B31G-0365
Soil Carbon Chronosequnces from Post-Agricultural Land in Western New England
Using quantitative soil pits, we sampled chronosequences of post-agricultural northern hardwood forest soils in the Hopkins Memorial Forest (Williamstown, MA) to determine the amount of carbon lost during the period of agricultural use, as well as the rates at which C accumulates after abandonment. Chronosequences based on the time of abandonment were developed for the three main agricultural uses: cultivated cropland, pasture or hay, and woodlot. Active farms served as our theoretical zero time points and old growth stands in the region served as our likely maximum for C-accumulation. We then tested this chronosequence model throughout the three main physiographic provinces of the Berkshire-Taconic landscape: carbonate lowlands, Taconic uplands, and Berkshire highlands. Our data show a significant direct relationship between time since abandonment and carbon amount for the organic horizons (Oe and Oa) of cultivated as well as pastured or hayed plots but not for stands formerly used as woodlots. Likewise there was a significant relationship between C content and time for plowed horizons (0-20 cm) of cultivated ground, but not for the top 20 cm of mineral soils that were formerly pasture, hay, or woodlot. Our best estimate suggests that cultivation reduced the C-content of plowed soils by 50% to a depth of 20 cm, and that complete recovery of the C-pool requires approximately 120 years. Management practices of post-settlement New England farms differ significantly from those used by modern farms. These methodological differences complicate efforts to quantify the recovery of carbon in the western New England landscape.
B31G-0366
Accounting for Risk in Valuing Forest Carbon Offsets
Forests can sequester carbon dioxide, thereby reducing atmospheric concentrations and slowing global warming. U.S. Forest carbon stocks have increased as a result of regrowth following land abandonment and in-growth due to fire suppression. Increasing carbon density and reducing emissions from disturbances (fire, pest outbreaks) are two potential strategies for using forests to slow the rise of atmospheric CO2. The recent increase in frequency of large and severe fires due to past fire suppression and ongoing climate change represents risk in forest carbon offset investment. Under current carbon accounting mechanisms, all forest carbon offset projects are equivalent provided they meet additionality and permanence standards. Risk of loss from disturbance is not incorporated into quantifying permanence, even though some forests are at greater risk than others. We used the fire regime condition class (FRCC) departure index and mean fire return interval (mFRI) data products developed for the LANDFIRE project to discount the market value of forest carbon as a function of the risk of loss due to wildfire. Based on our risk assessment valuation method, the value of carbon varies depending on forest type and condition. For example, a unit carbon in fire-prone ponderosa pine forests of the Southwestern U.S. is worth only 24% of that in redwood forest. FRCC departure can be altered, making this equation robust to management actions and allowing for site specific quantification of the carbon market value of a management action. Substitution of FRCC and mFRI with the appropriate metrics would allow application of this approach to discounting market value of forest carbon due to risks of other disturbances such as forest pest outbreaks.
B31G-0367
The impact of iron fertilization on the upper ocean heat budget
Oceanic iron fertilization has been suggested as a mitigation mechanism to enhance the biological sequestration of anthropogenic CO2 in the deep ocean. However, the phytoplankton blooms that are intended to sequester CO2 also change the upper ocean heat budget by increasing the attenuation of solar radiation near the surface. This process is in some ways analogous to the trade-off between enhanced carbon uptake and reduced albedo that accompanies reforestation. Field data and a 1D model show that iron-induced phytoplankton blooms increase the net heat flux from ocean to atmosphere by as much as 12 W/m2, depending on the geographic location of the bloom (the Southern Ocean, equatorial Pacific and sub- arctic Pacific are considered here). Heating of the mixed layer also increases stratification, slowing the vertical transport of nutrients that are necessary for sustaining the bloom.
