Burning the legacy? Influence of wildfire reburn on dead wood dynamics in a temperate conifer forest

Abstract

Abstract Dynamics of dead wood, a key component of forest structure, are not well described for mixed‐severity fire regimes with widely varying fire intervals. A prominent form of such variation is when two stand‐replacing fires occur in rapid succession, commonly termed an early‐seral “reburn.” These events are thought to strongly influence dead wood abundance in a regenerating forest, but this hypothesis has scarcely been tested. We measured dead wood following two overlapping wildfires in conifer‐dominated forests of the Klamath Mountains, Oregon (USA), to assess whether reburning (15‐yr interval, with >90% vegetation mortality) resulted in lower dead wood abundance and altered character relative to once‐burned stands, and how any differences may project through succession. Total dead wood mass (standing + down) following the reburn (169 ± 83 Mg/ha [95%CI]) was 45% lower than after a single fire (309 ± 87 Mg/ha). Lower levels in reburn stands were due to, in roughly equal parts, additional combustion and greater time for decay. Although a single fire in mature forest both consumed and created dead wood (by killing large live trees), a reburn only consumed dead wood (few large live trees to kill). Charred biomass (black carbon generation) was higher in reburned stands by a factor of 2 for logs and 8 for snags. Projecting these stands forward (notwithstanding future disturbances) suggests: (1) the near‐halving of dead‐wood mass in reburn stands will persist for ~50 yr until the recruitment of new material begins, and (2) the reburn signature on dead wood abundance will remain apparent for over a century. These findings demonstrate how a single stochastic variation in disturbance interval can impart lasting influence on dead‐wood succession, reinforcing the notion that many temperate forests exist in a state of dead‐wood disequilibrium governed by site‐specific disturbance history. Accounting for such variation in disturbance impacts is crucial to better understanding forests with complex mixed‐severity disturbance regimes and with increasing stochasticity under climatic change.

Keywords

• biomass
• black carbon
• char
• coarse woody debris
• combustion
• decay