Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
ABSTRACT: Evidence from woodrat middens and tree rings at Dutch John Mountain (DJM) in northeastern Utah reveal spatiotemporal patterns of pinyon pine (Pinus edulis Engelm.) colonization and expansion in the past millennium. The DJM population, a northern outpost of pinyon, was established by long-distance dispersal (~40 km). Growth of this isolate was markedly episodic and tracked multidecadal variability in precipitation. Initial colonization occurred by AD 1246, but expansion was forestalled by catastrophic drought (1250–1288), which we speculate produced extensive mortality of Utah Juniper (Juniperus osteosperma (Torr.) Little), the dominant tree at DJM for the previous ~8700 years. Pinyon then quickly replaced juniper across DJM during a few wet decades (1330–1339 and 1368–1377). Such alternating decadal-scale droughts and pluvial events play a key role in structuring plant communities at the landscape to regional level. These decadal-length precipitation anomalies tend to be regionally coherent and can synchronize physical and biological processes across large areas. Vegetation forecast models must incorporate these temporal and geographic aspects of climate variability to accurately predict the effects of future climate change.
Cole, K.L., N. Henderson, D. S. Shafer (1997). Holocene vegetation and historic grazing impacts at Capitol Reef National Park reconstructed using packrat middens. Great Basin Naturalist 57 (4): 315-326
ABSTRACT: Mid- to Late Holocene vegetation change from a remote high desert site was reconstructed using plant macrofossils and pollen from nine packrat middens ranging from 0 to 5400 years in age. Presettlement middens consistently contained abundant macrofossils of plant species palatable to large herbivores that are now absent or reduced, such as winterfat (Ceratoides lanata ) and ricegrass (Stipa hymenoides ). Macrofossils and pollen of pinyon pine (Pinus edulis ) , sagebrush (Artemisia spp.) and roundleaf buffaloberry (Sheperdia rotundifolia ) were also recently reduced to their lowest levels for the 5400 year record. Conversely, species typical of overgrazed range, such as snakeweed (Gutterrezia sarothrae ), viscid rabbitbrush (Chrysothamnus visidiflorus ), and Russian thistle (Salsola sp.) were not recorded prior to the historic introduction of grazing animals. Pollen of Utah juniper (Juniperus osteosperma ) also increased during the last 200 years. These records demonstrate that the most severe vegetation changes of the last 5400 years occurred during the last 200 years. The nature and timing of these changes suggest that they were primarily caused by nineteenth century open-land sheep and cattle ranching. The reduction of pinyon and sagebrush concurrent with the other grazing impacts suggest that the effects of cattle grazing at modern stocking levels may be a poor analog for the effects of intense sheep grazing during drought.
ABSTRACT: The existing warm (Larrea) deserts of the Southwest are Holocene expansions replacing late—Pleistocene, evergreen woodlands of low—statured junipers, pinyon pines, and live oaks; these woodlands have been isolated by complementary contraction to the slopes of higher mountains that rise like islands from the modern desert sea. Because pinyon—juniper woodland is now so widespread on the similar fault—block mountains of the Great Basin, even as far north as southern Idaho, it would seem reasonable to suppose that the modern "cold" (Artemisia ,Atriplex ) deserts were similarly wooded during the last glacial. However, conclusive Neotoma macrofossil evidence (45 14°C—dated assemblages are reported here) documents major latitudinal displacement of vegetation that precludes pinyon—juniper woodland in the northern and central Great Basin at that time. On the other hand, the entire Mohave Desert sector (south of 37°N) served as an extensive Pleistocene refugium for pinyon—juniper woodland, as documented