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

Abstract

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.

Differentiating moss from higher plants is critical in studying the carbon cycle of the boreal biome

“…The moss contribution to the NDVI signal is similar to the reported trend, which provides independent validation of the K_NDVI derived from this study. Moreover, the partitioning of GPP between moss and vascular plants by the EC-LUE-2p model matched well with the observations at seven fire chronosequence sites 20 ( Supplementary Fig. 5).…”

“…Boreal forests are relatively open due to narrow tree crowns and low stand density of dominant trees; as a result, moss can substantially contribute to measured satellite signals 19 . This contribution from moss can be illustrated using a chronosequence of seven adjacent sites recovering from fire disturbances 20 . Figure 2 shows the leaf area index (LAI) of the vascular plants measured from the ground at these sites and their NDVI values derived from satellite data.…”

Wildfires in boreal ecosystems: past, present and some emerging trends

“…Weather related to propagation and to fire ignition, surficial deposit-drainage and forest fuel composition influences fire size, intervals and patchiness Hély et al 2010;Madoui et al 2010;Mansuy et al 2010). The long-term perspective from the paleoecological studies presented here show that the boreal forest may experience important changes in fire activity without experiencing major transformation in its vegetation.…”

“…The study by Hély et al (2010) reports on a long-range fire growth model system, the Prescribed Fire Analysis System (PFAS) based upon meteorology, which is used to analyse the effect of landscape composition on fire size in Canadian boreal forests. The authors' results point to the effect of weather on fire propagation as the most important factor influencing fire size, followed by forest fuel composition and, to a lesser extent, by weather conditions directly related to fire ignition.…”

“…through moisture availability and lengthening of the growing season) can be altered by a second-order impact via changes in the age class distribution of forest landscapes that results directly from changes in fire activity (e.g. Kurz et al 2008;Goulden et al 2010). Better predictions of future fire activity at mid-term timescales can contribute to better long-term forest planning in managed boreal forests and better estimation of future carbon balances.…”