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347 results for “forest carbon”
Carbon Budget at the Harvard Forest 1992-2015
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-year-old closed-canopy forests. These data answered four questions: (i) where and how much C is presently stored in dominant forest types; (ii) what are current rates of C accrual or loss; (iii) what biotic and abiotic factors contribute to variability in these rates; and (iv) is climate change affecting 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 750–970 g C m-2 yr-1; belowground NPP contributed 30–60% of the total. Mineral soil C measured in the same inventory plots in 1992 and 2013 were 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 prior to infestation by the hemlock woolly adelgid (HWA) in 2013, and then became a net C source. Stand dynamics and climate change in the last three decades enhanced the C sink in hardwood stands; NPP increased 26% between 2000–2014 (p = 0.02) and NEP increased 93% between 1992–2015 (p = 0.13). 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. Median forest biomass in the surrounding ecoregion was only 78% of that at the Harvard Forest due to higher timber harvesting rates across the region. Results of this synthesis and comparison to simulation models suggest that forests across the reg
Net Carbon Exchange of an Old-Growth Hemlock Forest at Harvard Forest HEM Tower since 2000
This project estimates carbon exchange rates of multiple forest types at Harvard Forest (see HF072) and compares them to long-term ongoing carbon exchange measurements at the EMS, which is located in a mesic, 60-90 year old red oak and red maple dominated forest on abandoned farmland (HF004). Measurements in each forest type are used to investigate climatic influences on carbon exchange. This mesic hemlock-dominated forest with most trees 100-200 years old on undisturbed soils stored only about 3 Mg/ha of carbon in 2001, compared to over 4 Mg/ha in the 60-90 year old oak/maple stand. However, both sites stored more carbon in 2001 than was measured in the oak/maple stand in any previous year since 1991 (see HF004). The hemlock forest behaved very differently from the oak-maple stand in that the highest rates of carbon storage occurred in spring, while there was very little carbon storage in mid to late summer. Statistical models of carbon exchange in the hemlock forest showed that carbon storage was positively related to daily minimum air temperature in spring, but negatively correlated with soil temperature in the summer. The first effect was attributable to a positive influence of above-freezing minimum temperatures on photosynthesis by hemlock foliage. The negative relationship of soil temperature to carbon storage by hemlock forest in summer was due to exponentially increasing soil and ecosystem respiration, accompanied by a neutral or negative effect of high air temperature on photosynthesis by hemlock trees (see HF063). These effects indicate that carbon storage in the hemlock forest could be strongly affected by climate warming, but the effects will probably be in opposite directions in spring and summer.
Long-Term Impacts of the Hemlock Woolly Adelgid on Forest Carbon at Harvard Forest 2008-2011
The abundance of eastern hemlock (Tsuga canadensis) in eastern US forests has declined since the 1950s owing to the introduction of the non-native insect, hemlock woolly adelgid (HWA, Adelges tsugae). In southern New England, eastern hemlock is being replaced by the deciduous tree species, black birch (Betula lenta). To date there is little understanding of whether hemlock loss will fundamentally alter ecosystem C balance and component fluxes. In this study, we use a comparative approach to study potential changes in C fluxes and storage and N cycling associated with HWA-induced hemlock decline and replacement. The stands include primary- and secondary-growth hemlock forests (230 and 132 years old, respectively), recently disturbed stands (5 and 18 years old) that now have rapidly growing black birch saplings, and a mature black birch stand of age similar to the second-growth hemlock stand. We addressed the question of whether the quantity and distribution of C pools in black birch forests are the same as those found in the hemlock stands they replace and, if so, over what time scales. We found that if HWA did not infest hemlock stands in central MA, C stocks in these secondary stands could still increase by at least 30% over a period of 100 years. Girdling, intended to simulate HWA infestation, resulted in a large transfer of C from live biomass to coarse woody debris five years after treatment, but had little effect on total ecosystem C content. A former hemlock stand killed by HWA and now dominated by black birch saplings also had a large pool of highly decayed CWD and a rapidly aggrading C pool in live biomass. C pools in biomass in a mature, secondary growth black birch stand 135 years since pastureland abandonment were as large as those in a primary-growth hemlock stand 235 years of age. We also found that aboveground net primary production was higher in the aggrading black birch stand and significantly so at 18-years post-HWA compared to the secondary-hemlock
Impacts of Deer and Moose on Soil Carbon, Soil Respiration, and Root Biomass at Harvard Forest since 2017
Over the past decade, several deer and moose exclosures have been built at Harvard Forest to study the effect of ungulate browsing on tree regeneration, species diversity, and composition. We built on the existing infrastructure to study the impacts of deer and moose browsing on soil carbon stocks (soil C, root biomass) in regenerating forests.