by an additional 48 dated Neotoma deposits. During the Wisconsinan glacial in the southeastern corner of Oregon, a 42°27'N, there was a subarctic landscape of hyperboreal, prostrate shrublet—junipers (Juniperus horizontalis andJ. communis ) and widespread patterned ground, even at the near—basal elevation of 1460 m. The pleniglacial vegetation of the central Great Basin at 39°N in eastern Nevada and western Utah, was dominated by a regional subalpine forest of bristlecone pine (Pinus longaeva ), associated with minor but consistent boreal juniper (J. communis ) down to 1660 m, close to the base level imposed by pluvial Lake Bonneville. Spruce has not been recorded below 1900 m during the last glacial. At a lower range of elevation (1350—1525 m), available south of the southeastern rim of the Bonneville basin at 37°30'N. Pinus longaeva was replaced by limber pine (P. flexilis ), Douglas—fir (Pseudotsuga ), and montane red cedar (J. scopulorum ); existing woodland juniper (J. osteosperma ) was lacking, but the subalpineJ. communis was present at this local base level. Theory of island biogeography, as applied to ecological islands atop the high mountains of the Great Basin, is reexamined in the light of the drastic vegetational displacements documented in the detailed Quaternary macrofossil record. Species/area plots of montane—subalpine conifers presently distributed on 54 Great Basin mountaintops show an overall insular pattern that is especially well developed on the subset of 38 ecological islands east of 116°W; the slope of z = 0.26 is close to the theoretical value for islands in equilibrium. All 11 taxa of montane—subalpine conifers that penetrate the Great Basin deeply have their main distributions in the Rocky Mountains; only three wide—ranging species occur also in the Sierra Nevada. A long sundering trough in the western Great Basin parallels and isolates the Cascade—Sierran uplift with low—elevation barriers that impede migration, but in the eastern Great Basin there are high connecting divides to the western Rockies, especially via an axial route southeast of the Bonneville basin. There is an east—west pattern of declining species richness of11 montane conifers in the Great Basin that correlates with distance from the rocky Mountain pool of 12 coniferous species. The pleniglacial subalpine forests in the lowlands of the central Great Basin had only one to three species of conifers (e.g.,Pinus longaeva ,Picea engelmannii ,Juniperus communis ). During the great late—glacial/Holocene (12 000—8000 yr BP) warming of climate, these shifted upward in elevation and were augmented in the east (but not in the west) by as many as five additional species of montane conifers. Macrofossil evidence indicted that the later Holocene arrivals dispersed across barriers of woodland and desert that by then isolated the shrunken montane islands. Moderately long—range transport of seeds by birds is deduced as follows: a northward latitudinal shift of 500—640 km during the Holocene is documented for several species of relatively thermophilous conifers, including the heavy—seeded, late—maturing pinyon pine. A 640—km migration in 8000 yr (80 m/yr) is indicated for pinyon, but the most generous estimate of its dispersal rate via the wind/gravity mode is a plodding 0.4 m/yr (3.2 km/8000 yr), orders of magnitude too slow. Seed dispersal by Clark's Nutcrackers and Pinyon Jays, however, is both the prevalent mode and amply swift enough to fit the known migrational history. Hence, the islands—in—equilibrium pattern indicated by the typically insular slope (z = 0.26) for montane conifers on the eastern set of mountaintops in the Great Basin is a reflection of Holocene immigration via sweepstakes dispersal being offset by extinction on the smaller islands. Both extinction and immigration of conifers are documented in the late—glacial/early—Holocene Neotoma record from the small Confusion Range in the east—central Great Basin of western Utah.
