Flora and vegetation. – The vast territory includes two broad categories of formations: the Northern region, which includes the Pacific and Canadian dominions at Hudson Bay, and Middle America, which includes the Californian dominion that goes from Virginia to Florida and two internal domains with a xerophytic character; of them the richest is that of the South which includes northern Mexico and Texas, while that of the North includes the steppes of Missouri and the Rocky Mountains, reaching as far as Canada.
The Northern region belongs almost entirely to Canada: here are the arctic formations of the tundras that descend to the fjords of Labrador; here the forests that reach as far as the Great Lakes abound.
In the woody vegetation of the United States there are 40 species of oak; The Castanopsis chrysophylla is characteristic of western America, reaching down to California, the Castanea vesca instead from the mountains of South Carolina comes to Ohio, and Michigan to Maine; in Florida, Texas and Pennsylvania grows C. pumila. In the forests of the northern area grow: Fatsia horrida, the same species (4) as Ericacee Vacciniee from central Europe and some American characteristics such as: Andromeda polifolia, Lyonia calyculata, Cassiope, and other shrub forms. Betula nana, Linnaea and Empetrum are found in the peat bogs of the woods and high mountains. The Rocky Mountains provide large numbers of alpine species, mixed with arctic plants: similar associations are observed in the White Mountains in New Hampshire near the Atlantic. Here the glacial formations appear at 1200 m. and they go up to the top: Picea alba and Abies balsamea mark the limits of the trees, the broad-leaved trees reach up to 600 m. Instead in the Allegani Mountains the woods reach up to the peaks.
The southern half of the Middle American domain is characterized by coniferous and deciduous forests. Lauraceae are represented by deciduous species such as sassafras and Feverbush ; The Persea carolinensis persistent leaves stretches back into the marshes of Delaware.
The species of Gymnocladus, Gleditschia, Pavia, Liriodendron approach forms of the warmer subtropical districts and show themselves together with the persistent-leaved Magnoliaceae in the southernmost areas of the region we are dealing with. Large Ericaceae (Andromeda, Leucothoë, Oxydendron arboreum) show all the transitions from persistent to deciduous plants.
The Quercus virens reminiscent Q. sessiliflora of southern Europe is with the Osmanthus americana the species that goes farthest: followed by the Pinus australis, some Magnolia and Gordonia and the Sabal palmetto which is the northernmost representative of the Palm family.
The coastal area of the Pacific is poorer and does not have these groups of plants of arctertiary origin which are found both in East Asia and on the Atlantic coasts of North America. Castanopsis chrysophylla and Quercus chrysolepis are characteristic: the Pritchardia flabelliform palms (Washingtonia) replace the Sabal in this peaceful area. The Conifers in oregono-Californian region are represented by Pseudotsuga douglasii, by the two Sequoia whose S. gigantea occupies a very limited area, from Chamaecyparis nutkaënsis, Ch. Lawsoniana, Thuja gigantea, Libocedrus decurrens: there are also some endemic species of Abies, Tsuga, Pinus, Picea as well as Larix occidentalis and Lyallii, very close to the northern congeneric species. Through vast prairies we reach that region that goes from eastern Virginia to Florida where they grow: Taxodium distichum (found fossil in certain localities in the Tertiary of Europe), Chamaecyparis thyioides. Thuja occidentalis, Juni perus virginiana and several pines.
The forests are interrupted by vast steppes, deserts and plains covered with grasses that lie between the Rocky Mountains to the west and Missouri to the east, reaching as far as Canada.
Below 35 ° and 37 ° lat. N. new characteristic forms appear: Cereus giganteus from Arizona, Larrea mexicana which secretes a resin from which emanates an acute smell of creosote, so much so that the plant is called “creosote tree”, Prosopis, etc. The desert steppes of the Rocky Mountains are lined with vivid greyish herbs: Artemisia tridentata, Eurotia lanata, Sarcobatus vermiculatus, Atriplex, Suaeda. The prairies of the NE. are due to the migratory action of bison and to the fires annually set by the Indians: H. Mayr and O. Drude believe that the fires have contributed to extending them towards the east.