B31G-0368
The Wood-Growth-and-Burial Process (WGBP) Permanent Wood Sequestration to Solve the Global Carbon Dioxide Problem
Among all global environmental problems there is one which dominates over all others: this is the excessive
release of carbon dioxide due to burning of fossil fuels like coal, oil, and gas. The only way to achieve a
permanent removal of anthropogenic CO2 must make use of photosynthesis since, so-far, no other
technology is able to bind the necessary huge amounts of carbon. Therefore, we propose to grow wood on
any available areas, and to bury the wood under anaerobic conditions, e.g., in emptied open pits of coal
mining, any other available pits, and possibly also in emptied underground mines. At these places the wood
will keep for practically unlimited times, undergoing only very slow carbonization reactions. Simple
calculations allow concluding that humans could already now scavenge even all the released CO2, but a
more realistic goal may be to bind 20, 30, or 60 percent. This is more a political question than a scientific
one. General features of the WGBP are: The growth of woods will transform deforested areas and fallow land
to some kind of natural vegetation with the accompanying positive side effects of restoring biotopes,
improving the water balance and thus also improving the climate. The growth of woods will produce enormous
amounts of oxygen and thus it will add to a sound oxygen balance. It will improve the air quality because of
the filtering effect of woods. The growth of woods will improve the soil quality because leaves and roots will
stay on and in the ground when the wood is harvested. The WGBP will create jobs in areas where there is an
urgent demand for these. The WGBP will offer the opportunity to re-cultivate open pit mining areas. The
WGBP will offer the possibility to fill underground mines in a way to prevent earth quakes caused by
collapsing mine shafts. The WGBP will enable mankind to survive the time span ahead of us in which
mankind will still use fossil fuels. The WGBP can be easily financed by societies via very small additional
taxes, or/and via very slightly increased energy prices. It is a great advantage of the WGBP that it will not be
competitive with the agriculture, as the areas most suitable for the process are not attractive for the growth of
food or energy plants. The WGBP does not need fertilizers and irrigation, and it does not need genetically
engineered plants. It is completely ecological and environmentally friendly. The WGBP can be performed at
almost any place of the world, and it is not necessary to perform the process at the sites of carbon dioxide
emission. The WGBP will contribute to a fair international trade. The WGBP will be equally available to all
countries and societies of the world. There is no discrimination of poorer or less advanced societies. The
WGBP will produce wood deposits for future generation, which once may become sources for biomass
processing technologies, be it for the production of chemicals of energy. The burial sites will be saving banks
of precious material.
Ref.: F. Scholz, U. Hasse: ChemSusChem 1 (2008) 381-384
http://www.chemie.uni-
greifswald.de/~analytik/
B31G-0369
Biological Degradation of Black Carbon in Temperate Forest Soils: Effects of Clay Mineralogy and Nitrogen Availability
A critical knowledge gap in soil organic carbon (SOC) cycling concerns the SOC portion collectively known as pyrogenic C or black carbon (BC), which is a chemically heterogeneous class of highly reduced compounds produced by incomplete combustion. While the stocks of BC are significant in surface soils worldwide, this SOC pool has been considered to be relatively inert with negligible biologically mediated degradation of BC occurring. We will present findings from a laboratory incubation of dual-labeled (13C/15N) BC and its precursor wood (Pinus ponderosa) in two temperate soils (Haploxeralfs) that differ in their clay mineralogy (granitic versus andesitic parent material) and organic C content. In addition, we used N additions in the granitic soil to investigate the effects of N availability on soil and substrate C and N cycling. Sterile controls were used to demonstrate that the BC turnover observed was biotic. The laboratory incubations were carried out at 25°C and at 55% of soil water holding capacity. We are measuring the flux of mineralized 13C in respired CO2, dissolved organic C, soil microbial biomass, specific microbial groups (13C-phospholipid fatty acids) and density-defined soil organic matter fractions. The overall flux of 15N is being observed in the microbial biomass, soluble organic and inorganic pools, and organic matter fractions. We will present rates of biologically-mediated decomposition of BC and its precursor wood, as well as the effects of soil mineralogy and N availability on these rates and on products of decomposition. We will also present decomposition rates of native SOM in incubations with and without substrate to investigate C priming.
