Information is drawn from the Commission for Enviromental Cooperation
Materials are available on-line under "Environmental Conservation."
This region is associated with hilly terrain. Precambrian granitic bedrock outcrops are interspersed with shallow-to-deep deposits of moraine. The bedrock of the Canadian Shield is among the oldest on Earth, having been formed between 2.5 and 3.6 billion years ago. Morainal deposits date from the retreat of the last glaciers, which took place 10,000 to 12,000 years ago. Some fluvial material (including numerous eskers) and colluvium are present. Soils derived from these materials are generally coarse-textured and nutrient-poor. Limited areas of fine-textured silts and clays occur. The landscape is dotted with numerous lakes. The ecological region includes the headwaters of numerous large drainage basin systems.
The climate is characterized by long, cold winters and short, warm summers. The continental climate is influenced by maritime conditions in coastal areas and by cold arctic air masses from the north. The mean annual temperature ranges between 4°C in the north to 5.5°C in the east. Mean summer temperatures range between 11°C to 18°C. Mean winter temperatures range between 20.5°C in the west to 1°C in the east. Mean annual precipitation varies from 400 mm in the north to 1,000 mm in east. In some areas, the maritime influence results in a higher level of precipitation, ranging between 900-1600 mm. Very large lakes have a moderating effect on the climate of adjacent lands, warming them in winter and cooling them in summer.
NORTHWESTERN FORESTED MOUNTAINS
This ecological region consists of extensive mountains and plateaus separated by wide valleys and lowlands. Most of these plains and valleys are covered by moraine and, to some degree, fluvial and lacustrine deposits, whereas the mountains consist largely of colluvium and rock outcrops. Numerous glacial lakes occur at higher elevations. Soils are variable, encompassing shallow soils of alpine sites and nutrient-poor forest soils of the mountain slopes, as well as soils suitable for agriculture and those rich in calcium that support natural dry grasslands.
The climate is subarid to arid and mild in southern lower valleys, humid and cold at higher elevations within the central reaches, and cold and subarid in the north. Moist Pacific air and the effect of orographic rainfall control the precipitation pattern such that both rain shadows and wet belts are generated, often in close geographic proximity to each other. The rain shadow cast by the massive coast mountains results in a relatively dry climate. Tall mountains also impede the westward flow of cold, continental Arctic air masses. Mean annual temperatures range between 6°C in the north to 7°C to 10°C in south. Mean summer temperatures range from 10°C to 21°C, whereas mean winter temperatures range from 23°C to 0°C. Annual precipitation varies with elevation, from 2,600 mm in the mountains to the north, to 400 mm in other mountainous areas, to between 250500 mm in the valleys.
Mountainous topography dominates, cut through by numerous fjords and glacial valleys, and bordered by coastal plains along the ocean margin. Igneous and sedimentary rocks underlie most of the area. Colluvium and morainal deposits are the main surface materials. The soils are largely leached, nutrient-poor forest soils. Island areas that escaped glaciation are unique because they now contain many endemic species: that is, ones that are peculiar to those habitats. Ice-free coastal waters are associated with the narrow continental shelf and slope. The region has some of the most productive rivers for salmon production and there are many important estuaries.
This maritime influence is responsible for a high level of precipitation, long growing season and moderate temperatures. Mean annual temperatures range from 5°C in the north to 9°C in the north. The mean summer temperature ranges from 10°C in the north to 16°C in the south, whereas mean winter temperatures range from 1°C to 3°C. The annual precipitation ranges from as little as 600 mm in some island areas to over 5,000 mm along the north coast. Overall, the windward slopes typically receive between 1,500 to 3,000 mm of precipitation per year.
A variety of geologic materials and landforms are present. Younger-age sedimentary coastal plains in the south and east abut the older, folded and faulted sedimentary, metamorphic and igneous rocks that reach elevations over 2,000 m. A mixed limestone- dolomite terrain of plains and hills dominate much of the central part of the region, with other sedimentary rock found on the plateaux and plains in the north and west. Glacially derived materials and landforms and areas of glacial lake deposits shape the landscape in the north. Soils are mostly leached, being nutrient-poor to calcium-rich. Surface waters are characterized by an abundance of perennial streams, small areas with high densities of lakes, a diversity of wetland communities and a rich array of maritime ecosystems.
