a call to action, galvanizing efforts to forge partnerships with .... cies, including the National Park Service, the National .... Death Valley National Monument ...
Seeing the Forest and the Trees: Ecological Classification for Conservation
The classification that this publication describes was authored by: Mark Anderson Patrick Bourgeron Mark T. Bryer Rex Crawford Lisa Engelking Don Faber-Langendoen Mark Gallyoun Kathleen L. Goodin
Dennis H. Grossman Sally Landaal Kenneth J. Metzler Karen D. Patterson Milo Pyne Marion S. Reid Lesley Sneddon Alan S. Weakley
and by ecologists in the network of Natural Heritage programs and Conservation Data Centers (see back cover).
Citation: Maybury, Kathleen P., editor. 1999. Seeing the Forest and the Trees: Ecological Classification for Conservation. The Nature Conservancy, Arlington, Virginia. ISBN 0-9624590-2-X Copyright 1999 The Nature Conservancy
Acknowledgements Don Faber-Langendoen, Alan Weakley, Marion Reid, and Dennis Grossman, deserve special acknowledgement for their ideas, careful review, and other contributions to this publication. Thoughtful review and comments were also provided by Jonathan Adams, Mark Anderson, Mark Bryer, Patrick Comer, Christine A. De Joy, Beth Duris, Stephanie R. Flack, Kathleen L. Goodin, Sally Landaal, Julie Lundgren, Karen D. Patterson, Milo Pyne, Carol Reschke, Lesley Sneddon, and Bruce A. Stein. Deborah A. Gries provided research assistance. Jim Drake, Jonathan L. Haferman, and Stuart Sheppard assisted with maps. Design and Production: Nicole S. Rousmaniere
Table of Contents Preface ............................................................................................................................. 2
Introduction ....................................................................................................................... 3
Why Communities? ............................................................................................................. 4
Why Is a Classification System Important? .............................................................................. 6
What Is the USNVC? .......................................................................................................... 7
What Is the Current Status of the USNVC? ........................................................................... 10
How Is the USNVC Being Used? ........................................................................................ 12 Within the Conservancy ............................................................................................. 12 Beyond the Conservancy ............................................................................................ 19
Summary and Future Challenges ......................................................................................... 23
Appendices: The Nuts and Bolts of the USNVC System ........................................................... 24 Appendix A—Key Attributes ....................................................................................... 24 Appendix B—Structure and Type Definition ................................................................... 26 Appendix C—Partners in Development and Application .................................................. 29
Cited References .............................................................................................................. 36
I
n the early summer of 1991, a biologist invento-
Classifications such as the one developed in North Caro-
rying a pine savanna on the North Carolina
lina have now been compiled, integrated, and expanded
Coastal Plain came across a 3-foot-tall plant he couldn’t
into a system that is applicable across the nation: the U.S.
identify. The puzzling plant species, a member of the sedge
National Vegetation Classification, or USNVC. The prod-
family, turned out to be unknown to science—and all the
uct of a two-decade-long collaboration between the Con-
more intriguing because its nearest close relatives were
servancy and the network of Natural Heritage programs,†
found to be boreal species that occur almost 500 miles
the USNVC greatly enhances our ability to recognize,
away. Subsequent inventories at this same small site have
assess, and conserve natural communities everywhere we
documented the presence of an astounding 500 species
work, in the United States and beyond. It represents the
of vascular plants, as well as large populations of several
first U.S. community classification system that is national
globally endangered plants and invertebrates.
in scope and detailed enough in its consideration of
For those dedicated to preserving the nation’s biodiversity, remarkable discoveries like these are usually
natural diversity to be useful in making local, site-specific conservation decisions.
a call to action, galvanizing efforts to forge
In the case of the North Carolina site, a
partnerships with members of the local
community classification system allowed bi-
community, negotiate land deals, and initiate protection agreements. These efforts
Preface
ologists to recognize and document that at least one plant community found there was
are often imbued with a sense of urgency,
extremely rare on a global basis. That real-
as many sites of exceptional biological value
ization was a principal factor in the decision
face encroaching development or other threats. In this
to make the site a Conservancy preserve long before com-
case, however, no sense of crisis ever arose; nothing out
prehensive inventories of species had been conducted there.
of the ordinary happened at all. At the time the scientist
In this report, we present several examples of how
discovered the anomalous sedge, large portions of the site
scientists within and beyond the Conservancy are using
had been a Conservancy preserve for more than five years.
the USNVC to accomplish the best possible conservation.