B31G-0370
Soil 13C Dynamics in Aggregates Across a Soil Profile Under an Established Miscanthus System
Soils are the largest pool of terrestrial organic carbon (C), containing nearly three times the amount of C as the atmosphere. Environmental changes that affect soil C dynamics could slow down the rise in atmospheric CO2 and associated warming by promoting soil C storage. Our capacity to predict the consequences for global change therefore depends on a better understanding of the distribution and controls of soil organic C and how vegetation change may affect SOC distributions. One land cover change of particular interest involves the establishment of bio energy crop stands. The full mitigation potential of bio energy crops cannot be considered without taking into account their effect on soil C dynamics. Miscanthus, a perennial C4 grass from Eastern Asia, has recently received considerable interest as a bio-energy crop. For that reason, we analyzed the C content and the 13C signatures across the soil profile in a 14 year old Miscanthus system, established on former arable land. We combined SOM fractionation techniques by size and density, allowing us to investigate small shifts in soil C stores that would be significant in the long term, but that might not be detected by conventional methodologies. The 13C signal of the various SOM fractions allowed us to distinguish between Miscanthus-derived vs. native soil organic C. Soils under Miscanthus contained 796 g C/m2 in the 0-15 cm layer, and 1233g C/m2 in the 15- 30 cm layer. These values are significantly higher than soil C contents in the arable land. Macroaggregates under Miscanthus contain more than twice as much C compared to arable land, showing a decrease in soil C content with decreasing aggregate size. These differences are largely caused by soil C storage in the microaggregate within macroaggregates fraction. Under Miscanthus, this fraction contains 440 g C/m2 and 488 g C/m2 at 0-15 cm and 15-30 cm respectively, while under the arable land it has mean values of 174 g C/m2 and 353 g C/m2. Our data suggest a large potential for soil C storage under Miscanthus. Moreover, we determined that after 14 years of Miscanthus plantation, differences in soil C contents can mainly be attributed to soil C storage in the microaggregate within macroaggregates fraction.
B31G-0371
Utilizing in Situ Directional Hyperpectral Measurements to Validate Reflectance and Bio- Indicator Simulations for Vegetation Canopies
Modeling directional reflectance in conjunction with in situ measurements provides an opportunity to quantitatively examine vegetation responses expressed under a variety of viewing geometries and illumination conditions and to mprove our understanding of physiology related to carbon exchange between plants and the atmosphere. Recent studies have demonstrated that light use efficiency can be remotely acquired by utilizing Photochemical Reflectance Index to account for physiological responses of foliage exposed to different illumination conditions. In this study, BRDF was simulated with three radiative transfer models, SAILh, rowMCRM and the FLAIR, and compared with in situ measurements for validations. During the summers of 2007 and 2008, field campaigns were conducted at experimental tree plots and a corn field maintained by the USDA BARC. Hyperspectral measurements (~1 nm) were acquired for sectors where illumination conditions for foliage were either sunlit, shaded, or mixed sunlit/shaded, based on the relative azimuth angle between the observer and the sun. The shaded foliage was associated with the darkspot of the BRDF while the sunlit canopy is situated in the hotspot. These measurements were utilized for model input and for validation, using the original spectra and vegetation indices derived from them. The agreements between model simulations and in situ measurements varied for the models used and varied among canopy illumination sectors and species. Simulations from the FLAIR model showed satisfactory results, especially for the shaded portions. For the corn field, the best agreements were simulations from rowMCRM. Simulations from SAILh were better for the sunlit canopy while reflectance generated with rowMCRM showed better agreement for both sunlit and shaded partitions. For the FLAIR model, the simulations showed better results in the visible spectrum while errors in SAILh- and rowMCRM- simulated reflectance were relatively uniform in the visible and NIR region. Simulated PRI and NDVI also showed satisfactory results
B31G-0372
Effects of Management on Soil Carbon Pools in California Rangeland Ecosystems
Rangeland ecosystems managed for livestock production represent the largest land-use footprint globally, covering more than one-quarter of the world's land surface (Asner et al. 2004). In California, rangelands cover an estimated 17 million hectares or approximately 40% of the land area (FRAP 2003). These ecosystems have considerable potential to sequester carbon (C) in soil and offset greenhouse gas emissions through changes in land management practices. Climate policies and C markets may provide incentives for rangeland managers to pursue strategies that optimize soil C storage, yet we lack a thorough understanding of the effects of management on soil C pools in rangelands over time and space. We sampled soil C pools on rangelands in a 260 km2 region of Marin and Sonoma counties to determine if patterns in soil C storage exist with management. Replicate soil samples were collected from 35 fields that spanned the dominant soil orders, plant communities, and management practices in the region while controlling for slope and bioclimatic zone (n = 1050). Management practices included organic amendments, intensive (dairy) and extensive (other) grazing practices, and subsoiling. Soil C pools ranged from approximately 50 to 140 Mg C ha-1 to 1 m depth, with a mean of 99 ± 22 (sd) Mg C ha-1. Differences among sites were due primarily to C concentrations, which exhibited a much larger coefficient of variation than bulk density at all depths. There were no statistically significant differences among the dominant soil orders. Subsoiling appeared to significantly increase soil C content in the top 50 cm, even though subsoiling had only occurred for the first time the previous Nov. Organic amendments also appeared to greatly increase soil C pools, and was the dominant factor that distinguished soil C pools in intensive and extensive land uses. Our results indicate that management has the potential to significantly increase soil C pools. Future research will determine the location of sequestered C within the soil matrix and its turnover time.
