B31B-0320
Chemical Composition of Soil Horizons and Aggregate Size Fractions Under the Hawaiian Fern Dicranopteris and Angiosperm Cheirodendrom
Soil organic matter (SOM) inherits much of its chemical nature from the dominant vegetation, including phenolic (lignin-derived), aromatic, and aliphatic (cutin and wax-derived) compounds. However, relatively stable recalcitrant compounds may also be formed as a result of condensation and complexation reactions through decomposition and protected with association with mineral particles. The Hawaiian fern species Dicranopteris decomposes more slowly than the angiosperm, Cheirodendrom due to high concentrations of recalcitrant C compounds. These aliphatic fern leaf waxes are well-preserved and may comprise a large portion of the recalcitrant organic matter in these soils. Our objective was to determine the chemical composition of the SOM under the O- (litter-dominated) and the A- (mineral) horizons formed under fern and angiosperm vegetation. To determine the effect of mineral-association, we fractioned the soil into four size classes; 850-590 μm, 590-180 μm, 180-53 μm and <53 μm and characterized the SOM via pyrolysis-gas chromatography-mass spectrometry (py-GC/MS). As the soils developed from the O- to the A-horizon, there was a decrease of lignin-derived phenolic compounds and an increase in more recalcitrant, aromatic and aliphatic C. Soils under ferns had greater relative concentrations of phenolic compounds, while the angiosperms had greater concentrations of fatty-acid methyl esters and furans (some polysaccharide-derived). Differences between size fractions were most evident in the O-horizon of both species. Recalcitrant fern-derived cutin and leaf waxes (alkene and alkanes structures) occurred in the 180-53 μm fraction, which has been shown to be the most stable of the aggregate-size fractions. Soils developed under fern versus angiosperm vegetation have distinct chemical signatures, which likely determine the recalcitrance of the SOM.
B31B-0321
Fluxes Of Carbon Dioxide, Methane, And Nitrous Oxide In A Cool-Temperate Brackish Marsh
To estimate carbon and nitrogen emissions from a marsh ecosystem to the atmosphere, seasonal changes in CO2, CH4 and N2O fluxes were monthly measured for a year using a closed chamber technique in a cool-temperate brackish marsh located at northern Japan. Vegetation of the brackish marsh was classified into Phragmites australis-dominated, Juncus tenuis-dominated and `miscellaneous' ones, often including tall-herbaceous species and dwarf trees. Ecosystem respiration rate and CH4 flux depended positively on soil temperature, exponentially increasing with the rise of soil temperature. On the other hand, N2O flux did not show the dependence on soil temperature, ranging from -0.49 to 0.73, from -0.50 to 0.34 and from -0.68 to 0.83 mg N m-2 h-1 for Phragmites australis-dominated, Juncus tenuis- dominated and `miscellaneous' vegetations, respectively. Nonlinear regression analysis with soil temperature showed that annual ecosystem respiration was 3.0 × 102, 2.3 × 102 and 7.1 × 102 g C m-2 yr-1 and annual methane emission was 6.4, 6.4 and 3.8 g C m-2 yr-1 for the three vegetations mentioned above, respectively.
B31B-0322
Incorporation of leaf Nitrogen Observations for Biochemical and Environmental Modeling of Photosynthesis and Evapotranspiration
Lack of knowledge concerning regional and global nitrogen (N) availability and its impact on CO2 sequestration processes complicates the modeling of carbon cycle feedbacks to climate change. The use of remote sensing constitutes a valuable data source to quantify and investigate impacts of bulk leaf N contents, however information on the vertical leaf N distribution and its relation to photosynthetic (Rubisco) capacity should also be known to quantify leaf N impacts on canopy photosynthesis. In this study, impacts of the amount and vertical distribution of leaf N contents on canopy photosynthesis were investigated by combining field measurements and photosynthesis modelling. While most canopy photosynthesis models assume an exponential vertical profile of leaf N contents in the canopy, the field measurements showed that well-fertilized fields may have a uniform or exponential profile, and senescent canopies have reduced levels of N contents in upper leaves. The sensitivity of simulated canopy photosynthesis to the different (observed) N profiles was examined using a multi-layer sun/shade biochemically based photosynthesis model and found to be important; ie. for a well-fertilized barley field, the use of exponential instead of uniform vertical N profiles increased the annual assimilate by 12 percent. Perspectives for remote sensing based estimation of leaf N contents for photosynthesis modeling are finally discussed.
