default_aspen_tree_top, derived from default_pine_tree_top (by paramat)
default_aspen_wood, derived from default_pine_wood (by paramat)
+sofar (WTFPL):
+ default_gravel.png -- Derived from Gambit's PixelBOX texture pack light gravel
+
Neuromancer (CC BY-SA 2.0):
default_cobble.png, based on texture by Brane praefect
default_mossycobble.png, based on texture by Brane praefect