Forest ecosystem respiration estimated from eddy covariance and chamber measurements under high turbulence and substantial tree mortality from bark beetles

Abstract

Eddy covariance nighttime fluxes are uncertain due to potential measurement biases. Many studies report eddy covariance nighttime flux lower than flux from extrapolated chamber measurements, despite corrections for low turbulence. We compared eddy covariance and chamber estimates of ecosystem respiration at the GLEES Ameriflux site over seven growing seasons under high turbulence [summer night mean friction velocity (u*) = 0.7 m s(-1)], during which bark beetles killed or infested 85% of the aboveground respiring biomass. Chamber-based estimates of ecosystem respiration during the growth season, developed from foliage, wood, and soil CO2 efflux measurements, declined 35% after 85% of the forest basal area had been killed or impaired by bark beetles (from 7.1 ± 0.22 μmol m(-2) s(-1) in 2005 to 4.6 ± 0.16 μmol m(-2) s(-1) in 2011). Soil efflux remained at ~3.3 μmol m(-2) s(-1) throughout the mortality, while the loss of live wood and foliage and their respiration drove the decline of the chamber estimate. Eddy covariance estimates of fluxes at night remained constant over the same period, ~3.0 μmol m(-2) s(-1) for both 2005 (intact forest) and 2011 (85% basal area killed or impaired). Eddy covariance fluxes were lower than chamber estimates of ecosystem respiration (60% lower in 2005, and 32% in 2011), but the mean night estimates from the two techniques were correlated within a year (r(2) from 0.18 to 0.60). The difference between the two techniques was not the result of inadequate turbulence, because the results were robust to a u* filter of >0.7 m s(-1). The decline in the average seasonal difference between the two techniques was strongly correlated with overstory leaf area (r(2) = 0.92). The discrepancy between methods of respiration estimation should be resolved to have confidence in ecosystem carbon flux estimates.

Decadal-Scale Reduction in Forest Net Ecosystem Production Following Insect Defoliation Contrasts with Short-Term Impacts of Prescribed Fires

“…Simultaneously, an increase or decrease in detrital pools can occur, and respiration of previously-fixed C can lead to increased R h [27][28][29][30]69]. The initial reduction in R e during defoliation by gypsy moth in 2007 and 2008 at the oak stand is consistent with patterns of reduced R e and soil CO 2 flux reported following mortality by mountain pine beetle in the Rocky Mountains of the western USA [22,31,32,68], and with girdling treatments in a variety of forests (e.g., [67,70,71]). Although we lack long-term measurements of soil respiration, fine root productivity, and changes in O horizon and soil C pools, estimated partitioning of R e following [17,51] indicates that R a was relatively small in magnitude while R h was similar to pre-disturbance values, suggesting that the supply of labile C to fine roots and associated mycorrhizal fungi in the rhizosphere was limited during and immediately following insect defoliation at the oak stand.…”

“…Non-stand-replacing disturbances can initially lead to reduced R e , R a and soil respiration, because reduction in leaf area and canopy photosynthesis results in reduced C supply to fine roots and the rhizosphere [22,32,67,68], and alters the allocation of NSC to storage pools [54,55]. Simultaneously, an increase or decrease in detrital pools can occur, and respiration of previously-fixed C can lead to increased R h [27][28][29][30]69].…”

“…Eddy covariance measurements of NEP from a limited number of eastern forests where tree mortality and increased standing dead and coarse woody debris (CWD) have resulted in increased R h have either reported little effect on R e and NEP was similar to pre-disturbance levels [30], or increased R e and reduced NEP [27]. These results contrast somewhat with a number of studies that have documented little change to R e and reduced soil respiration following infestations of mountain pine beetle (Dendroctonus ponderosae Hopkins) and significant tree mortality in the Rocky Mountains of the western USA [22,31,32], leading to the conclusion that these forests are more resilient to insect damage than previously predicted (e.g., [26,29]). Because few long-term measurements of NEP following non-stand-replacing disturbance in eastern forests exist to evaluate process-based models, considerable uncertainty continues to exist in our ability to accurately predict future C dynamics of forests of the mid-Atlantic region.…”

Climate controls over ecosystem metabolism: insights from a fifteen-year inductive artificial neural network synthesis for a subalpine forest

“…5a). Extrapolations from nighttime respiration to daytime respiration are imperfect (Goulden et al 1996;Speckman et al 2014), and may exclude the effect of light-inhibition on leaf respiration (Wehr et al 2016). That said, high respiration rates in warm temperatures likely contributed to the reversal in the response of NEP daytime to air temperature at high values (Fig.…”

Improving the CO2 storage measurements with a single profile system in a tall-dense-canopy temperate forest

“…Sample size (N), determination coefficient (R 2 ), and 95% confidence interval (CI) are given. nocturnal ecosystem respiration (Lavigne et al, 1997;Speckman et al, 2015) may be reduced if a short time-window for averaging c was used for calculating F s , because of the large positive intercept (1.058 mol m −2 s −1 ) in the leaf-on season and large slope (1.140) in the leaf-off season (Table 3). However, the long-term NEE might be less affected than the gross primary production and ecosystem respiration after flux partitioning (Papale et al, 2006) due to partial offsets of the underestimations of both CO 2 uptake and release.…”