NORTH AMERICA Geography The continent of North America in the Atlas of the World’s Conifers comprises Canada and the continental United States of America, i.e. Alaska and the ‘lower 48’ states, plus Greenland. Of Greenland, only some small ice-free coastal areas in the southern part are relevant to conifers and in the statistics that follow Greenland is not included; no conifer taxa occur there that do not also occur in North America. North America (N of Mexico) has a total land area of 19.27 million km². A large part of this territory is situated in the High Arctic beyond 70° N where no conifers occur; this includes Baffin Island and the Canadian Arctic Islands as well as the Arctic continental coast- line from the Beaufort Sea in Alaska to Hudson Strait between Baffin Island and the N coast of Quebec. The most striking topographical division of North America is the mountainous West, extending from Alaska into Mexico, and the lowland central and eastern parts of the continent, only interrupted in the E by the lower and much more ancient Appalachian Mountains. Hud- son Bay and the large lakes in Canada and the USA, all the result of expansive Pleistocene ice caps, form large bodies of water in the N and NE of the continent. Nearly the whole of Canada is dotted with numerous lakes across a broad boreal forest zone stretching across the continent from the Atlantic to the Pacific. In contrast, and this is the second major division, the SW of the continent is not only mountainous but also dry, with extensive areas classified as deserts. Nearly flat lowlands surround the Gulf of Mexico and extend northwards along the Atlantic coast on the E-side of the Appalachian Mountains. The interior of the continent, from southern Saskatchewan to Texas, was an expanse of treeless plains (before agriculture) dissected by rivers that drain into the Missouri-Mississippi River system, the largest drainage in the continent. Eastwards, the prairies gradually merged with deciduous angiosperm-dominated forests. Westwards they still rise into the foothills of the Rocky Mountains, with the ca. 60 million bison completely replaced (but reintroduced) by European cattle. The Rocky Mountains are a broad and complex system of geologically young mountain ranges rising to 4401 m (Mt. Elbert) with many other summits in Colorado and Wyoming over 4000 m. The highest mountains are situated in Alaska and the Yukon Territory, with Denali (Mt. McKinley) at 6194 m the highest mountain in the continent. Between the Rocky Mountains in the USA and the Pacific Ocean lie a series of N-S oriented mountain ranges and interspersed basins, culminating in the Sierra Nevada of California with Mt. Whitney at 4421 m. In Canada and Alaska, the Rocky Mountains lie adjacent to the Coast Ranges, the latter in part submerged in the Pacific Ocean forming an extensive archipelago. Cli- matically, the continent is diverse, ranging from extreme arctic in N Greenland and the Canadian Arctic to subtropical in Florida and from the cold and wet coasts of Labrador and Newfoundland to one of the hottest and driest spots on earth, Death Valley in California, dropping to 86 m below sea level. Extensive cool temperate rainforests dominated by conifers occur in the Pacific Northwest of the USA (W Oregon, W Washington), coastal British Columbia and the Alexander Archipelago in S Alaska. north america 35 Conifers in North America Families Genera Species Species + infra Countries with Area of occupancy Endemic taxa conifers in km² 3/8 17/70 99/615 126/794 2/2 106,850/19,269,000 113 Numbers after ‘/’ are global or continent totals. Few species occur in the boreal forests of Alaska and Canada, but they are widespread and abun- dant. Herbarium collection data are inadequate to cover the occurrence of these conifer species and as a result there are far too few dots on the map; the white areas between them would be filled too if the specimens had been available. Collections of herbarium specimens are particu- larly few in Quebec and Ontario around Hudson Bay (Larix laricina, Picea glauca, P. mariana) and in N Saskatchewan (the same species + Pinus banksiana). The density in California reflects the high number of species there, not a continuous conifer forest, and the same applies to other areas with many dots on the map. The accuracy of the map is much greater in the contiguous United States, i.e. S of the Canadian border. There are several striking patterns to be observed. The richest areas for conifers are in California around the empty Central Valley, and N into the western halves of Oregon and Washington. Some areas of the Rocky Mountains stand out, in Idaho-W Montana, Wyoming and Colorado into N New Mexico. In the eastern part of the con- tinent the southern Appalachians, Florida and the Mexican Gulf Coast to the east, and an area from Virginia to New Hampshire stand out as rich in conifer species. The Midwestern states are more thinly populated and conifers are very scarce in the (former) prairie states, with large parts of these states devoid of conifers. North Dakota, South Dakota, Nebraska and Kansas; also large parts of E Montana, Minnesota, Iowa and Missouri, as well as S Texas, have few if any conifers. In the western USA, Nevada has large areas without conifers, as do substantial parts of the Mojave Desert in California and the Sonora desert in Arizona. In the eastern USA, the original dominance of deciduous angiosperm forest (now experiencing a come-back with the decline of agriculture especially in New England) limited the extent of conifers, which probably explains the many blank areas. Aridity is the main constraint further west, where tree growth in general, not just conifers, is limited to banks of rivers, or in deserts virtually absent. At high altitudes conifers are more abundant although trees such as aspen (Populus tremuloides) often grow alongside them covering large areas. In the far west the montane forests are nearly pure conifer forests, often with a relatively high number of species. Fire-prone habitats that allow tree growth are also mostly dominated by conifers and are common in California but also in the boreal forests of the N and in certain parts of the Rocky Mountains. Map NA-1. Distribution of conifer species in North America (N of Mexico) and Greenland..