B31B-0323
Impacts of an Anomalously Warm Year on Soil Nitrogen Availability in Experimentally Manipulated Intact Tallgrass Prairie Ecosystems
Modeling analyses suggest that changes in the growth rate of atmospheric CO2 concentrations in response to an anomalously warm year may be caused by warming-induced increases in nitrogen (N) availability feeding back to net primary productivity (NPP), and ultimately net ecosystem productivity (NEP). To test this hypothesis, twelve intact soil monoliths were excavated from a tallgrass prairie site in Oklahoma, USA and divided among four large dynamic flux chambers (EcoCELLs) allowing for direct measurement of NEP. During the first year, all EcoCELLs were subjected to Oklahoma climate conditions. During the second year, air temperature in two EcoCELLs was increased by 4°C. During the third and fourth year temperatures in the warmed EcoCELLs returned back to ambient conditions. We used several methods to assess soil N availability including plant N uptake, soil solution and drainage chemistry and resin techniques (resin capsules and plant-root simulator (PRS) probes). During the warming and first post-warming year, plant N content in the warmed EcoCELLs increased relative to the controls indicating that soil N availability increased in response to warming. Despite increased N availability, NEP decreased during the warm year most likely due to a drought-induced reduction in NPP. The PRS probes showed increased N availability during the summer of the warm year but none of the other measurements showed any effect of the warming. Both resin techniques correlated well with each other but correlations between resin techniques and plant N were limited. In general, PRS N was negatively correlated with plant N indicating that the PRS probes capture ‘leftover N' after plant demand was satisfied.
B31B-0324
Results from the CCSM Carbon-Land Model Intercomparison Project (C-LAMP)
The National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM) Biogeochemistry Working Group has initiated an intercomparison of terrestrial biosphere models running within the CCSM framework. Called the CCSM Carbon-Land Model Intercomparison Project (C-LAMP), its purpose is to allow the U.S. scientific community to evaluate the performance of biogeochemical cycling models within CCSM and to identify the most important processes for inclusion in future versions of CCSM. Two terrestrial biogeochemistry modules coupled to CCSM---CLM3-CASA' and CLM3-CN---have been evaluated following a set of carefully crafted experiments that build upon the C4MIP Phase 1 protocol. In Experiment 1, the models were forced with an improved NCEP/NCAR reanalysis data set, while in Experiment 2, the models were coupled to the Community Atmosphere Model Version 3 (CAM3) with carbon, water, and energy exchanges over the 20th century. Unlike with most model intercomparisons, for C-LAMP a model performance methodology based on comparison against best-available observational data sets has been developed. Scalar metrics for each model are derived from comparisons against measurements of net primary production, leaf area index, the seasonal cycle of CO2, carbon stocks, and energy. Results from both experiments for CLM3- CASA' and CLM3-CN will be presented, along with recommendations for future evaluations of terrestrial models. C-LAMP model output will be made available by the Program for Climate Model Diagnosis and Intercomparison (PCMDI) via the Earth System Grid (ESG). C-LAMP is a sub-project of the Computational Climate Science End Station headed by Dr. Warren Washington, using computing resources at the U.S. Department of Energy's National Center for Computational Sciences (NCCS). http://www.climatemodeling.org/bgcmip/
B31B-0325
Distribution of 15N Tracers Applied to the Canopy of a Mature Spruce-Hemlock Stand: Implications for Carbon Sequestration
Fertilization, through increases in N deposition, can enhance plant growth and thus impact other elemental cycles including that of carbon. However, in many N fertilization experiments chemical amendments are added to soils, making soils and not plants the short term recipient of additional N (years to decades). In 2001, a dissolved fertilizer addition of 18 kg N/ha to a 21 ha plot in a Maine spruce-hemlock forest was initiated to investigate the importance of canopy N processes and impacts on C sequestration. In smaller subplots (0.3 ha), additional N inputs were made with tracer levels of enriched N, as either 15NH4+ or 15NO3-. Ecosystem pools, canopy gaseous N losses, and dissolved N fluxes in the 15N subplots were analyzed to determine ecosystem N retention and estimate the impact on C sequestration. Ecosystem retention of 15NH4+ and 15NO3- was 38% and 70% respectively, much of this (~75%) was recovered in the canopy, yet little N (<5%) was recovered in woody matter with a high C:N ratio. Despite a large canopy N retention potential in this forest, C sequestration into new wood growth was ~4-5 g C m-2 y-1 or about 2% above the current net annual C sequestration for this site after 3 years of fertilization.
