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Susanna Lehvavirta - One of the best experts on this subject based on the ideXlab platform.
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tree species composition affects the abundance of rowan sorbus aucuparia l in urban forests in finland
Journal of Environmental Management, 2015Co-Authors: Leena Hamberg, Susanna Lehvavirta, Johan D Kotze, Juha HeikkinenAbstract:Abstract Recent studies have shown a considerable increase in the abundance of rowan ( Sorbus aucuparia ) saplings in urban forests in Finland, yet the reasons for this increase are not well understood. Here we investigated whether canopy cover or tree species composition, i.e., the basal areas of different tree species in Norway spruce dominated urban forests, affects the abundances of rowan seedlings, saplings and trees. Altogether 24 urban forest patches were investigated. We sampled the number of rowan and other saplings, and calculated the basal areas of trees. We showed that rowan abundance was affected by tree species composition. The basal area of rowan trees (≥5 cm in diameter at breast height, dbh) decreased with increasing basal area of Norway spruce, while the cover of rowan seedlings increased with an increase in Norway spruce basal area. However, a decrease in the abundance of birch ( Betula pendula ) and an increase in the broad-leaved tree group ( Acer platanoides , Alnus glutinosa , Alnus incana , Amelanchier spicata , Prunus padus , Quercus robur , Rhamnus frangula and Salix caprea ) coincided with a decreasing number of rowans. Furthermore, rowan saplings were scarce in the vicinity of mature rowan trees. Although it seems that tree species composition has an effect on rowan, the relationship between rowan saplings and mature trees is complex, and therefore we conclude that regulating tree species composition is not an easy way to keep rowan thickets under control in urban forests in Finland.
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Barriers against wear affect the spatial distribution of tree saplings in urban woodlands
Urban Forestry & Urban Greening, 2004Co-Authors: Susanna Lehvavirta, Hannu Rita, Matti KoivulaAbstract:Abstract In order to maintain indigenous, self-regenerating tree populations in urban woodlands, it is essential to identify factors affecting the survival of tree seedlings and saplings. In densely populated areas, intensive recreational use may cause considerable wear of the vegetation and soil, and decrease the total number of saplings. At the same time trees, high stones and other structural elements in a woodland patch can act as natural barriers and give shelter against wear. Hence, we hypothesised that with an increasing amount of wear, a greater proportion of tree saplings survive, and is thus found, close to these natural barriers. We tested this hypothesis with observational data, and described the microhabitat associations of different sapling species in detail to define the most favourable or unfavourable microhabitats. We recorded the microhabitats of saplings and randomly chosen points in 30 medium-fertile Picea abies dominant woodlands in Helsinki and the surroundings, Finland. The description included location in relation to physical objects (stones, trees, topography, etc.), other saplings, vegetation and canopy. We then compared the sapling microhabitats to those available (the random points). Our results suggest that the microhabitat associations of saplings change with increasing wear: Sorbus aucuparia , Populus tremula , Rhamnus frangula , Picea abies and Acer platanoides saplings grew more often close to natural barriers (obstacles ⩾30 cm high excluding other saplings), the first three showing a statistically significant response to wear in logistic regression models. The saplings were able to grow in a variety of microhabitats, but the species also differed in their microhabitat associations. In general, saplings grew in groups, and in worn sites the grouping was more pronounced. With increasing wear the saplings associated more positively with trees, canopy cover and lush vegetation.
Robert T. Eckert - One of the best experts on this subject based on the ideXlab platform.
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Experimental Removal of the Non-indigenous Shrub Rhamnus frangula (Glossy Buckthorn): Effects on Native Herbs and Woody Seedlings
Northeastern Naturalist, 2004Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:Abstract Effects of the non-indigenous shrub Rhamnus frangula L. (glossy buckthorn) on tree recruitment, herb cover, forest floor plant species richness, and R. frangula recruitment were tested in two southeastern New Hampshire Pinus forests using a randomized complete-block field experiment. The treatment, applied in January of 2000, was the presence of well-established R. frangula populations with three levels: R. frangula absent prior to experiment (“uninvaded”), > 90% R. frangula cover (“Rhamnus present”), and removal of > 90% R. frangula cover (“Rhamnus removed”). After 2 years of measurements, Rhamnus present had significantly lower first-year native tree seedling density than Rhamnus removed and uninvaded plots (0.11, 0.40, and 0.40 seedlings/m2 respectively). First-year native tree seedling density in the Rhamnus removed and uninvaded treatments were similar. Neither percent herb cover nor plant species richness were significantly affected by the removal of R. frangula in the two years following t...
