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Geology topics

W.B. Krohn

Publications and source records attributed to W.B. Krohn.

At least 19 recordsLinked to original sources
USGS2010

Effects of precommercial thinning on snowshoe hares in Maine

Snowshoe hares (Lepus americanus) are an important prey species and a dominant herbivore across much of their North American range, and researchers have questioned the influences of forestry practices that alter habitat for hares and the potential community-level effects on carnivores. We examined the effects of precommercial thinning (PCT) from 1 to 11 years posttreatment on snowshoe hares. In the commercial forests of northern Maine, USA, we counted and cleared hare pellets twice a year during 2001 and 2002 on >46 km of pellet transects across 30 regenerating conifer stands (17 treated with PCT) previously treated with an aerial application of herbicide. We compared densities of snowshoe hare pellets among 3 development classes with (1 yr after thinning, 6 yr after thinning, and 11 yr after thinning) and without thinning (stands with a similar history of clearcut and herbicide treatment but no thinning). During both years, densities of hares were lower in stands treated with PCT than in similar unthinned stands across the 3 development classes and during both leaf-off and leaf-on seasons (P < 0.001). Within both thinned and unthinned stands, hare density was greatest in stands in the 1-year development class when compared to the 6-year and 11-year development classes, but a statistical difference (P = 0.048) among classes was evident only during leaf-off seasons. Precommercial thinning was associated with densities of snowshoe hares that were approximately half of those in similar unthinned stands up to at least 11 years posttreatment; however, thinned stands may retain densities of hares greater than stands managed using other forest harvesting regimes. Our results apply to core portions of stands with crop trees spaced at 1.8-2.4-m intervals following complete overstory removal and herbicide treatment. We advocate caution when applying our results to other thinning regimes or across broader spatial scales.

Journal of Wildlife Management↗
USGS2008

Dispersal leads to spatial autocorrelation in species distributions: A simulation model

Compared to population growth regulated by local conditions, dispersal has been underappreciated as a central process shaping the spatial distribution of populations. This paper asks: (a) which conditions increase the importance of dispersers relative to local recruits in determining population sizes? and (b) how does dispersal influence the spatial distribution patterns of abundances among connected populations? We approached these questions with a simulation model of populations on a coupled lattice with cells of continuously varying habitat quality expressed as carrying capacities. Each cell contained a population with the basic dynamics of density-regulated growth, and was connected to other populations by immigration and emigration. The degree to which dispersal influenced the distribution of population sizes depended most strongly on the absolute amount of dispersal, and then on the potential population growth rate. Dispersal decaying in intensity with distance left close neighbours more alike in population size than distant populations, leading to an increase in spatial autocorrelation. The spatial distribution of species with low potential growth rates is more dependent on dispersal than that of species with high growth rates; therefore, distribution modelling for species with low growth rates requires particular attention to autocorrelation, and conservation management of these species requires attention to factors curtailing dispersal, such as fragmentation and dispersal barriers. ?? 2007 Elsevier B.V. All rights reserved.

Ecological Modelling↗
USGS2006

Effect of dispersal at range edges on the structure of species ranges

Range edges are of particular interest to ecology because they hold key insights into the limits of the realized niche and associated population dynamics. A recent feature of Oikos summarized the state of the art on range edge ecology. While the typical question is what causes range edges, another important question is how range edges influence the distribution of abundances across a species geographic range when dispersal is present. We used a single species population dynamics model on a coupled-lattice to determine the effects of dispersal on peripheral populations as compared to populations at the core of the range. In the absence of resource gradients, the reduced neighborhood and thus lower connectivity or higher isolation among populations at the range edge alone led to significantly lower population sizes in the periphery of the range than in the core. Lower population sizes mean higher extinction risks and lower adaptability at the range edge, which could inhibit or slow range expansions, and thus effectively stabilize range edges. The strength of this effect depended on the potential population growth rate and the maximum dispersal distance. Lower potential population growth rates led to a stronger effect of dispersal resulting in a higher difference in population sizes between the two areas. The differential effect of dispersal on population sizes at the core and periphery of the range in the absence of resource gradients implies that traditional, habitat-based distribution models could result in misleading conclusions about the habitat quality in the periphery. Lower population sizes at the periphery are also relevant to conservation, because habitat removal not only eliminates populations but also creates new edges. Populations bordering these new edges may experience declines, due to their increased isolation. ?? OIKOS.

