Observations on Bog and Pollen Stratigraphy of the Des Moines Glacial Lobe, lowa

As part of an investigation into the effect of environmental changes of landscape and soils on the Des Moines lobe (Cary till), three deep bogs (Colo, Jewell, McCulloch) were examined in detail. The center profile of each has a surface peat underlain by deep, dark-colored, calcareous silts; these in turn are underlain by a second peat zone which passes into basal calcareous silts and eventually to till. Preliminary pollen data on the Colo bog shows six zones. The key zones are Zone 1 (0 to 75 inches), in which the pollen is of dominantly herbaceous genera indicating an open grassland environment, and Zones IV and V (102 to 155 to 212 inches) dominated by pollen of forest species. The changes in bog and pollen strata were probably related to a marked change from a cool climate in the early postglacial to a warmer climate in the latter part of the postglacial continuing to the present

The value of paleoecology as an aid to monitoring ecosystems and landscapes, chiefly with reference to North America

Paleoecological indicators are examined as to their accuracy in reconstructing past biotic communities and environmental conditions, their utility in answering important questions about such communities and conditions, and the temporal and spatial scales over which they are effective. Next, environmental problems susceptible of paleoecological analysis are considered, as are the ecosystem and landscape properties that can be inferred from such an analysis. The usefulness of paleoecology in anticipating ecological surprises is then discussed. Finally, a set of conclusions and recommendations is presented

POLLEN CLUMPING AND WIND DISPERSAL IN AN INVASIVE ANGIOSPERM

Pollen dispersal is a fundamental aspect of plant reproductive biology that maintains connectivity between spatially separated populations. Pollen clumping, a characteristic feature of insect-pollinated plants, is generally assumed to be a detriment to wind pollination because clumps disperse shorter distances than do solitary pollen grains. Yet pollen clumps have been observed in dispersion studies of some widely distributed wind-pollinated species. We used Ambrosia artemisiifolia (common ragweed; Asteraceae), a successful invasive angiosperm, to investigate the effect of clumping on wind dispersal of pollen under natural conditions in a large field. Results of simultaneous measurements of clump size both in pollen shedding from male flowers and airborne pollen being dispersed in the atmosphere are combined with a transport model to show that rather than being detrimental, clumps may actually be advantageous for wind pollination. Initial clumps can pollinate the parent population, while smaller clumps that arise from breakup of larger clumps can cross-pollinate distant populations

Down by the riverside: urban riparian ecology

Riparian areas are hotspots of interactions between plants, soil, water, microbes, and people. While urban land use change has been shown to have dramatic effects on watershed hydrology, there has been surpris- ingly little analysis of its effects on riparian areas. Here we examine the ecology of urban riparian zones, focusing on work done in the Baltimore Ecosystem Study, a component of the US National Science Foundation's Long Term Ecological Research network. Research in the Baltimore study has addressed how changes in hydrology associated with urbanization create riparian "hydrologic drought" by lowering water tables, which in turn alters soil, vegetation, and microbial processes. We analyze the nature of past and cur- rent human interactions with riparian ecosystems, and review other urban ecosystem studies to show how our observations mirror those in other cities

Sedimentation Cycles in a River-Mouth Tidal Freshwater Marsh

Tidal freshwater marshes are critical buffers that exist at the interface between watersheds and estuaries. Little is known about the physical dynamics of tidal freshwater marsh evolution. Over a 21 month period from July 1995 to March 1997, measurements were made of biweekly sediment deposition at 23 locations in a 3.8 hectare tidal freshwater marsh in the Bush River subestuary of the upper Chesapeake Bay. Bi-weekly accumulation showed high spatial and temporal variability, ranging from -0.28 to 1.15 g cm-2. Spatial variability is accounted for by habitat differences including plant associations, elevation, and hydrology. Temporal variability is accounted for by interannual climate variability, the growth cycles of marsh plants, stream-marsh interactions, forest-marsh interactions, and animal activity

Supplement 1. The R source code for fitting extreme value distributions.

<h2>File List</h2><blockquote> <p> <a href="rextreme.txt">rextreme.txt</a> - R source code for fitting extreme value distributions<br> </p> <p> </p> </blockquote><h2>Description</h2><blockquote> <p>This is a text file containing R-language source code for fitting extreme value distributions. These functions were originally written in S by Stuart Coles and converted to R by Alec Stephenson. For an explanation of how to use these functions, see the Appendix in: Stuart Coles, 2001. <i> An introduction to the statistical modeling of extreme values</i>. Springer-Verlag, London, UK.</p> <p>These functions are included to document how the results in the paper were obtained. For other use, it is recommended that the entire suite of functions for extreme value analysis be downloaded. The Extremes Toolkit includes this suite of functions, as well as a graphical user interface (currently available at: <a href="http://www.esig.ucar.edu/extremevalues/evtk.html">www.esig.ucar.edu/extremevalues/evtk.html</a>). </p><p>gev.fit is a R function that estimates the parameters of the generalized extreme value distribution by the method of maximum likelihood.</p> <p>gpd.fit is a R function that estimates the parameters of the generalized Pareto distribution by the method of maximum likelihood.</p> <p>pp.fit is a R function that estimates the parameters of the generalized extreme value distribution, via the point process representation, by the method of maximum likelihood.</p> </blockquote

