H. GREG McDONALD (1) AND DANIEL J. CHURE (2)
(1) Geologic Resources Division, National Park Service, P.O. Box 25287 Denver, CO, 80225
(2) Dinosaur National Monument, Jensen, UT 84035
AbstractThe fossil record, particularly from the early Holocene and Pleistocene, can provide an historical basis for understanding long-term ecological change. Available data on the rate and types of environmental change in modern ecosystems is often limited to a few decades, whereas similar information provided by paleontological evidence can provide a record spanning thousands of years. This perspective becomes especially important in recognizing naturally occurring events that have a periodicity exceeding human observation. Thus the fossil record establishes a useful baseline for ascertaining whether changes impacting habitat have natural or anthropogenic causes. Fossil remains can also provide relaible documentation on the paleo- distribution of endangered species and indicate areas favorable for reintroduction. Occasionally fossil preservation permits the recovery of DNA, allowing a very precise match between fossil and extant populations. More importantly, the paleoecological reconstruction of the former habitat has the potential for identifying new ranges where endangered species may be successfully introduced.
We do not advocate that the entire paleontological record will always be applicable to modern ecosystem management However, we do maintain that part of the record from "semi-deep time" extending tens to hundreds of thousands of years in the past is certainly relevant. Therefore, proper management of fossil resources is essential in preserving an irreplaceable record of environmental change. In turn, documentation of long term ecological history represents a potentially critical input in the decision-making process with regard to current ecological problems.
"A science of land health needs, first of all, a base datum of normality, a picture of how healthy land maintains itself as a organism."
- Aldo Leopold (1941)
Paleontology as an historical science plays the key role in our understanding of the history of life on this planet, is it possible or even reasonable to think that this information can be used as a basis for decision-making in any contemporary environmental issues? The operative word is that paleontology is an historical science. As such, it can provide important background information on changes in the environment through time, and the subsequent response of plants and animals to environmental change, whether byadaptation, dispersal, local extirpation or extinction. It can therefore provide critical information and a historical perspective relevant to the management of modern ecosystems. It is in a very real sense necessary for establishing the "base datum of normality" identified by Leopold in the introductory quote. Certainly it can provide a foundation to distinguish processes and events that occur on a natural perhaps-cyclic basis and those that are anthropogenic. If management of natural processes is an objective, how do we identify changes that are the direct result of natural processes? The fossil record can provide a long-term view and in some cases direct documentation of changes that are an outcome of ongoing natural processes. This allows us to extract those that are the result of human activities.
Our purpose is to identify some sources of paleontological information that can aid managers of contemporary ecosystems. As an outgrowth of this main thesis, we believe that proper management of fossil resources on public lands is a critical component of a land managers obligations, not only because of their importance as part of a shared natural heritage, but because of the wealth of information from these resources related to modern ecosystems and their proper management.
Recognition of the potential contribution of paleontology to our understanding of the origin and history of modern ecological systems and long-term trends has been discussed by other workers, Archer et al. (1991), Graham (1992), Knudson (1999) and Swetham et al. (1999). Dayton et al. (1998) recognized that the detection of trends in ecosystems depends upon (1) a good description of the foundation or benchmark against which changes are measured and (2) a distinction between natural and anthropogenic changes. Although their study of a kelp forest was based on 25 years of direct observation, they recognized that this did not provide the needed time depth as many of the original species present in this ecosystem had disappeared before the study began. The fossil record can help distinguish between natural and anthropogenic changes to an environment by providing ecological and environmental information about an area prior to the appearance of humans. The source of information is not limited to the paleontological record and the archaeological record can also be used to provide continuity from the late Pleistocene and early Holocene to present (Lipe, 1995). Since the archeological record is the result of human activity allowances must be made for biases created by the human component.
