Ecological Gardeners, Think Like a Forest When You Plant a Tree

By Heather McCargo

All images courtesy of author

About 385 million years ago, the first trees appeared on Earth. This was the Devonian period, when the great explosion of plant life left the water and transformed the land. At first there were only tiny low-growing plants, the ancestors of mosses. Then came the first trees with their increasingly large biomass stretching high above the ground and deep into the earth. These early forests created the world we know today. Before the Earth was a forested planet, it was a harsh and barren place. It was trees that made it hospitable for the rest of life. 

The oldest known fossilized forest is in Cairo, New York. These trees were the first to have tall woody trunks and branches, green leaves for expanded photosynthesis, and extensive root systems that turned the rocky earth into soil. Some of the trees that we know and recognize today, such as conifers and early flowering plants like Magnolia, first appeared alongside the dinosaurs, while oaks and other groups appeared after their demise.

500 years ago, much of eastern north American forests were old growth, sustained through millennia by indigenous Americans who relied on these healthy ecosystems.

With hundreds of millions of years of tree history behind us, planting native trees is a powerful action that all of us can take in our communities today to buffer local ecosystems as the climate changes. Trees are an important natural solution that can help repair degraded and fragmented landscapes. Choosing our region’s indigenous trees is critical because it is the native species that are the foundation of the local food webs that support all land-based life, including animals, fungi and the microbial life in the soil. This is true wherever you live on earth.

The great deciduous forest biome of eastern North America has nearly 200 beautiful and resilient tree species that grow in the varied woodlands that once stretched from Canada to the Gulf Coast. We have trees for every situation, from rich, moist forest soils to acidic soils, dry sandy sites to wetlands, and we even have species that grow well in our urban areas. 

The vertical vegetation of trees creates a protective and cooling canopy over the landscape while storing CO2 above and below ground. Trees prevent erosion as they slow and filter precipitation, preventing nutrients and pollution from washing into streams and shores. Trees are also biodiversity powerhouses, with their large year-round woody trunks, branches, and roots—supporting a wide variety of woodland birds, pollinating insects, and many other small creatures from the canopy to the ground. This diversity sustains us all. 

Follow the steps below to think like a forest when you plant a tree, and you will find yourself reaping the rewards of trees’ magical qualities.

Elder Trees

Heather standing in front of an Elder tree.

Have Reverence for Elder Trees

Modern society rarely values older trees for their age and size. Indigenous people understand this, but contemporary Western civilization has lost this reverence. There is no such thing as an over-mature or overgrown tree. Elder trees have witnessed another time and have wisdom to teach us about past climates and how we might cope in the future.

Large old urban trees also need to be recognized as an asset—not a nuisance. The shade they cast, the life they support, and their beauty is desperately needed in urban areas. Of course urban trees take more maintenance, such as careful pruning to keep dead branches from harming people or buildings. 

Bob Leverett, co-founder of the Native Tree Society, produced a powerful graphic showing how many trees it takes to store 8 tons of carbon a year. He found that large older trees and forests are carbon rockstars: 

Mark Anderson of the Nature Conservancy has an excellent article highlighting the superior carbon storage abilities of mature trees and forest: https://newildernesstrust.org/about/wild-works/.

I hope this powerful data inspires you to be active in preserving existing trees and forests, and to plant more trees in your yards and communities.

Protect Childhood with Trees

Along with the climatic benefits and biodiversity they support, trees are vital for the physical and mental health of humans, especially the next generation. I consider trees critical infrastructure for childhood. As a child I was always up in a tree, and living in rural Maine I was able to offer this childhood to my now 20-something son and daughter, but many of their peers raised in urban or suburban areas missed out.  

A healthy mature forest has layers of vegetation from the canopy to the ground.

Think Like a Forest When You Plant Trees

When planting or designing a landscape  with native trees, look at the characteristics of a healthy, diverse forest for inspiration. Trees do not grow as isolated individuals; a healthy forest has layers of vegetation and a huge diversity of species mingling together. 

