A long-term vegetation history of the Mojave-Colorado desert ecotone at Joshua Tree National Park

2010 ◽  
Vol 25 (2) ◽  
pp. 222-236 ◽  
Author(s):  
Camille A. Holmgren ◽  
Julio L. Betancourt ◽  
Kate A. Rylander



Author(s):  
Cathy Barnosky

The late-Quaternary vegetation history of the northern Rocky Mountains has thus far been inferred largely from isolated records. These data suggest that conifer forests were established early in postglacial time and were little modified thereafter. The similarity of early postglacial vegetation to modern communities over broad areas gives rise to two hypotheses: (1) that glacial refugia were close to the ice margin, and (2) that vegetation soon colonized the deglaciated areas and has been only subtly affected by climatic perturbations since that time. It is the goal of this project to test these two hypotheses in the region of Grand Teton National Park.



2003 ◽  
Vol 81 (8) ◽  
pp. 833-847 ◽  
Author(s):  
Ilka E Bauer ◽  
L Dennis Gignac ◽  
Dale H Vitt

The spatial development and vegetation history of a large boreal peatland complex in east-central Alberta was reconstructed to examine factors that control peatland development in continental regions. Peat depth throughout the site was interpolated from over 300 depth measurements, and basal radiocarbon dates were obtained from 16 cores. Peat first initiated about 7400 calibrated 14C years BP (cal. BP), and early peat-forming communities were wet fens or marshes. Rates of expansion from these nucleation sites were dependent on both moisture availability and topography, with asynchronous expansion in different regions. Basal macrofossil assemblages suggest that paludification on slopes of large basins was the result of flooding caused by rising peatland water tables. In many areas that initiated after 3000 cal. BP, paludification involved invasion of upland forest by Sphagnum. Long-term apparent rates of peat accumulation were fastest in wet, moderate-rich fen areas where little community change has occurred over time. Macrofossil analysis of core profiles reveals a tendency for sites that initiated wet and minerotrophic to eventually be colonized by Sphagnum. However, the thickness of surficial Sphagnum layers differs between cores, and there are several examples of minimal or apparently reverse successional development.Key words: peatlands, boreal, paleoecology, vegetation succession, peat accumulation, paludification.



2021 ◽  
pp. 1-17
Author(s):  
Christopher M. Schiller ◽  
Cathy Whitlock ◽  
Sabrina R. Brown

Abstract Changes in climate and fire regime have long been recognized as drivers of the postglacial vegetation history of Yellowstone National Park, but the effects of locally dramatic hydrothermal activity are poorly known. Multi-proxy records from Goose Lake have been used to describe the history of Lower Geyser Basin where modern hydrothermal activity is widespread. From 10,300 cal yr BP to 3800 cal yr BP, thermal waters discharged into the lake, as evidenced by the deposition of arsenic-rich sediment, fluorite mud, and relatively high δ13Csediment values. Partially thermal conditions affected the limnobiotic composition, but prevailing climate, fire regime, and rhyolitic substrate maintained Pinus contorta forest in the basin, as found throughout the region. At 3800 cal yr BP, thermal water discharge into Goose Lake ceased, as evidenced by a shift in sediment geochemistry and limnobiota. Pollen and charcoal data indicate concurrent grassland development with limited fuel biomass and less fire activity, despite late Holocene climate conditions that were conducive to expanded forest cover. The shift in hydrothermal activity at Goose Lake and establishment of the treeless geyser basin may have been the result of a tectonic event or change in hydroclimate. This record illustrates the complex interactions of geology and climate that govern the development of an active hydrothermal geo-ecosystem.



Oryx ◽  
2020 ◽  
pp. 1-8 ◽  
Author(s):  
Esther van der Meer ◽  
Lara L. Sousa ◽  
Andrew J. Loveridge

Abstract Translocations are used to mitigate human–wildlife conflict, secure population viability of isolated populations and introduce or reintroduce populations in former or new range. With wild species increasingly confined to small patches of habitat embedded in human-dominated landscapes, the use of translocations is likely to increase. The cheetah Acinonyx jubatus is a large carnivore species with a long history of translocations. As for other species, evaluation of the success of cheetah translocations is complicated by a scarcity of published results, especially of failed attempts. Yet, such information is crucial to improve future translocations. A relatively well documented case is the translocation of alleged problem cheetahs into Matusadona National Park, Zimbabwe, in the early 1990s. In this study we used a combination of survey methods to reassess the status of Matusadona's cheetah population and model current occupancy in relation to densities of competing carnivores and altitude. Our findings indicate this cheetah population has effectively been extirpated, highlighting the importance of thorough planning and standardized long-term monitoring of translocated populations for the understanding of the factors that affect translocation success.