Soil Carbon and Nitrogen at the Harvard Farm at Harvard Forest since 2015
These data represent baseline soil bulk density and total soil carbon and nitrogen concentrations for the three grazing treatments at Harvard Farm: hay (no grazing), rotational grazing, and intensive grazing. These samples were collected at the beginning of the study, so any differences across plots or treatments are due to inherent soil variability at the site rather than the treatments themselves. These data were collected to establish the starting conditions with which to compare potential treatment effects at later sampling dates.
Effects of Forest Fragmentation on Carbon Sequestration and Respiration at Harvard Forest since 2016
Forest loss/fragmentation can have profound impacts on the terrestrial carbon (C) cycle by reducing forest uptake of carbon dioxide (CO2; the primary driver of anthropogenic climate change) through photosynthesis and C storage in forest biomass. Relative to intact rural forests, trees growing in forest fragments within developed landscapes typically experience conditions that can enhance growth such as warmer and longer growing seasons (i.e. urban heat island effect) and greater light and nutrient availability (e.g., nitrogen deposition) as well as conditions that can hinder growth such as increased exposure to damaging pollutants such as ozone and higher rates of disturbance. Our research quantifies the impact of fragmentation on C uptake and respiration near forest edges. In 2016 six 600‐m2 plots were installed along forest edges at the HF, measuring 20 m along the forest edge and extending 30 m into the forest perpendicular to the forest edge. Plot biomass was mapped and tree cores were taken in all trees >10cm diameter. The plots were installed at multiple edge aspects and adjacent land cover types (three meadows, two pastures, and one road). Within each plot, a pair of polyvinyl chloride soil respiration collars 20 cm in diameter × 7 cm tall and located 10 m apart was inserted approximately 2 cm into the soil at four distances from the edge (0, 10, 20, and 30m). Each plot had n = 8 collars for a total of n = 48 collars. Following installation, collars were left in the soil for at least 2 weeks to equilibrate. Air temperature, relative humidity, soil temperature, and soil moisture were logged along the center plot transect.
Nonstructural Carbon, Phenology and Wood Formation in Three Tree Species at Harvard Forest 2017-2019
This data set comprises various observations and measurements across the 2017 to 2019 growing season for seven red maple (Acer rubrum), eight red oak (Quercus rubra), and six white pine (Pinus strobus) in the Prospect Hill Tract of Harvard Forest. The observations include spring and fall leaf phenology and basic allometry, such as diameter at breast height and height. For the leaf phenology, we followed the protocol from John O’Keefe (HF003). Measurements include wood growth data from weekly microcores and a three time characterisation of growing season nonstructural carbon concentrations (soluble sugars and starch) for stems and leaves. Additionally, stem CO2 efflux was measured once a month for the 2018 growing season and weekly for the 2019 growing season.
Effects of Soil Warming and Substrate Complexity on Microbial Carbon Use Efficiency at Harvard Forest 2017
Soil microbial carbon use efficiency (CUE) is a combination of growth and respiration, which may respond differently to climate change depending on physical protection of soil carbon (C) and its availability to microbes. In a mid-latitude hardwood forest in central Massachusetts, 27 years of soil warming (+5 ◦C) has resulted in C loss and altered soil organic matter (SOM) quality, yet the underlying mechanisms remain unclear. Here, we hypothesized that long-term warming reduces physical aggregate protection of SOM, microbial CUE, and its temperature sensitivity. Soil was separated into macroaggregate (250–2000 μm) and microaggregate (less than 250 μm) fractions, and CUE was measured with 18O-enriched water in samples incubated at 15 and 25 ◦C for 24 h. We found that long-term warming reduced soil C and nitrogen concentrations and extracellular enzyme activity in macroaggregates, but did not affect physical protection of SOM. Long-term warming showed little effect on CUE or microbial biomass turnover time because it reduced both growth and respiration. However, CUE was less temperature sensitive in macroaggregates from the warmed compared to the control plots. Our findings suggest that microbial thermal responses to long-term warming occur mostly in soil compartments where SOM is less physically protected and thus more vulnerable to microbial degradation.