Oikos↗
USGS2005

Long-term effects of precommercial thinning on small mammals in northern Maine

Precommercial thinning (PCT) is being practiced increasingly throughout the Acadian forest of eastern North America to meet silvicultural objectives; however, effects of this practice on wildlife, both immediately and several years post-treatment are not well understood. Forest dependent small mammals have ecological roles as prey for numerous avian and mammalian predators, dispersers of seeds, fruit, and spores, and contribute to nutrient cycling. Researchers in the northwestern USA have suggested that thinning of young, regenerating clearcuts may increase the abundance and diversity of some forest-dependent small mammals by increasing rates of forest development and enhancing the ecological representation of mid-successional stands across managed landscapes. We examined the effects of PCT within conifer-dominated forest stands 1-, 6-, 11-, and 16-years post-treatment, on abundances of mice, voles, and shrews, and on within-stand structure in the commercially managed, Acadian forests of northern Maine. We live-trapped small mammals on 24 herbicide-treated clearcuts treated with PCT and on 13 similar, unthinned stands during summers of 2000 and 2001. Thinning of mid-successional conifer stands resulted in increased abundances, (red-backed voles, Clethrionomys gapperi, P = 0.008; masked shrews, Sorex cinereus, P < 0.001) or had no detectable effect on (deer mice, Peromyscus maniculatus, P = 0.544; short-tailed shrews, Blarina brevicauda, P = 0.517) the 4 most common species of Muridae and Soricidae in northern Maine. In general, abundance of deer mice responded more positively to increasing development class and to the number of years since thinning than other species of small mammals. Several within-stand habitat characteristics associated with stand maturity, such as larger stem diameters and a partially open canopy, occurred in thinned stands. Thus, PCT may accelerate the development of habitat attributes typical of mid-successional conifer stands in intensively managed stands within the Acadian Forest. PCT may increase abundances of small mammal species associated with mid-seral forest conditions at the scale of the forest stand. ?? 2004 Elsevier B.V. All rights reserved.

Forest Ecology and Management↗
USGS2005

Prenatal development in fishers (Martes pennanti)

We evaluated and quantified prenatal growth of fishers (Martes pennanti) using ultrasonography. Seven females gave birth to 21 kits. The first identifiable embryonic structures were seen 42 d prepartum; these appeared to be unimplanted blastocysts or gestational sacs, which subsequently implanted in the uterine horns. Maternal and fetal heart rates were monitored from first detection to birth. Maternal heart rates did not differ among sampling periods, while fetal hearts rates increased from first detection to birth. Head and body differentiation, visible limbs and skeletal ossification were visible by 30, 23 and 21 d prepartum, respectively. Mean diameter of gestational sacs and crown-rump lengths were linearly related to gestational age (P < 0.001). Biparietal and body diameters were also linearly related to gestational age (P < 0.001) and correctly predicted parturition dates within 1-2 d. ?? 2004 Elsevier Inc. All rights reserved.

Theriogenology↗
USGS2005

A Fall fur-hunt from Maine to New Brunswick, Canada: The 1858 journal of Manly Hardy

Ecologists, conservationists, and others increasingly ask questions that require a reliable understanding of natural conditions in the past. For example, when the US Fish and Wildlife Service proposed to list the Canada lynx (Lynx canadensis) under the Federal Endangered Species Act, there was a need to know the historical status of this species in the northeastern US. The natural history writings of Manly Hardy, a successful, nineteenth-century businessman and respected amateur naturalist from Brewer, ME, proved useful in assessing the lynx's historical status. Because of the wide array of potential uses of Hardy's writings, the objective of this paper is to make biologists and other scholars aware of Hardy, especially his 15 surviving journals, 1852-1899. Hardy left the most extensive published record of any of the naturalists who wrote about wildlife in Maine from the late 1800s through the early 1900s. His articles and essays covered a wide range of subjects about a variety of bird and mammal species. A recently published biographical sketch of Hardy contains an annotated bibliography of his publications along with the republication of 14 of his mammalian works. In contrast, this article contains an example of his unpublished journal writing with significant wildlife observations.

