The next instalment examines the northern coniferous forests. The programme begins in northern Norway, 500 kilometres north of the Arctic Circle. Here, there is only just enough light for the pine trees to survive, but it is extremely cold during the winter. Pine cone seeds provide one of the few foods available at this time of year, and large herbivores such as the moose must also rely on their fat reserves. However, there are predators, including lynxes, wolverines and eagle owls. The coniferous forest grows in a belt right around the globe, some 1,900 kilometres across at its widest. On each continent, many migratory animals arrive in the spring, and even more during the summer. In years when the vole population is high, the numbers of their main predator, the owls, increase correspondingly and spread out. Further south, the warmer climate sees the pine trees give way to broad-leaved species, such as the oak and beech. More birds occupy the forest canopy during the summer than at any other time of year, feeding on a myriad of insects. At the onset of winter, many animals in these forests hibernate, and in America, Attenborough uncovers the den of a black bear, which can be asleep for six months at a time. Finally, further south still, Attenborough discovers the effects of forest fires, which are not so destructive as they appear - the areas affected rejuvenate themselves within a couple of months, with more flowers than before.