have most biomes been substantially altered by?
by human activity, however the ‘footprint’ (or impact) of this activity varies across different biomes
Arctic Tundra
(look at slides)
- occurs above 60 degrees N&S of the equator
- characterised by vegetation
- surface defrosts but the inside doesn’t
- high pressure zone so there is very little precipitation
- many plants rely on the blanket of snow as it may be warmer underneath the snow cover which is on the inside
Boreal Forest
(look at slides)
- 50-65 degrees North
- most extensive forest system as distribution is scarce
- tree growth form reflects environmental stresses: in the smi-frozen boreal environment, conical tree shapes has 3 distinct advantages over branching shape
What are the 3 advantages of the conical tree shape?
- snow accumulation is prevented and limbs do not break
–> the tree has adapted to snow accumulation which allows the snow to fall off, so the branches don’t break - the lower surface-to-volume area minimises the exposure and transpiration stress, especially outside the summer
- the vertical orientation of canopy limbs instead of horizontal orientation improves the efficiency of low-angle light conditions. the reverse is true in lower latitude/higher light angle environments
Temperate deciduous forest
(look at slides)
- 30-50 degrees North
- the trees drop their leaves because of the water stress
- the leaves form in autumn and inflate/expand in spring & summer
- vertebrates are more abundant and diverse than in the boreal forest
- herbs with underground storage organs are abundant
Temperate evergreen forest/rainforest
(look at slides)
- 45-50 degrees N&S
- there is no limit of growth per plant
- native forests in west and southwest Ireland display a climate and evergreen moss/fern vegetation is more typical of rainforests
Temperate shrubland: Mediterranean scrub, Chapparal
(look at slides)
- 30-40 degrees N&S
- plant can survive the summer drought using a variety of strategies
What ways can plants survive the summer drought in temperate shrubland?
- they can have a sclerophyllous habit comprising small waxy leaves (often semi-deciduous), which limit transpiration stress
- deep roots (to tap permanent water table)
- limited size (to maintain sustainable biomass)
- trees can be very long-lived
What is another way plants survive the summer drought in temperate shrubland?
- they use dormancy either as the seeds in the top soil layer (which germinate and reproduce quickly in spring)
- or they use underground storage organs (like bulbs, tubers) which allow the plants to achieve large biomass in a short growing period
What is the contrasting appearance of the temperate shrubland in the mild, wet spring and the hot, dry summer due to?
- it is caused by this switch between growth/leaf development and dormancy/leaf loss.
- this switch also determines the behaviour, life cycle and abundance of all animals in the biome
Temperate grassland: prairie, steppe, pampas
(look at slides)
- 30-50 degrees N&S
What does the relative proportion of apical meristems at ground/below ground level impact?
- it impacts the ability of each habitat to cope with physical disturbance, especially fire and excessive grazing
- after the fire or grazing, aboveground plant tissue is destroyed
- afterwards, grasses regenerate quickly, but trees and shrubs are often destroyed
How do seeds play a major role in helping vegetation recover?
- the seed bank in the soil is crucial
- weeds are seed bank specialists
