Quaking aspen stands in many areas of the intermountain west are currently dominated by older (>100 year) age classes and may be in decline. The goals of my research are to: (1) place current observations of aspen decline into context by using historical and ecological data to investigate the interaction of fire, ungulate browsing, climate and human institutions in the regeneration of aspen stands over the last two centuries; (2) evaluate the challenges and limitations associated with using ecological history for management of aspen and other systems; and (3) compare current and historical aspen regeneration across three elk winter range areas in the intermountain West. Based on results from stand age structures, aspen regeneration in the Jackson Valley has occurred episodically since 1830, with three major periods of regeneration: 1860-1885; 1915-1940; and 1955-1990. These multi-decadal episodes of aspen regeneration are related to similar variability in precipitation, where above average periods of annual precipitation are associated with aspen regeneration. However, significant levels of aspen regeneration have only coincided with low or moderate elk population estimates and fewer aspen have regenerated than expected when elk populations are high (X² = 59.92, p < 0.0001). Current aspen reproduction, though minimal, is strongly affected by elk browse with percent browse significantly higher in elk winter range than outside of elk winter range (p = 0.051). Though extensive or frequent fires may have maintained aspen communities during the pre-settlement era, current management controlled fires have not affected aspen sucker density. The influence of multiple interacting processes and drivers in the Jackson Valley suggests that reconstructing past ecosystems as benchmarks for ecological management should be considered carefully. Given future environmental variability, reconstructions of past systems should focus on ecological relationships rather than on single states or processes. Comparison of aspen in the three elk winter range areas indicates that heavy browsing by elk populations has had a strong influence on episodes of aspen regeneration for the last 150 years in all three elk winter ranges. However, elk are not having strong impacts on aspen outside of elk winter range.

Cupriferous swamps are characterized by high concentrations of copper in the soil and water. The Aboushagan swamp, situated 8km northwest of Sackville, New Brunswick is a unique metalliferous wetland where copper is naturally sequestered in the peat without having a significant negative effect on the vegetation. This paleoecological history of this region is not well known and few studies have attempted to characterize the local vegetation trends. This study investigates the post-glacial vegetation history of the swamp as well as any relationship it may have with the copper present in the peat. Surface peats (dry weight) have previously been found to contain up to 10% copper. This study found Cu content in two peat cores ranged from trace values to a high of 4800 µg/g and 25 000 µg/g (0.48 and 2.5 % dry weight copper). Despite the increased values, there was no detectable change in pollen due to copper concentration and any increase of copper in the peat material is likely a result of post depositional hydrological processes transporting copper into the layers of peat where it is being sequestered in the organic material and never becoming bioavailable to the surface vegetation. Pollen revealed that following deglaciation, the Aboushagan swamp began to develop as a rich fen around 10.7 ka BP that transitioned into a poor fen with Sphagnum around 9.9 ka BP as the wetland basin filled in. Around 8290 ka BP, temperatures warmed and the soil dried up leading to more canopy cover and fern abundance which yielded a mixed coniferous-deciduous swamp with Sphagnum in the understory that persisted until approximately 1.4 ka BP. Maritime vegetation trends in other studies describe a pine maxima (7.5 ka BP) and hemlock maxima (6.5-4.5 ka BP), neither of which were not found in the pollen record here due to a lack of peat accumulation between 8290 and 4350 ka BP. This is likely due to a regional climatic change that increased temperatures and decreased summer precipitation between 8 and 4 ka BP. In the last 1.5ka BP, the swamp has been dominated by spruce but other trees such as pine, fir, and birch have grown in abundance in the last few hundred years. A decrease in overall pollen abundance and concentration near the top of the core may be evidence for the little ice age event (1450 cal years BP). Today the swamp is a typical mixed coniferous-deciduous swamp with Picea mariana, Larix laricina, Acer rubrum, and Abies balsamea. An understanding of the swamp’s ability to sequester copper from becoming bioavailable has implications for the rehabilitation of contaminated industrial landscapes with wetland technologies. This study also highlights the high sensitivity with which wetlands can be used to detect and differentiate between autogenic (local) and allogenic (regional) climatic and vegetation changes while describing the vegetation community succession in the Aboushagan basin since the last deglaciation.

