Community Change: disturbance and succession

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Community Change: disturbance and succession. Reading: Chap. 13 I. Disturbance A. Disturbance: type, time, severity, and scale B. Stability: Resistance/resilience. II. Succession A. Primary and secondary succession B. Changes in species composition C. Changes C cycling - PowerPoint PPT Presentation


  • Community Change: disturbance and successionReading: Chap. 13

    I. DisturbanceA. Disturbance: type, time, severity, and scale B. Stability: Resistance/resilience

    II. SuccessionA. Primary and secondary successionB. Changes in species compositionC. Changes C cyclingD. Changes in nutrient cyclingE. Changes in trophic interactionsF. Changes in water and energy balance

  • I. DisturbanceA. Disturbance: Any physical force that results in mortality of organisms or loss of biomass.Any physical force?What qualifies as disturbance?CMM - "a discrete event in time and space that alters the structure of populations, communities, and ecosystems andcauses changes in resource availability or the physical environment."


  • Note geologists for scale in yellow circle

  • What about?A single tree fall?A log rolling against rocks in the intertidal zone?A gopher mound?An outbreak of gypsy moths?

  • I. DisturbanceA. Disturbance: Timing: - frequency (how often)- when, relative to other eventsSeverity - how much mortality/change is caused(Intensity - how strong the force is [energy/area/time].)Scale - how large an area it coversAny physical force that results in mortality of organisms or loss of biomass.Type what kind of disturbance event occurs

  • How do biotic communities respond to disturbance?

  • B. Stability: resistance, resilienceResistance: the ability of a community or ecosystem to maintain structure and/or function in the face of potential disturbanceResilience: the ability of a community or ecosystem to return to its original conditions following disturbanceDraw it

  • What affects resistance and resilience?

  • Grasslands, California

  • Dry forest, HawaiiNon-native, easy burning, fire-tolerant grassesOhia (Metrosideros polymorpha)Native trees

  • Effects of fire suppression

  • The extent of resistance or resilience to a given disturbance will depend on the adaptations of the organisms affected.This depends on their historic exposure to that disturbance over evolutionary time.Humans are greatly altering disturbance cycles.

  • II. SuccessionDirectional change in ecosystem structure and functioning over time following disturbance. Results from changes in species composition in response to biotically-driven changes in resource availability

  • A. Primary and Secondary SuccessionPrimary succession - growth on a new mineral substrate

    Volcanic depositionGlaciationLandslideSand dunesRiver bars

  • A. Primary and Secondary SuccessionSecondary succession - new organisms but soil remains intact from previous community.

    FireClearcutInsect outbreakHurricane/storm damageAgriculture - old fields

  • Severity of disturbance

  • 1. Early and late successional speciesB. Changes in species composition

  • Early and late successional species Glacier BaySee this site:

  • Early and late successional species

  • Climax communitiesEarly successional species: pioneer species

    Late successional species: climax community- monoclimax: one community type, determined by climate- polyclimax: many community types depending on soils, topography, etc.

  • Monoclimax communities BC coastal forests many different successional trajectories lead to similar western hemlock/red cedar communityBC coastal forestsKimmins 1997, Fig. 15.2

  • Polyclimax, California grasslands: same climate, but very different plant communities because of different soil typesSerpentine soils mostly native forbs and grassesSandstone soils Eurasian annual grasses, oak savannaKirby Canyon, South San Jose, CA

  • 2. Mechanisms of successionFacilitationInhibition First two influence changes in abiotic conditions and resource availability.

    - All can operate simultaneouslyFunctional traitsHerbivory

  • Facilitation and inhibition can operate simultaneously.

  • 3. Changes in resourcesLightNitrogenLake Michigan dunes, primary succession (Lichter 1998)BIOTIC INFLUENCES: Light availability declines and N availability increases.

