Biodiversity refers to having a diverse variety of plant and animal species within an ecosystem. This diversity ensures the resilience of the ecosystem. The implications of a monoculture, a system with low diversity, is the risk of the eradication of entire species that were dependent on the dominant plant or animal in the case of a disruption to the dominant plant or animal.
“... monoculture is poorly fitted to the way nature seems to work. Very simply, a field of identical plants will be exquisitely vulnerable to insects, weeds and disease. Monoculture is at the root of virtually every problem that bedevils the modern farmer, and that virtually every input has been designed to solve”. – Michael Pollan, Playing God in the Garden
Invasive species are plants and animals that are not native to B.C. and that have negative effects on the natural environment and biodiversity. Most invasive species are unintentionally introduced by human activities. Invasive species can spread rapidly to new areas and will often out-compete native species as there are no relevant predators or diseases to keep them under control. This leads to monocultures, where there isn’t a diversity of habitats. Invasive plants and animals are the second greatest threat to biodiversity after habitat loss.
In Everett Crowley invasive species that can be found include:
Blackberries have stiff stems with large, flattened, and hooked or straight prickles, toothed evergreen leaves, and small, white to pinkish, 5-petalled flowers that form into blackberries on second year canes and ripen from mid-summer to fall. Birds and omnivorous mammals can consume berries and disperse seeds. Humans also contribute to blackberry spread by purposefully planting canes. Himalayan blackberry forms large, dense, impenetrable thickets that limit the movement of large animals, takes over stream channels and stream banks, and reduces sight lines along right-of-ways. Thickets increase flooding and erosion potential by preventing the establishment of deep-rooted native shrubs that would otherwise provide bank stability.
Knotweeds have small white-green flowers that grow in showy, plume-like, branched clusters along the stem and leaf joints. Knotweeds are dispersed by human activities or by water to downstream areas, and are of particular concern in riparian areas and areas prone to seasonal high water or flooding. Plants emerge in early spring and produce large leaves that can shade out other plant species.
Knotweeds threaten biodiversity and disrupt the food chain by reducing available habitat and increasing soil erosion potential.
Scotch broom is an evergreen shrub, with bright yellow, pea-like flowers that may have red markings in the middle.The plant can also spread to new disturbed areas through seed transport by vehicles and machinery. Scotch broom invades rangelands, replacing forage plants, and is a serious competitor to conifer seedlings; Douglas fir plantation failures in Oregon and Washington have been credited to infestations of this plant.
A plant commonly used for ground and building/wall covers that quickly smothers other plants and robs them of light, space, nutrients and minerals. Invasive in much of SW BC, the plant assumes two types of complex root growing habits: horizontal and vertical, the latter being its reproductively mature state which can quickly overtake and debilitate or choke out trees and infrastructure. The plant also produces a large volume of seed which is eaten and widely distributed by a number of wildlife species.
A herbaceous perennial, this plant is a species of bindweed that rapidly and effectively twines around other plants, in a counter-clockwise direction, to a height of up to 2–4 m. Because of its quick growth, clinging vines and broad leaves, it can overwhelm and pull down cultivated plants including shrubs and small trees. Due to its aggressive self-seeding (seeds can remain viable as long as 30 years) and the success of its creeping roots (they can be as long as 3–4 m) the plant is a persistent weed.
English holly (Ilex aquifolium) is grown for its bright red berries and spiny, dark green evergreen foliage. A large shrub or small tree, English holly has become a serious invasive because of its adaptability to grow in shade or sun, and the ease with which its seeds are spread by birds. English holly grows rapidly 7 to 10 m tall, casting deep shade that deprives native plants of light. Its roots effectively out-compete many native species for nutrients and water; it is a notorious water hog, thus preventing native plants from obtaining sufficient water.