Holocene Vegetation Changes Research Articles

Mire sediments in East Africa

Summary Mires (peat-forming systems) are very localized within East Africa, being concentrated in areas of higher rainfall and lower temperature. The main centre is the high ground of the wetter part of the Western Rift, in southwestern Uganda, Rwanda, Burundi and probably Zaire. Peat-forming species include trees, such as Erica and Syzygium , sedges and Sphagnum . Mire stratigraphy is very variable between sites, reflecting a diversity of environmental contexts. Many changes in the characteristics of mire sediments in particular profiles appear to be related to climatic events. Some recent changes in mire vegetation are the result of human influence.

Late Holocene Vegetation Changes in Greenwater Valley, Mojave Desert, California

Small-scale late Holocene vegetation changes were determined from a series of 13 modern and fossil packrat middens collected from a site in the Greenwater Valley, northern Mojave Desert, California. Although the site is above the modern lower limit ofColeogyne ramosissima(black-brush), macrofossils of this shrub are only present in samples younger than 270 yr B.P. In order to measure changes more subtle than presence vs absence, macrofossil concentrations were quantified, and principal components and factor analyses were used to distinguish midden plant assemblages. Both the presence/absence data and the statistical analyses suggest a downward shift of 50 to 100 m forColeogyne(blackbrush) communities between 1435 and 1795 A.D.

Holocene Vegetational Changes in the Tombigbee River Valley, Eastern Mississippi

Stratigraphic studies of pollen from an oxbow on a Holocene terrace and from an upland swale near the Tombigbee River in eastern Mississippi provide a record of Holocene vegetational changes. From -11,000 to 7300 years B.P. the forests were dominated by oaks and hickories. Mesic forest species were common, at least locally. This suggests the existence of a significant moisture gradient between central Miss.-Ala. and the vicinity of Goshen Springs (Delcourt, 1980) in southern Alabama. Mesic taxa declined markedly beginning at about 9000 years B.P. Between 7300 and 3500 years B.P., water levels in the oxbow dropped. Regional forests were dominated by oak and hickory, and mesic taxa became uncommon. Nyssa was extremely common between 2400 and 500 years B.P.; this probably included black gum in the uplands and both black gum and tupelo gum in wet lowland sites. A regional increase in pine is evident beginning at about 2400 years B.P. This pine expansion is eventually associated with decreases in oak; hickory and Nyssa. We suggest that aboriginal land use and an increased frequency of fires caused the latter forest changes. An increase in Ambrosia in the uppermost levels marks European settlement. At this time cypress, wetland herbs and shrubs, and Orontium colonized the oxbow, perhaps because of generally higher water levels due to decreased evapotranspiration caused by land clearance.

Holocene vegetational changes in the southern Appalachian mountains, U.S.A.

During the late Pleistocene, tundra occurred at least as far south in the Appalachian Mountains as Cranberry Glades, West Virginia. Boreal forest of northern Diploxylon Pinus, Picea, Abies, and Larix was extensive over a wide altitudinal range in the southern Ridge and Valley and Blue Ridge provinces of southwestern Virginia, Tennessee, and North Carolina. Northern hardwoods forest of Acer, Fagus, and Tsuga replaced the boreal forest at low elevations in the late-glacial period as Picea and Abies were restricted to higher elevations. By 9000 yr B.P., warm-temperate oak-chestnut forests dominated by Quercus and Castanea were widespread in the region, with cool-temperate and boreal taxa restricted to elevations generally above 1000 m and 1500 m, respectively. Holocene paleoecological records from Sphagnum bogs and fens ranging in elevation from 500 m to over 1500 m indicate that current patterns of distribution of many rare plants in the Southern Appalachian Mountains are the result of climatic change, migrational history, past and present habitat diversity, and natural and anthropogenic disturbance history.

