AgriculturalAgricultural EcologyEcology

ByBy Dr.Dr. RensenRensen ZengZeng

DepartmentDepartment ofof EcologyEcology

CollegeCollege ofof AgricultureAgriculture

South China Agricultural University

Email: [email protected] ChapterChapter 1616

EcologicalEcological successionsuccession EcologicalEcological successionsuccession

• is defined as a continuous, unidirectional, sequential change in the species composition of a natural

• This sequence of community is termed as a sere （演替系列）, and culminates in the （顶极群落） LevelsLevels ofof bioticbiotic organizationorganization

– Individual – Population –

• Concept of Community • Ecosystem concept AutogenicAutogenic ((自生）自生） successionsuccession

• Is self-driven, resulting from the interaction between organisms and their environment. • Primary succession occurs on a newly formed substrate such as glacial till (冰川 沉积物）. • • Secondary succession follows , for example by flooding, fire or human activity VegetationVegetation DynamicsDynamics && PlantPlant SuccessionSuccession

• No vegetation is static with time. There is always changes happening in vegetation and the subject that studies changes in vegetation is called vegetation dynamics.

• Plant succession: Directional cumulative changes in species composition through time. • Time: 5 – 500 years • Seasonal changes in species composition a year is not considered as succession.

原生演替原生演替

Hydrarc succession: Beginning in wet (hydric) site. eg. pond, lake, bog. Xerarc succession: Beginning in dry (Xeric) site eg. rock surface（旱生演替） TwoTwo aspectsaspects ofof successionsuccession

i) Sequence of plant, animal and microbial communities that occupy an area over time ii) The processes by which this biotic communities replace each other and by which the physical environment becomes altered over time. In the later sense the product of succession is called sere, the characteristic sequence of biotic communities that successively occupy and replace each other in an environment over time. The various communities that together make up the sere is called seral stages BasisBasis ofof classificationclassification ofof successionsuccession

Initial condition (living propagules):

Primary succession（原生演替）: when it begins at a place devoid of plant propagules and microbs. eg. succession after volcanic eruption, landslide, glacier retreats. Secondary succession: （次生演替）begins at a place that already has plant propagules and microbs. eg. succession after fire, logging, insect epidemic. InitialInitial conditioncondition ((habitat moisture)moisture)

Xerarc succession: Beginning in dry (Xeric) site eg. rock surface（旱生演替） Hydrarc succession: Beginning in wet (hydric) site. eg. pond, lake, bog. Mesarc succession: Beginning in moist (mesic) site. eg. forest, old fields.

The resulting seres called Xerosere, and mesosere. Ecological Convergence ConceptConcept ofof ClimaxClimax

A self replacing seral stage that is relatively stable to other seral stage. eg if a dominant sp shows an inverted J curve the it is in a climax stage as opposed to a bell curve where the species is not self replacing and may be at a seral stage. ComplexityComplexity ofof ClimaxClimax CommunityCommunity

Progressive: Results into climax community with high structural and functional diversity. eg. Succession after a natural fire in black forest near Thunder Bay.

Retrogressive: Results into climax community with lower and structural and functional diversity. eg. Succession after clearcutting in black spruce forest with dense Kalmia understory in Newfoundland.

DrivingDriving forceforce behindbehind successionsuccession

Autogenic: Habitat biotic factor eg. replacement of existing community by the next results from the afterlife effects of the former that makes the habitat unsuitable to continue.

Allogenic: Habitat abiotic factors such as soil parent material, pH, nutrients drives the direction of succession. eg. filling of a lake with sediment and the further modified by the colonizing plants.

Biogenic: When a sudden interference with an autogenic and allogenic succession by a living organism that becomes a major agent of succession eg. , insect infestation etc.

