‘MAST YEARS‘
PERIODICALLY, trees such as English oak, field maple, beech, hawthorn, hornbeam and small leaved-trees appear to synchronise and produce prodigious amounts of seeds, fruits and nuts compared to some years where they hardly produce any.
These bountiful years are known as “mast years”. The term mast is derived from that Anglosaxon term “maest” that refers to the various kinds of nuts that accumulate on the forest floor providing winter food for various animals.
These mast years typically occur every five to ten years and what is more interesting is that different species of tree seem to synchronise the same behaviour over large geographic areas.
When there is so much food available, wildlife such as seed eating animals like as squirrels and jays are more likely to survive the winter in comparison to non-mast years.
The populations of these species are then likely to peak the following summer. However, the converse can occur during non-mast years.
The reasons behind this large swing in seed and nut productivity by trees are not fully understood. There are two key questions that are largely unanswered; the first is why a variability from year to year with respect to nut production by an individual tree is there, and secondly and the more puzzling is how and why trees synchronise this cycle with other trees over large areas.
Annual individual variability could be related to weather such that when rain and sunlight is abundant there would be more resources available to produce more nuts and fruits. However, variations in weather conditions do not seem to fully correlate with fruit and nut productivity. It is thought that annual variability is due to some form of evolutionary behaviour where resources are periodically shifted from reproduction to growth. Trees expend a lot of energy in producing the fruits and trees grow slower in mast years. As it only happens periodically there is an evolutionary advantage to the trees as it will ensure more of the crop germinate into saplings.
Three mechanisms have been considered with respect to the synchronisation of masting trees over large areas; chemical, reproductive and environmental. Chemical and reproductive mechanisms have been largely discounted due to the large distances involved.
It is thought that masting synchronisation is likely to be due to environmental factors. This conflicts with the individual variability phenomena where the effect of weather has been discounted.
There is a distinct difference between the weather and the climate, where the former is a short-term manifestation of the latter. A Californian study on oaks over a large geographical area demonstrated a clear correlation between April temperatures and the abundance of mast.
April is the time of year when the oaks develop the male and female flowers which in turn produce the acorns. 2010 and 2013 were both reported as the last two mast years in the UK, but there is no indication that 2021 will be one. With the global temperature increasing and temperature patterns becoming increasingly erratic, researchers are uncertain about the overall effect on masting, and what the downstream effect on seed predation will be.
Whether it is a mast year or not, why not head out to one of the Trust’s many reserves to experience autumn, with its beautiful autumnal colours, the large variety of fruits and nuts, diverse fungi and animals and birds preparing themselves for the cold winter months ahead. For more details go to http://www. nottinghamshirewildlife.org/