Fire, thinning, and the carbon economy: Effects of fire and fire surrogate treatments on estimated carbon storage and sequestration rate

Abstract

Changes in estimated standing stocks of carbon (C) in vegetation, forest floor, dead wood, and mineral soil for the fire and fire surrogate (FFS) network sites were evaluated in relation to the application of prescribed fire, mechanical treatments designed as surrogates for prescribed fire, and the combination of mechanical treatment and fire. Pre-treatment C stocks and changes in C stocks over two intervals (pre-treatment to first post-treatment year and first post-treatment to a 2nd, 3rd, or 4th post-treatment year, depending on site) were evaluated using meta-analytical methods. Total C storage across the network averaged 185 ± 8 (standard error) Mg C ha −1, of which 45% was in vegetation, 38% in soil organic matter, 10% in the forest floor and 7% in dead wood. C stored in vegetation was not significantly affected by prescribed fire, but decreased ∼30 Mg ha −1 as the result of mechanical or mechanical + fire treatment; in contrast, forest floor C storage was reduced by ∼1–7 Mg ha −1 by fire or mechanical + fire treatment, but unaffected by mechanical treatment alone. Neither dead wood C nor soil organic C was significantly affected by the treatments. At the network scale, total ecosystem C was not significantly affected by fire, though four individual sites did exhibit significant C losses to fire. Mechanical treatment, with or without fire, produced significant reductions of 16–32 Mg ha −1 during the first post-treatment year, but this was partially balanced by enhanced net C uptake of ∼12 Mg ha −1 during the subsequent 1–3 years. In terms of C storage and uptake, western coniferous forests responded differently to the FFS treatments than did eastern deciduous, coniferous, and mixed forests, suggesting that optimal management for fire, harvesting, and C sequestration may differ between regions.