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Understanding how past communities have been shaped by environmental alterations can provide insight into the impacts of future climate change. Local climate and river systems have changed significantly over the last glacial maximum, but little is known about the communities of the Georgian Coastal Plain earlier in the period. Plant fossils from Coffee Bluff, a Quaternary organic river deposit of the Ocmulgee River in southeastern Georgia, were used to determine past environmental and climatic conditions. The paleoflora were found imbedded in a mud matrix and were removed by a slaking method; they were later identified and separated to respective ecological environments. Of the eleven species identified, one was a wetland species (marsh sedges), while the remaining ten were woodland species. From using the coexistence approach with the plant fossils and aligning their growing conditions, we suggest that Coffee Bluff was a stream/riverine habitat with loamy and well-drained soils; local climate was humid, with temperatures and annual precipitation ranging from 10 to 21[degrees]C and 1016 to 1524 mm, respectively. Few gymnosperm specimens were recovered in the material, though groups like conifers were dominant in the coastal plain environment during the late Pleistocene. It is most likely that there were fewer conifer trees near the collection area. Keywords. paleobotany, Ocmulgee River, coastal plain, Quaternary, late-Pleistocene, riverine, INTRODUCTION The state of Georgia is divided into five distinct geographic regions as follows: Appalachian Plateau, Ridge and Valley, Blue Ridge, Piedmont, and Coastal Plain (Figure 1). The northwestern portion [...]

This article describes the history of plant introductions from Japan into North America, from the Perry Expedition in 1854 through the collections of George Rogers Hall of Bristol, Rhode Island and Thomas Hogg of New York City between 1861 and 1875. Both men sent plants to the innovative nurseryman, Samuel Bowne Parsons of Flushing, Long Island, who propagated and sold them to the gardening public. This process, which took more than twenty years from initial collection through commercial distribution, succeeded in adding innumerable Japanese species into the ornamental landscapes of North America, including Japanese maple, kousa dogwood, panicle hydrangea, and Sawara cypress. Unfortunately these early introductions also included a number of species which escaped cultivation and have become infamously invasive, including oriental bittersweet, kudzu, porcelain berry and Japanese honeysuckle. The pioneering work of these three horticulturists-compounded over the past hundred and fifty years-has had a profound impact on both cultivated and wild landscapes across North America. Keywords George Rogers Hall * James Hogg * Thomas Hogg * Invasive species * Japanese horticulture * Kissena nurseries * New York Botanical Garden * Samuel B. Parsons * Samuel Parsons, Jr., Introduction Landscape gardening the large-scale planting of trees, shrubs and lawns for ornamental purposes-did not really become popular in the United States until after the Revolutionary War, once the American [...]

The objective of this study was to evaluate growth-climate associations for northern red oak (Quercus rubra L.) across much of its geographic range in eastern North America and to compare these associations with those of white oak (Quercus alba L.). Tree-ring and climate data were obtained for a total of 82 sites, including 51 sites where both oak species were sampled. Northern red oak radial growth was most strongly and spatially consistently correlated with site water balance variables for the early growing season (May through July). Correlations with prior year autumn and winter precipitation were also identified at a smaller number of sites. The phenology of growth-climate correlations was virtually identical between northern red oak and white oak, although there was modest evidence that correlations were stronger for white oak. These results support the hypothesis that species with similar wood anatomy, geographic distribution, and habitat preferences may have similar growth-climate relationships. This suggests that functional groups of tree species may be defined a priori based on existing knowledge of their wood anatomy and ecology. L'objectif de cette etude consistait a evaluer les relations entre la croissance et le climat dans le cas du chene rouge (Quercus rubra L.) un peu partout dans son aire de repartition dans l'est de l'Amerique du Nord et de comparer ces relations a celles du chene blanc (Quercus alba L.). Des donnees dendrochronologiques et climatiques ont ete obtenues pour un total de 82 stations, incluant 51 stations ou les deux especes de chene ont ete echantillonnees. La croissance radiale du chene etait constamment le plus fortement et spatialement correlee avec les variables du bilan hydrique de la station au debut de la saison de croissance (mai a juillet). Des correlations avec les precipitations de l'automne et de l'hiver precedents ont aussi ete identifiees dans un plus petit nombre de stations. La phenologie des correlations entre le climat et la croissance etait pratiquement identique chez les chenes rouge et blanc malgre un certain indice que les correlations etaient plus fortes dans le cas du chene blanc. Ces resultats supportent l'hypothese voulant que la relation entre le climat et la croissance chez les especes dont l'anatomie du bois, la repartition geographique et les preferences d'habitat sont semblables puisse aussi etre semblable. Cela signifie que des groupes fonctionnels d'especes d'arbre peuvent etre definis a priori sur la base des connaissances que nous possedons au sujet de l'ecologie et de l'anatomie du bois de ces especes. [Traduit par la Redaction], Introduction Some researchers have proposed that models to project climate change effects on forests could be greatly simplified if climate responses for 'functional groups' of tree species were modeled rather [...]

There are only about 8000 Piping Plovers (Charadrius melodus Ord, 1834) in existence. Because they depend on environments that are under intense human pressures and controls in both their breeding and wintering grounds, these birds and their habitats are highly managed in many areas across their range. Efforts to recover this endangered and threatened species have engaged thousands of people from Newfoundland to the Caribbean, and have provoked a ground- swell of public support and, at times, fury, as well as a considerable body of research. Although populations have increased substantially in the U.S. Atlantic and U.S. Great Lakes, this is not true of all regions. Significant issues still exist with respect to the efficacy of predator management; need for more accurate model input information; effects of climate, pollutants, and water management; habitat loss and degradation from recreation and development; and whether the cost and effort of management for this species can be maintained or increased where needed. Il ne reste plus qu'environ 8000 pluviers siffleurs (Charadrius melodus Ord, 1834). Parce qu'ils sont dependants d'environnements qui subissent d'intenses pressions et controles de la part des humains, tant sur leurs aires de reproduction que d'hivernage, ces oiseaux et leurs habitats font l'objet d'une importante gestion dans plusieurs regions de leur aire de repartition. Les efforts pour retablir cette espece menacee et en peril impliquent des milliers de personnes de Terre-Neuve aux Antilles et ont suscite une vague d'appui et, a l'occasion, de colere de la part du public, de meme qu'un ensemble considerable de recherche. Alors que les populations ont cru de facon substantielle sur la cote atlantique et la region des Grands Lacs aux Etats-Unis, ce n'est pas le cas pour toutes les regions. Il reste des problemes importants relies a l'efficacite de la gestion des predateurs; a la necessite d'un modele plus precis pour la saisie d'information; aux effets du climat, des polluants et de la gestion de l' eau; et a la perte et la degradation des habitats associees au loisirs et au developpement. Il faudrait aussi savoir s'il est possible de maintenir les couts et les efforts necessaires pour la gestion de l'espece et meme de les augmenter la ou c' est requis. [Traduit par la Redaction], Introduction Piping Plovers (Charadrius melodus Ord, 1834) are small shorebirds that breed on sparsely vegetated shorelines of the Atlantic coast of Canada and the United States, the Great Lakes (primarily [...]