Although each of the above authors has cited specific examples of paleontology's role in contemporary land management issues this paper's goal is to provide a broader overview of the information preserved in the fossil record that may be utilized to provide a historical perspective to contemporary management issues. The data obtainable from the fossil record will vary from region to region, and there is no "one size fits all" for what will be available. However, land managers, wildlife specialists and ecologists should be cognizant of the potential information in the fossil record in their area. This should foster an awreness they will better appreciate that management of fossil resources can contribute to their own expertise. This awareness should in turn result in the management of fossils resources being an essential element in any land management plan.
It is difficult to directly measure physical parameters of past climate, but fossil evidence may often serve as a useful proxy. The collection of multiple data sets such as pollen, insects, and mammals to support paleoclimatic interpretation is essential for a more accurate and refined understanding of past climate (Graham and Grimm, 1990). These indirect methods of inferring paleoclimatic parameters rely on modern analogs. This information can be complemented by analysis of stable isotopes preserved in plant and animal tissues. Studies of isotope ratios in unaltered biological materials can provide more direct evidence of past temperatures, humidity and rainfall. Typically carbon, oxygen, nitrogen, and hydrogen are utilized, but ongoing studies suggest that other stable isotopes, such as strontium may expand the types of data that can be extracted from the fossil record.
In some cases unaltered tissue can preserve the original DNA of plants and animals. Analysis of this DNA can complement traditional studies based on gross morphology to confirm the taxonomic identity of a particular species (see discussion below).
Information on past ecological conditions can come from a variety of data sources. In additional to bones, shells and macrobotanical remains, other sources in the fossil record that may be of interest to land managers include coprolites (fossil dung), packrat middens, and pollen. These can all provide different types of information, as will be discussed below.
At the simplest level the physical evidence from the skeleton of vertebrates, shells of invertebrates, macrobotanical specimens such as wood, leaves and flowers, and microfossils such as pollen can provide documentation for the presence of a taxon in the area. If the material can be dated by carbon 14 or some other method of absolute dating then the fourth dimension of time is added and provides the critical historical component. While a single record may be of interest to a specific place, such as evidence for the former presence of wolves in Yellowstone, examination of multiple records over a broad geographic area can provide important information such as shifts in distribution in horizontal directions and in elevation. The recovery of multiple taxa can indicate the previous association of species not found together today - a non-analog community that no longer exists as a result of changes in the environment.
The documentation of the former presence of a species in an area has its greatest
relevance to species reintroduction. Rather than take the fossil evidence at
face value, the question needs to be asked - if a species was once here why
is it now gone? Is it merely a response to natural changes in the environment
or the result of human activity? If the former, are present conditions sufficiently
similar to permit a successful reintroduction or have the environmental parameters
that permitted the species to previously live in the area changed to such a
degree that its absence was a natural consequence of this change? With a sufficiently
rich fossil record, spanning both time and geography, it is possible to trace
changes in rates and patterns of a species' population and changes in its relative
abundance. Has a particular species always been rare in the area, has its abundance
decreased through time or is it a relative newcomer to the area? If a particular
species is rare in an area does this mean it is a relict or represents the early
stages of expansion of a species into the area? Houston and Schreiner (1995)
posed the question, "given the dramatic changes in species distribution
in North America from the close of the Pleistocene, what temporal and spatial
scales of species distribution are appropriate to consider in defining `alien'
and `natural' status in national parks?" "Is it appropriate for humans
to introduce a species that has become extinct from natural causes into a park
where the native fauna is to be retained intact?" As further noted by Houston
and Schreiner (1995) "a policy without defined temporal and spatial bounds
might lead to a `whatever feels right' approach to the management of a particular
species." Knowledge of the long-term history of a species based on the
fossil record can provide those bounds. While the answer to these questions
must be addressed on a case by case basis for each park, wilderness or natural
area, ultimately part of the answer and decision-making process must rely on
the fossil record. This data set should be local to establish the former presence
of a species in the area, but should also examine the issue on a broader geographic
scale, establishing within the limits of the fossil record, the former distribution
of a species and how that distribution has changed through time. The analysis
should consider the changes in environmental factors that have affected the
species' distribution, and identify former ecological associates and conditions
preserved in the fossil record that contributed to the distribution of the species.