2003 ◽  
Vol 33 (6) ◽  
pp. 1144-1166 ◽  
Author(s):  
Robyn Flakne

A vegetation history for Isle Royale National Park, Michigan, U.S.A., is reconstructed using pollen and spores extracted from two lake sediment cores. Lily Lake is on the southwestern end of the main island of Isle Royale surrounded by northern hardwoods forest. Lake Ojibway is on the northeastern end of the main island surrounded by boreal forest. Pollen and spore records were analyzed using pollen percentage diagrams, nonmetric multidimensional scaling ordination, and modern analog analysis. Squared chord distances for temporally paired subsamples from each site were calculated to determine palynological dissimilarities between the sites through time. These analyses revealed an overall vegetation history that is consistent with other regional reconstructions. High percentages of spruce pollen, indicating a cool climate, are present in the early Holocene, whereas high percentages of pine pollen, indicating a dry climate, occur in the mid-Holocene. The pollen records from the two sites diverge with increased precipitation during the late Holocene. At this time, birch-dominated forest is established near Lily Lake on till-derived soils. At Lake Ojibway, a mixed birch, pine, spruce, and fir forest is established on bedrock-derived soils. The divergence in forest composition is most pronounced within the last 500 years, and this divergence is tentatively attributed to the response of taxa on different substrates to increasing precipitation. Other possible explanations for the recent divergence include changing microclimates or disturbance regimes.



2020 ◽  
Vol 46 (1) ◽  
pp. 33976
Author(s):  
Marilia Teresinha De Sousa Machado ◽  
José Augusto Drummond ◽  
Cristiane Gomes Barreto

 The purpose of this text is to provide a long-term record of occurrences of the species Leucaena leucocephala (Lam.) de Wit. in the Brazilian territory, in order to (i) determine if its introduction occurred before the earliest official record, (ii) identify points of occurrence in Brazil, and (iii) assess its status as a useful although invasive plant. The text is partly based on research done on the confirmed presence of this plant in the Brasília National Park, located in Brazil’s Federal District. Three databases available on the Internet containing information from several herbariums were accessed to obtain the location and the dates of the relevant records of the plant in Brazilian territory. We found that the species was rather widely present in the Brazilian territory before the official record of its earliest introduction. In addition, we found that the plant’s current geographic distribution indicates that it continues to have a strong invasive potential in Brazil, especially because there are social and technical incentives to cultivate it in rural properties.***Leucaena leucocephala (Lam.) de Wit no Brasil: história de uma planta invasora***O objetivo deste texto é oferecer um histórico de longo prazo das ocorrências da espécie Leucaena leucocephala (Lam.) de Wit. no território brasileiro, para (i) determinar se a sua introdução aconteceu antes da data oficial de seu primeiro registro, (ii) identificar os seus pontos de ocorrência no Brasil e (iii) avaliar o seu status como uma planta útil, mesmo que invasiva. O texto se baseia em parte em pesquisa conduzida sobre a presença confirmada dessa espécie de origem exótica no Parque Nacional de Brasília, Distrito Federal. Foram acessadas três bases de dados disponíveis na Internet para obter a localização e as datas dos registros relevantes da planta no território brasileiro. A pesquisa constatou que a espécie tinha uma presença relativamente abrangente no Brasil muito antes do primeiro registro oficial de sua introdução. Além disso, foi constatado que a atual distribuição geográfica da planta indica que ela continua a ter um forte potencial invasivo no Brasil, especialmente porque existem incentivos econômicos e técnicos para o seu cultivo em propriedades rurais.Palavras-chave: Leucaena leucocephala. ocorrência geográfica. espécies invasivas. Brasil.



Koedoe ◽  
1995 ◽  
Vol 38 (1) ◽  
Author(s):  
N. Zambatis ◽  
H.C. Biggs

Rainfall and temperatures during the 1991/92 drought, the severest in the recorded history of the Kruger National Park (KNP), are described. Mean total rainfall for the KNP was 235.6 mm (44.1 of the long- term mean), with a median of 239.9 mm. The num- ber of days on which rain occurred also decreased significantly from a mean annual total of 48.3 to a mean of 24.2 in 1991/92. Daily maximum, minimum and average temperatures for some months increased significantly, as did the number of days within certain maximum temperature range classes.







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