L7 Flashcards
What is the devensian cold stage?
115,000- 10,000 BP
Generally cold but considerable temperature fluctuation
Interstadials
Interstadials
warm periods
- Summer temperatures similar to now
- Winter temperatures much colder
- Some interstadials had forest, others not
- Rich vertebrate fauna, including temperate and boreal species
Dimlington stadial
Extensive ice sheets
- Polar desert or tundra in the periglacial fridge - Large herbivores probably forced south - But some mammoths remained
Loch Lomond stadial
- Ice sheet retreat
- Patchy permafrost
- Not fully artic
- Brings us to about 10,000 years ago
- Tree birches and pine survived
Goodwin zonation (pollen)
- Pollen analysis in peat cores
- Gradual appearance of increasingly thermophilous (warm loving) trees (elm, oak etc)
- Birch is cold tolerant - often forms northern tree line
- Emergence of pine as temperatures increases slightly
- Leads to the forest ‘maximum’
- UK essentially was totally forest covered
The forest maximum conditions
- Warm and wet
- 2.5c warmer than today
- Followed by cooler, wetter conditions resulting in some tree decline
- Only 5000 years ago
- Development of other UK systems is linked to the fall of the forest maximum
Uk woodland cover over the years
5000BP uk largely covered by woodland
2000BP end of iron age = 50% woodland
1400 = 10% woodland cover
1900 = 5% woodland cover
currently = 13%
what is the woodland today composed of in the UK?
52% conifer plantation, remainder largely broadleaf
= 50 native species of trees and shrubs
woodland types
ancient woodland
semi-natural woodland / primary
recent and plantation woodland (planted)
Ancient woodland
- Continually wooded since before 1600
- 2.4% of land area
Semi-natural woodland
- Largely native species and largely not planted
Recent and plantation woodland
- Commercial forestry
- Conservation/ amenity value
woodland soils
brown forest soil (or brown Earth)
typical soil in UK woodland
relatively good quality, rich soil
highly valued for agriculture -many lowland forest cleared
very fertile land
vertical structure
- Most complex vertical structure of any vegetation type
- Typically seen in many woodlands
what are the two main approaches plants have for survival on the forest floor?
shade tolerance
complementary resource use
shade tolerance mechanisms
altered leaf morphology
- Often have large, thin leaves - Single palisade layer reduces light travel distance to reach chloroplasts - Minimises CO2 travel distance - Larger SA to weight ratio
Morphological plasticity to shading
- Typical of plants in partial shade conditions
lower respiration
- Carbon gain = photosynthesis - respiration
- The amount of light where photosynthesis = respiration is the light compensation point
- Shade tolerant plants may have a lower light compensation point than plants adapted to sunny areas as they have a low respiration point
- Shade leaves have advantage at low levels
- Disadvantage is that it cannot reach high photosynthesis
- However shade plants are always unlikely to so it is not that significant
Being evergreen
- Lower energy requirements
- This means they do not have to have shade type leaves
Way hair grass
- Narrow , bristle like leaves
- Tolerates partial shade
- But these leaves must respire through winter so have a low respiration rate and therefore grow slowly
Complementary resource use
- Early growth and flowering, occurring before canopy becomes too dense
- Eg dog’s mercury
- Their flowering finishes prior to tree canopy growth
- Resource use of light and avoids shade