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Small-scale invasion pattern, spread rate, and lag-phase behavior of Rhamnus frangula L.
Forest Ecology and Management, 2003Co-Authors: Brian Frappier, Thomas D. Lee, Kari F. Olson, Robert T. EckertAbstract:Abstract We tested the ability of the simple reaction–diffusion spread model to quantify the rate of spread of Rhamnus frangula L., a non-indigenous shrub, at the scale of a single forest stand in southeastern New Hampshire. Cut stems of R. frangula were collected in a Cartesian grid pattern within the invaded stand and aged. A contour map of the invasion pattern was produced using kriging. The empirical invasion rate was calculated as the linear distance per year since initial invasion. The intrinsic rate of increase and diffusion coefficient were estimated in the field and the model prediction calculated. Observed mean rate of linear expansion was measured to be 6.7 m per year with a standard deviation of 1.24 m per year, while the predicted linear asymptotic rate of spread was calculated be 6.3 m per year. Thus, the simple reaction–diffusion model yielded a very accurate prediction of actual spread rate. There may have been a lag-phase in the invasion at this site as the spread rate was found to be slower in the early stages of invasion compared to later stages. At the scale of single stands, the simple reaction–diffusion model may be accurate enough to predict the spread of new invaders without recourse to complex life-history spread rate models. Additionally, if lag-phases in spread rate occur with regular frequency, then attempts to retrospectively predict which species may be invasive will be hampered by incorrectly classifying a future invader as currently non-invasive.
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POTENTIAL IMPACTS OF THE INVASIVE EXOTIC SHRUB Rhamnus frangula L. (GLOSSY BUCKTHORN) ON FORESTS OF SOUTHERN NEW HAMPSHIRE
Northeastern Naturalist, 2003Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:Abstract This paper investigated the potential for the exotic shrub Rhamnus frangula L. (glossy buckthorn) to alter native plant community composition in southeastern New Hampshire. Stratified random sampling was performed with 2 m × 2 m plots randomly located in 5 m intervals along three 50 m transects in four even-aged Pinus-mixed hardwood forests, three of which were managed stands. The associations between R. frangula and the measured species abundances and environmental variables were investigated using linear, least-squares multiple regression and Non-metric Multidimensional Scaling Ordination. Plot basal area of R. frangula was inversely related to woody seedling density (p < 0.001), herb cover (p < 0.05), and species richness (p < 0.01). The relative contribution of R. frangula to explaining variance in seedling density was greater than canopy openness, soil pH, soil clay, or soil sand. Abundance of R. frangula was a statistically significant predictor (p < 0.05) of individual herb species abundan...
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Small-scale invasion pattern, spread rate, and lag-phase behavior of Rhamnus frangula L.