In the canopy, tall trunks and branches reach towards the sky, with millions of leaves capturing direct sunlight. In the Northeast, the canopy typically has a handful of species—dry upland sites may contain oak and hickory, while moister soils may have forests of maple, birch, beech, and hemlock.

In the mid-story, every niche is filled. There are juveniles of the future canopy trees, which may be the same or different species if conditions are changing.  There are species that favor this middle zone, such as dogwood, musclewood, hop hornbeam, holly, and witch hazel. The shaggy bark and cavities in the trunks provide habitat for insects, birds, and small animals to shelter, including bats. Dead trees in various stages of decay are a natural part of a healthy forest and support as much life as when they were alive, particularly hosting insects that attract woodland birds. 

It is on the forest floor where most plant diversity resides. In a healthy forest, the understory has seedling trees, shrubs, wildflowers, ferns, and mosses carpeting the ground and filling every available space. Tree roots reach deep into the soil, joined by many species of fungal partners. Young forests on former agricultural land are lacking this diversity, as farming drastically changes the soils and the recovery of plant diversity takes centuries.

In deciduous forests, direct sunlight only reaches the forest floor in spring, fall, and winter; this is why many woodland wildflowers bloom in the spring. Evergreen trees cast shade year-round and so have a different ground layer. (See Wild Seed Projects groundcover guide or blog for ideas.)

Mimic the Natural Cycles of the Forest

Move beyond isolated single trees planted in a sea of lawn or pavement, and instead plant multiple trees with layers of plantings underneath. Ideally, at least two or more of each species are planted for healthy cross pollination. Plant as many as different kinds as possible—combining species that grow in similar conditions. Even a small area can have dozens of species of woody and herbaceous plants. Diversity creates resilience, and it is our simplification that has led to so many ecological problems.   

In a built environment, the nature of shade is different than in a forest. The north side of a building may get no direct sun, while the east or west sides will have direct sun for part of the day and full shade for the rest. Adding layers with trees and shrubs will create a more dappled light and will lead to a buildup of leaf litter to create a more forest-like environment that encourages healthy plant growth.

Create layers of vegetation with trees, shrubs and groundcovers

In a healthy natural system, all nutrients are recycled. Leaves, branches, rotting logs, animal droppings, and the bodies of dead insects and small animals drop down from the canopy and return to the earth. Fungi, bacteria, and other microbial life in the soil help recycle these dead plants and animals and release the mineral nutrients in the soil. While trees receive all their required carbon energy from photosynthesis, they can only get their necessary nutrients from the nutrient cycling that happens in the soil food web. Leaf litter plays a critical role year-round providing nesting habitat for butterflies, birds and small animals, protecting the roots and soil creatures from temperature extremes and erosion, and creating an insulating blanket for the life underneath. 

Recycling resources on site begins with you “leaving the leaves.” This also means finding ways to incorporate woody prunings into your landscape. Chop prunings and sprinkle them around as mulch. If you require a more tidy look, there are clever ways to include branches (see photo). Leave dead wood whenever possible. A tree snag will attract woodpeckers, and a rotting stump or log on the ground is beautiful covered in moss or with mushrooms: Learn to see the beauty in these natural processes and find ways to include them in your garden.

And most important of all, use organic gardening practices. Chemical fertilizers or pesticides kill the life in the soil—this microbiome is critical for healthy plant growth and all life. 

There are lots of clever ways to keep leaves and woody debris in the landscape

Choose Native Tree Species to Plant 

Wild Seed Project has extensive resources—available for free online and in print.  Our Native Tree Guide covers 30 tree species, grouped by size and shape, and gives information on each tree’s rate of growth and life span; its native range and wild habitat;  growing conditions (soil, moisture, light requirements, and urban tolerances); flowering and fruit/seed ripening; and what wildlife it supports. We also have numerous blog posts and printable species lists to assist you in choosing the best plants for your site. (See a sample species list below).

