Dramatic rainfall differences between westside and eastside drainages create areas of diverse vegetation with over 1,700 vascular plant species. Estimates of fungal plant species exceed three thousand. In order to determine the health of the North Cascades ecosystem, park biologists must monitor its vital signs. Ecosystem vital signs can range from ice samples and measurements of high-mountain glaciers to the presence and health of aquatic insect larvae at the bottom of the Skagit River. Presence and quantities of pollutants in glaciers and waterways can indicate human impacts on the ecosystem, and the extent of those impacts can be revealed by indicator species .
Indicator species can be sub-classified as keystone or umbrella species.
A keystone species is one that affects the livelihood of a large, interconnected web of species. Scarcity or absence of certain macroinvertebrates at the bottom of a stream or river can indicate water quality and a loss of overall diversity in the food chain. Umbrella species are those that mirror the health of many other species. Bald eagles are an example of an umbrella species. If eagle populations decline, for example, due to chemical ingestion, it is likely that other species in the eagles' food chain are contaminated as well.