We studied microsatellite DNA variation in 15 populations of northwestern North American pygmy whitefish (Prosopium coulterii (Eigenmann and Eigenmann, 1892)), an enigmatic freshwater fish thought to be highly fragmented by residency in deep, cold postglacial lakes. Population subdivision (θ) across 10 loci was 0.12 (P < 0.001) across samples, but one western Alaskan population was more divergent than all others (θ = 0.31-0.41, P < 0.001). Within the Williston Reservoir watershed (WRW), θ averaged 0.08 (P < 0.001) and was positively associated with both the geographic distance between localities ([r.sup.2] = 0.36, P < 0.001) and the number of branch points interconnecting them ([r.sup.2] = 0.33, P < 0.001). Differentiation among populations was modeled as the sum of the genetic distances for the stream sections interconnecting them ([r.sup.2] = 0.74). Differences among subwatersheds with the WRW accounted for 5.1% of the total variation in allele frequencies (P < 0.001). Assignment tests suggested limited movement among lakes, with most inferred dispersal between adjacent watersheds. Coalescent analysis strongly supported a gene flow-drift equilibrium model of population structure over a drift-only model. Effective management of diversity in pygmy whitefish requires the maintenance of stream networks that interconnect lakes within a watershed. Nous etudions la variation de l'ADN des microsatellites dans 15 populations du nord-ouest de l'Amerique du Nord du menomini pygmee, Prosopium coulterii (Eigenmann et Eigenmann, 1892), un poisson d'eau douce enigmatique dont on croit les populations fortement fragmentees a cause de leur residence dans des lacs postglaciaires profonds et froids. La subdivision de la population (θ) dans 10 locus est de 0,12 (P < 0,001) dans l'ensemble des echantillons, bien qu'une population de l'ouest de l'Alaska soit plus divergente que toutes les autres (θ = 0,31-0,41, P < 0,001). Dans le bassin hydrographique du reservoir Williston (WRW), θ a une valeur moyenne de 0,08 (P < 0,001) et est en correlation positive tant avec la distance geographique entre les localites ([r.sup.2] = 0,36, P < 0,001) qu'avec le nombre de points de branchement qui les relie ([r.sup.2] = 0,33, P < 0,001). La differentiation entre les populations peut se modeliser comme la somme des distances genetiques des sections de cours d' eau qui les rattachent ([r.sup.2] = 0,74). La differenciation entre les sous-bassins au sein de WRW explique 5,1 % de la variation totale dans la frequence des alleles (P < 0,001). Des tests d'assignation indiquent des deplacements limites entre les lacs, avec la dispersion le plus souvent retrouvee entre des bassins versants adjacents. Une analyse de coalescence appuie fortement un modele de structure de population avec equilibre entre le flux genique et la derive, plutot qu'un modele de derive seule. Une gestion efficace de la diversite chez les menominis pygmees necessite le maintien des reseaux de cours d'eau qui relient les lacs dans un meme bassin versant. [Traduit par la Redaction], Introduction In geographically widespread species, the extent of population subdivision, or the degree to which species are subdivided into at least partially genetically distinct units, will be a function both [...]

The management of water resources in arid and semiarid areas has long been a challenge, from ancient Mesopotamia to the modern southwestern United States. As our understanding of the hydrological and climatological cycles has improved, and our ability to manipulate the hydrologic cycle has increased, so too have the challenges associated with managing a limited natural resource for a growing population. Modern civilization has made remarkable progress in water management in the past few centuries. Burgeoning cities now survive in desert regions, relying on a mix of simple and complex technologies and management systems to bring adequate water and remove wastewater. These systems have permitted agricultural production and urban concentrations to expand in regions previously thought to have inadequate moisture. However, evidence is also mounting that our current management and use of water is unsustainable. Physical, economic, and ecological limits constrain the development of new supplies and additional water withdrawals, even in regions not previously thought vulnerable to water constraints. New kinds of limits are forcing water managers and policy makers to rethink previous assumptions about population, technology, regional planning, and forms of development. In addition, new threats, especially the challenges posed by climatic changes, are now apparent. Sustainably managing and using water in arid and semiarid regions such as the southwestern United States will require new thinking about water in an interdisciplinary and integrated way. The good news is that a wide range of options suggest a roadmap for sustainable water management and use in the coming decades. climate change | soft path | freshwater | sustainability | water management doi/ 10.1073/pnas.1005473107

A key feature of anticipated 21st century droughts in Southwest North America is the concurrence of elevated temperatures and increased aridity. Instrumental records and paleoclimatic evidence for past prolonged drought in the Southwest that coincide with elevated temperatures can be assessed to provide insights on temperature-drought relations and to develop worst-case scenarios for the future. In particular, during the medieval period, ~AD 900-1300, the Northern Hemisphere experienced temperatures warmer than all but the most recent decades. Paleoclimatic and model data indicate increased temperatures in western North America of approximately 1[degrees]C over the long-term mean. This was a period of extensive and persistent aridity over western North America. Paleoclimatic evidence suggests drought in the mid-12th century far exceeded the severity, duration, and extent of subsequent droughts. The driest decade of this drought was anomalously warm, though not as warm as the late 20th and early 21st centuries. The convergence of prolonged warming and arid conditions suggests the mid-12th century may serve as a conservative analogue for severe droughts that might occur in the future. The severity, extent, and persistence of the 12th century drought that occurred under natural climate variability, have important implications for water resource management. The causes of past and future drought will not be identical but warm droughts, inferred from paleoclimatic records, demonstrate the plausibility of extensive, severe droughts, provide a long-term perspective on the ongoing drought conditions in the Southwest, and suggest the need for regional sustainability planning for the future. climate change | water resources | paleoclimatology | medieval period doi/ 10.1073/pnas.0911197107

The Nearctic has been recognized as a biogeographic region since the 19th century. We analyzed distributional patterns of the mammals inhabiting North and Central America, from Alaska to Panama, to delimit the boundaries of the Nearctic region. We performed 6 optimality analyses, using a grid of 4[degrees] latitude--longitude, based on families, genera, species, and combinations of these. The analysis of the matrix with the 3 taxonomic levels yielded better results in terms of the largest number of endemics and the best delimitation of the Nearctic region. We also found 3 patterns--western, eastern, and northern--within the region that coincide partially with previous biogeographic characterizations. Although mammals seem to represent appropriate taxa to delimit this region, we conclude that a more robust delimitation might be obtained by analyzing other plant and animal taxa. DOI: 10.1644/10-MAMM-A-136.1. Key words: biogeographic provinces, endemism, mammals, North America, software NDM