B31B-0326
The Biogeochemical Dynamics of a Large-lake Ecosystem and Past Environmental Changes Recorded by a Sediment Core From Lake Erie, 1900-2003
We have examined the sedimentary organic matter accumulation record and its changes in isotopic compositions in response to changes in trophic status in Lake Erie between 1900 to 2003. Del 13C values of organic matter showed a strong positive correlation with total organic carbon (TOC) contents (r= 0.847), and both displayed temporal patterns corresponding with the documented changes of P loadings, suggesting TOC and C isotopes are reliable proxies for primary productivity and trophic status of the lake. Although CN atomic ratios indicated phytoplankton as the primary sources for the TOC in the sediment, TOC also showed positive correlations with interannual variations of precipitation at Erie, suggesting external carbon sources brought by precipitation was also an important source for TOC in sediment of Lake Erie. The positive correlation between CN atomic ratios and the annual precipitation variations provided collateral evidence by showing that the proportions of terrestrial organic matter is higher with an increase of precipitation. Calcite concentrations in the sediment showed a strong negative relation with TOC and did not show any apparent correlations with P loadings, temperature or precipitation, suggesting calcite dissolution caused by the remineralization of TOC played the major role in modifying calcite sedimentation. However, the carbon isotopic composition of calcite was primarily controlled by the primary productivity by demonstrating strong correlations with both TOC and organic carbon isotopic values. Nitrogen isotopic values increased in response to the increased primary productivity but did not show an apparent response to the decreases of productivity after the P abatement program. However, the positive correlation between nitrogen and carbon isotopic compositions (r=0.288) suggests that the primary productivity played an important role in the nitrogen isotopic variations. The uncertainty of del 15N in reflecting primary productivity were attributed to the external N sources and the changes in lake ecosystems, such as shifts in food chains and changes in phytoplankton communities.
B31B-0327
Environmental Effects on Plant Communities of Abandoned Agricultural Fields in Southern Indiana.
Plant community characteristics are influenced by different environmental factors depending on geologic setting, climate, species composition, successional stage, land use, and geographic and temporal scales. Plant communities that have colonized abandoned agricultural fields (old fields) in Southern Indiana vary in composition, structure, and diversity. They vary on a regional scale manifesting as differences between old fields. They vary at local scales manifesting as differences within old fields. In a study of 6 old fields in Southern Indiana, certain environmental variables were found to correlate more strongly with plant community characteristics in some fields than they did in others. Water table depth was a larger component in multiple regression models for fields that exhibited a greater range of water table depths. An old field with a perched spring water table contained facultative wetland species while others did not. Soil acidity correlated more strongly with biodiversity in 1 of the fields than it did in the others. Acid tolerant species were present in this field and not in the others. Multiple regression models were constructed using environmental variables (nutrient levels, base cation concentrations, water table depth, soil moisture, photosynthetically available radiation, soil acidity, slope, aspect and thickness of organic rich soil horizons) as the independent variables and plant community characteristics as dependent variables. The multiple regression models with species distributions as the dependent variables, described a greater percentage (70 per cent in some cases) of the variance than models with biodiversity and plant density dependent variables, which described between 10 and 40 per cent of the variance. These differences were also observed in strengths of correlations in simple linear regression analysis. Soil , hydrologic, slope, and light characteristics can account for some of the variety observed in successional plant communities. The important influences on plant communities differ based on geographic scale and geologic setting.
