Courtesy of the Nature Photography Society of New Zealand website:

Nature photography depicts living, untamed animals and uncultivated plants in a natural habitat, natural landscapes including geology and the wide diversity of natural phenomena, from insects to icebergs.

Photographs of animals which are domesticated, caged or under any form of restraint, as well as photographs of cultivated plants are ineligible.

Minimal evidence of humans is acceptable for nature subjects, such as welcome swallows or monarch butterflies, adapting to an environment modified by humans, or natural forces, like hurricanes or tidal waves, reclaiming it.

You can find out more about NPSNZ on their website: http://www.naturephotography.org.nz/