Laboratory for Biogeochemical Ecology
at the University of Arizona, Dept. of Ecology & Evolutionary Biology              P.I. Scott Saleska

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I. Current Projects

II. Data Exchange

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Understanding tropical vegetation-climate interactions in the Amazon basin

(right: Long-term eddy flux tower for measuring net ecosystem exchange of CO2 in central eastern Amazon forest of Brazil, with Dr. Natalia Restrepo and Daniel Amaral conducting maintenance)

Our current Amazon work -- supported by NSF Partnerships for International Research and Education (Amazon-PIRE) and building on the strong legacy of support from NASA -- focuses on integrating remote sensing techniques and ground based measurements to extrapolate our understanding of local controls on carbon cycling in old-growth Amazon forest to derive landscape and regional scale carbon balance. The goal of this work is to build upon our ongoing investigations of how forest demography and disturbance dynamics control carbon cycling in old-growth Amazon forest, which uses long-term eddy covariance observations of net ecosystem exchange of CO2, integrated with classical methods of forest ecology.

Our ground-based site is the Tapajós National Forest near Santarém (see figure, above right, of long-term eddy flux tower for measuring net ecosystem exchange of CO2 in this central eastern Amazon forest of Brazil). The net CO2 flux from this tower shows the forest losing carbon, an observation not previously seen in the Amazon that will help reconcile an Amazon carbon-budget problem (See Saleska et al., 2003). The carbon budget problem arose from previous studies showing carbon uptake of 1-3 Pg C yr-1 in Amazônia alone, comparable to the whole global terrestrial carbon sink.

We collaborated with Chris Martens at UNC to test of the accuracy of our eddy flux measurements using radon gas as a transport tracer (Martens et al., 2004). This work independently confirms our approach to estimating carbon balance using eddy flux measurements.

Forest biometric observations allow us to attribute observed carbon loss to ecological mechanism: disturbance-recovery dynamics thought characteristic of old-growth forest but not yet observed in tropical carbon balance studies. For a good paper on what we are learning from the vegetation dynamics, see Rice et al., 2004 (view pdf), first-authored by an undergraduate who worked with us in Brazil.

This work is part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA).

For more details, see the Tapajós project (which I began while I was a post-doc with Steve Wofsy at Harvard University). Data from the project is available.

Left: detailed measurements on 2600 individual trees in footprint of Amazonian flux tower (Rice et al. 2004). Shown here is a Brazilian forester using a ladder to measure tree diameter above buttresses.

Collaborators and participants on this project include:

  • Saleska lab members Dr. Natalia Restrepo, Joost van Haren, Brad Christoffersen, Dr. Luciana Alves, Jin Wu, Tara Woodcock
  • PIRE graduate fellows Sarah White, Brian Chaszar, Chris Meehan, Lindsey Hovland, Loren Albert, Jacob Meuth, and Gabriel Moreno
  • PIRE Co-Investigators Alfredo Huete, Jim Shuttleworth, and Steven Wofsy (from Harvard University)
  • Professors Plinio Camargo, Humberto da Rocha, Paulo Artaxo (University of Sao Paulo, Brazil)
  • Cosme Oliveira (Embrapa), and Rodrigo da Silva (Federal University of East-Para), in Santarem
  • Dr. Antonio Manzi, and students Lissandra Souza and Suellen Marostica (INPA-Manaus)
  • Rafael Oliveira, University of Campinas
  • Many others in Brazil, including researchers of the Museu Goeldi (Belem), and the Biological Dynamics of Forest Fragments Project (Manaus).



    Using LIDAR remote sensing to scale carbon cycling from individuals to ecosystem in the Amazon

    Amazon forests form the largest contiguous intact tropical forest on Earth, a vast storehouse of carbon that could influence the trajectory of global climate change.  However, even the present-day carbon balance of Amazônia remains poorly characterized, and the literature vigorously debates whether reports of substantial carbon uptake in study plots present sufficient evidence to reject the null hypothesis that old-growth forests of the Amazon have a landscape-scale carbon balance of zero.  

    This project seeks to use the first aircraft-based LIDAR remote sensing surveys of Amazon forests to scale forest function from individual trees to the landscape.  We aim to develop insight into the fundamental  rules governing scaling relationships, and relation between structure and function, in tropical forests, thereby helping, among other things to help resolve the debate about whether intact Amazon forests are a source or a sink for atmospheric CO2.

