Some plants are rare because they naturally occur in very specialized habitats or in very low numbers; others may be rare because they have suffered setbacks because of natural processes or pressures from human activities. The highest number of rare plant species is in southern Ontario, where human activity is intensive and extensive. Farming, deforestation, draining of wetlands, and the use of insecticides and herbicides has reduced the populations and areas of distribution of numerous species. The map shows the rare plant diversity per ecoregion.