Conventional plant growth analysis (Blackman 1919) and recent advances in it (Causton and Venus 1... more Conventional plant growth analysis (Blackman 1919) and recent advances in it (Causton and Venus 1981, Kauffman 1981, Parsons and Hunt 1981, Hunt 1982) have provided useful tools for describing plant growth in terms of biomass accumulation. However, for cer-tain kinds ...
Ailanthus altissima is an invasive, dioecious deciduous tree common at the interface between urba... more Ailanthus altissima is an invasive, dioecious deciduous tree common at the interface between urban and rural areas in the mid-Atlantic region, U.S.A. To examine spatial patterns of abundance and associations with land use type, we mapped all mature female trees in nine 89.5 ha plots (805.5 ha total area) across a typical urban-to-rural land use gradient using aerial images obtained via remote sensing supplemented by detailed ground referencing. Rural plots were dominated by forest and had the lowest density of mature females (0.007 females ha−1); urban and suburban plots did not differ significantly in mean density (0.37 females ha−1 vs. 0.34 females ha−1, respectively). Individuals in urban plots were more evenly distributed, but were not associated with a wider variety of land uses and were closer to roads or openings than those in suburban plots. Given less available habitat per unit area in urban than in suburban environments, these patterns suggest that Ailanthus fits the profi...
Local climatic adaptation can influence species' response to climate change. If populations w... more Local climatic adaptation can influence species' response to climate change. If populations within a species are adapted to local climate, directional change away from mean climatic conditions may negatively affect fitness of populations throughout the species' range. Adaptive differentiation to temperature was tested for in American ginseng (Panax quinquefolius) by reciprocally transplanting individuals from two populations, originating at different elevations, among temperature treatments in a controlled growth chamber environment. Fitness-related traits were measured in order to test for a population × temperature treatment interaction, and key physiological and phenological traits were measured to explain population differences in response to temperature. Response to temperature treatments differed between populations, suggesting genetic differentiation of populations. However, the pattern of response of fitness-related variables generally did not suggest 'home tempe...
Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to ... more Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to site and from individual to individual. To determine whether some of this variation could be explained by variation in other stress factors, red oak (Quercus rubra L.) seedlings were exposed to low and high light, water, mineral nutrient, and defoliation treatments, in a complete factorial design in a greenhouse. Significant interactions were observed among factors for photosynthesis, growth, and mortality, indicating that the response to defoliation was influenced by other stresses. Defoliation increased the photosynthetic capacity per unit leaf area of seedlings grown in the low-water, but not in the high-water, regime. In response to defoliation, growth of seedlings in a low-mineral-nutrient, or low-light, regime was depressed less than that of seedlings grown in a high-mineral-nutrient, or high-light, regime. However, defoliation resulted in a similar percent reduction in biomass in ...
ABSTRACT Background/Question/Methods One of the most important issues in biogeography is to under... more ABSTRACT Background/Question/Methods One of the most important issues in biogeography is to understand species' range limits. It has been suggested that because of less suitable conditions peripheral populations are smaller, less dense, more isolated and produce less seeds than central populations. As a consequence they should exhibit lower genetic diversity and greater genetic differentiation than central populations. We compared population characteristics and individual reproduction as well as genetic diversity and genetic differentiation of populations of the perennial, insect-pollinated rock plant Carduus defloratus (Asteraceae) along a gradient from the center to the margin of its distribution in Central Europe. Results/Conclusions As expected, peripheral populations were smaller, less dense and produced less viable seeds than central populations. Amplified fragment length polymorphism analysis indicated that genetic diversity was lower in peripheral than in central populations. However, the genetic distance between peripheral was lower than between central populations. The pairwise genetic distance between populations increased with their geographic distance. There was significant genetic differentiation between the two types of populations, but variation among populations within types was higher, and most of the genetic variation was among individuals within populations. In C. defloratus, the range limit may be influenced by the reduced reproductive success of peripheral populations. Seed abortion was higher in peripheral than in central population and increased with decreasing genetic diversity, indicating early inbreeding depression.
ABSTRACT American ginseng (Panax quinquefolius) is an uncommon perennial understory herb found in... more ABSTRACT American ginseng (Panax quinquefolius) is an uncommon perennial understory herb found in eastern deciduous forest. The species is harvested for the international medicinal plant trade. While previous research has inferred that seed dispersal is limited, the production of bright red, fleshy berries suggests long-distance dispersal may be facilitated by songbirds. The objective of this study was to determine how songbirds interacted with ginseng and whether they dispersed or predated ginseng seeds. We used infrared, motion-activated cameras to observe animal—ginseng interactions in the field. To determine the disperser potential of songbirds observed visiting ginseng in the field, we conducted a captive feeding study at the Tennessee Aquarium. Thrushes removed berries from ginseng infructescences more frequently, compared to other potential dispersers, and regurgitated viable seeds 5–37 minutes after ingestion in feeding trials. By dispersing ginseng seeds, thrushes provide a mechanism for ginseng to improve its probability of persistence in the face of 3 primary threats to populations: deer browse, harvest, and climate change.
