What eddy-covariance measurements tell us about prior land flux errors in CO2-flux inversion schemes

0.2 after 200 km). Separating out the plant functional types did not increase the spatial correlations, except for the deciduous broad-leaved forests. Using the statistics of the flux measurements as a proxy for the statistics of the prior flux errors was shown not to be a viable approach. A statistical model allowed us to upscale the site-level flux error statistics to the coarser spatial and temporal resolutions used in regional or global models. This approach allowed us to quantify how aggregation reduces error variances, while increasing correlations. As an example, for a typical inversion of grid point (300 km × 300 km) monthly fluxes, we found that the prior flux error follows an approximate e-folding correlation length of 500 km only, with correlations from one month to the next as large as 0.6

Carbon budget of the Harvard Forest Long- Term Ecological Research site: pattern, process, and response to global change

How, where, and why carbon (C) moves into and out of an ecosystem through time are long- standing questions in biogeochemistry. Here, we bring together hundreds of thousands of C- cycle observations at the Harvard Forest in central Massachusetts, USA, a mid- latitude landscape dominated by 80- 120- yr- old closed- canopy forests. These data answered four questions: (1) where and how much C is presently stored in dominant forest types; (2) what are current rates of C accrual and loss; (3) what biotic and abiotic factors contribute to variability in these rates; and (4) how has climate change affected the forest- s C cycle? Harvard Forest is an active C sink resulting from forest regrowth following land abandonment. Soil and tree biomass comprise nearly equal portions of existing C stocks. Net primary production (NPP) averaged 680- 750 g C·m- 2·yr- 1; belowground NPP contributed 38- 47% of the total, but with large uncertainty. Mineral soil C measured in the same inventory plots in 1992 and 2013 was too heterogeneous to detect change in soil- C pools; however, radiocarbon data suggest a small but persistent sink of 10- 30 g C·m- 2·yr- 1. Net ecosystem production (NEP) in hardwood stands averaged ~300 g C·m- 2·yr- 1. NEP in hemlock- dominated forests averaged ~450 g C·m- 2·yr- 1 until infestation by the hemlock woolly adelgid turned these stands into a net C source. Since 2000, NPP has increased by 26%. For the period 1992- 2015, NEP increased 93%. The increase in mean annual temperature and growing season length alone accounted for ~30% of the increase in productivity. Interannual variations in GPP and NEP were also correlated with increases in red oak biomass, forest leaf area, and canopy- scale light- use efficiency. Compared to long- term global change experiments at the Harvard Forest, the C sink in regrowing biomass equaled or exceeded C cycle modifications imposed by soil warming, N saturation, and hemlock removal. Results of this synthesis and comparison to simulation models suggest that forests across the region are likely to accrue C for decades to come but may be disrupted if the frequency or severity of biotic and abiotic disturbances increases.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163495/3/ecm1423_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163495/2/ecm1423-sup-0001-AppendixS1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163495/1/ecm1423.pd

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

Flux de carbone à l'échelle de l'écosystème avant et après scarifiage au sein d'un parterre de coupe en forêt boréale dans l'est du Canada

Les échanges de carbone sous forme de CO2 entre l’atmosphère et un parterre de coupe forestière situé en forêt boréale québécoise, le site HBS00 du réseau de recherche Fluxnet-Canada, ont été étudiés à l’aide de la technique de covariance de turbulences pendant une durée d’un an avant l’application d’un traitement de scarifiage et un an après le traitement. Les émissions de carbone ont augmenté suite au scarifiage, passant de 111 à 175 g m-2 an-1, en raison de la destruction d’une partie de la végétation vivante présente sur le site. Le taux de respiration de l’écosystème a peu varié. Les échanges de carbone étaient aussi influencés par les conditions environnementales. Une analyse des résidus des courbes de réponse à la lumière a démontré qu’avant le scarifiage le contenu en eau du sol était, après la lumière, le facteur ayant le plus d’influence sur les flux de carbone. Suite au scarifiage, le déficit de pression de vapeur était le deuxième plus important facteur.CO2 fluxes between the atmosphere and a recently-harvested site located in Québec’s boreal forest, Fluxnet-Canada Research Network’s HBS00 site, were studied using the eddy covariance technique for one year before application of a scarification treatment and one year after treatment. Carbon emissions were greater after scarification, rising from 111 to 175 g m-2 year-1, because of the destruction of part of the living aboveground vegetation on the site. Ecosystem respiration rates showed little variation between years. Carbon fluxes were also influenced by environmental conditions. Analysis of the residuals of the light response curves indicated that before scarification soil water content was, after light, the factor having the most influence on carbon fluxes. Following scarification, water vapor pressure deficit was the second most important factor

Moving towards carbon neutrality: CO₂ exchange of a black spruce forest ecosystem during the first 10 years of recovery after harvest

Disturbances control the landscape-level C dynamics of boreal forests, but post-disturbance C dynamics are usually poorly quantified. In the current study, we use 10 years of CO2 flux measurements at a boreal black spruce ( Picea mariana (Mill.) B.S.P.) cutover in eastern Canada to estimate time to C neutrality, quantify the relative role of respiration versus photosynthesis during recovery, and determine the agreement between cumulated CO2 fluxes and plot-level changes in C content. The site was a net source of 139 g C·m–2·year–1 2 years post-harvest, dropped further to a source of 173 g C·m–2·year–1 4 years post-harvest, following a scarification treatment, and was nearly C neutral 10 years post-harvest. Gross ecosystem productivity (GEP) increased by 50 g C·m–2·year–1 post-scarification, while ecosystem respiration (ER) increased by only 23 g C·m–2·year–1. The resulting net rate of increase of 27 g C·m–2·year–1 in net ecosystem productivity was driven by changes in increasing leaf area. In fact, vegetation regrowth had a much greater impact on annual fluxes than did interannual variability in climate. Biometric-based measurements of total C losses after harvest were in relatively good agreement with eddy-covariance-based estimates 8 years after the harvest. </jats:p