Climate change models predict that much of western North America is becoming significantly warmer and drier, resulting in overall reductions in availability of water for ecosystems. Herein, I demonstrate that significant declines in the reproductive success of female insectivorous bats occur in years when annual environmental conditions mimic the long-term predictions of regional climate change models. Using a data set gathered on bat populations from 1996 through 2008 along the Front Range of Colorado, I compare trends in population numbers and reproductive outcomes of six species of vespertilionid bats with data on mean annual high temperature, precipitation, snow pack, and stream discharge rates. I show that levels of precipitation and flow rates of small streams near maternity colonies is fundamentally tied to successful reproduction in female bats, particularly during the lactation phase. Across years that experienced greater than average mean temperatures with less than average precipitation and stream flow, bat populations responded by slight to profound reductions in reproductive output depending on the severity of drought conditions. In particular, reproductive outputs showed profound declines (32-51%) when discharge rates of the largest stream in the field area dropped below 7 [m.sup.3]/s, indicating a threshold response. Such sensitivity to environmental change portends severe impacts to regional bat populations if current scenarios for climate Change in western North America are accurate. In addition, bats act as early-warning indicators of large-scale ecological effects resulting from further regional warming and drying trends currently at play in western North America. Key words: bats; climate change; hydrology; lactation; reproduction; water.

The objective of this research was to examine the performance of five North American bioreactor landfills. This paper represents the second of a two-part series and addresses biological and chemical aspects of bioreactor performance including gas production and management, and leachate chemistry. The data support accelerated methane generation at several landfills (k =0.08-0.21 l/year) relative to the AP-42 default decay rate (k=0.04 1/year). While the data indicate that gas collection increases at bioreactor landfills, a general relationship between decay rate and moisture added or wet weight water content could not be identified. There was no indication that gas collection increases appreciably when the water content reaches 40%. Most of the leachates at the landfills in this study were commingled from cells operating as a bioreactor and conventionally. Nevertheless, trends in pH and BOD:COD in the bioreactor leachates were consistent with the impacts of enhanced biological activity. Ammonia concentrations also increased over time but remained below levels reported to be inhibitory. For both heavy metals and speciated organic chemicals, there was no indication that bioreactor landfill leachate is significantly different from leachate generated at conventional landfills. DOI: 10.1061/(ASCE)EE.1943-7870.0000220 CE Database subject headings: Landfills; Reactors; Solid wastes; Methane; Chemical treatment; Biological processes. Author keywords: Landfills; Bioreactor; Solid waste; Leachate quality; Methane.

An assessment of state-of-the-practice at five full-scale North American landfills operating as bioreactors is presented in this two-paper set. This paper focuses on effectiveness of liners and leachate collection systems, leachate generation rates, leachate recirculation practices and rates, effectiveness in moistening the waste, and settlement of the waste over time. Except in one case, the liner and leachate collection systems at the bioreactor landfills were similar to those used for landfills operated conventionally. Leachate generation rates increased approximately linearly with recirculation rate, but in all cases, the leachate generation rate was DOI: 10.1061/(ASCE)EE.1943-7870.0000219 CE Database subject headings: Landfills; Reactors; Solid wastes; Liners; Hydrology; Settlement. Author keywords: Landfills; Bioreactor: Solid waste; Liners; Leachate: Hydrology; Settlement.

The timing of ocean entry by salmon smolts is presumed adaptive to maximize survival during this critical life transition. We analyzed the peak timing, duration, and interannual variation in timing of smolt migrations for 53 coho salmon (Oncorhynchus kisutch) populations from central California to Kodiak Island, Alaska. The objective was to examine potential influences of both local watershed characteristics and larger-scale processes in the marine environment on smolt migration patterns. Multivariate analyses demonstrated a strong latitudinal gradient in migration patterns with trends toward later, shorter, and more predictable migrations with increasing latitude. Cluster analysis performed on migration descriptors indicated three major population groupings that coincide with major coastal oceanic regions in the northeast Pacific: a northern group from Kodiak Island to the Queen Charlotte Islands, British Columbia, a central group from the Queen Charlotte Islands south to the Columbia River, and a southern group from the Columbia River southward. These regional patterns transcended local variability associated with watershed characteristics and trap location, suggesting that the patterns reflect adaptation to differences in timing and relative predictability of favorable conditions in the marine environments that smolts enter. Resume: Le calendrier de l'entree des saumoneaux dans locean est presume etre une adaptation pour maximiser la survie durant cette transition importante dans la vie des saumons. Nous avons analyse le moment des migrations maximales, la duree des migrations et la variation interannuelle du calendrier de la migration des saumoneaux dans 53 populations de saumons coho (Oncorhynchus kisutch) reparties du centre de la Californie a lile Kodiak, Alaska. Notre object if etait d'examinerles influences possibles a la fois des caracteristiques du bassin versant local et des processus a plus grande echelle dans le milieu marin sur les patrons de migration des saumoneaux. Des analyses multidimensionnelles indiquent un fort gradient latitudinal dans les patrons de migration, avec une tendance vers des migrations plus tardives, plus courtes et plus previsibles aux latitudes plus elevees. Des analyses de groupement effectuees sur les descripteurs de la migration identifient trois principaux regroupements de populations qui coincident avec les trois regions cotieres principales du nordest du Pacifique: un groupe boreal de lile Kodiak aux iles de la Reine-Charlotte, Colombie-Britannique, un groupe central des iles de la Reine-Charlotte vers le sud jusquau fleuve Columbia et un groupe austral au sud du Columbia. Ces patrons regionaux transcendent la variabilite locale associee aux caracteristiques du bassin versant et a la position du piege, ce qui laisse croire que les patrons sont le reflet dune adaptation aux differences dans la presence et la previsibilite relative des conditions favorables des environnements marins dans lesquels les saumoneaux vont penetrer. [Traduit par la Redaction], Introduction The migrations of diadromous fishes between freshwater and marine ecosystems presumably evolved to allow species to exploit favorable conditions for growth and reproduction (Northcote 1978; Gross et al. 1988). [...]

Colonists arriving in eastern North America at the start of the historical period faced not only new topographies and new plant and animal communities, but also new climatic regimes. The transition from the Medieval Warm Period to the Little Ice Age several centuries earlier presented Viking settlers in the North Atlantic region with the task of learning that their new environments were more fragile and changed more rapidly than the familiar forms of those environments suggested at the outset of colonization. North American colonists arriving from England expected different environments, but also expected them to vary consistently according to latitude. Examination of these two examples of colonization using the landscape learning model, particularly the concept of limitational knowledge, shows clear time gaps between practical and archaeologically identifiable adjustments to local climatic conditions and updating of the wider social understanding of the regional environments.

