The shapes of most fruit trees can be manipulated by pruning and training in order to increase yield, or to improve their suitability for different situations and conditions. Pruning a tree to a pyramid shape means that trees can be planted closer together. An open bowl or cup form increases the penetration of sunlight, thus encouraging a high fruit yield whilst keeping the tree short and easy to pick from. Other shapes such as cordons, espaliers and fans offer opportunities for growing trees two dimensionally against walls or fences, or can themselves be trained as barriers.