thorns on plants is a feature of trees in
Thorns, spines, and prickles There are also spines derived from roots, like the ones on the trunk of the "Root Spine Palms" (Cryosophila spp.). The trunk roots of Cryosophila guagara grow downwards to a length of 6–12 cm, then stop growing and transform into a spine.[5] The anatomy of crown roots on this species (roots among the bases of the living fronds) also alters during their life.[5] They initially grow upwards and then turn down and finally they, too, become spinous.[5] Lateral roots on these two types of roots, as well as those on the stilt roots on this species, also become spinous.[5] Some authors believe that some of these short spiny laterals have a ventilating function so they are 'pneumorhizae'.[5] Short spiny laterals that may have a ventilating funcion may also be found on roots of Iriartea exorrhiza.[5] There are also spines that function as pneumorhizae on the palm Euterpe oleracea.[5] In Cryosophila nana (formerly Acanthorhiza aculeata) there are spine roots or root spines, some authors may prefer "root spines" if the length of the root is less than 10x the thickness, and "spine roots" if the length is more than 10x the thickness.[5] Adventitious spiny roots have also been described on the trunks of dicotyledonous trees from tropical Africa (e.g. Euphorbiaceae, as in Macaranga barteri, Bridelia micrantha and B. pubescens; Ixonanthaceae, Sterculiaceae), and may also be found protecting perennating organs such as tubers and corms (e.g. Dioscorea prehensilis -Dioscoreaceae- and Moraea spp. -Iridaceae- respectively).[5] Short root spines cover the tuberous base of the epiphytic ant-plant Myrmecodia tuberosa (Rubiaceae), these probably give protection to ants which inhabit chambers within the tuber as they wander over the plant's surface. (Jackson 1986[5] and references therein). In many respects the pattern of spine formation is similar to that which occurs in the development of thorns from lateral shoots. (Jackson 1986[5] and references therein).
Slash-and-burn Large families or clans wandering in the lush woodlands long continued to be the most common form of life through human prehistory. Axes to fell trees and sickles for harvesting grain were the only tools people might bring with them. All other tools were made from materials they found at the site, such as fire stakes of birch, long rods (Vanko), and harrows made of spruce tops. The extended family conquered the lush virgin forest, burned and cultivated their carefully selected swidden plots, sowed one or more crops, and then proceeded on to forests that had been noted in their wanderings. In the temperate zone, the forest regenerated in the course of a lifetime. So swidden was repeated several times in the same area over the years. But in the tropics the forest floor gradually depleted. It was not only in the moors, as in Northern Europe, but also in the steppe, Savannah, prairie, pampas and barren desert in tropical areas where shifting cultivation is the oldest type of farming. Cultivation is similar to slash-and-burn. (Clark 1952 91â€“107).[10]