Sara Hotchkiss
University of Wisconsin-Madison, Botany, Faculty Member
... available Hawaiian temperature estimates temperature depression of 13 °C at the ocean surface (Lee ... lines of evidence suggest that the northeast trade winds persisted during the lateQuaternary in the ... Remains of trees and... more
... available Hawaiian temperature estimates temperature depression of 13 °C at the ocean surface (Lee ... lines of evidence suggest that the northeast trade winds persisted during the lateQuaternary in the ... Remains of trees and palms in the Salt Lake Tuff, deposited during a low ...
ABSTRACT A pollen record from Ka‘au Crater, O‘ahu, Hawai‘i contains evidence for changes in vegetation and climate since about 28,000 14C yr B.P. Zone 1 (ca. 28,100–ca. 22,800 14C yr B.P.) has pollen of dry to mesic forest species,... more
ABSTRACT A pollen record from Ka‘au Crater, O‘ahu, Hawai‘i contains evidence for changes in vegetation and climate since about 28,000 14C yr B.P. Zone 1 (ca. 28,100–ca. 22,800 14C yr B.P.) has pollen of dry to mesic forest species, including Pipturus-type, Dodonaea viscosa, Acacia koa, Chenopodium oahuense, Claoxylon sandwicense, Myrsine, and Metrosideros-type. In zone 2 (ca. 22,800–ca. 16,200 14C yr B.P.) Myrsine and Coprosma increase, with herbs, fern allies, and Grammitidaceae suggesting open canopies. Zone 3 (ca. 16,200–ca. 9700 14C yr B.P.) has pollen of wet forest species, including Freycinetia arborea, abundant Pritchardia, and Metrosideros-type. Zone 4 (ca. 9700–ca. 7000 14C yr B.P.) is similar, with less Pritchardia and more Metrosideros-type. Climate reconstruction was based on modern climatic ranges of flowering plants and an index derived from abundance of pollen in surface samples. Both methods agree on a qualitative reconstruction, although the ages are poorly constrained: 28,000–25,000 14C yr B.P. cool and dry; 25,000–23,000 14C yr B.P. dry and warmer; 23,000–20,000 14C yr B.P. moderately dry with declining temperature; 20,000–16,000 14C yr B.P. moderately dry and cool; 16,000–9000 14C yr B.P. warm and wet; 9000–7000 14C yr B.P. warm and possibly drier. Lower precipitation at Ka‘au Crater during the late glacial period and last glacial maximum is consistent with the interpretation that the North Pacific subtropical anticyclone was south of its present position. The pollen-derived temperature index yields an estimate of 3°–5°C temperature depression during the last glacial maximum.
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... ML Alexander (&) US Fish and Wildlife Service, 500 E. McCarty Lane, San Marcos, TX 78666, USA e-mail: Mara_Alexander@fws.gov 123 ... in predation by plank-tivorous fish due to the refuge the plants provide for small-bodied fish... more
... ML Alexander (&) US Fish and Wildlife Service, 500 E. McCarty Lane, San Marcos, TX 78666, USA e-mail: Mara_Alexander@fws.gov 123 ... in predation by plank-tivorous fish due to the refuge the plants provide for small-bodied fish against piscivory (Persson and Crowder 1998 ...
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Research Interests: Ecology, Hawaii, Nitrogen, Trees, Ferns, and 3 moreEcosystem, Time Factors, and Ecological Applications
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... Sciences, University of Wisconsin - Madison, Madison, WI and Sara C. Hotchkiss, Department of Botany, University of Wisconsin, Madison, WI ... Charcoal accumulation rates in lake sediment samples from Circle Lily Lake were compared... more
... Sciences, University of Wisconsin - Madison, Madison, WI and Sara C. Hotchkiss, Department of Botany, University of Wisconsin, Madison, WI ... Charcoal accumulation rates in lake sediment samples from Circle Lily Lake were compared with historical records of logging and ...