Canopy-Atmosphere Exchange of Carbon, Water and Energy at Harvard Forest EMS Tower since 1991
The tower-based CO2 measurements and key meteorological drivers are intended to examine how regional and ecosystem level processes in a mid-latitude forest contribute to global carbon cycling. Specifically, we endeavor to understand quantitatively how and why forested ecosystems take up or release carbon, on time scales from hours to decades, and to elucidate responses to climate changes and management interventions. The tower was installed 1989 and the resulting eddy-flux measurements constitute the longest running record of the net-ecosystem carbon exchange in a North American Forest. The resulting long-term record of Net Ecosystem Exchange (NEE) has shown the effects of climate anomalies on carbon fluxes for seasonal and annual time scales. For example, reduced soil frost allows greater respiration in the winter leading to lower C sequestration. Cumulative gross photosynthesis depends on when the canopy emerges in the spring. Warmer springtime temperatures lead to greater uptake of C. As the NEE record is extended and augmented by supporting ecological measurements, we can further identify longer-term effects of climate perturbations on carbon fluxes and further define the relationship between stand history and carbon sequestration. Climatic anomalies in one season or year may have a longer-term effect on the sequestration of carbon in subsequent seasons or years. The flux and ecological measurements are coordinated with studies at other sites through the AmeriFlux network. By examining the relationships between carbon fluxes and the driving physical and biological variables across a range of sites we are enhancing understanding of the processes that control NEE.
Carbon Biogeochemistry of Forested Headwater Streams at Harvard Forest 2006-2007
Headwater streams make up greater than 80% of total channel length in the United States and play important roles in regulating nutrient, organic matter, and sediment fluxes from terrestrial to downstream ecosystems. Headwater streams are common features of many upland-forested watersheds in New England, yet are not explicitly factored into forest water, carbon, and nutrient budgets. Here we report on recent efforts to examine terrestrial and stream ecosystem linkages in carbon biogeochemistry in a hemlock-dominated watershed. A prototype stream biogeochemical system (SBS) was tested at the Harvard Forest LTER. The SBS allows a suite of stream water properties to be characterized in real-time over extended periods of time thus allowing questions to be asked at a wide range of time scales. The prototype SBS was field-tested in Bigelow Brook West on the Prospect Hill research tract at Harvard Forest. Bigelow Brook West was selected because the watershed’s hydrology, stream ecology, forest composition, land-use history, and carbon sequestration have been characterized, thus aiding the interpretation of SBS data and facilitating multi-disciplinary research. The prototype system monitors stream and air temperature, pCO2 , colored dissolved organic matter, total suspended sediments, PAR, water depth, pH, and dissolved O2. Independent estimates of organic and inorganic water chemistry were used to validate and interpret SBS data. Here we report on preliminary findings from the pilot SBS at Harvard Forest to highlight the usefulness of headwater stream chemistry data to a wide-diversity of ecosystem scientists. 1) Low pH constrains dissolved inorganic carbon solute fluxes to downstream ecosystems. 2) CO2 concentrations were always supersaturated in Bigelow Brook, averaging about 6x atmospheric values in summer, thus the stream is an important source of CO2 to the atmosphere. Variation in CO2 appears to be linked to multiple mechanisms including changes in stream temperature,
Belowground Carbon Observatory Network (BeCON) at Harvard Forest since 2020
A central goal of the recent Harvard Forest C Synthesis activity was to identify high-priority needs for C-cycle research at the forest. While there were a number of areas needing follow-up research, belowground C pools and fluxes remain the single largest gap in the C budget and therefore our understanding of the C cycle of the forest. To this end, we developed the Belowground Carbon Observatory Network (BeCON) as a part of the LTER-VI grant proposal. The long-term goal of BeCON is to understand temporal and spatial variations in belowground C pools in response to the various environmental changes the forest now faces [e.g., rising CO2, changes in atmospheric N, S and O3 chemistry, invading insects, land-use change, immigrating (large) herbivores]. There are two great challenges in achieving this goal: (1) excessive spatial heterogeneity in belowground C pools; and (2) lack of automated systems for analysis. These characteristics make it very difficult to quantify changes because the work is intrinsically labor intensive with low replication and the noisy data lead to low statistical power. Here, we measured soil carbon content, root biomass and carbon content, and annual root productivity following the protocols for BeCON.