Ties to the community were already strong, and protec-
Our hope is to make the classification, and its enormous
tion efforts had long been part of the day-to-day work of
potential for improving conservation decisions, accessible
the Conservancy’s North Carolina Field Office.
to a wider audience of conservation practitioners. Essen-
How did the Conservancy come to identify this
tially, we want this tool to be in the hands of those who
specific place as being of critical conservation concern years
need it, wherever they need it, to carry out effective and
before many of the important species discoveries had been
efficient conservation.
made? In large part, the answer has to do with a scientific
The ecologists of
approach created expressly to meet conservation needs:
The Nature Conservancy,
a classification system for ecological communities.
August 1998
†
The Natural Heritage network is an informal designation of state and other programs that work cooperatively to collect and manage information on rare species and natural communities.
2
Seeing the Forest and the Trees: Ecological Classification for Conservation
W
hat types of natural vegetation exist across
This standardized approach is allowing assess-
the landscape? Which types are intrinsically
ments of conservation status, trends, and management
rare or have been severely degraded by human activities?
practices for ecological communities across local,
How do we identify the best remaining occurrences of natu-
regional, and national landscapes. It has enhanced the
ral communities across their geographic ranges? To direct
Conservancy’s ability to identify the most important
our limited conservation resources to the specific places
sites for conserving our nation’s biodiversity, and it is
where they will have the greatest impact, we must have
playing an important role in our efforts to identify a
clear answers to questions such as these—answers that
portfolio of conservation sites representative of each
ultimately hinge on how we define and categorize the rich
ecoregion.† Beyond the Conservancy and Heritage pro-
ecological diversity that is one of our nation’s greatest trea-
grams, the system’s utility has been widely appreciated:
sures. To answer these questions, The Nature Conservancy,
it is now accepted as the standard for classification,
in partnership with the network of Natural Heritage pro-
inventory, and mapping work in all U.S. federal agen-
grams, has developed a scientifically sound, consistent, and
cies, including the National Park Service, the National
flexible classification system that can
Forest Service, and the Fish and
be applied to terrestrial ecological
Wildlife Service. These agencies,
communities throughout the world. The system can be used to classify
Introduction
all types of vegetated communities,
along with other academic and professional conservation and management organizations, are
from verdant wetlands to arid deserts nearly lacking in plant
increasingly becoming the Conservancy’s partners in
life, and from the most pristine old-growth forests to
the ongoing development and application of the clas-
cultivated annual crop fields. Using this system, a team of
sification and its provision to a burgeoning number of
Conservancy and Heritage ecologists has now completed a
users and contributors.
first iteration of the natural vegetation types of the United
This report briefly describes the classification
States. This represents the first time the country’s natural
system and identifies major opportunities for applying
terrestrial communities have been classified using a single
it to meet our current conservation challenges, as well as
system on a scale fine enough to be useful for the conser-
those that lie ahead.
vation of specific sites.
†
An ecoregion is a relatively large unit of land and water delineated by the biotic and abiotic factors that regulate the structure and function of the communities within it. It provides a unit of geography that is more relevant than political units for organizing and prioritizing conservation planning efforts.1
Seeing the Forest and the Trees: Ecological Classification for Conservation
3
A
ttempts to conserve biological diversity can
species-by-species approach to conservation. Saving
be directed at different biological and eco-
individual species once they are on the brink of extinc-
logical levels, ranging from genes to species to commu-
tion often demands large amounts of time, societal
nities and ecosystems. Communities can be described
concern, and money. Such an approach is clearly neces-
as assemblages of species that co-occur in defined areas
sary for species that are facing particular threats, and it
at certain times and that have the potential to interact
is also reasonable for large mammals, birds, and plants
2,3,4
with one another.