The cultivated plants of North America almost all come from the ancient continent: few are of local origin and some, such as Zizania aquatica, some Pinus for the seeds and some oaks for the acorns are used in the feeding of the natives. Perhaps some species of Phaseolus and Jerusalem artichoke (Helianthus tuberosus) are also native to this region. The cultivation of cereals in Canada goes as far north as the polar circle.
The vegetation regions of the North American territory are twelve, according to O. Drude, and so distinct:
- Lakes Region – Represents more than half of the North American forest region; here there are Tsuga canadensis, Ulmus americana, Pinus strobus, Juglans nigra (this is much more abundant in the Mississippi forests), besides two species of Fraxinus and Tilia americana. In the forests of these territories 14 conifers grow, 8 Quercus (alba, macrocarpa, bicolor, rubra, etc.), 6 Betula, 1 Castanea, 2 Alnus, Fagus ferruginea, 2 Corylus, Ostrya virginica, Carpinus caroliniana, 14 Salix, 5 Populus, 2 Juglans, 4 Carya and Platanus occidentalis.
- Columbia Coastal Forest Region. – Castanopsis chrysophylla and Pseudotsuga Douglasii are characteristic ; in this region grow the gigantic Araliacee known under the name of “devil ‘s walking stick “, the Thuja excelsa and gigantea and the Picea sitchensis. The Ps. Douglasii includes two distinct forms due to the different resistance to cold. In the Cascade Chain beyond the Pseudotsuga there are on the peaks and on the eastern side: Picea sitchensis, Tsuga Mertensiana and Pattoniana, silver firs (Abies amabilis, grandis, nobilis); Pinus ponderosa, Lambertiana, monticola, contorta, albicaulis, Juniperus occidentalis characterize the mountainous forests of the following region.
- Forest region and the northern part of the Rocky Mountains. – The main trees are the same as on the northern Pacific coast, but this fact cannot be explained by an exchange of plants between the two territories. Only to the east of the Cascade Range do the species of the Rocky Mountains begin to predominate: Pinus ponderosa holds the first place ; there is also the Rosacea Cercocarpus ledifolius, whose wood takes the name of mountain acajou.
They also grow in the Rocky Mountains: Juniperus virginiana and occidentalis, Abies concolor and subalpina, Pseudotsuga Douglasii, Picea Engelmanni and pungens ; Pinus Balfouriana, contorta, edulis, flexilis, ponderosa while the genera Tsugaand Larix are completely missing. Among the Cupuliferae: Betula occidentalis, Alnus incana, Quercus macrocarpa and undulata ; Populus angulata, angustifolia, balsamifera, tremuloides ; also many Salix, Acer granulidentatum and negundo, Ulmus americana, Celtis occidentalis, Fraxinus pubescens and viridis. The forests around Helena, in the state of Montana, consist mainly of poplars and willows: along the streams the Eleagnacea Shepherdia argentea (buffaloberry) abounds, in the lower parts of the mountains grows Pinus ponderosa, while on the flanks of them are located Picea, firs and Populus tremuloides and the tops are occupied by Pinus contorta and flexilis. In Colorado the altitudinal limit of the trees exceeds 4000 msm and at this height there is an area of dwarf trees represented by the same species of Conifers which at lower levels are large trees. According to A. Gray and R. Hook, the alpine species of this area are 184, of which 86 are endemic, among which the genus Eriogonum is characteristic.
Northern region of grasslands and forests. – It occupies the northern corner of the great grass steppes extending between the Lakes region and the Rocky Mountains. There is a remarkable mixture of elements of the different floras, but the Pacific species are completely missing. The trees are not very numerous especially on the Assiniboine and Saskatchewan rivers: oaks and ash trees are gathered in groups; poplars, elms and willows are more abundant, while Betula papyraceaand Pinus Murrayana provide the timber for construction. La Rosa bland and Viburnum lentago form impenetrable, where the hops, the ‘ Ampelopsis quinquefolia and Vitis riparia are the lianas.
Region of the Missouri prairies.- It is a vast steppe territory with Grasses subject to an excessive climate with severe winter colds (up to −40 °): the rains, although not abundant, allow the cultivation of cereals on large expanses. West of the Rocky Mountains the climate is drier and in the steppe the grasses are replaced by Artemisias and Salsolaceae. In the E. the woods increase in size and number and from the prairies we gradually pass to the forests of the Mississippi and those of the south of the Lakes region. On the flanks of the mountains, dwarf pines, trees, alpine shrubs and vibrant plants recall the flora and vegetation of the third region.
