In biology, biodiversity is the degree of variation of life forms within a given species, ecosystem, biome, or planet. Biodiversity is important to humans and wildlife alike, as a wide range of plants and organisms contribute to the stability of ecosystems. Many relationships in ecosystems are intertwined and if biodiversity decreases, the ecosystem becomes more vulnerable to pests, disease, or invasive species.
For homeowners thinking about planting BMPs with native plants, a diverse group of species is a good idea because the BMP will become more resilient. For example, is a pest sweeps through and severely damages or kills off one species of plant, the other plants will take over. If you had only 1 or 2 species planted, the pests could have a much more dramatic impact on your garden.