April is a time of rebirth. Take a walk in the neighborhood or a nearby park, and you will see that trees are undergoing a remarkable change. In late winter, leaf buds, which house tiny new leaves, begin to swell. In spring they break out, revealing perfectly formed miniature leaves that grow in a matter of days to their full size. Take photos of the same bud over a few days to see the change unfolding before you. Notice patterns in the neighborhood. Does a tree on a sunny south-facing slope leaf out earlier than one in a shady hollow? Do some types of trees put out leaves sooner than others?
The cycle of rebirth in plants is linked to the way they produce energy. Like most other organisms, plants need energy to grow. Unlike other organisms, they can make their own food using energy from the sun. This process is called photosynthesis, a word derived from the Greek photo (light), and synthesis (to put together). A plant’s energy factory is located in its leaves and other green tissues. Chlorophyll, the same compound that makes leaves green, allows plants to harness energy from sunlight to make energy-rich sugars, by combining carbon dioxide and water found in air. These sugars can be used immediately, or stored as starches to be used another time.
In winter, when days are short and sunlight is weak, it is too energetically “expensive” for trees to produce chlorophyll and maintain their leaves, so they discard them, and hunker down, living off of stored energy. In spring, deciduous trees use their stored energy to produce new leaves and restart their energy factories. The energy plants make is vital for their growth and reproduction. Oxygen is a byproduct from this process that is necessary for life on Earth.
Plants wait for just the right conditions to unfurl their leaves. If they do so too early, new leaves could be lost in a late frost. Too late, and they lose precious time to make energy. The timing of buds “bursting” can also vary based on climatic conditions, and scientists all over the world are studying the effects of changing climate on leaf emergence. A citizen science project, BudBurst, is looking for observations from citizens around the country. Scientists will use this information to look for patterns and correlate this with other data, such as the emergence of caterpillars that need to feed on the leaves to survive. The website also has a new page called BudBurst For Families with activities that can be enjoyed by amateur scientists of all ages. So get outdoors, and take time to witness the yearly rebirth of nature in your own neighborhood!