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Biodiversity Notes

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Western University
Biology 3484A/B
Nina Zitani

Biodiversity – Nov. 19/12 - Latitude is the primary factor that affects the distribution of the terrestrial biomes. The tropics get the most intense direct sunlight for the longest duration. As you move north or south of the equator, the sun’s rays are not as direct. The earth’s tilt results in seasonality. Incoming sunlight/solar energy per unit area varies with latitude. Regardless of the time of year, as you move towards the poles from the equator, the sunlight/solar energy (photons for photosynthesis and heat to warm the air) decreases per unit area. An equal amount of sunlight/solar energy is spread over a larger area as you move towards the poles. Therefore, an equal surface area in the tropics and the temperate zone get unequal amounts of energy. The earth is on a tilt or angle. During winters in the northern hemisphere, we are tilted away from the sun. During summers in the northern hemisphere, we are tilted towards the sun. The effect of earth’s tilt is that there is yearly variation in the intensity of sunlight reaching earth’s surface. In the tropics, there is no noticeable change in the intensity of sunlight at different times of the year. The air temperature and day length are more or less the same all year. The tropics do have seasonality in precipitation, however. In the temperate zone and polar regions, there is dramatic change in the intensity of sunlight throughout the year. Air temperature and day length varies with the seasons. The hemisphere tilted towards the sun experiences more hours of sunlight each day, which contributes to warm air temperatures in spring and summer. In conclusion, the tropics get the most sunlight (energy) per unit area with the least variation throughout the year. - Terrestrial biomes: The temperate zone extends from about 23.5-52ᵒ N. Most land (earth’s land masses) is in the northern hemisphere. This is due to plate tectonics and how the continents have moved. - Boreal forest or taiga: This biome is also called the coniferous forest. It is located south of the tundra and north of the temperate zones. It extends across a large portion of Canada and Russia. There are a lot of wetlands located here and the parts that aren’t wetland have coniferous trees. Boreal forest distribution – It is located in the high north latitudes from 52ᵒN to 66ᵒN (the arctic circle). 60% of the land area of Canada is boreal forest. The boreal forest is the world’s largest terrestrial biome. The dominant vegetation is coniferous, evergreen forest. Most coniferous trees are evergreen trees that don’t drop their leaves all at the same time. It has the second lowest annual precipitation with 20- 75cm or 8-30in (tundra has lowest). Its extreme minimum temperature is lower than the tundra. It has long cold winters and short but warm and relatively humid summers. Its soil is nutrient-poor. - Conifers are cone-bearing plants. They are mostly evergreen. They have long, thin, needle-like leaves or flat, scale-like leaves. The have ecological and economic importance. - Family Pinaceae (pine, spruce, larch, hemlock): These are coniferous trees with long, thin, needle-like
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