ProcessesProcesses inin SuccessionSuccession

• Nudation • Colonization • Establishment • Reaction • Displacement • Facilitation • Recolonization MechanismMechanism ofof SuccessionSuccession

• Colonization (vegetative, seeds)

• Alteration of habitat (physical and chemical characteristics)

• Displacement of species (, allelopathy, insects, animals) Mechanisms,Mechanisms, PathwaysPathways && ModelsModels

• Mechanisms: Process or interaction that contributes to successional change eg. competition, , organic accumulation. • Pathways: Temporal pattern of ecosystem change ie. the sequence of plant community and habitat changes over time. • Models: Abstract conceptual representation to describe successional pathways & mechanisms eg. Word, pictorial, diagrammatic and computer based models ClassicalClassical andand modernmodern conceptsconcepts andand modelsmodels ofof successionsuccession Early references to succession: Theoprestus (300 BC): Pattern of development of bog vegetation. Thorea (1863): succession of hardwood stands replaced after logging pine in NE USA. Coined the term forest succession. Cowles and Clements: developed the formal concept of succession after studying sand dunes of lake Michigan. Clements (1916) Monoclimax theory of succession MonoclimaxMonoclimax TheoryTheory • Species composition and structure of the terminal community of all seres is determined by the regional macroclimate. • Plants of climax community can reproduce beneath their own shade and maintain the composition indefinitely. • The linear development towards climax can be arrested by SERECLIMAX: a steep exposed rock, springfed bog SUBCLIMAX: regularly burned Calluna heathland DISCLIMAX: communities are held in a stable early stage eg. farmlands, subalpine meadows by burrowing animals.

TwoTwo TenetsTenets ofof ClementsianClementsian ofof SuccessionSuccession (Clements 1916)

1) The community as superorganism 2) The climatic climax is a predictable endpoint

He emphasized the biotic processes and de-emphasized the importance of abiotic factors that drive succession ReasonsReasons forfor PolyclimaxPolyclimax TheoryTheory (Tansley 1920, 1935 1939,1941) Many factors can intervene to prevent an area from reaching the climatic climax eg. 1. frequent natural fires maintain grassland or forest of mid-seral stage, 2. outcrops of serpentine soils rich in Mg or limestone soils rich in Ca 3. Areas of then soil and steep topography support stable communities that are different from those that are on flat valley-bottom. Climax vegetation of these sites are all floristically different from the regional climax TheThe PolyclimaxPolyclimax TheoryTheory

Succession in a region does not lead towards a single climax but tward a mosaic of different climax communities determined by the mosaics of Therefore in addition to climatic climax there may be: Pyral climax (Fire) Edaphic climax (Soil) Biotic climax (Animal influence) TheThe ClimaxClimax PatternPattern HypothesisHypothesis (Whittaker(Whittaker 1953)1953)

Vegetation is a complex pattern of integrating communities rather than a mosaic of distinct communities.

This hypothesis has not proven as popular and persistent as either the monoclimax or the polyclimax theory. ClimaxClimax RecentRecent ModelsModels ofof SuccessionSuccession

• Recognition of the importance of individual species (Gleason 1926, 1927, 1929) • Importance of life history characteristics (Drury and Nesbitt 1973) • Plant strategies (CRS of Grime 1974, 1979) • Plant strategies and changing level (Resource ratio hypothesis of Tilman 1982, 1985, 1988,190a,b) • Three pathway model: Facilitation, Tolerance and Inhibition pathway (Connell and Slatyer 1977) VitalVital AttributesAttributes ModelModel ofof SuccessionSuccession (Noble and Slatyer 1977, 1979)

1. Mode of persistence (four classes) D–Species (dispersed by seeds) S–Species (stored seeds , seed bank) C–Species (canopy seeds) V–Species (vegetatively regenerating) 2. Conditions for establishment (three classes) T–Species (able to tolerate competition, establish any time) I–Species (intolerant of competition, establish at initial stage) R–species (Establish under other species after habitat change) 3. Timing of critical life history events (five classes) o- time when disturbance occurs p- time taken for propagules to arrive m- time taken for individuals to rich reproductive maturity l- life span, after which individuals are lost from the community e- time taken for species to be locally extinct. RatesRates ofof SuccessionalSuccessional ChangeChange