Texas coastal wetlands will be increasingly endangered over the coming century as sea level rises due to global warming. Since estimates of sea-level rise may be similar to trends interpreted from Holocene sediments, a paleoecologic analysis of wetland peats may provide a predictive model for wetland succession. Three areas of focus are necessary to achieve predictive power, however: ecologic, sedimentalogic, and taphonomic. No single microtaxonomic group is well preserved in all depositional environments. Foraminiferal assemblages delineate salt to brackish marsh environments, but are absent in fresh marsh sediments. Ostracodes and diatoms occur in all marsh types, but ostracodes are sporadically preserved and diatom thanatocoenoses from different environments become too similar to significantly indicate different biocoenoses. A combined thanatocoenosis composed of microtaxa with similar ecological requirements but different taphonomic signatures provides an effective method of identifying sea-level history from wetland sediment cores, however, since taphonomic effects on selected groups overlap. Calcium carbonate and silicate dissolve according to pH, while proteinaceous cements of many agglutinated foraminifera withstand dissolution and are removed only through oxidation-reduction reactions. An analysis of these trends in the Galveston Bay system supports the following taphonomic model: During accretionary still stands, in-situ preservation is high for each thanatocoenosis. This is due to the effects of time averaging over an otherwise harsh and patchy chemical environment. During rapid sea-level rise, fresh marsh sediments become inundated with brackish to salt water. This tends to raise the pH and Eh, enhancing preservation. The thanatocoenoses grade sharply from mixed to distinct. During flooding, or progradation, fresh water inundates brackish to salt water sediments. This tends to lower pH and Eh, decreasing preservation. In situ thanatocoenoses are reduced to only a few species or eliminated completely. This taphonomic model suggests that the traditional approach of using a single microfossil group to interpret sea-level trends may be inadequate. The combined thanatocoenosis approach can produce better controls on paleoecologic and paleoclimatic interpretations, and will allow for better predictions of future trends.

As part of Parks Canada’s management initiatives, St. Lawrence Islands National Park (SLINP) funded this study to learn more about the natural local fire regime, learn about the risks associated with fire in a changing climate scenario, and to aid in protection efforts of the fire-dependent species Pinus rigida (pitch pine), which is listed provincially as a species at risk. The study site selected was Little Black Lake (44º 32'45.20" N, 76 º 03'12.06” W), which is ideal because of its small size and isolated watershed. A 4.5 m Livingston-piston core and a 0.5 m Glew gravity core were extracted from the lake basin. Charcoal macrofossils >125 µm were quantified at 0.5 cm intervals to produce a high-resolution (14 years) fire record. A chronology was created for each of the two cores together using a combination of 13 14C dates and 20 210Pb dates to complete a record spanning from 2008 to >11000 Cal yrs BP. In general, the fire regime appears to be non-stationary with overall low CHAR (charcoal particles per cm2 of sediment per year) throughout the Holocene. The mean fire return interval for the entire record was on the century scale, at 244 years. The early- and mid-Holocene show low CHAR and few peaks during a period dominated by spruce and pine. Contrastingly, the late Holocene shows an increase in CHAR and peaks during hardwood dominance, which may be due to a change in fuel, as suggested by charcoal morphotypes. A detailed look at the Late Holocene through an analysis of the Glew gravity core, shows a shorter mean fire interval. Comparisons of the Little Black Lake fire record with other vegetation and charcoal records from this region indicate interactions between climate and changing fuel sources may be explanations for the non-stationarity of the fire regime. Management steps for St. Lawrence Islands National Park could include continuing small, isolated and infrequent burns and continued monitoring of local Pitch Pine populations provided spatial and temporal heterogeneity are taken into account. / Thesis (Master, Environmental Studies) -- Queen's University, 2010-01-31 23:58:09.579

The Saluda Formation, a lithologically distinct but spatially variable unit, is mappable in the subsurface. Lithologic characters such as dolomitic and laminated finegrained carbonates, paucity of fossils and terriginous detritus, birdseye structures, and intraclasts distinguish the formation and aid in interpreting the depositional environment. Similarities of features for modern and ancient carbonate tidal-flats and those of the Saluda suggest a tidal-flat environment of origin for the formation. Lateral and vertical lithologic relationships with contiguous formations record spatially variable but time transgressive subenvironments of deposition for the tidal-flat complex and surrounding sea.

