Take oak and beech as an example again. Animals like squirrels, jays , mice and badgers feed on the acorns and beech nuts. When the trees produce smaller crops for a few consecutive years, they are in effect keeping the populations of these animals in check.
But during a mast year, the trees produce more food than the animals can possibly eat. This abundance causes a boom in populations of small mammals like mice.
More importantly, it guarantees some will be left over to survive and grow into new trees. Mast years have a major evolutionary advantage for the tree.
Our A-Z guide to British trees from native species to naturalised and widely planted non-natives. Research has shown major mast years for beech trees are synchronised across all of northern and western Europe! Mast years are not just one off events for individual trees. The vast majority of trees in a particular species will have a fantastic crop all across the UK in the same year.
Weather certainly has a part to play. To produce a healthy crop, the trees need the right combination of temperature and rainfall in the spring. Phenology — the study of the timing of natural events in relation to the weather — can help us better understand this.
Dr Andrew Hacket-Pain has used records from our Nature's Calendar phenology project to research masting. When spring is warm and dry, pollination of oak flowers is very effective and this results in a large crop of acorns. Sure, a wet, cool spring can affect pollination and a hot, dry summer can affect acorn maturation.
But annual rainfall and temperature fluctuations are much smaller in magnitude than acorn crop sizes. In other words, weather variables cannot account for the excessive nutty production of acorns in a mast year.
So what does trigger a mast year? Scientists have proposed a range of explanations—from environmental triggers to chemical signaling to pollen availability—but our understanding is not clear. Years of lean acorn production keep predator populations low, so there are fewer animals to eat all the seeds in a mast year.
Ultimately, a higher proportion of nuts overall escape the jaws of hungry animals. Whatever the reasons and mechanisms behind acorn cycles, mast years do have ecological consequences for years to come.
More acorns, for example, may mean more deer and mice. Unfortunately, more deer and mice may mean more ticks and consequently more Lyme disease.
Many animals depend upon the highly nutritious acorn for survival. Oak trees, meanwhile, depend upon boom and bust cycles, and a few uneaten acorns, for theirs.
Amazing Acorn Facts. Can't find an answer in our FAQ? Try our Plant and Gardening Guides. Even so, precious few make it even to the sapling stage.
Producing a bumper crop of acorns comes at some cost to the tree, making significant inroads into its store of sugars and starch. To replenish its store of starches, the oak needs a period of recuperation, forcing it to concentrate on less demanding activities, such as increasing its production of leaves and wood.
If follows the precedent of , then acorns are likely to be thin on the ground. While the branches of oaks were bowing under the weight of their crops of acorns in , the following year the Forestry Commission were reporting that there were barely any. As well as providing the oak with a well-earned rest, the masting cycle also has an impact on the population of those creatures that feast on acorns. Although a mast year will mean that predator populations increase, a run of lean years will put pressure on numbers so that by the time the next mast year occurs, there are fewer predators to eat the seeds, thereby further enhancing the chances of the seeds germinating.
Clever, really. It is still a matter of some debate as to why mast years occur precisely when they do and why all the trees seem to synchronise their behaviour.
One theory is that weather conditions have an important part to play in the process. Similarly, a dry summer will kill the developing seeds and force the oak to close the pores in their leaves to conserve water, reducing its ability to make carbon dioxide for photosynthesis. This spring was dry and warm and the summer wet, ideal conditions for the oak to develop its crop of acorns. As all the trees in a particular area experience the same weather conditions, it makes sense that these climatic triggers will influence their behaviour in the same way.
Intriguingly, some scientists think that the trees may synchronise the mass production of fruits by releasing some form of chemical signal, as they do to kick start defensive mechanisms when neighbouring species are damaged. Whatever the reason, our local frugivores have had a bumper crop of acorns to feast on and, who knows, some seeds might even survive to produce the next generation of the mighty oak, that most distinctive and ancient symbol of our woodlands.
Let us hope so.
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