Direct impacts of invasive plants include competition for space, soil, light, or water with native plants, which can lead to reductions in populations of native species or even elimination of entire populations of rare or endangered species. Indirect effects are harder to quantify. Often, these impacts are only discovered after the species is well established and widespread or through careful analysis. Competition by invasive plants can prevent the establishment of native trees and shrubs after a disturbance event like a fire or flood, disrupting the natural successional processes of grassland, shrubland, or forest development. Displacement of native plant communities can lead to loss of food sources and habitat for wildlife. Invasive plants can also induce drastic changes in ecosystem function by affecting critical elements like soil chemistry, groundwater tables, or the frequency and intensity of wildfires. Economic impacts are widespread in today's society. The most obvious case occurs through competition with crop plants used for food or forage. Other adverse effects of invasive plants include livestock poisoning, structural damage, clogged waterways, and losses to sport and commercial fisheries.