Chapter Concepts z Community changes during succession include increases in species diversity and changes in species composition Chapter 20 z Ecosystem changes during succession include increases in biomass, primary SUCCESSION AND STABILITY production, respiration, and nutrient retention z Mechanisms that drive ecological succession include facilitation, tolerance, and inhibition z Community stability may be due to lack of disturbance or community resistance
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Primary Succession – Glacier Bay, Definitions Alaska z Succession – Gradual change in plant and z Reiners et al. (1971) studied changes in animal communities in an area following plant diversity during succession disturbance 9 Total number of plant species (species 9 Primary – Succession on newly exposed richness) increased with plot age geological substrates 9 Species richness increased rapidly in early 9 Secondary – Succession following disturbance that does not destroy soil years of succession and more slowly during later stages z Climax Community – Late successional community - remains stable until disrupted Not all groups increased in density throughout by disturbance succession (different composition)
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Secondary Succession in Temperate Forests z Oosting (1942) found number of woody plant species increased during secondary succession at Piedmont Plateau z Johnston and Odum found increase in bird diversity across successional sequence closely paralleled increase in woody plant diversity observed by Oosting
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2 Succession in Rocky Intertidal Communities z Easy manipulation z The first species – green alga (Ulva) and the barnacle z The next – perennial red algae z Finally - perennial red algae (Gigartina canaliculata) dominated z 1.5 years as compared to 1500 yrs in Glacier Bay and 150 yrs in Piedmont Plateau
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Succession in Stream Communities
z Fisher et al. (1982) studied rapid succession in Sycamore Creek, AZ 9 Evaporation nearly equals precipitation – flows generally low and intermittent Subject to flash floods (disturbance) 9 Observed rapid changes in diversity and composition of algae and invertebrates Invertebrates found refuge because many adults in aerial stage
¾ Re-colonized after flooding
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Ecosystem Changes During Ecosystem Changes at Glacial Bay Succession z Chapin (1994), Glacier Bay 9 Total soil depth and depth of all major soil z Ecosystem changes during succession horizons show significant increase from include increases in biomass, primary pioneer community production, respiration, and nutrient 9 Soil properties (influencing the kinds of retention organisms that can grow) also changed during succession, i.e., Organic content, moisture, and N concentrations all increased
¾ Physical and biological systems inseparable
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z Hedin et al. (2003) – Hawaii islands, Four million years of changes chronoseqence of forest ecosystem 9 Different islands have different historic z Studies at Glacial Bay development (300 to 4,100,000 yrs) in their z Chronosequence – the sequence of ages rocks due to volcanic lava flows represented by the study sites
Molles: Ecology 3rd Ed.
5 z Change pattern in P z Organic matter Organic Total increased in carbon nitrogen Total P content in soils was 40 1.5 Refractory P Form different soils over the Total P Weatherable P of P first 150,000 0.6 z No obvious pattern years 30 was found z Analogous 1.0 75 0.4 z But, the form of P increases in soil changed organic matter 20 50 substantially z Also, the 0.5 0.2 z Become a limiting changes in soil 10 N content 25 factor on primary followed production when the precisely content is low in 0.1 11000 0.3 2.1 20 150 1400 4100 Soil age older soils Soil age
z There are changes Recovery of nutrient retention after in rates of nutrient N loss P loss disturbance 10 loss across the 0.1 z chronosequence Bormann and Likens (1981) in the 8 0.08 Hubbard Brook Experimental Forest z Higher rate of N loss 6 0.06 z Cut forest and suppress vegetation growth by herbicides z Decreased rates of 4 0.04 P loss z High nutrient losses during the 2 z Most of the losses 0.02 suppressed period are due to leaching z When the herbicide applications were to groundwater 0.1 1 10 100 1000 stopped, succession proceeded and Soil age nutrient losses decreased dramatically
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6 Model of Ecosystem Recovery z Bormann and Likens proposed the biomass accumulation model z Four phases 9 Reorganization (10-20 yrs) Forest loses biomass and nutrients 9 Aggradation (100+ yrs) Ecosystem reaches peak biomass 9 Transition Biomass declines from peak 9 Steady-State Biomass fluctuates around mean
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Succession and stream ecosystem properties z Sycamore Creek, Arizona z Succession happened within in 63 days after flooding z Show similar pattern as proposed by the biomass accumulation model
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7 Succession and stream ecosystem properties z Algal biomass increased rapidly for the first 13 days and then decreased more slowly afterwards z Ecosystem metabolic parameters (e.g., photosynthetic rate) show leveling off z The level of retention increased rapidly during succession, then leveling off to eventually 0 (balance state, input = output)
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8 Mechanisms of Succession
z Clements (1916): 9 Facilitation z Connell and Slayter (1977): 9 Facilitation 9 Tolerance 9 Inhibition z Most of the current evidences support the facilitation model, the inhibition model, or some combination
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Facilitation Tolerance
z Proposes many species may attempt to z Initial Stages of colonization not limited to colonize newly available space Pioneer Species 9 Only certain species will establish 9 Early successional species do not facilitate Colonizers – “Pioneer Species” – modify later successional species environment so it becomes less suitable for themselves and more suitable for species of later successional stages