Northeastern Naturalist↗
USGS2005

Broad-scale predictors of canada lynx occurrence in eastern North America

The Canada lynx (Lynx canadensis) is listed as a threatened species throughout the southern extent of its geographic range in the United States. Most research on lynx has been conducted in the western United States and Canada; little is known about the ecology of lynx in eastern North America. To fill critical knowledge gaps about this species, we modeled and mapped lynx occurrence using habitat and weather data from 7 eastern states and 3 Canadian provinces. Annual snowfall, road density, bobcat (L. rufus) harvest, deciduous forest, and coniferous forest were compared at 1,150 lynx locations and 1,288 random locations. Nineteen a priori models were developed using the information-theoretic approach, and logistic regression models were ranked using Akaike's Information Criterion (AIC) and by our ability to correctly classify reserved data (Kappa). Annual snowfall and deciduous forest predicted lynx presence and absence for a reserved dataset (n = 278) with 94% accuracy. A map of the probability of lynx occurrence throughout the region revealed that 92% of the potential habitat (i.e., >50% probability of occurrence) was concentrated in a relatively contiguous complex encompassing northern Maine, New Brunswick, and the Gaspe?? peninsula of Quebec. Most of the remaining potential habitat (5%) was on northern Cape Breton Island in Nova Scotia. Potential habitat in New Hampshire, Vermont, and New York was small (1,252 km2), fragmented, and isolated (>200 km) from known lynx populations. When federally listed as threatened in the contiguous United States in 2000, inadequate regulations on federal lands were cited as the primary threat to Canada lynx. However, the majority of potential lynx habitat in the eastern United States is on private lands and continuous with potential habitat in Canada. Therefore, lynx conservation in eastern North America will need to develop partnerships across national, state, and provincial boundaries as well as with private landowners.

Journal of Wildlife Management↗
USGS2004

Canada lynx Lynx canadensis habitat and forest succession in northern Maine, USA

The contiguous United States population of Canada lynx Lynx canadensis was listed as threatened in 2000. The long-term viability of lynx populations at the southern edge of their geographic range has been hypothesized to be dependent on old growth forests; however, lynx are a specialist predator on snowshoe hare Lepus americanus, a species associated with early-successional forests. To quantify the effects of succession and forest management on landscape-scale (100 km 2 ) patterns of habitat occupancy by lynx, we compared landscape attributes in northern Maine, USA, where lynx had been detected on snow track surveys to landscape attributes where surveys had been conducted, but lynx tracks had not been detected. Models were constructed a priori and compared using logistic regression and Akaike's Information Criterion (AIC), which quantitatively balances data fit and parsimony. In the models with the lowest (i.e. best) AIC, lynx were more likely to occur in landscapes with much regenerating forest, and less likely to occur in landscapes with much recent clearcut, partial harvest and forested wetland. Lynx were not associated positively or negatively with mature coniferous forest. A probabilistic map of the model indicated a patchy distribution of lynx habitat in northern Maine. According to an additional survey of the study area for lynx tracks during the winter of 2003, the model correctly classified 63.5% of the lynx occurrences and absences. Lynx were more closely associated with young forests than mature forests; however, old-growth forests were functionally absent from the landscape. Lynx habitat could be reduced in northern Maine, given recent trends in forest management practices. Harvest strategies have shifted from clearcutting to partial harvesting. If this trend continues, future landscapes will shift away from extensive regenerating forests and toward landscapes dominated by pole-sized and larger stands. Because Maine presently supports the only verified populations of this federally threatened species in the eastern United States, changes in forest management practices could affect recovery efforts throughout that region.

Maine↗
USGS2003

Recent and historical distributions of Canada lynx in Maine and the Northeast

The contiguous United States population of Canada lynx ( Lynx canadensis Kerr) is listed as threatened under the federal Endangered Species Act. However, the historic distribution of lynx in the Northeast is poorly understood. We used museum records, bibliographic records, and interviews to reconstruct the past distribution of lynx in Maine, which is at the current southern limit of the species' distribution in the eastern United States. We found a total of 118 records, representing at least 509 lynx in Maine. Lynx were observed throughout Maine, 1833–1912, with the exception of coastal areas. After 1913, lynx were most common in the forests of western and northern Maine, and absent to rare along the coast, but had not returned to southern Maine by 1999. Thirty-nine kittens representing at least 21 litters were distributed throughout northern and western Maine, 1864–1999. Populations apparently fluctuated, and in some years 200–300 lynx were harvested in Maine. Prior to the 1900s, lynx were much more widely distributed in the Northeast, ranging from Pennsylvania north into Quebec. Because Canada lynx have had a long presence in northern New England, and at times were relatively common, this species merits serious consideration in conservation planning in this region.