A late Wisconsin and Holocene vegetation history from the central brooks range: Implications for Alaskan palaeoecology

Five pollen diagrams reveal late Wisconsin and Holocene vegetation changes in the Walker Lake/Alatna Valley region of the central Brooks Range, approximately 100 km west of the area studied by D. A. Livingstone (1955, Ecology 36, 587–600). New insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate Picea glauca and P. mariana pollen. Three major pollen zones are identified: (1) a basal herb zone, characterized by high percentages of Cyperaceae, Gramineae, Salix, and Artemisia, and low total pollen influx; (2) a shrub Betula zone with increased total pollen influx and very high percentages of Betula pollen, predominantly in the size range of B. nana and B. glandulosa; and (3) and Alnus zone dominated by Alnus pollen. Lakes currently within the boreal forest or near tree line show relatively high percentages of Picea pollen in the Alnus zone. Several striking vegetation changes occurred between ca. 10,000 and 7000 yr B.P. Between ca. 11,000 and 10,000 yr B.P., Populus balsamifera pollen percentages as great as 30% indicate that this species was present at low-elevation sites near Walker Lake. These populations declined abruptly ca. 10,000 yr ago and have never regained prominence. About 8500 yr B.P., Picea glauca pollen reached 10–15%, indicating the arrival of P. glauca in or near the study area. P. glauca populations evidently decreased ca. 8000 yr ago, when Picea pollen percentages and influx fell to low values. About 7000 yr B.P., Alnus pollen percentages and influx rose sharply as alder shrubs became established widely. Picea once more expanded ca. 5000 yr ago, but these populations were dominated by P. mariana rather than P. glauca, which increased slowly at this time and may still be advancing northward. Some vegetation changes have been remarkably synchronous over wide areas of interior Alaska, and probably reflect responses of in situ vegetation to environmental changes, but others may reflect the lagged responses of species migrating into new areas.

Holocene vegetational history of the Kootenai River Valley, Montana

Pollen records in the Kootenai and Fisher River drainages in western Montana reveal a fivezone sequence of Holocene vegetation change. Deposition of Glacier Peak Ash-Layer G (ca. 10,540 ± 660 yr B.P.) in the lowermost sediments (clay intermixed with pebbles) at Tepee Lake gives a minimum date for the initiation of sedimentation. Initial vegetation on the newly deglaciated terrain was dominated by Pinus (probably white bark pine) with small amounts of Gramineae, Picea and Abies, reflecting a relatively cool, moist macroclimate. Two vegetation units appear to contribute to Pollen Zone II (ca. 11,000–7100 yr B.P.): arboreal communities with pines, along with Pseudotsuga or Larix, or both, and treeless vegetation dominated by Artemisia. Pollen Zone II represents an overall warmer macroclimate than occurred upon ice withdrawal. After ca. 7100 yr B.P. (Pollen Zone III) diploxylon pines became a major pollen contributor near both Tepee Lake and McKillop Creek Pond, indicating an expansion of xerophytic forest ( P. contorta and P. ponderosa) along with an increase in the prominence of Pseudotsuga menziesii or Larix occidentalis, or both. Artemisia briefly expanded coverage near Tepee Lake concomitant with the Mazama ashfall ca. 6700 yr B.P. A short-term climatic trend with more available water began after ca. 4000 yr B.P. as Abies (probably A. grandis) along with Picea engelmannii became a more regular component of the forest surrounding both sites. Emergence of the modern macroclimate is indicated primarily with the first regular appearance of Tsuga heterophylla in the pollen record by ca. 2700 yr B.P., synchronous with the development of western hemlock forest within the same latitudes in northern Idaho and northeastern Washington.

Fire history and grassland vegetation change: three pollen diagrams from southern British Columbia

Recent vegetation change in the grasslands of southern British Columbia is examined using pollen analysis, and the results are compared with documentary records. The increasing dominance of the grasslands after 1890 by Artemisia tridentata and other woody shrubs has often been attributed to overgrazing by domestic livestock, but pollen data indicate that shrub populations were substantial in presettlement times, and that the recent "invasion" represents a recovery from anomalously low population levels during the middle 19th century. These low Artemisia populations were probably due to a high frequency of fire in the early settlement period, and the subsequent recovery is probably related to fire suppression. Fire appears to have been an important element in the ecology of these grasslands over a long period, and it may have a place in modern management schemes.