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9 Successional Mechanisms in Inhibition Rocky Intertidal Zone z Early occupants of an area modify env. in a z Sousa investigated mechanism behind way that makes it less suitable for both early succession of algae and barnacles in and late successional species intertidal boulder fields. 9 Early arrivals inhibit colonization by later 9 If inhibition model is in effect, early arrivals successional species should be more 9 Assures late successional species dominate vulnerable to mortality an area because they live a long time and Results showed early successional species resist damage by physical and biological had lowest survivorship and were more factors vulnerable to herbivores
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10 Successional Mechanisms in Forests
z Hundreds of years
z Old field succession z Primary succession on a volcanic substrate z Primary succession following deglaciation
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Mechanisms in Primary Succession Mechanisms in Old Field Succession on a Volcanic Substrate z Keever (1950), Piedmont Plateau z 1980 - Mt St. Helens, Washington erupted z What was the causes of early species 9 Disturbance set stage for succession replacements? Avalanche debris, hot volcanic ash and z Results support the inhibition model and pumice killed all plant life the facilitation model z Morris and Wood studied influences of facilitation, tolerance, and inhibition on early succession on pumice plains 9 Found complex blend of influences
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11 Mount St. Helens Three pioneering species
z Pearly everlasting (Anaphlis margaritacea) z Fireweed (Epilobium angustifolium) z Perennial Lupine (Lupinus lepidus) – a N- fixer
z The first two species disperse by wind and rapidly colonize z The third species does not disperse easily
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Pearly everlasting (Anaphlis margaritacea) Fireweed (Epilobium angustifolium)
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12 Perennial Lupine (Lupinus lepidus) Experiment results
z Consistent with the inhibition and facilitation models z Seedling survival during the first growing season was highest on the barren control plot (inhibition) z But, during the second growing season, the pattern reserved, the survival seedlings was lowest (facilitation)
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Mechanism of primary succession
z Glacial Bay z Field observations, field experiments, and greenhouse experiments z Chapin (1994) found no single factor or mechanism determines the pattern of primary succession – complex influences
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13 Community and Ecosystem Stability
z Community stability may be due to lack of disturbance or community resistance
z Stability – Absence of change z Resistance – Ability to maintain structure and function in face of potential disturbance z Resilience – Ability to recover from disturbance
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Park Grass Experiment
z Succession restores a community z Hertfordshire, England disrupted by disturbance 9 Studied effects of fertilizer treatments z Succession is the basis of resilience Continued for almost 150 years z Silverton (1987) investigated ecosystem z Take long time to study stability 9 Used community composition variability as measure of stability 9 Represented composition as proportion of community consisting of each plant form
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14 z The proportions of grasses, legumes, and other species remained fairly constant z Mainly affected by precipitation z However, population of individual species changed substantially
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Community and Ecosystem Stability
z Dodd et al. (1995) showed although community stability is present, populations of individual species can change substantially 9 Stability depends on spatial resolution an area is investigated at 9 Landscape, form, and species levels
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15 Replicate Disturbances and Desert Stream Stability z Sycamore Creek, Arizona z Valett studied interaction between surface and subsurface waters z Valett et al. (1994) tested the hypothesis that ecosystem resilience is higher where 9 Flash floods devastated biotic hydrologic linkages between the surface community and subsurface water increase the supply Spatial relationships of zones stable of N – a nutrient limiting the primary ¾ Geomorphology of landscape production
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z Measured vertical hydraulic gradient – hydrologic maps 9 Positive vertical – flow from streambed to the surface – upwelling zone 9 Negative vertical – flow from the surface to the streambed – downwelling zone 9 Zero vertical – stationary zone
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16 z The concentration of nitrate in surface water varies directly with vertical hydraulic gradient z Upwelling zones – have the highest nitrate concentration due to upwelling from the sediments z Nitrate concentrations gradually decline
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The higher nitrate concentrations z The rate of algal biomass accumulation are associated can be used as a measure of rate of with higher recovery from disturbance algae z Therefore, the rate of ecosystem recovery production is higher in upwelling zones since the rate of algal biomass accumulation is higher in this region z i.e., algal communities in upwelling zones are more resilient
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17 大冠鷲 領角鴞 Summary z Community changes during succession include increases in species diversity and changes in species composition z Ecosystem changes during succession include increases in biomass, primary production, respiration, and nutrient retention z Mechanisms that drive ecological succession include facilitation, tolerance, and inhibition z Community stability may be due to lack of disturbance or community resistance
Molles: Ecology 3rd Ed.
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