Forest Ecology and Management, 2003Co-Authors: Brian Frappier, Thomas D. Lee, Kari F. Olson, Robert T. EckertAbstract:We tested, the ability of the simple reaction-diffusion spread model to quantify the rate of spread of Rhamnus frangula L., a non-indigenous shrub, at the scale of a single forest stand in southeastern New Hampshire. Cut stems of R. frangula were collected in a Cartesian grid pattern within the invaded stand and aged. A contour map of the invasion pattern was produced using kriging. The empirical invasion rate was calculated as the linear distance per year since initial invasion. The intrinsic rate of increase and diffusion coefficient were estimated in the field and the model prediction calculated. Observed mean rate of linear expansion was measured to be 6.7 in per year with a standard deviation of 1.24 m per year, while the predicted linear asymptotic rate of spread was calculated be 6.3 m per year. Thus, the simple reaction-diffusion model yielded a very accurate prediction of actual spread rate. There may have been a lag-phase in the invasion at this site as the spread rate was found to be slower in the early stages of invasion compared to later stages. At the scale of single stands, the simple reaction-diffusion model may be accurate enough to predict the spread of new invaders without recourse to complex life-history spread rate models. Additionally, if lag-phases in spread rate occur with regular frequency, then attempts to retrospectively predict which species may be invasive will be hampered by incorrectly classifying a future invader as currently non-invasive. (C) 2003 Elsevier B.V. All rights reserved
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Potential Impacts of the Invasive Exotic Shrub Rhamnus frangula L. (Glossy Buckthorn) on Forests of Southern New Hampshire
Northeastern Naturalist, 2003Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:This paper investigated the potential for the exotic shrub Rhamnus frangula L. (glossy buckthorn) to alter native plant community composition in southeastern New Hampshire. Stratified random sampling was performed with 2 m x 2 m plots randomly located in 5 m intervals along three 50 m transects in four even-aged Pinus-mixed hardwood forests, three of which were managed stands. The associations between R. frangula and the measured species abundances and environmental variables were investigated using linear, least-squares multiple regression and Non-metric Multidimensional Scaling Ordination. Plot basal area of R. frangula was inversely related to woody seedling density (p \u3c 0.001), herb cover (p \u3c 0.05), and species richness (p \u3c 0.01). The relative contribution of R. frangula to explaining variance in seedling density was greater than canopy openness, soil pH, soil clay, or soil sand. Abundance of R. frangula was a statistically significant predictor (p \u3c 0.05) of individual herb species abundances for all study sites. This evidence supports the hypothesis that R. frangula causes a decline in seedling density and alters native ground level plant species abundances. Furthermore, the patterns agree with the suppression of ground level plant species abundances by R. frangula found in removal experiments
Thomas D. Lee - One of the best experts on this subject based on the ideXlab platform.
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Experimental Removal of the Non-indigenous Shrub Rhamnus frangula (Glossy Buckthorn): Effects on Native Herbs and Woody Seedlings
Northeastern Naturalist, 2004Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:Abstract Effects of the non-indigenous shrub Rhamnus frangula L. (glossy buckthorn) on tree recruitment, herb cover, forest floor plant species richness, and R. frangula recruitment were tested in two southeastern New Hampshire Pinus forests using a randomized complete-block field experiment. The treatment, applied in January of 2000, was the presence of well-established R. frangula populations with three levels: R. frangula absent prior to experiment (“uninvaded”), > 90% R. frangula cover (“Rhamnus present”), and removal of > 90% R. frangula cover (“Rhamnus removed”). After 2 years of measurements, Rhamnus present had significantly lower first-year native tree seedling density than Rhamnus removed and uninvaded plots (0.11, 0.40, and 0.40 seedlings/m2 respectively). First-year native tree seedling density in the Rhamnus removed and uninvaded treatments were similar. Neither percent herb cover nor plant species richness were significantly affected by the removal of R. frangula in the two years following t...
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Small-scale invasion pattern, spread rate, and lag-phase behavior of Rhamnus frangula L.
Forest Ecology and Management, 2003Co-Authors: Brian Frappier, Thomas D. Lee, Kari F. Olson, Robert T. EckertAbstract:Abstract We tested the ability of the simple reaction–diffusion spread model to quantify the rate of spread of Rhamnus frangula L., a non-indigenous shrub, at the scale of a single forest stand in southeastern New Hampshire. Cut stems of R. frangula were collected in a Cartesian grid pattern within the invaded stand and aged. A contour map of the invasion pattern was produced using kriging. The empirical invasion rate was calculated as the linear distance per year since initial invasion. The intrinsic rate of increase and diffusion coefficient were estimated in the field and the model prediction calculated. Observed mean rate of linear expansion was measured to be 6.7 m per year with a standard deviation of 1.24 m per year, while the predicted linear asymptotic rate of spread was calculated be 6.3 m per year. Thus, the simple reaction–diffusion model yielded a very accurate prediction of actual spread rate. There may have been a lag-phase in the invasion at this site as the spread rate was found to be slower in the early stages of invasion compared to later stages. At the scale of single stands, the simple reaction–diffusion model may be accurate enough to predict the spread of new invaders without recourse to complex life-history spread rate models. Additionally, if lag-phases in spread rate occur with regular frequency, then attempts to retrospectively predict which species may be invasive will be hampered by incorrectly classifying a future invader as currently non-invasive.