But com-
that are of particular signifi-
munities are more than the
cance to humans, especially
sum of their species; they also represent the myriad biological and environmental interactions that are inherently a part of
Why Communities?
each unique natural system.
those that inspire a sense of awe or affinity. But there are an estimated 10 million to 100 million species on Earth, only a fraction of which are known
Thus, by describing, tracking, and preserving commu-
to science. 5 These include the little, less glamorous
nities, ecologists can protect a complex suite of organ-
species that create soils, pollinate plants, and play
isms and interactions not easily identified and protected
numerous other ecological roles. Protecting the vast
through other means.
majority of them will require a broader, natural com-
In addition, a consensus has emerged within the conservation community about the inadequacy of a
munity-based approach that conserves habitats and species assemblages as a whole.
The best approach to protecting many of our most imperiled species, such as the elusive and rare San Gabriel Mountain slender salamander, is to preserve the habitats on which they depend. Natural assemblages of plants are widely regarded as biological expressions of the complex factors that make up a particular habitat—factors such as climate, soils, natural disturbance processes, and the structure of the plants themselves. Thus, natural plant communities can be used as a “coarse filter” for protecting numerous species, even the less glamorous species whose very existence—let alone habitat needs—we may have yet to discover.
San Gabriel Mountain slender salamander
© Kate Spencer
4
Seeing the Forest and the Trees: Ecological Classification for Conservation
The ecological community concept has been recognized as an important conservation planning tool for the following reasons: • Communities have inherent value that is worth conserving. They encompass a unique set of interactions among species and contribute to important ecosystem functions. • Communities can be used as surrogates for species and for ecological processes, particularly in species-rich and data-poor areas such as the tropics. • By protecting communities, we protect many species not specifically targeted for conservation. This is especially important for poorly known groups such as fungi and invertebrates. • Monitoring change over time is often most meaningful when done at the level of communities. Changes may be detected in overall species abundance, including the proportion of non-native species; in structure, such as the development of old-growth characteristics; and in function, such as alterations in nutrient cycling. • Communities are an important tool for systematically characterizing the current pattern and condition of
© James R. Snyder
ecosystems and landscapes.
More Than the Sum of Its Parts Tropical forest communities may comprise an especially high number of species. Like all communities, they also comprise a complex array of interactions among species and between species and their environments. Shown here: a seasonally flooded tropical forest, south Florida.
Seeing the Forest and the Trees: Ecological Classification for Conservation
5
T
he Conservancy and the Natural Heritage network
concluded that a basic question—to what extent the natu-
have recognized ecological communities as
ral ecosystems in the United States have been reduced in
important elements of conservation for many years. The
area or degraded in quality due to human activities—
best, most viable occurrences of these communities,
could only be answered “by a relatively crude approach
along with occurrences of rare and imperiled species,
because a systematic approach to understanding these
have formed the basis for protection decisions through-
systems at a national scale was not yet available.”6 Other
out the Conservancy’s history.
basic questions, such as, What are the key environmental
In the past, despite the recognized importance of
factors in relationship to a particular community across
ecological communities, no accepted framework for
its entire range? and, What is the complete geographic
national or international community classification existed.
distribution of a particular community? often could not be answered at all.
Without a standard approach, community protection decisions were made only on a state-bystate or agency-by-agency basis, based on independently developed classifications. These classifications worked effectively for the conservation of important areas within states or jurisdic-
Why Is a Classification System Important?
Recognizing the need for a national and international system for classifying terrestrial communities to carry out its mission effectively, the Conservancy, in conjunction with the Natural Heritage network, undertook development of the U.S. National Vegetation Classification
tions, but from a national and international perspective, they risked unnecessarily redun-
(USNVC) system. A team of more than 100 Conservancy
dant protection of a few communities and inadequate
and Heritage ecologists established the standardized
protection of many others. In addition, in the absence of
classification framework and defined the first iteration
a common classification, the results of many inventory
of U.S. communities within it.† In the coming years, the
and monitoring programs, such as those conducted in
USNVC will be continuously refined and developed by
national forests and parks, state forests and parks, or fish
the Conservancy and an expanding network of partners
and wildlife refuges, could not be integrated or compared.
who are using the system to accomplish their conserva-
As recently as 1995, several prominent researchers
tion and management goals.
†
More detailed information about the classification system, including its development, status, and applications, can be found in the recent publication International Classification of Ecological Communities: Terrestrial Vegetation of the United States.7 A first iteration of the list of community types can be found in the second volume of that publication.8 Both volumes are available on the World Wide Web at www.tnc.org.
