Old growth temperate rainforests are extraordinarily complex ecosystems, filled with thousands of species, many of which have yet to be even identified. In order to preserve this diversity, the team focused on tree species. Tree distribution is well know, and in protecting reprentative stands of old growth sitka spruce, red and yellow cedar, western hemlock, amabalis fir and Douglas fir, the scientific team felt confident they would also be protecting the thousands of other rainforest species whose names are not yet known.

The Core Intact Areas selected by the team make up 57% (1.35 million hectares) of the study area. These are watershed where less than 10% of forested area has been logged, with low road density (less than 0.2 km of road in each km2) and presence of old growth structures (defined by trees older than 250 years, and taller than 37.5 m).

On the map, the Core Intact Areas are shown in mid-green.