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POTENTIAL IMPACTS OF THE INVASIVE EXOTIC SHRUB Rhamnus frangula L. (GLOSSY BUCKTHORN) ON FORESTS OF SOUTHERN NEW HAMPSHIRE
Northeastern Naturalist, 2003Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:Abstract This paper investigated the potential for the exotic shrub Rhamnus frangula L. (glossy buckthorn) to alter native plant community composition in southeastern New Hampshire. Stratified random sampling was performed with 2 m × 2 m plots randomly located in 5 m intervals along three 50 m transects in four even-aged Pinus-mixed hardwood forests, three of which were managed stands. The associations between R. frangula and the measured species abundances and environmental variables were investigated using linear, least-squares multiple regression and Non-metric Multidimensional Scaling Ordination. Plot basal area of R. frangula was inversely related to woody seedling density (p < 0.001), herb cover (p < 0.05), and species richness (p < 0.01). The relative contribution of R. frangula to explaining variance in seedling density was greater than canopy openness, soil pH, soil clay, or soil sand. Abundance of R. frangula was a statistically significant predictor (p < 0.05) of individual herb species abundan...
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Small-scale invasion pattern, spread rate, and lag-phase behavior of Rhamnus frangula L.
Forest Ecology and Management, 2003Co-Authors: Brian Frappier, Thomas D. Lee, Kari F. Olson, Robert T. EckertAbstract:We tested, the ability of the simple reaction-diffusion spread model to quantify the rate of spread of Rhamnus frangula L., a non-indigenous shrub, at the scale of a single forest stand in southeastern New Hampshire. Cut stems of R. frangula were collected in a Cartesian grid pattern within the invaded stand and aged. A contour map of the invasion pattern was produced using kriging. The empirical invasion rate was calculated as the linear distance per year since initial invasion. The intrinsic rate of increase and diffusion coefficient were estimated in the field and the model prediction calculated. Observed mean rate of linear expansion was measured to be 6.7 in per year with a standard deviation of 1.24 m per year, while the predicted linear asymptotic rate of spread was calculated be 6.3 m per year. Thus, the simple reaction-diffusion model yielded a very accurate prediction of actual spread rate. There may have been a lag-phase in the invasion at this site as the spread rate was found to be slower in the early stages of invasion compared to later stages. At the scale of single stands, the simple reaction-diffusion model may be accurate enough to predict the spread of new invaders without recourse to complex life-history spread rate models. Additionally, if lag-phases in spread rate occur with regular frequency, then attempts to retrospectively predict which species may be invasive will be hampered by incorrectly classifying a future invader as currently non-invasive. (C) 2003 Elsevier B.V. All rights reserved
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Potential Impacts of the Invasive Exotic Shrub Rhamnus frangula L. (Glossy Buckthorn) on Forests of Southern New Hampshire
Northeastern Naturalist, 2003Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:This paper investigated the potential for the exotic shrub Rhamnus frangula L. (glossy buckthorn) to alter native plant community composition in southeastern New Hampshire. Stratified random sampling was performed with 2 m x 2 m plots randomly located in 5 m intervals along three 50 m transects in four even-aged Pinus-mixed hardwood forests, three of which were managed stands. The associations between R. frangula and the measured species abundances and environmental variables were investigated using linear, least-squares multiple regression and Non-metric Multidimensional Scaling Ordination. Plot basal area of R. frangula was inversely related to woody seedling density (p \u3c 0.001), herb cover (p \u3c 0.05), and species richness (p \u3c 0.01). The relative contribution of R. frangula to explaining variance in seedling density was greater than canopy openness, soil pH, soil clay, or soil sand. Abundance of R. frangula was a statistically significant predictor (p \u3c 0.05) of individual herb species abundances for all study sites. This evidence supports the hypothesis that R. frangula causes a decline in seedling density and alters native ground level plant species abundances. Furthermore, the patterns agree with the suppression of ground level plant species abundances by R. frangula found in removal experiments
Brian Frappier - One of the best experts on this subject based on the ideXlab platform.
