Trees have fascinated humans for thousands of years and have played a major role in mythologies around the world, largely due to their usefulness, their longevity and their often impressive stature. Additionally, trees play a major role in Earth's ecology by reducing erosion and moderating climate by removing CO2 from the atmosphere and storing large amounts of carbon in their tissues (Kozlowski 1971). Trees have many uses for all different types of plants and animals; food, shelter, fuel and wood are some of the most common uses. There is no universally accepted precise definition of trees. It is not a distinct taxonomic group, but rather a collection of plant species that have independently evolved similar traits. The most characteristic of these traits is a wooden trunk and branches that are used to tower over other plants. One of the broadest definitions of trees classifies them as: "any plant having the general shape of an elongated stem or trunk, which supports photosynthetic leaves or branches some distance above the ground » (Tokuhisa). More generally, trees are often defined by their height, with smaller plants classified as shrubs, although the minimum height varies considerably. Another specification used to differentiate trees is the presence of a wooden trunk, although this excludes herbaceous trees like bananas and papayas (What is a tree?). Although they are herbaceous and never produce wood, palms and bamboos can produce a wood-like substance by lignifying cells produced during primary growth, and are able to remain tall and stiff due to cellular pressure water called “turgor” (What is a tree?). Trees exist in two different groups of vascular plants, the gymnosperms and the angiosperms... middle of article...... High altitude treeline research. Retrieved March 29, 2014 from https://plantecology.unibas.ch/treeline_elevation/Sexual reproduction in trees. (2014). Accessed March 30, 2014, from http://www.fao.org/docrep/006/ad230e/ad230e02.html Tokuhisa, J. (June 2012). Definition of tree. Retrieved April 29, 2014 from http://www.newton.dep.anl.gov/askasci/bot00/bot00761.htmlTree evolution. (2014). Retrieved March 30, 2014 from http://www.rfs.org.uk/learning/tree-evolution#timelineStein, WE, Mannolini, F., Hernick, LV, Landing, E. and Berry, CM (2007, April 19 ). Giant cladoxylopsids solve the riddle of Earth's first forest roots in Gilboa. Retrieved March 30, 2014, from http://www.nature.com/nature/journal/v446/n7138/abs/nature05705.htmlWhat is a tree? (2012). Retrieved April 14, 2014 from http://www.as.miami.edu/qr/arboretum/what_is_a_tree.html