Both the physical environment and the living community of plants, animals and other organisms determine an ecosystem.Each ecosystem has a characteristic physical environment, including its climate and altitude, which produces a dominant type of vegetation. To learn more about several North American ecosystems, click on a type of ecosystem from the list below:
Forests are fascinating ecosystems. How can you recognize a forest? The defining feature of a forest is its dense growth of trees. But why do forests grow where they do? Generally speaking, two key variables dictate the geographical distribution of Earth's different habitat types: precipitation and temperature. Forests grow where there is enough water available to fulfill trees' needs. The extent of forest growth also depends on temperature ranges, soil nutrients, adequate growing season and altitude.
All of the forests in the continental United States are temperate forests (located between the boreal and sub-tropical zone). Eastern temperate forests tend to have cold winters and wet, hot summers. Deciduous trees (those that lose their leaves in the fall) like oak and maple thrive in these conditions. In fact, most eastern forests are defined by the mix of oak, maple, birch and other trees that grow there. These trees create a canopy that shades the forest floor and provides a variety of habitats for many creatures, such as gray squirrels, white-footed mice, white-tailed deer, blue jays and much more.
Generally speaking, deciduous trees dominate the forests of the Eastern United States, while coniferous trees (those that keep their leaves year-round) predominate in western forests. What kind of wildlife would you expect to live in the forests Western United States?
Grasslands are characterized as areas where grasses are the predominant vegetation and the subsoil is dry with seasonal moisture in the upper soil layers. Their evolution was shaped by periodic fires and the presence of grazing animals. These conditions resulted in the establishment of vast areas of grassland on all of the continents except Antarctica. Today, a quarter of the earth's land surface remains covered by this rapidly vanishing ecosystem.
All grasslands share several common traits. In general, the term grassland refers to land which:
As different from one another as deserts of the world are, they all share one characteristic: they are very dry. Scientists define deserts as areas that get less than 10 inches of rainfall a year and have a very high rate of evaporation. If the annual evaporation rate of an area is higher than the annual amount of rainfall, the area is considered a desert. Evaporation rates are high because deserts tend to have very little cloud cover and strong winds.
Another characteristic of deserts is sporadic rainfall. If the limited rainfall in deserts fell a little at a time throughout the year, many deserts probably would not look much like deserts. Instead, they'd have a lot more vegetation. Rain doesn't fall evenly throughout the year in a desert, though. It usually comes in big bursts. In some deserts, none at all may fall for more than a year. And then a huge thunderstorm may dump over 5 inches all at once!
Deserts have some of the most variable temperatures of any places on earth. Because the desert skies are nearly cloudless, the temperatures during the day may sizzle. But without cloud cover to hold in the heat, it radiates into the atmosphere very quickly once the sun goes down. In some deserts, the temperature may drop as much as 77 degrees Fahrenheit in 12 hours.
As the name implies, wetlands are areas where water is present at least part of the year, generally for at least a portion of the plant-growing season. In addition, wetland soils differ considerably from nearby or surrounding uplands. Hydric soils, found in wetlands, are wet, low in oxygen, and often black with muck. Finally, wetlands support plants — called hydrophytes — that are adapted to living in wet, oxygen-poor soils. Together, these water, soil and vegetation characteristics make up a broad definition for wetlands.
Though all wetlands contain water at least periodically, the volume of water and the amount of time a wetland is "wet" varies greatly. They also vary in size, from wading-pool sized vernal pools to thousands of acres along coastlines or rivers.
Wetlands are found all over North America, along coastlines, far inland, in rural areas, and even in the middle of well-populated urban areas. There are generally five kinds of areas where we find wetlands:
2) near coasts and inland lakes;
3) in depressions where land is low compared to surrounding landscapes;
4) areas where groundwater seeps out of the ground, and;
5) in broad, flat areas that receive significant rainfall (such as the Everglades).
The arctic tundra is circumpolar, meaning that it is an ecosystem surrounding the polar region, above roughly 60 degrees north latitude. The Arctic circle occurs at 66 degrees north latitude.
In the tundra, short days for much of the year and a harsh cold climate result in a brief growing season of 50-60 days. By contrast, the growing season in temperate forests is about six months long and in tropical forests lasts the entire year.
Strong winter winds challenge the stability of any plants that grow more than an inch or two above ground surface. Below a thin layer of soil that thaws every summer is ground that remains frozen year-round, called permafrost. The permafrost may be very deep, reaching more than 1000 feet thick in some locations. Although the tundra receives less than ten inches of precipitation each year (which is why it is sometimes referred to as an arctic desert), there can be plenty of standing water when the upper layer of soil thaws each summer.
Due to its high latitude and the tilt of the earth, the arctic experiences light and temperature extremes throughout the calendar year. The plants and animals of the tundra must be adapted to face these challenges, including not only extremes of day length and temperatures, but also harsh winter winds, long periods of below-freezing temperatures, and permanently frozen ground.