B31G-0373
Whole-Ecosystem Labile Carbon Production in a North Temperate Deciduous Forest
Management for forest carbon (C) sequestration requires knowledge of the fate of photosynthetic C. Labile C is an essential intermediary between C assimilation and growth in deciduous forests, accumulating when photosynthetic C supply exceeds demand and later depleting when reallocated to growth during periods of depressed photosynthesis. We developed a new approach that combined meteorological and biometric C cycling data for a mixed deciduous forest in Michigan, USA, to provide novel estimates of whole-ecosystem labile C production (PLC) and reallocation to growth inferred from the temporal imbalance between carbon supply from canopy net C assimilation (Ac) and C demand for net primary production (NPP). We substantiated these estimates with measurements of Populus grandidentata and Quercus rubra wood non-structural carbohydrate (NSC) concentration and mass over two years. Our analysis showed that half of annual Ac was allocated to PLC rather than to immediate growth. Labile C produced during the latter half of summer later supported dormant-season growth and respiration, with 35% of NPP in a given year requiring labile C stored during previous years. Seasonal changes in wood NSC concentration and mass generally corroborated patterns of labile C production and reallocation to growth. We observed a negative relationship between current-year PLC and NPP, indicating that disparities between same-year meteorological and biometric net ecosystem production (NEP) estimates can arise when C assimilated via photosynthesis, a flux incorporated into meteorological NEP estimates, is diverted away from NPP, a flux included in biometric NEP estimates, and instead allocated to PLC. A large, annually recharging pool of labile C also may buffer growth from climate conditions that immediately affect Ac. We conclude that a broader understanding of labile C production and reallocation across ecosystems may be important to interpreting lagged canopy C cycling and growth processes.
B31G-0374
Potential Carbon Sequestration of Global Terrestrial Ecosystems under a CO2-enriched World
We developed a new method to examine the relationships between CO2 enhancement of productivity and precipitation derived from Free-air CO2 Enrichment (FACE) experiments. A new pattern emerged to indicate that elevated CO2 does enhance precipitation use efficiency for productivity and that such an effect would be greater in drier ecosystems. Total precipitation use efficiency of the ecosystem, which depends on available precipitation, is enhanced by about 22% across landscapes ranging from desert to moist deciduous forest. The analysis also provides insights regarding how the impact of elevated CO2 on precipitation use efficiency is manifested in different ecosystems. For example, a unique combination of water, heat and light conditions in the North Central United States causes a different response compared with the FACE experiments in other forested regions. The information and general equation developed in this work provides essential knowledge of enhanced efficiency of water use across ecosystems under increasing atmospheric CO2. We calculated the potential effect of enhanced precipitation use efficiency on the global carbon cycle and conclude that temperate and xeric ecosystems (excluding croplands), which cover about 70% of the area of global terrestrial ecosystems, can potentially increase global ANPP by 2.5 Pg C under a high CO2 environment (150-200% of current atmospheric CO2 concentration level). Our global estimate for aboveground productivity will be modified by other factors, particularly the impact of elevated CO2 on root growth which is highly uncertain, acclimation of plants to CO2 effects, factors that limit NPP such as nitrogen availability and tropospheric ozone, and natural or anthropogenic disturbances. This 2.5 Pg C yr-1 is likely the upper limit of additional global C sequestration from terrestrial aboveground vegetation under a CO2-enriched world.
