Sun Angle and Temperature - MA

Sugar Maple Trees

Every spring, some people in eastern Canada and the northern parts of the central and eastern United States wait for the weather to warm up so it is just below freezing. As soon as this happens, these people head into the woods. This is because this temperature is the ideal time to go “tapping.”

Tapping refers to the process of collecting sap from maple trees. Sap is a fluid made up of water, dissolved sugars, minerals, and vitamins. It is a primary ingredient in maple syrup, so people who make maple syrup depend on maple trees producing sap. “May your sap run strong and sweet” is a common way that maple sugar producers say “good luck.”

Maple trees depend on the temperature differences caused by seasons (periods of time characterized by specific weather patterns and by the length of day and night). When temperatures drop below freezing in late fall and winter, pressure within the tree decreases. This causes the tree to draw in water through its roots. As winter turns into spring, nights tend to remain cold but temperatures during the day are warmer. This temperature difference creates pressure that pushes water down to the bottom of the tree. This causes the tree’s sap to flow.

Because they depend on cold winters and warmer springs, maple trees are found primarily in latitudes that experience the four seasons: fall, winter, spring, and summer. Latitude is a measurement of a location’s position relative to the equator. The equator’s latitude is 0 degrees, while the poles’ latitude is 90 degrees.

Heat Powers the Cycling of Water

As the map of Earth’s albedo shows, the majority of the sun’s energy is absorbed by the ocean. When enough thermal energy is transferred to the water, liquid water will evaporate into the atmosphere. Evaporation is the process of liquid water changing into water vapor, its gas state.

Water evaporates when enough thermal energy is present. Like all liquids, the atoms and molecules that make up liquid water are less tightly packed than they are in a solid. They are in constant contact with one another, but they have enough energy to slide past one another. This is why matter in a liquid state takes the shape of its container but has no shape of its own.

All water on Earth is part of a system called the hydrosphere. Remember that a system is a set of connected, interacting parts that form a more complex whole. Earth is so massive and so complex that scientists study smaller systems to better understand how everything works. There are four main Earth systems: the hydrosphere, atmosphere, geosphere, and biosphere. Sugar maple trees are part of the biosphere. This system includes all living things on Earth.

Maple trees depend on the hydrosphere because all living things need water to survive. As maple trees transpire, they interact with the atmosphere. The atmosphere is the mixture of gasses, dust, water vapor, and other molecules above Earth’s crust. Living things also interact with the geosphere. The geosphere is made up of Earth’s landforms, including rocks and soil.

Living things depend on all of the other systems for survival. At the same time, living things impact their surroundings as they breathe air, drink water, and live on Earth’s surface.

Once water evaporates from Earth’s surface, it moves into the atmosphere. There is always water in the atmosphere. Cold liquid water can also evaporate if the air above it isn’t already full of water vapor. About 90 percent comes from evaporation from bodies of water, while the other 10 percent comes from plant transpiration—the process of water moving through plants from their roots to their leaves, where it is released back to the atmosphere as water vapor.

Remember the sugar maple trees. Their roots absorb water from the soil. They use some of the water to function, store some of it, and release the rest back to the atmosphere through transpiration. When living things die and their bodies decompose, the water they’ve stored in their bodies returns to Earth’s surface.

Water vapor in the atmosphere transfers some of its thermal energy to the cooler atmosphere. This causes it to cool off and condense, turning back into liquid water and forming clouds. Precipitation is water falling back to Earth’s surface in the form of rain, snow, sleet, or hail. Some of that water is absorbed into the ground as groundwater. Some is absorbed by living things, including plants through their roots and animals when they drink. The rest of the water collects on Earth’s surface in the ocean, lakes, and rivers, where it moves downhill, pulled by the force of Earth’s gravity.

This circulation of water through the hydrosphere from Earth’s surface to the atmosphere and back is called the water cycle. The water cycle connects all of Earth’s systems as water moves from one state to another. It is complex, and it varies in different parts of the world and at different times of year depending on the amount of thermal energy from the sun. For example, most of the fresh water on Earth is stored in glaciers and ice caps, where it can remain frozen for thousands of years. In contrast, in hot climates and seasons, precipitation sometimes evaporates just seconds after it falls to Earth’s surface.

Sugar Maples on the Move

Because of the different ways that Earth’s surface is heated, as well as the cycling of water around the planet, there are complex variables that influence Earth’s temperature at any given time. For example, it depends on how much solar radiation is reflected back out to space and how much is absorbed. If Earth’s temperature cools, causing more snow and ice to form, more solar radiation will be reflected back out to space, which will make the climate even cooler. When the planet begins to warm, causing snow and ice to melt, darker- colored surfaces and ocean are exposed. As a result, less solar energy is reflected out to space, causing the warming to increase. These are called feedback loops—changes in the climate that cause an impact that changes the climate further.

In recent years, Earth’s temperature has been warming. This rise in global average temperature near Earth's surface is called global warming. Some scientists are interested in how global warming is affecting living things. For example, in one study, scientists looked at 15 northern species of trees, including the sugar maple. They focused on where young trees are growing compared to older trees. They did this by looking at the latitudes of the two groups of trees. They found that the young trees of 11 of the 15 species are now growing 20 kilometers (12 miles) farther north, on average, compared to the older trees. Within those species, the sugar maple tree has moved more than the average. Young sugar maple trees are now growing as much as 50 kilometers (30 miles) farther north compared to the older trees.

Scientists believe that global warming is the likely explanation for why younger trees are now growing farther north than older trees. They depend on cooler temperatures to survive, so seeds that are carried north by wind, water, or animals are more likely to survive and grow into trees than seeds in the now-warmer locations.