The most frequent grasses of the prairies are: Bouteloua oligostachya and Buchloë dactyloides which form from 70% to 90% of the prairie: the first extends from the states of Montana and Dakota to Texas and is the grass of the buffalo, the Buchloë is smaller and it is more widespread. Among the other Graminaceae we can mention: Agropyrum glaucum, Andropogon virginicus and macrurus, Oryzopsis hymenoides, Stipa viridula and setigera, etc. In spring and summer the prairie is always in bloom: first the flowers of Amorpha canescens, Bartsia, Castilleja, Pentstemon, Cypripedium candidum, then those of the large lively herbs: Petalostemon, Baptisia, Phlox aristata, Asclepias tuberosa, Lilium canadense, Melanthium virginicum ; at the end of the summer the Compotes dominate from the great Helianthus to the humble Aster sericeus.
Region of the steppes and salty deserts of the Rocky Mountains. – Between these and the Cascade Range and Sierra Nevada in the states of Montana, Wyoming, Colorado, Washington, Oregon and California lies a desert region of which the Great Salt Lake roughly forms the center. This territory was reunited with Arizona with the name of the North American desert “, but it is not exclusively desert and there is a notable difference between the northern and southern areas in terms of vegetation. Xerophilous or halophilous plants with a columnar appearance abound. alone or in groups: apart from salty soils, which are rather limited, the vegetation is not completely lacking. In salty soils there are Sarcobatus in small groups; as the soil improves there are: Suaeda, Salicornia herbacea, Kochia prostrata, Eurotia lanata, Graya polygaloides, Schoberia occidentalis, Atriplex and several Salsolaceae. Among the Graminaceae are mentioned: Distichlis maritima, Spartina gracilis, Sporobolus asperifolius ; among the willows and poplars (Populus monilifera and trichocarpa); among the bushes Artemisia tridentata whose development ranges from 30 to 360 cm. high; to these are added other Artemisia more humble, then Bigelowia graveolens and Tetradymia canescens. The desert flora includes more than 300 species, of which a third are endemic.
Californian Depression and the Forested Mountain and High Range Region of California. – Includes the Pacific side of the Cascade Range and the Sierra Nevada; it has a rich flora of many endemic genera and species. South of the 40th lat. N. the Pacific coast forests change appearance and southern species replace Picea sitchensis, Tsuga Mertensiana, Thuja gigantea: Pinus Lambertiana appears and Lauracea Umbellularia californica covers the river valleys.
The boundary of the two regions is marked by Chamaecyparis Lawsonians. Between the Sierra Nevada and the Coast Range are bushy steppes, highly fertile grasslands of subtropical character and here and there there is the Cypressus macrocarpawhich is missing in Northern California. Here grow the two Sequoia (S. Gigantea or tree Mammoth and S. Sempervirens or Redwood); in the region of the high mountains live numerous endemic alpine forms and arctic species such as Saxifraga nivalis, caespitosa, oppositifolia. Endemic species belong to genera Cymopterus, Eriogonum and Ivesia.
Missouri Basin Summer Forest Region. – It is intermediate between the forests of the Atlantic domain of the Lakes and the forests and shrubs with leaves. persistent states of the South at the Atlantic. Conifers are numerous, but broad-leaved dicotyledons abound with the genera Juglans (nigra and cinerea), Carya (with 7 species, of which the most important are: alba, amara, glabrous and tomentosa), Quercus (with 18 species: alba, macrocarpa, nigra, palustris, prinus, rubra, etc.); the persistent leaf oaks (cinerea and virens) arrive in the southern part of the region in the form of dwarf shrubs. Maclura aurantiaca originates in these territories and some Magnolias and Liriodendron tulipifera grow.