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Experimental Removal of the Non-indigenous Shrub Rhamnus frangula (Glossy Buckthorn): Effects on Native Herbs and Woody Seedlings
Northeastern Naturalist, 2004Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:Abstract Effects of the non-indigenous shrub Rhamnus frangula L. (glossy buckthorn) on tree recruitment, herb cover, forest floor plant species richness, and R. frangula recruitment were tested in two southeastern New Hampshire Pinus forests using a randomized complete-block field experiment. The treatment, applied in January of 2000, was the presence of well-established R. frangula populations with three levels: R. frangula absent prior to experiment (“uninvaded”), > 90% R. frangula cover (“Rhamnus present”), and removal of > 90% R. frangula cover (“Rhamnus removed”). After 2 years of measurements, Rhamnus present had significantly lower first-year native tree seedling density than Rhamnus removed and uninvaded plots (0.11, 0.40, and 0.40 seedlings/m2 respectively). First-year native tree seedling density in the Rhamnus removed and uninvaded treatments were similar. Neither percent herb cover nor plant species richness were significantly affected by the removal of R. frangula in the two years following t...
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Small-scale invasion pattern, spread rate, and lag-phase behavior of Rhamnus frangula L.
Forest Ecology and Management, 2003Co-Authors: Brian Frappier, Thomas D. Lee, Kari F. Olson, Robert T. EckertAbstract:Abstract We tested the ability of the simple reaction–diffusion spread model to quantify the rate of spread of Rhamnus frangula L., a non-indigenous shrub, at the scale of a single forest stand in southeastern New Hampshire. Cut stems of R. frangula were collected in a Cartesian grid pattern within the invaded stand and aged. A contour map of the invasion pattern was produced using kriging. The empirical invasion rate was calculated as the linear distance per year since initial invasion. The intrinsic rate of increase and diffusion coefficient were estimated in the field and the model prediction calculated. Observed mean rate of linear expansion was measured to be 6.7 m per year with a standard deviation of 1.24 m per year, while the predicted linear asymptotic rate of spread was calculated be 6.3 m per year. Thus, the simple reaction–diffusion model yielded a very accurate prediction of actual spread rate. There may have been a lag-phase in the invasion at this site as the spread rate was found to be slower in the early stages of invasion compared to later stages. At the scale of single stands, the simple reaction–diffusion model may be accurate enough to predict the spread of new invaders without recourse to complex life-history spread rate models. Additionally, if lag-phases in spread rate occur with regular frequency, then attempts to retrospectively predict which species may be invasive will be hampered by incorrectly classifying a future invader as currently non-invasive.
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POTENTIAL IMPACTS OF THE INVASIVE EXOTIC SHRUB Rhamnus frangula L. (GLOSSY BUCKTHORN) ON FORESTS OF SOUTHERN NEW HAMPSHIRE
Northeastern Naturalist, 2003Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:Abstract This paper investigated the potential for the exotic shrub Rhamnus frangula L. (glossy buckthorn) to alter native plant community composition in southeastern New Hampshire. Stratified random sampling was performed with 2 m × 2 m plots randomly located in 5 m intervals along three 50 m transects in four even-aged Pinus-mixed hardwood forests, three of which were managed stands. The associations between R. frangula and the measured species abundances and environmental variables were investigated using linear, least-squares multiple regression and Non-metric Multidimensional Scaling Ordination. Plot basal area of R. frangula was inversely related to woody seedling density (p < 0.001), herb cover (p < 0.05), and species richness (p < 0.01). The relative contribution of R. frangula to explaining variance in seedling density was greater than canopy openness, soil pH, soil clay, or soil sand. Abundance of R. frangula was a statistically significant predictor (p < 0.05) of individual herb species abundan...
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Small-scale invasion pattern, spread rate, and lag-phase behavior of Rhamnus frangula L.
