2. ECOLOGICAL SUCCESSION IS…
• THE OBSERVED PROCESS OF CHANGE IN THE
SPECIES STRUCTURE OF AN ECOLOGICAL
COMMUNITY OVER TIME.
• THE COMMUNITY BEGINS WITH RELATIVELY FEW
PIONEERING PLANTS AND ANIMALS AND DEVELOPS
THROUGH INCREASING COMPLEXITY UNTIL IT
BECOMES STABLE OR SELF-PERPETUATING AS A
CLIMAX COMMUNITY.
• SUCCESSION OCCURS IN ALL NATURAL
ENVIRONMENTS. EACH ENVIRONMENT HAS A
PARTICULAR NAME THAT EXPRESSES THE NATURE
OF THEIR ECOLOGICAL SUCCESSION: PRIMARY
AND SECONDARY
3. 1st year
Horseweed
dominant;
crabgrass,
pigweed
2nd year
Asters
dominant;
crabgrass
3rd to 18th
year
Grass scrub
community;
broomsedge
grass, pines
coming in
during this
stage
19th to 30th
year
Young pine
forest
30th to 70th
year
Mature pine
forest;
Understory
of young
hardwoods
70th to 100th
year
Pine to
hardwood
transition
100th year
plus
Climax oak-
hickory
forest
ECOLOGICAL SUCCESSION
4. THERE ARE TWO MAIN TYPES
OF ECOLOGICAL
SUCCESSION• PRIMARY SUCCESSION: THE PROCESS OF CREATING LIFE IN
AN AREA WHERE NO LIFE PREVIOUSLY EXISTED.
• SECONDARY SUCCESSION: THE PROCESS OF RE-
STABILIZATION THAT FOLLOWS A DISTURBANCE IN AN AREA
WHERE LIFE HAS FORMED AN ECOSYSTEM.
6. PRIMARY SUCCESSION
• THE DEVELOPMENT OF
AN ECOSYSTEMIN AN
AREA THAT HAS NEVER
HADA COMMUNITY
LIVING WITHIN IT
OCCURS BY A PROCESS
CALLEDPRIMARY
SUCCESSION.
• AN EXAMPLE OF AN AREA
IN WHICHA COMMUNITY
HAS NEVERLIVED
BEFORE, WOULDBE A
NEWLAVA ORROCK
FROMA VOLCANO THAT
MAKES A NEWISLAND.
8. SECONDARY SUCCESSION
• SECONDARY SUCCESSION BEGINS IN HABITATS WHERE
COMMUNITIES WERE ENTIRELY ORPARTIALLY
DESTROYEDBY SOME KINDOF DAMAGING EVENT.
• WHEN AN EXISTINGCOMMUNITY HAS BEEN CLEAREDBY
A DISTURBANCE SUCHAS A FIRE, TORNADO, ETC...AND
THE SOIL REMAINS INTACT, THE AREA BEGINS TO
RETURN TOITS NATURAL COMMUNITY. BECAUSE THESE
HABITATS PREVIOUSLY SUPPORTEDLIFE, SECONDARY
SUCCESSION, UNLIKE PRIMARY SUCCESSION, BEGINS
ON SUBSTRATES THAT ALREADY BEARSOIL. IN
ADDITION, THE SOIL CONTAINS A NATIVE SEEDBANK.
• SINCE THE SOIL IS ALREADY IN PLACE, SECONDARY
SUCCESSION CAN TAKE PLACE FIVE TOTEN TIMES
FASTERTHAN PRIMARY SUCCESSION.
10. WHY DOES ECOLOGICAL
SUCCESSION OCCUR?
• BECAUSE IT IS THE PROCESS OF LIFE FOR
PLANTS, SOIL ANDOTHERLIVING
ORGANISMS.