Wild Seed Project guide to native trees sample page (image copywrite Wild seed Project)

Plant Young Trees

Trees do best when planted young. A bare root sapling or small seedling in a deep pot will establish much more quickly than a larger transplanted ball and burlap or pot-bound, container-grown tree. Young plants adapt better to existing soil conditions, develop a healthier root system, and become more drought resistant than older specimens. To plant under existing trees without damaging roots, consider smothering existing grass with brown paper, cardboard mulch, or shredded bark, and wait 3 months or more before planting. Seek out nurseries who offer seed grown species and use organic practices. (See resources below for guidance.)

Plant Trees in Cities

Our cities should be tree towns, because shade is critical in urban areas for reducing the heat absorbed by all the buildings and paving. Urban street trees and even small mini forests (aka Miyawaki Forests) cool the city; filter the air, water, and soil; attract birds and butterflies and bees; and make a healthier environment for humans—mentally and physically. Many native trees do well as street trees: oaks, red maple, black gum, and others. (Wild Seed Project resources will point you to trees tolerant of urban conditions.)

We can do better than this, but sadly this is the norm.

Paris has undertaken ambitious plantings to create canopy and layers of vegetation.

Design With Intention

Consider the following design ideas.

1. Planting with an existing oak in a lawn     

Here is a way to take an existing oak tree surrounded by lawn and layer plantings underneath, providing lots of year round habitat for wildlife. If it is an older tree, let some of the acorns sprout for the next generation of oaks. Understory/edge trees could be dogwoods, shad, or witch hazel, with lower growing shrubs such as azalea, blueberry, clethra, and bush honeysuckle. Adding an herbaceous layer boosts overall diversity; see our groundcover guide or blog on native groundcovers for ideas on specific combinations.

Planting with an existing oak tree.

2. Protecting the edge of the woods

Where the edge of a woodland has been exposed by a road or new development, sealing off that edge with diverse layers of trees, shrubs and herbaceous species will protect the remaining forest from desiccating exposure and invasive species. The orientation (north, south, east, or west) will determine the choice of trees. Mixing faster-growing species like birch, aspen or tulip tree with slower-growing oaks or maples will quickly fill in the edge and extend protection well into the future. Edge -loving smaller trees and shrubs such as shad, dogwoods, redbud, viburnums will protect the forest interior. 

3. Savanna planting

You can also create a more open, savanna-like planting. There are native trees that grow in more open forests such as gray birch, pitch pine, oaks (scarlet, post, or bear oak), beach plum, and red cedar . These species all thrive in hot, dry sandy or gravelly soils. Drought-tolerant herbaceous species can be planted as the ground cover with an un-mulched sandy surface is very important for ground-nesting pollinators

4. Layering under street tree plantings

Here is a typical planting in a parking lot, with trees and turf grass. This could be diversified with tough suckering shrubs such as bush honeysuckle (Diervilla sp.), bayberry, aronia, sweetfern, and Virginia rose. Every few years they can be pruned back to ground level to keep them low (or if damaged by a snow plow). An alternative to shrubs is an herbaceous ground layer of pussytoes, beardtongue, tall anemone, black-eyed cornflower, white wood aster, and bluestem or gray goldenrod. Or, plant a mixture of shrubs and herbaceous plants.

Layering under trees in a parking lot

In my home city of Portland, ME, I planted a shade-loving herbaceous layer under my street-side honey locust tree. I removed some of the brick paving to create a planting bed 2 ½ feet by 12 feet, added a thick layer of aged leaves, and planted large-leaved and white wood aster, Canada anemone, and zig-zag goldenrod. It has been very resilient, surviving lots of dog pee, drought, and roadside pollution.

Create a Different Trajectory For the Future

We humans have dominated the planet in a way that has been detrimental to the rest of life on earth. We can change this. Planting native trees is one of many actions that can help heal ourselves and our earth. Let’s create a different trajectory for the future and give the next generation some trees to climb!

