Healthy conifer
Under mass attack
Dead (brood source)
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Bark beetle outbreaks — the mountain pine beetle epidemics that killed tens of millions of hectares of conifer forest across western North America since the late 1990s — are driven by a specific climate mechanism: cold winters that used to kill most of the overwintering brood are getting rarer, and hot summers are pushing populations from one generation a year to two. This simulation runs a real spatial forest of conifers through repeated annual cycles, applying a logistic cold-hardening survival curve to a beetle population index each winter, switching voltinism (generations per year) once summer temperature crosses the bivoltine threshold, and spreading mass-attacks outward from newly dead "brood" trees to their healthy neighbors — weighted by distance and damped by a tunable tree-defense slider. Watch a forest hold steady at endemic levels, or tip into a spreading red-then-gray die-off, purely from the winter and summer temperature sliders.