One of our Colorado customers recently discovered that some local porcupines like their Trestlewood II "Salty Fir" Weathered Timbers almost as much as they do. The above photo shows one of their exterior Trestlewood II timbers after it has been chewed on by some porcupines.
We have had other customers who have mentioned that moose and deer also show an affinity for Trestlewood II. A Wikipedia "Mineral lick" entry suggests that these animals are probably just looking for nutrients.
Our Colorado customers are going to make their exterior timbers less accessible to the porcupines by putting rock around the lower portions of the exterior timbers.