Recently Cooper et al. (1996) performed a genetic study of bones of small ducks recovered from late Pleistocene and Holocene deposits on the chief Hawaiian Islands. Comparison of the DNA sequence of the fossil material with that of samples from living specimens of the endangered Laysan duck (currently known only from Laysan Island) showed that they were the same species. The fossil material had been recovered from sites in habitat varying from sea level to formerly forested areas at high elevations (60 _ 1,800 m), far from permanent water on the Hawaiian Islands, demonstrating that this endangered species is not as restricted ecologically as its present distribution would suggest. Consequently the data has important implications for the recovery of this species and offers a wider range of options for reintroduction into its former range. As the authors point out, the utilization of DNA analysis to confirm the identity of a species that may not be possible based on gross morphology, can be applied to other threatened insular species as part of an integrated recovery plan.
An interesting collateral issue related to species reintroduction is the introduction of "exotic species". Proposals that exotic species be introduced into a region have centered on two lines of thought. Martin (1975) suggested that certain modern species could serve as ecological equivalents to now extinct Pleistocene species in an area. While viewed as exotic, it was argued that some modern species, such as the burro in the Grand Canyon, filled a now vacant ecological niche created by the disappearance of horses in North America at the end of the Pleistocene. Martin (1981) proposed three levels of faunal introduction in order to restore lost biodiversity in a habitat, based on taxonomic affinities. Mellink (1995) extended Martin's proposal a step further by suggesting exotic species introduced onto rangeland need not be taxonomically close to now extinct species, but only be ecologically similar in habits. The presence of open niches also requires an assessment of whether an exotic species utilizes previously unused resources and hence is not in competition with any native species. Mellink (1995) provided an outline for increased carrying capacity in a multispecies community composed of exotic species selected from a variety of sources. In engineering this complex and totally artificial mammalian community, the selection of species was partially based on body size along a gradient in order to minimize competition. Identification of optimum body sizes was in part based on examining the fossil record to determine the body size of extinct species that formerly lived in the area. Whether or not one agrees philosophically with the concept of "ecological engineering" as an approach to economic development of rural areas as proposed by Mellink, his proposal illustrates an intrigueing use of the fossil record.
A basic ecological tenet is that communities are not static, but constantly changing. The concept of ecological succession in plant communities and associated fauna is well established. This type of ecological change is temporally restricted, and any disturbance has been viewed as a temporary resetting of the system, that will restart as soon as the disturbance is over. This view of ecological change has not taken into account long-term climatic change that may affect ecological succession. The fossil record can also document the frequency and intensity of ecological disturbances. One such disturbance that has received considerable attention is wildland fire. While ecological recovery from a fire may remove most of the evidence, there are often places, such as pond deposits and cave sediments, where fire history is preserved. Fire history for the Yellowstone region has been documented based on study of sediments in ponds (Millspaugh and Whitlock, 1995; Whitlock and Millspaugh, 1996; and Millspaugh, Whitlock, and Bartlein, 2000).
