Ecological Function #3
Plants as Contributors to Environmental Regulation:
- Water – According to the EPA, about 30% of the average household’s water use in the United States is used outdoors, mostly for irrigating lawns and gardens. Besides the fact that people tend not to like the look of dormant grass (commonly referred to as a “dead lawn”), lawn grasses tend to have shallow root systems that make them more vulnerable to water stress. In contrast, because the roots of perennials, shrubs, and trees are much longer, they are able to tap into a much larger area of underground water. Therefore, irrigating isn’t usually necessary. Furthermore, their long and extensive root systems facilitate water percolation into the soil, filtering the water and reducing the amount of runoff that damages ecosystems. In other words, plants with deep roots help to recharge underground aquifers, a source that many municipalities rely on for drinking water.
- Carbon – Plants contribute to soil organic carbon (SOC), an important determinant of soil health. Most of us recognize that they do this via decaying leaves and other “plant litter” (detritus). But the compounds that plants produce and secrete from their roots (a.k.a., root exudates) are an even more significant class of SOC. Root exudates serve as carbon sources for soil microbes, which then form relationships with the plants, helping with nutrient uptake into roots – a fascinating mutualistic relationship! For refugia gardeners, SOC is also crucially important as a form of carbon sequestration: plants remove CO2 from the atmosphere via photosynthesis and that carbon eventually becomes SOC via root exudates and detritus. Unless soil is disturbed, much of that carbon can remain there for long periods of time, acting as a significant “carbon sink” that helps to reduce the greenhouse effect.
- Soil – In addition to modulating SOC, plants also help to conserve and restore soil. Roots help to hold soil in place, reducing erosion risks. This is one of the reasons why it is beneficial to plant species with deep roots along streambanks and on sloped land. Furthermore, because plant roots are good at taking up compounds from water in the soil and producing root exudates, they perform a regenerative function. The exudates “feed” beneficial microbes (as explained above), and the uptake of chemicals from the soil allows remediation. In fact, different species of plants are sometimes intentionally planted in contaminated soils to remove the contaminants via a process known as phytoremediation. Plants’ abilities to take up chemicals is another reason to get soils tested before planting an edible garden, especially in urban environments where lead contamination is not uncommon. A few years of phytoremediation may be needed in such instances.
- Oxygen – Plants release oxygen (O2) as a byproduct of photosynthesis. This occurs in a water-splitting reaction: the oxygen in H2O is the source of the O2. In turn, this O2 is essential for all aerobic organisms – including animals, humans, plants, and many microbes – for the process of cell respiration, which provides the energy cells need for life.
Implications for Gardeners:
- By replacing lawn grasses with perennials, shrubs, and trees, refugia gardeners are making their landscapes significantly more drought and flood tolerant. They are also aiding water filtration and percolation that is essential for freshwater aquifers.
- Make regular use of practices that enrich soil organic content (SOC visible as dark-coloration): companion-planting, cover-cropping, composting, and using plant litter as an organic mulch.
- Before starting an edible garden (such as a vegetable garden), get your soil tested for SOC, nutrients, and contaminants. If the soil is contaminated, consult with an expert on phytoremediation.
1-Diversifying for the future
2-Focusing on ecological functions
Food
Protection
Regulation
Resilience
3-Fitting the natural landscape
4-Co-creating with nature
5-Cultivating relational caring
Refugia Gardening 