9. Forest dynamics Flashcards
1
Q
How does gause’s law of competitive exclusion apply to trees? 3
A
- no 2 species can occupy the same ecological niche and coexist
- trees superficially have the same nice and use the same light, water, mineral nutrients
- however, natural forests always show mix of species, even over short distances
2
Q
How can tree species coexist? 7
A
- ecosystems aren’t uniform or constant
- have species variation eg. soil changes, water availability and mineral composition
- have temporal changes eg. seasons
- primary succession- development of ecosystem from bare rock
- secondary succession - change in ecosystem
- cyclical succession - constant changing in semi-stable ecosystems
- disturbancem- natural (wind, fire, grazing) or human (fire, feeling, management) - gives rise to changes that allow cyclical succession
3
Q
What is primary succession and how does it apply to forests? 4
A
- rapid transition from bare rock to broad leaf forest
- begins with primitive soil, then grass, then shrubs, then small and large trees
- takes about 300 years
- succession doesn’t end when forest has been established
4
Q
How does primary succession of British forests occur? 9
A
- about 10 000 years ago, earth got warmer, ice retreated from 2/3 of uk to arctic, allowing primary succession
- Birch arrived first, about 10 500 years ago
- most northerly broad leaf, good at tolerating extreme temperatures
- grows quickly as an invasive
- mature canopy at 10 years, vs 50/60 for oak
- forest composition changed over 1000s of years, with addition of hazel, oak, pine and ask
- beech began to flourish after channel closed about 4000 year ago, wind dispersed
- invasive but not regarded as such
- sycamore, also invasive, arrived from calais about 1000 years ago
5
Q
What is secondary succession and how does it apply to woodland? 5
A
- development of ecosystem on previously vegetated land eg. old fields
- follows a similar pattern to that from mid-primary succession
- in europe, rapid development of woodland supports temperate deciduous forest climax community
- in uk, typically scrub, then birch, then oak
- commonly seen in urban areas as there is fully formed soil exposed where trees can be established quickly
6
Q
What is the structure of an ideal beech wood? 4
A
- young trees provide heavy shade
- tree seedlings compete, bigger ones grow
- canopy opens as lighter shade provided
- understory begins to grow
7
Q
How are gaps in the woodland in the uk filled in by other species? 8
A
- centre of gap dominated by ash - mobile seeds and fast growing. gap created by large beech tree falling - lots of light
- When a fallen beech tree creates a canopy hole, ash will fill the gap
- ash seeds are like sycamore - spread fast
- quirkus/oak not mobile but squirrels and jays like to spread acorns
- oak doesn’t like shade, so competes with as, often loses as it is slower growing
- beech seedlings grow in the shade of other trees at the edge of the gap
- in reality, mature woodland is a mix of all phases
- oak may fill spaces left by fallen ash
8
Q
Which species will dominate in a given woodland? 5
A
- depends on year - trees produce more seeds in mast years
- weather - temp/rainfall impacts
- replacement a matter of chance - different species exploit different conditions at different times
- once a tree is dominant, it stays there
- different species use different strategies
9
Q
What is strategy theory and how does it apply to trees? 7
A
- R ———- K
- R is reproduction selected so reproduce quickly eg. mice
- R favour disturbance eg. birch. disturbance disfavours forest
- R are often weeds - exploit environment, then leave
- K rely on carrying capacity, so long-lived and stable
- K includes oak
- this is a comparative scale
10
Q
What was the impact of the great storm of 1987 in the UK? 7
A
- hurricane-force storm
- biggest since 1703
- about 15m trees felled, incl 6 of the oaks at sevenoaks, kent
- toys hill, kent, regrowth dominated by birch
- this is secondary succession, but it will be replaced
- oak will grow underneath and outcompete
- natural reorganization as we lacked seedling banks
11
Q
What are some forest diseases and what impact do they have? 8
A
- dutch elm disease killed most of uk elms in 70s
- now recovering
- casue dby fungus-carrying elm bark beetle. bores and lays eggs under bark, fungus kills trees
- likely originated in asia, problem in usa and europe
- elm is clonal (suckers not seeds) so little genetic variation
- Similar events occurred before eg. great elm decline
- oak diseases - sudden oak death or Phytophthora is not serious in british oaks but effects plantation trees and other species
- acute oak decline - bacterial - kills british oaks
12
Q
Describe ask dieback. 5
A
- caused by airborne fungus
- spread from central europe, took about 20 years to reach uk
- expected to kill most of uk ash trees, despite our diverse native population
- denmark lost 90% of ash, all planted from same genetic stock
- we have imported seeds from denmark for some stupid reason
13
Q
How do animals cause forest disturbance? 8
A
- insects incl. leaf eaters eg. ash sawfly and sap feeders eg. aphids
- small mammals and birds eat seeds
- may eat bark or buds
- major effects on seeds and seedlings
- important in dispersal
- large herbivores may eat seedlings or leaves
- inhibit forest regeneration
- shift ecosystem towards grassland
14
Q
What is the impact of deer on forests? 6
A
- populations have increased since 1960s
- due to changing weather and farming practices
- changes woodland ground flora
- changes species mixture in tree populations eg. beech less sensitive than oak
- scots pine woodland prevented rom regenerating as deer eating seedlings
- solutions include fencing, culling and reintroduction of predators eg. wolves
15
Q
What impact does coppicing have? 3
A
- human disturbance
- productivity peaks in mid-succession
- coppicing returns forest to earlier in succession
