Effects of the Younger Dryas were of varying intensity throughout North America. In western North America, its effects were less intense than in Europe or northeast North America; however, evidence of a glacial re-advance indicates that Younger Dryas cooling occurred in the Pacific Northwest. Speleothems from the Oregon Caves National Monument and Preserve in southern Oregon's Klamath Mountains yield evidence of climatic cooling contemporaneous to the Younger Dryas. Other features include the following:   The Younger Dryas is a period significant to the study of the response of biota to abrupt climate change and to the study of how humans coped with such rapid changes. The effects of sudden cooling in the North Atlantic had strongly regional effects in North America, with some areas experiencing more abrupt changes than others. The effects of the Younger Dryas cooling impacted New England and parts of maritime Canada more rapidly than the rest of the United States at the beginning and the end of the Younger Dryas chronozone. Proxy indicators show that summer temperature conditions in Maine decreased by up to 7.5oC. Cool summers, combined with cold winters and low precipitation, resulted in a treeless tundra up to the onset of the Holocene, when the boreal forests shifted north. Vegetation in the central Appalachian Mountains east towards the Atlantic Ocean was dominated by spruce ("Picea" spp.) and tamarack ("Larix laricina)" boreal forests that later changed rapidly to temperate, more broad-leaf tree forest conditions at the end of the Younger Dryas period. Conversely, pollen and macrofossil evidence from near Lake Ontario indicates that cool, boreal forests persisted into the early Holocene. West of the Appalachians, in the Ohio River Valley and south to Florida rapid, no-analog vegetation responses seem to have been the result of rapid climate changes, but the area remained generally cool, with hardwood forest dominating. During the Younger Dryas, the Southeastern United States was warmer and wetter than the region had been during the Pleistocene because of trapped heat from the Caribbean within the North Atlantic Gyre caused by a weakened Atlantic meridional overturning circulation (AMOC). Also, a gradient of changing effects occurred from the Great Lakes region south to Texas and Louisiana. Climatic forcing moved cold air into the northern portion of the American interior, much as it did the Northeast. Although there was not as abrupt a delineation as seen on the Eastern Seaboard, the Midwest was significantly colder in the northern interior than it was south, towards the warmer climatic influence of the Gulf of Mexico.