Your breakfast cereal, the wood framing your home, the cotton in your shirt and the paper in a notebook all began as sugars made by photosynthesis. Plants are the base of nearly every food chain on land, and human societies are built on them. The challenge is to use plants in ways that keep soils fertile, protect biodiversity and leave enough for future generations. This topic looks at what plants provide, what sustainable use looks like (including long-standing Indigenous agricultural knowledge), and how plant communities rebuild themselves after a disturbance.
What plants provide
| Use | Examples | Why it matters |
|---|---|---|
| Food | Wheat, canola, corn, soybeans, potatoes, fruits and vegetables | Canada is a major producer of wheat and canola, an oilseed crop developed by Canadian plant breeders from rapeseed. |
| Building materials and fibres | Lumber from spruce, pine and fir; paper from wood cellulose; cotton; linen from flax; straw bales as wall insulation | Wood is renewable if forests are harvested no faster than they regrow. |
| Fuels and bioproducts | Ethanol fermented from corn or wheat starch; biodiesel from canola oil | Can replace some fossil fuel, but land used for fuel crops is not growing food, which can raise food prices. |
| Environmental services | Roots binding soil; riverbank and wetland plants; forests | Roots hold soil against erosion, wetland plants slow floodwater and filter nutrients from runoff, and photosynthesis stores carbon and releases oxygen. |
| Recreation | Forests, parks and wild spaces | Support tourism, recreation and well-being. |
Plants as medicines
Plants cannot run from insects or grazing animals, so many defend themselves chemically. Some of those defensive chemicals affect the human body, which is why a number of important medicines were first discovered in plants. Scientists isolate the active compound, test its safety and effective dose in clinical trials, and often modify it or make it synthetically. The same compounds can be poisonous in the wrong amount (foxglove and yew are both toxic plants), so being plant-derived does not make something safe. The examples below are well-established medicines; this is educational information only.
| Medicine | Plant origin | Used for |
|---|---|---|
| ASA (aspirin) | Salicin in the bark of willow trees (genus Salix); in the late 1800s chemists modified the related salicylic acid into acetylsalicylic acid | Pain, fever and inflammation |
| Morphine and codeine | Opium poppy, Papaver somniferum | Relief of severe pain |
| Quinine | Bark of the cinchona tree of South America | Historically the main treatment for malaria |
| Paclitaxel | Bark of the Pacific yew, Taxus brevifolia | Cancer chemotherapy |
| Vincristine and vinblastine | Madagascar periwinkle, Catharanthus roseus | Cancer chemotherapy |
| Digoxin | Foxglove (genus Digitalis) | Certain heart conditions |
First Nations, Métis and Inuit communities hold detailed knowledge of the plants of their own lands for food, medicine, materials and ceremony. That knowledge is specific to each nation and place rather than one shared set of practices. For example, for many Anishinaabe communities, tobacco, sweetgrass, sage and cedar are four sacred medicines used in ceremony. This knowledge belongs to the communities that hold it, so respectful research is done in partnership, with consent and shared benefits. Development and resource extraction that destroy harvesting areas threaten both the plants and the passing on of that knowledge.
Sustainable agriculture
- The problem with monoculture: planting one crop over huge areas year after year drains the same nutrients from the soil, lets that crop's pests and diseases build up, and leaves the whole field equally vulnerable because the plants are so genetically similar.
- Crop rotation: growing different crops on the same field in successive years. Rotating in a legume (soybeans, peas, beans, clover) is especially valuable, because legume roots form root nodules containing bacteria that convert nitrogen gas from the air into ammonium that plants can use. The next crop, such as corn, then needs less added nitrogen fertilizer. Changing crops also breaks the life cycles of pests that specialize on one crop.
- Seed saving: keeping seed from the best plants to plant next season. Open-pollinated and heirloom varieties breed true, and saving seed over many seasons selects plants suited to local soil and climate and keeps genetic diversity in farmers' hands. Seed from F1 hybrid plants does not breed true, because the offspring show new combinations of the parents' alleles. Seed banks store seeds of many varieties as a back-up against crop loss.
- Cover crops and reduced tillage: plants such as clover or rye grown between main crops, and ploughing less, keep roots in the ground and residue on the surface, which reduces erosion and adds organic matter.
The Three Sisters: a Haudenosaunee agricultural practice
The Haudenosaunee (the Six Nations Confederacy of the Mohawk, Oneida, Onondaga, Cayuga, Seneca and Tuscarora) have homelands centred in what is now New York State, with communities today in Ontario, including Six Nations of the Grand River, and in Quebec. For many generations they have grown corn, beans and squash together as the Three Sisters. Corn is grown in low mounds of soil, which keep the roots from becoming waterlogged. Beans are planted with it, often once the corn has started to grow, so their vines can climb the corn stalks, and squash is planted nearby so its broad leaves spread across the ground. Details of spacing and timing vary between communities and families. In Haudenosaunee culture the Three Sisters also hold an important place in ceremony and story; those teachings are shared by Haudenosaunee knowledge keepers, and this lesson focuses on the growing practice and the biology that helps explain why it works.
| Plant | Role in the field | Role in the diet |
|---|---|---|
| Corn | Its tall, sturdy stalk gives the bean vines a support to climb toward the light | Starch for energy |
| Beans | Root nodules house nitrogen-fixing bacteria, adding usable nitrogen that enriches the soil, especially as roots and plant remains break down | Protein, including amino acids such as lysine that corn is low in |
| Squash | Broad leaves shade the soil, which holds in moisture and suppresses weeds | Vitamins, and seeds rich in oil and protein |
Ecological succession
Ecological succession is the gradual, fairly predictable change in the species of a community over time. Plants drive it: each group of plants changes the soil, light and moisture in ways that favour the next group. In an abandoned farm field in southern Ontario, annual weeds arrive first, followed by perennial grasses and wildflowers such as goldenrod, then shrubs such as sumac and dogwood, then sun-loving trees such as trembling aspen and white birch, and finally shade-tolerant trees such as sugar maple and American beech, whose seedlings can grow in the shade of the earlier trees. A community with high plant diversity tends to recover faster after a disturbance, because seeds in the soil, roots that resprout (aspen can send up new shoots from its roots after a fire) and fire-adapted species (jack pine cones open in the heat of a fire) are ready to restart growth, rebuilding habitat and food for animals.
- Starts where there is no soil: bare rock exposed by a retreating glacier, or cooled lava
- Pioneer species are lichens and mosses, which break down rock and add organic matter
- Soil must be built from scratch, so it takes a very long time
- Starts where soil remains after a disturbance: forest fire, logging, flood, abandoned farm field
- Pioneers are fast-growing weeds and grasses, often from seeds already in the soil
- Much faster than primary succession, because soil, seeds and roots survive