• Climate and soil condition • Degree of environmental change during succession • Rate at which biota change the environment • Longevity of the dominant species • Degree to which the communities dominate the site resist invasion • Frequency and severity of disturbance. ChangesChanges inin EcosystemEcosystem FunctionFunction DuringDuring SuccessionSuccession

• Ecological energetics • Biogeochemistry i) Geochemical cycle ii) iii) Biochemical or internal cycle ForestForest SeralSeral StagesStages

1. Stand initiation 2. Understory suppression 3. Stand differentiation 4. Understory reinitiation These correspond to: 1. Regeneration stage 2. Canopy closure stage 3. Self-thinning stage 4. Reestablishment of understory in gaps DisturbanceDisturbance && EcosystemEcosystem propertiesproperties

• Constancy: Lack of change in some parameters eg. Number of species, life form

• Persistence: Length of time over which the ecosystem is constant or maintains a particular condition within specied bounds

• Inertia: The ability of the cosystem to remain constant or to persist in the face of disturbing factors eg. Wind, fire, disease, herbivore. DisturbanceDisturbance && EcosystemEcosystem propertiesproperties

• Resilience/ Elasticity: The speed with which the ecosystem returns to its original condition after disturbance. • Amplitude: The extent to which an ecosystem can be changed and still return rapidly to its original condition. • Cyclical stability: The property of an ecosystem to change through a sequence of conditions that bring it back to the original condition eg. Calluna cycle • Trajectory stability: The tendency of to return to a single final condition after disturbance has alterd the initial condition to a variety of new conditions eg. retrogressive succession after fire LinearLinear andand CyclicalCyclical SuccessionSuccession

• Prescribed Burning in Calluna Heathland in Scotland

• Regeneration Complex in Sheep’s Fescue grassland in England.

ConceptConcept ofof ClimaxClimax

A self replacing seral stage that is relatively stable to other seral stage. eg if a dominant sp shows an inverted J curve the it is in a climax stage as opposed to a bell curve where the species is not self replacing and may be at a seral stage. DeterminingDetermining successionalsuccessional changeschanges

• Repeated sampling in permanent plots. • Contiguous plot sampling with known disturbance history, Chronosequence. • Toposequence • Time interval photography. SPECIESSPECIES INTERACTIONINTERACTION

Category of Type of interaction Species Species interactions A B + + Proto-cooperation + + + 0 Antagonism Exploitation Physical + - + - Predation + - /Allelopathy + - Competition - -

NutrientNutrient contentscontents (kg/ha/yr)(kg/ha/yr) inin rainfallrainfall andand throughfallthroughfall inin oakoak forest.forest. DataData fromfrom CarlisleCarlisle etet al.al. 1966.1966.

Nutrients In rainfall In throughfall N 9.57 8.82 P 0.43 1.31 K 2.96 28.14 Ca 7.30 17.18 Mg 4.63 9.36 Na 35.37 55.55 Total 60.20 120.36 EffectsEffects ofof canopycanopy andand understoryunderstory plantsplants onon pH,pH, B.D.B.D. && nutrientnutrient contentscontents ofof litterfalllitterfall && soilsoil (kg/ha)(kg/ha) andand turnoverturnover ratesrates (yrs.)(yrs.) Data frofromm Tappeiner & Alm (1975) Canopy/under pH B.D. CaNKMgP story g/cm3 Litter Ca K

Red pine 4.1 0.66 121 470 29 13 7 5.0 4.9 3.9 /none Red pine 4.1 0.54 111 335 29 14 7 3.2 2.5 3.1 /hazel Red pine 4.2 0.62 128 524 30 14 8 4.1 3.8 2.1 /-shrub Birch/hazel 5.0 0.44 304 617 47 43 8 1.7 1.4 0.2

Birch/herb- 5.1 0.48 337 602 50 44 9 2.3 1.9 0.3 shrub VegetationVegetation DynamicsDynamics && PlantPlant SuccessionSuccession

• No vegetation is static with time. There is always changes happening in vegetation and the subject that studies changes in vegetation is called vegetation dynamics.