Data from: Herbarium specimens reveal a historical shift in phylogeographic structure of common ragweed during native range disturbance

Invasive plants provide ample opportunity to study evolutionary shifts that occur after introduction to novel environments. However, although genetic characters pre-dating introduction can be important determinants of later success, large-scale investigations of historical genetic structure have not been feasible. Common ragweed (Ambrosia artemisiifolia L.) is an invasive weed native to North America that is known for its allergenic pollen. Palynological records from sediment cores indicate that this species was uncommon before European colonization of North America, and ragweed populations expanded rapidly as settlers deforested the landscape on a massive scale, later becoming an aggressive invasive with populations established globally. Toward a direct comparison of genetic structure now and during intense anthropogenic disturbance of the late 19th century, we sampled 45 natural populations of common ragweed across its native range as well as historical herbarium specimens collected up to 140 years ago. Bayesian clustering analyses of 453 modern and 473 historical samples genotyped at three chloroplast spacer regions and six nuclear microsatellite loci reveal that historical ragweed’s spatial-genetic structure mirrors both the paleo-record of Ambrosia pollen deposition and the historical pattern of agricultural density across the landscape. Furthermore, for unknown reasons this spatial-genetic pattern has changed substantially in the intervening years. Following on previous work relating morphology and and genetic expression between plants collected from eastern North America and Western Europe, we speculate that the cluster associated with humans’ rapid transformation of the landscape is a likely source of these aggressive invasive populations

Data from: Herbarium specimens reveal a historical shift in phylogeographic structure of common ragweed during native range disturbance

Invasive plants provide ample opportunity to study evolutionary shifts that occur after introduction to novel environments. However, although genetic characters pre-dating introduction can be important determinants of later success, large-scale investigations of historical genetic structure have not been feasible. Common ragweed (Ambrosia artemisiifolia L.) is an invasive weed native to North America that is known for its allergenic pollen. Palynological records from sediment cores indicate that this species was uncommon before European colonization of North America, and ragweed populations expanded rapidly as settlers deforested the landscape on a massive scale, later becoming an aggressive invasive with populations established globally. Toward a direct comparison of genetic structure now and during intense anthropogenic disturbance of the late 19th century, we sampled 45 natural populations of common ragweed across its native range as well as historical herbarium specimens collected up to 140 years ago. Bayesian clustering analyses of 453 modern and 473 historical samples genotyped at three chloroplast spacer regions and six nuclear microsatellite loci reveal that historical ragweed’s spatial-genetic structure mirrors both the paleo-record of Ambrosia pollen deposition and the historical pattern of agricultural density across the landscape. Furthermore, for unknown reasons this spatial-genetic pattern has changed substantially in the intervening years. Following on previous work relating morphology and and genetic expression between plants collected from eastern North America and Western Europe, we speculate that the cluster associated with humans’ rapid transformation of the landscape is a likely source of these aggressive invasive populations

Data from: Herbarium specimens reveal a historical shift in phylogeographic structure of common ragweed during native range disturbance

Invasive plants provide ample opportunity to study evolutionary shifts that occur after introduction to novel environments. However, although genetic characters pre-dating introduction can be important determinants of later success, large-scale investigations of historical genetic structure have not been feasible. Common ragweed (Ambrosia artemisiifolia L.) is an invasive weed native to North America that is known for its allergenic pollen. Palynological records from sediment cores indicate that this species was uncommon before European colonization of North America, and ragweed populations expanded rapidly as settlers deforested the landscape on a massive scale, later becoming an aggressive invasive with populations established globally. Toward a direct comparison of genetic structure now and during intense anthropogenic disturbance of the late 19th century, we sampled 45 natural populations of common ragweed across its native range as well as historical herbarium specimens collected up to 140 years ago. Bayesian clustering analyses of 453 modern and 473 historical samples genotyped at three chloroplast spacer regions and six nuclear microsatellite loci reveal that historical ragweed’s spatial-genetic structure mirrors both the paleo-record of Ambrosia pollen deposition and the historical pattern of agricultural density across the landscape. Furthermore, for unknown reasons this spatial-genetic pattern has changed substantially in the intervening years. Following on previous work relating morphology and and genetic expression between plants collected from eastern North America and Western Europe, we speculate that the cluster associated with humans’ rapid transformation of the landscape is a likely source of these aggressive invasive populations