RESOURCES FOR PLANTING NATIVE TREES:

RECOMMENDED NATIVE TREES – All species listed are adaptable to landscape and garden situations and once established make beautiful low maintenance plantings that support a wide diversity of fauna, fungi and other soil biodiversity. Younger, smaller trees will establish more easily and within a few years surpass the growth and vigor or larger and more costly specimens. Species labeled with # work well as street trees.

Large Deciduous Shade Trees

• Maples Acer rubrum#, A. saccharinum, A. saccharum
• Yellow Buckeye Aesculus flava
• Birches Betula papyrifera, B. populifolia, B. alleghaniensis, B.lenta#
• Hickory Carya ovata, C.glabra
• Northern Catalpa Catalpa speciosa# 
• Common Hackberry Celtis occidentalis#
• Kentucky Yellow-wood Cladrastis kentukea# 
• American Beech Fagus grandifolia
• Walnut and Butternut Juglans nigra, J. cinerea
• Sweetgum Liquidambar styraciflua#
• Tulip Tree Liriodendron tulipifera
• Big Leaf Magnolia Magnolia macrophylla
• Black-gum Nyssa sylvatica#
• American Sycamore Platanus occidentalis#
• Aspens Populus grandidentata, P. tremuloides#
• Black Cherry Prunus serotina
• Oak# Quercus alba, Q. bicolor, Q. coccinea, Q. montana, Q. macrocarpa, Q. muehlenbergii, Q.palustrus, Q. rubra, Q.stellata, Q velutina (and many more) 
• Black Willow Salix nigra
• American Linden Tilia americana
• American Elm Ulmus americana #

Small to Medium Flowering Trees

• Striped Maple Acer pensylvanicum
• Serviceberry# Amelanchier arborea, A.laevis, A.canadensis
• Dogwood Bethamidia florida, Swida alternifolia
• Musclewood Carpinus caroliniana#
• Redbud Cercis canadensis#
• Witch Hazel Hamamelis virginiana#
• American Holly Ilex opaca
• Spicebush Lindera benzoin#
• Sweetbay Magnolia Magnolia virginiana
• Hophornbeam Oystra virginiana#
• Sourwood Oxydendron arboretum
• Beach Plum Prunus maritima#
• American Plum Prunus Americana
• Sassafras Sassafras albidum 
• Blackhaw Viburnum prunifolium#

Conifers

• Balsam fir Abies balsamea
• Atlantic white cedar Chamaecyparis thyoides#
• Eastern red cedar Juniperus virginiana#
• American larch Larix laricina
• Spruce Picea glauca, P.rubens
• Pines Pinus resinosa, P. rigida#, P. strobus, P. banksiana
• Northern white-cedar Thuja occidentalis#
• Eastern hemlock Tsuga canadensis

Wild Seed Project Guides:

https://shop.wildseedproject.net/collections/publications/products/native-trees-for-northeast-landscapes-guide

Wild Seed Project blog posts on topics related to native tree plantings including species list for different planting scenarios: 

https://wildseedproject.net/wild-seed-blog/

Leave the Leaves

Creating Canopy 

Small Flowering Trees

Native Groundcovers

Hellstrip plantings

In the Shade

Navigating the Nurseries- finding seed grown native plants

What to Plant– Species list for a variety of site conditions: https://wildseedproject.net/plant-lists/

About the Author: 

Heather McCargo is the founder of Wild Seed Project, 501(c)(3) non-profit, which is located within the ancestral Wabanaki territory now called Maine. She is an educator with 30 years of expertise in plant propagation, landscape design, and conservation. She was the head plant propagator at the New England Wildflower Society’s Garden in the Woods in the 90’s, worked at several landscape architecture/planning firms specializing in ecological design, has been a contributor to several research projects with USAID, National Gardening Association, and with MOFGA. She has lectured nationally and is widely published in journals and magazines such as Horticulture and American Nurseryman. Heather has a MA from the Conway School of Landscape Design and BA in plant ecology from Hampshire College.