Understanding the long‐term impacts of invasive mammalian browsers and granivores in mixed forest... more Understanding the long‐term impacts of invasive mammalian browsers and granivores in mixed forests is difficult due to the many processes potentially affecting the demography of long‐lived trees. We constructed individual‐based spatially explicit simulation models of two mixed conifer–angiosperm forests, growing on soils of contrasting phosphorus (P) availability, to investigate how browsing by invasive red deer (Cervus elaphus scoticus) and granivory by invasive rodents (primarily house mouse Mus musculus) might alter forest dynamics. Models were parameterized with field data. Seedling growth and survival rates were estimated inside and outside deer exclosures. Seed predation rates were estimated at high and low rodent densities in mast and non‐mast seeding years. For the alluvial terrace forest, which grew on P‐rich soil, our model contained 15 tree species dominated by angiosperms; our model of the P‐poor marine terrace forest contained seven species dominated by conifers. The tw...
ABSTRACT Background/Question/Methods Biotic effects, such as seed predation by small mammals, hav... more ABSTRACT Background/Question/Methods Biotic effects, such as seed predation by small mammals, have been shown to be an important first filter in short-term patterns of seedling recruitment in temperate deciduous forests. However, few, if any, studies have examined if these patterns persist in the long-term. In 1994 we established 36 1x2m hardware cloth small mammal exclosures paired with control plots at Great Mountain Forest in Norfolk, CT, USA. Seed rain was collected at these sites in 1994-1996, and all tree seedlings that established both inside and outside of exclosures were counted in 1995, 1996, 1997, 2005 and 2012. Results/Conclusions In 1995, after a large seed crop in 1994, exclosures had significantly more total seedlings than controls (t=2.976, P=0.005). However, in 1996 and 1997, when seed rain was lower, we observed no significant differences between exclosures and controls in total seedlings recruited. After 10 years of protection from seed predators we observed significantly more seedlings inside the exclosures (average = 16) than in control plots (average = 8; t=2.219, P=0.032). Similarly, after 18 years of small mammal exclusion the higher number of seedlings in the exclosures persisted but the difference had declined in magnitude (exclosure mean = 6, control mean = 3; t= -1.983, P=0.052). Species-specific responses to exclosures varied through time; for example, black cherry (Prunus serotina) had significantly more seedlings inside exclosures in 1996 (average exclosure = 5, average control = 3; t=2.874, P=0.005), 1997 (exclosure: 1.2, control: 0.4; t=2.747, P=0.009) and 2012 (exclosure = 1.8; control = 0.4; t= - 2.839, P= 0.007) whereas red maple had significantly more seedlings in exclosures only in 1995 (average = 32 vs controls = 7; t=2.909, P=0.006). Through time protection from seed predators allows for short-term increases in seedling recruitment, which persisted but appeared to have weakened over 18 years. Whether the large short-term effects of small mammal exclusion result in changes in the composition of mature tree species might depend on the frequency of disturbances such as gap formation that permit long-term seedling survival.
In the northeastern US, the availability of light and nitrogen (N) limits the rate of woody plant... more In the northeastern US, the availability of light and nitrogen (N) limits the rate of woody plant growth in the forest understory and N limits forest productivity. Interspecific differences in the growth responses of saplings to the availability of these resources could affect the species composition of forest communities. While many studies have examined the relationship between shade-tolerance and forest
Canadian Journal of Forest Research-revue Canadienne De Recherche Forestiere, 2004
We have developed extensions of traditional distance-dependent, spatial competition analyses that... more We have developed extensions of traditional distance-dependent, spatial competition analyses that estimate the magnitude of the competitive effects of neighboring trees on target tree growth as a function of the species, size, and distance to neighboring trees. Our analyses also estimate inter- and intra-specific competition coefficients and ex- plicitly partition the competitive effects of neighbors into the effects of shading
Summary 1. Allelopathic interactions between invasive and native species have been suggested to b... more Summary 1. Allelopathic interactions between invasive and native species have been suggested to be an important mechanism for the success of some of the most aggressive plant invaders. However, field experiments that test the effects of natural levels of allelopathic compounds on coexisting native species are exceptionally rare. 2. In this study, we analyzed the allelopathic effects of the invasive
Forests are often subject to multiple, compounded disturbances, representing both natural and hum... more Forests are often subject to multiple, compounded disturbances, representing both natural and human-induced processes. Predicting forest dynamics requires that we consider how these disturbances interact to affect species demography. Here we present results of an individual based, spatially explicit forest simulator that we developed to analyze the compounded affects of hurricane disturbance and land use legacies on the dynamics of
Summary 1. Effects of invasive species on ecosystem processes are often thought to underlie the e... more Summary 1. Effects of invasive species on ecosystem processes are often thought to underlie the effects of invaders on community dynamics. Specifically, positive feedbacks in which invasive species alter ecosystem function in ways that favour their own growth have been suggested as an important mechanism contributing to the success of invasion. 2. In this study, we analysed the impacts of
Understanding the long‐term impacts of invasive mammalian browsers and granivores in mixed forest... more Understanding the long‐term impacts of invasive mammalian browsers and granivores in mixed forests is difficult due to the many processes potentially affecting the demography of long‐lived trees. We constructed individual‐based spatially explicit simulation models of two mixed conifer–angiosperm forests, growing on soils of contrasting phosphorus (P) availability, to investigate how browsing by invasive red deer (Cervus elaphus scoticus) and granivory by invasive rodents (primarily house mouse Mus musculus) might alter forest dynamics. Models were parameterized with field data. Seedling growth and survival rates were estimated inside and outside deer exclosures. Seed predation rates were estimated at high and low rodent densities in mast and non‐mast seeding years. For the alluvial terrace forest, which grew on P‐rich soil, our model contained 15 tree species dominated by angiosperms; our model of the P‐poor marine terrace forest contained seven species dominated by conifers. The tw...