Carbon Cycle Dynamics in Soil Warming Experiments at Harvard Forest 2019
Microbes are responsible for cycling carbon (C) through soils, and predicted changes in soil C stocks under climate change are highly sensitive to shifts in the mechanisms assumed to control the microbial physiological response to warming. Two mechanisms have been suggested to explain the long-term warming impact on microbial physiology: microbial thermal acclimation and changes in the quantity and quality of substrates available for microbial metabolism. Yet studies disentangling these two mechanisms are lacking. To resolve the drivers of changes in microbial physiology in response to long-term warming, we sampled soils from 13- and 28-year-old soil warming experiments in different seasons. We performed short-term laboratory incubations across a range of temperatures to measure the relationships between temperature sensitivity of physiology (growth, respiration, carbon use efficiency, and extracellular enzyme activity) and the chemical composition of soil organic matter. We observed apparent thermal acclimation of microbial respiration, but only in summer, when warming had exacerbated the seasonally-induced, already small dissolved organic matter pools. Irrespective of warming, greater quantity and quality of soil carbon increased the extracellular enzymatic pool and its temperature sensitivity. We propose that fresh litter input into the system seasonally cancels apparent thermal acclimation of C-cycling processes to decadal warming. Our findings reveal that long-term warming has indirectly affected microbial physiology via reduced C availability in this system, implying that earth system models including these negative feedbacks may be best suited to describe long-term warming effects on these soils.
Column-Averaged Atmospheric Carbon and Water at Harvard Forest since 2018
Ground-based total-atmospheric column measurements of CO2, CH4, CO, and H2O began at Harvard Forest in May 2018 using a solar-viewing Fourier Transform Spectrometer (Bruker EM27/Sun). Observations are made from a platform near the Fisher Meteorological Tower throughout the year on sunny days. Total column observations are sensitive to regional carbon fluxes, and are less impacted by changes in the boundary layer height than tower based in-situ observations. The Harvard Forest observations are complemented by an identical instrument operated on the Harvard campus in Cambridge MA. The two sensors are used to support studies of urban emissions, regional transport, and forest-atmosphere exchange. In addition, the total-column measurements provide key validation data for satellite measurements of greenhouse gases.
Net Carbon Exchange of a Young Upper-Slope Deciduous Forest at Harvard Forest LPH Tower 2002-2010
This data set contains sensible heat exchange, water vapor exchange and carbon exchange as well as environmental data for a deciduous forest dominated by red oak (Quercus rubra). It is 1.1 km WNW of the EMS tower where continuous eddy covariance measurements began in 1992 (see HF004). The High Deciduous site is about 385 m a.s.l., or 35 m higher in elevation than the EMS, which is situated in a relatively low area near a stream. The forest near this eddy covariance tower is broadly similar in species composition to the EMS site, but it is younger and shorter in stature. The site was cleared for pasture, but not deeply plowed or planted, in the 18th and19th centuries. Agriculture on the site was abandoned near the end of the 19th century. The forest within 200 to 300 m of the eddy covariance tower to the NW, W, SW, and S burned in an intense fire in 1957, which left few or no surviving trees.
Dataset on tree diversity metrics and aboveground carbon storage in Southeastern U.S. oak-pine forests, 2009–2019
This dataset contains measurements of tree structural and taxonomic diversity, stand attributes, and aboveground carbon storage from mixed oak-pine forests in Florida, Georgia, and Alabama, located in the southeastern United States. Data were collected from 946 mixed oak-pine, and 7224 longleaf-slash pine and oak-pine Forest Inventory and Analysis (FIA) plots respectively spanning the years 2009 to 2019. Variables include aboveground carbon, aboveground biomass, tree density, basal area, stand age, and diversity metrics such as Shannon indices for tree species and diameter-based structural classes. Functional diversity metrics—including functional dominance and functional divergence—are also included. These data were used to support a published study examining the interactive effects of diversity metrics on carbon storage using structural equation modeling. The geographic coverage represents humid subtropical forest regions of the southeastern U.S.
