[Pollinator] Proposed definition for "Native Plant"

[Kimberly Winter]

From

Larry E. Morse

L.E.M. Natural Diversity
P.O. Box. 77157
Washington, D.C. 20013
(202)-543-2488

Larry.E.Morse at LEM-Natural-Diversity.com

A general-purpose definition for the commonly used term "native plant" is
offered here for consideration for use in floristics and biogeography,
conservation and habitat management, horticulture, environmental education,
legal and regulatory documents, and other purposes.  This presentation draws
not only on my decades of personal floristic and biogeographical research
experience (beginning in the 1950's), but also on definitions and practices
of numerous other researchers, organizations, land-management agencies, and
other parties, as well as numerous personal and internet discussions, and
consultation of published and shared unpublished works, all far too many to
attempt to list here.  However, it is no mere coincidence that the
definition and discussion offered here correspond closely to longstanding
usage of the U.S. National Park Service, The Nature Conservancy, and Dr.
John T. Kartesz.

Terminology.  The term "native plant" has become quite firmly established in
the realms of botany, horticulture, conservation, and law, as well as in
general-public environmental education and natural-diversity awareness.
Furthermore, dozens of state-based U.S. organizations have named themselves
as a "native plant society," or otherwise note their interest in and concern
for "native plants" in their mission statements.

However, as has been noted by others from time to time, both words in the
"native plant" term have their problems.  "Native" in some other contexts
implies birth or origin in a specified place or area, with the frequently
used alternative term "indigenous" also having a similar alternative
meaning.  Also, the word "plant" is quite widely and commonly used to refer
to an individual organism, probably moreso than its use here to refer to a
species or other entire taxon.

As has occasionally been noted elsewhere, if these original literal views of
"native" and "plant" are followed, then a "native plant" would be any
individual plant, of any species whatsoever, that germinated or otherwise
established itself in exactly the spot where now found, .  For example, if
these views are followed, the now-mature Asiatic-origin mimosa tree (Albizia
julibrissin)  that sprouted about 20 years ago from dispersed seed in my
back yard on Capitol Hill in Washington, D.C., would be considered native to
my back yard, and hence native to the District of Columbia, to the United
States, and to North America, much as I am personally considered a native to
Dayton, Ohio (where I was born), and hence native to Ohio, to the U.S.A. and
to North America.  While leading to some interesting thoughts and
consequences, this strange concept of botanical nativeness is useless in
most scientific, conservation, legal, and other conventional contexts, and
is not pursued further here.

One might think that the term "native plant species" would be an improvement
on the term "native plant" for present purposes.  This replacement term
works well if only species-level taxa are being commonly considered in a
particular context, for example in some instances in environmental education
or when labelling nursery material, when rare exceptions can be addressed if
encountered.  However, more generally, especially in scientific,
conservation, and legal contexts, the distinction between native and
non-native is usefully applied at any taxonomic level, not just the species,
for example in the often important separate consideration of native or
non-native subspecies or varieties of a particular species.

Taking a step further, one might then consider "native plant taxon" to be
the more appropriate general term, but  that involves a quite specialized
technical word virtually unknown to the general public, including many
native plant enthusiasts.  Furthermore, the word "taxon" has the additional
complication of following Greek rather than English conventions in
generating its plural ("taxa"), a phenomenon with few if any parallels in
familiar everyday American English.  I therefore consider it totally
unrealistic to expect or encourage widespread substitution of the
technically better phrase "native plant taxon" for the solidly established
but admittedly doubly questionable term "native plant"  -- is anyone ready
for an "Oregon Native Plant Taxa Society"?  "Native plants" it will continue
to be!

The related term "naturalized" also needs brief mention.  Naturalized plants
are non-native plants that have become thoroughly established within one or
more non-managed ("wild") habitats or ecosystems in one or more places
within an a region of interest.  While descendants of a nation's naturalized
citizens may in turn be natives to that nation, under the definition of
"native plant" offered here, the same is not true of a nation's (or other
area's) naturalized plants (despite some published claims to the contrary),
since descendants of non-native plants still have direct or indirect human
intervention somewhere in their history.  Mere passage of time does not turn
a non-native into a native in the botanical world.