In their study of plant communities in the Appalachian Mountains, Delcourt and Delcourt (1998) noted that the current landscape was not stable and was composed of a fine-grained, heterogeneous mosaic of habitats resulting from increased seasonality of climate that occurred during the changeover from glacial to interglacial conditions in the late Pleistocene and Holocene. The overall effect produced a diverse biota often represented by localized disjunct populations of limited distribution. Such relict habitats, and their included species, both plant and animal, are particularly vulnerable to environmental change, either locally or globally. Based on their study of the response of various plant communities during the Pleistocene and shifts in the ecotones between alpine, boreal and temperate ecosystems, they project that continued warming due to increased levels of greenhouse gases would result in the loss of alpine tundra between 44º and 57º N and that the Picea rubens-Abies fraseri forests would become extinct in the southern Appalachians. The preservation of relict, often fragile, habitats tend to figure prominently in park management plans. If such habitats are within a land manager's jurisdiction and long-term management strategy includes the preservation of these relict biotas, then an understanding of the response of these biotas to climatic change through time may provide critical information related to that strategy. While the database utilized by the Delcourts covered a wide geographic region from Labrador in the north to Louisiana in the south, it was composed of numerous individual sites such as ponds that preserved pollen and other biological materials. Each of these sites played a dual role, providing both the local history of biotic change, and when combined with numerous other sites, generating a broader regional picture of climatic and biotic change. Preservation of the fossils that are source of this information resulted not only in the historical documentation of how these plant communities have responded to climatic change but also permitted the construction of a predictive model of how they would respond to future changes.
INDIVIDUAL SPECIES RESPONSE VS. COMMUNITIES
When did the modern range of a species become established or is it even possible to say that a species is in an established range? Many species are still dispersing into available habitat, thus making them an invader. One such example is the western larch, Larix occidentalis (Whitlock, 1995). Today the range of the western larch is restricted and discontinuous. This current distribution may indicate either a fragmentation of a once widespread distribution now limited due to unfavorable conditions, or alternatively is the result of dispersal with isolated stands indicating range expansion resulting from ameliorating conditions. This presents a manager with two diametrically opposed processes. Is a rare species a relict population that is on the decline or indicative of the early stages of the species reestablishing itself in former habitat? If considered to be an invading alien species the management approach will be different than if it is viewed as a recovering species in need of special attention. If the species is not an exotic introduced species and is spreading through natural processes, then it would not be considered an alien and management should remain neutral with regard to its management. If on the other hand its spread is the result of human activities then active involvement in its managmeent may be required. Resolution of this question may be dependent on the fossil record, both from the pollen record and macrobotanical remains, utilizing both local and regional data. The same approach can be applied to small mammals, insects and other parts of the biota as well.
Recognition of the dynamics of species through time and how they respond to climatic or environmental change may be critical in the design and space allocation for biological preserves. Studies of changes in the composition of mammalian communities during the Pleistocene has shown that each species reacts independently to changes in climatic parameters and that many past communities lack modern analogs (FAUNMAP, 1996). Dayton et al. (1998) in their study of kelp forest communities indicated that the community was not tightly integrated with mutual dependencies and that many species could be removed without much effect on the rest of the ecosystem. If this is the case, although we now have an extant species missing from a habitat when its former presence is indicated by the fossil record, then the question for a manager is whether that species should be reintroduced into that ecosystem. Adjustments to changes in various environmental parameters reflected in the range of small mammals continued through the Holocene (Semken, 1983). Hence the community structure present in a given area may be of relatively recent origin and indicate a single stage in a dynamic ongoing process. This individualistic response is also true of plant associations (Jackson and Overpeck, 2000) and results in non-analog floras.
Reconstruction of former plant communities can come from pollen preserved in the sediments in current or former lakes. In the arid southwest additional information has come from plants preserved in the middnes of packrats, Neotoma spp. in which organic material has been cemented and preserved by the urine of the animals. These middens increase in size due the collecting habits of packrats over many generations and can span thousands of years, thus providing a long-term record of vegetation change in the area. Packrat middens will also contain other organic material such as bones and insect remains (Betancourt et al., 1990; Clark and Sankey, 1999).
If the current philosophy of land managers is to preserve and protect natural ecological processes and not to establish a static assemblage of plants and animals based on an arbritary time standard (usually just before European appearance in a given area) then it is necessary to gain a long term perspective of those processes and their dynamics. We are not managing for ecological stasis. Our fixation on the impact by European settlers is unrealistic and ignores human influence on the environment prior to 1492 (Kay, 1994). As noted by Dayton et al. (1998) the lack of long_term historical data for most ecosystems forces ecologists to use sliding baselines in evaluating the degree of impact and amount of change occurring in an ecosystem. While there will never be a single baseline that is applicable to all situations, the fossil record, within the limits of what is preserved in a given area, can provide data not otherwise available and improve our knowledge of how "natural" a particular system may be.
