4)Impacts. Some observations: Measuring impact is complex What should be measured and how?

4) Impacts

4) Impacts

Some observations:• Measuring impact is complex

What should be measured and how?

4) Impacts


What should be measured and how?For individual plant, individual species, or multiple species?

4) Impacts


What should be measured and how?For individual plant, individual species, or multiple species?Over what time frame?

4) Impacts

Some observations:• Measuring impact is complex• Lack of comprehensive data

4) Impactsa) Ecological

Conceptual model: From Walker & Smith in Lukens & Thieret (1997)• Invasive species affect different community & ecosystem

processes


Conceptual model: From Walker & Smith in Lukens & Thieret (1997)• Invasive species affect:

Nutrient & water availability



Nutrient & water availabilityPrimary productivity



Nutrient & water availabilityPrimary productivityDisturbance regimes



Nutrient & water availabilityPrimary productivityDisturbance regimesCommunity dynamics

i) Species replacement• Direct competition From Sherer-Lorenzen in Mooney & Hobbs

(2000)Moist, nutrient rich, disturbed sites in central Europe


i) Species replacement• Direct competition From Sherer-

Lorenzen in Mooney & Hobbs (2000)Moist, nutrient rich, disturbed

sites in central EuropeTypically dominated by native

herb Urtica dioica (stinging nettle)

Helianthus tuberosus (Jerusalem artichoke) invading

Urtica (native)Helianthus (invasive)4) Impactsa) Ecological

i) Species replacement• Direct competition From Sherer-

Lorenzen in Mooney & Hobbs (2000)Moist, nutrient rich, disturbed

sites in central EuropeTypically dominated by native herb

Urtica dioica (stinging nettle)Helianthus tuberosus (Jerusalem

artichoke) invadingHelianthus undermines and

outshades Urtica, displacing it

Urtica (native)Helianthus (invasive)4) Impactsa) Ecological

i) Species replacement• Direct competition• Large scale species displacements

From Alvarez & Cushman (2002) Ecological Applications 12:1434-14443 coastal habitats in SF Bay AreaInvasive = Delairea odorata (Cape

ivy) evergreen vine native to South Africa



From Alvarez & Cushman (2002)Cape ivy invading coastal habitatsDecreases species richness for

natives (36%)




natives & non-natives (37%)




natives & non-natives and species diversity (31%)



From Alvarez & Cushman (2002) Cape ivy invading coastal habitatsFewer native & non-native speciesDecreases occur across all habitat

types



From Alvarez & Cushman (2002)Cape ivy invading coastal habitatsFewer native & non-native species

across all habitats and for all plant life forms



From Alvarez & Cushman (2002)Cape ivy invading coastal habitatsFewer native & non-native speciesExperimentally removed Cape ivy:

Control = no removalDisturbance = insert pitchfork

into soil to simulate soil disturbance that accompanies plant removal

Reduction = hand weeded Cape ivy




Natives richness ↑ (10%)



From Alvarez & Cushman (2002) Cape ivy invading coastal habitatsFewer native & non-native speciesExperimentally removed Cape ivy:

Natives richness ↑ (10%)Non-natives richness ↑ (43%)




Natives richness ↑ (10%)Non-natives richness ↑ (43%)Diversity ↑ (32%)




Other species recover,especially forbs (other life

forms NS)


i) Species replacement• Direct competition• Large scale species displacements• Interacting factors

From D’Antonio et al. (2000) Austral Ecology 25: 507-522Series of 14 study sites (#’s) from eastern coastal lowlands to

seasonal submontane zone on Big Island, Hawaii



From D’Antonio et al. (2000)Series of 14 study sites (#’s) from eastern coastal lowlands to

seasonal submontane zone on Big Island, HawaiiLowlands: warm tropical zone with 1500-2000 mm yr-1, but dry

summers; elevation from sea level to 400 mSubmontane: several °C cooler, but similar amount and

seasonality of precipitation; 400 – 1200 m elevation



From D’Antonio et al. (2000)Series of 14 study sites (#’s) from eastern coastal lowlands to

seasonal submontane zone on Big Island, HawaiiLowlands: warm tropical zone with 1500-2000 mm yr-1, but dry

summers; elevation from sea level to 400 mSubmontane: several °C cooler, but similar amount and seasonality

of precipitation; 400 – 1200 m elevationIn both zones, fires occur; most ignited by lava or by humansDo fires consistently favor invasives across this elevational

gradient?


