Slash compression treatment reduced tree mortality from prescribed fire in southwestern Ponderosa pine

Intensive thinning prescriptions intended to restore historic,forest structure have produced heavy broadcast slash fuel loads in northwestern Arizona, sometimes leading to high tree mortality,,following prescribed burning. Mechanical slash compression with a D-6 bulldozer to reduce the severity of fire effects on residual trees was evaluated. Ten of 42 measured trees (24%) died within 2 Years after burning of broadcast slash, and crown scorch of trees without slash compression treatment averaged 26%. In contrast, no trees died after burning of compressed slash and crown scorch averaged <3%, even though the total fuel loading was indistinguishable from the broadcast slash treatment. The practice of raking fuels away from the boles of old-growth trees also contributed to reduced scorch as compared to younger, unraked trees. Slash compression is a viable method of reducing mortality, offering ecological and economical tradeoffs. Benefits include the ability to reduce large quantities of slash, safeguarding old-growth tree survival while rapidly achieving open forest structure. Costs include paying for equipment operation as well as the possibility of damage to soils or plants.