COMMUNITY CHANGE (SUCCESSION)

1
COMMUNITY CHANGE (SUCCESSION)

• Krebs cpt. 21 pages 403-424 431

2
SUCCESSION . Is the non-seasonal, directional
and continuous pattern of colonization and
extinction on a site by populations. Is the
replacement of one kind of community by another
kind the progressive changes in vegetation and
animal life that may culminate in the climax
community (Krebs 622)
3
PRIMARY SUCCESSION . recovery from a new
sterile area that has been uncovered by a
retreating glacier, or created by an erupting
volcano. SECONDARY SUCCESSION . recovery of
a disturbed site.
4
PRIMARY SUCCESSION
Mt. St. Helens pp403-405
Lake Michigan dunes pp416-419
Glacier Bay pp413-416
5
SECONDARY SUCCESSION
Krebs pp419-422
6

• Connell and Slatyer 1977
• Succession driven by interactions between
  species
• FACILITATION
• TOLERANCE (COMPETITION)
• INHIBITION

7
FACILITATION only certain pioneer species can
establish after disturbance. Early species
enhance the ability of later species to establish.
TOLERANCE any species can invade. Early species
have little or no effect on abilities of later
species to invade. Later species can displace
early species by reducing resources to levels
below those tolerated by earlier occupants.
INHIBITION any species can invade. Once
established, species resist further invasion and
are displaced only by death or further
disturbance.
8
SUCCESSION PATHWAYS
A
B
C
D
Facilitation
Tolerance Inhibition
A
B
D
C
9
(No Transcript)
10
FACILITATION
TOLERANCE
INHIBITION
11
A study from abandoned farmland illustrates some
aspects of Facilitation, Tolerance and Inhibition
(see Krebs pp 419-422)

• FIELD ABANDONED IN FALL
• 1. INITIAL INVASION
• Horseweed
• a winter annual
• produces abundant seed
• self-allelopathic

Conyza canadensis
12

• 2. NEXT SEASON
• Asters
• More susceptible to decaying roots of horseweed,
  than horseweed
• Tolerant of dry conditions

13

• 3. SECOND AND THIRD SEASONS
• Bluestem
• Seedlings invading since initial abandonment
• Broomsedge
• Seedlings invading since initial abandonment
• More tolerant of dry conditions than Asters
• Decaying roots of Horseweed promote growth

14
Bluestem
Broomsedge
15
SUMMARY

• FACILITATION
• Broomsedge is promoted by decaying roots of
  horseweed aster
• TOLERANCE
• Broomsedge displaces aster through competition
  for water
• INHIBITION
• Horseweed litter prevents aster from persisting

16
FORCIER 1975 Succession driven by interaction
of disturbance life history traits of species

• Studied trees in a New Hampshire forest
• Trees with dbh gt2 cm (400 plots)
• 90 of canopy
• Sugar maple
• American beech
• Yellow birch

17
Eastern deciduous hardwood forests Several tree
species
18
Grey Birch, Betula populifera
Black Gum, Nyssa sylvatica
19
Beech, Fagus sylvatica
Red Maple, Acer rubrum
20
SUGAR MAPLE
YELLOW BIRCH
BEECH
r K
21
SPECIES Density (/m2) (dmin/dmax ) x 100 plots with at least 1 seedling Mass/ind (mg)
Yellow birch 21.3 2 92 8
Sugar maple 10 57 73 268
Beech 3.9 66 55 569
22
Number of cohort alive at beginning of interval Number of cohort alive at beginning of interval Number of cohort alive at beginning of interval
Age interval Yellow birch Sugar maple Beech
0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 1000 70 lt30 1000 583 317 225 166 118 84 54 48 42 1000 410 262 188 138 121 110 92 87 83
23
CANOPY SEEDLINGS SEEDLINGS SAPLINGS
lt 0.5m tall lt 0.5m tall 0.5 2 m tall
Yellow birch Yellow birch Sugar maple Beech 0 - -
Sugar maple Yellow birch Sugar maple Beech 0 0 0
Beech Yellow birch Sugar maple Beech 0 0 0 0 Seed - Sprouts
24
CLIMAX MICROSUCCESSION
Beech (seed)
Beech (sprouts)
MINOR DISTURBANCE
Sugar Maple
Yellow birch
CATASTROPHIC DISTURBANCE
Successional communities