Annual Carbon Loss Research Articles

Respiration of downed logs in an old-growth temperate forest in north-eastern China

Carbon dioxide (CO2) flux from coarse woody debris is an important source of carbon emission in forests with large amounts of coarse woody debris (CWD). Respiration from downed logs of Korean pine (Pinus koraiensis Sieb. et Zucc.) and Amur linden (Tilia amurensis Rupr.) and their response to meteorological factors were investigated using the closed static chamber–gas chromatography technique in an old-growth temperate forest in Changbai Mountain region, north-eastern China. On a yearly timescale, daily respiration rates (R log) varied over two orders of magnitude (8.7–252.3 mg Ckg−1), and were significantly correlated with wood water content and temperature (p<0.05). The temperature-dependent empirical exponential models for each decay class explained more than 67% of the observed variations in R log. More decayed wood had a greater water content and pore space than less decayed wood, and these differences were probably responsible for the observed difference in respiration rate among decay classes. The annual carbon loss rate due to respiration was estimated to be 28.0±3.7 g Cm−2, which contributed only about 3% of total carbon loss from forest floor, but net carbon flux from downed logs accounted for up to 15% of net ecosystem exchange in this old temperate forest. Downed logs represent a small, but substantial carbon flux that is expected to increase over the next several decades in old-growth forest.

Effects of seasonal drought on net carbon dioxide exchange from a woody‐plant‐encroached semiarid grassland

Annual precipitation in the central and southern warm‐desert region of North America is distributed climatologically between summer and winter periods with two prominent dry periods between them. We used energy and carbon dioxide (CO2) fluxes from eddy covariance along with standard meteorological and soil moisture measurements at a semiarid savanna in southern Arizona, United States, to better understand the consequences of warm or cool season drought on ecosystem CO2 exchange in these bimodally forced water‐limited regions. Over the last 100 years, this historic grassland has converted to a savanna by the encroachment of the native mesquite tree (Prosopis velutina Woot.). During each of the 4 years of observation (2004–2007), annual precipitation (P) was below average, but monsoon (July–September) P was both above and below average while cool‐season (December–March) P was always less than average by varying degrees. The ecosystem was a net source of CO2 to the atmosphere, ranging from 14 to 95 g C m−2 yr−1 with the strength of the source increasing with decreasing precipitation. When the rainfall was closest to the long‐term average in its distribution and amount, the ecosystem was essentially carbon neutral. Summer drought resulted in increased carbon losses due mainly to a shortening of the growing season and the length of time later in the season when photosynthetic gain exceeds respiration loss. Severe cool season drought led to decreased spring carbon uptake and seemingly enhanced summer respiration, resulting in conditions that led to the greatest annual net carbon loss.

Photochemically induced carbon dioxide production as a mechanism for carbon loss from plant litter in arid ecosystems

We investigated the potential for abiotic mineralization to carbon dioxide (CO2) via photodegradation to account for carbon (C) loss from plant litter under conditions typical of arid ecosystems. We exposed five species of grass and oak litter collected from arid and mesic sites to a factorial design of ultraviolet (UV) radiation (UV pass, UV block), and sterilization under dry conditions in the laboratory. UV pass treatments produced 10 times the amount of CO2 produced in UV block treatments. CO2 production rates were unaffected by litter chemistry or sterilization. We also exposed litter to natural solar radiation outdoors on clear, sunny days close to the summer solstice at midlatitudes and found that UV radiation (280–400 nm) accounted for 55% of photochemically induced CO2 production, while shortwave visible radiation (400–500 nm) accounted for 45% of CO2 production. Rates of photochemically induced CO2 production on a per‐unit‐mass basis decreased with litter density, indicating that rates depend on litter surface area. We found no evidence for leaching, methane production, or facilitation of microbial decomposition as alternative mechanisms for significant photochemically induced C loss from litter. We conclude that abiotic mineralization to CO2 is the primary mechanism by which C is lost from litter during photodegradation. We estimate that CO2 production via photodegradation could be between 1 and 4 g C m−2 a−1 in arid ecosystems in the southwestern United States. Taken together with low levels of litter production in arid systems, photochemical mineralization to CO2 could account for a significant proportion of annual carbon loss from litter in arid ecosystems.

