" The panda’s habitat, however, made me feel right at home. As we climbed
the narrow switchback trail that had begun in neatly terraced fields, we entered
a region of huge old-growth trees covered with snow that had fallen the
previous night.  (The panda’s depend on these old trees for dens.)  Many of
the tree species - pine, fir, hemlock, larch and birch - were familiar, as
was the cool misty weather.  Except for the dense bamboo thickets, I
could almost have been walking in an old-growth forest of the Pacific
Northwest.  But above all, it is the bamboo under-story that makes these
mountain habitats the place for pandas. 

They feed almost exclusively on this difficult-to-digest and nutrient-poor plant.
  As descendents of the ancient carnivore ancestor of modern bears, pandas
lack the digestive adaptations that might allow them to use their plant food
to the maximum, and so they compensate by eating constantly and digesting
quickly, on average eighteen pounds a day.  To conserve energy, they
generally sleep whenever they’re not eating, but this still leaves them
close to the edge of malnutrition.  When a species of bamboo suddenly
flowers and dies off - as it may do once in many years - the panda
population can drop catastrophically.  This is a particular problem now
that logging has cleared the lower slopes, where different bamboo
species provided an alternate food source."
 Robert Bateman