Ecosystems - How do ecosystems and associated services respond to climatic change? [Past]
Stephen T. Jackson
Department of Botany and Program in Ecology, University of Wyoming, Laramie, USA; Jackson@uwyo.edu
Although “ecosystem services” is a relatively new term, the concept has a long history. For example, the 1895 New York State Constitution designated the Adirondack Forest Preserve to be “forever wild” in order to maintain water quality and supply in the Hudson River watershed. Ancient societies utilized such ecological goods as fuels, fibers, and foods deriving from natural or lightly managed ecosystems, and many came to recognize the ecological services provided by vegetated watersheds and floodplains. Such recognition often came the hard way, just as it does for modern societies.
Studies of the past play important roles in assessing risks and vulnerabilities for ecosystem services in two ways: by providing records of interactions among environmental change, ecosystem services, and societal activities, and by showing how ecosystem properties that underlie ecosystem services have been affected by climatic changes. Because human activities have affected ecosystems for centuries to millennia, it is particularly important to establish baselines for ecosystem properties and services, and to determine how those baselines have already been altered by humans. Teams of marine biologists and paleobiologists have documented history of human impacts on North American fisheries (Jackson et al. 2001; Jackson 2001). Although Native Americans harvested fish and shellfish, often intensively, estuarine ecosystems were little affected. However, introduction of European technologies led to rapid size decline of fish at the top of the food chain, and intensive oyster harvesting resulted in estuarine eutrophication. Both trends accelerated with industrial fishing of the 20th century, with multiple consequences for ecosystem goods and services.
In another example, alpine lake sediments in the western United States record a five-fold increase in dust deposition concurrent with intensive cattle and sheep grazing in the 19th century (Neff et al. 2008). Modeling studies reveal that the dust emissions, caused by breakup of soil crust and reduction of vegetation cover at low elevations, were sufficient to reduce snow albedo, shortening high-elevation snow-cover by several weeks and altering seasonal and total stream discharge (Painter et al. 2010). The sediment studies also show that federal grazing regulations introduced in the 1930s had mitigating effects on dust deposition (Neff et al. 2008).
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Figure 1: Geohistorical records of temporal changes in ecosystem properties and services. This 3000-year composite record of regional ecosystem attributes (land cover, erosion, flood intensity) inferred from sediments of Lake Erhai and monsoon intensity inferred from a speleothem shows ecosystem responses to changes in human population, cultural practices, and climate. The five green bands show primary periods of human effects on the regional environment (left to right): Bronze-Age culture, Han irrigated period, Nanzhao Kingdom, Dali Kingdom, and late Ming/early Qing environmental crisis. (From Dearing 2008). |
These studies focus on impacts during the historical period, but ancient societies also provide object lessons on interactions among cultural practices, climate change, and ecosystem services (Costanza et al. 2007; Büntgen et al. 2011). Sediments from Lake Erhai in southwestern China show vividly how a succession of late Holocene cultures influenced land-cover, soil erosion, and flooding (Fig. 1), culminating in a peak of land clearance and soil erosion in the 17th and 18th centuries (Dearing 2008; Dearing et al. 2008). Consequences of land-use practices may have interacted with increasing monsoon intensity, leading to a well-documented environmental crisis that began to abate only in the 20th century.
Studies of environmental and ecological changes, even without direct links to cultural practices or consequences, play important roles in assessing ecosystem services. Ecosystem services ultimately derive from structural, functional, and compositional properties of ecosystems, and understanding how those properties have responded to past climate changes can provide insight into vulnerability of ecosystem services to ongoing and future climate change (Williams et al. 2004; Jackson 2006; Jackson et al. 2009). North American mid-continental droughts in the Holocene provide a series of case studies. Most recently, multidecadal droughts associated with the Medieval Climate Anomaly led to widespread changes in fire regime and vegetation composition in the central and western Great Lakes region (Shuman et al. 2009; Booth et al. 2012). In the mid-Holocene, a severe and persistent drought (ca. 4200-4000 a BP) resulted in forest disturbance and compositional change in the western Great Lakes as well as dune mobilization in the Upper Mississippi Valley (Booth et al. 2005). In the early Holocene, the mid-continent experienced a gradual, time-transgressive drying, punctuated by a rapid, region-wide drying associated with final collapse of the Laurentide ice sheet. Ecosystem responses show both gradual and time-transgressive trends and a step-change associated with the rapid event (Williams et al. 2009, 2010). Timing varied widely among individual sites, suggesting different thresholds and sensitivities of local systems. All these case studies indicate that ecosystem properties, and ultimately ecosystem services, are vulnerable to climatic change, whether transient or persistent, and that sensitivity varies substantially among ecosystems and regions.
selected references
Full reference list online under: http://pastglobalchanges.org/products/newsletters/ref2012_1.pdf
Costanza R, Graumlich LJ and Steffen W (2007) Sustainability or Collapse? An Integrated History and Future of People on Earth, MIT, 520 pp
Dearing JA (2008) The Holocene 18: 117-127
Jackson JBC et al. (2001) Science 293: 629-638