Impact of past and present land‐management on the C‐balance of a grassland in the Swiss Alps

AbstractGrasslands cover about 40% of the ice‐free global terrestrial surface, but their quantitative importance in global carbon exchange with the atmosphere is still highly uncertain, and thus their potential for carbon sequestration remains speculative. Here, we report on CO2 exchange of an extensively used mountain hay meadow and pasture in the Swiss pre‐Alps on high‐organic soils (7–45% C by mass) over a 3‐year period (18 May 2002–20 September 2005), including the European summer 2003 heat‐wave period. During all 3 years, the ecosystem was a net source of CO2 (116–256 g C m−2 yr−1). Harvests and grazing cows (mostly via C export in milk) further increased these C losses, which were estimated at 355 g C m−2 yr−1 during 2003 (95% confidence interval 257–454 g C m−2 yr−1). Although annual carbon losses varied considerably among years, the CO2 budget during summer 2003 was not very different from the other two summers. However, and much more importantly, the winter that followed the warm summer of 2003 observed a significantly higher carbon loss when there was snow (133±6 g C m−2) than under comparable conditions during the other two winters (73±5 and 70±4 g C m−2, respectively). The continued annual C losses can most likely be attributed to the long‐term effects of drainage and peat exploitation that began 119 years ago, with the last significant drainage activities during the Second World War around 1940. The most realistic estimate based on depth profiles of ash content after combustion suggests that there is an 500–910 g C m−2 yr−1 loss associated with the decomposition of organic matter. Our results clearly suggest that putting efforts into preserving still existing carbon stocks may be more successful than attempts to increase sequestration rates in such high‐organic mountain grassland soils.

Public land, timber harvests, and climate mitigation: Quantifying carbon sequestration potential on U.S. public timberlands

Scientists and policy makers have long recognized the role that forests can play in countering the atmospheric buildup of carbon dioxide (CO 2), a greenhouse gas (GHG). In the United States, terrestrial carbon sequestration in private and public forests offsets approximately 11% of all GHG emissions from all sectors of the economy on an annual basis. Although much of the attention on forest carbon sequestration strategy in the United States has been on the role of private lands, public forests in the United States represent approximately 20% of the U.S. timberland area and also hold a significantly large share (30%) of the U.S. timber volume. With such a large standing timber inventory, these forested lands have considerable impact on the U.S. forest carbon balance. To help decision makers understand the carbon implications of potential changes in public timberland management, we compared a baseline timber harvest scenario with two alternative harvest scenarios and estimated annual carbon stock changes associated with each. Our analysis found that a “no timber harvest” scenario eliminating harvests on public lands would result in an annual increase of 17–29 million metric tonnes of carbon (MMTC) per year between 2010 and 2050—as much as a 43% increase over current sequestration levels on public timberlands and would offset up to 1.5% of total U.S. GHG emissions. In contrast, moving to a more intense harvesting policy similar to that which prevailed in the 1980s may result in annual carbon losses of 27–35 MMTC per year between 2010 and 2050. These losses would represent a significant decline (50–80%) in anticipated carbon sequestration associated with the existing timber harvest policies. If carbon sequestration were valued in the marketplace as part of a GHG offset program, the economic value of sequestered carbon on public lands could be substantial relative to timber harvest revenues.

Carbon balance in the soils of abandoned lands in Moscow region

A quantitative assessment of the carbon balance was performed in gray forest soils of the former agricultural lands abandoned in different time periods in the southern part of Moscow oblast. It was based on the field measurements of the total and heterotrophic soil respiration and the productivity of biocenoses. Geobotanical investigations demonstrated that the transformation of the species composition of herbs from weeds to predominantly meadow plants occurred in five–ten years after the soil was no more used for farming. The amount of carbon assimilated in the NPP changed from 97 g C/m2 year in the recently abandoned field to 1103 g C/m2 year in the 10-year-old fallow, and the total annual loss of carbon from the soil in the form of CO2 varied from 347 to 845 g C/m2 year. In five years, the former arable lands were transformed into meadow ecosystems that functioned as a stable sink of carbon in the phytomass and the soil organic matter.

