November 17, 2023
4 minimum reading
Trees can outsmart animals like squirrels and birds by synchronizing their seed production.
The following essay is reprinted with the permission of The conversationan online publication covering the latest research.
If you have oak trees in your neighborhood, you may have noticed that some years the floor is carpeted with its acorns, and some years there are hardly any. Biologists call this pattern, in which all oaks for miles around produce many or almost no acorns, “masting.”
Naturalists have declared this fall as the most important year for many trees: Not only oak trees, but also walnut trees, beech trees and more produce tons of nuts at the same time.
Many other types of trees, from familiar North American species such as pines and walnuts to the enormous dipterocarps of the rainforests of Southeast Asia, show similar synchronization in seed production. But why and how do trees do it?
Benefits of synchronized seeds
Each seed contains a packet of energy-rich starch to feed the baby tree lying dormant inside. This makes them a tasty treat for all kinds of animals, from beetles to squirrels and wild boars.
If trees coordinate their seed production, these seed-eating animals are likely to fill long before eating all the seeds produced in another year, leaving the rest to sprout.
For trees like oaks, which rely on animals like squirrels to snatch their seeds from the parent tree and bury them, a mast year has an added benefit. When there are many nuts, squirrels bury more of them instead of eating them immediately, scattering oaks across the landscape.
How trees synchronize their seed production to obtain these benefits remains a mystery, but several elements appear to be important.
First, produce a large crop of seeds. requires a lot of energy. Trees make their food through photosynthesis: use the Sun’s energy to convert carbon dioxide into sugars and starch. However, there are a limited amount of resources to go around. Once trees produce a large number of seeds, they may need to grow new leaves and wood again for a while, or take a year or two to replenish stored starches, before another mast.
But how do individual trees decide when that peak year should be? Weather conditions seem to be important, especially spring weather. If there is a cold snap that freezes the tree’s flowers (and yes, oaks have flowers, they are just extremely small), then the tree cannot produce many seeds the following fall.
TO drought during summer It could also kill developing seeds. Trees often close the pores in their leaves to save water, which also reduces their ability to absorb carbon dioxide for photosynthesis.
Because all trees within a local area experience essentially the same climate, these environmental cues can help coordinate their seed production, acting like a reset button that everyone has pressed at the same time.
A third intriguing possibility that researchers are still investigating is that the trees are “talking” to each other through chemical signals. Scientists know that when a plant is damaged by insects, it often releases chemicals into the air that indicate to its other branches and to the neighboring plants that must activate their defenses. Similar signals could help trees coordinate seed production.
However, tree-to-tree communication research is still in its infancy. For example, environmentalists recently discovered that chemicals released from roots of the leafy vegetable mizuna can affect the flowering time of neighboring plants. While this type of communication is unlikely to account for the rough synchronization of seed production over tens or even hundreds of kilometers, it could be important for synchronizing a local area.
Masting’s effects spread through the food web
Whatever the causes, mastation has consequences that flow up and down the food chain.
For example, rodent populations often increase in response to high seed production. This, in turn, results in more food for rodent-eating predators such as hawks and foxes; lower nesting success for songbirds, if rodents eat their eggs; and potentially increased risk of disease transmission like hantavirus to people.
If the following year, with a shortage of seeds, causes the rodent population to collapse, the effects are reversed.
The seeds of mast trees have also been historically important for feeding human populations, either directly or as food for livestock. Acorns were a staple in the diet of California Native Americans, and families carefully cultivated them. caring for particular oak trees and storing the nuts for winter. In Spain, the most prized ham still comes from pigs wandering through the oak forestseating up to 20 pounds of acorns each day.
So next time you take an autumn walk, look at the ground under your local oak tree; You may see evidence of this amazing process.