Appalachian‐Interior‐Northeastern Mesic Forest
Geography also needs to be considered when classifying ecosystems. Two alkaline eutrophic lakes that share a very similar biota would probably be considered the same type of ecosystem even if they are hundreds of kilometers apart and on either side of a mountain range. On the other hand, if the mountain range was a geographic barrier for many species and the two lakes had quite different biotas we might decide that they are different types of ecosystems.
How can we recognize both the basic physical similarity of the two alkaline eutrophic lakes and the biological differences that occur because of their geographic separation? One approach involves dividing the world into regions based on biologically meaningful patterns that shape the distribution and abundance of species such as climatic zones, mountain ranges, oceans that isolate terrestrial biota, or continents that isolate marine biota. There are many examples of such maps and they use a variety of criteria and names such as ecoregions, ecoclimatic zones, biogeographic provinces, and biophysical regions (Bailey 1996 , 2005 ; Loveland and Merchant 2005). One set of maps originally created by World Wildlife Fund‐US and The Nature Conservancy delineated 867 terrestrial ecoregions (Olson et al. 2001, see Fig. 4.2 for latest version), 426 freshwater ecoregions (feow.org; Abell et al. 2008), and 232 coastal marine ecoregions (Spalding et al. 2007). By using such maps we can recognize the differences that exist between the two lakes because they are in different ecological regions, but we could still recognize their basic similarity by calling them both alkaline eutrophic lakes.
Figure 4.2 This map depicts the Earth’s terrestrial ecoregions; see text about analogous maps for freshwater and coastal ecoregions and Dinerstein et al. (2017). An interactive version of this map is available at http://ecoregions2017.appspot.com.
From a conservation perspective we could largely avoid the issue by organizing conservation efforts for each ecological region. However, conservation efforts are usually organized around political units – states, provinces, nations – and political boundaries do not usually coincide with ecological boundaries.
The Values of Ecosystems
Species cannot survive in isolation from other species; they are all part of some ecosystem. Therefore all ecosystems have value because the species they support have value. In other words, at a minimum the value of an ecosystem is the summation of the value of all its constituent organisms. This idea is simple enough, but it is not the end of the story. We must also consider that ecosystems probably have special attributes that emerge from interactions among the component species and make them valuable beyond the sum of species‐specific values. Let us consider each of the major types of values that we evaluated in Chapter 3 from this perspective.
Intrinsic Value
Whether or not ecosystems have intrinsic value independent of the intrinsic value of their constituent species is an issue that hinges on a complex and controversial question. Are ecosystems superorganisms composed of tightly connected, synergistic systems built around a set of closely coevolved species? Or are they based on a loose assemblage of species that happen to share similar habitat needs and end up interacting with one another to varying degrees because they are in the same place at the same time (Fig. 4.3)? This question has stimulated ecologists for decades (McIntosh 1980). Undoubtedly, the truth lies somewhere between the poles presented here and varies somewhat from ecosystem to ecosystem, but for our purposes it is sufficient to note that the closer ecosystems lie to the “tightly connected” pole of the spectrum, the easier it is to acknowledge that they have intrinsic value.
Figure 4.3 Are ecosystems tightly connected systems of closely coevolved species, or are they a loose assemblage of species that happen to share similar habitat needs and end up interacting with one another?
If ecosystems do have intrinsic value, then conservationists need to protect some examples of each different type of ecosystem, especially those that are in danger of disappearing. Some types of ecosystems are rare because they occur only in uncommon environments. For example, cool forests and alpine areas are rare in Africa because the continent has relatively few mountains tall enough to support these ecosystems (Kingdon 1989). Other ecosystem types have become uncommon because of human activities. In particular, most types of forest and grassland ecosystems associated with fertile soils and benign climates have largely been converted to agricultural lands.
Conservationists recognize the importance of protecting a representative array of ecosystems, especially those that are extensive and undegraded (Watson et al. 2020), but they have not yet developed many endangered ecosystem lists, especially ones with legal status analogous to various official endangered species lists (see Fig. 4.4 and Table 4.3 for examples). An ambitious effort to create a global “Red List of Ecosystems” is underway; see iucnrle.org, Keith et al. (2013) and J.P. Rodriguez et al. (2015). Political hurdles may be paramount, but the challenges of classifying ecosystems discussed previously also play a role (Boitani et al. 2015). Are the spruce–fir forests that occur on a few summits in the southern Appalachians a different type of ecosystem from the spruce–fir forests that stretch across Canada? If so, they are a very rare ecosystem; if not, they are just a peripheral variation of one of the planet’s most widespread ecosystems. Decisions like this are absolutely critical if you are trying to protect ecosystems for their intrinsic values, but they are not nearly so important if your focus is on the instrumental values of ecosystems.
Figure 4.4 Some types of ecosystems are rare because most examples have been destroyed, for example tall grass prairies. Others, like Mediterranean temporary pools, were always a small portion of the landscape and have shrunk further. This is particularly unfortunate given their rich flora and fauna, especially invertebrates and amphibians that thrive where there are no fish.
(Viktor Loki/Shutterstock)
Table 4.3 A few governments have begun the process of protecting endangered types of ecosystems by listing types that are rare or threatened. Listed here are a few examples from four much longer lists.
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