What to trees do at night?

   When I arrive daily in Golden Gate Park for my walk, it's often pretty dark, depending on the weather and the time of year. The two trees that you see in the photograph below are located near the southeast corner of Stow Lake, and I am often drawn to look at them, partially because of their shape, but also because of their place on a very small island in the lake. As the sun is just beginning to illuminate the area, it looks to me at times like these trees have been kind of guardians of the lake, and as corny and hippie as this may sound (and I do find that somewhat embarrassing), it's the way I feel.
   If myself and many of the animals found there have been sleeping when it's dark, what have these trees been doing?