Why do plant sizes, shapes, and survival strategies defer?
Arctic soils are wet and nutrient-rich. So why are there no trees in The Arctic, and why are the plants so close to the ground? Why don't desert plants like cacti have leaves? Why should trees in most forests found in both the tropics and in cold areas such as Canada and Sweden keep their lives here around? Why do most trees in temperate forests in between losing their leaves in winter?
The plant communities found in various biomes have distinct physical appearances depending on their plant species' types, relative sizes, and stratification (layering). Climate and soil type play a role in determining these characteristics. Research has shown, however, that the size and shape of a plant species represent the best Strategy for gathering sunlight for photosynthesis and not becoming too hot or too cold.
Plants exposed to cold air year-round or during winter need a design that keeps them from losing too much heat and water. For example, trees or tall plants in the cold, windy arctic grasslands (tundra) would lose too much of their heat for survival.
Desert plants exposed to the sun all day long must lose enough heat so that they don't overheat and die. They must also conserve enough water for survival. Succulent (fleshy) plants, such as saguaro cacti survive in dry climates by having a stick-like shape, no leaves, and the ability to store water and synthesize food in their Expandable fleshy tissue. The plant’s shape and lack of leaves give it the smallest possible surface area exposed to sunlight and the largest possible area away from the Sun for radiating heat out. It also reduces water loss by opening its pores (stomata) only at night.
Trees in the canopies of wet Tropical rainforests tend to be broadleaf evergreen plants, which keep most of their broad leaves year-round. The large surface area of the leaves allows them to collect ample sunlight for photosynthesis and also radiate out heat during the hot summer
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In a climate with cold ( and sometimes dry ) winter, keeping such leaves would cause plants to lose too much heat and water for survival. In such climate, broad leaves deciduous plants, such as oak and Maple trees, survive drought and Cold by shedding their leaves and becoming dominant during such period.
If we move further north to areas like Canada and Sweden, where summers are cool and Short, this strategy is less successful. The evolutionary solution in such areas is coniferous (cone-bearing) evergreen plants (such as spruces, pines, and firs). These plants keep some of their narrow pointed leaves (needles) all year. The waxy coating and shapes and clusters of the needles of coniferous slow down heat loss and evaporation during the long, cold winter. Additionally, by keeping their leaves all winter, such trees are ready to take advantage of the area’s brief warm summer without having to take time to grow new needles.
In the tropical desert (Saudi Arabia), the mean monthly temperature is 25 degrees Celsius, and the mean monthly precipitation is 300 - 325 mm.
In the temperate desert (Reno, Nevada), the mean monthly temperature is 0 degrees Celsius, and the mean monthly precipitation is 200 - 225 mm.
In the polar desert (Northwest China), the mean monthly temperature is -5 - 0 degrees Celsius, and the mean monthly precipitation is 175 - 200 mm.
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