When was the Devensian cold stage?
115,000 to 10,000 BP, Arctic conditions and periods of warm were similar to boreal conditions
What are stadials and interstadials?
stadials= embedded periods of cold conditions
interstadials = embedded periods of temporarily warm conditions
What were the conditions like at the start of the Devensian cold stage?
- Coldest, permafrost in arctic and shrubby wildlife
- interstadials allow for some productive vegetation to come in
- 16 degree in summer and -10 in winter
- Rich vertebrae such as mammoth, bison, woolly rhino
What was the dimlington stadial?
- 21,000 ya wit extensive ice sheets and polar deserts and tundra
- large herbivores forced south but some mammoths remained
What was the loch Lomond Stadial?
- Last period of proper intense cold
- The species that survived went on to form species we have now
- Occurred after teeny warm period
When did the Forest form?
10,000 BC
How can we see the forest forming?
- Pollen gets trapped in the peat, take pollen in different layers by taking peat cores and look at the abundance of different tree species
- Gradual appearance of increasingly thermophilous trees (warm-loving trees)
- Birch starts to decline as its the most cold-tolerant
- As things warm up even more (moving up the peat core) we get elms, limes start to come in and oak which stays very abundant
When was the ‘Forest Maximum’ and what were its characteristics?
7,500,5000 years BP
- ‘Warm and Wet’
It was about 2.5 degree warmer than it is today
What happened after the forest maximum?
- Slightly cooler period resulting in some tree decline
brought us to about 2500 years ago
What is our % woodland cover now?
13% (compared to 50% 2000 ya)
Around 52% of this is conifer plantation and the rest is mainly broadleaf
What are the different woodland types and their characteristics?
Ancient Woodland:
Continuously wooded since before 1600
2.4% of land area
Semi-natural Woodland:
Largely native species and largely not planted
A bit more recent than ancient
Recent and plantation Woodland:
Commercial forestry
Conservation values
What is the difference between primary and secondary forest?
Primary= Semi-natural/ancient woodland
Secondary = Woodland or forest developed on cleared land
What are the characteristics of brown forest soil?
- High quality from deciduous leaf litter
- Transpiring trees stop wet soil
- Typical Uk woodland soil
- Highly valued for agriculture
- Invertebrates aid soil cycling and nutrient burying/lifting
What is the vertical structure of forests?
Tree layer
Shrub layer
Field layer
ground layer
(Not all of these layers will be present depending on habitat conditions e.g. too much leaf litter stops a ground layer from forming)
What are the three main distribution types for horizontal structure?
Regular = overdispersed and widely spread
Random = Small random groups of individuals
Clumped = underdispersed (most common) patches of species clumped together
What is varied horizontal structure caused by?
Morphology and growth characteristics of the plant species
Seed dispersal mechanisms (e.g. by wind or by animals)
Environmental heterogeneity
Species interactions (e.g. competition)
What are the two main approaches for plants for survival on the forest floor?
Shade tolerance
Complementary resource use
Explain how shade tolerance is a survival mechanism
- Shade plants often have a single palisade layer and large thin leaves
- Large surface area to weight ratio
- High photosynthesis but low respiration (low compensation point)
- Evergreen - low energy requirements
- Grow slowly as the leaves must respire through winter
What does a low compensation point mean?
Don’t need much light before photosynthesis outweighs respiration
Don’t lose much carbon in dark conditions
How is Complementary resource use a survival mechanism?
Early growth and flowering of ground species before trees dump loads of litter and have coverage
So they use the light levels in early spring to the best of their ability e.g. bluebells
How were heliophiles supported in the post glacial period?
Grasslands supporting heliophiles
Development of forests confined helophiles to open habitats
Explain the vera cycle
a way grazers make an open habitat within woodlands
Open → scrub → woodland → breakup through disturbance leading to expansion of open area good for heliophile species
What is the evidence of a ‘slash and burn’ agricultural approach in the neolithic period
Decline in tree pollen
Increase in arable weed pollen
Cereal pollen recorded
Sometimes a charcoal layer
How was the vera cycle enhanced under neolithic influence?
neolithic used advantage of woodland areas cleared by animals
(vera cycles)
hunting and removing top predators, vera cycles are enhanced as herbivore populations increase
Leads to permanent deforestation