Forest Ecology and Management, 2003Co-Authors: Brian Frappier, Thomas D. Lee, Kari F. Olson, Robert T. EckertAbstract:We tested, the ability of the simple reaction-diffusion spread model to quantify the rate of spread of Rhamnus frangula L., a non-indigenous shrub, at the scale of a single forest stand in southeastern New Hampshire. Cut stems of R. frangula were collected in a Cartesian grid pattern within the invaded stand and aged. A contour map of the invasion pattern was produced using kriging. The empirical invasion rate was calculated as the linear distance per year since initial invasion. The intrinsic rate of increase and diffusion coefficient were estimated in the field and the model prediction calculated. Observed mean rate of linear expansion was measured to be 6.7 in per year with a standard deviation of 1.24 m per year, while the predicted linear asymptotic rate of spread was calculated be 6.3 m per year. Thus, the simple reaction-diffusion model yielded a very accurate prediction of actual spread rate. There may have been a lag-phase in the invasion at this site as the spread rate was found to be slower in the early stages of invasion compared to later stages. At the scale of single stands, the simple reaction-diffusion model may be accurate enough to predict the spread of new invaders without recourse to complex life-history spread rate models. Additionally, if lag-phases in spread rate occur with regular frequency, then attempts to retrospectively predict which species may be invasive will be hampered by incorrectly classifying a future invader as currently non-invasive. (C) 2003 Elsevier B.V. All rights reserved
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Potential Impacts of the Invasive Exotic Shrub Rhamnus frangula L. (Glossy Buckthorn) on Forests of Southern New Hampshire
Northeastern Naturalist, 2003Co-Authors: Brian Frappier, Robert T. Eckert, Thomas D. LeeAbstract:This paper investigated the potential for the exotic shrub Rhamnus frangula L. (glossy buckthorn) to alter native plant community composition in southeastern New Hampshire. Stratified random sampling was performed with 2 m x 2 m plots randomly located in 5 m intervals along three 50 m transects in four even-aged Pinus-mixed hardwood forests, three of which were managed stands. The associations between R. frangula and the measured species abundances and environmental variables were investigated using linear, least-squares multiple regression and Non-metric Multidimensional Scaling Ordination. Plot basal area of R. frangula was inversely related to woody seedling density (p \u3c 0.001), herb cover (p \u3c 0.05), and species richness (p \u3c 0.01). The relative contribution of R. frangula to explaining variance in seedling density was greater than canopy openness, soil pH, soil clay, or soil sand. Abundance of R. frangula was a statistically significant predictor (p \u3c 0.05) of individual herb species abundances for all study sites. This evidence supports the hypothesis that R. frangula causes a decline in seedling density and alters native ground level plant species abundances. Furthermore, the patterns agree with the suppression of ground level plant species abundances by R. frangula found in removal experiments
Juha Heikkinen - One of the best experts on this subject based on the ideXlab platform.
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tree species composition affects the abundance of rowan sorbus aucuparia l in urban forests in finland
Journal of Environmental Management, 2015Co-Authors: Leena Hamberg, Susanna Lehvavirta, Johan D Kotze, Juha HeikkinenAbstract:Abstract Recent studies have shown a considerable increase in the abundance of rowan ( Sorbus aucuparia ) saplings in urban forests in Finland, yet the reasons for this increase are not well understood. Here we investigated whether canopy cover or tree species composition, i.e., the basal areas of different tree species in Norway spruce dominated urban forests, affects the abundances of rowan seedlings, saplings and trees. Altogether 24 urban forest patches were investigated. We sampled the number of rowan and other saplings, and calculated the basal areas of trees. We showed that rowan abundance was affected by tree species composition. The basal area of rowan trees (≥5 cm in diameter at breast height, dbh) decreased with increasing basal area of Norway spruce, while the cover of rowan seedlings increased with an increase in Norway spruce basal area. However, a decrease in the abundance of birch ( Betula pendula ) and an increase in the broad-leaved tree group ( Acer platanoides , Alnus glutinosa , Alnus incana , Amelanchier spicata , Prunus padus , Quercus robur , Rhamnus frangula and Salix caprea ) coincided with a decreasing number of rowans. Furthermore, rowan saplings were scarce in the vicinity of mature rowan trees. Although it seems that tree species composition has an effect on rowan, the relationship between rowan saplings and mature trees is complex, and therefore we conclude that regulating tree species composition is not an easy way to keep rowan thickets under control in urban forests in Finland.