Southern Atlantic region with persistent leafy woody plants. – It includes the whole southeastern part of the United States with the exception of the southernmost part where Antillean plants grow, which give the Florida vegetation a certain tropical character. There are plants with persistent leaves such as: Quercus virens, Sabal palmetto, Pinus australis ; the Magnoliaceae are represented by 7 Magnolia, Illicium, Liriodendron ; the Anonaceae from the genus Asimina and N. of Florida from Clethra ; the Ericaceae from some Andromeda, Rhododendron maximum, 4 Gaylussacia, Vaccinium arboreum which is a tree up to 5 m high, Leucothoë, Oxydendron arboreum. The Styracaceae recall those of East Africa; in Florida grow Canella flava, Simaruba glauca, Bursera gummifera, etc., which are species of the Antilles.
Arizona desert and steppe region.
Chaparals region of Texas and northern Mexico: these regions have common traits; plants of the subtropical steppes (Agave, Dasylirion, Yucca, Prosopis juliflora, etc.) grow in the two territories. But Texas is covered with prairies and those thorny shrubs called Chaparals, while Arizona and northern Mexico have a steppe aspect that reaches its maximum in the desert areas of Mohawe and Gila to the SE. of California. The most characteristic plant of this region is the Zigofillacea Larrea mexicana ; then there are: Cereus giganteus 6 to 15 m high, Fouguiera, Agave Palmeri and Parryi, Rosacea Canatia, Leguminosae of the genera Acacia, Mimosa, Astragalus, Frutescent compotes (Baccharis, Pluchea borealis), Yucca brevifolia with 5-10 m tall individuals. In Texas, on the other hand, the bushes are more varied and less thorny: Juglans nana, Morus parvifolia, Aesculus discolor, Prunus rivularis, Cercis occidentalis: the Cactaceae are represented by bushes of Opuntia, Echinocactus and Mamillaria. In eastern Texas trees of the Atlantic area are observed in the prairies: Yucca canaliculata is very developed.
Montane forest region of northern Mexico. – This region is remembered for the necessary connection of the vegetation of the United States with that of Mexico, because it is clearly Mexican: oaks grow on the slopes of the mountains, cypresses in the valleys and, at heights above 1800 m., Pines. The Quercus emoryi stretches from northern Mexico to the Mexican provinces of the center.
Fauna. – It is very interesting and belongs for most of its extension to the sonoran region. Among the mammals, the bison is one of the most characteristic forms of the region: it once inhabited the great prairies of the interior of the United States, then spread both towards the Mississippi delta to the south and to the north. The active hunting of the American bison has increasingly reduced the number of these large mammals which are now protected by special hunting laws. Interesting are the Virginia deer and the Rocky Mountain long-eared deer. We will also mention the American antelope, the Carolina squirrel, the flavo-bellied marmot, the lined spermophilus, the prairie dog of the arid regions of the Rocky Mountains, the red beaver of the Sierra. Varî hamsters and neosomes as well as geomids or bag mice are variously widespread in the region. Among the Carnivores we will mention the puma, various lynxes, the howling wolf, the Virginia fox, the American bear, various raccoons, the American badger, various martens. Among the Insectivores we will notice various shrews, the American mole. Finally, the Chiroptera are represented by various forms including the American trumpet and the California bat. Noteworthy is the presence of the opossum, the only Marsupial that currently lives in the Artogea region. Finally, the Chiroptera are represented by various forms including the American trumpet and the California bat. Noteworthy is the presence of the opossum, the only Marsupial that currently lives in the Artogea region. Finally, the Chiroptera are represented by various forms including the American trumpet and the California bat. Noteworthy is the presence of the opossum, the only Marsupial that currently lives in the Artogea region.
Richly represented is the avifauna, with forms generally common both to the western Olartic region and to the Neogea. We will mention the Virginia nightjar, some Trochilus, some parrots (Conurus), the American shrike, the Virginia owl, the American hawk and finally the California condor.
Among the Reptiles we will mention the American tortoise common in the rivers of Texas, the horned tortoise, notable the presence of the caiman, a frequent alligator in the rivers of the southern United States. We will also note various species of agame, with a stocky appearance and skin bristling with spikes, numerous Ophidis of the genera Crotalus, Trigonocephalus, etc. The forms of Amphibî of which we will mention are interesting: the Siredon lacertina from Carolina, the Amblystoma, the Amphiuma from Florida, as well as various Anuri, especially frogs. Among the freshwater fishes the presence of a ganoid is interesting: the Amia calva of the rivers of Carolina. The fauna of invertebrates is very rich, especially terrestrial molluscs and insects.
