Theory 115/Forestry & Fire Ecology
Beetles Need Drought Stress
The claim
Bark beetle outbreaks occur when the ratio of drought stress to tree defensive capacity exceeds a threshold, not when beetle populations are high.
01The mechanism
Trees under drought cannot produce resin; beetles succeed where defences fail, so population size matters only after the threshold.
02Predictions
- P1Outbreaks should track the ratio.
- P2Beetle counts alone should mispredict.
03Refutation
Outbreaks tracking beetle counts would remove the defence term.