Abstract It is unclear whether inter-tree competition plays a role in determining the woody plant... more Abstract It is unclear whether inter-tree competition plays a role in determining the woody plant cover of humid savannas. Spatial point-pattern analysis can give insights to the underlying processes affecting the individuals in a population. We assessed the spatial patterns of Acacia karroo trees from savannas in KwaZulu-Natal, using conventional nearest neighbour analysis and second-order spatial statistics such as Ripley's K-and L-functions, and the univariate and bivariate O-ring statistics. We predicted that juvenile trees would be ...
Woody plant encroachment has serious negative consequences for ranchers because of the reduction ... more Woody plant encroachment has serious negative consequences for ranchers because of the reduction in herbaceous fodder for domestic livestock. A long-term monitoring of a tree-thinning experiment was established near Magudu (northern KwaZulu-Natal, South Africa) in 1990. The objective of this experiment was to determine the optimal tree density that would maximize grass production while benefiting grasses from nitrogen fixation, hydraulic lift, and/or shade from the leguminous trees. The initial dominant species was the nitrogen-fixing tree, Dichrostachys cinerea. There were 12 plots (6 pairs) with trees removed to approximate 0, 179, 277, 428, and 625 trees ha–1, with 1 pair left as a control (unmanipulated). One plot of each replicate (except the controls) was treated with short-acting herbicide (picloram) once in 1990. We collected data on herbaceous cover and species composition, tree species composition, sizes, and mortality. We also used remote sensing to examine the patterns o...
It is unclear whether inter-tree competition plays a role in determining the woody plant cover of... more It is unclear whether inter-tree competition plays a role in determining the woody plant cover of humid savannas. Spatial point-pattern analysis can give insights to the underlying processes affecting the individuals in a population. We assessed the spatial patterns of Acacia karroo trees from savannas in KwaZulu-Natal, using conventional nearest neighbour analysis and second-order spatial statistics such as Ripley's K-and L-functions, and the univariate and bivariate O-ring statistics. We predicted that juvenile trees would be ...
Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachm... more Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachment. This change in land cover is thought to alter soil carbon (C) and nitrogen (N) storage in these ecosystems. Some studies have reported a negative correlation between soil C and N and mean annual precipitation while others have indicated that there is no relationship with mean annual precipitation. We quantified the changes in C and N pools and δC and δN values to a depth of 1 m in pairs of encroached and adjacent open grassland sites along a precipitation gradient from 300 mm to 1500 mm per annum in South Africa. Our study showed a negative correlation between changes in soil organic C stocks in the 0-100 cm soil layer and mean annual precipitation (MAP). The most humid site (1500 mm MAP) had less C in shrub-encroached sites while the drier sites (300-350 mm MAP) had more C than their paired open grasslands. This study generally showed soil organic C gains in low precipitation areas...
Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachm... more Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachment. This change in land cover is thought to alter soil carbon (C) and nitrogen (N) storage in these ecosystems. Some studies have reported a negative correlation between soil C and N and mean annual precipitation while others have indicated that there is no relationship with mean annual precipitation. We quantified the changes in C and N pools and δC and δN values to a depth of 1 m in pairs of encroached and adjacent open grassland sites along a precipitation gradient from 300 mm to 1500 mm per annum in South Africa. Our study showed a negative correlation between changes in soil organic C stocks in the 0-100 cm soil layer and mean annual precipitation (MAP). The most humid site (1500 mm MAP) had less C in shrub-encroached sites while the drier sites (300-350 mm MAP) had more C than their paired open grasslands. This study generally showed soil organic C gains in low precipitation areas...
It is unclear whether inter-tree competition
plays a role in determining the woody plant cover of... more It is unclear whether inter-tree competition plays a role in determining the woody plant cover of humid savannas. Spatial point-pattern analysis can give insights to the underlying processes affecting the individuals in a population. We assessed the spatial patterns of Acacia karroo trees from savannas in KwaZulu-Natal, using conventional nearest neighbour analysis and second-order spatial statistics such as Ripley’s K- and L-functions, and the univariate and bivariate O-ring statistics. We predicted that juvenile trees would be spatially aggregated, because of facilitation between shrubs when zones of overlap are relatively small, while adult trees would be regularly spaced because of the effects of densitydependent mortality (i.e. consistent with the honeycomb rippling model).