B31G-0375
Understanding Human Decision Making as a Driver for Carbon Sequestration on Land
As society begins to grapple with reducing the concentration of carbon dioxide and other greenhouse gases in the atmosphere in order to address climate change, policy discussions have emerged on the role of land use as a means to sequester carbon. Land use is already a key player in the global carbon budget through manipulations of vegetation and soils for agriculture and forestry. At the heart of land use is human decision making. The land use pattern and its attendant carbon impacts are a manifestation of a complex set of policy, economic, and cultural drivers that are channeled and expressed through individuals making decisions about land use. In order to understand the current pattern of carbon fluxes on managed land, and any future potential for land use to play a greater role in sequestering carbon, it is essential to understand the drivers of land use decision making at different scales, and their intersection with new imperatives and opportunities coming from climate mitigation goals. To this end, we have conducted a case study on land use decision making in the U.S. state of Colorado, a western state with significant portions of land managed by U.S. Federal governmental agencies in addition to privately-owned agricultural, grazing and forested lands. Our main goal was to put together a first-order look at the types of decision makers involved in managing land, what influences their decisions, and how the potential for storage of additional carbon on land might vary according to ownership category and land vegetation type. Our study has three significant components: 1. examining ownership patterns; 2. calculating the flux and carbon storage by land ownership category; and 3. illuminating the influences on land use decisions at different scales. In this paper, we will report the preliminary results of GIS work examining carbon fluxes by ownership category and the potential for additional storage of carbon based on policy and economic incentives.
B31G-0376
Effect of Rehabilitation on Carbon Sequestration in Estuarine Wetlands
If left undisturbed, carbon in estuarine wetlands can be stored for millennia, whereas terrestrial stores are typically transient. If subject to reduction in tidal flows, estuarine wetland soils typically experience increased soil aeration and decomposition of soil organic matter, whereas reintroduction of tidal flows can increase the rate of carbon sequestration by increasing vertical accretion of the soil profile. Research at a wetland in the Hunter estuary, southeast Australia compared carbon sequestration rates in a rehabilitated and a natural estuarine wetland, both comprised of mangrove and saltmarsh. At the rehabilitated site, total carbon concentration ranged from 1.4-7.4% and bulk density from 0.56-1.37 Mg.m-3. Approximately 97% of soil carbon was present as organic carbon (range 94-100%). At the natural site, total carbon concentration ranged from 8.0-11.6% and bulk density from 0.50 0.85 Mg.m-3. These data were significantly different to rehabilitated site in terms of both higher total carbon (F(1,22)=90.14, p<0.001) and lower bulk density (F(1,22)=11.39, p=0.003). The suppressed carbon stores and elevated bulk density at the rehabilitated site are related to the substantial reduction in tidal flows that occurred in the 1960s, whereas the estuarine communities at the natural site have existed in a relatively undisturbed state since at least the 1850s and there are no artificial constraints to tidal flow. Carbon sequestration at the rehabilitated site (1.05 Mg C.ha-1.y-1 for mangrove and 1.37 Mg C.ha-1.y-1 for saltmarsh), however, was substantially higher than that at the natural site (0.89 Mg C.ha-1.y-1 for mangrove and 0.64 Mg C.ha-1.y-1 for saltmarsh). These results are consistent with a soil carbon rehabilitation trajectory where high vertical accretion rates in rehabilitated sites drive an asymptotic increase in soil carbon stores, and support the potential for substantial gains in carbon sequestration associated with reinstatement of tidal flows to degraded estuarine wetlands.
