Above and Below Olson heads back to his lab on foot. He always takes photos during his flights so he can study how the leaves spread out to capture sunlight. From the air, Olson can see how tree
branches and leaves are arranged. Some look like a head of broccoli. Some look like a brain. T e moringa looks like a green cloud of feathers. T ese patterns help each tree get as much
sunlight as possible. A tree with large leaves has leaves spaced far apart from each other. T ey grow on thick branches. T e giant leaves of the African raffia palm are the largest tree leaves in the world. One leaf may grow as long as 20 meters (65 feet). By growing far apart from each other, each leaf can collect sunlight. Trees with small leaves, like Olson’s
moringa trees, have leaves close together. T ey grow on many skinny branches. Leaves have other ways to get light, too.
Some leaves grow in a spiral around their stems. Others grow across from each other on the stem. Many leaves have notched or cutout edges. Light can shine around them onto the leaves growing below.
Keeping Their Leaves
Not all trees lose their leaves in winter. Most conifers keep their leaves year-round. The leaves on these trees are hard and narrow. They look like needles. These needles may be thin, but they can gather sunlight. Like the leaves of other trees, they carry out photosynthesis.
Life and Death In many places, tree leaves collect sunlight and make food during spring and summer. T is changes in autumn. T e days shorten, and the temperature
starts to drop. Deciduous trees sense that it’s time to shut down for the winter. Without enough sunlight, photosynthesis
slows down. T e chlorophyll in the leaves starts to go away. To us, it looks like fall leaves change color when they turn red, yellow, and brown. In fact, these colors are always in the leaves. T e strong green of the chlorophyll usually hides them. When that fades, the other colors get their chance to shine. Finally, all the leaves’ food is gone. T e
leaves die and drop off . T e trees are inactive until the spring when new leaves grow.
Into the Air Early the next morning, Olson gets up and heads for an open field. He wants to study the moringa trees in the early morning light. He buckles himself into the harness of
his paraglider. He revs up the motor. T e propeller starts to spin. He moves forward. Behind him, the parachute rises off the ground. Suddenly, he’s airborne. Over the trees he soars. Birds fly under
him. Above, the sky is wide and blue. T e warm sun shines down onto the leafy trees below. As Olson knows, those leaves are just beginning their day of hard work.
chlorophyll: a chemical in leaves that catches the sun’s energy
conifer: a tree that stays green year-round
deciduous tree: a tree that sheds its leaves at the end of a season
photosynthesis: the process by which organisms use sunlight to make food
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