B31B-0328
FeedbackBetweenHumanActivitiesAndTerrestrialCarbonCyclesInSystemsOfShadeCoffeePro ductionInMexico
Coffee production in Mexico is carried out within a strong natural context. Coffee is grown under a canopy of several native and introduced tree species. This fact ensures a greater diversity of natural resources and environmental services available for local inhabitants to sustain their livelihoods. However, the lack of opportunities for coffee farmers is increasing the demand over the remaining forest areas by exacerbating non- sustainable timber extraction practices and promoting conversion of forests to pasture lands. This situation hampers the landscapes equilibrium and threatens the wellbeing of rural livelihoods. To understand the interactions between human activities and ecological functions associated with shaded coffee systems, this research has explored the extent to which socio-economic and cultural factors have influenced the use and management of natural resources sustaining coffee livelihoods. At the same time, it examines how customary patterns of resource use have induced changes in the terrestrial carbon cycle at the local level. The empirical study was carried out in a coffee-growing region in Mexico. It involved substantial fieldwork, use of satellite imagery, and participatory research methods in order to gauge a variety of biophysical and socio- economic factors, including forest cover, land use, and carbon balances, as well as, farming practices and off- farming strategies. In addition, a livelihood perspective was applied to approach the linkages between the management of natural resources, the environmental goods and services, and the socio-economic conditions in the coffee-growing region. The empirical evidence from the research marks out shade coffee systems as important supporters for broader natural systems as suppliers of environmental services. However, it also suggests that non-climatic factors might have significant impacts on the local environment and therefore on the terrestrial carbon cycle. According to the research estimations, in the mid-term, rural farmers would have to incorporate a larger extent of land under shifting cultivation and pasture in order to obtain a similar income to that of one hectare of shade coffee. Consequently, the research points out feedback mechanisms between human activities and the natural environment, in order to gain insight into adaptive response mechanisms, which might enhance possibilities for socioeconomic viability in systems of shaded coffee production and proper maintenance of biophysical conditions, environmental services, and human activities.
B31B-0329
Bark Beetles as Significant Forest Disturbances: Estimating Susceptibility Based On Stand Structure
In the western United States, bark beetle outbreaks affect millions of hectares of forests. These disturbances have multiple effects on ecosystems, including modifications to biogeochemical cycles, interactions with fire, and changes in land cover type and species composition. In recent years, extensive outbreaks have occurred in multiple forest ecosystems in the West, thought to be caused by climate variability and stand structure. In this study, we focus on epidemics of mountain pine beetle. We used USDA Forest Service inventories and a model to estimate lodgepole pine susceptibility to mountain pine beetle attack in the West. The model considers stand age, stem density, and percentage of large lodgepole pine to estimate stand susceptibility. Over 150,000 trees in 4454 plots across the western United States were used to compute susceptibility at the plot scale as well as map susceptibility at the county scale. We found that regional susceptibility was high (estimated potential of losses of 34% of stand basal area) for 2.8 Mha, or 46%, of lodgepole pine forests. The highest susceptibility occurred in the Rocky Mountains, with lower susceptibility in coastal states. This study reveals that a substantial fraction of lodgepole pine forest could be subjected to bark beetle outbreaks under current climate conditions. Because climate and weather affect beetle populations, projected future warming will influence outbreak regimes. Thus, forest ecosystems in the West may experience more frequent, extensive, and/or severe disturbances than in recent decades due to current stand structure, and these disturbances may be intensified under climate change.