B31G-0377
Ocean fertilization, carbon credits and the Kyoto Protocol
Commercial interest in ocean fertilization as a carbon sequestration tool was excited by the December 1997 agreement of the Kyoto Protocol to the United Nations Convention on Climate Change. The Protocol commits industrialized countries to caps on net greenhouse gas emissions and allows for various flexible mechanisms to achieve these caps in the most economically efficient manner possible, including trade in carbon credits from projects that reduce emissions or enhance sinks. The carbon market was valued at $64 billion in 2007, with the bulk of the trading ($50 billion) taking place in the highly regulated European Union Emission Trading Scheme, which deals primarily in emission allowances in the energy sector. A much smaller amount, worth $265 million, was traded in the largely unregulated "voluntary" market (Capoor and Ambrosi 2008). As the voluntary market grows, so do calls for its regulation, with several efforts underway to set rules and standards for the sale of voluntary carbon credits using the Kyoto Protocol as a starting point. Four US-based companies and an Australian company currently seek to develop ocean fertilization technologies for the generation of carbon credits. We review these plans through the lens of the Kyoto Protocol and its flexible mechanisms, and examine whether and how ocean fertilization could generate tradable carbon credits. We note that at present, ocean sinks are not included in the Kyoto Protocol, and that furthermore, the Kyoto Protocol only addresses sources and sinks of greenhouse gases within national boundaries, making open-ocean fertilization projects a jurisdictional challenge. We discuss the negotiating history behind the limited inclusion of land use, land use change and forestry in the Kyoto Protocol and the controversy and eventual compromise concerning methodologies for terrestrial carbon accounting. We conclude that current technologies for measuring and monitoring carbon sequestration following ocean fertilization are unlikely to meet the Kyoto Protocol's verification and accounting standards for trading carbon credits on the regulated market. The marketability of ocean fertilization in the voluntary carbon marketplace will likely depend on companies' efforts to minimize environmental risks and consumers' willingness to accept remaining risks.
B31G-0378
A Comparison of Microbial Community Structures by Depth and Season Under Switchgrass
As part of a multidisciplinary study of C sequestration in switchgrass production systems, the soil microbial community structure was monitored at 6 different depths (reaching 90 cm) in both spring and autumn. Microbial community structure was assessed using ribosomal intergenic spacer analysis (RISA), and primers were used specific to either bacteria or fungi, generating microbial community fingerprints for each taxonomic group. Diverse microbial communities for both groups were detected throughout the soil profile. It is notable that while community structure clearly changed with depth, there was the deepest soil samples still retained relatively diverse communities. Seasonally, differences are clearly evident within plots at the surface. As the plots were replicated, significant differences in the community fingerprints with depth and season are reported.
B31G-0379
An Exploration of the Physico-chemical Diversity of a Suite of Biochars
The production of biochar from biomass and its subsequent storage in soils offers a potential way of sequestering C and enhancing soil fertility while generating carbon-negative energy. Biochars, however, are highly diverse in their properties, and not all biochar is necessarily suitable for incorporation into soils. To help understand the factors that control the physico-chemical properties of biochars, a suite of biochars produced by a variety of processes including fast, slow, and flash pyrolysis, as well as hydrothermal carbonization were characterized. Properties measured include pH, specific surface by N2 adsorption, moisture sorption capacity, surface functional groups by Boehm titration, structural functional groups by 13C- NMR, crystallinity by X-ray diffraction, and micro-structure and composition by focused-ion-beam SEM. The results of these analyses demonstrate the heterogeneity of biochars in general, but also show that the process by which they are formed is more important than the feedstock in determining the majority of their properties.
B31G-0380
Do Agricultural Soils of California have the Potential to Sequester Carbon and Mitigate Greenhouse Gases?
Agricultural ecosystems play a major role in the global carbon cycle and can be both sources of carbon emissions to the atmosphere and also carbon sinks which may be used to offset any future greenhouse gas (GHG) emissions. In California, climate change predictions indicate major impacts and substantial alterations of agricultural systems over the next decades. In 2006, California passed the California Global Warming Solutions Act of 2006 (AB 32) that requires reduction of the three major GHG's (CO2, N2O and CH4) to 1990 levels by 2020. We surveyed and synthesized available data from recent studies describing the potential to sequester carbon and reduce other GHG emissions in California agricultural soils. The studies evaluated various management practices in both annual row and perennial cropping systems, with other studies focusing upon biogeochemical model predictions for carbon sequestration and GHG mitigation calibrated towards California agriculture. Management practices considered included minimum or no tillage, cover cropping, organic residue (low and high inputs) and nitrogen fertilizer management. Though practices involving inputs of carbon, such as cover cropping and organic amendments, were often associated with increases in soil organic carbon (SOC) in the top soil layer (0-20 cm), results were not consistent across farming systems. Several studies indicated that conservation tillage, alone, increased above-ground biomass, especially when used with a cover crop. However, the reduced soil disturbance from conservation tillage merely resulted in a redistribution of the soil carbon rather than an overall accumulation, when compared with standard tillage and cover cropping practices together. Predictions from biogeochemical models indicated that increased inputs of manure and increased organic residues led to substantial carbon sequestration but did not consistently reduce non-CO2 related GHG emissions. The most effective way to reduce non-CO2 GHG emissions, and simultaneously add organic matter to soil, was to employ reduced tillage techniques and low input farming which is based upon the reduction of chemical fertilizers, pesticides and herbicides without their complete elimination and to also add carbon to the soils through the addition and incorporation of organic amendments and cover crops.