Year-round soil and ecosystem respiration in a temperate broad-leaved Korean Pine forest

As part of ChinaFlux program, forest soil and ecosystem respiration were measured using two sets of eddy covariance systems in a 300-year-old mixed forest in northeast China in 2003, and soil respiration was also measured in situ by chamber method. The forest showed a clear old-age effect, i.e. high assimilation and respiration rates. The estimates of annual gross carbon gain and loss at the forest were 1511 and 1327 gC m −2. The annual soil respiration was 1017 gC m −2, which accounted for 76% of the total ecosystem respiration. The forest showed a reasonable positive carbon uptake during growing season, but even during the coldest winter month, it still acted as a sink for a few hours around noon. The annual net carbon sequestration was 184.4 gC m −2. Close relations were found between 5 cm depth soil temperature and soil respiration, as well as ecosystem respiration, both can be well explained by first-order exponential equations. A more reasonable method to calculate Q 10 values of soil based on weighted mean respiratory contribution rates of temperature in each layer was suggested. There was moderate correlation between soil respiration rates and volumetric soil water content. Very dry or very wet soil generally depressed the soil respiration. However, when soil temperature increased, the wet forest soil ( W s > 0.35 m 3 m −3) had greater respiratory potential. When the atmosphere was regularly mixed by turbulence, soil respiration measured by EC was in good agreement with the chamber data. On a daily basis, the soil respiration data obtained from below-canopy EC system is quite acceptable.

Decline in the Primary Productivity of Northwestern European Forests as a Consequence of Climate Aridization

Average annual age-dependent changes of carbon accumulation in the stemwood of major forest species (pine, spruce, and birch) of the taiga zone of the northwestern European Russia (Karelia) were analyzed. The changes in carbon accumulation were assessed by comparing carbon reserves in tree stands of various ages. Net primary productivity of photosynthesis (NPP) and the proportionality coefficient between respiratory decarboxylation and carbon reserves in wood were calculated. NPP clearly decreased with increasing climate aridization (aridity index). However, the time of the attainment of climax state by a stand did not depend on the latitudinal climate gradient. Hence, only the size of heterotrophic part of phytomass determines annual carbon losses in northern-taiga stands. It is concluded that the climate dependency of the long-term carbon storage in the phytomass of boreal forests is mainly determined by the climate effect on photosynthetic carbon sequestration.

Intensive management modifies soil CO 2 efflux in 6-year-old Pinus taeda L. stands

Intensive forestry may reduce net CO 2 emission into atmosphere by storing carbon in living biomass, dead organic matter and soil, and durable wood products. Because quantification of belowground carbon dynamics is important for reliable estimation of the carbon sequestered by intensively managed plantations, we examined soil CO 2 efflux ( S C O 2 ) in a 6-year-old loblolly pine ( Pinus taeda L.) plantation in response to weed control (W), weed control plus irrigation (WI), weed control plus irrigation and fertigation (addition of fertilizer to the irrigation water) (WIF), and weed control plus irrigation, fertigation and pest control (WIFP) since plantation establishment. Average S C O 2 ranged from 1.27 to 5.59 μmol m −2 s −1, and linear models indicated that soil temperature explained up to 56% of the variation in S C O 2 . Plot position explained an additional 2–11% of the variation in S C O 2 . Soil moisture was only weakly correlated with S C O 2 in the W treatment, and S C O 2 was not significantly correlated to fine root mass. Predicted carbon loss from forest floor respiration ranged between 778 and 966 g C m −2 year −1 and was 20% lower in the WIF treatment relative to the W treatment. Annual soil carbon loss through soil respiration declined linearly with increasing carbon content in total root biomass (tap + coarse + fine) at age 6.

The annual carbon budget of a French pine forest (Pinus pinaster) following harvest

AbstractEddy covariance measurements of net ecosystem exchange (NEE) of carbon dioxide and sensible and latent heat have operated since clear felling of a 50‐year old maritime pine stand in Les Landes, in Southwestern France. Turbulent fluxes from the closed‐path system are computed via different methodologies, including those recommended from EUROFLUX (Adv. Ecol. Res. 30 (2000) 113; Agric. Forest Meteorol. 107 (2001a, b) 43 and 71), and sensitivity analysis demonstrates the merit of post‐processing for accurate flux calculation. Footprint modeling, energy balance closure, and empirical modeling corroborate the eddy flux measurements, indicating best reliability in the daytime.The ecosystem, a net source of atmospheric CO2, is capable of fixing carbon during fair weather during any season due to the abundance of re‐growing species (mostly grass), formerly from the understorey. Annual carbon loss of 200–340 g m−2 depends on the period chosen, with inter‐annual variability evident during the 18‐month measurement period and apparently related to available light. Empirical models, with weekly photosynthetic parameters corresponding to seasonal vegetation and respiration depending on soil temperature, fit the data well and allow partitioning of annual NEE into GPP and TER components. Comparison with a similar nearby mature forest (Agric. Forest Meteorol. 108 (2001) 183) indicates that clear‐cutting reduces GPP by two thirds but TER by only one third, transforming a strong forest sink into a source of CO2. Likewise, the loss of 50% of evapotranspiration (by the trees) leads to increased temperatures and thus reduced net radiation (by one third), and a 50% increase in sensible heat loss by the clear cut.