ABSTRACT NOT AVAILABLE
ABSTRACT: Plant macrofossils extracted from fossil woodrat (Neotoma spp.) middens at a single locale in the northwestern Great Basin were used to examine vegetation dynamics during the last 30 000 yr. Although the modern assemblage of xeric species at the study site is a recent occurrence, a large proportion of the modern plant taxa near the study locale were also found 12 000 - 30 000 yr BP. The persistence of extant species through time was likely facilitated by within-species genetic diversity and the formation of coenospecies. The diverse topographic and microhabitat features in the northwestern Great Basin also allowed different species to coexist during glacial periods. Changes in species composition occurred during two time intervals: 20 000 - 30 000 and 10 000 - 12 000 yr BP. Vegetation changes during 20 000 - 30 000 yr BP were cyclic; community composition oscillated between two groups of taxa. Vegetation changes between 10 000 - 12 000 yr BP occurred during the Pleistocene-Holocene transition and were largely directional from the Pleistocene assemblages through two transition assemblages to a Holocene assemblage. These changes in species composition generally reflect changes in climate. The presence of relatively mesic species during 10 000 - 30 000 yr BP is consistent with the regional late-Pleistocene climate, and the gradual loss of relatively mesic species during the Holocene parallels the change to a more xeric climate. Contrasted with other areas of North America and Europe, the magnitude of vegetation changes at our study area were relatively small. Furthermore, the persistence of many species through time at this site in the northwestern Great Basin also differs from results at other study sites in North America and Europe. These differences are probably related to land form characteristics and genetic diversity within species.
PUBLISHER'S DESCRIPTION: A fundamental aspect of the work of ecosystem restoration is to rediscover the past and bring it into the present-to determine what needs to be restored, why it was lost, and how best to make it live again. Yet until now, there has been no guide to the various techniques available for determining that information and how those techniques can be used.
For the first time, The Historical Ecology Handbook makes essential connections between past and future ecosystems, bringing together leading experts to offer a much-needed introduction to the field of historical ecology and its practical application by on-the-ground restorationists.
The book begins with an overview chapter that introduces important concepts from ecology and restoration, and discusses various factors that need to be taken into account when attempting to discover and use historical information. Following that is a chapter-by-chapter presentation of individual techniques focusing on both culturally derived evidence (documents, maps, photographs, land surveys, oral history) and biological records (woodlot surveys, tree rings, pollen, packrat middens, opal phytoliths, animal remains, records of changes in soil and hydrology). Each chapter is written by a leading expert and offers essential background, tools, and resources needed for using the technique in a restoration effort. The book ends with four in-depth case studies that demonstrate how various combinations of techniques have been used in restoration projects.
Case studies are from Nantucket, the Indiana Dunes, the Greater Grand Canyon Region, and the San Francisco Area Historical Project. Among the contributors are M. Kat Anderson, Kenneth L. Cole, Owen K. Davis, Peter W. Dunwiddie, Robin Grossinger, Michael L. Morrison, Michael J. O'Brien, Thomas W. Swetnam, Stanley W. Trimble, Gordon G. Whitney, and many others.
The Historical Ecology Handbook is a unique and groundbreaking guide to determining historic reference conditions of a landscape. It offers an invaluable compendium of tools and techniques, and will be essential reading for anyone working in the field of ecological restoration.
ABSTRACT: Over the past thirty years, late Quaternary environments in the arid interior of western North America have been revealed by a unique source of fossils: well-preserved fragments of plants and animals accumulated locally by packrats and quite often encased, amberlike, in large masses of crystallized urine. These packrat middens are ubiquitous in caves and rock crevices throughout the arid West, where they can lie preserved for tens of thousands of years. More than a thousand of these deposits have been dated and analyzed, and middens have supplanted pollen records as a touchstone for studying vegetation dynamics and climatic change in radiocarbon time (the last 40,000 years). Now, similar deposits made by other mammals like hyraxes are being reported from other parts of the world. This book brings together the most recent findings and views of many of the researchers now investigating fossil middens in the United States, Mexico, Africa, the Middle East, and Australia. The contributions serve to open a forum for methodological concerns, update the fossil record of various geographic regions, introduce new applications, and display the vast potential for fossil midden analysis in arid regions worldwide. The findings presented here will serve to foster regional research and to promote general studies devoted to global climate change. Included in the text are more than two hundred charts, photographs, and maps.
Jackson, S.T., J. L. Betancourt, M.E. Lyford, S.T. Gray, K.A. Rylander (2005). A 40,000-year woodrat-midden record of vegetational and biogeographical dynamics in north-eastern Utah, USA. Journal of Biogeography 32 (6): 1085-1106
ABSTRACT: Aim A conspicuous climatic and biogeographical transition occurs at 40–45° N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) middens to the south]. To overcome these limitations, we are extending the woodrat-midden record northward into the lowlands of the central Rocky Mountains.
