Patterns of NPP, GPP, respiration, and NEP during boreal forest succession.

摘要

We combined year-round eddy covariance with biometry and biomass harvests along a chronosequence of boreal forest stands that were 1, 6, 15, 23, 40, ~74, and ~154 years old to understand how ecosystem production and carbon stocks change during recovery from stand-replacing crown fire. Live biomass (C_live) was low in the 1- and 6-year-old stands, and increased following a logistic pattern to high levels in the 74- and 154-year-old stands. Carbon stocks in the forest floor (C_{forest floor}) and coarse woody debris (C_CWD) were comparatively high in the 1-year-old stand, reduced in the 6- through 40-year-old stands, and highest in the 74- and 154-year-old stands. Total net primary production (TNPP) was reduced in the 1- and 6-year-old stands, highest in the 23- through 74-year-old stands and somewhat reduced in the 154-year-old stand. The NPP decline at the 154-year-old stand was related to increased autotrophic respiration rather than decreased gross primary production (GPP). Net ecosystem production (NEP), calculated by integrated eddy covariance, indicated the 1- and 6-year-old stands were losing carbon, the 15-year-old stand was gaining a small amount of carbon, the 23- and 74-year-old stands were gaining considerable carbon, and the 40- and 154-year-old stands were gaining modest amounts of carbon. The recovery from fire was rapid; a linear fit through the NEP observations at the 6- and 15-year-old stands indicated the transition from carbon source to sink occurred within 11-12 years. The NEP decline at the 154-year-old stand appears related to increased losses from C_live by tree mortality and possibly from C_{forest floor} by decomposition. Our findings support the idea that NPP, carbon production efficiency (NPP/GPP), NEP, and carbon storage efficiency (NEP/TNPP) all decrease in old boreal stands.Digital Object Identifier http://dx.doi.org/10.1111/j.1365-2486.2010.02274.x