Harold (Hal) Mooney’s contributions to understanding California’s ecology began in 1962, the same year Silent Spring was published. 45 years later, Hal and I embarked on a synthesis of current understanding of California’s ecology that asked: What do we know about the trajectories of California’s ecosystems, from the deep past into the next century? The effort brought together 169 scientists to address this question across 24 marine, freshwater and terrestrial systems, from natural to highly managed, and 16 additional key drivers, threats and responses. The field of ecology has evolved to embrace dynamism, historical contingency and cross-scale interactions and to attend to function and processes as well as structure. Hal’s contributions to this shift are global, but I focus here on how he has shaped understanding of California’s hyperdiverse, globally significant ecosystems.
Three patterns emerged from this cross-scale, past-to-future, interdisciplinary inquiry into California’s ecology. First, across ecosystems we found remarkably consistent recovery of species and systems from a nadir of environmental quality roughly 40-50 years ago. Trends from decreasing urban air quality to declining species facing toxic pollutants, over-harvesting and invasive species have been successfully reversed. Widespread damage caused by 19th-century overgrazing and gold mining has faded with time and been addressed by restoration, remediation, and management. These successes are tempered by ongoing habitat loss and climate change. Second, cross-ecosystem interactions prevail and shape all of California’s ecosystems: movement of sediment, nutrients, propagules and fire, for example, shape source-sink relationships and create profound integrators of multi-decade, regional-scale dynamics such as the last trajectory of Emerald Lake’s acid neutralizing capacity. Finally, although California’s ecosystem types turnover mainly longitudinally, each ecosystem type’s dynamics and trajectories vary substantially from north to south.
Hal’s most crucial contribution to California’s ecology could be his insistence that we treat it as integrated with, rather than artificially separated from, the state’s economy, culture, and human communities – both in historical perspective and today. For decades he has studied ecosystems defined by natural processes, like wetlands and redwood forests, alongside those defined by human activity, like rangelands and agriculture. He has also encouraged us to look across marine and terrestrial ecosystems, across ecological scales from individuals to biosphere-atmosphere interactions, Finally, he has pushed us to look at history, policy and social issues alongside ecology and to mobilize this integrated understanding to chart a better course forward.