Year-long carbon dioxide exchange above a broadleaf deciduous forest in Sapporo, Northern Japan

This paper reports the results of a full year (2000) of measurements of CO2 flux at a successional forest of mature birch and growing oak with Sasa-bamboo in Sapporo, Japan. Eddy covariance fluxes of CO2 were obtained using a closed-path infrared gas analyzer. Changes in CO2 storage under the eddy-flux measurement level were quantified using vertical profiles of the CO2 concentration. Seasonal variations in net CO2 exchange between the forest and the atmosphere are discussed in terms of both phenological developments of the forest canopy and micrometeorological variables. To estimate the annual exchange of CO2, the net CO2 exchange data both during periods of poor turbulence and during periods of missing data were replaced by simple parametric models based on measurements of soil temperatures and photosynthetically active radiation. The corrected annual carbon sequestration estimate was 260 g C m−2. The estimates of annual gross carbon gain and loss at the forest were 1120 and 860 g C m−2.

Isoprene emission inventory for the BOREAS southern study area.

An isoprene emission inventory for a section of boreal forest in central Saskatchewan was developed based on measured emission rates from the two dominant isoprene-emitting species, black spruce (Picea mariana (Mill.) BSP) and aspen (Populus tremuloides Michx.). The micrometeorological gradient technique was used to determine isoprene emission factors for establishing the inventory. Isoprene fluxes were measured during each of the three BOREAS intensive field campaigns (IFCs) during the 1994 growing season. Measured isoprene fluxes varied from 0.04 to 3.3 mg C m(-2) h(-1) over the black spruce canopy, and from 0.05 to 7.3 mg C m(-2) h(-1) above the aspen forest. Midsummer standard isoprene emission fluxes were 1.2 mg C m(-2) h(-1) and 2.3 mg C m(-2) h(-1) (at 20 degrees C and photosynthetically active radiation (PAR) of 1000 &mgr;mol m(-2) s(-1)) for black spruce and aspen, respectively. With light and temperature differences accounted for, there was an apparent seasonal effect on emissions with the highest rates in the summer months. The total amount of isoprene emitted from this section of the boreal forest was estimated to be 8.6 Gg C year(-1), which is about 1% of the net ecosystem carbon exchange for the study area. Aspen was the largest contributor, accounting for approximately 70% of the total. Branch enclosure and relaxed eddy accumulation measurements made at the black spruce site were used to define the uncertainty associated with flux measurements. Emission rates obtained by the gradient, enclosure and relaxed eddy accumulation methods showed good agreement when normalized to standard light and temperature conditions. The coefficient of variance between the three techniques was 12% for summer (IFC-2) measurements. The sensitivity of the annual isoprene emission total to the assignment of mean irradiance and temperature was also examined. If the hourly mean temperatures were increased by 1 degrees C throughout the growing season, annual carbon loss due to isoprene emission would increase by 14% from 8.6 to 9.8 Gg C.

SOIL CARBON DIFFERENCES AMONG FOREST, AGRICULTURE, AND SECONDARY VEGETATION IN LOWER MONTANE ECUADOR

In the lower montane region of northwestern Ecuador, forest clearing for sugar cane and pasture production occurs simultaneously with recolonization of secondary forest vegetation on abandoned agricultural lands. We estimated the loss of forest-derived soil C (light in 13C) and the accumulation of C from replicate sugar cane and pasture vegetation (heavy in 13C) using a stable C isotope technique. We also measured differences in the proportion of soil C derived from C3 and C4 plants across a land-use progression from agricultural fields through successional communities and undisturbed forest. Total soil C was 23 Mg/ha lower in the upper 30 cm following 50 yr of sugar cane production (24% decrease) compared to old-growth forest. The net change (−0.4 Mg·ha−1·yr−1) in soil C consisted of 1.3 Mg/ha annual losses of original forest C and 0.9 Mg/ha annual gains of C from sugar cane. After 15 yr beneath pasture, soil C was 11 Mg/ha less in the upper 30 cm than beneath forest (12% decrease). During that period, 33% of the original forest C was lost, compared to 68% released during 50 yr of sugar cane cultivation. Rate of forest C loss, C4-C accumulation, and net soil C change differed little between two distinct pasture types. Setaria sphacelata pasture and a traditional mixed-species pasture both contained more total soil C and added C4-C more rapidly than sugar cane. Under second-growth forest, soil C increased by 1.9 Mg·ha−1·yr−1, the result of a 3 Mg/ha annual increase in C3 carbon and a 1.1 Mg/ha annual loss of C4 carbon. The total soil C pool returned to preclearing levels within 20 yr. While widespread reforestation may be thwarted by high demands for land in northwestern Ecuador, agricultural land-use options exist that can contribute to increased soil C stocks.