Northeast United States↗
USGS2001

Partitioning sources of variation in vertebrate species richness

Aim: To explore biogeographic patterns of terrestrial vertebrates in Maine, USA using techniques that would describe local and spatial correlations with the environment. Location: Maine, USA. Methods: We delineated the ranges within Maine (86,156 km2) of 275 species using literature and expert review. Ranges were combined into species richness maps, and compared to geomorphology, climate, and woody plant distributions. Methods were adapted that compared richness of all vertebrate classes to each environmental correlate, rather than assessing a single explanatory theory. We partitioned variation in species richness into components using tree and multiple linear regression. Methods were used that allowed for useful comparisons between tree and linear regression results. For both methods we partitioned variation into broad-scale (spatially autocorrelated) and fine-scale (spatially uncorrelated) explained and unexplained components. By partitioning variance, and using both tree and linear regression in analyses, we explored the degree of variation in species richness for each vertebrate group that Could be explained by the relative contribution of each environmental variable. Results: In tree regression, climate variation explained richness better (92% of mean deviance explained for all species) than woody plant variation (87%) and geomorphology (86%). Reptiles were highly correlated with environmental variation (93%), followed by mammals, amphibians, and birds (each with 84-82% deviance explained). In multiple linear regression, climate was most closely associated with total vertebrate richness (78%), followed by woody plants (67%) and geomorphology (56%). Again, reptiles were closely correlated with the environment (95%), followed by mammals (73%), amphibians (63%) and birds (57%). Main conclusions: Comparing variation explained using tree and multiple linear regression quantified the importance of nonlinear relationships and local interactions between species richness and environmental variation, identifying the importance of linear relationships between reptiles and the environment, and nonlinear relationships between birds and woody plants, for example. Conservation planners should capture climatic variation in broad-scale designs; temperatures may shift during climate change, but the underlying correlations between the environment and species richness will presumably remain.

Journal of Biogeography↗
USGS2000

Predicting broad-scale occurrences of vertebrates in patchy landscapes

Spatially explicit landscape-scale models that predict species distributions, where patches of habitat are shown as having potential to be occupied or unoccupied, are increasingly common. To successfully use such data, one should understand how these predicted distributions are created and how their relative accuracies are assessed. Geographic ranges, defined upon observations (e.g., atlases), literature review, and expert review, are a primary data layer. A map of land cover is created, often from interpretation of satellite imagery or other remotely-sensed data. Species/habitat associations are defined based upon a literature review and expert review, describing associations for habitats derived from the cover map. Included as ancillary associations are how species relate to physical features, where appropriate, such as elevation and hydrography. The three layers of information (range, land cover, and associations) are merged, often using raster-based algebraic statements that exclude unused habitats or patches outside the range of a species. The accuracy of predictions for a suite of species is typically assessed with surveys by comparing the species predicted to occur in an area to the species observed. Omission (i.e., present in species lists but not predicted) and commission (i.e., predicted but not present in lists) errors are reported. Errors may be due to many sources. For example, ranges of species change, cover types may be misidentified, species/habitat associations may be incorrect or change, or species may be rare and unlikely to be seen in surveys and judged in-error even though the species may be present. An example is given of an appropriate use of broad-scale species predicted distributions, in which patterns and threats to Maine terrestrial vertebrate diversity are summarized.

Landscape Ecology↗
USGS1997

Spring prey use by double-crested cormorants on the Penobscot River, Maine, USA

We analyzed 2 sets of data for Double-crested Cormorant (Phalacrocorax auritus) stomach contents (including esophageal contents) that were collected from April through June of 1986-1988 (N = 580) and 1992-1993 (N = 200) on the Penobscot River, Maine. Our objectives were to examine temporal and spatial variation in the spring diet and estimate the importance of Atlantic salmon (Salmo salar) smolts to the cormorant diet. We analyzed stomach contents relative to samples from 3 river sections: 5 mainstem dams collectively, above the head of tide, and free-flowing areas above and below the head of tide. Between years composition of taxa lists were compared (P = 0.05) relative to time and river section. We estimated taxon importance for data collected during 1992-1993 by ranking taxa according to 3 statistics: frequency of occurrence, mean percent volume, and numerical abundance. Data from 1986-88 were analyzed by frequency of occurrence only. Across the 3 river sections, the number of prey species recovered from cormorant stomachs increased from 15 in late April to at least 31 through May. Cormorants collected above the head of tide consumed 12 fish species (including freshwater, anadromous, and catadromous types), whereas birds collected below the head of tide consumed 28 freshwater and seasonally-available estuarine, marine benthic, and pelagic species. Salmon smolts were not recovered from stomachs collected in April, rare in stomach samples during the first week of June, and absent from the diet thereafter. In contrast, smolts were among the 5 most frequently occurring (1986-88) and highest ranking (1992-1993) prey taxa across the 3 river sections through May.