B31G-0381
Soil Carbon Storage in Christmas Tree Farms: Maximizing Ecosystem Management and Sustainability for Carbon Sequestration
Management of agroecosystems for the purpose of manipulating soil carbon stocks could be a viable approach for countering rising atmospheric carbon dioxide concentrations, while maximizing sustainability of the agroforestry industry. We investigated the carbon storage potential of Christmas tree farms in the southern Appalachian mountains as a potential model for the impacts of land management on soil carbon. We quantified soil carbon stocks across a gradient of cultivation duration and herbicide management. We compared soil carbon in farms to that in adjacent pastures and native forests that represent a control group to account for variability in other soil-forming factors. We partitioned tree farm soil carbon into fractions delineated by stability, an important determinant of long-term sequestration potential. Soil carbon stocks in the intermediate pool are significantly greater in the tree farms under cultivation for longer periods of time than in the younger tree farms. This pool can be quite large, yet has the ability to repond to biological environmental changes on the centennial time scale. Pasture soil carbon was significantly greater than both forest and tree farm soil carbon, which were not different from each other. These data can help inform land management and soil carbon sequestration strategies.
B31G-0382
Empirical Estimates of Tree Carbon Storage Over a Century due to Fire Reduction in California Montane Conifer Forests.
Fire reduction policies are globally widespread and cause large changes in natural disturbance regimes. They should affect C accrual rates, but there is uncertainty in both modeling- and empirically-based estimates on the rate, and sometimes even the sign thereof, due to a lack of high quality data and to the confounding by logging or other ecological changes. Here I present data on tree density and C stock changes over 93 years from a never-logged, mid-montane (1370 to 2130 m) landscape in the central Sierra Nevada, California. Literature-based mean pre-1870 fire return intervals in the region were on the order of 8 to 20 years, but declined precipitously afterwards. The area was originally sampled without bias in 1911, and in 2004 I randomly re-sampled 20 1.6 ha plots in the area. I found very large increases in tree density and tree C, with mean tree densities increasing in each of 13 diameter classes. Total density increased from 54 to 289 trees per ha (530 percent); the smallest diameter class increased 1100 percent while progressively larger classes had smaller relative increases. Allometrically estimated increases in tree C across the size classes were more uniform, and total tree C, excluding fine roots, increased from 100 to 228 Mg C per ha. These values very likely underestimate ecosystem C gain, because likely increases in snags, down logs, small trees, shrubs, and forest litter and duff are not included. Also, sheep grazing likely hampered regeneration in the few decades following initial fire declines, and recent controlled burns in 65 percent of the plots have likely reduced C levels somewhat. In many Sierran locations, controlled burns are now quite risky due to increased fuel loads and the consequent risk of historically unnatural catastrophic crown fires. Such fires instantly release very high C amounts and continue to emit C for many years due to dead wood decomposition and increased soil respiration. There is also a substantial risk of permanent conversion to shrub dominated systems in a warmer dryer climate, as forests and shrublands comprise a climatically-determined unstable equilibrium in the Sierra. These results are important relative to GHG reduction and land management policies in landscapes naturally prone to burning.