6
Seeing the Forest and the Trees: Ecological Classification for Conservation
T
he USNVC system blends the features of many
vegetation structure and that occur under similar habi-
existing classification systems that are most
tat conditions.
useful for conservation. It essentially represents a
The association concept encompasses both the
structured compilation of an enormous amount of
dominant species (those that cover the greatest area) and
fine-scale state and local information on vegetation,
diagnostic species (those found consistently in some
and an integration of this information with a modified
vegetation types but not others) regardless of whether
version of UNESCO’s worldwide framework for coarse-
they are large trees or diminutive understory plants.
scale vegetation classification.9
This means associations can reflect a greater ecological
Terrestrial ecological communities are classified
specificity than can a “cover type” or other type based
based on vegetation as it currently exists across the land-
solely on the dominant species of the upper stratum.
scape. Because of their conservation objectives, the
Dominant cover species are often widespread, and may
Conservancy and the Natural Heri-
occur with many different species
tage network are classifying and
over large, heterogeneous land-
describing only the more natural types of vegetation. The USNVC framework, however, may be used
What Is the USNVC?
scapes.10,11 For example, in northern Minnesota and adjacent parts of Canada, on moist bedrock sub-
to classify all existing vegetation,
strates the “generalist” species jack
including heavily human-influ-
pine (Pinus banksiana) occurs with
enced types such as those in developed areas, crop-
an understory of balsam fir (Abies balsamea), whereas
lands, and places severely altered by past logging or
on dry sandplains jack pine grows with bearberry (Arcto-
farming. (See Appendix A for additional information
staphylos uva-ursi) under its canopy.12 These two distinct
about the key attributes of the USNVC.)
plant assemblages, and the profoundly different environ-
In the USNVC, terrestrial vegetation is classified
mental conditions under which they occur, undoubtedly
within a nested, seven-level hierarchy, the finest level of
represent differences of real ecological significance.
which is called the association. (See Appendix B for a com-
The differences are captured by including dominant
plete explanation of the system’s hierarchical structure.)
and diagnostic species in both the over- and understory,
The confluence of three interrelated criteria—species
as well as habitat conditions, in the association concept.
composition, structure, and habitat—conceptually
Despite their relatively high degree of ecological speci-
defines an association: it represents those plant assem-
ficity, associations must repeat across the landscape.† Indi-
blages that exhibit similar total species composition and
vidual occurrences of the same or different associations,
The association concept is intended to be fine enough to be useful for identifying specific, ecologically meaningful sites for conservation, but broad enough to be connected to landscape-scale processes and patterns. †
A few associations that are restricted to specific and unusual environmental conditions are exceptions to this general rule.
Seeing the Forest and the Trees: Ecological Classification for Conservation
7
© Charlie Ott and Gunther Matschke
Hawaiian cloud forests m
Death Valley m
Towering redwoods m
The Everglades m
Tallgrass prairies Encompassing the boreal and the tropical, alpine summits and deserts well below sea level, the United States is blessed with a great and beautiful variety of natural vegetation. Conceptualizing—even in a general way—the diversity and pattern of this vegetation across the landscape is a daunting prospect. Doing so in a way that helps us understand relatively small-scale but ecologically meaningful patterns is even Death Valley National Monument
more of a challenge.
however, may range greatly in size. For example, some west-
characteristics of the leaves, such as seasonality, shape,
ern grasslands occur naturally in patches of tens of thou-
and texture. These features are referred to as physiognomic
sands of acres. In contrast, southern Appalachian “beech
characteristics, and they are generally much more useful
gaps,” characterized by stunted, gnarled beech trees,
than species composition for rapidly categorizing veg-
often occur in sharply bounded mountaintop patches of
etation over large geographic areas (or in areas where
only a few acres.
little is known about the species composition).