Host--pathogen interactions may be governed by the number of pathogens coexisting within an individual host (i.e., coinfection) and among different hosts, although most sampling in natural systems focuses on the prevalence of single pathogens and/or single hosts. We measured the prevalence of four barley and cereal yellow dwarf viruses (B/CYDVs) in three grass species at 26 natural grasslands along a 2000-km latitudinal gradient in the western United States and Canada. B/CYDVs are aphid-vectored RNA viruses that cause one of the most prevalent of all plant diseases worldwide. Pathogen prevalence and coinfection were uncorrelated, suggesting that different forces likely drive them. Coinfection, the number of viruses in a single infected host ([alpha] diversity), did not differ among host species but increased roughly twofold across our latitudinal transect. This increase in coinfection corresponded with a decline in among-host pathogen turnover ([beta] diversity), suggesting that B/CYDVs in northern populations experience less transmission limitation than in southern populations. In contrast to pathogen diversity, pathogen prevalence was a function of host identity as well as biotic and abiotic environmental conditions. Prevalence declined with precipitation and increased with soil nitrate concentration, an important limiting nutrient for hosts and vectors of B/CYDVs. This work demonstrates the need for further studies of processes governing coinfection, and the utility of applying theory developed to explain diversity in communities of free-living organisms to pathogen systems. Key words: alpha diversity; aphid-vectored RNA virus; barley and cereal yellow dwarf virus (B/CYDV) ; beta diversity; community ecology; disease ecology; Pacific coast, North America, grasslands.

The Eocene-Oligocene boundary (EOB) marks a period of dramatic global climatic change correlated with pronounced mammalian faunal change. The timing of these events is well constrained in North America and Europe, but the Asian record has yet to produce a synthetic section linking environmental change, mammalian fossils, and precise geochronological dates. Here we present the first magnetostratigraphic section for the Hsanda Gol Formation, Mongolia, which yields significant Oligocene fossils and also marks a pattern of aridification that is tightly correlated to the EOB (33.9 Ma), supporting a broader pattern of aridification in the central Asian plateau across the EOB. Oligocene faunas of Asia can now be confidently correlated to those of North America, Europe, and Africa. These results suggest that mammalian faunal turnover within Asia occurred slightly later than similar events within Europe, and question the influence of Asian immigrants on the Grande Coupure faunal turnover. doi: 10.1130/G30619.1

In the lowermost layer of the atmosphere--the troposphere--ozone is an important source of the hydroxyl radical, an oxidant that breaks down most pollutants and some greenhouse gases (1). High concentrations of tropospheric ozone are toxic, however, and have a detrimental effect on human health and ecosystem productivity (1). Moreover, tropospheric ozone itself acts as an effective greenhouse gas (2). Much of the present tropospheric ozone burden is a consequence of anthropogenic emissions of ozone precursors (3) resulting in widespread increases in ozone concentrations since the late 1800s (3-7). At present, east Asia has the fastest-growing ozone precursor emissions (8). Much of the springtime east Asian pollution is exported eastwards towards western North America?. Despite evidence that the exported Asian pollution produces ozone (10), no previous study has found a significant increase in free tropospheric ozone concentrations above the western USA since measurements began in the late 1970s (5,11,12). Here we compile springtime ozone measurements from many different platforms across western North America. We show a strong increase in springtime ozone mixing ratios during 1995-2008 and we have some additional evidence that a similar rate of increase in ozone mixing ratio has occurred since 1984. We find that the rate of increase in ozone mixing ratio is greatest when measurements are more heavily influenced by direct transport from Asia. Our result agrees with previous modelling studies, which indicate that global ozone concentrations should be increasing during the early part of the twenty-first century as a result of increasing precursor emissions, especially at northern mid-latitudes (13), with western North America being particularly sensitive to rising Asian emissions (14). We suggest that the observed increase in springtime background ozone mixing ratio may hinder the USA's compliance with its ozone air quality standard., Inventoried global anthropogenic ozone precursor emissions of nitrogen oxides (NO + N[O.sub.2] = N[O.sub.x]) and volatile organic compounds increased rapidly during 1960-1990, but levelled off in the 1990s (15). Comprehensive [...]

The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago ([approximately equal to] 13,800-11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000-10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant. climate change | extraterrestrial impact | overkill | Quaternary extinctions | radiocarbon dates doi/10.1073/pnas.0908153106

ABSTRACT The Intermountain West is currently experiencing increased growth in oil and gas production, which has the potential to affect the visibility and air quality of various Class I areas [...]

Aquatic macrophytes play an important role in the survival and proliferation of invertebrates in freshwater ecosystems. Epiphytic invertebrate communities may be altered through the replacement of native macrophytes by exotic macrophytes, even when the macrophytes are close relatives and have similar morphology. We sampled an invasive exotic macrophyte, Eurasian watermilfoil (Myriophyllum spicatum), and native milfoils Myriophyllum sibericum and Myriophyllum alterniflorum in four bodies of water in southern Quebec and upstate New York during the summer of 2005. Within each waterbody, we compared the abundance, diversity, and community composition of epiphytic macroinvertebrates on exotic and native Myriophyllum. In general, both M. sibericum and M. alterniflorum had higher invertebrate diversity and higher invertebrate biomass and supported more gastropods than the exotic M. spicatum. In late summer, invertebrate density tended to be higher on M. sibericum than on M. spicatum, but lower on M. alterniflorum than on M. spicatum. Our results demonstrate that M. spicatum supports macroinvertebrate communities that may differ from those on structurally similar native macrophytes, although these differences vary across sites and sampling dates. Thus, the replacement of native milfoils by M. spicatum may have indirect effects on aquatic food webs. Les macrophytes aquatiques jouent un role important dans la survie et la proliferation des invertebres dans les ecosystemes d'eau douce. Les communautes d'invertebres epiphytes peuvent etre modifiees par le remplacement des macrophytes indigenes par des marcophytes exotiques, meme lorsque ces macrophytes sont de proches parents et possedent une morphologie similaire. Nous avons echantillonne un macrophyte exotique envahissant, le myriophylle a epis (Myriophyllum spicatum), et des myriophylles indigenes (Myriophyllum sibericum et Myriophyllum alterniflorum) dans des plans d'eau du sud du Quebec et du nord de l'etat de New York durant l'ete 2005. Dans chaque plan d'eau, nous avons compare l'abondance, la diversite et la composition de la communaute de macroinvertebres epiphytes sur les Myriophyllum exotique et indigenes. En general, tant M. sibericum que M. alterniflorum portent une plus grande diversite et une biomasse plus importante d'invertebres ainsi qu'un plus grand nombre de gasteropodes que le M. spicatum exotique. En fm d'ete, la densite des invertebres tend a etre plus importante sur M. sibericum que sur M. spicatum, mais plus faible sur M. alterniflorum que sur M. spicatum. Nos resultats demontrent que M. spicatum porte des communautes de macroinvertebres qui peuvent differer de celles qui se retrouvent sur les macrophytes indigenes de structure similaire, bien que ces differences puissent varier d'un site a un autre et d'une date d'echantillonnage a l'autre. Ainsi, le remplacement des myriophylles indigenes par M. spicatum peut avoir des effets indirects sur les reseaux alimentaires aquatiques. [Traduit par la Redaction], Introduction Aquatic macrophytes play key ecological roles in lakes and rivers, primarily as a source of primary productivity and as a habitat for abundant and diverse faunal communities (Kershner and [...]