The climate is generally warm, humid and temperate, although there is a latitudinal gradient from cool, continental temperatures to those that are subtropical. Summers are hot and humid, and winters are mild to cool. The average daily minimum temperature in winter is 12°C in the north and 4°C in the south. Average daily maximum summer temperatures are 27°C to 32°C. Precipitation amounts of 1,000-1,500 mm per year are relatively evenly distributed throughout the year, with most areas having either a summer or spring maximum.
The Prairies range from smooth to irregular plains. In the north, they are generally flat to slightly rolling plains. Sizable portions are hilly or classified as tablelands with moderate relief (100-175 m). In the south, the landscape alternates flat areas and low hills. Much of the prairie landscape has been shaped by a variety of glacial deposits consisting mostly of undulating and kettled glacial till, and level to gently- rolling lacustrine deposits. These landforms are associated with intermittent sloughs and ponds. Surficial geology in the remainder of this ecological region is varied. Major portions are eolian, others are stream deposits, and much of the region is comprised of thin residual sediments. The southern portion is underlain by Cenozoic sedimentary rocks with recent continental deposits, mainly in the coast. In the northern and central areas, most of the rivers originate in the mountains where rainfall, snowmelt and glacial runoff contribute to their formation. The soils are commonly deep and throughout most of the region were originally highly fertile. Today, soils of agricultural potential throughout this area face problems of reduced nutrient potential, increasing salinity and susceptibility to wind and water erosion.
The climate is dry and continental, characterized in the north by short, hot summers and long, cold winters. High winds are an important climatic factor in this ecological region. It is also subject to periodic, intense droughts and frosts.
The North American Deserts are comprised of a mix of physiographic features but, in general, the area consists of plains with hills, plains with mountains, and tablelands of high relief. In the north, the flat to rolling topography consists of loess and volcanic ash deposits on basaltic plains. The Great Basin and and it adjacent mountains contain hundreds of northsouth trending fault-block mountain ranges separated by broad valleys; the valley floor elevations are often over 900 m above sea level and many of the ranges exceed 3,100 m. To the south, the mountatin ranges are smaller and less regularly oriented and rise from lower base levels. The lowest basin point is 86 m below sea level. Within the basin are found many dry lake beds, or playas, with alluvial fans and bajadas at the margin slopes. Sand dunes occur in some areas. Spectacular landscapes occur on uplifted and deeply dissected sedimentary rocks. Wind and water erosion has left impressive canyons, cliffs, buttes and mesas. Soils of the region are dry‹generally lacking organic material and distinct soil profiles‹and are high in calcium carbonate.
This ecological region has a desert and steppe climate: arid to semi-arid, with marked seasonal temperature extremes. This aridity is the result of the rain shadow of mountain ranges as they intercept the wet winter air masses brought by the westerly and easterly winds. High mountains also block some moist Gulf Coast air masses that cross the Great Plains. Large valleys occupy the southernmost region of the North American deserts. The climatic condition in these regions are the result of "rain shadow" effects. Average annual precipitation ranges from about 130 mm to 380 mm. The southern deserts have higher average temperatures and evaporation rates, with record-high temperatures reaching 57°C. Some southern areas are dominated by a more episodic summer rainfall pattern, while the northern deserts tend toward a winter moisture regime with some precipitation falling as snow.
The ecological region is comprised of a mixture of mountains, hills, tablelands and plains. It occupies an area of tectonic instability at the interface of the North American and Pacific tectonic plates and contains a variety of active faults. The coastal ranges contain a series of linear mountain ranges with crests averaging 6001,200 m with interspersed valleys. The central valley is a broad trough has rivers and is filled with large quantities of silt, sand and gravel washed down from surrounding mountains. In the south, rugged transverse ranges include the highest peak in the region at 3,506 m. The peninsular ranges have peaks of 1,5003,000 m. Lower hills, valleys and coastal terraces parallel the coast, and there are several islands across coastal channels. Soil patterns are complex, mostly dry, and weakly developed with high calcium concentrations.
This ecological region occupies the only portion of the continent with a dry summer mediterranean climate. This climate is characterized by hot, dry summers and mild winters, with precipitation associated with winter frontal storms from the Pacific Ocean. The average summer temperatures are above 18ºC and average winter temperatures are above 0ºC. Annual precipitation is 2001,000 mm depending on elevation and latitude, and falls mostly from November to April. Southern areas receive about 250 mm, while the northern part gets about 500 mm. There is a great annual variability of total precipitation, and extreme droughts are not uncommon. Coastal fog is common, particularly from May through July. The frost-free period ranges from 250 days in the north and on uplands to 350 days along the southern coast.