Associations are grouped into the next level of the
At the coarsest level of the USNVC hierarchy,
USNVC hierarchy, the alliance, primarily on the basis of
the class, vegetation is divided into seven types: Forest,
having common dominant species in the upper stratum
Woodland, Shrubland, Dwarf-shrubland, Herbaceous,
of the vegetation. Alliances, in turn, are nested into
Nonvascular, and Sparse Vegetation. A summary of the
progressively coarser levels of the hierarchy, primarily
USNVC’s seven levels is provided in the box on the
based on characteristics related to the structure (height
facing page.
and spacing) and overall shape of the plants, and to
8
Seeing the Forest and the Trees: Ecological Classification for Conservation
© Julie Moore, TNC
A Summary of the U.S. National Vegetation Classification System LEVEL
PRIMARY BASIS FOR CLASSIFICATION
EXAMPLE (SEE PHOTO)
Class
Structure of vegetation
Woodland
Subclass
Leaf phenology
Evergreen Woodland
Group
Leaf types, corresponding to climate
Temperate or Subpolar Needle-Leaved Evergreen Woodland
Subgroup
Relative human impact (natural/semi-natural, or cultural)
Natural/Semi-natural
Formation
Additional physiognomic and environmental factors, including hydrology
Saturated Temperate or Subpolar Needle-Leaved Evergreen Woodland
Alliance
Dominant/diagnostic species of the uppermost or dominant stratum
Longleaf Pine -- (Slash Pine, Pond Pine) Saturated Woodland Alliance †
Association
Additional dominant/diagnostic species from any strata
Longleaf Pine / Little Gallberry / Carolina Wiregrass Woodland † The Longleaf Pine / Little Gallberry / Carolina Wiregrass Woodland. This association is found on flat, poorly drained sites on the Coastal Plain of North and South Carolina.
†
Rules for naming alliances and associations: The names of dominant and diagnostic species are used in alliance and association names. Those species occurring in the same stratum are separated by a hyphen ( - ); those occurring in different strata are separated by a slash ( / ). Species found less consistently either in all associations of an alliance, or in all occurrences of an association, are placed in parentheses. In most cases, the word “alliance” appears in alliance names to distinguish them from associations. Examples of alliance names: American Beech - Southern Magnolia Forest Alliance [Fagus grandifolia - Magnolia grandiflora Forest Alliance]; Longleaf Pine / Oak Species Woodland Alliance [Pinus palustris / Quercus spp. Woodland Alliance]. Examples of association names: Subalpine Fir / Grouseberry Forest [Abies lasiocarpa / Vaccinium scoparium Forest]; Saltgrass - (Saltmarsh Dropseed) Herbaceous Vegetation [Distichlis spicata - (Sporobolus virginicus) Herbaceous Vegetation].
Seeing the Forest and the Trees: Ecological Classification for Conservation
9
T
he number of currently defined USNVC types at
environments does this type occur? How much varia-
each level of the system’s hierarchy and the per-
tion (in structure and in species composition) is recog-
centage of associations in each class are presented
nized within the type? How does this type differ from
below. The number of types at the coarser levels of the
similar types? and, How does this type respond to dis-
hierarchy will not change significantly as the classifica-
turbances, both natural and human induced?
tion develops. However, changes will occur at the finest
Conservancy ecologists are providing answers to
levels as the existing alliances and associations are
these questions in the form of detailed descriptions of
refined and new types are added through additional
alliances and associations. Thus far, descriptions have
inventories and analyses.
been completed for about 80 per-
Each of the currently defined associations has a minimum set of information associated with it, including the association’s conservation status, and a list of states and U.S. Forest Service ecoregions
13
where it is known or thought to occur. However, to understand
What Is the Current Status of the USNVC?
cent of the currently defined alliances and about 40 percent of the associations. An example of a typical description appears on the facing page. It depicts the Blackjack Oak Eastern Red Cedar / Little Bluestem - Orange-Grass St. John’s -Wort
alliances and associations in depth and to recognize
Wooded Herbaceous Vegetation Association. Otherwise
them in the field, ecologists will need answers to more
known as the Shawnee Sandstone Glade, this midwestern
detailed questions about specific types. Important
savanna is naturally restricted to unusually thin-soiled
questions regarding each type include: In what types of
places where droughty conditions prevail.
Total Number of Vegetation Types at Each Level of the USNVC Level Class Subclass Group Formation Alliance Association
Number of Types 7 22 62 231 1,642 4,515
Note: Data shown are current as of August 1998 and represent types in the Natural/Semi-natural Subgroup only.
10
Dwarf-shrublands 3%
Herbaceous Vegetation 27%
Shrublands 16%
Woodlands 18%
Nonvascular Vegetation