By Christine Menapace
From the April 2024 Issue
When it comes to specifying landscape plants, most of us start with the USDA Plant Hardiness Zone Map. Based on the average annual extreme minimum Winter temperature, displayed as 10˚F zones and 5˚F half zones, the Map is the standard by which one can determine which perennial plants are most likely to thrive at a location. In fact, an updated Map (the first since 2012) was just released this past November — with about half of the country shifting to the next warmer half zone.
The 2023 map is based on 30-year averages and includes data measured at weather stations from 1991 to 2020. The new map also uses more data representing the state’s mountain regions where, during Winter, warm air overlies cold air that settles into low elevation valleys, creating warmer temperatures.
Yet despite its recent update and expanded use of data, the Hardiness Zones don’t provide a complete picture, say some native plant enthusiasts, who instead point to the less well-known and more highly complex Ecoregions.
Ecoregions
Ecoregions are areas where ecosystems (and the type, quality, and quantity of environmental resources) are generally similar. Determining factors include geology, landforms, soils, vegetation, climate, land use, wildlife, and hydrology.
In the U.S., the Ecoregion framework is derived from a study done by James N. Omernik in 1987 and from mapping done in collaboration with EPA regional offices, other Federal agencies, state resource management agencies, and neighboring North American countries. Ecoregions are divided by Roman numeral levels that start as large geographic areas (Level I) which are then divided into smaller and more specific regions culminating in the most detail at Level IV.
In other words, the continental U.S. has been divided into:
12 broad, Level I Ecoregions;
25 Level II Ecoregions intended to provide a more detailed description of the large ecological areas nested within the Level I regions; and
105 Level III Ecoregions, which are smaller ecological areas nested within Level II regions; and
967 Level IV Ecoregions, which are the smallest, most specific Ecoregion level.
Obviously, Level IV has the most detail and viewing all of the U.S. divided up into 967 regions is a bit mind-boggling. But you can access a Level IV map of just your state here. In my own small state of New Jersey, we have 17 different Level IV Ecoregions. Not surprisingly, I find my own hometown (bordering a bay across from New York City) straddles two Ecoregions — both Inner Coastal Plain and a tiny pocket of Barrier Islands — Coastal Marshes. Perhaps this helps explain why my neighbors closer to the shoreline have sandy soil (Barrier Islands), while my own is clay (Inner Coastal Plain).
A black-eyed Susan attracts a butterfly. Silvery checkerspot butterflies nectar on their flowers and lay eggs on their foliage. (Photo: AdobeStock/deja vu designs)
Use Of Ecoregions
While Ecoregions are used by federal agencies and experts for ecological research, land management, and planning, it can also help guide us in knowing what types of plant communities will thrive in a given location. For instance, Grow Native Massachusetts, designates nine principal management zones within the state based on U.S. Forest Service Ecoregions. They write, “Each region’s characteristics give us a baseline for knowing what plant species and natural communities we might expect to find in those locales.” For instance, in Massachusetts the Ecoregions tell us the Boston Basin experiences an urban heat island effect, while the North Shore “is significantly colder than coastal areas just to the south.”
Wild Ones, a non-profit proponent of native plants, says “Selecting native plant species from within your Ecoregion is the best way to incorporate natives in your garden or habitat landscape to help restore the natural environment.” They continue, “This environmentally sound landscaping practice helps to preserve biodiversity, the health of the environment, and the unique character of where you live.”
Keystone Plants By Ecoregion
Homegrown National Park (HNP), which also promotes native plants, has created a useful resource for U.S. Ecoregions. They list “keystone” plants by Ecoregion. Keystone plants are the most productive plants that support the most species. Based on the research of Doug Tallamy, a famed ecologist at the University of Delaware, a few genera of native plants, or keystone genera, form the backbone of local ecosystems, particularly in terms of producing the food that fuels insects. Planting just one of these keystone plants can help restore native biodiversity, while landscapes that do not contain one or more species of keystone genera will have failed food webs, even if the diversity of other plants is high.
New Plants & Trends For 2024
But first, a little background about HNP and its founder, Tallamy. HNP is a term coined by Tallamy, whose 2020 NY Times Best Seller, Nature’s Best Hope, showed homeowners how to turn their yards into conservation corridors. His latest book, The Nature of Oaks, released in March 2021, showed why oaks should be among the “keystone” plants in a landscape. In an article written for Turf in April 2022, he made the simple point that oaks are a powerhouse of biodiversity support as the primary host for more than 950 caterpillar species nationwide! For reference, native tulip poplars support 21 caterpillar species, crepe myrtles support three, and ginkgos support none.
Today, HNP is a grassroots call-to-action catalyzing the collective effort of individual homeowners, property owners, land managers, and anyone with some soil to plant in, to regenerate biodiversity and ecosystem function by planting native plants and creating new ecological networks. The group has created an interactive map, the HNP Ecoregion Explorer, of 25 Level I and II Ecoregions, and then lists “keystone plants” for each Ecoregion.
For instance, once again, when I search New Jersey, I find my Ecoregion Level II is 8.5 Mississippi Alluvial and Southeast USA Coastal Plains, which stretches from the tip of Massachusetts down along the East coast, encompassing much of Florida, then bordering the Gulf of Mexico until hitting New Orleans and stretching up along the Mississippi River (see map above).
(Photo: Adobe Stock / Tyler)
When I click on that region, I find keystone plants for that area include:
Maryland golden-aster (Chrysopsis mariana)
Lanceleaf coreopsis (Coreopsis lanceolata)
Woodland sunflower (Helianthus divaricatus)
Common evening primrose (Oenothera biennis)
Black-eyed Susan (Rudbeckia hirta) Shown above.
Wreath goldenrod (Solidago caesia)
Wrinkleleaf goldenrod (Solidago rugosa)
Calico aster (Symphyotrichum lateriflorum) Shown above.
There’s also a separate section for keystone trees and shrubs. Those in Region 8.5 include:
Black cherry (Prunus serotina)
Black willow (Salix negra) Not native to central and southern Florida. Shown below.
Carolina cherry laurel (Prunus caroliniana) Not native to northern portions of ecoregion.
N. highbush blueberry (Vaccinium corymbosum)
Post oak (Quercus stellata) Not native to central and southern Florida.
Red maple (Acer rubrum)
Saltbush (Baccharis halimifolia) Not native to northern portions of ecoregion.
San Laurel oak (Quercus hemisphaerica) Not native to northern portions of ecoregion.
Find your own Ecoregion and keystone plants here.
Tree recommendations can be found here.
Do you have a comment? Share your thoughts in the Comments section below, or send an e-mail to the Editor at cmenapace@groupc.com.