i) Species replacement• Direct competition• Large scale species displacements• Interacting factors From D’Antonio et al. (2000)

Do fires favor invasives across elevational gradient?Measured cover of native species



Do fires favor invasives across elevational gradient?Measured cover of native and exotic species



Do fires favor invasives across elevational gradient?Measured cover of native and exotic species in adjacent

unburned




unburned and burned sites along gradient




unburned and burned sites along gradient

Indi

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Do fires favor invasives across elevational gradient?For seasonal submontane:

For 26 of 35 (74%) occurrences, native had ↓ cover in burned areas

Indi

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Do fires favor invasives across elevational gradient?For seasonal submontane:

For 26 of 35 (74%) occurrences, native had ↓ cover in burned areas

For 28 of 41 (68%) occurrences, exotics had ↑ cover

Indi

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Do fires favor invasives across elevational gradient?Submontane: Many natives ↓ & many exotics ↑ with fire

Indi

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Do fires favor invasives across elevational gradient?Submontane: Many natives ↓ & many exotics ↑ with fireFor coastal lowlands:

14 of 26 (54%) natives ↓6 of 29 (29%) of exotics ↑

Indi

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Do fires favor invasives across elevational gradient?Submontane: Many natives ↓ & many exotics ↑ with fireLowlands: Fewer natives ↓ & fewer exotics ↑ with fire

Indi

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Do fires favor invasives across elevational gradient?Yes, but not uniformly

Indi

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Do fires favor invasives across elevational gradient?Yes, but not uniformlyNot due to differences in rainfall amount or seasonality

Indi

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Indi

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Do fires favor invasives across elevational gradient?Yes, but not uniformlyNot due to differences in rainfall amount or seasonalityAppears to be due to differences in native species

composition: some of the species in coastal lowlands appear to be fire tolerant


ii) Ecosystem functions• Overview

From Walker & Smith in Lukens & Thieret (1997)

Summarized: Typical effects of invasive on specific processes




Summarized: Typical effects of invasive on specific processesAnd how this change on a specific process then feeds back and affects community function or structure






















ii) Ecosystem functions• Overview• Specific example: Ecosystem C storage

From Jackson et al. (2002) Nature 418:623-626Woody plant invasion into grasslands thought to increase

amount of C storedIf so, then woody plant invasions are good for C sequestration



From Jackson et al. (2002)Does woody plant invasion increase C sequestration?Examined 6 sites along precipitation gradient (200 – 1100 mm)



From Jackson et al. (2002)Does woody plant invasion increase C sequestration?Examined 6 sites along precipitation gradient (200 – 1100 mm)

that had similar age of woody plant invasion



From Jackson et al. (2002)Does woody plant invasion increase C sequestration?Sites along precipitation gradientMeasured total soil organic carbon

in soil profileCalculated total soil organic C for

0-3 m depth for both grass &invaded sites



From Jackson et al. (2002)Does woody plant invasion increase C sequestration?Sites along precipitation gradientPlot proportion of total soil organic C

in woody invaded / grass(>1 means more SOC in woody)



From Jackson et al. (2002)Does woody plant invasion increase C sequestration?Sites along precipitation gradientPlot proportion of total soil organic C

in woody invaded / grassvs. precipitation



From Jackson et al. (2002)Does woody plant invasion increase C sequestration?