Questions: What is the effect of neighbour competition on the survival, growth and biomass of mes... more Questions: What is the effect of neighbour competition on the survival, growth and biomass of mesic and humid savanna tree species? Can competitive effect and response be linked to plant functional traits? Location: Neil Tainton Arboretum, University of KwaZulu-Natal, Pietermaritzburg, ZA. Methods: Using a target–neighbour design, all combinations of four humid and four mesic savanna tree seedlings were tested in a greenhouse experiment, to establish the effects of neighbourhood competition on target plant performance. The competitive response and effect of each species was quantified, and regressed against several functional traits to determine which traits are predictive of competitive ability. Results: We found that neighbour density negatively affected the survival of mesic tree seedlings but not humid tree seedlings. Mesic plants were able to maintain their relative growth rates (RGRs) despite increasing neighbourhood competition. The RGRs of humid species significantly decreased as the density of neighbours increased, indicating that competition may be a factor affecting plants in savannas receiving more than 650 mm mean annual rainfall. We used the quantile regression method to showthat the biomass of humid tree seedlings decreased with increased neighbour biomass, when considering competitive response only. We also found that resource-acquiring traits (such as maximum RGR, plant height and root biomass) were positively correlated with the competitive effect of mesic savanna seedlings, while specific leaf area captured the competitive response of humid savanna seedlings to neighbour competition. Conclusions: Competitive interactions between savanna trees negatively affect survival and growth rate, although the competitive effect or response of a particular species depends on its adaptation to either high- or low-resource environments. Our results show significant relationships between plant traits and competitive ability, which may be used to predict competitive interactions between tree seedlings fromhumid and mesic savannas.
Abstract It is unclear whether inter-tree competition plays a role in determining the woody plant... more Abstract It is unclear whether inter-tree competition plays a role in determining the woody plant cover of humid savannas. Spatial point-pattern analysis can give insights to the underlying processes affecting the individuals in a population. We assessed the spatial patterns of Acacia karroo trees from savannas in KwaZulu-Natal, using conventional nearest neighbour analysis and second-order spatial statistics such as Ripley's K-and L-functions, and the univariate and bivariate O-ring statistics. We predicted that juvenile trees would be ...
Woody plant encroachment has serious negative consequences for ranchers because of the reduction ... more Woody plant encroachment has serious negative consequences for ranchers because of the reduction in herbaceous fodder for domestic livestock. A long-term monitoring of a tree-thinning experiment was established near Magudu (northern KwaZulu-Natal, South Africa) in 1990. The objective of this experiment was to determine the optimal tree density that would maximize grass production while benefiting grasses from nitrogen fixation, hydraulic lift, and/or shade from the leguminous trees. The initial dominant species was the nitrogen-fixing tree, Dichrostachys cinerea. There were 12 plots (6 pairs) with trees removed to approximate 0, 179, 277, 428, and 625 trees ha–1, with 1 pair left as a control (unmanipulated). One plot of each replicate (except the controls) was treated with short-acting herbicide (picloram) once in 1990. We collected data on herbaceous cover and species composition, tree species composition, sizes, and mortality. We also used remote sensing to examine the patterns o...
It is unclear whether inter-tree competition plays a role in determining the woody plant cover of... more It is unclear whether inter-tree competition plays a role in determining the woody plant cover of humid savannas. Spatial point-pattern analysis can give insights to the underlying processes affecting the individuals in a population. We assessed the spatial patterns of Acacia karroo trees from savannas in KwaZulu-Natal, using conventional nearest neighbour analysis and second-order spatial statistics such as Ripley's K-and L-functions, and the univariate and bivariate O-ring statistics. We predicted that juvenile trees would be ...
Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachm... more Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachment. This change in land cover is thought to alter soil carbon (C) and nitrogen (N) storage in these ecosystems. Some studies have reported a negative correlation between soil C and N and mean annual precipitation while others have indicated that there is no relationship with mean annual precipitation. We quantified the changes in C and N pools and δC and δN values to a depth of 1 m in pairs of encroached and adjacent open grassland sites along a precipitation gradient from 300 mm to 1500 mm per annum in South Africa. Our study showed a negative correlation between changes in soil organic C stocks in the 0-100 cm soil layer and mean annual precipitation (MAP). The most humid site (1500 mm MAP) had less C in shrub-encroached sites while the drier sites (300-350 mm MAP) had more C than their paired open grasslands. This study generally showed soil organic C gains in low precipitation areas...
Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachm... more Grasslands and savannas are experiencing intensive land-cover change due to woody plant encroachment. This change in land cover is thought to alter soil carbon (C) and nitrogen (N) storage in these ecosystems. Some studies have reported a negative correlation between soil C and N and mean annual precipitation while others have indicated that there is no relationship with mean annual precipitation. We quantified the changes in C and N pools and δC and δN values to a depth of 1 m in pairs of encroached and adjacent open grassland sites along a precipitation gradient from 300 mm to 1500 mm per annum in South Africa. Our study showed a negative correlation between changes in soil organic C stocks in the 0-100 cm soil layer and mean annual precipitation (MAP). The most humid site (1500 mm MAP) had less C in shrub-encroached sites while the drier sites (300-350 mm MAP) had more C than their paired open grasslands. This study generally showed soil organic C gains in low precipitation areas...
It is unclear whether inter-tree competition
plays a role in determining the woody plant cover of... more It is unclear whether inter-tree competition plays a role in determining the woody plant cover of humid savannas. Spatial point-pattern analysis can give insights to the underlying processes affecting the individuals in a population. We assessed the spatial patterns of Acacia karroo trees from savannas in KwaZulu-Natal, using conventional nearest neighbour analysis and second-order spatial statistics such as Ripley’s K- and L-functions, and the univariate and bivariate O-ring statistics. We predicted that juvenile trees would be spatially aggregated, because of facilitation between shrubs when zones of overlap are relatively small, while adult trees would be regularly spaced because of the effects of densitydependent mortality (i.e. consistent with the honeycomb rippling model).
Questions: What is the effect of neighbour competition on the survival, growth and biomass of mes... more Questions: What is the effect of neighbour competition on the survival, growth and biomass of mesic and humid savanna tree species? Can competitive effect and response be linked to plant functional traits? Location: Neil Tainton Arboretum, University of KwaZulu-Natal, Pietermaritzburg, ZA. Methods: Using a target–neighbour design, all combinations of four humid and four mesic savanna tree seedlings were tested in a greenhouse experiment, to establish the effects of neighbourhood competition on target plant performance. The competitive response and effect of each species was quantified, and regressed against several functional traits to determine which traits are predictive of competitive ability. Results: We found that neighbour density negatively affected the survival of mesic tree seedlings but not humid tree seedlings. Mesic plants were able to maintain their relative growth rates (RGRs) despite increasing neighbourhood competition. The RGRs of humid species significantly decreased as the density of neighbours increased, indicating that competition may be a factor affecting plants in savannas receiving more than 650 mm mean annual rainfall. We used the quantile regression method to showthat the biomass of humid tree seedlings decreased with increased neighbour biomass, when considering competitive response only. We also found that resource-acquiring traits (such as maximum RGR, plant height and root biomass) were positively correlated with the competitive effect of mesic savanna seedlings, while specific leaf area captured the competitive response of humid savanna seedlings to neighbour competition. Conclusions: Competitive interactions between savanna trees negatively affect survival and growth rate, although the competitive effect or response of a particular species depends on its adaptation to either high- or low-resource environments. Our results show significant relationships between plant traits and competitive ability, which may be used to predict competitive interactions between tree seedlings fromhumid and mesic savannas.