The Fire and Fire Surrogates (FFS) network is composed of 12 forest sites that span the continental United States, all of which historically had frequent low-severity fire. The goal of the FFS study was to assess the efficacy of three management treatments (prescribed fire, mechanical thinning, and their combination) in reducing wildfire hazard and increasing ecosystem sustainability. This paper describes the impact of the FFS treatments on nitrogen (N) storage and distribution. At the network scale, total ecosystem N averaged 4480 kg x [ha.sup.-1], with ~9% in vegetation, ~9% in forest floor, ~2% in deadwood, and ~80% in soil. The loss of vegetation N to fire averaged (±SE) 25 ± 11 kg x [ha.sup.- 1], whereas the mechanical and combined mechanical and fire treatments resulted in N losses of 133 ± 21 and 145 ± 19 kg x [ha.sup.- 1], respectively. Western coniferous forests lost more N from each treatment than did eastern forests. None of the manipulative FFS treatments impacted >10%-15% of total N of these ecosystems. Management strategies that maximize ecosystem carbon (C) gain by minimizing loss of N should be a focus in western forests, where C and N cycling are tightly linked, but perhaps not in those eastern forests where atmospheric N deposition has decoupled C and N cycles. Le reseau national sur l'utilisation du feu et d'un substitut du feu comprend 12 stations forestieres qui couvrent le continent americain. Toutes ces stations ont subi dans le passe de frequents incendies de faible intensite. Le but du reseau etait d'evaluer l'efficacite de trois traitements d'amenagement (brulage dirige, eclaircie mecanique et leur combinaison) pour reduire les risques d'incendie et augmenter la durabilite des ecosystemes. Cet article decrit l'impact des traitements appliques dans le reseau sur la distribution et le stockage de N. A l'echelle du reseau, N total dans les ecosystemes atteignait en moyenne 4480 kg x [ha.sup.-1], dont ~9 % se retrouvaient dans la vegetation, ~9 % dans la couverture morte, ~2 % dans le bois mort et ~80% dans le sol. La perte de N dans la vegetation causee par le feu atteignait en moyenne 25 ± 11 kg x [ha.sup.-1] tandis que l'eclaircie mecanique seule et l'eclaircie mecanique accompagnee du brulage dirige causaient des pertes respectives de 133 ± 21 et 145 ± 19 kg x [ha.sup.-1]. Les forets de coniferes de l'ouest ont perdu plus de N que les forets de l'est a la suite de chaque traitement. Aucun des traitements n'a eu d'impact sur plus de 10-15 % de la quantite totale de N dans ces ecosystemes. Les strategies d'amenagement devraient avoir comme objectif de maximiser le gain en C des ecosystemes en minimisant la perte de N dans les forets de l'ouest ou le recyclage de C et le recyclage de N sont etroitement relies mais peut-etre pas dans les forets de l'est ou les depots atmospheriques de N ont decouple les cycles de C et N. [Traduit par la Redaction], Introduction The forests of North America have been actively managed by humans for several millennia (Mann 2005). The selective removal of trees and other plants of various species and sizes [...]

ABSTRACT An assessment of how future climate change will impact regional air quality requires projecting emissions many decades into the future in a consistent manner. An approach that integrates the [...]

Garlic mustard (Alliaria petiolata) is a nonnative, shade-tolerant forb that was introduced into North America in the mid-1800s. Currently, garlic mustard is spreading across the landscape at a rate of [...]

Abstract: Ethnographic literature documents the pervasiveness of plant-management strategies, such as prescribed burning and other kinds of cultivation, among Northwest Peoples after European contact. In contrast, definitive evidence of precontact [...]

We presentan estimate of net C[O.sub.2] exchange between the terrestrial biosphere and the atmosphere across North America for every week in the period 2000 through 2005. This estimate is derived from a set of 28,000 C[O.sub.2] mole fraction observations in the global atmosphere that are fed into a state-of-the-art data assimilation system for C[O.sub.2] called CarbonTracker. By design, the surface fluxes produced in CarbonTracker are consistent with the recent history of C[O.sub.2] in the atmosphere and provide constraints on the net carbon flux independent from national inventories derived from accounting efforts. We find the North American terrestrial biosphere to have absorbed -0.65 PgC/yr (1 petagram = [10.sup.15] g; negative signs are used for carbon sinks) averaged over the period studied, partly offsetting the estimated 1.85 PgC/yr release by fossil fuel burning and cement manufacturing. Uncertainty on this estimate is derived from a set of sensitivity experiments and places the sink within a range of -0.4 to -1.0 PgC/yr. The estimated sink is located mainly in the deciduous forests along the East Coast (32%) and the boreal coniferous forests (22%). Terrestrial uptake fell to -0.32 PgC/yr during the large-scale drought of 2002, suggesting sensitivity of the contemporary carbon sinks to climate extremes. CarbonTracker results are in excellent agreement with a wide collection of carbon inventories that form the basis of the first North American State of the Carbon Cycle Report (SOCCR), to be released in 2007. All CarbonTracker results are freely available at http://carbontracker.noaa.gov. carbon cycle | greenhouse gases | data assimilation | biogeochemistry | atmospheric composition

Because of a lack of regular, direct measurements, little information is available about the frequency and spatial and temporal distribution of icing conditions aloft, including supercooled large drops (SLD). Research aircraft provide in situ observations of these conditions, but the sample set is small and can be biased. Other techniques must be used to create a more unbiased climatology. The presence and absence of icing and SLD aloft can be inferred using surface weather observations in conjunction with vertical profiles of temperature and moisture. In this study, such a climatology was created using 14 yr of coincident, 12-hourly Canadian and continental U.S. surface weather reports and balloonborne soundings. The conditions were found to be most common along the Pacific Coast from Alaska to Oregon, and in a large swath from the Canadian Maritimes to the Midwest. Prime locations migrated seasonally. Most SLD events appeared to occur below 4 km, were less than 1 km deep, and were formed via the collision-coalescence process.

