What is a Native Plant?

The definition of a native plant has been controversial in the past but now there is an emerging consensus on a science-based definition.  A plant is native if it occurs naturally without human introduction, having evolved over a long time in a specific region. It will be intricately connected to the physical environment and organisms of its region. 

 This definition means that what qualifies as a native plant will vary from one region to the next. North America has been divided into a number of eco-regions, defined by a commonality of climate, geography and other features. Nova Scotia is part of the Northeast eco-region, comprised of the New England states and the Canadian Atlantic provinces.  Therefore, for us, plants of the northeast region are considered native and we should refer to recommended plant lists for the Northeast region.

The Importance of Native Plants

   The importance of native plants is easily understood by unpacking the previous definition. When we say that native plants have co-evolved with other living organisms in their specific region, this means that over a long period of time they have developed special relationships.  One of the more well known is the Monarch Butterfly’s preference to lay its eggs on plants in the milkweed family. The Monarch caterpillar has developed the ability to detoxify chemicals in the milkweed that are toxic to other insects. Many other butterflies and moths have developed similar plant-specific dependencies to help protect their caterpillars. The plants they prefer are called host plants. In another dependent relationship, birds rely heavily on nutrient rich caterpillars to feed their babies, which means that ultimately their survival also depends on native plants.

    Insects are needed to pollinate 85.5% of all plants on earth and of course this includes the plants we need for food.  Research has shown that native plants are four times more likely than non-native plants to attract native bees. The more we lose native plants, the more we lose our pollinator insects and the greater the danger to our own survival.

Why Put Native Plants in Our Gardens?

   World-wide, we are in the midst of a biodiversity crisis, with insects and other wildlife disappearing at an alarming rate. There are multiple human-based causes for this such as the effects of climate change and the use of pesticides. But by far the biggest cause is loss of habitat. Calculations for the United States have determined that there is now only 5% of land left as undisturbed natural wildlife habitat. Much of this land is fragmented and often contains invasive non-native plants which choke out the native plants.

   Traditionally we have viewed nature and wild areas as existing outside of and apart from our human communities. However, supporting wildlife in rural preserves and parks is not enough. We need to give back more land and one of the biggest untapped resources is outdoor urban and suburban areas, including our own gardens.   If all of these areas were filled with appropriate communities of native plants, the result would be a vast connected landscape that would support a huge amount of insects, birds and other animals.

   These new wildlife habitat areas, with less lawn and a rich layering of trees, shrubs and herbaceous plants, will have many other benefits besides supporting wildlife. These include carbon sequestration, urban shading and cooling, watershed protection, weather moderation, and air cleaning.  In the individual garden, more native plants would mean the use of less water, chemical fertilizers, herbicides and pesticides, and motorized equipment, and ultimately, less maintenance.

   Gardeners joining this movement should refer to recommended plant lists for native plants.  There are “keystone species” which support larger numbers of wildlife.  For example the oak tree (most commonly red oak in our region) supports 517 species of butterflies and moths. Besides this, the caterpillars support birds, and the tree provides nuts and shelter to many other animals.  In contrast to this the imported Asian Ginkgo tree, even after being here for a few hundred years, only supports five caterpillars.

 If you wish to find out more about developing a wildlife support garden, see adjoining article “Planting a Butterfly Garden” and also the references in the Resources section.

By Carolyn Green