Wintertime CO2 efflux from Arctic soils: Implications for annual carbon budgets

Estimates of annual carbon loss from arctic tundra ecosystems are based nearly entirely on measurements taken during the growing season in part because of methodological limitations but also reflecting the assumption that respiration during winter is near zero. Measurements of CO2 flux during winter, however, indicate significant amounts of carbon loss from tundra ecosystems throughout the 240‐day nongrowing season. In our study during the 1996 and 1997 nongrowing seasons, winter carbon losses ranged from 2.0 g CO2 m−2 season−1 in moist dwarf shrub communities to 97 g CO2 m−2 season−1 in natural snowdrift communities, with an average wintertime CO2 efflux of 45 g CO2 m−2 for all Low Arctic tundra communities (0.14 Pg CO2 yr−1 worldwide). These measurements indicate that current estimates of annual carbon loss from tundra ecosystems are low. Inclusion of wintertime losses of CO2 into annual carbon budgets increases the annual carbon efflux of arctic tundra ecosystems by 17% and changes some ecosystems from net annual sinks to net sources of CO2 to the atmosphere.

Field measurements of carbon leaching from leaves in beech and alder forests of northern Germany

Summary Carbon compounds were measured in solutes from crown drip and stem flow collected by rain gauges in a beech and an alder stand in northern Germany. The amount of leachate was calculated by using the concept of a canopy deposition model. Under this aspect leaching rate is the difference between canopy and bulk deposition. The calculations comprise direct leaching from leaves as well as carbon loss to honey-suckling insects and carbon loss used to compensate loss of inorganic substances. Leaching of organic carbon depends mainly on the amount of rainfall, the activity of phytophages and on the water repellance of the leaf cuticles. The annual loss of organic carbon by leaching was about 300 kg · ha −1 per year in the alder forest, that was 1,4% of the annual gross carbon production. The loss in the beech forest was lower with about 60 kg C · ha −1 year −1 , corresponding to 0,8%.

Brazil's carbon checkbook

The carbon budget in Brazil may well be balanced. Regrowth of secondary forests in Brazil may sequester as much atmospheric carbon as is released from deforestation each year, according to a new study by scientists with the Environmental Protection Agency (EPA) in Corvallis, Ore. Recent studies have shown that the deforestation rates overall have been slowing down in Brazil. But the earlier studies mainly focused on gross releases of carbon caused by deforestation in the Amazon basin and generally concluded that there was a net annual loss of carbon. The new study estimates both the CO2‐C emissions from changes in land use and uptake by regrowing forests across Brazil, which are key components of the global carbon cycle. The EPA scientists found that net carbon accumulation was greater than measurements taken in previous years, on the basis of an ERL‐C model of ecosystem carbon storage and flux, a remote sensing vegetation map, and published data on various carbon parameters.

Influence of environmental factors on the decomposition of penguin guano in Antarctica

The microbial activity of guano samples from an age sequence of penguin rookery sites and adjacent areas at Cape Bird, Antarctica, was examined. Field moist and artificially moistened samples were buried at the sites (4°C) and duplicate samples incubated in the hut (10°C). Samples were then frozen and transported to New Zealand. Gas from above the frozen samples was analysed for CO2 using gas chromatography. The samples were thawed and further incubated at 25°C. Microbial activity in the guano depended on the degree of penguin influence and was low in the field moist samples from all sites incubated both ‘in situ’, in the hut and at 25°C. In contrast microbial activity was higher in samples with added water, and very high in guano incubated at 25°C. Under favourable moisture and temperature conditions there may be rapid breakdown of penguin guano, but averaged over a year the estimated annual loss of carbon is less than 0.5% of the total carbon present.

Methane Release from a Brackish Intertidal Salt-Marsh Embayment of Chesapeake Bay, Maryland

Gaseous methane loss from a brackish, intertidal salt marsh sediment was measured in April, June, August, and October 1977. Twenty-four sediment cores were taken on each date. Annual loss of methane carbon from the mud flats was 10.7 g CH4−C per m2 per year, a value closer to freshwater values than marine systems. Loss of methane fromSpartina peat was low.