Concentration and Age of Nonstructural Carbon Reserves in Two Trees at Harvard Forest 2012
We know surprisingly little about whole-tree nonstructural carbon (NSC; primarily sugars and starch) budgets. Even less well understood is the mixing between recent photosynthetic assimilates (new NSC) and previously stored reserves. And, NSC turnover times are poorly constrained. We characterized the distribution of NSC in the stemwood, branches, and roots of two temperate trees, and we used the continuous label offered by the radiocarbon (14C) bomb spike to estimate the mean age of NSC in different tissues. NSC in branches and outermost stemwood growth rings had the 14C signature of the current growing season. However, NSC in older above- and below-ground tissues was enriched in 14C, indicating that it was produced from older assimilates. Radial patterns of 14C in stemwood NSC showed strong mixing of NSC across the youngest growth rings, with limited.
Estimating Forest Productivity Using Carbon Isotopes in Tree Rings at Harvard Forest 1992-2010
We investigated relationships between tree-ring δ13C and growth, and flux tower estimates of gross primary productivity (GPP) at Harvard Forest from 1992 to 2010. Seasonal variations of derived photosynthetic isotope discrimination (Δ13C) and leaf intercellular CO2 concentration (ci) showed significant increasing trends for the dominant deciduous and coniferous species. Δ13C was positively correlated to growing-season GPP and is primarily controlled by precipitation and soil moisture indicating that site conditions maintained high stomatal conductance under increasing atmospheric CO2 levels. Increasing Δ13C over the 1992-2010 period is attributed to increasing annual and summer water availability identified at Harvard Forest and across the region. Higher Δ13C is coincident with an enhancement in growth and ecosystem-level net carbon uptake. This work suggests that tree-ring δ13C could serve as a measure of forest GPP and be used to improve the calibration and predictive skill of ecosystem and carbon cycle models.
Phenology and Carbon Allocation of Roots at Harvard Forest 2011-2013
The objective of this study is to estimate the phenology and partitioning of C allocated belowground across the growing season at Harvard Forest in two hardwood stands dominated by Quercus rubra and Fraxinus americana, respectively, and one conifer stand dominated by Tsuga canadensis. The phenology of fine root production was characterized by multiple flushes of growth and mortality, especially in the red oak (Q. rubra) stand. Root exudation rate did not have a clear seasonal signal. The deciduous hardwood stands allocated C belowground earlier in the season compared to the conifer-dominated stand. Deciduous stands also allocated a greater proportion of total belowground C flux (TBCF) to root growth compared to the conifer-dominated hemlock (T. canadensis) stand. Of the three stands, red oak partitioned the greatest proportion of TBCF (~50%) to root growth, while hemlock partitioned the least.
Soil Carbon in a Hemlock Stand Infected by Hemlock Woolly Adelgid at Harvard Forest since 2015
The main objective of this research is to study changes in soil carbon stocks (soil C, root biomass) and fluxes (soil respiration) in a hemlock stand that is currently infested by the hemlock woolly adelgid, and where trees are declining in vigor and dying off. Soil respiration is measured throughout the growing season using an automated system, which produces a long-term, high-temporal-resolution series of soil respiration over multiple locations. Soil carbon stocks and root biomass are estimated by sampling soil in multiple locations throughout the hemlock stand following the sampling design used by Serita Frey at Harvard Farm (“Conant plots”). The large number of samples will be used to determine how many should be resampled in the future to be able to determine if any difference in soil C content or root biomass is statistically significant. Soil and roots will be sampled every 5 to 10 years to evaluate the trends in soil carbon stocks during and after the decline of hemlock caused by the hemlock woolly adelgid infestation.
Atmospheric Oxygen and Carbon Dioxide at Harvard Forest EMS Tower since 2006
This archive features long-term measurements of the atmospheric mixing ratios of O2 and CO2 at two heights on the Harvard Forest EMS flux tower. The data fields include the time of data collection, the height from which the samples were drawn, the O2 mixing ratio and the CO2 mixing ratio.
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Allen Brain Atlas
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International Brain Laboratory public data
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OpenNeuro
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