Mast (botany) facts for kids

Mast is a special word for the fruits and seeds that forest trees and shrubs produce. Think of things like acorns and other nuts. The word "mast" comes from an old English word, mæst, which meant the nuts that fell from forest trees onto the ground.

Historically, people used mast to feed and fatten up pigs. Today, it's a super important food source for many wild animals. In some parts of the world, like the tropical forests of Southeast Asia, huge areas of forest, with hundreds of different plant types, produce a lot of mast all at once. This happens at irregular times, usually every 2 to 12 years.

More generally, mast includes any edible parts of trees and shrubs that animals eat. Trees and shrubs produce mast in huge amounts during special events called "mast seeding" or "masting." These events happen regularly, but not every year. They are a big deal for entire animal populations. Scientists think masting happens for many reasons. These include how many nutrients are available, how efficient it is for plants to produce seeds all at once, weather patterns, and even as a way to protect seeds from being eaten too much. These big bursts of mast production affect many things in an ecosystem.

Kinds of Mast: Hard and Soft

An abundance of acorns on the ground often occurs during mast seeding years

Mast can be split into two main kinds: hard mast and soft mast.

• Hard mast comes from trees like oaks, hickorys, and beech trees. These are the hard, tough nuts like acorns, hickory nuts, and beechnuts. In the past, people would let pigs roam in forests to eat these nuts and get fat. This practice was called pannage.
• Soft mast comes from other trees and shrubs. These are softer fruits like raspberries, blueberries, and the berries from greenbriar plants.

What is Mast Seeding?

Mast seeding, also called mast reproduction, is when a group of trees or shrubs produces a very different amount of fruit each year. Sometimes they make a lot, sometimes not much. These big, sudden increases in food production really affect how ecosystems work and how forests grow.

For example, in a mast seeding year, there might be thousands more acorns, hickory nuts, or beechnuts than in a non-mast year. Mast seeding mostly happens with trees that are pollinated by wind, but it's also seen in some grasses and Dipterocarp trees.

Scientists have different ideas about why mast seeding evolved. These ideas generally fall into three groups:

• Economies of scale: This means it's more efficient to do something in a big way.
• Resource matching: This means plants produce seeds when they have enough resources.
• Proximate cues: This refers to things like weather that trigger masting.

Why Plants Mast: Economies of Scale

One idea is called the predator satiation hypothesis. Imagine a plant's seeds are like prey for animals that eat them. If plants produce a huge amount of seeds all at once, there are too many for the animals to eat them all. This means a small number of seeds can escape being eaten and grow into new plants. In the years when there aren't many seeds, the animal populations that eat seeds stay low. This strategy helps ensure that some seeds survive.

Another idea is the pollination efficiency hypothesis. This suggests that mast seeding helps plants get pollinated better. If all the plants in an area produce flowers and seeds at the same time, it's easier for pollen to spread. This is especially true for wind-pollinated plants, which many masting species are. Both of these ideas suggest that it's better for plants to have a big, uneven effort in reproduction rather than a small, steady one. This helps the masting plant population survive and thrive.

Why Plants Mast: Resources and Weather

The resource matching hypothesis says that plants reproduce based on how many resources they have. Making fruits and seeds takes a lot of energy and nutrients. Plants need things like water, stored energy (carbohydrates), and nutrients like nitrogen and phosphorus. Studies have shown that these resources often get used up after a big mast seeding event.

Weather is also a big factor that can trigger mast seeding. Different weather conditions can affect whether masting happens in a certain year. The exact effects of weather depend on the plant species and where it grows. For some types of oak trees, mast seeding is affected by regional weather patterns. For example, spring temperature, summer droughts, and spring frosts can play a role. These weather conditions are important during key times for fruit to grow and for fertilization to happen.

Effects of Mast Seeding

Mast seeding provides a lot of food not just for wild animals, but also for farm animals. It can also cause big increases in populations of animals like mice, rats, and stoats. Their numbers can grow a lot during a mast year because there's so much food. Then, in years with less food, their populations go down.

However, when these animal populations boom, there can be other effects. For example, more rats might invade nearby farms.

Mast seeding can have both good and bad effects on ecosystems. Let's look at the white-footed mouse. When a mast seeding event happens, the number of white-footed mice goes up. This can lead to more cases of Lyme disease, because these mice carry ticks, which spread the disease. But there's also a good side: more white-footed mice mean they eat more Gypsy moths, which are a major pest in forests in the eastern United States.

The combination of forest fires and mast seeding is very important for how white spruce trees grow back in the boreal mixed-wood forest. Studies have found that there are many more white spruce trees in areas that had fires during mast years compared to areas that had fires during years with few cones. This shows how important it is for seeds to be available right after a fire, before the ground becomes less suitable for new seeds to grow.

Mast Seeding and Climate Change

Many mast seeding species are considered "foundation species," meaning they are very important to their ecosystems. Scientists are trying to figure out how climate change might affect how often and how much mast seeding happens. This will help them understand how much food will be available for wildlife and how forests will change.

Globally, mast seeding has become more varied over the last century. Scientists are still trying to fully understand why these long-term changes are happening. For example, in Europe, the intensity of mast seeding seems to be connected to the North Atlantic Oscillation, which is a weather pattern. In tropical South Asia, mast events seem to be linked to the El Niño–Southern Oscillation, another major climate pattern.