The Urbane Ecologist

Evaluating what is natural: long-term perspectives in conservation studies

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Oftentimes, conservation priorities are based on short-term ecological data or satellite imagery spanning only a few decades. This short time scale makes it very difficult, if not impossible, to disentangled natural variability from other trends. In a review article titled “What is Natural? The Need for a Long-Term Perspective in Biodiversity Conservation”, KJ Willis and HJB Birks advocate the use of paleoecological records in conservation studies to provide a longer temporal perspective when addressing specific conservation issues. Some studies relating to biological invasions, wildfires, climate change, and the determination of natural variability have already used this approach successfully.

Paleoecological records include fossil pollen, seeds and fruits, animal remains, tree rings, and charcoal. They span tens to million of years and can provide valuable long-term perspective on the dynamics of contemporary ecological systems.1 Such information is often ignored by conservationists: Willis and Birks point out that no temporal record spanning more than 50 years has been included in any of the key biodiversity assessments published over the past 7 years (the article was published in 2006).7,8 While once upon a time paleoecological records were considered too descriptive and imprecise, there is now a wealth of information providing detailed spatial and temporal resolution (1-5). Many areas of conservation biology (such as biodiversity maintenance, habitat alteration, changing disturbance regimes) can make use of paleoecological records.

In their review, Willis and Birks go through several applied paleoecological studies that have successfully provided direct management information for biodiversity conservation at local, regional, and global scales. In this blog post, I am just going to give an overview of the benefits of applying paleoecological studies to various fields of conservation, based on their review.

Biological invasions

Invasive species are responsible for widespread community change and many extinctions, and are the focus of many conservation advocates and scientists.4 Biological invasions are complex. For example, some regions are more prone to invasion, or some species are more successful invaders than others.

Surprisingly often, it is unclear whether a species is alien or native. A species is classified as native or exotic according to whether it is located in its presumed area of evolutionary origin and/or whether human agency is responsible for its current distribution. But in the absence of a temporal record to assess a species history, the distinction can become blurred.9 The same species can be classified as “alien” or “native” in the different studies based on personal interpretation.10 There is also no standard on how far back one takes “human” activity in determining whether a species is native or alien.1 The problem with labeling some species as “non-native” is that the label often excludes them from lists of threatened or near-extinct species, automatically relegating them to a position of lower conservation value–even when these organisms have been in serious decline for centuries and have not caused any harm to their communities.1 Paleoecology often helps solve questions in biodiversity conservation by teasing out details such as how long an organism has been present in the area, whether or not it has historically been deleterious, and what enabled its spread. It is also often assumed that invasive species are the triggering mechanism for ecosystem change. However, it may be the case that an invasive species is actually an opportunist taking advantage of an environmental change caused by one or many other environmental factors. Paleoecology helps answer that question, too.

Paleoecology also helps determine which habitats are especially prone to exotic invasion and are thus of higher conservation priority.1 Ancient land use has the potential to influence the vulnerability of a site of invasions for decades to centuries, by changing soil pH or carbon or nitrogen values, for example.1,11 In addition, paleoecology can help determine when an ecosystem is “ripe” for invasion. Introductions of non-native species can fail multiple times, due to a variety of factors, such as environmental variables, extreme events, demographic factors, and biotic factors.4,5 Thus, sometimes it is the life history characteristics and biology of resident species (not the properties of invading species) that are responsible for invasions.

Wildfires

Wildfires are important in shaping the structure and function of fire-prone communities throughout Earth’s history.12 Conservationists have become concerned with the changes in frequency, severity, and extent of burning from those perceived as the “norm” and seek to understand several questions: 13

  • What processes are driving this change?
  • How will the composition of plants and animals in ecosystems be affected, particularly in those identified as vulnerable?
  • Are there particular management techniques that can be implemented to alter fire regimes?