• BECAUSE ORGANISMS ALTERSOIL
STRUCTURE, CHEMISTRY, AND
MICROCLIMATES, THE SPECIES
COMPOSITION OF ECOLOGICAL
COMMUNITIES CONSTANTLY CHANGES OVER
TIME.
• SUCCESSION WILL CONTINUE UNTIL THE
ENVIRONMENT REACHES IT’S FINAL
STAGE…THE CLIMAXCOMMUNITY.
11. THE CLIMAX COMMUNITY
• A CLIMAXCOMMUNITY IS A MATURE, STABLE
COMMUNITY THAT IS THE FINAL STAGE OF ECOLOGICAL
SUCCESSION. IN AN ECOSYSTEMWITHA CLIMAX
COMMUNITY, THE CONDITIONS CONTINUE TOBE
SUITABLE FORALL THE MEMBERS OF THE COMMUNITY.
• ANY PARTICULARREGION HAS ITS OWN SET OF CLIMAX
SPECIES, WHICHARE THE PLANTS THAT ARE BEST
ADAPTEDFORTHE AREA ANDWILL PERSIST AFTER
SUCCESSION HAS FINISHED, UNTIL ANOTHER
DISTURBANCE CLEARS THE AREA.
13. • TWOMAIN PHYSICAL FACTORS DETERMINE THE NATURE
OF THE COMMUNITY THAT DEVELOPS IN AN AREA.
THESE ARE TEMPERATURE ANDTHE AMOUNT OF
RAINFALL.
• IF WE PLACE THE AMOUNT OF RAINFALL ON A GRAPH’S
“X” AXIS, FROM0-10, 10-20,AND20-30+ INCHES ANDTHE
TEMPERATURE ALONG THE “Y” AXIS FROMHOT,
MODERATE, TOCOLD, THE VARIOUS TYPES OF
ECOSYSTEMS WILL FIT INTOTHE GRAPHBASEDON THE
CONDITIONS THAT THEY REQUIRE.Temperature
Cold Cold desert Tundra Taiga
Moderate Temperate forest Grassland Deciduous forest
Hot Hot desert Savanna Tropical forest
Rainfall (inches) 0-10 10-20 20-30+
14. A SUMMARY OF CHANGES THAT
OCCURDURING SUCCESSION:
• PIONEERSPECIES COLONIZE A BARE ORDISTURBEDSITE. SOIL
BUILDING.
• CHANGES IN THE PHYSICAL ENVIRONMENT OCCUR(E.G., LIGHT,
MOISTURE).
• NEWSPECIES OF PLANTS DISPLACE EXISTING PLANTS BECAUSE
THEIRSEEDLINGS ARE BETTERABLE TOBECOME ESTABLISHED
IN THE CHANGEDENVIRONMENT.
• NEWLY ARRIVING SPECIES ALTERTHE PHYSICAL CONDITIONS,
OFTEN IN WAYS THAT ENABLE OTHERSPECIES TOBECOME
ESTABLISHED.
• ANIMALS COME IN WITHORAFTERTHE PLANTS THEY NEEDTO
SURVIVE.
• EVENTUALLY A CLIMAXCOMMUNITY THAT IS MORE ORLESS
STABLE WILL BECOME ESTABLISHEDANDHAVE THE ABILITY TO
REPRODUCE ITSELF.
15. THREATS TO SUCCESSION
• THE GRASSES THAT
MOVE IN AS PIONEER
SPECIES ARE OFTEN
THOUGHT OF AS
WEEDS.
• THE SUBSEQUENT
GROWTHOF SHRUBS
ARE CONSIDERED
UNDESIRABLE "BRUSH".
16. • WITHOUT THESE INTERMEDIATE STAGES, THE
DISTURBEDHABITAT CAN'T RETURN TO A
NATURAL FOREST.
• THE FRAGILITY ANDSTABILITY OF THE
ECOLOGICAL COMMUNITY ARE DEPENDENT
UPON SEVERAL FACTORS.
