Soft Landings
Diverse Native Plantings Under Keystone Trees
Keystone Plants
In order to understand the ecological benefits of a Soft Landings planting in our managed landscapes, it’s important to review the function of keystone trees and perennials and their substantial role in a soft landing.
Keystone plants are native plants that support a significant number of interactions with other organisms in a food web. For example, larval host plants that support a high diversity of insect herbivores (plant-feeding insects), or pollen-specialist bees, are keystone plants. Planting native keystone plants helps build complex and functional food webs by forming the essential foundation — native plants and insects — that subsequently provides food for other organisms, directly and indirectly.
Specializations
Insect herbivores (plant-feeding insects) have specific and co-evolved relationships with keystone plants.
Research by Desiree Narango, Douglas Tallamy, and Kimberly Shropshire has identified that "functional food webs are essential for the successful conservation of ecological communities ...
Artwork: Elsa Cousins
... and in terrestrial systems, food webs are built on a foundation of coevolved interactions between plants and their consumers."
Keystone plants are the primary "hubs or nodes" in a food web and support a significant number of insects, compared with other plants in the food web.
"Remove keystone plants and the diversity and abundance of many essential insect species, which 96% of terrestrial birds rely on for food sources, will be diminished. The ecosystem collapses in a similar way that the removal of the “key” stone in ancient Roman arch will trigger its demise." Source: Keystone Plants by Ecoregion
Illustration commissioned for Narango, D.L., Tallamy, D.W., and Shropshire, K.J. (2020) Few keystone plant genera support the majority of Lepidoptera species. Nature Communications, 11, 5751
Connections
Connecting Keystone Plants and Insect Specializations to Soft Landings Plantings
After feeding on native tree foliage, many moth and butterfly caterpillars spend their next life cycle stage (pupae) in the leaf litter or in the soil below their host plant tree. For example, a Red-Spotted Purple Butterfly (Limenitis arthemis astyanax) caterpillar feeds on black cherry leaves. This caterpillar creates a pupation and overwintering shelter in a rolled leaf.
Regularly mowed or compacted turf grass under trees — hard landings — lacks the necessary habitat for these beneficial insects to complete their life cycles.
Safe undisturbed native plantings under keystone trees — Soft Landings — will enable these butterflies, moths, and many other beneficial insects to complete their life cycles. Photo: Vicki Bonk
Soft Landings
Interestingly, when it comes to supporting these plant feeding caterpillars, the top genera are trees rather than flowers or grasses. This is why a native tree, especially a keystone tree, is a required component of a Soft Landings planting.
Soft landings are diverse native plantings under keystone native trees (or any other regionally appropriate native tree). Photo: Layne Harrison Knoche, University of Illinois Extension
These plantings provide critical shelter and habitat for one or more life cycle stages of moths and butterflies. Photo: Layne Harrison Knoche, University of Illinois Extension
Soft landings plantings that are regionally native also provide pollen and nectar for flower-associated insects such as beetles, flower flies, wasps, true bugs, butterflies, and moths. In addition, native bees — including ones that require specific pollen for survival (specialists) — rely on native host plants.
Andrena distans is a pollen specialist of Geranium
Soft Landings plantings provide larval host plants for butterflies and moths, refuge for beneficial insects such as beetles and lacewings, and protection for insects that overwinter underground such as fireflies. Photo: Linda McCaughey
The native perennials in a Soft Landings planting can also be keystone plants. For example, asters and goldenrods are larval host plants for a significant number of caterpillars and also provide pollen to pollen-specialist native bees (oligoleges). Photo: Big-Leaved Aster (Eurybia macrophylla)
Soft Landings are regionally native plantings under a tree's dripline. A dripline is like the tree's umbrella; it is the area under the horizontal reach of the tree's branches.
Native Trees
Sample Keystone Trees
OAK - genus Quercus
Oaks are universally the top keystone trees that support moths and butterflies. Across the United States, more than 940 types of caterpillars feed on oaks.
Oaks are:
- extremely drought tolerant,
- thrive in grassland and fire-dependent ecosystems,
- provide important food (acorns) for wildlife, and
- offer habitat for a diversity of wildlife including birds. Find an oak species native to your state or county.
PLUM - genus Prunus
In eastern North American, native plums are one of the the top keystone plants.
Flowering in spring, native plums offer nectar and pollen to a wide variety of insects including bees, butterflies, flies, wasps, moths, beetles, and sawflies. Also, the thicket-forming habit and dense growth of native plums provides safe nesting opportunities for songbirds.
Find a plum native to your region: American Plum (Prunus americana) Chicksaw Plum (Prunus angustifolia) Hortulan Plum (Prunus hortulana) Beach Plum (Prunus maritima) Mexican Plum (Prunus mexicana) Munson Plum (Prunus munsoniana) Flatwoods Plum (Prunus umbellata)
PINE - genus Pinus
Prior to Euro-American settlement in North America, pines (and oaks) were the two dominant tree genera in most ecoregions. Both fire-adapted, these trees thrived in grassland habitats that Native Americans maintained with frequent fires. In the Eastern Temperate Forest ecoregion, pines are larval host plants for 200 species of caterpillars. Also, pine resin (pitch or sap) is an important natural material with antimicrobial properties that some cavity-nesting native bees collect to line their nest and brood cells.
ASPEN - genus Populus
In the Eastern Temperate Forest ecoregion, aspen, cottonwood, and poplar are larval host plants for 249 species of caterpillars. We don't recommend planting an aspen, cottonwood, or poplar in a small residential landscape due to their clonal growth habit (aspen and poplar) or shallow root system adapted for floodplain forests (cottonwood). If you own a large property, consider planting trees in this genus.
MAPLE - genus Acer
In the Eastern Temperate Forest (ecoregion 8)*, maples are larval host plants for 238 species of caterpillars.
Note: Some maple species may be climate losers or susceptible to the warming climate. Check with your local native plant or botanical society to determine some appropriate climate-resilient native maples for your region.
Native Perennials
Selecting Soft Landings Plants
First determine the site conditions:
- Soil Type and Texture: Sand, silt, clay, or loam soil? How quickly does water infiltrate?
- Amount of Sun: Sun, part-sun, part-shade, or shade? How many hours of direct sun does the site receive? No sun or dappled light = shade Morning sun = part-shade Afternoon sun = part-sun or sun.
- Match the plants to the site conditions: After determining the above conditions, select a variety of native flowering perennials, ferns, sedges, and grasses that thrive in your growing conditions. For a tidy looking and aesthetically pleasing Soft Landings planting, choose plants that don't grow taller than 24 inches.
Ready to start planting?
Benefits
Planting intentional Soft Landings under keystone trees:
- supports various life cycle stages of beneficial insects,
- builds healthy soil,
- provides food for songbirds and pollinators,
- sequesters more carbon than turf grass, and
- reduces soil compaction and time spent mowing.
