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Updated 1 December 2007
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Ecosystems |
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Changing EcosystemsRecent Accomplishments Archived News Postings (June 2000 - July 2005)
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The following are selected highlights of recent research supported by CCSP participating agencies (as reported in the fiscal year 2008 edition of the annual report, Our Changing Planet). Quantifying Potential Ecosystem Feedbacks to Climatic Change.1 Historical evidence shows that atmospheric greenhouse gas concentrations increase during periods of warming, implying a positive feedback from ecosystems to future climatic change. The feedbacks for carbon dioxide (CO2) and methane (CH4) were quantified by combining the mathematics of feedback with empirical ice core information and general circulation model (GCM) climatic sensitivity. It was found that the warming of 1.5 to 4.5°C associated with anthropogenic doubling of CO2 in GCMs is amplified to 1.6 to 6.0°C warming. Indeed, there is growing experimental evidence that terrestrial ecosystems will amplify warming in the next century through changes in primary production, soil carbon storage, and CH4 emissions due to changes in the length of growing seasons, changes in soil moisture, and reductions in permafrost. As a result, anthropogenic emissions that cause warming will result in higher final greenhouse gas concentrations, and therefore more warming, than would be predicted in the absence of these ecosystem feedbacks. Because key ecological feedbacks to climatic change are unrepresented in GCMs, and because asymmetrical uncertainty about those feedbacks favors higher temperatures, it is likely that the future will be warmer than implied by present GCMs.
Climate Impacts Fish Recruitment by Affecting Larval Transport.2Scientists have developed a tool to predict how climate and weather affect the transport of fish larvae to their nursery areas. Fisheries biologists and physical oceanographers constructed a numerical model to predict the larval transport of an economically important flatfish, northern rock sole (Lepidopsetta polyxystra), in the southeastern Bering Sea based on their vertical position in the water column. Sustained shoreward transport during the 1980s led to a decade of above-average recruitment, and along-shelf or offshore transport in the 1990s resulted in a decade of below-average recruitment. This new model can now be used with Intergovernmental Panel on Climate Change climate projections to investigate the effects of changing climate on larval fish transport and recruitment due to changes in currents and regional wind patterns.Complex Responses of Subalpine Forests to Climatic Change.3 Changing climates in the 21st century are anticipated to significantly alter subalpine forest distributions. Studies of medieval paleoclimates and forest distribution shifts in the high Sierra Nevada, California, are revealing potential influences of future climate change. Tree-ring analysis and wood anatomy of deadwood preserved above current treeline (>3,000 m) has documented the existence of a mixed-conifer forest growing from AD 815 to 1350 on mountain summits in the eastern Sierra where currently no forests occur (see Figure 11). The Medieval forest was composed of six species, including five whose current upper ranges are 200 to 500 m below the deadwood forest elevation in the eastern Sierra and one species that is now native only to the west slope of the Sierra Nevada at elevations more than 700 m below the deadwood location. Climates of the Medieval forest based on these data were significantly warmer (+3.2°C annual minimum temperature) and slightly drier (-24 mm annual precipitation) than present, values similar to those
estimated for 2100 in the Sierra Nevada. The significant changes evidenced by the Medieval forest provide a case study of potential forest responses to be encountered in the future and indicate a much higher level of complexity than has been anticipated.
Climatic Synchronization of Periods of Prehistoric Widespread Forest Wildfires.4The ability of climate variation to synchronize widespread forest fires across much of western North America was recently documented for a multi-century period. During the past 400 years, the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) were the primary drivers of interannual to decadal variation in fire synchrony, whereas the Atlantic Multidecadal Oscillation (AMO) affected the strength of ENSO and PDO effects on wildfire synchrony at multidecadal scales. During certain phases of ENSO and PDO, fire was synchronous within broad subregions and sometimes asynchronous among those regions. In contrast, fires were most commonly synchronous across the West during warm phases of the AMO. The research is the first to demonstrate that synchrony in forest wildfires across western North America is directly related to surface conditions of the Atlantic Ocean. Current shifts to positive AMO conditions imply a potential for increased wildfire synchrony during the next few decades, in addition to that attributed to global warming.Invasive Species Patterns Track Those of Native Species.5A review of patterns of species richness (the number of species in a given area) and species density (the mean number of species per square kilometer) for both native species and non-indigenous or invasive species of plants, birds, and fishes in the continental United States and Hawaii shows that the species densities of native and non-indigenous species are positively correlated for plants, birds, and fishes. The correlations of species densities between native and non-indigenous plants and native and non-indigenous birds are especially strong (r = 0.86 and 0.93, respectively). Densities of non-indigenous plant and bird species are also highly predictable with the densities of native plant species and native bird species being by far the strongest predictive variables. These results support the hypothesis that, at least for plant and bird species, "the rich get richer," in that areas with high densities of native species tend to be more susceptible to invasion by non-indigenous species. For plant and bird taxa in the continental United States, biodiversity itself does not appear to act as a barrier to species invasions.Estimates of Tropical Pacific Ocean Productivity Lowered.6 Ten field studies over the years 1994 to 2006 collected more than 140,000 in situ measurements of the chlorophyll fluorescence characteristics of phytoplankton in the surface mixed layer of the tropical Pacific Ocean. These measurements allowed the delineation of three major ecophysiological regimes in the tropical Pacific based on the factors constraining phytoplankton growth, hence the primary productivity, of these regions. Iron has a key role in regulating phytoplankton growth in both high-nitrate low-chlorophyll and oligotrophic waters near the equator and further south, whereas nitrogen and zooplankton grazing are the primary factors that regulate biomass production north of the equatorial regions. Application of these findings to the interpretation of existing
chlorophyll information derived from satellites shows that productivity in the tropical Pacific basin may be 1.2 to 2.5 GtC yr-1 lower than previous estimates have suggested, a difference that is comparable to the global change in ocean production that accompanied the largest El Niño to La Niña transition on record.
