Real or cut trees are used only for a short time, but can be recycled and used as mulch, wildlife habitat, or used to prevent erosion. Real trees are carbon-neutral, they emit no more carbon dioxide by being cut down and disposed of than they absorb while growing. However, emissions can occur from farming activities and transportation. An independent life-cycle assessment study, conducted by a firm of experts in sustainable development, states that a natural tree will generate of greenhouse gases every year (based on purchasing from home) whereas the artificial tree will produce over its lifetime. Some people use living Christmas or potted trees for several seasons, providing a longer life cycle for each tree. Living Christmas trees can be purchased or rented from local market growers. Rentals are picked up after the holidays, while purchased trees can be planted by the owner after use or donated to local tree adoption or urban reforestation services. Smaller and younger trees may be replanted after each season, with the following year running up to the next Christmas allowing the tree to carry out further growth.