• Plant succession: Directional cumulative changes in species composition through time. • Time: 5 – 500 years • Seasonal changes in species composition a year is not considered as succession.

ComplexityComplexity ofof ClimaxClimax CommunityCommunity

Progressive: Results into climax community with high structural and functional diversity. eg. Succession after a natural fire in black spruce forest near Thunder Bay.

Retrogressive: Results into climax community with lower and structural and functional diversity. eg. Succession after clearcutting in black spruce forest with dense Kalmia understory in Newfoundland. DrivingDriving forceforce behindbehind successionsuccession

Autogenic: Habitat biotic factor eg. replacement of existing community by the next results from the afterlife effects of the former that makes the habitat unsuitable to continue.

Allogenic: Habitat abiotic factors such as soil parent material, pH, nutrients drives the direction of succession. eg. filling of a lake with sediment and the further modified by the colonizing plants.

Biogenic: When a sudden interference with an autogenic and allogenic succession by a living organism that becomes a major agent of succession eg. herbivore, insect infestation etc.

ProcessesProcesses inin SuccessionSuccession

• Nudation • Colonization • Establishment • Reaction • Displacement • Facilitation • Recolonization MechanismMechanism ofof SuccessionSuccession

• Colonization (vegetative, seeds)

• Alteration of habitat (physical and chemical characteristics)

• Displacement of species (competition, allelopathy, insects, animals) Mechanisms,Mechanisms, PathwaysPathways && ModelsModels

• Mechanisms: Process or interaction that contributes to successional change eg. competition, predation, organic accumulation. • Pathways: Temporal pattern of ecosystem change ie. the sequence of plant community and habitat changes over time. • Models: Abstract conceptual representation to describe successional pathways & mechanisms eg. Word, pictorial, diagrammatic and computer based models ClassicalClassical andand modernmodern conceptsconcepts andand modelsmodels ofof successionsuccession Early references to succession: Theoprestus (300 BC): Pattern of development of bog vegetation. Thorea (1863): succession of hardwood stands replaced after logging pine in NE USA. Coined the term forest succession. Cowles and Clements: developed the formal concept of succession after studying sand dunes of lake Michigan. Clements (1916) Monoclimax theory of succession MonoclimaxMonoclimax TheoryTheory • Species composition and structure of the terminal community of all seres is determined by the regional macroclimate. • Plants of climax community can reproduce beneath their own shade and maintain the composition indefinitely. • The linear development towards climax can be arrested by: SERECLIMAX: lichen on steep exposed rock, springfed bog SUBCLIMAX: regularly burned Calluna heathland DISCLIMAX: communities are held in a stable early stage eg. farmlands, subalpine meadows by burrowing animals. TwoTwo TenetsTenets ofof ClementsianClementsian ofof SuccessionSuccession (Clements 1916)

1) The community as superorganism 2) The climatic climax is a predictable endpoint

He emphasized the biotic processes and de-emphasized the importance of abiotic factors that drive succession DeviationsDeviations fromfrom monoclimaxmonoclimax TheoryTheory (Tansley 1920, 1935 1939,1941) Many factors can intervene to prevent an area from reaching the climatic climax eg. 1. frequent natural fires maintain grassland or forest of mid-seral stage, 2. outcrops of serpentine soils rich in Mg or limestone soils rich in Ca 3. Areas of thin soil and steep topography support stable communities that are different from those that are on flat valley-bottom. Climax vegetation of these sites are all floristically different from the regional climax

TheThe PolyclimaxPolyclimax TheoryTheory

Succession in a region does not lead towards a single climax but toward a mosaic of different climax communities determined by the mosaics of habitats Therefore in addition to climatic climax there may be: Pyral climax (Fire) Edaphic climax (Soil) Biotic climax (Animal influence) TheThe ClimaxClimax PatternPattern HypothesisHypothesis (Whittaker(Whittaker 1953)1953)

Vegetation is a complex pattern of integrating communities rather than a mosaic of distinct communities.