B31G-0383
Enhancement of Carbon Sequestration in west coast Douglas-fir Forests with Nitrogen Fertilization
Fertilization is one of the eligible management practices for C sequestering and hence reducing CO2 emissions under Article 3.4 of the Kyoto Protocol. In the coastal regions of British Columbia, which have very little nitrogen (N) deposition from pollution sources owing to their remote location, and soils deficient in N (Hanley et al., 1996), Douglas-fir stands respond to N fertilization (Brix, 1981; Fisher and Binkley, 2000; Chapin et al., 2002). However, a major concern with N fertilization is the potential loss from the soil surface of the highly potent greenhouse gas N2O, and little is known about such losses in N-fertilized forest soils. While it is necessary to determine and quantify the effects of N fertilization on stand C sequestration, it is also important to address environmental concerns by measuring N2O emissions to determine the net greenhouse gas (GHG) global warming potential (GWP). The GWP of N2O is 296 times (100-year time horizon) greater than that of CO2 (Ehhalt and Prather, 2001), yet there is little information on its net radiative forcing as a result of forest fertilization. We report two years of results on the effects of N fertilization in a chronosequence of three Douglas-fir stands (7, 19 and 58 years old, hereafter referred to as HDF00, HDF88 and DF49, respectively) on net C sequestration or net primary productivity measured using the eddy-covariance technique. DF49 (110 ha) and HDF88 (20 ha) were aerially fertilized with urea at 200 kg N ha-1 on Jan 13 and Feb 17, 2007, respectively, while due to its young age and competing understory, fertilizer to HDF00 (5 ha) was manually applied at 80 g urea/tree (60 kg N ha-1) along the tree drip line on Feb 13-14, 2007. Additionally, we calculate the net change in GHG GWP resulting from fertilization of DF49 by accounting for N2O emissions and energy costs of fertilizer production, transport, and application. We also compare polymer-coated slow-release urea (Environmentally Smart Nitrogen (ESN), Agrium Inc., Calgary, AB, Canada) with regular urea for its potential effectiveness in reducing N2O emissions from the forest-floor.
B31G-0384
Detecting CO2 Fertilization in Tree Ring Records: Evidence from Natural Populations of Boreal Forest Species
Global increases of atmospheric CO2 concentration are predicted to enhance tree growth, particularly where water limitation is important, but evidence of CO2 fertilization in Canada's forests is limited. This study examined the effect of increasing atmospheric CO2 concentration on tree ring increments in south-east Yukon, west-central Manitoba and northern Ontario, sampling the dominant tree species at each site: lodgepole pine (Pinus contorta), white spruce (Picea glauca) and black spruce (Picea mariana), respectively. Over 50 tree cores from each site were sampled, analysed for ring-width, cross- dated and averaged, generating a ~100 y chronology for each population. We examined the residuals following a regression with climate variables for a positive trend over time, which has been interpreted in prior studies as evidence for a CO2 fertilization effect. We were only able to detect an increase in ring width residuals over time in the Manitoba white spruce population, which were located at the most water-limited site. We did further analyses to see whether CO2 fertilization was stronger or more detectable in younger trees or more water-limited years. Although we were unable to find any evidence that drier years experienced increases in relative growth as a result of increased CO2 availability, we did find stronger CO2 responses in younger trees. In conclusion, forest populations that are water-limited or young in age are more likely to benefit from global increases in atmospheric CO2 concentration, and are better able to contribute to overall boreal forest carbon sequestration.
B31G-0385
Enhancing Carbon Sequestration Through Afforestation and Reforestation in China as Simulated by the Dynamic Land Ecosystem Model
After a dramatic decrease in the 1950s, the forest area in China has been greatly increased. The forest coverage in China has rocketed from about 8.6% in 1950 to 18.21% at present. Most of the increased forest area are either afforested or reforested plantations. Forest plantation accounts for about 29% of the total forest area in 2000 and the total area ranks the first throughout the world. There are currently no national analyses on the impacts of afforestation and reforestation on carbon sequestration in China. In this study, we made a complete assessment to the changing carbon sequestration induced by forest plantation from 1950 to 2005 in China by using a Dynamic Land Ecosystem model (DLEM), which is a process-based model with coupled carbon, nitrogen and water cycling and is extensively validated in Asia and North America. Six experiments were designed: plantation area change only, environmental (Climate, nitrogen deposition and tropospheric ozone) change only, land use and land cover change (including plantation area change) only, and land use and land cover change and environmental change. The model simulation results were evaluated against the field data from five long-term monitoring sites in China. The simulated carbon storage under these experiments was compared. In addition, we have examined how water availability might limit the capacity of carbon sequestration in the afforested and reforested areas of China.