Seed dispersal by wind: a guide to flying seeds
Many UK native plants rely on the wind to disperse their seeds. This is known as anemochory.
Plants have exploited this natural highway for centuries and have evolved many different designs along the way. The variations in the designs mean the seeds will disperse at different times. Some seeds will be carried off in a light breeze and others will require stronger winds to dislodge them.
Winged seeds are known as samaras. The seed can be centred, as in birch and elms, or off to one side like ash. The structure of the seed changes its aerodynamics, producing visibly different ways of floating through the air. Seeds that are off-centred will spin, whereas centred seeds with two lateral wings will glide.
Parachutes and fluffy seed
Some seeds have evolved a structure similar to a parachute. The dandelion, with a single seed attached to a fluffy parachute, has been entertaining children for generations, all the while demonstrating how easily their seeds disperse. Trees also produce fluffy seeds and this is often seen in willows.
So how does the seed stay in the air?
A seed that is designed to glide is not only dependent on the wind to carry it but also needs lift; otherwise gravity will pull it back down to earth, right under the parent tree. Lift can be achieved using thermals; hot air will rise and carry the seeds upwards. Equally lift can be generated when wind blows against an obstruction, like buildings or hills; air is displaced and forced up, carrying the seeds away with it.
Helicopter seeds: which trees are they from and how do they fly?
Spinning seeds like ash, maple and hornbeam don’t need to rely solely on external factors to generate lift. Nature has designed their wings in just the right way to produce the lift needed as they spin, creating a type of flight known as autorotation.
The Woodland Trust is a partner in the UK National Tree Seed Project which involves collecting native tree seeds to store at the Millennium Seed Bank. Take a look at some of the techniques used in collecting seed on the UKNTSP. The UKNTSP is generously funded through players of the People’s Postcode Lottery and supported by volunteers.