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Background/Question/Methods Understanding the patterns, causes, and consequences of disturbance-regeneration dynamics in tropical forests has been difficult to achieve due to difficulties in reconstructing stand dynamics caused by the... more
Background/Question/Methods Understanding the patterns, causes, and consequences of disturbance-regeneration dynamics in tropical forests has been difficult to achieve due to difficulties in reconstructing stand dynamics caused by the lack of annual tree rings and the sparseness of long-term observations in most tropical forests. In the tropical montane rainforests of Hawai`i characterizing plant community response to disturbance is further complicated by the lack of a guild of fast-growing, gap-colonizing species to indicate areas of recent disturbance. At 4000 feet elevation in the Laupahoehoe Experimental Tropical Forest on the Island of Hawai`i we used direct multi-scale ordination (mso) and spatial variance partitioning analysis to determine whether the montane rainforest plant community shows any consistent species compositional variability associated with signs of disturbance and whether there is underlying spatial autocorrelation not explained by other gradients that may ind...
Background/Question/Methods Background: Land management strategies to address the impacts of rapid climate change on a variety of ecological systems include creating habitat corridors, replacement of invasive species, re-establishment of... more
Background/Question/Methods Background: Land management strategies to address the impacts of rapid climate change on a variety of ecological systems include creating habitat corridors, replacement of invasive species, re-establishment of disturbance regimes, restoration of communities and species translocation. All of the proposed strategies imply that land management in the future will largely be involved in explicitly designing and establishing ecological systems to meet management objectives. Whether we are designing intensive agro-ecosystems or biodiversity reserves, robust ecological systems design is improved by insights gathered from the study of patterns and processes in unintentional systems. Approach: In three landscapes across an elevation gradient in the Laupâhoehoe Experimental Tropical Forest on the Island of Hawai`i (3200 to 4700 feet elevation) we determined the species-specific distribution patterns of a Hawaiian montane rainforest plant community in response to und...
Background/Question/Methods Ecosystems are difficult to comprehend not only because they respond to drivers-of-change on multiple interacting spatial scales but also because they exhibit substantial variation across time. Paleoecologists... more
Background/Question/Methods Ecosystems are difficult to comprehend not only because they respond to drivers-of-change on multiple interacting spatial scales but also because they exhibit substantial variation across time. Paleoecologists have increasing access to techniques to look at temporal variation in ecosystems beyond the scope of repeated measures of plot data. An additional part of the complexity of ecosystems is that the vagaries of field sampling and the sometimes uncooperative nature of sediment records prevent straight-forward analysis. We encountered such travails when developing age chronologies of sediment records using lead-210 isotopes in a set of unconventional forest hollow cores from the rainforest of windward Mauna kea in Hawai`i. The initial lead-210 curves did not approach a steady background level (the “supported” lead-210) and so could not be used accurately in conventional age chronology calculations. We used a technique from Bayesian statistics, the Gibbs ...
Background/Question/Methods Understanding the relative sensitivity of different types of forests to past climate change provides important context for predicting future changes. We analyzed vegetation changes over the last 3500 years, a... more
Background/Question/Methods Understanding the relative sensitivity of different types of forests to past climate change provides important context for predicting future changes. We analyzed vegetation changes over the last 3500 years, a time when a long-term increase in moisture led to an increase in yellow birch (Betula alleganiensis) and eastern hemlock (Tsuga canadensis). We analyzed pollen from a 280 cm 3500 year sediment core from Eska Lake, Taylor County and compared our results with regional pollen data from a variety of soil types including sandy soils where hemlock does not grow. Pollen based vegetation history was also compared with vegetation-independent climate reconstructions to aid in a regional interpretation of forest changes in response to century scale changes in moisture availability. Results/Conclusions Hemlock abundance at Eska Lake increased from 0-3% before 1500 years ago to >5% after. A period of low moisture availability from 1800 to at least 1500 years a...
