In case you hadn’t noticed, it’s getting colder, leaves are dropping and everything’s looking pretty miserable. But far from going to bed for the year, nature’s at work more than ever. Seed dispersal is a key process in paving the way for new growth next year.
For most plants, autumn’s the time for producing seeds. Conkers, acorns, dead flower heads in the back garden – these seeds are all being shed now. But they also need to be scattered around so that they can start growing roots. There are four main methods of seed dispersal.
Animal dispersal – who’d have thought animal droppings were helping to spread plant growth? When birds eat berries, they also eat the seed. Wherever they poo, they’re also dropping seeds for new plants. And it’s not just by eating that animals do their part. Think of those goosegrass seeds (below) which stick to your clothes. Their little spikes can piggy back on birds, squirrels, foxes, even people, and drop off far away.
Wind dispersal – those chilly breezes aren’t just there to make you shiver. They’re able to blow lighter seeds, sometimes over great distances, allowing new plants to take root far away. Watch how easily these dandelion seeds are swept away. When you’re next outdoors, look out for poppy seeds (very small and light) and sycamore seeds (with their “propeller blades”). These designs make them ideal for travelling further.
Explosive dispersal – if you’ve ever sat near gorse on a sunny day, you might have heard mini explosions. When the pods of some plants dry out, they tighten around the seeds until they explode. This shoots seeds around the area, allowing an effective dispersal. Check out these exploding seed pods. You don’t have to go far to find this phenomenon either. Runner beans, broad beans, really almost any beans, explode to shed their seeds.
Water dispersal – rivers and larger bodies of water can deposit seeds miles from their original plant. Similarly to wind dispersal, this is most effective when the seeds are light. That’s one reason why willow and silver birch trees (often found near water) have such small seeds.
For all of these methods, an important goal is to spread the seeds as far as possible. This prevents over-crowding which can seriously affect growth. Ever tried planting seeds too close together on the veg patch? It doesn’t work!