In our attempts to distinguish natural processes vs. anthropogenic impact the usual reference point in time is pre- and post- appearance of Europeans. This is especially true with evaluation of the impact on an environment caused by the European introduction of domestic species that have since established feral populations. Although wild horses and donkeys have received a lot of attention as to whether they are merely filling empty niches left by the Pleistocene extinctions (Martin, 1975), there are other feral domesticates such as hogs in the eastern Unites States and goats on the Channel Islands of California that create management challenges. This is further complicated by popular species introduced for hunting such as pheasant and chukar partridges whose management may conflict with the protection of native species with less appeal such as foxes and coyotes. Even the reintroduction of native species into an area often results in controversy, such as mountain goat on the Olympic Peninsula. Both sides of the controversy have supported their claims for the eradication or preservation of the mountain goat utilizing knowledge from both the fossil and archeological records of the area. (Lyman, 1988). As is often the case in paleontology, the differences in opinion are due to the lack of direct evidence, in this case, of the former presence of mountain goats on the Olympic Peninsula. But does that argument have much merit? It can be argued that their absence in the area can be explained as nonpreservation in the fossil record rather than never having lived there. While the fossil record is silent on this particular issue, it does illustrate that one well preserved fossil locality containing mountain goat on the Olympic Peninsula could change the entire complexion of the argument regarding the Park Service's plan for either removal or management. Foes of the eradication program seem to have the current advantage by arguing that the animal was present but the right fossil has just not yet been found. However, is this a valid use of the fossil record, to use absence of evidence to support an argument. Rather than this selective use of the fossil record the entire distribution of the fossil and modern record of the species needs to be examined. By looking at patterns of distribution and biogeographic barriers it then becomes possible to at least make a reasonable extrapolation as to the former presence of a species in a particular spot.
While there is a general recognition that the extinction of the Pleistocene megafauna must have had some impact on various ecosystems (Burkhardt, 1996) there has been little work done to determine the long-term impact resulting from their disappearance. Have the ecosystems rebounded, adapted, and returned to some type of equilibrium or are they still in flux? Recently Janzen and Martin (1982) pointed out that the structures of certain neotropical fruits suggest that they may have relied on being ingested by megaherbivores to facilitate propagation. Any plans by managers to maintain a tract of tropical forest with these plant species may need to provide alternative methods for the plants to propagate. Some type of artificial means of propagation may be required if the species involved are to maintain a reasonable level of recruitment of new individuals that would not otherwise occur naturally. This does pose the bigger question as to whether this is the appropriate management strategy. If these species of plants have co-evolved with now extinct species of mammals then perhaps the appropriate action is not to interfere but let the natural process of their eventual extinction occur.
While the above example is based on an inferred relationship between the plants and an extinct species, there are also sources of direct evidence for plant-animal interaction. Recently James and Burney (1997) analyzed the coprolites (fossil fecal matter) from five species of large flightless waterfowl from Hawaii. All species were primarily folivorous and ferns were an important part of their diet. A close coevolutionary relationship between some waterfowl and plants, such as the lobelia, Cyanea, was proposed. Among the conclusions drawn from their study is that the loss of avian herbivores may have affected the nature of selection that certain plants are exposed to and the nature of competition for light among plants on the forest floor. Both factors affect regeneration in certain species. Certainly such information needs to be taken into account as part of the management of these species.
