Emerald Ash Borer

The emerald ash borer invasion of North America demonstrates S-curve invasion dynamics with mathematical precision. Arrived from Asia in the 1990s (likely in wood packaging), spent years in an invisible lag phase, then exhibited four distinct spread periods with varying rates as it encountered different environmental resistance. Analysis of over 900,000 occurrence records shows classic Amara's Law misjudgment: during lag phase, the threat seemed contained; during rapid spread phases, extrapolation suggested unstoppable expansion; during slow phases, observers assumed control measures were working. The reality: spread rate depended on ash tree density, climate suitability, and human-mediated transport, creating alternating periods of rapid and slow expansion. The beetle has killed hundreds of millions of ash trees across North America, with economic damage exceeding $10 billion. What makes the emerald ash borer particularly instructive is the documented failure of early containment efforts—officials consistently underestimated spread during lag phases and overestimated ability to stop spread during exponential phases. The invasion pattern wasn't smooth exponential growth; it was punctuated equilibrium with phase transitions. Observers optimized for linear change couldn't predict sigmoid dynamics. The lag phase prepared the invasion invisibly (population building, adaptation to North American ash species). The exponential phases deployed it explosively (doubling range annually during peak spread). The varying rates revealed constraints invisible during rapid growth (unsuitable climates, geographic barriers).