How do conservationists make use of
watersheds and ecozones? why is this
important?

Ecozones divide Canada into 15 parts, depending on their biophysical characteristics.
Ecozone is a distinct ecological system, where plants, animals, people, soils, water and climate interact.

This division helps in keeping track of various biological statistics, so that it's easier to estimate if there is a threat of extinction of certain species, or if there is some abnormal climate change due to human activity. 
Conservationists, who believe in sustainable usage of natural resources, are able to determine in which fields, the natural resources are being overly exploited.