Even the coprolites of an extinct species can provide important information on long-term changes in vegetation for an area. Rampart Cave in the Grand Canyon contains a large stratified layer of dung of the extinct ground sloth, Nothrotheriops shastensis. Analysis of the dung permitted the identification of plants growing in the vicinity of the cave over the last 40,000 years. While the animal producing the dung is now extinct many of the plant species found in the dung are still in the area. As a result of the animal's eclectic eating habits and the preservation of the dung we have gained a long-term perspective on the history of the ecosystem in this part of the Grand Canyon. This also presents the interesting paradox that many of the types of plants preserved in the dung are still found in the vicinity of the cave that preserved the dung, even though the animal that fed on the plants is extinct.
Land managers, wildlife biologists, ecologists and all individuals interested in the conservation and long-term management of our living natural resources require the best possible information in order to make informed decisions. An often overlooked source of information is the fossil record which can provide critical historical information on ecological trends, community structure and history of individual species for an area. Often the source of this information is preserved in the same place as the contemporary ecological communities that they are responsible for managing. While current ecological problems, threatened and endangered species and human impact may seem consuming and of more immediate concern, land managers should be equally concerned with the protection and preservation of fossil resources as well. It may be that the information preserved in the fossil record when properly studied and deciphered can aid them in making those informed decisions that will ultimately affect the fate of the modern ecosystems they are charged with protecting and delay their entry into the fossil record.
Archer, M., S.J. Hand, and H. Godthelp, 1991. Back to the future: the contribution of palaeontology to the conservation of Australian forest faunas. pp. 67-80 in D. Lunney (ed.). Conservation of Australia's Forest Fauna. Royal Zoological Society of New South Wales.
Archer, M., S.J. Hand, and H. Godthelp, 1999. The Power of Paleontology, a new tool for conservation. pp. 233-244 in Australia's Lost World, Prehistoric Animals of Riversleigh. Indiana University Press, Bloomington.
Betancourt, J.L., T.R. Van Devender, and P.S. Martin, 1990. Packrat middens: the last 40 000 years of biotic change. University of Arizona Press, Tucson, Arizona, USA.
Burkhardt, J.W., 1996. Herbivory in the Intermountain West. Idaho Forest, Wildlife and Range Experiment Station, Moscow, Idaho Station Bulletin 58:1-35.
Clark, W.H. and J.T. Sankey, 1999. Late Holocene Sonoran Desert arthropod remains from a packrat midden, Cataviña, Baja California Norte, México. Pan-Pacific Entomologist 75:183-199.
Cooper, A., J. Rhymer, H.F. James, S.L. Olson, C.E. McIntosh, M.D. Sorenson, and R.C. Fleischer, 1996. Ancient DNA and island endemics. Nature 381:484.
Dayton, P.K., M.J. Tegner, P.B. Edwards, and K.L. Riser, 1998. Sliding baselines, ghosts, and reduced expectations in kelp forest communities. Ecological Applications 8(2):309-322.
Delcourt, P.A. and H.R. Delcourt, 1998. Paleoecological insights on conservation of biodiversity: a focus on species, ecosystems, and landscapes. Ecological Applications 8(4):921-934.
FAUNMAP Working Group: R.W. Graham, E.L. Lundelius Jr., M.A. Graham, E.K. Schroeder, R.S. Toomey III, E.Anderson, A.D. Barnosky, J.A. Burns, C.S. Churcher, D.K. Grayson, R.D. Guthrie, C.R. Harington, G.T. Jefferson, L.D. Martin, H.G. McDonald, R.E. Morlan, H.A. Semken Jr., S.D. Webb, L. Werdelin, and M.C. Wilson, 1996. Spatial response of mammals to late Quaternary environmental fluctuations. Science 272(5268):1601-1606.
Graham, R.W., 1992. Late Pleistocene faunal changes as a guide to understanding effects of greenhouse warming on the mammalian fauna of North America. pp. 76 _ 87 in R.L. Peters and T.E. Lovejoy (eds.). Global Warming and Biological Diversity, Yale University Press, New Haven.