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Papers by Tiffany Pillay
plays a role in determining the woody plant cover of
humid savannas. Spatial point-pattern analysis can
give insights to the underlying processes affecting the
individuals in a population. We assessed the spatial
patterns of Acacia karroo trees from savannas in
KwaZulu-Natal, using conventional nearest neighbour
analysis and second-order spatial statistics such as
Ripley’s K- and L-functions, and the univariate and
bivariate O-ring statistics. We predicted that juvenile
trees would be spatially aggregated, because of
facilitation between shrubs when zones of overlap
are relatively small, while adult trees would be
regularly spaced because of the effects of densitydependent
mortality (i.e. consistent with the honeycomb
rippling model).
Location: Neil Tainton Arboretum, University of KwaZulu-Natal, Pietermaritzburg, ZA.
Methods: Using a target–neighbour design, all combinations of four humid and four mesic savanna tree seedlings were tested in a greenhouse experiment, to establish the effects of neighbourhood competition on target plant performance. The competitive response and effect of each species was quantified, and regressed against several functional traits to determine which traits are predictive of competitive ability.
Results: We found that neighbour density negatively affected the survival of mesic tree seedlings but not humid tree seedlings. Mesic plants were able to maintain their relative growth rates (RGRs) despite increasing neighbourhood competition. The RGRs of humid species significantly decreased as the density of neighbours increased, indicating that competition may be a factor affecting plants in savannas receiving more than 650 mm mean annual rainfall. We used the quantile regression method to showthat the biomass of humid tree seedlings decreased with increased neighbour biomass, when considering competitive response only. We also found that resource-acquiring traits (such as maximum RGR, plant height and root biomass) were positively correlated with the competitive effect of mesic savanna seedlings, while specific leaf area captured the competitive response of humid savanna seedlings to neighbour competition.
Conclusions: Competitive interactions between savanna trees negatively affect survival and growth rate, although the competitive effect or response of a particular species depends on its adaptation to either high- or low-resource environments.
Our results show significant relationships between plant traits and
competitive ability, which may be used to predict competitive interactions between tree seedlings fromhumid and mesic savannas.
plays a role in determining the woody plant cover of
humid savannas. Spatial point-pattern analysis can
give insights to the underlying processes affecting the
individuals in a population. We assessed the spatial
patterns of Acacia karroo trees from savannas in
KwaZulu-Natal, using conventional nearest neighbour
analysis and second-order spatial statistics such as
Ripley’s K- and L-functions, and the univariate and
bivariate O-ring statistics. We predicted that juvenile
trees would be spatially aggregated, because of
facilitation between shrubs when zones of overlap
are relatively small, while adult trees would be
regularly spaced because of the effects of densitydependent
mortality (i.e. consistent with the honeycomb
rippling model).
Location: Neil Tainton Arboretum, University of KwaZulu-Natal, Pietermaritzburg, ZA.
Methods: Using a target–neighbour design, all combinations of four humid and four mesic savanna tree seedlings were tested in a greenhouse experiment, to establish the effects of neighbourhood competition on target plant performance. The competitive response and effect of each species was quantified, and regressed against several functional traits to determine which traits are predictive of competitive ability.
Results: We found that neighbour density negatively affected the survival of mesic tree seedlings but not humid tree seedlings. Mesic plants were able to maintain their relative growth rates (RGRs) despite increasing neighbourhood competition. The RGRs of humid species significantly decreased as the density of neighbours increased, indicating that competition may be a factor affecting plants in savannas receiving more than 650 mm mean annual rainfall. We used the quantile regression method to showthat the biomass of humid tree seedlings decreased with increased neighbour biomass, when considering competitive response only. We also found that resource-acquiring traits (such as maximum RGR, plant height and root biomass) were positively correlated with the competitive effect of mesic savanna seedlings, while specific leaf area captured the competitive response of humid savanna seedlings to neighbour competition.
Conclusions: Competitive interactions between savanna trees negatively affect survival and growth rate, although the competitive effect or response of a particular species depends on its adaptation to either high- or low-resource environments.
Our results show significant relationships between plant traits and
competitive ability, which may be used to predict competitive interactions between tree seedlings fromhumid and mesic savannas.