Geographical scoping.  In all cases when considering whether a particular
plant taxon is native or non-native, or in any other discussion of "native
plants," the geographical region being considered must always be explicitly
or implicitly stated.  For example, some U.S. government policies consider
"native plants" to be those plant taxa considered native in at least one
place anywhere in the United States.  Under this nationwide geographical
scoping, the yellowwood (Cladrastis kentukea)  that I planted a decade ago
in my front yard would be a "native plant," since it is native elsewhere in
the United States (although not in the mid-Atlantic region), while my
backyard mimosa, despite its spontaneous appearance from alleyway seed,
would (appropriately, in my view) not be considered a (nationally) native
plant. When the geographical scale is tightened to the District of Columbia,
then my  yellowwood becomes non-native to my local state-level jurisdiction,
while such recurrent yard-invaders as black walnut (Juglans nigra)  or
willow oak (Quercus phellos), which represent locally native species, are
rightly called "native plants" in D.C.  If no geographical limitation is
provided, then the "native plant" term could be applied to any plant from
anywhere on our planet, with the traditional Aztec view of corn or maize
(Zea mays)  as a "Gift from the Gods" being a possible exception.

Limitations in floristic knowledge.  Note that the tighter the geographical
scoping, the more difficult it generally is to determine whether or not a
particular regionally native plant species (or other plant taxon) should be
considered native to the particular area of interest.  Early observations or
collections of a species demonstrably from within the actual area of
interest of course answer the question quickly, but for most localized
places, such knowledge is thin or nonexistent.  Known current or historical
presence as a native nearby (within routine dispersal range), coupled with
presence of appropriate native habitat within the area of interest, is also
persuasive evidence (but not proof) that the species is native within that
area.  If the area of interest is located well within the presumed native
range of a widespread and readily dispersed species, and appropriate habitat
is furthermore naturally present within the area, then nativeness in that
area can generally be assumed (but again not proven), in lack of evidence to
the contrary.  Floristic information provides the baseline of geographical
distributions and habitat preferences necessary to such lines of reasoning.

In the United States, the presence of nationally native trees, wildflowers,
and other vascular plant species is documented with accuracy approaching 99%
at the state level, providing a firm national foundation for presenting
state-by-state distribution lists and maps.  Distribution data for vascular
plants is dramatically less well known at the county (or equivalent) level,
varying substantially from state to state, with this knowledge
disappointingly weak in Georgia, Maryland, and a few other places.  On the
other hand, county-level plant records are surprisingly complete for
state-native vascular plant species for hundreds of particular individual
counties across the nation, generally those with universities, major
museums, scenic attractions, field stations, regionally unusual topography,
substrates, or habitats, or otherwise now or at some time of high personal
interest to one or more field botanists.

The state and the county have long been the geographical units customarily
recorded for the great proportion of botanical specimens and locality
reports.  Discovery of a new state record for a species usually leads to
publication.  Newly documented county records for a species are also
frequently published, or nowadays submitted instead to editors of
state-based or national county-level distribution atlases or databases for
inclusion in these works with appropriate attribution or acknowledgement.

On the other hand, for a variety of reasons, physiographic provinces,
ecological regions, major watersheds, or similar tessellations of the
landscape are rarely recorded in consistent form (if at all) with individual
specimens or other documented observations.  Distribution summaries by such
tessellations are accordingly rarely produced directly from site-based
primary documentation.  However, such distribution presentations can now be
readily approximated (on a yes/maybe/no scale) from distribution data for
the pertinent fully and partially included counties.  Further resolution of
'maybe' cases can then be made through herbarium and literature review as
well as focused field research.  On the other hand, floristic documentation
at localized, within-county levels requires the luxury of intensive field
study, generally involving samplings in various seasons for more than a
single year.

Not all regionally native plants are locally native everywhere in their
regions.  Nativeness at scales smaller than states is rarely addressed
systematically, although presumed native ranges have been worked out for a
fair number of continentally native U.S. species that have been introduced
into areas beyond their original distributions, or that have become
established in places within their natural dispersal ranges that lacked
appropriate habitats or substrates before modern human activity provided
niches for them (such as limestone ferns on old mortar, aquatic plants in
farm ponds, or saline-habitat plants along heavily salted highways).

Challenges in determining native ranges of certain species.  Many mysteries
remain regarding the locally native status of some of our most familiar and
otherwise well-known plants.  As one dramatic example, the black locust
(Robinia pseudoacacia),  a tree native to the Appalachians, was widely
planted in the Atlantic states, the Midwest, and various other areas where
it soon became established and often naturalized.

In the mid-Atlantic region around Washington, D.C., there is no question
that black locust is native in the mountainous region from the Blue Ridge
westward.  Within the Piedmont and Coastal Plain areas near Washington, this
abundant species is generally considered non-native, although obviously
often at least well naturalized.  Black locusts along and near the Potomac
River, however, pose a further question of nativeness, still unresolved.
Most of the Potomac's headwater streams arise deep in Appalachia, in the
region where black locust is unquestionably native.  The Potomac watershed
regularly experiences tropical storms or hurricanes as well as occasional
quickly melting deep snowfalls, with the river readily flooding grandly
following such broad-scale meteorological events.