Holocene vegetation and climatic change in the Peace River district, Canada

A sediment core from a pond on the Alberta Plateau in the Peace River district of British Columbia was studied using pollen analysis and radiocarbon dating. Percentage and influx diagrams were produced, and radiocarbon dates were corrected to calendar years to calculate the sedimentation rate. The 231 cm core terminated in clay, and a basal date of 7250 ± 120 years BP was obtained, several thousand years after the recession of Glacial Lake Peace. The formation of the pond is interpreted as resulting from a climatic change, probably a transition from the peak of the Hypsithermal. Zone 1, from 7250 to 5500 years BP, is interpreted as representing a seasonal slough, with upland vegetation percentages consistent with a boreal forest. At about 5500 years BP a permanent pond with surrounding sedge wetlands was formed. Vegetation has been essentially modern during the last 3100 years. Measurements of spruce grains suggest the presence of black and white spruce throughout the pollen record. The formation of permanent ponds and wetlands on the Alberta Plateau at about 5500 years BP is thought to have been the most important vegetation change of the last 7000 years, which may have affected faunal and human populations.

Man and the Variable Vulnerability of Island Life : A Study of Recent Vegetation Change in the Bahamas

The subject of the dissertation which produced these data was an analysis of the extent to which man modified the woodland of Cat Island, a small island in the Bahamas. The methods employed in the research were basically of two kinds: analysis of historical evidence for vegetation change, and analysis of the contemporary vegetation. The data file contains variables relating to a description of the woodland specie(s) found on the old field: age class, habitat type, height class, soil type, moisture class, distance class, and area covered by specie.

Vegetation and Soil Patterns on a Chihuahuan Desert Bajada

Vegetation and soils were sampled along a 1100-m transect on a bajada in southern New Mexico to determine if present vegetation patterns can be interpreted from soil patterns. Species cover was measured in 66 plots, each 50.3 M2. Of these, 22 were randomly chosen as sites for soil pits, which were described and analyses conducted on the top (Al) horizon. The plots were clustered into four communities: Erioneuron pulchellum desert grassland transition, Larrea tridentata desert shrub, Bouteloua curtipendula semidesert grassland and Bouteloua eriopoda desert grassland. Soils of these communities differ significantly in pH, Mg, organic carbon and total nitrogen. These soil chemistry differences could be due to relatively recent changes from Bouteloua grassland to Larrea shrubland, as indicated by our dead shrub data and as documented for many bajadas in southern New Mexico. However, soil series and geomorphic surface patterns, which are not readily affected by recent vegetation changes, suggest that Larrea may always have been an important shrub on shallow calcareous soils (of erosional surfaces) in southern New Mexico. Its importance as a mosaic type in the once extensive desert grasslands has probably been underestimated.

The palynology and palaeoclimatic significance of a dated core of Holocene peat, Okanagan Valley, southern British Columbia

Holocene vegetation and climatic changes of the Okanagan Valley, British Columbia, are inferred from fossil pollen assemblages recovered from Kelowna Bog in the central part of the valley. Broad climatic changes inferred from relict postglacial landforms in the valley are correlated with the above changes.The Okanagan Valley was ice-free and Glacial Lake Penticton drained before 8900 yr BP. A forest consisting mainly of pine (Pinus) and stands of spruce (Picea) had colonized the valley sides prior to draining of the lake. Soon after 8400 yr BP, moist conditions gave way to aridity during which grass (Gramineae) and sagebrush (Artemisia) predominated. This warm, dry interval is correlated with the Hypsithermal. Bare areas in the valley bottom were exposed to wind erosion; sand dunes formed in some areas, whereas in others, a veneer of aeolian sediment was laid down. At approximately 6600 yr BP, the climate became cooler and moister, aeolian activity diminished, and the dunes became stabilized by vegetation. During the ensuing latest climatic interval, three moister phases affected Kelowna Bog and were characterized by large increases in birch (Betula), alder (Alnus), and hazel (Corylus). These phases, which were related to increased runoff from the adjacent uplands, are tentatively correlated with the stades of the Neoglaciation recognized in southcentral British Columbia and neighbouring United States.

RECENT CHANGES IN VEGETATION OF THE CASS AREA OF CANTERBURY*

New Zealand GeographerVolume 16, Issue 1 p. 57-70 RECENT CHANGES IN VEGETATION OF THE CASS AREA OF CANTERBURY* C. J. BURROWS, C. J. BURROWSSearch for more papers by this author C. J. BURROWS, C. J. BURROWSSearch for more papers by this author First published: April 1960 https://doi.org/10.1111/j.1745-7939.1960.tb00293.xCitations: 13 † *The implications of these changes for plant variation are discussed in C. J. Burrows: Variation in Some Species of the Genus Pimelea, Unpublished M.Sc. Thesis, University of Canterbury, 1958. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume16, Issue1April 1960Pages 57-70 RelatedInformation