Plant growth rate is often assumed to be an ecologically important life history trait. However, c... more Plant growth rate is often assumed to be an ecologically important life history trait. However, conventional plant growth analysis, while providing a useful accounting of rates of weight gain and its components, is ill-suited for testing relationships between growth and fitness, particularly in natural populations. Two new approaches that are suitable for testing such relationships have evolved over the past several years. The first - the population biology of plant parts, or 'modular demography' - permits non-destructive measures of growth rate in natural field populations. When modular demography is performed using matrix population models, controls over growth rate can be examined, as well as consequences of growth variation for reproduction. The second - demographic growth analysis - provides growth parameters analogous to those of conventional growth analysis, but can be performed in natural field populations. Demographic growth analysis allows measures of individual growth-rate variation, which, in turn, can be related to plant performance.
Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to ... more Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to site and from individual to individual. To determine whether some of this variation could be explained by variation in other stress factors, red oak (Quercus rubra L.) seedlings were exposed to low and high light, water, mineral nutrient, and defoliation treatments, in a complete factorial design in a greenhouse. Significant interactions were observed among factors for photosynthesis, growth, and mortality, indicating that the response to defoliation was influenced by other stresses. Defoliation increased the photosynthetic capacity per unit leaf area of seedlings grown in the low-water, but not in the high-water, regime. In response to defoliation, growth of seedlings in a low-mineral-nutrient, or low-light, regime was depressed less than that of seedlings grown in a high-mineral-nutrient, or high-light, regime. However, defoliation resulted in a similar percent reduction in biomass in all seedlings in both the high and the low light, water, and mineral nutrient treatments. Defoliation-induced mortality of shaded plants was twice that of plants grown in full sun.
Science in China Series E: Technological Sciences, 2006
In this paper we investigate the use of a shadow-based delineation program for identifying segmen... more In this paper we investigate the use of a shadow-based delineation program for identifying segments in imagery of a closed canopy, deciduous forest, in West Virginia, USA, as a way to reduce the noise associated with per-pixel classification in forested environments. Shadows typically cluster along the boundaries of trees and therefore can be used to provide a network of nodes
Conventional plant growth analysis (Blackman 1919) and recent advances in it (Causton and Venus 1... more Conventional plant growth analysis (Blackman 1919) and recent advances in it (Causton and Venus 1981, Kauffman 1981, Parsons and Hunt 1981, Hunt 1982) have provided useful tools for describing plant growth in terms of biomass accumulation. However, for cer-tain kinds ...
Ailanthus altissima is an invasive, dioecious deciduous tree common at the interface between urba... more Ailanthus altissima is an invasive, dioecious deciduous tree common at the interface between urban and rural areas in the mid-Atlantic region, U.S.A. To examine spatial patterns of abundance and associations with land use type, we mapped all mature female trees in nine 89.5 ha plots (805.5 ha total area) across a typical urban-to-rural land use gradient using aerial images obtained via remote sensing supplemented by detailed ground referencing. Rural plots were dominated by forest and had the lowest density of mature females (0.007 females ha−1); urban and suburban plots did not differ significantly in mean density (0.37 females ha−1 vs. 0.34 females ha−1, respectively). Individuals in urban plots were more evenly distributed, but were not associated with a wider variety of land uses and were closer to roads or openings than those in suburban plots. Given less available habitat per unit area in urban than in suburban environments, these patterns suggest that Ailanthus fits the profi...
Local climatic adaptation can influence species' response to climate change. If populations w... more Local climatic adaptation can influence species' response to climate change. If populations within a species are adapted to local climate, directional change away from mean climatic conditions may negatively affect fitness of populations throughout the species' range. Adaptive differentiation to temperature was tested for in American ginseng (Panax quinquefolius) by reciprocally transplanting individuals from two populations, originating at different elevations, among temperature treatments in a controlled growth chamber environment. Fitness-related traits were measured in order to test for a population × temperature treatment interaction, and key physiological and phenological traits were measured to explain population differences in response to temperature. Response to temperature treatments differed between populations, suggesting genetic differentiation of populations. However, the pattern of response of fitness-related variables generally did not suggest 'home tempe...
Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to ... more Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to site and from individual to individual. To determine whether some of this variation could be explained by variation in other stress factors, red oak (Quercus rubra L.) seedlings were exposed to low and high light, water, mineral nutrient, and defoliation treatments, in a complete factorial design in a greenhouse. Significant interactions were observed among factors for photosynthesis, growth, and mortality, indicating that the response to defoliation was influenced by other stresses. Defoliation increased the photosynthetic capacity per unit leaf area of seedlings grown in the low-water, but not in the high-water, regime. In response to defoliation, growth of seedlings in a low-mineral-nutrient, or low-light, regime was depressed less than that of seedlings grown in a high-mineral-nutrient, or high-light, regime. However, defoliation resulted in a similar percent reduction in biomass in ...
