Plant succession

1. Plant succession

2. The Concept
 Succession is the natural, orderly change
in plant and animal communities that
occurs over time. If left undisturbed, an
open field may become an "aging" forest in
150-300 years. However soil conditions,
climate, permafrost, topography, and
natural and unnatural forces may affect the
pattern of succession

3.  Weather, fire, flood, insects, and human
activity can disrupt the forest, altering the
pattern of succession

4. The Stages

5. Herb Stage
 In this stage it contains seed plants whose
stems wither away to the ground each
winter.
 insects and small rodents feed on the
grasses, herbaceous plants, and seeds
 As the diversity of plants increases so does
the variety of wildlife species.

6. Shrub Stage
 usually low woody plants with several
permanent stems instead of a single trunk
 Larger variety of wild-life attracts predators

7. Young Forest Stage
 the quantity and diversity of shrubs and
herbaceous plants decreases
 With less variety in food available, the
number of wildlife species decreases.
 birds of prey nest in the trees of a young
forest

8. Mature Forest Stage
 hardwood trees begin to die, opening the
canopy for the growth of spruce
 Shrubs return and make more food and
cover available to songbirds, game birds,
and rodents.

9. Climax Forest Stage
 dead trees called snags provide homes for
woodpeckers and other cavity-nesting
birds. Porcupines, squirrels, spruce grouse,
and several songbird species are typical of
old stands of spruce trees.

10. Types of Succession
 Primary
 Secondary
 Allogenic
 Autogenic
 Progressive
 Retrogressive

11. Primary
 Establishment of plants on land previously
not cultivated.

12. Secondary
 Invasion by plants on land that that was
previously vegetated.
 Possible causes include natural or human
such as fire logging, cultivation or
hurricanes

13. Allogenic
 Change in Environmental conditions
 E.g.. Salt marsh to woodland.
 The environmental changes the
composition of the plant community

14. Autogenic
 Where both plant community and
environment change
 Caused by the activities of plants over time
 E.g.. Eruption of Mt. St.Helens

15. Progressive
 Where community becomes more complex
with time
 Contains more species
 Contains more biomass over time.

16. Retrogressive
 The community regresses.
 Becomes more simplistic
 Contains fewer species and less biomass
 Some retrogressive successions are
allogenic in nature
 E.g. Introduction of grazing animals results
in degradation of farmland.

17. The Facilitation Model
 "pioneer species" establish a presence on the site
of a disturbance.
 They modify a site, for instance, by regenerating
the soil with organic material making the area
more attractive for invasion by other species.
 Eventually, new species move in, edging out the
pioneers.
 This process may repeat itself several times, until
the ecosystem reaches the climax stage.

18. The Tolerance Model
 all species involved in succession are equally
capable of establishing themselves on a recently
disturbed site
 but those capable of attaining a large population
size quickly are likely to become dominant
 Unlike the facilitation model, the tolerance model
does not depict earlier inhabitants as preparing
the site biologically.
 this model is more akin to natural selection.

19. The Inhibition Model
 all species have equal opportunity to
establish populations after a disturbance
 some of the early species actually make the
site less suitable for the development of
other species
 An example of this is when plants secrete
toxins in the soil, thus inhibiting the
establishment and growth of other species

20. Climax
 When a biological community reaches a state of stability and
is in equilibrium with environmental conditions
 Dominant species in a climax community are those that are
tolerant of the biological stresses that come with competition
 frequent enough events of disturbance within small sections
of the biological community may prevent climax from even
occurring
 Once reached change will slow down bringing an end to the
stages of succession.
 Climax remains a theoretical notion.

21. What can cause Succession
 Seismic Events: earthquakes, tidal waves, or
volcanic eruptions
 hurricanes or tornadoes.
 the movement of glaciers or even of plates in
Earth's crust
 wildfires or sudden infestations of insects
 Humans causes such as plowing up ground,
logging, clearance for construction even by
causing explosions on a military reservation or
battlefield