A planted Olearia hedgerow - ca 50 years old, 206 m long adjacent to a drain, was surveyed to test Hooper's Law in NZ - (the average number of woody spp in 30.5m sections x 99) - 16 is the age of the hedgerow. It is definitely a 'rule of thumb' and there are 18 woody spp - native and exotic (excluding vines) within the total length.