Sven Zacek / Ural owl (Strix uralensis) perching on an Apsen tree during the blue hour of dawn, Tartumaa, Estonia, April.

Donald M. Jones / American Elk (Cervus elaphus nelsoni) bull with aspens, western Alberta, Canada

Tim Fitzharris / Aspens at Independence Pass, Colorado

Sven Zacek / Ural owl (Strix uralensis) perched in Aspen tree in summer. Tartumaa county, Southern Estonia. May.

Jeff Foott / Beaver (Castor canadensis) feeding on Aspen, Grand Teton National Park, Wyoming, USA, August.

Mike Read / Insh Marshes RSPB reserve and Aspen (Populus tremula) Strathspey, Highland Region, Scotland, March.

Danny Green / Beaver kits (Castor fiber) eating aspen, Finland, July

Danny Green / Beaver (Castor fiber) kits eating aspen, Finland, July.

Jack Dykinga / Aspens (Populus tremuloides) in soft morning light. Utah, USA, October.

Jack Dykinga / Aspens with bent trunks shaped by heavy snow load. Grand Canyon National Park, Arizona, USA, August.

Kirkendall-Spring / Aspen trees and Mount Moran from Ox Bow Bend on Snake River, Grand Teton National Park, Wyoming, USA. September 2015.

Kirkendall-Spring / Autumn colours below Mount Moran, Grand Teton National Park, Wyoming, USA. September 2015.