It was lodgepole I was thinking of. Thanks for the correction, Rapaire.

Rocky Mountain lodgepole pine produces serotinous cones which do not open at maturity because they are sealed shut by a resinous bond between the cone scales. These cones remain on the tree for years and require temperatures between 113 and 140 degrees F (45-60 C) to melt the resin and release the seed. In nature, only forest fires generate temperatures of this magnitude within a tree's crown.


From this site.