Given the quantity of plant material, including whole trees, dispersed
downriver by these major Potomac floods, it would be expected that seeds,
seed pods, and viable roots of the black locust would be frequently
flood-dispersed and deposited in numerous places on the river's floodplain
or riparian shore as far downriver as the Coastal Plain well southeast of
Washington.  Trees arising from these dispersed propagules would be expected
to flower and fruit and spread locally in this riparian habitat, and perhaps
eventually disperse naturally further from the river corridor.  My current
personal view is that many (but not necessarily all) of the black locusts
near the Potomac are native, at least as far downstream as Charles Co.,
Maryland, and King George Co., Virginia.  What if any upland mid-Atlantic
black locusts away from the Potomac are also native remains a mystery.

Note that the black locust question posed here is not where the species
currently occurs -- that is quickly determined as needed -- but in which
places the species' presence is not due solely to direct or indirect human
activity.   Since black locust trees are conspicuous and distinctive in
flower, historical accounts may prove useful here (as has been the case in
documenting the presettlement distribution of black locust near the Ohio
River), making this a true question of "natural history" and not merely
natural science.  On the other hand, high-tech modern science (such as
biochemical comparisons) might instead be applied to try to resolve the
affinities of the black locusts in various places in the Potomac watershed.

Toward an improved definition.  Given the lively discussion stimulated by
most attempts to define "native plants" or related terms, I hope and expect
that this presentation will before too long need significant revision,
perhaps by November.  Questions, suggested revisions or corrections, and any
other comments are all quite welcome.  In particular, the current rather
detailed consideration of various kinds of direct and indirect human
intervention is clearly quite preliminary, and deserves substantial further
attention before the next version can be considered ready.

*  *  *

Definition:
A native plant, within a specified geographical region of interest, is a
plant species (or other plant taxon) currently or historically present there
without direct or indirect human intervention.


For purposes of this definition:

1. A plant is any living organism that is:
   (a)  A member of one of the following major formal or informal taxonomic
groups (as commonly and traditionally treated):  Flowering plants,
gymnosperms (conifers and relatives), pteridophytes (ferns and fern allies),
bryophytes (mosses, liverworts, and hornworts), algae (including the
Cyanobacteria or blue-green algae), fungi (including lichens [lichenized
fungi];  or

(b)  A member of any other smaller taxonomic group traditionally considered
a plant (rather than an animal, a bacterium, or a virus), for example the
water molds (such as the sudden oak death pathogen) or the various slime
molds.

2. A geographical region of interest is an unambiguous, bounded, contiguous
or non-contiguous geographical area specified by a legal or other commonly
recognized name and/or by a precise description, for example:
West Virginia
Montgomery and Greene Counties, Ohio
The schoolyard of Horace Mann Elementary School, Dayton, Ohio
Coastal Plain of Alabama and Mississippi
Yellowstone National Park
Chesapeake Bay Watershed
U.S. Caribbean Territories and Possessions
Ridge and Valley Region of Virginia and West Virginia as bounded by the
center lines of highways U.S. 50, W.Va. 28, U.S. 250, and U.S. 220
Note that a map, or a comparable representation within a geographical
information system, can be helpful in visualizing the extent and boundaries
of a geographical area, but does not substitute for a written name or
description.


3. A taxon (plural, taxa) is a taxonomic group of any rank (such as a
kingdom, phylum, class, order, family, genus, species, subspecies, or
botanical variety) as recognized in a particular scientific classification.
While most taxa have Latin-form scientific names, unnamed taxa are
occasionally recognized, for example some interspecific hybrids that are
identified by formulas rather than by names. or newly discovered species not
yet formally named.

Note that hybrids between two or more taxa may themselves be considered
taxa.

Note also that a named plant cultivar is not itself a taxon, but is instead
a member of a botanical species or other botanical taxon.


4. A plant taxon is considered present within a geographical region at a
specified time if it is known to occur in at least one place there then as a
rooted or otherwise established living individual (and not, for example,
occurring within the region solely as dispersed seeds, spores, pollen, or
other non-established propagules, or as dispersed nonviable or dead material
such as flood deposits, tornado debris, or beach drift).


5. Historical presence of a plant taxon within a geographical region is here
taken to include presence in at least one place there at any time since the
advent of modern traditional biological classifications (hence approximately
the year 1500 A.D. onward), but  here excludes presence within the region
only in earlier times, as for example indicated by historical,
archaeological, or paleontological evidence.