ABSTRACT Background/Question/Methods Biotic effects, such as seed predation by small mammals, hav... more ABSTRACT Background/Question/Methods Biotic effects, such as seed predation by small mammals, have been shown to be an important first filter in short-term patterns of seedling recruitment in temperate deciduous forests. However, few, if any, studies have examined if these patterns persist in the long-term. In 1994 we established 36 1x2m hardware cloth small mammal exclosures paired with control plots at Great Mountain Forest in Norfolk, CT, USA. Seed rain was collected at these sites in 1994-1996, and all tree seedlings that established both inside and outside of exclosures were counted in 1995, 1996, 1997, 2005 and 2012. Results/Conclusions In 1995, after a large seed crop in 1994, exclosures had significantly more total seedlings than controls (t=2.976, P=0.005). However, in 1996 and 1997, when seed rain was lower, we observed no significant differences between exclosures and controls in total seedlings recruited. After 10 years of protection from seed predators we observed significantly more seedlings inside the exclosures (average = 16) than in control plots (average = 8; t=2.219, P=0.032). Similarly, after 18 years of small mammal exclusion the higher number of seedlings in the exclosures persisted but the difference had declined in magnitude (exclosure mean = 6, control mean = 3; t= -1.983, P=0.052). Species-specific responses to exclosures varied through time; for example, black cherry (Prunus serotina) had significantly more seedlings inside exclosures in 1996 (average exclosure = 5, average control = 3; t=2.874, P=0.005), 1997 (exclosure: 1.2, control: 0.4; t=2.747, P=0.009) and 2012 (exclosure = 1.8; control = 0.4; t= - 2.839, P= 0.007) whereas red maple had significantly more seedlings in exclosures only in 1995 (average = 32 vs controls = 7; t=2.909, P=0.006). Through time protection from seed predators allows for short-term increases in seedling recruitment, which persisted but appeared to have weakened over 18 years. Whether the large short-term effects of small mammal exclusion result in changes in the composition of mature tree species might depend on the frequency of disturbances such as gap formation that permit long-term seedling survival.
In the northeastern US, the availability of light and nitrogen (N) limits the rate of woody plant... more In the northeastern US, the availability of light and nitrogen (N) limits the rate of woody plant growth in the forest understory and N limits forest productivity. Interspecific differences in the growth responses of saplings to the availability of these resources could affect the species composition of forest communities. While many studies have examined the relationship between shade-tolerance and forest
Canadian Journal of Forest Research-revue Canadienne De Recherche Forestiere, 2004
We have developed extensions of traditional distance-dependent, spatial competition analyses that... more We have developed extensions of traditional distance-dependent, spatial competition analyses that estimate the magnitude of the competitive effects of neighboring trees on target tree growth as a function of the species, size, and distance to neighboring trees. Our analyses also estimate inter- and intra-specific competition coefficients and ex- plicitly partition the competitive effects of neighbors into the effects of shading
Summary 1. Allelopathic interactions between invasive and native species have been suggested to b... more Summary 1. Allelopathic interactions between invasive and native species have been suggested to be an important mechanism for the success of some of the most aggressive plant invaders. However, field experiments that test the effects of natural levels of allelopathic compounds on coexisting native species are exceptionally rare. 2. In this study, we analyzed the allelopathic effects of the invasive
Forests are often subject to multiple, compounded disturbances, representing both natural and hum... more Forests are often subject to multiple, compounded disturbances, representing both natural and human-induced processes. Predicting forest dynamics requires that we consider how these disturbances interact to affect species demography. Here we present results of an individual based, spatially explicit forest simulator that we developed to analyze the compounded affects of hurricane disturbance and land use legacies on the dynamics of
Summary 1. Effects of invasive species on ecosystem processes are often thought to underlie the e... more Summary 1. Effects of invasive species on ecosystem processes are often thought to underlie the effects of invaders on community dynamics. Specifically, positive feedbacks in which invasive species alter ecosystem function in ways that favour their own growth have been suggested as an important mechanism contributing to the success of invasion. 2. In this study, we analysed the impacts of
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Papers by Charles Canham