Contrary to expectations, ↑ onlyfor dry sites

As precipitation ↑, get less SOCin woody invaded areas


ii) Ecosystem functions• Overview• Specific example: Soil N change

From Vitousek & Walker (1989) Ecological Monographs 59:247-265Myrica faya small evergreen tree native to Canary Islands &

other islands in North Atlantic OceanActinorhizal N-fixerBrought to Hawaii, where is invading young lava flows that

had been dominated by natives



From Vitousek & Walker (1989)Exotic Myrica faya, actinorhizal N-fixer, greatly ↑ annual N

input into young lava flowsLB = Lower Byron; high density of Myrica for >10 yearsUB = Upper Byron; kept free of Myrica

>

>



From Vitousek & Walker (1989)Exotic Myrica faya, actinorhizal N-fixer, greatly ↑ annual N

input into young lava flowsHigh N facilitates the invasion of other exotic plants

>

>


ii) Ecosystem functions• Overview• Specific examples: Fire effects

From D’Antonio in Mooney & Hobbs (2002)Compiled 20 examples from around the world where invaders

have altered fire regimes



From D’Antonio in Mooney & Hobbs (2002)20 examples where invaders have altered fire regimesMajority involve perennial grasses (13 of 20 = 65%)

4 (20%) involve annual grasses – All are in arid WestOther 3 are trees / shrubs (Florida, South Africa)





Majority of invaders represent new life form (14 of 20 = 70%)





Majority of invaders represent new life form (14 of 20 = 70%)Majority ↑ fire frequency (14; 70%)

Only 2 (10%) ↓ frequency





Majority of invaders represent new life form (14 of 20 = 70%)Majority ↑ fire frequency (14; 70%)

Only 2 (10%) ↓ frequencyMajority ↑ fire size or intensity (11; 55%)


ii) Ecosystem functions• Overview• Specific examples: General compilation

From Crooks (2002)


ii) Ecosystem functions• Overview• Specific examples

From Crooks (2002)

Ecosystem engineers:• Alter ecosystem physical processes (water use, N cycling) • Change habitat structure (more complexity, less complexity)• Effects cascade through community


iii) Threatened & endangered species• Overview

~400 of 958 federally listed species (~42%) are because of invasives (includes plants plus other organisms)


iii) Threatened & endangered species• Overview

~42% are because of invasivesEffects can be by:

Direct species replacementIndirect through effects on community structure or function


iii) Threatened & endangered species• Overview• Specific examples: King Ranch bluestem

Bothriochloa ischaemum (Caucasian bluestem) brought in to southern Great Plains (NM, OK, TX) from Russia in 1929

C4 perennial bunchgrass:establishes readily from seedlong growing seasontolerates heavy grazingfair forage qualityforms dense sod in mature pastures




C4 perennial bunchgrass: desirable forage speciesSeeded extensively (for example, ~2 million acres in western

OK)




C4 perennial bunchgrass: desirable forage speciesSeeded extensivelyBut extremely invasive:

Spread along highways into native areas (cemetaries, native grasslands)

Difficult to controlThreatens federally listed endangered plant Ambrosia

cheiranthefolia (south Texas ambrosia)


iii) Threatened & endangered species• Overview• Specific examples: Hawaii

80-90 native plant species extinct270 plant species listed as threatened or endangered


Summary• Ecological impacts typically involve: (1) nutrients/water flow; (2)

primary production impacts; (3) alterations of disturbance regimes; and (4) changes in community dynamics




• Effects observed as:Species replacements (direct/individual or large scale, w/ or

w/o interactions with other factors such as fire)




• Effects observed as:Species replacements (direct/individual or large scale, w/ or w/o

interactions with other factors such as fire)Ecosystem functions (C sequestration, N fixation, fire

frequency/intensity)




• Effects observed as:Species replacements (direct/individual or large scale, w/ or w/o

interactions with other factors such as fire)Ecosystem functions (C sequestration, N fixation, fire

frequency/intensity)Complete or nearly complete loss of native species

(threatened or endangered species)


Documents

4)Impacts. Some observations: Measuring impact is complex What should be measured and how?