For example, the dawn redwood [Metasequoia glyptostroboides, and/or related
species] occurred widely in the United States and Canada many millions of
years ago, as shown by numerous fossils, but that fact does not make the
genus Metasequoia  native to North America for present purposes;  all modern
North American Metasequoia  plants are instead direct introductions from its
modern native range in China, or descendants of such introduced plants, even
when established here outside cultivation.


6. Human intervention (direct or indirect) includes:
(a)  Deliberate or accidental transport of previously absent plants into the
region of interest from elsewhere by humans or by human activity, including
transport by domesticated animals, livestock, pack animals, or pets, as well
as transport by wild animals (whether managed or not) that are themselves
non-native to the region of interest.

(b)  Subsequent spread or dispersal of plants into that region from
individuals elsewhere that at any point in their ancestry had been
deliberately or accidentally transported by humans or by human activity;

(c)  Presence of a plant taxon within that region solely as a result of
recent or historical provision by humans, directly or indirectly, of
additional, clearly distinct and different habitats, substrates,
microclimates, or other environmental settings otherwise absent anywhere in
the region of interest, for example:
Roadsides, alleyways, walkways, railroad embankments, fencerows, powerline
or pipeline corridors, and other regularly managed rights-of-way
Agricultural, silvicultural, or other regularly maintained lands
Lawns, yards, gardens, parking lots, rooftops, and other similar settings or
substrates
Urban, suburban, industrial, and other substantially altered developed areas
Mortar, cement, concrete, and other calcareous building materials
Lakes, ponds, pools, ditches, canals, impoundments, or other hydrographic
features
Water diversions
Warm-water or cool-water discharges, such as those below power plants or
high dams
Breakwaters, jetties, retaining walls, riprap, dams, dikes, spillways, or
other shore-stabilization or water-management features
Point-source or localized habitat-altering pollution or other environmental
alteration
Intensive localized habitat management, such as for timber-species
promotion, enhanced production of favored fish, wildlife, or wildflower
species, or control of pests, diseases, or invasive species
Mines, quarries, gravel or sand pits, landfills, tunnel portals, cuts or
fills, and other settings involving removal or burial of original soil or
substrate
(d)  Changes to water chemistry, for example acid-mine drainage or
deliberate liming of streams for sportfish promotion.
Note that widespread, diffuse environmental changes due or apparently due to
cumulative effects of diverse human activities are generally ignored in
determining the local nativeness of various plant taxa, including for
example any that may be due to such factors as:
regional or widespread air, water, or soil pollution or contamination
regional or large-scale hydrological changes due to dams, channelizations,
diversions, deliberate water releases, drainage, groundwater withdrawal, or
similar causes
changes in frequency or intensity of floods or other hydrological events due
to regional land-use change such as agricultural clearing or substantial
introduction of impervious surfaces
long-term changes in upper-atmosphere gas proportions
Note also that a plant taxon resulting from artificial or naturally
occurring hybridization between a plant taxon native to a region of
interest, and another plant taxon not native there, must be considered
non-native because all of its individuals include genes having direct or
indirect human intervention in their ancestries.  Furthermore, all
descendants of such hybrids, including any backcrosses, polyploids, or other
derived taxa, are correspondingly also non-native to the region of interest.

On the other hand, since the taxon and not the individual or population is
the entity of assessment under this definition, the determination of
nativeness of a taxon to a specified geographical region applies to that
taxon in its entirety.  For a particular taxon that is considered native to
the region of interest, plants of the same taxon from elsewhere that are
brought into the region of interest, or otherwise become present there, are
also considered native in that region (at the level of the specified taxon,
even if not as individuals populations, or genotypes), and their presence
there does not affect the native status of other members of that species
there, even if some or all of these plants interbreed or otherwise
co-mingle.  However the nature and characteristics of individual plants or
propagating stock of a native species that originate from outside the region
of interest may nevertheless be a legitimate consideration when planning
restorations, reintroductions, or other habitat-management needs, or when
obtaining material of a native species for landscaping or educational
displays.


Any questions, comments, or suggested revisions or clarifications may be
directed to the author.

*  *  *
Copyright (C) 2006 L.E.M. Natural Diversity

Permission is hereby granted to reproduce or further distribute this work,
provided that it is presented in its entirety (without any alterations,
deletions, revisions, or significant changes to flow or formatting),
including this concluding notice regarding copyright, permissions, and
suggested citation.

Suggested citation:

Morse, Larry E.  2006.  Definition of a "Native Plant" -- 24 August 2006
Version. L.E.M. Natural Diversity, Washington, D.C.