Pollen analysis of lake sediments was used to reconstruct the postglacial vegetation history of Hippa Island (53°31'50” N, 132°58'24” W), located on the exposed west coast of Haida Gwaii (Queen Charlotte Islands) on the northern British Columbia coast. A 3.55 m sediment core was extracted from Hippa Lake, a small, shallow lake on Hippa Island. Five radiocarbon ages were obtained on organic-rich sediment. A linear age-depth model estimated the base of the sediment core to be 14,000 cal yr BP (12,000 14C yr BP). Pollen and spores extracted from sediment subsamples (1 cm3) taken along the length of the core were identified and counted to a minimum sum of 500 pollen and spores, except for four basal samples, which had low pollen concentrations. Hippa Island’s vegetation history shares broad similarities to other vegetation records from Haida Gwaii and elsewhere along the British Columbia coast; however, climate fluctuations are not well recorded by the predominantly mesic pollen assemblages. The late-glacial period (14,000–13,500 cal yr BP; 12,000–11,400 14C yr BP) records a diverse herb-dominated vegetation community composed of Cyperaceae, Artemisia, Salix, and many other herbs. Transition to Pinus woodland by 13,250 cal yr BP (11,250 14C yr BP) is followed by increases in Alnus viridis and Alnus rubra, and the arrival of Picea. A decrease in Pinus and minor increases in ferns and herbs coincide with the Younger Dryas cold period; however, regression to tundra or increased Tsuga mertensiana, which characterized Younger Dryas cooling at other sites along the north Pacific coast, did not occur on Hippa Island. After 11,000 cal yr BP (9750 14C yr BP), a sharp change in vegetation occurs with Pinus, Alnus viridis, and Cyperaceae being replaced by Picea, Tsuga heterophylla and Lysichiton americanus. Despite well-documented evidence of a warmer and drier interval during the early Holocene, the composition of the mesic vegetation communities on Hippa Island was relatively stable during this time. Increases in Cupressaceae after 6000 cal yr BP (5300 14C yr BP) suggest increasing precipitation in the mid-Holocene. Modern mixed Cupressaceae-Picea-T. heterophylla forest formed by 4500 cal yr BP (4000 14C yr BP). / Graduate

<p> While the processes that led to the formation of modern plant communities are often cryptic, biogeographic patterns of extant species can provide clues to their origin. The Midriff Islands, an archipelago in the Gulf of California at the center of the Sonoran Desert, provide an opportunity to investigate the origins of the desert. This research uses three case studies at three different time scales to better understand the factors responsible for modern biodiversity. </p><p> Chapter 1 revisits the theory of island biogeography and incorporates the long history of humans on the Midriff Islands to determine factors controlling plant species richness. Area, habitat diversity, island type, and seabird dynamics explain 98% of the variability in species richness across this archipelago. Interestingly, human presence is not predictive, suggesting an island system with ancient human interactions that functions in a pre-Anthropocene state. </p><p> Chapter 2 investigates Holocene extinctions. In 1975, bighorn sheep (<i> Ovis canadensis</i>) were introduced as a novel element to Isla Tibur&oacute;n as a conservation measure. Fossil dung found on Isla Tibur&oacute;n was 14C-dated to 1476-1632 years before present and identified as <i>Ovis canadensis </i> by morphological and ancient DNA analysis. Bighorn sheep went locally extinct on the island sometime in the last ~1500 years prior to their "unintentional rewilding." This discovery questions the definition of a non-native species and extends an ecological and conservation baseline. </p><p> Disjunct long-lived plant taxa on Isla Tibur&oacute;n suggests climate and vegetation change on the Midriff Islands in the Pleistocene. Chapter 3 is a phylogeographic study of the desert edge species <i>Canotia holacantha </i> (Celastraceae) that tests whether <i>Canotia</i> on Isla Tibur&oacute;n is a Pleistocene relict or a recent dispersal event. Results suggest long isolation and divergence of <i>Canotia</i> on Tibur&oacute;n but recent arrival in the core of its modern day distribution in Arizona. In contradiction to an expected temperate origin, <i>Canotia</i> seems to have tracked the northward shift of the desert's edge at the end of the last Ice Age from glacial refugia in Sonora or Chihuahua. </p><p> Collectively, this research helps illuminate the history of the desert and establishes baselines to support management decisions of the world's best-preserved archipelago.</p>

Thesis (M.S.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 207-218)

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: p. 366-393.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed July 21, 2009). PDF text: xi, 160 p. : ill. (some col.), col. maps ; 5.84 Mb. UMI publication number: AAT 3350458. Includes bibliographical references. Also available in microfilm and microfiche formats.