9. Forest dynamics

Question 1

How does gause’s law of competitive exclusion apply to trees? 3

Answer 1

1. no 2 species can occupy the same ecological niche and coexist
2. trees superficially have the same nice and use the same light, water, mineral nutrients
3. however, natural forests always show mix of species, even over short distances

Question 2

How can tree species coexist? 7

Answer 2

1. ecosystems aren’t uniform or constant
2. have species variation eg. soil changes, water availability and mineral composition
3. have temporal changes eg. seasons
4. primary succession- development of ecosystem from bare rock
5. secondary succession - change in ecosystem
6. cyclical succession - constant changing in semi-stable ecosystems
7. disturbancem- natural (wind, fire, grazing) or human (fire, feeling, management) - gives rise to changes that allow cyclical succession

Question 3

What is primary succession and how does it apply to forests? 4

Answer 3

1. rapid transition from bare rock to broad leaf forest
2. begins with primitive soil, then grass, then shrubs, then small and large trees
3. takes about 300 years
4. succession doesn’t end when forest has been established

Question 4

How does primary succession of British forests occur? 9

Answer 4

1. about 10 000 years ago, earth got warmer, ice retreated from 2/3 of uk to arctic, allowing primary succession
2. Birch arrived first, about 10 500 years ago
3. most northerly broad leaf, good at tolerating extreme temperatures
4. grows quickly as an invasive
5. mature canopy at 10 years, vs 50/60 for oak
6. forest composition changed over 1000s of years, with addition of hazel, oak, pine and ask
7. beech began to flourish after channel closed about 4000 year ago, wind dispersed
8. invasive but not regarded as such
9. sycamore, also invasive, arrived from calais about 1000 years ago

Question 5

What is secondary succession and how does it apply to woodland? 5

Answer 5

1. development of ecosystem on previously vegetated land eg. old fields
2. follows a similar pattern to that from mid-primary succession
3. in europe, rapid development of woodland supports temperate deciduous forest climax community
4. in uk, typically scrub, then birch, then oak
5. commonly seen in urban areas as there is fully formed soil exposed where trees can be established quickly

Question 6

What is the structure of an ideal beech wood? 4

Answer 6

1. young trees provide heavy shade
2. tree seedlings compete, bigger ones grow
3. canopy opens as lighter shade provided
4. understory begins to grow

Question 7

How are gaps in the woodland in the uk filled in by other species? 8

Answer 7

1. centre of gap dominated by ash - mobile seeds and fast growing. gap created by large beech tree falling - lots of light
2. When a fallen beech tree creates a canopy hole, ash will fill the gap
3. ash seeds are like sycamore - spread fast
4. quirkus/oak not mobile but squirrels and jays like to spread acorns
5. oak doesn’t like shade, so competes with as, often loses as it is slower growing
6. beech seedlings grow in the shade of other trees at the edge of the gap
7. in reality, mature woodland is a mix of all phases
8. oak may fill spaces left by fallen ash

Question 8

Which species will dominate in a given woodland? 5

Answer 8

1. depends on year - trees produce more seeds in mast years
2. weather - temp/rainfall impacts
3. replacement a matter of chance - different species exploit different conditions at different times
4. once a tree is dominant, it stays there
5. different species use different strategies

Question 9

What is strategy theory and how does it apply to trees? 7

Answer 9

1. R ———- K
2. R is reproduction selected so reproduce quickly eg. mice
3. R favour disturbance eg. birch. disturbance disfavours forest
4. R are often weeds - exploit environment, then leave
5. K rely on carrying capacity, so long-lived and stable
6. K includes oak
7. this is a comparative scale

Question 10

What was the impact of the great storm of 1987 in the UK? 7

Answer 10

1. hurricane-force storm
2. biggest since 1703
3. about 15m trees felled, incl 6 of the oaks at sevenoaks, kent
4. toys hill, kent, regrowth dominated by birch
5. this is secondary succession, but it will be replaced
6. oak will grow underneath and outcompete
7. natural reorganization as we lacked seedling banks

Question 11

What are some forest diseases and what impact do they have? 8

Answer 11

1. dutch elm disease killed most of uk elms in 70s
2. now recovering
3. casue dby fungus-carrying elm bark beetle. bores and lays eggs under bark, fungus kills trees
4. likely originated in asia, problem in usa and europe
5. elm is clonal (suckers not seeds) so little genetic variation
6. Similar events occurred before eg. great elm decline
7. oak diseases - sudden oak death or Phytophthora is not serious in british oaks but effects plantation trees and other species
8. acute oak decline - bacterial - kills british oaks

Question 12

Describe ask dieback. 5

Answer 12

1. caused by airborne fungus
2. spread from central europe, took about 20 years to reach uk
3. expected to kill most of uk ash trees, despite our diverse native population
4. denmark lost 90% of ash, all planted from same genetic stock
5. we have imported seeds from denmark for some stupid reason

Question 13

How do animals cause forest disturbance? 8

Answer 13

1. insects incl. leaf eaters eg. ash sawfly and sap feeders eg. aphids
2. small mammals and birds eat seeds
3. may eat bark or buds
4. major effects on seeds and seedlings
5. important in dispersal
6. large herbivores may eat seedlings or leaves
7. inhibit forest regeneration
8. shift ecosystem towards grassland

Question 14

What is the impact of deer on forests? 6

Answer 14

1. populations have increased since 1960s
2. due to changing weather and farming practices
3. changes woodland ground flora
4. changes species mixture in tree populations eg. beech less sensitive than oak
5. scots pine woodland prevented rom regenerating as deer eating seedlings
6. solutions include fencing, culling and reintroduction of predators eg. wolves

Question 15

What impact does coppicing have? 3

Answer 15

1. human disturbance
2. productivity peaks in mid-succession
3. coppicing returns forest to earlier in succession

Question 16

The impact of deer on woodland biodiversity. R. gill. 2000.

What are the general problems that deer are causing in woodlands? 7

Answer 16

1. high deer populations due to lack of predators
2. perfect habitats provided by coppicing
3. prevent young tree growth
4. reduces diversity of vegetation
5. changes woodland composition due to preferences
6. can allow ground and canopy to grow but lack middle layer
7. prevent forest regeneration

Question 17

The impact of deer on woodland biodiversity. R. gill. 2000.

What impact does deer grazing have on fauna? 4

Answer 17

1. less species plant could impact herbivores
2. lack of middle layer reduced hiding places for carnivores
3. habitat changes impact invertebrates
4. small mammals suffer from lack of vegetation eg. bankvoles and shrews