This hypothesis has not proven as popular and persistent as either the monoclimax or the polyclimax theory. RecentRecent ModelsModels ofof SuccessionSuccession

• Recognition of the importance of individual species (Gleason 1926, 1927, 1929) • Importance of life history characteristics (Drury and Nesbitt 1973) • Plant strategies (CRS of Grime 1974, 1979) • Plant strategies and changing resource level (Resource ratio hypothesis of Tilman 1982, 1985, 1988,190a,b) • Three pathway model: Facilitation, Tolerance and Inhibition pathway (Connell and Slatyer 1977)

VitalVital AttributesAttributes ModelModel ofof SuccessionSuccession (Noble and Slatyer 1977, 1979)

1. Mode of persistence (four classes) D–Species (dispersed by seeds) S–Species (stored seeds , seed bank) C–Species (canopy seeds) V–Species (vegetatively regenerating) 2. Conditions for establishment (three classes) T–Species (able to tolerate competition, establish any time) I–Species (intolerant of competition, establish at initial stage) R–species (establish under other species after habitat change) 3. Timing of critical life history events (five classes) o- time when disturbance occurs p- time taken for propagules to arrive m- time taken for individuals to rich reproductive maturity l- life span, after which individuals are lost from the community e- time taken for species to be locally extinct. RatesRates ofof SuccessionalSuccessional ChangeChange

• Climate and soil condition • Degree of environmental change during succession • Rate at which biota change the environment • Longevity of the dominant species • Degree to which the communities dominate the site resist invasion • Frequency and severity of disturbance. ChangesChanges inin EcosystemEcosystem FunctionFunction DuringDuring SuccessionSuccession

• Ecological energetics • Biogeochemistry i) Geochemical cycle ii) Biogeochemical cycle iii) Biochemical or internal cycle DeterminingDetermining successionalsuccessional changeschanges

• Repeated sampling in permanent plots. • Contiguous plot sampling with known disturbance history, Chronosequence. • Toposequence • Time interval photography. ForestForest SeralSeral StagesStages

1. Stand initiation 2. Understory suppression 3. Stand differentiation 4. Understory reinitiation These correspond to: 1. Regeneration stage 2. Canopy closure stage 3. Self-thinning stage 4. Reestablishment of understory in gaps DisturbanceDisturbance && EcosystemEcosystem propertiesproperties

• Constancy: Lack of change in some parameters eg. number of species, life form

• Persistence: Length of time over which the ecosystem is constant or maintains a particular condition within specified bounds

• Inertia: The ability of the ecosystem to remain constant or to persist in the face of disturbing factors eg. wind, fire, disease, herbivore. LinearLinear andand CyclicalCyclical SuccessionSuccession

• Prescribed Burning in Calluna Heathland in Scotland

• Regeneration Complex in Sheep’s Fescue grassland in England. EcologicalEcological succession:succession: changechange inin communitycommunity structurestructure followingfollowing aa disturbancedisturbance PrimaryPrimary successionsuccession beginsbegins inin aa virtuallyvirtually lifelesslifeless areaarea wherewhere soilsoil hashas notnot yetyet beenbeen established.established. Example:Example: GlacierGlacier BayBay inin AlaskaAlaska

retreating glaciers leave pioneering plant moraines. autotrophic and are species are next bacteria are first first macroscopic colonizers. . soil forms gradually SuccessionSuccession continuescontinues untiluntil aa climaxclimax communitycommunity isis formed.formed.

final stage is a spruce replace alder spruce and hemlock and cottonwood forest Soil changes over time. Nitrogen levels start out low and increase because of symbiotic nitrogen-fixing bacteria in alder. Then other can survive. SecondarySecondary successionsuccession occursoccurs afterafter disturbancedisturbance thatthat leavesleaves thethe soilsoil intact.intact. OtherOther examples?examples?