Climate change is thought to promote the poleward movement of geographic ranges; however, the spatial dynamics, mechanisms, and regional anthropogenic drivers associated with these trends have not been fully explored. We estimated changes in latitude of northern range boundaries, center of occurrence, and center of abundance for 254 species of winter avifauna in North America from 1975 to 2004. After accounting for the effect of range size and the location of the northern boundary, positive latitudinal trends were evident for the northern boundary (1.48 km/yr), center of occurrence (0.45 km/yr), and center of abundance (1.03 km/yr). The northern boundary, when examined across individual species, had the most variable trends (SD = 7.46 km/yr) relative to the center of occurrence (SD = 2.36 km/yr) and center of abundance (SD = 5.57 km/yr). Trends did not differ based on migratory status, but there was evidence that trends differed for species with ranges centered in the southern vs. northern portion of the study area. Species occurred more sporadically over time at northern range boundaries, and northern boundaries were associated with a concentration of colonization and extirpation events, with a greater prevalence of colonization events likely promoting poleward trends. Regional anthropogenic drivers explained ~8% of the trend for the northern boundary, 14% for the center of occurrence, and 18% for the center of abundance; however, these effects were localized in the northern portion of species' ranges and were associated with distributional changes within ranges, primarily abundance, producing patterns that mimicked poleward movements. We conclude that poleward distributional shifts represent the interaction between climate change and regional factors whose outcome is determined by the scale of the analysis and the biotic and abiotic features in the region, and how anthropogenic activities have impacted these features. Key words: abundance; Christmas Bird Count; common species; distribution of avifauna; geographical range; global climate change; North America; temporal turnover; winter range.

Abstract: We summarize the effects of major weather events such as ice storms, wind storms, and flooding on the abundance and diversity of terrestrial forest insects and their allies. This [...]

Severe drought is the greatest recurring natural disaster to strike North America. A remarkable network of centuries-long annual tree-ring chronologies has now allowed for the reconstruction of past drought over North America covering the past 1000 or more years in most regions. These reconstructions reveal the occurrence of past 'megadroughts' of unprecedented severity and duration, ones that have never been experienced by modern societies in North America. There is strong archaeological evidence for the destabilizing influence of these past droughts on advanced agricultural societies, examples that should resonate today given the increasing vulnerability of modern water-based systems to relatively short-term droughts. Understanding how these megadroughts develop and persist is a timely scientific problem. Very recently, climate models have succeeded in simulating all of the major droughts over North America from the Civil War to the severe 1998-2004 drought in the western U.S. These numerical experiments indicate the dominating importance of tropical Pacific Ocean sea surface temperatures (SSTs) in determining how much precipitation falls over large parts of North America. Of central importance to drought formation is the development of cool 'La Nina-like' SSTs in the eastern tropical Pacific region. This development appears to be partially linked to changes in radiative forcing over that region, which affects the Bjerknes feedback mechanism of the ENSO cycle there. Paradoxically, warmer conditions over the tropical Pacific region lead to the development of cool La Nina-like SSTs there, which is drought inducing over North America. Whether or not this process will lead to a greater prevalence of drought in the future as the world warms due to accumulating greenhouse gases is unclear at this time. Keywords: North American drought; Palmer drought index; tree rings; drought reconstructions; drought causes and consequences; ENSO variability

A model diagnosis has been performed on the nocturnal Great Plains low-level jet (LLJ), which is one of the key elements of the warm season regional climate over North America. The horizontal-vertical structure, diurnal phase, and amplitude of the LLJ are well simulated by an atmospheric general circulation model (AGCM), thus justifying a reevaluation of the physical mechanisms for the formation of the LLJ based on output from this model. A diagnosis of the AGCM data confirms that two planetary boundary layer (PBL) processes, the diurnal oscillation of the pressure gradient force and of vertical diffusion, are of comparable importance in regulating the inertial oscillation of the winds, which leads to the occurrence of maximum LLJ strength during nighttime. These two processes are highlighted in the theories for the LLJ proposed by Holton (1967) and Blackadar (1957). A simple model is constructed in order to study the relative roles of these two mechanisms. This model incorporates the diurnal variation of the pressure gradient force and vertical diffusion coefficients as obtained from the AGCM simulation. The results reveal that the observed diurnal phase and amplitude of the LLJ can be attributed to the combination of these two mechanisms. The LLJ generated by either Holton's or Blackadar's mechanism alone is characterized by an unrealistic meridional phase shift and weaker amplitude. It is also shown that the diurnal phase of the LLJ exhibits vertical variations in the PBL. more clearly at higher latitudes, with the upper PBL wind attaining a southerly peak several hours earlier than the lower PBL. The simple model demonstrates that this phase tilt is due mainly to sequential triggering of the inertial oscillation from upper to lower PBL when surface cooling commences after sunset. At lower latitudes, due to the change of orientation of prevailing mean wind vectors and the longer inertial period, the inertial oscillation in the lower PBL tends to be interrupted by strong vertical mixing in the following day, whereas in the upper PBL, the inertial oscillation can proceed in a low-friction environment for a relatively longer duration. Thus, the vertical phase tilt initiated at sunset is less evident at lower latitudes.

General circulation model simulations suggest that during the Last Glacial Maximum, the northern circumpolar vortex intensified and enlarged, a glacial anticyclone developed over the Laurentide Ice Sheet, and the position of the jet stream was shifted southward. However, observations directly related to shifts in wind patterns across the North American continent have not yet been reported. We examined tree-ring cellulose from the Holocene and the last glacial period for: (1) covariation between precipitation [[delta].sup.18]O (and [delta]D) and relative humidity, and (2) variation of cellulose [[delta].sup.18]O and [delta]D with longitude. Holocene isotopic features are consistent with modern moisture trajectories. The isotopic features during the last glaciation are dissimilar to those in the Holocene, and constitute direct evidence for an expansion of the polar easterlies to latitudes as low as 40[degrees]N. This is the first time that moisture transport patterns have been inferred from covariation between isotopic composition in precipitation and relative humidity, a technique that holds much promise for future studies of atmospheric circulation. Keywords: North America, continental glaciation, atmospheric circulation, paleoclimate, humidity, isotope ratios.