  • C. Changes in Carbon Cycling1. Biomass2. GPP, NPP3. Het. respiration, NEP

  • C. Changes in Carbon Cycling1. Biomass increases to a maximumLichter 1998

  • C. Changes in Carbon Cycling2. NPP typically maximum in mid-successionWhy?a. Increased plant resp.?NPP

  • C. Changes in Carbon CyclingWhy?a. Increasedplant resp.b. Hydraulicconductance c. Soil nutrients RpGPP2. NPP typically maximum in mid-successionNPP

  • C. Changes in Carbon Cycling2. GPP, NPP - summary

  • C. Changes in Carbon Cycling3. NEP peaks in mid-succession, ~0 in late succession (GPP = Rtotal)Heterotrophic respiration increases to a maxSchlesinger 1995

  • 3. Heterotrophic resp. and NEPa. Primary SuccessionStand age (yr)

  • 3. Heterotrophic respiration, NEP b. Secondary Succession

  • Can we pull more CO2 out of the atmosphere by converting old growth forests to young forests?GPP higher in young than old forestsNPP higher in young than old forestsNEP higher in young than old forests

    So, should we cut old growth forests that arent pulling CO2 out of the atmosphere and replace them with young tree plantations?

  • But, total C storage higher in old than young growth forestsHarmon et al. 1990 Science

  • Where does the C go from logging?Harmon et al. 1990 ScienceOver half goes to fast turnover pools, then to the atmosphere.

  • ~250 years for C storage to return to old growth levelsHarmon et al. 1990 Science

  • Most rotations are 60-80 yearsHarmon et al. 1990 Science

  • D. Changes in nutrient cycling1. Primary succession- Increased N availability early (inputs)- Open closed- Decreased N availability late (litter quality)

  • Soil properties(Lichter 1998)

  • Soil properties - Glacier Bay: increased soil C leads to increased CEC(to 45 cm depth)

  • D. Changes in nutrient cycling2. Secondary succession- Nutrient loss following disturbance removing plant biomass.- Results from both decreased plant uptake and decreased microbial immobilization.

  • D. Changes in nutrient cycling2. Secondary succession: limiting nutrient (often N) controls uptake/loss of other essential elements

  • And increased runoff:

    Runoff increases after disturbanceLess transpirationMore runoff (leftovers after plant water uptake)13.13

  • See book (pp. 298-301):E. Changes in trophic interactions

    F. Changes in water and energy balance

  • Additional questions25. How useful was the book?26. Extent to which journal articles helped connect lecture material and current topics in global change research?27. Extent to which discussion helped in understanding the journal articles?28. Extent to which discussion helped in understanding ecosystem ecology concepts from lecture?Extent to which you read the journal articles for discussion: Ex = read all, studied til I understood them; VG = read all, came to class with questions I wanted to discuss; G = read most, came to class with questions; F = read some, skimmed others, had a basic idea of what papers were about, but not details; P = didnt read any papers in detail, but knew generally what they were about; VP = didnt read papers much at all.

  • Data from Finzi et al. 2002Given the data shown below (Fig. 3a from Finzi et al. 2002), how do you expect elevated CO2 to affect total ecosystem decomposition rates, based on its effects on lignin concentration of leaves? Why? Name two other direct or indirect effects of elevated CO2 that might influence ecosystem decomposition and briefly describe the mechanism. Fig. 3a from Finzi et al. 2002, showing percent of initial mass remaining following 24 months of decomposition for litter of different species. The different symbol styles represent different species, with open symbols being from ambient CO2 and dark symbols from elevated CO2 (3 replicates per species from each treatment).

    Most evidence shows that Plant respiration (Rp) is a relatively constant fraction of GPP (~50%) and that GPP shows a mid succession peak, with increases in early succession associated with increases in plant biomass (total photosynthetic area) and decreases in later succession because of limitations to water conduction within the plant and decreased availability of soil nutrients (as they get tied up in undecomposed litter).Point out differences in 1o and 2o succession for NEP and Rh (note this shows NPP and Rh instead of GPP and Rt)(also note that Rh is shown as a negative flux, i.e., loss of C to atmosphere)- initial negative NEP for 2o succ.- increases in Rh due to altered physical conditions (usually warmer) shortly after disturbance.- decline in Rh as available C used up- increase in Rh again as litter builds up with increasing plant biomass.What does this suggest about the ability of old growth forests to sequester CO2 from the atmosphere?

    Build up of organic matter and associated nutrients in both litter layer and mineral soil.Remind the students what CEC is


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