B31B-0330
De-trending for Climatic Variations to Reveal Stressed Ecosystems
Short-term variation in climatic conditions results in dramatic fluxuations in ecosystem performance, particularly in water-limited ecosystems. These climatic-driven variations confound the effects of management, insect infestations, and changing soil conditions such as a thickening active soil layer in high latitudes. In this study, we presented a method to account for the influence of climatic variations on ecosystem performance, so that changes in underlying ecological condition are emphasized. We adopted a growing season integration of coarse resolution, remotely sensed, Normalized Difference Vegetation Index (NDVI) as a surrogate for actual ecosystem performance. Piecewise regression models were used to predict expected growing season performance. The models were developed using large samples of random pixels over multiple years from areas with the same land cover and within an ecoregion class. Independent variables in the models include seasonal (winter, spring, and summer) climate data (precipitation and temperature) and site potential or long-term historical performance. Model results were then used to construct annual maps representing the deviations, or performance anomalies, between expected ecosystem performance and actual ecosystem performance. Regression confidence limits were used to identify significant anomalies on the maps. Performance outside the confidence limits over multiple years indicates areas with consistent management, insect, fire, or ecosystem stress impacts. The trend in ecosystem anomalies over several years identifies areas where ecosystem stress is becoming more severe or less severe. This approach has been applied to sagebrush lands and boreal forests in the western United States using both 250 m resolution Moderate Resolution Imaging Spectroradiometer and 1 km resolution Advanced Very High Resolution Radiometer NDVI. Piecewise regression R2 values have varied from 0.84 in the Yukon River Basin to 0.96 in Wyoming sagebrush regions, and from 0.86 to 0.95 for sagebrush and grasslands in a portion of southern Idaho. This approach holds promise for identifying stressed ecosystems that are vulnerable to changing to a new ecological state.
B31B-0331
Amazon rainforest regrowth with nutrient stress: A biosphere-atmosphere interaction problem
Recent literature has demonstrated that precipitation decreases with the increase of tropical deforestation, being proportional to the extent of deforestation. After a tropical deforestation, the regrowth of the secondary forest may be limited by climate and nutrient limitations. In this study we investigate the regrowth of the Amazon rainforest after an hypothetical full deforestation, under nutrient stress. This is a 2-way biosphere-atmosphere interaction problem: The response of the regional climate system to the land cover varies with the forest growth, which, in turn, depends on climate and nutrient stress. Nutrient stress also varies with forest age, being most severe for young forests and declining as forests mature. In this experiment, we ran four simulations (3 ensembles each) with the fully coupled climate-biosphere model CCM3-IBIS. The model was calibrated against LBA tower results, and validated against spatial fields of precipitation, incoming solar radiation, land cover patterns, net primary production, wood NPP, leaf area index, and biomass. The experiment evaluated different initial conditions (forest/pastureland) and different types of nutrient stress. We conclude that the reduction of precipitation caused by a large-scale deforestation is not sufficient to prevent the regrowth of the secondary forest, but the decrease of precipitation combined with nutrient limitations may prevent the regrowth of the secondary forest in southern and eastern Amazonia.