Location Woodrat middens were collected from crevices and rock shelters on south-facing slopes of Dutch John Mountain (2000–2200 m, 40°57' N, 109°25' W), situated on the eastern flanks of the Uinta Mountains in north-eastern Utah. The site is near the regional limits forPinus ponderosa ,P. edulis ,P. contorta ,Cercocarpus ledifolius var.intricatus ,Abies concolor ,Ephedra viridis and other important western species.
Methods We analysed pollen and plant macrofossils from the 40,000-year midden sequence. The middens represent brief, depositional episodes (mostly years to decades). Four middens represent the early to full-glacial period (40,000–18,000 cal-yr bp), eight middens are from the late-glacial/early Holocene transition (13,500–9000 cal yr bp), and 33 middens span the mid-to-late Holocene (last 7500 years). Temporal density of our Holocene middens (one every c. 210 years) is comparable with typical Holocene pollen sequences from lake sediments.
Results Early to full-glacial assemblages are characterized by low diversity and occurrence of montane conifers (Picea pungens ,Pseudotsuga menziesii ,P. flexilis ,Juniperus communis ) absent from the site today. Diversity increases in the late-glacial samples with the addition ofJ. scopulorum ,J. horizontalis ,C. montanus ,C. ledifolius var.intricatus and mesic understory species. The coniferous trees and J. communis declined andJ. osteosperma appeared during the late-glacial/Holocene transition.Juniperus osteosperma populations have occupied the site throughout the Holocene.Pinus ponderosa was established by 7500 cal-yr bp, and has occurred at least locally ever since. Montane conifers andJ. horizontalis persisted until c. 5500 cal-yr bp. The signature events of the late Holocene were the invasions ofP. edulis andEphedra viridis and establishment of pinyon–juniper woodland in the last 800 years.
Main conclusions The Dutch John Mountain midden record adds to an emerging picture in which mid-elevation conifers (P. flexilis ,Pseudotsuga menziesii ,Picea pungens ,J. scopulorum ,J. communis ) dominated vegetation over a wide area of the Colorado Plateau and adjacent Rocky Mountains. Rather than being fragmented, as often assumed in phylogeographical studies, these species had broader and more-connected distributions than they do in the region today. Paradoxically, subalpine conifers (Picea engelmannii ,A. lasiocarpa ) occurred at higher elevations to the south, possibly representing declining precipitation from south to north owing to southward displacement of the polar jet stream. The Dutch John Mountain record displays a series of extinction and invasion events. Most of the extinctions were local in scale; nearly all constituents of fossil midden assemblages occur within a few kilometres of Dutch John Mountain, and some occur at least locally on its slopes. The sole exception isJ. horizontalis , which is regionally extinct. In contrast to extinctions, Holocene invasions were regional in scale;J. osteosperma ,P. ponderosa ,P. edulis andEphedra viridis immigrated from glacial-age source populations far to the south.
ABSTRACT: Plant macrofossils in ancient packrat middens document the presence of woodland communities in most of the present Chihuahuan, Sonoran, and Mohave deserts in the southwestern United States during the late Wisconsinan (22,000 to 11,000 years before present by radiocarbon dating). Warm desert species were common in the woodlands at lower elevations and mixed conifer and subalpine forests were present at high elevations. Inferred mild, wet winters and cool summers produced unusual plant and animal associations compared to those of today. Montane communities acquired modern aspects and more mesophytic species disappeared from lower woodlands about 11,000 years ago. Early Holocene xeric woodlands and an inferred winter precipitation regime persisted until about 8000 years ago. The present circulation patterns, rainfall regimes, and biotic distributions probably formed as a result of the melting of the continental ice sheets. Southwestern communities appear to have responded quickly to climatic changes compared to the gradual responses of central and eastern United States forest communities.