Two factors of prairie maintenance are fire and grazing. Grazing animals play an important role in maintaining the ecosystem by stimulating plants to grow. This triggers biological activity and nutrient exchanges. Bison, deer, and cattle compact the soil with their hooves and open new areas for seeds and the generation of plants to take root. The role of fire is prevalent in almost every ecosystem. However, few involve fire as frequently as does prairie. Tallgrass prairie can accumulate an enormous amount of biomass (dead plants) in one year. The leaves die in the fall and the roots go dormant during the cold winter months. The following spring, new shoots grow. As years progress, the old dead leaf litter accumulates and creates a thick thatch covering the ground. New shoots find it harder to take in sunlight, while the ground stays cold and insulating causing a delay in the spring plant growth. Nutrients are locked up in plants yet to decay.