The giant flightless terror bird Titanis walled is known from Florida and Texas during the late Neogene. The age of T. walled is problematic because this taxon co-occurs with temporally mixed (i.e., time-averaged) faunas at two key sites. Thus, prior to this study, T. walled from the Santa Fe River, Florida (type locality), was either as old as late Pliocene (ca. 2.2 Ma) or as young as latest Pleistocene (ca. 15 ka). Likewise, T. walled from the Nueces River, Texas, was either early Pliocene (ca. 5 Ma) or latest Pleistocene (ca. 15 ka). In order to better resolve this age range, the rare earth element (REE) patterns of T. walled from the Santa Fe River, Florida, were compared to two biochronologically distinctive groups (late Pliocene versus late Pleistocene) of fossil mammals from the same locality. Similarly, the REE patterns of T. walleri from Texas were compared to two groups (early Pliocene versus latest Pleistocene) of fossil mammals from the same locality. The REE patterns of T. walleri from Florida are indistinguishable from those of the co-occurring late Pliocene mammals. Likewise, the REE pattern of T. walled from Texas is indistinguishable from those of the co-occurring early Pliocene mammals. Given these REE constraints, the revised age of T. walled is early Pliocene in Texas (ca. 5 Ma) and late Pliocene (ca. 2.2-1.8 Ma) in Florida. As such, T. walled is interpreted as an early immigrant during the Great American Interchange prior to the formation of the Isthmian land bridge. No evidence currently exists for Pleistocene T. walled in North America. Keywords: bone, diagenesis, extinction, Florida, Pleistocene, Pliocene, rare earths, taphonomy, Timnis walleri, Texas, Great American Interchange.

Abstract--The eastern Steller sea lion (Eumetopias jubatus) population comprises animals that breed along the west coast of North America between California and southeastern Alaska. There are currently 13 major rookeries [...]

The difficult task of engineering a route for Alaska's proposed natural gas pipeline, particularly when it would run through the most earthquake-prone region in North America, has raised much debate and controversy. The issue was put to rest on November 3, 2002, when the Denali Fault in central Alaska slipped approximately 5.5 meters (18 feet) laterally and more than 1 meter (3 feet) vertically beneath the Trans-Alaska Pipeline during a magnitude-7.9 earthquake without causing a single drop of oil to spill.

The most prominent of the two major global [[delta].sup.13]C excursions in the Ordovician, the Hirnantian [[delta].sup.13]C excursion (HICE), which is previously recorded from the uppermost Ordovician in a few sections in Nevada, Quebec, Arctic Canada, Baltoscandia, Scotland and China, is documented for the first time from the North American Midcontinent. Samples through the Girardeau Limestone and Leemon Formation in Missouri and Illinois show elevated [[delta].sup.13]C values of +4 [per thousand] to +5 [per thousand]. Although not determined precisely, the beginning of the HICE is likely to be in the upper part of the Orchard Creek Shale, and it ends in the upper Leemon Formation. Being extraordinarily useful chronostratigraphically, the presence of the HICE makes it possible to provide a firm dating of the study interval, whose age has long been controversial. Comparison between the study sections and coeval HICE sequences in North America and Europe show striking similarities, especially in sea-level history, indicating that major local lowstands reflect eustatic sea-level changes. A comparison with Hirnantian diamictite successions in North and South Africa and Argentina suggests that these lowstands correspond to two major Gondwanan glacial episodes. Keywords: carbon isotope excursion, Hirnantian, Upper Ordovician, Missouri-Illinois, Gondwana glaciation, sea-level changes.

Abstract: The acidification of forest soils and surface waters and their relatively poor recovery record following reductions in atmospheric sulphur emissions is a major ongoing environmental problem, particularly in northeastern [...]

The North American Monsoon Experiment (NAME) is an internationally coordinated process study aimed at determining the sources and limits of predictability of warm-season precipitation over North America. The scientific objectives of NAME are to promote a better understanding and more realistic simulation of warm-season convective processes in complex terrain, intraseasonal variability of the monsoon, and the response of the warm-season atmospheric circulation and precipitation patterns to slowly varying, potentially predictable surface boundary conditions. During the summer of 2004, the NAME community implemented an international (United States, Mexico, Central America), multiagency (NOAA, NASA, NSF, USDA) field experiment called NAME 2004. This article presents early results from the NAME 2004 campaign and describes how the NAME modeling community will leverage the NAME 2004 data to accelerate improvements in warm-season precipitation forecasts for North America.

Radiocarbon ages and lichen-dated moraines from 17 glaciers in coastal and near-coastal British Columbia and Alaska document a widespread glacier advance during the first millennium A.D. Glaciers at several sites began advancing ca. A.D. 200-300 based on radiocarbon-dated overridden forests. The advance is centered on A.D. 400-700, when glaciers along an ~2000 km transect of the Pacific North American cordillera overrode forests, impounded lakes, and deposited moraines. The synchroneity of this glacier advance and inferred cooling over a large area suggest a regional climate forcing and, together with other proxy evidence for late Holocene environmental change during the Medieval Warm Period and Little Ice Age, provide support for millennial-scale climate variability in the North Pacific region. Keywords: Alaska, British Columbia, glacier, Holocene, neoglaciation, paleoclimate.

The gastropod Ilyanassa obsoleta (Say) is native to the east coast of North America where it is locally abundant on sandflats, mudflats, and in saltmarsh creeks. The local disturbances created by snails and their movements affect soft-sediment community composition. Movements of individually marked snails were followed on an intertidal sandflat on Cape Henlopen, Delaware, U.S.A. In June 1991, 1,200 snails that had tested as trematode-uninfected were released and over 5 months 554 were sighted 971 times. Mean daily net distance moved was 1.7 m, but snails often moved 10-20 m [day.sup.-1] and one snail was 180 m distant after 130 days. Net dispersal of the released population was attained in [approximately equal to]10 days, by which time, a typical distance from release was 15-20 m. Snails were not found crossing sandbars and most moved away from shore into a tidal gully. In June 1993, 500 snails, both uninfected and trematode-infected, were released at the same position and over 6 months, 350 snails were sighted 949 times. Sandbars were again barriers to movement, but their changed positions allowed wider dispersal. Net dispersal was complete in [approximately equal to]20 days by which time a typical distance from release was 30-40 m. Mean daily net distance moved was 2.2 m, but within 10 days snails had moved 50-100 m. In both years, following initial dispersal, snails (infected or not) took up random directions from move to move. Infected and uninfected snails dispersed equal distances, but had different mean final dispersal directions. Dispersal of I. obsoleta individuals was extensive and affected by shifting sandbar positions and parasitism. Recognizing this will be important in appreciating the ecological dynamics of this gastropod and in determining its effects on soft-bottom communities., Introduction The neogastropod Ilyanassa obsoleta is native to the east coast of North America and is an abundant species (often over 1,000 [m.sup.-2]) in the intertidal zone on sandflats, mudflats, [...]

