Why is it so critical that we start to view our gardens as habitat? And why is landscaping with native plants is so important?

Biodiversity in Decline

One of the key reasons is biodiversity. Research from a broad geographic range and across different species indicates a clear trend—biodiversity is in steep decline.

A global assessment published in 2019 found that biodiversity is declining faster than at any time in human history, while a 2020 report by the World Wide Fund For Nature found that global populations of mammals, birds, amphibians, reptiles and fish have suffered an average two-thirds decline in less than half a century—with an alarming average drop of 68% since 1970 (IPBES, 2019; WWF, 2020).

Insect abundance, biomass, species richness, and range size are all declining (Wagner et al., 2021). Insects are vital to life as we know it. They pollinate 90% of all flowering plants, and are the primary means by which energy is transferred from plants to most other animals in food webs. Meanwhile, North America is suffering staggering losses in its bird population, with an estimated net loss of 2.9 billion breeding adults since 1970 (Rosenberg et al., 2019).

Ecosystems Destabilized

Ecosystems are incredibly complex. When we lose biodiversity, we destabilize these systems and risk their collapse. Without functioning ecosystems, we lose the vital ecosystem services that support life.

An ecosystem can be defined as a community of interdependent species, including humans, along with their non-living environment. Ecosystem services are the conditions, processes, and outputs of ecosystems that sustain and fulfill human life, or, more simply, the benefits people obtain from ecosystems. Some ecosystem services are vital for human life—such as the provision of oxygen, food, and fresh water—while others simply enhance our quality of life.

Native Plants to the Rescue

This is where native plants come in…because native plant communities support a great deal more biodiversity than introduced plants.

The great majority of insects are diet or host-plant specialists—they can only eat or live on plants that they have developed a relationship with through evolutionary time (Forister et al., 2015).

This host specificity has consequences throughout the ecosystem. For example, a study comparing hedgerows of native species with hedgerows of introduced species found 68% fewer caterpillar species, 91% fewer caterpillars, and 96% less caterpillar biomass in the study areas with introduced plants (Richard et al., 2018).

Caterpillars are one of the most important food sources for wildlife, so any reduction in caterpillar numbers impacts food availability. A study found that suburban yards dominated by introduced plants were 60% less likely to have breeding chickadees compared to primarily native landscapes (Narango et al., 2018).

Although plants introduced from other parts of the world can provide some ecosystem functions, there is almost always a loss in biodiversity when they are used in place of native plants.

By using native plants in our landscaping, we can support biodiversity and maintain functional ecosystems.

With so many environmental concerns worldwide, and with so many of our plant and wildlife populations declining and facing increasing threats, using our diverse native plants in landscaping is a way we can all do something and really make a difference.

Which Native Plants to Use

Include keystone plants, plant for insect specialists, increase native plant diversity.

Recent research indicates that a few genera are critical for local ecosystems, going “above and beyond” in terms of ecological productivity.

For example, a study that included more than 12,000 butterfly and moth (Lepidoptera) species and more than 2000 native plant genera (Narango et al., 2020) found:

  • On average across counties sampled in the US, 14% of local plant genera supported more than 90% of Lepidopteran diversity.
  • These keystone genera support orders of magnitude more Lepidopteran species than the majority of other local plant genera.
  • Planting these “keystone” native plants will have a disproportionately large impact on restoring biodiversity through the food chain and help to create the most productive landscapes possible.
  • In 84% of counties in which they occur in North America, oaks are the most powerful plant to plant.

Ideally, plants from keystone genera will be foundational in your plantings. Next choice, plant for other specialists (such as specialist bee species) to greatly increase the biodiversity supported by the habitat, as both specialist and generalist species can be supported. Aim to increase native plant diversity overall, with the intentional inclusion of these plants.

  • The National Wildlife Federation Native Plant Finder, developed in collaboration with Dr. Douglas Tallamy, can be used to search by zip code for the genera of highest value to Lepidoptera, with results ranked in each category—flowers and grasses; trees and shrubs.
  • The Indiana Wildlife Federation Native Plant Finder, produced in collaboration with INPS, can be used to find species within those genera that are native to Indiana..
  • The Biota of North America Program (BONAP) North American Plant Atlas (NAPA) has comprehensive US County-Level Species Maps, enabling searches by family or genus for plant species native to a particular US county.

Provide resources throughout the year. 

Ensuring that insects have floral and other resources for as long as possible through the year is vitally important. Include plants that have a long bloom time, that bloom early in spring or late in the fall, and that provide nesting and sheltering sites.

Be generous! Increasing the abundance of native plantings is critical.

Research suggests that plantings should include at least 70% native plants by biomass. This is a threshold below which the probability of sustaining some local bird populations plummets to zero (Narango et al., 2018).

Source Mindfully

Although “nativars” (cultivars of native plants) may be more attractive for some gardeners for aesthetic reasons, they can have ecological costs (Byrne et al., 2011; White, 2016a; Narango et al., 2019). Due to differences in their impacts on ecosystem function, biodiversity, and gene flow, straight native species are an ecologically safer option than nativars.

When sourcing plants, please ask about neonicotinoid use. Neonicotinoids, an especially prevalent class of systemic insecticides, are used routinely by some commercial nurseries, big box stores, and seed suppliers to treat plants and seeds. Neonicotinoids can harm benign and beneficial insects and have impacts throughout the food web. Actively source plants and seeds that have not been treated with neonicotinoids, and use your voice to help influence supply chains. The Xerces Society and the IPI Database have excellent, detailed information on this topic.

Design by Native Plant Communities

Where possible, landscape designs should echo native plant communities. Begin by assessing what plant community a property or area resembles (such as woodland, water’s edge, or prairie grassland) together with the conditions (soil, light, aspect, moisture level). Ecological value may be a primary consideration, but aesthetics or function (such as a screening bio-hedge or rain garden) might also be a priority.

Incorporating the latest scientific research into planting plans and landscaping decisions wherever possible can maximize the ecological value of plantings. For example, a recent study suggests that the layout of gardens strongly influences the extent to which milkweed plants are found and used by monarchs. The study found that monarch eggs and larvae were more abundant in experimental gardens where milkweed was evenly spaced in a corridor around the perimeter, surrounding the nectar plants and grasses, than in gardens in which milkweeds were surrounded by or intermixed with the other plants (Baker & Potter, 2019). Significantly more eggs and larvae were found in Monarch Waystation gardens where milkweeds were spatially isolated as opposed to closely intermixed with non-host plants, and in gardens having 100 meters north/south access unimpeded by structures. Another recent study found that Asclepias incarnata and Asclepias tuberosa appear to be the most cost-effective milkweed species to include in seed mixes (Lukens et al., 2020).