its usual freezing point). After water reaches , it spontaneously freezes and plant tissue is destroyed. This is called the nucleation point. The nucleation point can be lowered if dissolved solutes are present. Alternatively, plants have several different ways to tolerate freezing. Some plants allow freezing by allowing extracellular, but not intracellular freezing. Plants let water freeze in extracellular spaces, which creates a high vapor deficit that pulls water vapor out of the cell. This process dehydrates the cell and allows it to survive temperatures well below . Another problem associated with extreme cold is cavitation. Ring-porous wood is susceptible to cavitation because the large pores that are used for water transport easily freeze. Cavitation is much less of problem in trees with ring-diffuse wood. In ring-diffuse wood, there is a reduced risk of cavitation, as transport pores are smaller. The trade-off is that these species are not able to transport water as efficiently. History of Arctic ecology Early history Many different peoples had inhabited present-day Canada and Alaska by AD 1000. Most of these people lived by hunting, gathering and fishing; agriculture was not done often in the region. Most of these peoples were nomadic and their activity was largely seasonal. Early Archaic Culture influenced the Plano Culture by about 8000 BC. The Plano peoples and other cultural groups stemming from the Archaic Culture were notable for their use of spear-throwing technology, which likely made them able to maintain larger populations and expand their access to different foods. By AD 1000, the indigenous Arctic inhabitants have also developed other tools that improved their standard of living, such as fire which was set to the woodlands to be used to drive deer to be hunted. In the late eighteenth and early nineteenth centuries, English scientist William Scoresby explored the Arctic and wrote reports on its meteorology, zoology and geophysics. Around this time, the Arctic region was becoming a major subject of imperial science. Though permanent observatories were not yet established, traveling scientists began to gather magnetic data in the Arctic in the early nineteenth century. In June 1831, Sir James Ross and a group of Eskimos explored the Booth Peninsula in order to determine the exact location of the Magnetic North Pole. In the European Arctic, however, Scandinavian powers collected most of the scientific data as a result of early colonies established by Norsemen in Iceland and Greenland. Scientific expeditions