ABSTRACT Background/Question/Methods One of the most important issues in biogeography is to under... more ABSTRACT Background/Question/Methods One of the most important issues in biogeography is to understand species' range limits. It has been suggested that because of less suitable conditions peripheral populations are smaller, less dense, more isolated and produce less seeds than central populations. As a consequence they should exhibit lower genetic diversity and greater genetic differentiation than central populations. We compared population characteristics and individual reproduction as well as genetic diversity and genetic differentiation of populations of the perennial, insect-pollinated rock plant Carduus defloratus (Asteraceae) along a gradient from the center to the margin of its distribution in Central Europe. Results/Conclusions As expected, peripheral populations were smaller, less dense and produced less viable seeds than central populations. Amplified fragment length polymorphism analysis indicated that genetic diversity was lower in peripheral than in central populations. However, the genetic distance between peripheral was lower than between central populations. The pairwise genetic distance between populations increased with their geographic distance. There was significant genetic differentiation between the two types of populations, but variation among populations within types was higher, and most of the genetic variation was among individuals within populations. In C. defloratus, the range limit may be influenced by the reduced reproductive success of peripheral populations. Seed abortion was higher in peripheral than in central population and increased with decreasing genetic diversity, indicating early inbreeding depression.
ABSTRACT American ginseng (Panax quinquefolius) is an uncommon perennial understory herb found in... more ABSTRACT American ginseng (Panax quinquefolius) is an uncommon perennial understory herb found in eastern deciduous forest. The species is harvested for the international medicinal plant trade. While previous research has inferred that seed dispersal is limited, the production of bright red, fleshy berries suggests long-distance dispersal may be facilitated by songbirds. The objective of this study was to determine how songbirds interacted with ginseng and whether they dispersed or predated ginseng seeds. We used infrared, motion-activated cameras to observe animal—ginseng interactions in the field. To determine the disperser potential of songbirds observed visiting ginseng in the field, we conducted a captive feeding study at the Tennessee Aquarium. Thrushes removed berries from ginseng infructescences more frequently, compared to other potential dispersers, and regurgitated viable seeds 5–37 minutes after ingestion in feeding trials. By dispersing ginseng seeds, thrushes provide a mechanism for ginseng to improve its probability of persistence in the face of 3 primary threats to populations: deer browse, harvest, and climate change.
Plant growth rate is often assumed to be an ecologically important life history trait. However, c... more Plant growth rate is often assumed to be an ecologically important life history trait. However, conventional plant growth analysis, while providing a useful accounting of rates of weight gain and its components, is ill-suited for testing relationships between growth and fitness, particularly in natural populations. Two new approaches that are suitable for testing such relationships have evolved over the past several years. The first - the population biology of plant parts, or 'modular demography' - permits non-destructive measures of growth rate in natural field populations. When modular demography is performed using matrix population models, controls over growth rate can be examined, as well as consequences of growth variation for reproduction. The second - demographic growth analysis - provides growth parameters analogous to those of conventional growth analysis, but can be performed in natural field populations. Demographic growth analysis allows measures of individual growth-rate variation, which, in turn, can be related to plant performance.
Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to ... more Responses of forest trees to defoliation by insects such as gypsy moth vary greatly from site to site and from individual to individual. To determine whether some of this variation could be explained by variation in other stress factors, red oak (Quercus rubra L.) seedlings were exposed to low and high light, water, mineral nutrient, and defoliation treatments, in a complete factorial design in a greenhouse. Significant interactions were observed among factors for photosynthesis, growth, and mortality, indicating that the response to defoliation was influenced by other stresses. Defoliation increased the photosynthetic capacity per unit leaf area of seedlings grown in the low-water, but not in the high-water, regime. In response to defoliation, growth of seedlings in a low-mineral-nutrient, or low-light, regime was depressed less than that of seedlings grown in a high-mineral-nutrient, or high-light, regime. However, defoliation resulted in a similar percent reduction in biomass in all seedlings in both the high and the low light, water, and mineral nutrient treatments. Defoliation-induced mortality of shaded plants was twice that of plants grown in full sun.
Science in China Series E: Technological Sciences, 2006
In this paper we investigate the use of a shadow-based delineation program for identifying segmen... more In this paper we investigate the use of a shadow-based delineation program for identifying segments in imagery of a closed canopy, deciduous forest, in West Virginia, USA, as a way to reduce the noise associated with per-pixel classification in forested environments. Shadows typically cluster along the boundaries of trees and therefore can be used to provide a network of nodes
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