B31B-0332
Carbon Dioxide and Energy Exchange in Disturbed Southwestern Ponderosa Pine Forests
Our research characterizes the effect of disturbances by forest management and stand replacing fire on ecosystem fluxes in ponderosa pine forests of Northern Arizona. In this region fire suppression has had profound effects on forests, resulting in very dense forests subject to highly destructive fires. A widely accepted solution to this problem is to restore the forest stands to pre-settlement low density conditions by thinning and prescribed burning. Eddy covariance measurements are being made in three ponderosa pine stands: a) a control plot with no treatments in the last century b) a restored plot, subject to thinning and c) a stand burned by a stand replacing fire in 1996. Ten year after fire, ecosystem CO2 exchange was low and CO2 uptake was limited to a short growing season in the fire site, making the burnt stand a source of CO2, whereas the unburned forest was a net CO2 sink. In addition the fire altered the energy absorbed by the ecosystem and how this energy is partitioned between the different ecosystem components. The 2006 thinning occurred on 167 ha in the footprint of the eddy covariance system. Slash produced by the thinning was piled on site and will be prescribed burned. The thinning reduced tree density by 67% (465 to 154 trees ha-1), tree basal area by 39% (20.5 to 12.6 m2 ha-1), and leaf area index by 41% (1.6 to 0.9 m m-2). Ecosystem gas exchange was measured in the restored site and the control site for one year before the treatment, to assess if the two forests were similar and if their similarity was maintained during a seasonal yearly cycle. Next we analyzed how forest microclimate, ecosystem carbon, water and energy exchanges responded to the forest treatment in time and in different climatic conditions. http://www.for.nau.edu/cms/content/view/692/971
B31B-0333
Collared Pikas as a Model Species for Studying the Biological Impacts of Climate Change in Alpine Ecosystems
Climate models suggest that global temperatures could rise between 1.4o C and 5.8o C over the next 100 years, and that these effects will be most extreme in northern mountain regions. Pikas (Ochotona, Lagomorpha) are widespread small mammals in the alpine environments of Asia and North America. They are cold adapted and consequently sensitive to warming global temperatures. Considerable research has shown a poleward migration of many species as a result of rising temperatures, but high alpine dwelling species, like the pika, may already be trapped at the top of mountains. Little is known about the threshold values of environmental conditions under which pikas either persist or disappear. Collared pikas (Ochotona collaris) inhabit alpine meadows in the Kluane region of the southwest Yukon. Sites located along an environmental gradient from nunataks in the St Elias Icefields to the Ruby Range Mountains have experienced different climatic and glacial histories. Using baseline data from the long-term study in the Ruby Ranges, we report on differences in the ecological and climatic conditions of sites along this gradient and how this translates into differences in the behavioural and population ecology of the pikas living there. By looking at these differences we can infer the potential impacts of a warming climate, and the subsequent ecological changes on collared pika populations in order to clarify the causes of local extinction and allow us to develop models for predicting ecological responses as conditions change under future climate regimes.
B31B-0334
Terrestrial Carbon Dynamics in Prairie Remnants and Conservation Reserve Program Lands of the Palouse Region
Conversion of marginal agricultural lands to perennial grassland vegetation has been proposed as a way to enhance terrestrial carbon sequestration. The Conservation Reserve Program (CRP) has facilitated this transition and promoted carbon sequestration in highly erodible agricultural lands of the Palouse Region of northern Idaho and eastern Washington. Currently little is known about the potential of these lands to act as a carbon sinks in this region. We studied terrestrial carbon dynamics in CRP set asides planted with exotic grasses and in native prairie remnants of the Palouse Region. To study plant decomposition, the species Festuca idahoensis and Symphoricarpos albus were used as representatives of the native prairie community and Bromus inermis was used for CRP sites. Above- and belowground net primary productivity (from 170.9 to 216.0 g m-2 yr-1) and litter fall (from 15.6 to 31.0 g m-2 yr-1) were similar between grassland types. However, root biomass, soil macroaggregates and soil carbon were higher in prairie remnants. Decomposition rates of leaf litter were not different among plant species, however root decomposition was slower in S. albus (k = 0.28 yr-1) than in F. idahoensis (k = 0.56 yr-1) or B. inermis (k = 0.64 yr-1). These results demonstrate that aboveground processes and carbon inputs in CRP sites have reached similar levels to native prairies. However, belowground carbon pools (i.e. root biomass and soil carbon) are still higher in prairie remnants. Belowground decomposition rates were related to root chemical composition as S. albus roots had the highest lignin to nitrogen ratio. The results of this study suggest that efforts to promote carbon sequestration in CRP grasslands of the Palouse should be focused on belowground pools and processes. Management practices that could increase the amount of carbon sequestered in these CRP sites include increasing the amount of root biomass production through fertilization and increasing the density of plants with recalcitrant litter inputs.