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The Importance of Ecological Diversity in Plants

Updated: Feb 18, 2022

Native plant species have been getting quite the attention over the past few years, for many reasons. More gardeners, land owners and people conscious of the environment are using native plants in their natural landscaping efforts to help pollinators, filter rainwater, prevent erosion, and encourage healthy ecosystems. All of our outdoor spaces are part of the larger ecosystem, and our responsibility to the land and animals that we live with are just starting to be acknowledged. The land has lost a lot over the past few hundred years, largely due to modern farming practices and urban development. Our efforts to rehabilitate the land come at a time of biodiversity loss and climate change - we must start now, and we must choose the correct plants to give the environment a regenerative chance.

Plants that occur naturally in a particular region, ecosystem, or habitat without human intervention are called native plants. They have evolved naturally with local environments, climates and wildlife over thousands of years and offer the most sustainable habitat.

Biodiversity of plants and animals is very important. It ensures adaptability and allows species to withstand threats. Studies have shown that plant genetic diversity improves ecosystem resistance to exotic plant invasions, enhances plant community resistance to extreme climatic events and grazing, accelerates litter decomposition rates, maintains long-term species diversity, reduces plant disease severity and impacts arthropod diversity and community composition. With enough variation, there will always be some species that will be able to survive under any changing situation.

Native plants provide the best option when choosing plant species for our home landscapes, as well as restoration projects. Plants that occur naturally in your area and are native to your geographic region are generally the preferred choice. These regions do not have political boundaries, and fall into ecological categories often referred to as ecozones and ecoregions. It is better to get a native plant that has genetics from your ecological region. This will ensure that plants will be well adapted to the interaction of geologic, landform, soil, vegetative, climatic, wildlife, water, and human factors that are present.

North America comprises several ecological regions, and they can be viewed in the link below. Southern Ontario is part of the Eastern Temperate Forest (8.0) ecozone and the Mixed Wood Plains (8.1) ecozone. If we look to Ontario, we see that there are more specific ecoregions within Southern

Ontario - the Mixedwood Plains ecozone.

Click on this link for more information on ecological region maps:

In ecoregion 6E - More than 57% of the ecoregion exists as cropland, pasture and abandoned fields. Forest cover includes 30% and water covers 4% of the ecoregion.

In ecoregion 7E- About 78% of the ecoregion has been converted to cropland and pasture, 7% is developed land such as urban areas and road networks. The remaining forest remnants account for 12% of the ecoregion.

The image above shows North American cropland highlighted in bright green. In areas with the majority of our land used for crop, pasture, and developed land for urban areas, it is important to conserve and regenerate every piece of land that we can - even the land you live on. The types of plants we choose to accomplish this matter. Below is an explanation of the types of plants you will encounter when trying to do the good work of preserving the integrity of ecosystems.

Most nurseries that sell native plants will grow them from seed, and this ensures a high level of genetic diversity. Native plants reproduce through open pollination (thank you pollinators!), to produce their offspring as seeds that hold the genetic make-up of the plant.

The problem is that genetic diversity is disappearing fast due to the commercial nursery trade selling cultivars and exotic species.

Cultivars are bred for particular characteristics such as shape, size, colour or scent.. These altered plant species are propagated by tissue culture (asexually), not from seed (sexually), so every cultivar has the same genetic make-up. Cultivars are hybrids that have been highly manipulated to produce more “showy” flowers, but often they have been altered just enough that bees fail to recognize the scents, shapes or colours that they are familiar with. Double bloom flowers are not bee-friendly because their thick petals make it difficult to access nectar. Additionally, in many hybrids, the lovely scents, nectar and pollen may be missing altogether. The horticulture industry claims cultivars are a better or improved plant, but they could soon be considered inferior once a threat such as pests or environmental stress begins to affect them. This could cause them to be more vulnerable by virtue of their sameness. Genetically, they are missing a variety of ‘tools’ necessary to adapt to change.

“Nativar” is a term for a cultivar of a native species. They are the result of artificial selections made by humans from the natural variation found in native species. The purpose of nativars is to isolate a single traits such as: atypical colours or forms of flowers, compact size, insect or disease resistance, tolerance of certain challenging environmental conditions, and many others. This results in nursery stock that is almost always genetically identical to the original selection, since to preserve this genetic isolation, plants are propagated vegetatively (clones). These plants no longer participate in a natural reproduction pattern that would maintain genetic diversity, such as straight species do through open pollination. This may seem appropriate for the home gardener that wants specific characteristics in plants, but it deteriorates our home gardens as part of the larger ecosystem and thus the sustainability of our environments. By planting native species instead of cultivars, we will ensure the preservation of the amazing genetic diversity found in nature.

Check out our second blog post (in the works) to learn about the effect of cultivars and nativars on pollinators.

Exotic species that originated from places such as Eurasia should be planted sparingly. A good rule is 20% or less of the overall landscape. These exotic plants not only disrupt the food web, but many have become invasive pests, outcompeting native species and degrading habitat in remaining natural areas. Invasive species should never be planted. Since these species have not evolved over long periods in North America, there is a lag in natural predators, so these exotic pests can quickly get out of hand. We must preserve our natural heritage and thus our local biodiversity by planting species who have evolved with local fauna.

Fortunately, many local nurseries now feature native flowers, shrubs and trees. When shopping for native plant species, make sure you look at the label carefully. A common example is Black-eyed Susan;

The native plant will be labeled: Black-eyed Susan- Rudbeckia hirta.

The cultivar will be labeled: Rudbeckia hirta 'Goldilocks'

A cultivar may also denote numbers in single quotes such as Black Chockberry - Aronia melanocarpa 'UCONNAM165'.

Examples of plant tags illustrated below:

Garden centres and horticulture professions are still focused on the idea of plants as decoration, rather than playing a key role in ecosystem functions. Garden composition and aesthetics can absolutely be achieved with native plants, while getting ecological value of being a part of the larger body of nature, a benefit to wildlife and our local environments. There are many functions that native plants are performing in our outdoor spaces. Some of the benefits to humans, wildlife and the environment include:

  • connect corridors for songbirds, pollinators, and other animals

  • incorporate species of our natural heritage

  • reduce the use of potentially invasive garden plants

  • reduce water, fertilizer and chemical usage

  • learn and experience the diverse wildlife that visit our gardens

  • educate our family and neighbours

The erosion of biodiversity is destabilizing our environment that has been built on plant genetics for over 10,000 years. Genetic diversity is key to a healthy ecosystem, and native species offer the best way to ensure our ecosystems function successfully. Plants are the first trophic level of ecosystems, that which every other organism uses up the trophic chain. You can't have animal conservation without plant conservation. Native plants are used by many insects to carry out their development. Host plants are specific plant species that caterpillars eat to be able to mature into butterflies and moths. Bees require pollen and nectar to gain enough nutrition to carry over to their offspring. The seeds of plants are also used by insects and mammals for nutrition.

By propagating from seed, promoting and using straight species of native plants, gardeners and professionals alike can support a form of horticultural conservation—or at the very least, can avoid taking part in the continuing loss of genetic diversity. It is important for us to become land stewards, to take action to preserve our natural heritage, not only for the sake of biodiversity and the future of the world, but because we depend upon diverse and stable ecosystems for our own survival. Planting natives encompasses far more than just doing a good deed for wildlife. Our very existence depends on it.

Renowned environmentalist Aldo Leopold says— “keep every cog and wheel is the first precaution of intelligent tinkering”. Lets keep the genetic integrity of our plants - so we may have a diverse and adaptable future!

Photo by: Carrington Lauzon

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