Waterbirds↗
USGS1977

Fall migration of woodcock at Cape May, New Jersey

From 1968 to 1973, 2,337 American woodcock ( Philohela minor ) were banded during late fall on the Cape May Peninsula of southern New Jersey. Direct recovery rates averaged 3.6 percent for hatching-year birds and 1.7 percent for adults. Distribution of recoveries indicated that Cape May migrants wintered on the coastal plain of Virginia and North Carolina. Indirect recoveries showed that Peninsula woodcock originated from as far north as New England and eastern Canada. The percentage of woodcock seen which were caught by night-lighting averaged 2.5 times greater from a truck than on foot. Age-sex structure of ban dings was similar each year with the overall composition as follows: immaturemales, 57 percent; immature females, 28 percent; adult males, 10 percent; and adult females, 5 percent. Compared to the continental population, there was an unusually high proportion of immature woodcock at Cape May during late fall.

New Jersey↗
USGS1977

Earthworm populations as related to woodcock habitat usage in Central Maine

Lumbricid earthworms were sampled 'on two central Maine study areas between late April and early September, 1974, to relate earthworm abundance to use of feeding covers by American woodcock(Philoheli minor). On sampling days, occurring at 2 to 3 week intervals, a formalin solution was applied to thirty O.25m areas in heavjly, commonly, and rarely used woodcock covers (5 samples/type of feedjngcover/study area). The extent of cover usage was based on use of vegetation by 51 radio-equipped woodcock, 1970-73 (605 woodcockdays). A total of 2,546 earthworms of nine species was collected; species and age compositions of collected lumbricids were similar on both study areas. Similarly. number and biomass (dry weight) of earthworms extracted did not differ significantly between study areas. However. the number and biomass of sampled earthworms were directly and significantly related to the intensity to which woodcock used covers. Those diurnal covers most heavily used by woodcock sustained the highest lumbricid populations, ostensibly because these covers provided earthworms with preferred foods (i.e., leaf litters) and optimum soil moisture-temperature conditions. In terms of earthworms and woodcock supported per unit area, management of second-growth hardwoods appears more efficient than attempting to alter coniferous or mixed forests.

Book chapter↗
USGS1977

Band recovery distribution of eastern Maine woodcock

A total of 9,643 American woodcock (Philohela minor) was banded in eastern Maine during the summers of 1962-74. The fall migration of these woodcock, based on 620 recoveries, occurred along a broad front between the Appalachian Mountains and Atlantic Ocean. Most birds wintered in a region extending from southern Virginia to northern Florida; a few woodcock moved as far west as Louisiana and eastern Texas. The band-recovery distribution of Maine woodcock, and band-recovery records from birds wintering in Louisiana published by other investigators, support the idea of Atlantic and Central flyways. However, recoveries from woodcock banded in breeding localities other than eastern Maine must be studied to more precisely relate major breeding and wintering grounds

Wildlife Society Bulletin↗
USGS1973

Molt patterns and weight changes of the American woodcock

A study of molt and changes in body weight of American Woodcock was conducted to better understand the summer and fall behavior of these birds and to indicate periods of physiological stress. The postnuptial molt of adults was a complete molt beginning in late June and ending by the middle of October. In contrast, the postjuvenal molt was a less intensive partial molt beginning in mid-July but also extending to the middle of October. Both male and female adult birds experienced weight loss in August during peak molt. Young birds gradually gained weight throughout the summer. Fat deposition was negatively correlated with molt while fall body weights were positively correlated with fat deposition. The data indicated that the majority of Maine woodcock are not physiologically prepared for migration until mid-October. Weights of adult males during the spring suggested that this is an important period of stress for these birds.

The Wilson Bulletin↗