An Abundance of Acorns: What is a Mast Year? 🌳

Hello nature lovers! October is a beautiful time to walk the trails at Glade Trust Nature Reserve. The leaves are turning gold and russet, and if you look down, you'll see a truly remarkable sight: the ground is littered with acorns, being particularly evident on the roads that line the route and surround the Trust. This isn't just a regular autumn bounty; we're experiencing a "Mast Year" for our oak trees.

What is a Mast Year?

A mast year is a phenomenon where many species of trees in a forest ecosystem—particularly oaks, and beeches—produce an exceptionally large crop of fruit (like acorns or nuts) in the same year, far exceeding their usual output.

The term 'mast' originally referred to the nuts and fruits of forest trees, especially those used as food for livestock, like pigs.

Why does it happen?

The exact triggers are complex and not fully understood, but it's thought to be an evolutionary strategy linked to:

1. "Predator Satiation": By flooding the ecosystem with food every few years, the trees ensure that even after the local wildlife (like squirrels, jays, and deer) has eaten its fill, there are still plenty of seeds left over to germinate and grow into new trees. If they produced a consistent, moderate amount every year, the predators might develop a large, stable population that could consume almost the entire annual crop.

2. Weather and Resource Synchronization: Trees may 'wait' until they have built up enough stored energy from good growing seasons to invest in a massive seed production effort. It's often linked to specific weather patterns, such as a mild winter followed by a dry, warm spring during the critical flowering period. This year particularly has had extreme drought that has shocked these trees into this panic to produce.

3. Cross-Pollination: Synchronized flowering across the entire population ensures maximum cross-pollination, leading to a more successful seed set.

   
   

Note the way the acorns sit on the tree of two main oak species at the reserve, the Common Oak (Quercus robur), on a stem

and the Sessile Oak (Quercus petraea), stemless.

. They are both participating in this phenomenal natural event!

The Curious Case of the Oak Gall 🧐

While you’re admiring the acorn abundance, you might also spot some fascinating, often bizarre, growths on the leaves or twigs of our oaks. These are oak galls, and they are a sign of another incredible interaction in the natural world.

The image shows oak marble galls, which are growths on oak twigs caused by the oak marble gall wasp, Andricus kollari. 

• Galls are abnormal plant growths that form in response to insects, such as gall wasps, laying eggs or feeding on the plant. 

• The wasp larvae live inside the gall, feeding on the plant tissue. 

• Oak marble galls are typically round and turn brown as they mature. 

• The galls are not considered harmful to the host tree. 

• Historically, oak marble galls were used to make ink. 

The image above shows galls on the underside of a leaf, which are from a gall wasp and are commonly known as spangle galls.

Common Spangle Gall Wasp: The common spangle gall wasp (Neuroterus quercusbaccarum) produces these disc-shaped galls on the undersides of oak leaves.

Life Cycle: The wasp larvae feed on the leaf tissues inside the gall.

Appearance: The galls are small, disc-shaped, and can be found in large numbers on a single leaf.

Effect on the tree: While the larvae feed on the host plant, they typically cause little damage to the oak tree.

Common vs. Sessile Oak Galls

The appearance of the gall is determined by the specific species of wasp and the plant it targets. At Glade Trust, look for these on both the Common Oak and the Sessile Oak:

These galls serve as both food and shelter for the developing wasp larva inside. While they might look alarming, a few galls generally don't seriously harm a healthy, mature oak tree. They are simply part of the intricate tapestry of life that makes up our woodland ecosystem!

Why Does This Matter?

The mast year is a huge event for the entire reserve. This massive food supply fuels the wildlife for the coming winter.

• Grey Squirrels will be busy burying acorns for their winter stores.

  
  

• Jays will collect and hide hundreds of acorns, often burying them quite far from the parent tree—effectively acting as the oak's primary dispersal agent!

• A surge in food can lead to a boom in the population of small mammals next spring, which in turn supports predators like foxes and owls.

So, next time you visit, take a moment to appreciate the mighty oaks. They're not just beautiful; they are the heart of a complex ecosystem, and right now, they're putting on an incredible, synchronized show for the natural world! 🐿️