Coral Reef Management Guide.7A workshop of scientists and managers, co-led by several CCSP agencies under the auspices of the U.S. Coral Reef Task Force, resulted in compilation of A Reef Manager’s Guide to Coral Bleaching. The combined research results among state/territorial, Federal, academic, nongovernmental, and international scientists concluded that warming sea surface temperatures are a key factor in mass coral bleaching events. The Guide provides managers with strategies to support the natural resilience of coral reefs in the face of climate change.Marine Pelagic Ecosystems: The West Antarctic Peninsula.8 Penguins in the West Antarctic Peninsula are top consumers of marine resources, with diets of the most common species, the Adelie penguins, almost exclusively represented by one prey species, the Antarctic krill. The peninsula is experiencing some of the most rapid and significant warming on Earth, with two primary manifestations of change: the loss of sea ice and increased snow precipitation. One of the most striking responses is the change in
penguin community composition during the last 3 decades, as ice-dependent and snow-intolerant Adelies have decreased while Chinstrap and Gentoo penguins have increased during a period of unprecedented environmental conditions (see Figure 12).
Nitrogen Limitation Constrains Sustainability of Ecosystem Response to CO2.9Using free-air CO2 enrichment technology in a prairie at the Cedar Creek Natural History Area in Minnesota, researchers in the BioCON (a long-term grassland project studying Biodiversity, CO2 and N interactions) experiment found that some of Earth’s plant life will not be able to sequester carbon from rising atmospheric CO2 levels as well as scientists once thought. Instead, soil nutrients such as nitrogen will limit plant growth even when atmospheric CO2 levels are higher. This study is the longest of its kind and consistent with other studies of trees and agricultural crops, providing evidence that nitrogen limitations may be common in the future in much of the world, despite widespread nitrogen pollution.Additional Past Accomplishments:
References1) Torn, M.S. and J. Harte, 2006: Missing feedbacks, asymmetric uncertainties, and the under- estimation of future warming. Geophysical Research Letters, 33, L10703, doi:10.1029/2005GL025540.2) Lanksbury, J.A., J.T. Duffy-Anderson, K.L. Mier, M.S. Busby, and, P.J. Stabeno, 2007: Distribution and transport patterns of Northern rock sole, Lepidopsetta polyxystra, larvae in the southeastern Bering Sea. Progress in Oceanography, 72, 39-62. 3) Millar, C.I., J.C. King, R.D. Westfall, H.A. Alden, and D.L. Delany, 2006: Late Holocene forest dynamics, volcanism, and climate change at Whitewing Mountain and San Joaquin Ridge, Mono County, Sierra Nevada, CA, USA. Quaternary Research, 66, 273-287. 4) Kitzberger, T., P.M. Brown, E.K. Heyerdahl, T.W. Swetnam, and T.T. Veblen, 2007: Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over western North America. Proceedings of the National Academy of Sciences, 104, 543-548. 5) Stohlgren, T.J., D. Barnett, C. Flather, P. Fuller, B. Peterjohn, J. Kartesz, and L.L. Master, 2006: Species richness and patterns of invasion in plants, birds, and fishes in the United States. Biological Invasions, 8, 427-447. 6) Behrenfeld, M.J., K. Worthington, R.M. Sherrell, F.P. Chavez, P. Strutton, M. McPhaden, and D.M. Shea, 2006: Controls on tropical Pacific Ocean productivity revealed through nutrient stress diagnostics. Nature, 442, 1025-1028. 7) Marshall, P.A. and H.Z. Schuttenberg, 2006: A Reef Manager’s Guide to Coral Bleaching. Great Barrier Reef Marine Park Authority, Townsville, Australia. 8) Ducklow, H.W., K. Baker, D.G. Martinson, L.B. Quetin, R.M. Ross, R.C. Smith, S.E. Stammerjohn, M. Vernet, and W. Fraser, 2006. Marine pelagic ecosystems: the West Antarctic Peninsula. Philosophical Transactions of the Royal Society B, 362, 67-94. 9) Reich, P.B., S.E. Hobbie, T. Lee, D.S. Ellsworth, J.B. West, D. Tilman, J.M.H. Knops, S. Naeem, and J. Trost, 2006. Nitrogen limitation constrains sustainability of ecosystem response to CO2. Nature, 440, 922-925.
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