Paleoecological records can be used generate a benchmark against which to evaluate contemporary conditions and future alternatives because assessments based on short-term records can easily lead to misguided management plans.14,15 While climate change and human activities have long been acknowledged as drivers of wildfires, paleoecological studies show that these relationships are complex. For example, while an increase in aridity would naturally seem to result in more fires, several studies indicate otherwise.16,17 Shifts in fuel quantity and quality can cause changes in fire regimes.18

Prehistoric and historic human-induced wildfires are often assumed to have caused changes in ecosystem structure and degradation, especially in tropical forests where natural fires are rare and usually limited in extent. However, management plans to control such fires are often implemented without confirming that assumption. One paleoecological study, for example, shows that present-day fire activity in northeastern Cambodia is slower than it has been for over 9000 years.19 Thus, it is unlikely that fire activity was responsible for the forest-savanna shift. Rather, it was more likely a consequence of monsoonal activity while the high-frequency but low-intensity fire caused by humans may have, in fact, chelped onserve forest cover. In this case, the current conservation management plan was very much at odds with evidence from the paleoecological record!

Some studies have drawn very interesting conclusions by examining ecosystem composition in response to fire regimes. For example, fire is not necessarily a universal feature of an ecosystem, but may oscillate through time depending on climate.17

Climate Variability

Most conservation organizations have developed climate change conservation strategies designed to conserve biodiversity in a changing climate. Two fundamental questions in this field are whether biota will move in response to future climate change, and which species and regions are most at risk from future climate change. For these strategies, it is necessary that the species and regions which are most at risk are identified and protected, and that reserve boundaries accommodate potential species range shifts.20,21

Several studies have used paleoecological records for backward prediction (known as “hindcasting”) to assess errors in bioclimatic modeling. This involves (in chronological order):22, 23

  • running models for past intervals of time, using present-day species data but modeling the species’ response to climate change against paleoclimatic data as opposed to present-day climatic data
  • testing the predicted distributions against the distribution of species apparent in the fossil record for the time interval covered by the paleoclimatic data to assess the model’s robustness.

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Literature cited

1. National Research Council, The Geological Record of Ecological Dynamics: Understanding the Biotic Effects of Future Environmental Change (National Academies Press, Washington, DC, 2005).

2. J.P. Smol, Pollution of Lakes and Rivers–A Paleoenvironmental Approach (Arnold, London, 2002).

3. H.J.B. Birks,, Grana 44,1 (2005).

4. M.E. Lyford, S.T. Jackson, J.L. Betancourt, S.T. Gray, Ecol. Monogr. 73, 567 (2003).

5. S.T. Gray, J.L. Betancourt, S.T. Jackson, R.G. Eddy, Ecology 87, 1124 (2006).

6. J. Gurevitch, D.K. Padilla, Trends Ecol. Evol. 19, 470 (2004).

7. Graümlich, S. Sugita, L. B. Brubaker, V. M. Card, Ecology 86, 1667 (2005).

8. K.J. Willis, L. Gillson, T. Brncic, B. Figueroa-Rangel, Trends Ecol. Evol. 20, 107 (2005).

9. J. B. Calicott,J. Biosci. 27, 409 (2002)

10. C.D. Preston, D.A. Pearman, A.R. Hall, Bot. J. Linn. Soc. 145, 257 (2004).

11. D. R. Fosteret al., Bioscience53, 77 (2003).

12. W. J. Bond, J. E. Keeley,Trends Ecol. Evol.20, 387 (2005).

13. D. McKenzie, Z. Gedalof, D. L. Peterson, P. Mote,Conserv. Biol.18, 890 (2004).

14. P. Z. Fulé, W. W. Covington, M. M. Moore,Ecol. Appl.7, 895 (1997).

15. C. Whitlock,Nature432, 28 (2004).

16. J. A. Lynch, J. L. Hollis, F. Sheng Hu,J. Ecol.92, 477 (2004).

17. K. J. Brownet al., Proc. Natl. Acad. Sci. U.S.A.102, 8865 (2005).

18. J.S. Clark, P.D. Royall, C. Chumbley, Ecology 77, 2148 (1996).

19. A. L. Maxwell,J. Biogeogr. 31, 225 (2004).

20. M. B. Ara´ujo, M. Cabeza, W. Thuiller, L. Hannah, P. H. Williams,Glob. Change Biol.10, 1618 (2004).

21. C. D. Thomaset al., Nature427, 145 (2004).

22. E. Martínez-Meyer, A. Townsend Peterson, W. W. Hargrove, Glob. Ecol. Biogeogr.13, 305 (2004).

23. M. B. Araújo, C. Rahbek,Science313, 1396 (2006).

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