If you're lost in the woods without a compass, look for moss - it shuns the sun, and therefore only grows on the north side of trees.
Mosses will grow on the north, south, west and east of trees (and, indeed, buildings), wherever there is enough moisture to sustain them - and that depends on various factors, such as prevailing winds, and not exclusively on shade. Besides, if the south side of the tree you're looking at happens to be partly shaded - perhaps by another tree, this being, after all, a wood - moss will colonise it readily.
Noticing south-facing mosses in my own garden and on the roof of my house led me to search out the following expert testimony: 'Survival skills put to the test', The Observer, 1 Nov 2009; 'Improvised compasses', Atlas Quest; 'Slightly fickle moss', The Natural Navigator, 7 Aug 2008; 'Fact vs fiction in the outdoors', Scouting Magazine; 'Worst case scenarios: How to find your way when lost in the woods', Popular Mechanics, Feb 2004.
It may be that in certain places, and under certain circumstances, moss will be noticeably more present on the north than the south side - but not consistently enough for FT to advise hikers to leave their GPS at home.