An Ecological Approach to Designing with Native Trees
By Anna Fialkoff
This article first appeared in “Native Trees for the Northeast Landscapes: Wild Seed Project Guide” and is reprinted with the permission of the author.
Parks, arboreta and college campuses display many old and stately specimen trees, yet they are often contrived landscapes where trees look like islands in a sea of monoculture lawn. Each island’s borders are marked by a ring of bark mulch, intended to keep lawn mowers from damaging tree roots.
Maintaining these pristine settings takes inputs like fertilizers, pesticides and soil amendments, as well as frequent mowing. The harmful consequences of petroleum-based landscape practices multiply when this park-like look is replicated in residential yards, commercial landscaping, streetscapes and parking-lot islands.
Some public gardens, knowing that people take design cues from them, are now adopting more environmentally responsible landscaping. The Arnold Arboretum in Boston and nearby Mount Auburn Cemetery in Cambridge, for example, are working to replace mulch rings and sometimes entire lawn areas with native groundcovers and no-mow grasses.
Planting native species beneath isolated trees is a step in the right direction. However, more fundamental—rather than piecemeal—design changes are needed in developed landscapes to restore the health and resiliency of natural systems. Rewilding our landscapes and supporting biodiversity requires a paradigm shift from the individual to the group, and from the specimen tree to the forest.
Layer Plants Like a Forest
Forest trees are not singular specimens but are interdependent players in a dynamic natural community. Using forest ecosystems for inspiration, we can bring maximal biodiversity, resilience and biomass back into human landscapes.
Each layered tier in the forest has a particular ecological function. The tree canopy casts critical shade, moderates moisture and temperature, drops leaf litter to help build living soil, and provides sustenance for a diversity of life on roots, trunks, branches and leaves.
Understory trees, shrubs and herbaceous plants perform many similar landscape functions, and their flowers supply nectar and pollen sources for pollinators throughout the growing season. The herbaceous ground layer helps retain soil moisture and prevents erosion of the precious humus built up through years of fallen leaves, sticks and logs.
Even young forests can be great models for landscape design, demonstrating that we don’t need to follow old-school horticultural rules about spacing plants a certain distance apart. Consider stands of gray birch or white pine, pioneering species that form dense colonies in open fields, growing upward for light with their branches weaving together. They may appear less grand than a solitary outstretched tree, but the grove helps shelter each member tree from damage by wind, snow and ice.
Wildflower meadows are often seen as a mainstay for sustaining pollinators, but native trees managed in a forest-like setting can better support the full life cycles of moths and butterflies, which rely on leafy branches for larval food and fallen leaves for overwintering. University of Delaware entomologist Doug Tallamy has found that a single red oak in the Northeast can host up to 534 species of moth and butterfly caterpillars, but only if its leaf litter remains intact as it would on the forest floor.
Landscape designs should begin with those biodiversity magnets that Tallamy calls “keystone” trees: oaks, cherries, willows, birches and poplars. Once those keystone species are in place, more layered plants can be added to create a three-dimensional mini-forest that bustles with life.
Design With Change in Mind
Planting a tree is a long-term investment in the future. It often takes decades for a tree to reach its mature height and provide the full gamut of ecological services—from purifying the air and absorbing heavy rains to offering wildlife habitat and storing atmospheric carbon. That is why designing with trees involves more than choices about seasonal interest, height, placement and spacing of individual plants; it requires thinking about how your landscape will change over time.
As you set short- and long-term goals for a site, try mimicking how a young forest grows and develops. While awaiting the shade from a long-lived deciduous tree like sugar maple, consider planting one or more faster-growing and relatively short-lived trees, like birches, poplars or willows, that can offer temporary shade for understory plantings as the maple slowly matures.
Select Plants Suited to the Site
Trees and their associated understory layers will best thrive if sited in their ideal light, soil and moisture conditions. Analyze those elements first and choose trees accordingly, rather than trying to change the site to suit a desired tree’s needs.
By taking cues from where particular species grow in natural habitats, we can situate those plants in similar conditions within built landscapes. For example, beach plums typically grow on coastal sand plains, where they tolerate sunny, hot and dry conditions and even salt spray. They’re also able to flourish in urban and roadside plantings, where conditions are often similar to maritime landscapes.
Mimicking forest ecosystems can help restore soil health, particularly in built environments with compacted ground stripped of organic matter. A large canopy tree, such as maple, oak, or basswood, will help make humus as it grows if its leaf litter is left in place to improve soil structure, promote moisture retention, form mycorrhizal networks, and provide overwintering habitat for beneficial creatures such as butterflies, moths, frogs, salamanders and ground-nesting birds. Before trees start producing enough of their own leaf litter, they will benefit from a thick mulch of composted leaves or aged wood chips.
Group Plants Into Guilds
Plants that prefer similar growing conditions can be grouped and planted together––with each species serving a specific role in building soil, creating shade, providing structure, or covering the earth, much like in a forest or woodland plant community. These “plant guilds” can help guide plant selection for particular conditions. A guild should include trees of differing heights as well as understory shrubs and ground-layer plants to be an effective design tool for creating forest-inspired plantings.
* This article is adapted from a chapter in Wild Seed Project’s new guide-booklet, Native Trees for Northeast Landscapes, which profiles 31 stunning and stalwart native tree species for urban, suburban and rural landscapes of the Northeast. It offers readers an ecological lens through which to inspire thriving and impactful plantings in yards, neighborhoods and communities. Learn more and purchase your copy of Native Trees for Northeast Landscapes here.
About the Author
Anna Fialkoff is the new program manager ready to help Wild Seed Project further its educational programming, deepen relationships with partner organizations, and catalyze a movement to rewild Maine. Anna was most recently Senior Horticulturist at Native Plant Trust’s Garden in the Woods in Framingham, MA. She designed and installed native plant gardens, managed interns and volunteers, and taught the public ways to incorporate native plants in their own gardens. With a BA in Human Ecology from College of the Atlantic and an MS in Ecological Design from The Conway School, she brings with her a deep knowledge of native plant ecology, horticulture, conservation, and ecological landscape design.
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