Degradation of nesting habitat has been proposed as a factor contributing to Greater Sage-Grouse (Centrocercus urophasianus) population declines throughout North America. Delineating suitable nesting habitat across landscapes with relatively contiguous sagebrush cover is difficult but important to identify areas for protection. We used radio-telemetry to locate Greater Sage-Grouse nests in relatively contiguous sagebrush habitats in Wyoming to investigate the spatial arrangement of nests relative to lek and other nest locations. Nest distributions were spatially related to lek location within 3 and 5 km of a lek, and a 5-km buffer included 64% of the nests. There was no relationship between lek size and lek-to-nest distance, suggesting that accurate population trend evaluation might require lek surveys in addition to lek counts. Closest known lek-to-nest distance was greater for successfully hatched compared to destroyed nests, and closely spaced nests tended to experience lower success and have higher probabilities of both nests experiencing the same fate compared to isolated nests, suggesting that a mechanism of enhanced prey detection occurred at higher nest densities. A low probability that a given individual's consecutive-year nest spacing occurred randomly suggested nesting site-area fidelity. Although a grouped pattern of nests occurred within 5 km of a lek, the proportion of nesting females located farther than 5 km could be important for population viability. Managers should limit strategies that negatively influence nesting habitat regardless of lek locations, and preserve adequate amounts of unaltered nesting habitat within treatment boundaries to maintain nest dispersion and provide sites for philopatric individuals. Key words: Centrocercus urophasianus, fidelity, Greater Sage-Grouse, lek-to-nest distance, nest distribution, nest spacing, Wyoming. Se ha propuesto que la degradacion de habitat de nidificacion es un factor que contribuye a la disminucion poblacional de Centrocercus urophasianus a traves de toda America del Norte. La identificacion de habitat de nidificacion adecuado en paisajes con una cobertura relativamente contigua de Artemisa es dificil, pero es importante para identificar areas de proteccion. Usamos radio-telemetria para encontrar nidos de C. urophasianus en habitats de Artemisa relativamente contiguos en el centro y oeste de Wyoming con el fin de investigar la distribucion espacial de nidos con relacion a las asambleas de cortejo (zonas del pavoneo y exposicion) y a la localizacion de otros nidos. La distribucion de los nidos estuvo relacionada espacialmente con la localizacion de las asambleas de cortejo dentro de un radio entre 3 y 5 km alrededor de una asamblea de cortejo, y un circulo de radio de 5 km incluyo el 64% de los nidos. No hubo relacion entre el tamano de la asamblea de cortejo y la distancia del nido a esta, lo cual sugiere que una evaluacion precisa de las tendencias poblacionales puede requerir tanto estudios de cada asamblea de cortejo como de conteos anuales del numero de asambleas de cortejo. La distancia mas corta conocida de una asamblea de cortejo a un nido fue mayor para los nidos exitosos que para los nidos destruidos. Los nidos con una distribucion mas densa tendieron a experimentar un exito menor y a tener una mayor probabilidad de que dos nidos experimentaran la misma suerte en comparacion con otros nidos mas aislados, lo cual sugiere que ocurrio un mecanismo de deteccion acrecentada de presas en situaciones de mayor densidad de nidos. La baja probabilidad de que el espaciamiento de un nido de un individuo determinado en anos consecutivos ocurriera al azar sugirio fidelidad de sitio de nidificacion. Aunque se observo una distribucion agrupada de nidos dentro de un radio de 5 km alrededor de una asamblea de cortejo, la proporcion de hembras que se encontro anidando a mas de 5 km tambien podria ser importante para la viabilidad de la poblacion. Los manejadores de fauna deben limitar las estrategias que influyen negativamente sobre el habitat de nidificacion independientemente de las posiciones de las asambleas de cortejo, y deben preservar cantidades adecuadas de habitat de nidificacion inalterado dentro de los limites de tratamiento para mantener la dispersion de los nidos y proveer sitios para los individuos fieles a un sitio determinado.

Megathrust earthquakes in western North America may be preceded by a precursor phase several years prior to megathrust, induced earthquakes. For example, on 27 March 1964, a 9.2 magnitude (on the Richter scale) earthquake occurred on the coast of Alaska. Changes in foraminifera and diatom assemblages at Girdwood Flats, Alaska, provide evidence of a precursor to this earthquake, thereby detailing a previously unknown sequence of events. We describe further evidence of precursor phases from marshes in Turnagain Arm, Alaska, United States, and farther south in Netarts Bay, Oregon, United States; this is the first time that two widely spaced locations have been examined for earthquake-related precursor stages. The Alaska earthquake offers the possibility to compare a modern sequence (A.D. 1964) of events with the geologic record. The Netarts Bay marsh has experienced no modern earthquake that could be used for comparison, but the nature of megathrust zones implies that the modern and ancient events should be physically similar. New cores examined from Turnagain Arm include both the 1964 earthquake and an event identified and dated at 1800 yr B.P. Prior to the 1964 event, the foraminifera and thecamoebian assemblages changed from a forest phase to a mildly brackish stage; this sequence was dated as being 15 yr or less in length, using [Pb.sup.210] and [Cs.sup.137] dating techniques. The event at 1800 yr B.P. was also associated with a similar precursor stage, indicating a small subsidence prior to the megathrust earthquake-related subsidence event. In Netarts Bay a new core was taken at a previously cored site to make use of carbon-14 dates and the assurance that at least four events were known to have occurred over the past 3000 yr. The new core contains four transitions, each identified by a mineralic deposit, often sharply bounded below and gradationally overlain by marsh peat. Transition in this context refers to the section of core analyzed, ~15 cm above and below each of the four sand layers. Foraminiferal assemblage analyses indicate that these units represented a high marsh prequake phase followed by a lower marsh precursor stage, the earthquake-related deposition (sand layer), and then a rebound back into postquake marsh deposits. Sand deposits with either no or few foraminifera are inferred as tsunami/ earthquake-related deposition stages. These transitions in two widely separated geographic areas (Alaska and Oregon) indicate that similar mechanisms operate for large megathrust earthquakes at subduction zones from Alaska to northern California in the Cascadia Subduction Zone, thus implying that precursor events also occur and can be detected by foraminiferai zonation all along this area. In a recent article (Dragert et al., 2001), scientists from the west coast suggested that 'slow' or 'silent' earthquakes they measured with continuous geographical positioning systems might be indicators of megathrust earthquakes. The transitions we document may be the prehistoric representations of these 'silent' quakes. Foraminiferal evidence may help by allowing, more accurate positioning of seismometers along the west coast of North America and thereby lead to more precise and timely earthquake prediction methods. Keywords: precursor, megathrust earthquake, foraminifera, thecamoebian, marsh/ forest transition.