    This project is funded by NSF and NASA, with contribution from Center for Tropical forest Studies (CTFS). Participants in this project includes a significant group of collaborators, including:

    • Saleska lab members Scott Stark, Veronika Leitold
    • Professor Michael Lefsky (Colorado State University) and NASA graduate fellow Maria Hunter (University of New Hampshire)
    • Dr. Yosio Shimabukuro, Dr. Dalton Valeriano, and Monica Shimabukuro (INPE Sao Jose dos Campos)
    • Dr. Jess Parker (Smithsonian Environmental Research Center)
    • Professors Bill Magnusson and Flavia Costa, and graduate students Juliana Schietti and Diego Brandao (INPA Manaus)

    Methane cycling and climate feedbacks: integrating from genes to ecosystem in a subarctic wetland

    A fundamental challenge of modern biology is to understand how information encoded in the genes of organisms translates into physiological and biogeochemical processes manifested at ecosystem to global scales. A parallel challenge of earth system sciences is to understand how earth systems will respond to climate change. These grand challenges intersect in the need to understand the global carbon cycle, which is both mediated by biological processes and a key driver of climate through the greenhouse gases carbon dioxide (CO2) and methane (CH4).

    This DOE-funded project (see proposal, "Genes, isotopes, and ecosystem biogeochemistry: dissecting methane flux at the leading edge of global change") focuses on understanding the biological and earth system science aspects of CO2 and CH4 cycling at “the leading edge of lobal change” – a subarctic wetland system where climate change-induced permafrost melt is transforming methane sinks into sources. Our research goals are: (1) to discover functional relations for scaling microbial community composition and metabolism to the ecosystem biogeochemistry of CO2 and CH4; (2) to learn how these relations are affected by shifting environmental variables, and (3) apply this knowledge to better understand and predict changing carbon budgets in subarctic ecosystems already experiencing substantial climate change.

    The field site for this work is at Abisko Scientific Research Station in northern Sweden, and the project involves a large group of collaborators:

    Partitioning whole-ecosystem CO2 fluxes to understand mechanisms of carbon sequestration in a temperate forest

    Temperate forests in the Northeastern US are a large sink for atmospheric CO2, but better understanding of the mechanisms of carbon sequestration is needed to make long-term predictions of terrestrial ecosystem feedbacks to climate change.   We are using newly developed instrumentation for in situ observations of the isotopologues of CO2 to address the question:  what are the mechanisms of carbon sequestration in a northeastern deciduous forest (Harvard Forest, Massachusetts)?

    Recently developed quantum cascade laser (QCL)-based absorption spectrometers open the way for making in situ measurements of isotopic compositon of atmospheric gases at an accuracy previously unobtainable. We are collaborating with Aerodyne Research, Inc (a small business specializing in the development of high-precision optical instrumentation) to deploy a new QCL spectrometer to measure isotopic composition (13C/12C and 18O/16O) of ecosystem fluxes of CO2, with a goal of widening our window into physiological and ecological mechanisms controlling whole-ecosystem carbon exchange.

    This work is funded by a DOE-NICCR project (Isotope ratio partitioning of ecosystem CO2 fluxes to understand forest response to climate change: long-term measurements with novel instrumentation) which supports Dr. Rick Wehr in his work to deploy the new QCL Isotope Ratio Spectrometer (Nelson et al., in press) at Harvard Forest (near Petersham, MA).

    The instrument is described in Nelson et al (2005). Our simulations based on eddy flux measurements of net CO2 exchange and flask isotope data (Saleska et al., 2006) suggest that instrument characteristics are more than adequate to achieve science goals.

    Carbon-cycle climate feedbacks in a sub-alpine Rocky Mountain meadow

    This work investigates the question: how important are ecological feedbacks to climate change? We combine experimental manipulation, elevational gradients in temperature, and observed response to extreme climate events (e.g. drought). Our recent work (Harte, Saleska and Shih, 2006) shows that the effects of the large-scale western drought in 1999-2001 produced the same effect as that predicted by an ecosystem warming manipulation, for the same reason: drought stress shifts plant community composition, driving a decline in ecosystem photosynthetic carbon uptake, a positive feedback to climate.

    This work started with my Ph.D. dissertation at the Rocky Mountain Biological Laboratory in Colorado. For this I used a simple model to integrate data acquired at very different scales: (1) experimental manipulation at the plot scale to investigate short-term warming effects, and (2) a climate-gradient analysis at the landscape-scale to investigate long-term effects of climatic differences. This analysis (Saleska et al 2002) shows that shifts in plant community composition, brought about by heat-induced drought stress, can be more important to carbon balance than decomposition rates of soil organic carbon (assumed key in most global models). This work (with John Harte at U.C. Berkeley) implies that future atmospheric CO2 (and hence, future climate change) may depend on how species interactions structure ecosystem biogeochemistry.

    Right: meadow-warming experiment at the Rocky Mountain Biological Laboratory in Colorado to investigate ecologically-mediated carbon-cycle feedbacks to climate (Saleska et al, 1999 view pdf; Saleska et al., 2002 view pdf). Here, the effects of heaters on accelerating spring snowmelt can be clearly seen.