Background/Question/Methods Pollen-based studies indicate that mesic (less drought tolerant) taxa increased at the prairie-forest border and throughout the western Great Lakes region ~700 years ago.The timing of mesic taxa expansion... more
Background/Question/Methods Pollen-based studies indicate that mesic (less drought tolerant) taxa increased at the prairie-forest border and throughout the western Great Lakes region ~700 years ago.The timing of mesic taxa expansion corresponds with the Little Ice Age (LIA) found across much of the northern hemisphere. However, there are few climate records that are independent of vegetation in this region and inconsistencies between studies and research sites remain problematic. We analyzed lake sediment from a transect of shallow water cores from Cheney Lake, WI. Cheney Lake is a relatively small (<10 ha), climate responsive seepage lake with a deep basin (6.4 msimple bathymetry, surrounded by jack pine forest with no nearby buildings or roads. Diatom samples were analyzed at 0.5 cm resolution from a core in ~50cm of water with several sand lenses. A minimum of 300 valves per sample were counted to obtain a sub-decadal history of the diatom species assemblage in Cheney Lake. Mo...
ABSTRACT Global climate change has raised important questions about ecosystem resilience and the likelihood of unexpected and potentially irreversible ecosystem state shifts. Conceptual models provide a framework for generating hypotheses... more
ABSTRACT Global climate change has raised important questions about ecosystem resilience and the likelihood of unexpected and potentially irreversible ecosystem state shifts. Conceptual models provide a framework for generating hypotheses about long-term ecosystem processes and their responses to external perturbations. In this article, we review the classic model of autogenic peatland encroachment into closed-basin kettle lakes (terrestrialization) as well as studies that document patterns of terrestrialization that are inconsistent with this hypothesis. We then present a new conceptual model of episodic, drought-triggered terrestrialization, which is consistent with existing data and provides a mechanism by which climatic variability could cause non-linear patterns of peatland development in these ecosystems. Next, we review data from comparative studies of kettle lakes along a peatland-development gradient to explore potential ecological and biogeochemical consequences of non-linear patterns of terrestrialization. Finally, we identify research approaches that could be used to test conceptual models of terrestrialization, investigate the ecological implications of non-linear patterns of peatland development, and improve our ability to predict responses of kettle systems to climate changes of the coming decades and century.
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... yr BP (Umbanhowar, 2004). Charcoal records from laminated lake sediments suggest a decrease in fire frequency 400-100 cal. yr BP in northern Wisconsin (Swain, 1978) and north-central Minnesota (Clark, 1988, 1990), beginning long... more
... yr BP (Umbanhowar, 2004). Charcoal records from laminated lake sediments suggest a decrease in fire frequency 400-100 cal. yr BP in northern Wisconsin (Swain, 1978) and north-central Minnesota (Clark, 1988, 1990), beginning long before effective fire suppression efforts. ...
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Abstract We describe five common charcoal morphotypes observed in late-Holocene lake sediments from northern Wisconsin and compare them with charcoal produced by burning modern plant material. Our experiments show that grass cuticle,... more
Abstract We describe five common charcoal morphotypes observed in late-Holocene lake sediments from northern Wisconsin and compare them with charcoal produced by burning modern plant material. Our experiments show that grass cuticle, conifer wood and leaves ...
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A dilemma has long confronted paleoecologists: pollen data are required to assess past vegetational changes, and at the same time pollen data serve as a primary source of paleoclimate inference. Paleoecologists have had to use the same... more
A dilemma has long confronted paleoecologists: pollen data are required to assess past vegetational changes, and at the same time pollen data serve as a primary source of paleoclimate inference. Paleoecologists have had to use the same data sets to infer past climate changes and the ecological responses to those changes. The emergence of independent paleoclimate proxies and archives is providing relief from this dilemma. Peatland archives are especially effective at providing independent paleoclimatic records, ...