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Are natives the Answer?

Bert Cregg, Ph.D.Michigan State University

Department of HorticultureDepartment of Forestry

Photo: Dennis Fulbright

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Source: Philadelphia Inquirer

The case for natives

• Adaptedness• Enhancing Biodiversity• Creating a Sense of Place• Preventing Invasives

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DefinitionsWhen I use aword it meansjust what Ichoose it tomean — neithermore nor lessHumpty Dumpty in Lewis Carroll’s“Through the Looking Glass”

"Native species" means, with respectto a particular ecosystem, a speciesthat, other than as a result of anintroduction, historically occurred orcurrently occurs in that ecosystem.

"Ecosystem" means the complex of acommunity of organisms and itsenvironment.

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"Alien species" means, with respect toa particular ecosystem, any speciesthat is not native to that ecosystem.

= “Exotic”

= “Non-native”

"Introduction" means the intentional orunintentional escape, release,dissemination, or placement of aspecies into an ecosystem as a resultof human activity.

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What about non-human introductions?

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The case for natives

• Adaptedness• Enhancing Biodiversity• Creating a Sense of Place• Preventing Invasives

Adaptedness

“They (natives) do not requirewatering (except duringestablishment), chemical pesticidesand fertilizers, or frequent cutting.”

plantnative.org

Adaptedness

“Native plants grow well together(they evolved growing along side oneanother) and to predictable sizes.”

plantnative.org

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Adaptedness

“They are adapted to local conditionsand to local ‘bugs’”

plantnative.org

Evolution and natural selection• Presumes evolution results in optimal

fitness– Result of random natural introductions– World is full of stressful environments– Same suite of physiological adaptations

can evolve independently (convergentevolution)

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• Thus, the first-order rationale forpreferring native plants – that, aslocally evolved, they are bestadapted – cannot be sustained.”

-Stephen Jay Gould

Native environment?

Native environment?

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Native environment?• Most landscapes are impacts by

some form of human disturbance• Above ground – urban heat island• Below ground – soil disturbances

austintexas.gov

Urban Heat Island

Urban Soils

Exotic pests• Ever-narrowing list of natives• Globalization is not ending

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Keyhoe et al. 2010. J. of Great Lakes Res. 36 7–21.

Projected impacts of climate change in the Midwest

Adaptedness• Strength

The case for natives

• Adaptedness• Enhancing Biodiversity• Creating a Sense of Place• Preventing Invasives

Enhancing Biodiversity• Ecosystems are interconnected

assemblages of organisms –removing one piece can affect allothers

“Ecosystems are not only morecomplex than we think, they are morecomplex than we can think”

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Source: Head and Thompson

Enhancing biodiversityIssues of scale?

Genetic relatedness• Kingdom

–Division• Class

–Order»Family

• Genus• Species

• Kingdom• Division• Class• Order• Family• Genus• Species

White oakPlantaeMagnoliophytaMagnoliospidaFagalesFagaceaeQuercusalba

English oakPlantaeMagnoliophytaMagnoliospidaFagalesFagaceaeQuercusrobur

Congener

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• Kingdom• Division• Class• Order• Family• Genus• Species

White oakPlantaeMagnoliophytaMagnoliospidaFagalesFagaceaeQuercusalba

GinkgoPlantaeGinkgophytaGinkgoopsidaGinkgoalesGinkoaceaeGinkgobiloba

Non-congener

Burghardt and Tallamy. 2015 Ecology letters 18: 1087-1098.

Relatedness matters: Diversity index ofnative and non-native landscapes

Burghardt and Tallamy. 2015 Ecology letters 18: 1087-1098.

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Native, Near-native, ExoticNative. A species that arrived in the BritishIsles without anthropogenic intervention.Near-native. A species occurring naturallyonly in the Northern Hemisphere but notnative or naturalized in the British Isles,matched in terms of general growth habitand garden usage with one of the specieschosen as a native plant and taxonomicallyrelated to it at familial, and usually generic,level.

Native, Near-native, ExoticExotic. A species occurring naturally only inthe Southern Hemisphere, matched in termsof general habit and garden usage with oneof the species chosen as a native plant butnot necessarily related to it at any particulartaxonomic rank and not naturalized in theBritish Isles.

Pollinator visits were similar fornative and near-native plants

ExoticNativeNear-native

Salisbury et al. 2015 J. Appl. Ecol. 52:1156-1164

Synthesis and application“Gardens can be enhanced as ahabitat by planting a variety offlowering plants, biased towards nativeand near-native species but with aselection of exotics to extend theflowering season and potentiallyprovide resources for specialistgroups.”

Salisbury et al. 2015 J. Appl. Ecol. 52:1156-1164

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Tree species diversity (Species Richness) inMidwestern communities

Adapted from Wade 2010

Improving biodiversity• Strength

~ish

The case for natives

• Adaptedness• Enhancing Biodiversity• Creating a Sense of Place• Preventing Invasives

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Wildflowersmich.org

Are preferences for nativeplants a form a xenophobia? Creating sense of place

• Strength

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The case for natives

• Adaptedness• Enhancing Biodiversity• Creating a Sense of Place• Preventing Invasives

"Invasive species" means an alienspecies whose introduction does or islikely to cause economic orenvironmental harm or harm to humanhealth.

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• Introduction• Escape• Naturalized – self-sustaining

population• Invasive

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Preventing invasives• Strength

Summary• Arguments over the relative merits

of native vs exotic plants are rootedin both biology and value systems

• The adaptedness argument fornatives is weak, especially indisturbed environments

Summary (cont.)• The ‘sense of place’ argument is

often shunned by ecologists, but notnecessarily by public

• The biodiversity discussion related tonative/exotic is becomingincreasingly nuanced (provenance,near-native, congener)

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Summary (cont.)• Natives can be a hedge against

invasives but the utility of thisapproach is not universally accepted

What about cultivars ofnative plants?

• Provenance?• Clonally propagated

– Reduces genetic variability• Often grafted

– Root stock origin?

Hei

ght d

evia

tion

from

loca

l sou

rce

(%)

Mean temperature deviation (deg. F)

colder sources warmer sources

Moving seed sources northward increases growth……up to a point

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Schmidtling. 1994. Tree Physiology 14, 805-817

Southwide pine seed source trial

The case for natives

• Adaptedness• Biodiversity• Sense of place• Invasives