The Common Aspen (or Eurasian Aspen), a deciduous tree of the poplar family. It is a very hardy species and tolerates long, cold winters and short summers, and grows naturally inside the Arctic Circle in Scandinavia. Its leaves tremble in even light wind, and are the source for its botanical name.
The five typical aspens are all native to cold regions with cool summers, in the far north of the Northern Hemisphere, extending south only at high altitudes in mountains. The White Poplar by contrast is native to much warmer regions, with hot, dry summers. They are all medium-sized deciduous trees reaching 15 – 25 m tall, exceptionally to 30 m.
Some aspen colonies become very large with time, spreading about a metre per year, eventually covering many hectares. They are able to survive intense forest fires as the roots are below the heat of the fire, with new sprouts growing after the fire is out. However, aspens do not thrive very well in the shade, and it is difficult for aspen seedlings to grow in an already mature aspen stand. Fire indirectly benefits aspen trees, as it allows the saplings to flourish in open sunlight on account of the burned landscape. Lately aspen has increased its popularity in forestry, mostly because of its fast growth rate and ability to regenerate from sprouts, which makes the regeneration of the forest after harvesting much cheaper, as no planting or sowing is required.
Why do the leaves quake?
The unusual ability of the leaves of Populus to twist and bend due to the flattened petioles may not be fully understood. It is thought to help protect the trees from severe winds, perhaps by helping dissipate energy more uniformly throughout the canopy. It is also thought to improve the rate of photosynthesis throughout the tree by reducing the exposure of the outer leaves to extreme sunlight (thus reducing photo inhibition) by presenting the leaves at an oblique angle to the sun throughout the day, while at the same time allowing more light through to the lower leaves which are generally overshaded. This would enable leaves throughout the tree to photo synthesize more efficiently.