Graham, R.W. and E.C. Grimm, 1990. Effects of global climate change on the patterns of terrestrial biological communities. Trends in Ecology and Evolution 5(9):289-292.
Houston, D.B. and E.G. Schreiner, 1995. Alien species in National Parks: drawing lines in space and time. Conservation Biology 9(1):204-209.
Jackson, S.T. and J.T. Overpeck, 2000. Responses of plant populations and communities to environmental changes of the late Quaternary. pp. 194 _220 in D.H. Erwin and S.L. Wing (eds.) Deep Time. Paleobiology's Perspective. Paleobiology Supplement to Volume 26 (4).
James, H.F. and D.A. Burney, 1997. The diet and ecology of Hawaii's extinct flightless waterfowl: evidence from coprolites. Biological Journal of the Linnean Society 62:279-297.
Janzen, D.H. and P.S. Martin, 1982. Neotropical anachronisms: the fruits the gomphotheres ate. Science 215(4528);19-27.
Kay, C.E., 1994. Aboriginal overkill: the role of native Americans in structuring western ecosystems. Human Nature 5(4):359-398.
Knudson, R., 1999. Using the past to shape National Park Service policy for wildlife. The George Wright Forum 16(3):40-51.
Leopold, A., 1941. Wilderness as a land laboratory. Living Wilderness 6:3.
Lipe, W.D., 1995. The archeology of ecology. Federal Archeology 8(1):8-13.
Lunney, D., B. Pressey, M. Archer, S. Hand, H. Godthelp, and A. Curtin, 1997. Integrating ecology and economics: illustrating the need to resolve the conflicts of space and time. Ecological Economics 23:135-143.
Lyman, R.L., 1988. Significance for wildlife management of the late Quaternary biogeography of mountain goats (Oreamnos americanus) in the Pacific Northwest, USA. Arctic and Alpine Research 20:13-23.
Martin, P.S., 1975. Pleistocene niches for alien animals. Bioscience 20:218-221.
Martin, P.S., 1981. Beyond Bos: is nothing better? pp. 33-61 in C.E. Brock and J.H. Bock (eds.) Proceedings of Symposium on Southwestern Grasslands: Past, Present, and Future. Appleton-Whittell Research Ranch, Elsin, Arizona.
Mellink, E., 1995. Use of Sonoran rangelands: lessons from the Pleistocene. pp. 50-60 in D.W. Steadman and J.I. Mead (eds.). Late Quaternary Environments and Deep History, a tribute to Paul S. Martin. The Mammoth Site of Hot Springs, South Dakota, Inc. Scientific Papers 3.
Millspaugh, S.H. and C. Whitlock, 1995. A 750-year fire history based on lake sediment records in central Yellowstone National Park, USA. The Holocene 5(3):283-292.
Millspaugh, S.H., C. Whitlock, and P.J. Bartlein, 2000. Variations in fire frequency and climate over the past 17000 yr in central Yellowstone National Park. Geology 28(3):211-214.
Semken, H.A. Jr., 1983. Holocene mammalian biogeography and climatic change in the eastern and central United States. pp. 182 _207 in H.E. Wright Jr. (ed.). Late Quaternary Environments of the United States. Vol. 2, The Holocene. University of Minnesota Press, Minneapolis.
Swetham, T.W., C.D. Allen, and J.L. Betancourt, 1999. Applied historical ecology: using the past to manage for the future. Ecological Applications 9(4):1189-1206.
Whitlock, C., 1995. The history of Larix occidentalis during the last 20,000 years of environmental change. pp. 83-90 in Ecology and Management of Larix Forests: A Look Ahead. W.C. Schmidt and K.J. McDonald (eds.). United States Forest Service, Intermountain Research Station General Technical Report GTR-INT-319.
Whitlock, C. and S.H. Millspaugh, 1996. Testing the assumptions of fire-history studies: an examination of modern charcoal accumulation in Yellowstone National Park, USA. The Holocene 6(1):7-15.