Kristen Jennifer Williams, Simon Ferrier, Eric A Lehmann, Thomas D Harwood, Randall J Donohue, Kathryn M Giljohann, Roozbeh Valavi, Ning Liu, Chris Ware, Peter Lyon, Thomas G Van Niel, Tim R McVicar, Anna Richards, Cassandra Malley

Effective satellite-based monitoring of ecosystem integrity or condition needs to address four key challenges: (a) context dependency; (b) alternative ecological states; (c) short-term temporal ecosystem dynamics; and (d) scarcity of reference data where ecosystems retain high levels of integrity. Here we present a typology, and outline strengths and weaknesses, of different approaches to mapping and monitoring ecosystem integrity across entire regions or continents using time series satellite data. We then describe how one of these approaches, the Habitat Condition Assessment System (HCAS), addresses all of the above challenges, and provide an outline of the evolved method which includes annual outputs, and Australian continent applications. HCAS requires three readily available inputs (i.e., representative examples of relatively natural areas as reference sites, remotely sensed ecosystem characteristics, and environmental covariate data) and could be easily adapted and applied by other countries to provide an effective indicator of ecosystem integrity for nature-based decisions.