• FOREXAMPLE, IN TEMPERATE FORESTS, IF
THE SHRUBS ARE NOT ALLOWEDTO GROW,
INSECT PESTS BEGIN TO FEEDON YOUNG
TREES INSTEAD. THIS HAS HAPPENEDIN
MANY PLACES WHERE TREES ARE REPLANTED
AFTERAN AREA IS CLEAR-CUT. LARGE
QUANTITIES OF PESTICIDES ARE THEN
BROUGHT IN, POLLUTING THE SOIL AND
WATERANDALTERING THE NATURAL
ECOSYSTEMEVEN FURTHER.
17. HOWDO HUMANS AFFECT
ECOLOGICAL SUCCESSION?
• CLEARING THE LANDFORTHE GARDEN AND
PREPARING THE SOIL FORPLANTING REPRESENTS A
MAJOREXTERNAL EVENT THAT RADICALLY RE-
STRUCTURES ANDDISRUPTS A PREVIOUSLY
STABILIZEDECOSYSTEM. THE DISTURBED
ECOSYSTEMWILL IMMEDIATELY BEGIN A PROCESS
OF ECOLOGICAL SUCCESSION.
• PLANT SPECIES THAT ADAPT TO THE SUNNY
CONDITIONS ANDTHE BROKEN SOIL WILL RAPIDLY
INVADE THE SITE ANDWILL BECOME QUICKLY AND
DENSELY ESTABLISHED. THESE INVADING PLANTS
ARE WHAT WE CALL "WEEDS“ IN WHICHWE
CONSIDERA NUISANCE ORINVADERS.
18. HOWDOHUMANS AFFECT
ECOLOGICAL SUCCESSION?
• A GARDENER'S ONLY COURSE OF ACTION IS TO
SPENDA GREAT DEAL OF TIME ANDENERGY
WEEDING THE GARDEN ORUSING CHEMICALS TO
INFRINGE UPON THE WEEDS ANDTHE
ECOSYSTEMAROUNDIT.
• THE FARMERS ANDGARDENERS WHOARE
GROWING OURFOODS INCURAN IMMENSE COST
IN TERMS OF TIME, FUEL, HERBICIDES AND
PESTICIDES THAT HUMANS PAY EVERY
GROWING SEASON BECAUSE OF THE FORCE OF
ECOLOGICAL SUCCESSION.
19. DOES ECOLOGICAL SUCCESSION
EVER STOP?
• WE MUST RECOGNIZE THAT ANY
ECOSYSTEM, NOMATTERHOWINHERENTLY
STABLE ANDPERSISTENT, COULDBE
SUBJECT TOMASSIVE EXTERNAL
DISRUPTIVE FORCES (LIKE FIRES AND
STORMS) THAT COULDRE-SET ANDRE-
TRIGGERTHE SUCCESS IONAL PROCESS.
• AS LONG AS THESE RANDOMAND
POTENTIALLY CATASTROPHIC EVENTS ARE
POSSIBLE, IT IS NOT ABSOLUTELY
ACCURATE TOSAY THAT SUCCESSION HAS
STOPPED.
20. DOES ECOLOGICAL
SUCCESSION
EVER STOP?
• ALSO, OVERLONG PERIODS OF TIME
(“GEOLOGICAL TIME”) THE CLIMATE
CONDITIONS ANDOTHERFUNDAMENTAL
ASPECTS OF AN ECOSYSTEMCHANGE.
• THESE GEOLOGICAL TIME SCALE CHANGES
ARE NOT OBSERVABLE IN OUR“
ECOLOGICAL” TIME, BUT THEIR
FUNDAMENTAL EXISTENCE ANDHISTORICAL
REALITY CANNOT BE DISPUTED.
• NO ECOSYSTEM, THEN, HAS EXISTEDOR
WILL EXIST UNCHANGEDORUNCHANGING
OVERA GEOLOGICAL TIME SCALE.
