Edmund C. February | University of Cape Town (original) (raw)
Papers by Edmund C. February
Ecology, 2007
The amount of carbon stored in savannas represents a significant uncertainty in global carbon bud... more The amount of carbon stored in savannas represents a significant uncertainty in global carbon budgets, primarily because fire causes actual biomass to differ from potential biomass. We analyzed the structural response of woody plants to long-term experimental burning in savannas. The experiment uses a randomized block design to examine fire exclusion and the season and frequency of burn in 192 7-ha experimental plots located in four different savanna ecosystems. Although previous studies would lead us to expect tree density to respond to the fire regime, our results, obtained from four different savanna ecosystems, suggest that the density of woody individuals was unresponsive to fire. The relative dominance of small trees was, however, highly responsive to fire regime. The observed shift in the structure of tree populations has potentially large impacts on the carbon balance. However, the response of tree biomass to fire of the different savannas studied were different, making it d...
Abstract With a high percentage of endemics along the west coast of South Africa, especially in t... more Abstract With a high percentage of endemics along
the west coast of South Africa, especially in the family
Aizoaceae, the region is considered one of the earth’s
biodiversity hot spots. It has been suggested that the
diversity and radiation of the Aizoaceae are coincident
with low but predictable rainfall and lack of competition
between species. In this study we examine the
relationship between water source and the efficiency
of PSII photochemistry for representative Aizoaceae
and non-Aizoaceae. We do this to determine the extent
to which the different genera are adapted to the
frequent, low volume, precipitation characteristic of
the region and to ascertain the extent to which there is
competition for water. Our water isotope results show
that the Aizoaceae use shallow surface water while the
non-Aizoaceae use a deeper water source. We are
however not able to show the extent to which the
Aizoaceae utilize fog or dew. Our chlorophyll fluorescence
results show that there are no differences in
efficiency of PSII photochemistry between the species
in the wet season. The decline from wet to dry season
for the Aizoaceae is, however, more dramatic than that
of the non-Aizoaceae reflecting the differences in
rooting depth between the different families. These
results suggest that, during the dry season, there is no
competition for resources between families but there is
competition between species. We conclude that the
adaptation to using shallow water, coupled with
susceptibility to drought of adult short lived Aizoaceae
may be a, mechanism for the diversification of this
family.
Keywords d18O d2H Water source
Dwarf succulents persist in the arid Succulent Karoo despite the low-water storage capacities of ... more Dwarf succulents persist in the arid Succulent Karoo despite the low-water storage capacities of their contracted leaves and stems that are inadequate for enduring severe and prolonged drought. We examined the contribution of non-rainfall moisture (fog, dew, water vapour) to the water budgets and relative abundance of two endemic dwarf succulents Agyroderma pearsonii and Cephalophyllum spissum. Non-rainfall moisture was measured with automated lysimeters containing bare quartz-gravel soils and
introduced A. pearsonii and C. spissum individuals at hourly intervals spanning an 8-month wet winter to dry summer period. Total non-rainfall atmospheric moisture intercepted by the bare quartz-gravel substrate of 1376 mm, of which water vapour adsorption contributed 562 mm, fog 782mm and dew 34 mm, was virtually equivalent to the rainfall amount of 1427 mm. Agyroderma pearsonii intercepted 2284mm of non-rainfall moisture of which water vapour adsorption contributed 1171 mm, fog 1044mm and dew 69 mm. This was nearly three times the non-rainfall amount of 887mm y1 intercepted by C. spissum, of which water vapour contributed 443 mm, fog 413mm and dew 31 mm. The greater quantity of non-rainfall moisture intercepted by A. pearsonii corresponded with its threefold greater leaf abundance and twofold greater canopy cover than that of C. spissum. We conclude that non-rainfall moisture, especially the absorption of atmospheric water vapour by soils and its uptake
by the extensive network of superficial roots of dwarf quartz-field succulents are vital in sustaining their growth and survival and in determining their distributions and relative abundance.
KEY WORDS fog; dew; water vapour; dwarf-succulent; inland-arid; interception
a b s t r a c t Stem diameter variations relative to atmospheric vapour pressure deficits and the... more a b s t r a c t
Stem diameter variations relative to atmospheric vapour pressure deficits and the corresponding differences
in pre-dawn and late dusk foliar organic acids were measured in 4 evergreen and 2 partly drought
deciduous succulent shrubs. These methods were compared at two arid South African sites in distinguishing
CAM and C3 photosynthetic modes. Changes in stem diameter were continuously recorded at
2 h intervals using linear variable differential transducers, known as stem diameter variation sensors.
Annual data collected over varying climatic conditions revealed that rapid changes in the stem diameter
in response to vapour pressure deficit concurred with typical foliar acid trends expected for CAM and C3
photosynthetic modes. Nocturnal foliar acidification, which typifies the CAM mode, was predominant in
evergreen shrubs Cephalophyllum framesii, Ruschia bolusiae, Ruschia stricta and Zygophyllum cordifolium
whilst C3 mode was prevalent in drought deciduous Lycium cinereum and Tripteris sinuata. Diurnal trends
in foliar acidification concurred with the predicted patterns in stem diameter variations for CAM and C3
modes, thus confirming the potential application of stem diameter sensors in distinguishing CAM and C3
modes in arid environments. Daily amplitudes in stem diameter were significantly reduced by nocturnal
fog and dew precipitation in a C3–CAM shrub. This supports earlier studies that the CAM mode in facultative
and CAM-cycling plants does not only conserve water, but may also aid in water absorption. Stem
microvariation changes revealed CAM–C3 variations that were concealed when measuring CAM activity
from total foliar acids. This technique may be very important considering that even the dependable
carbon isotope technique under-estimates the number of CAM-equipped plants in natural systems.
Ecology, 2007
The amount of carbon stored in savannas represents a significant uncertainty in global carbon bud... more The amount of carbon stored in savannas represents a significant uncertainty in global carbon budgets, primarily because fire causes actual biomass to differ from potential biomass. We analyzed the structural response of woody plants to long-term experimental burning in savannas. The experiment uses a randomized block design to examine fire exclusion and the season and frequency of burn in 192 7-ha experimental plots located in four different savanna ecosystems. Although previous studies would lead us to expect tree density to respond to the fire regime, our results, obtained from four different savanna ecosystems, suggest that the density of woody individuals was unresponsive to fire. The relative dominance of small trees was, however, highly responsive to fire regime. The observed shift in the structure of tree populations has potentially large impacts on the carbon balance. However, the response of tree biomass to fire of the different savannas studied were different, making it d...
Abstract With a high percentage of endemics along the west coast of South Africa, especially in t... more Abstract With a high percentage of endemics along
the west coast of South Africa, especially in the family
Aizoaceae, the region is considered one of the earth’s
biodiversity hot spots. It has been suggested that the
diversity and radiation of the Aizoaceae are coincident
with low but predictable rainfall and lack of competition
between species. In this study we examine the
relationship between water source and the efficiency
of PSII photochemistry for representative Aizoaceae
and non-Aizoaceae. We do this to determine the extent
to which the different genera are adapted to the
frequent, low volume, precipitation characteristic of
the region and to ascertain the extent to which there is
competition for water. Our water isotope results show
that the Aizoaceae use shallow surface water while the
non-Aizoaceae use a deeper water source. We are
however not able to show the extent to which the
Aizoaceae utilize fog or dew. Our chlorophyll fluorescence
results show that there are no differences in
efficiency of PSII photochemistry between the species
in the wet season. The decline from wet to dry season
for the Aizoaceae is, however, more dramatic than that
of the non-Aizoaceae reflecting the differences in
rooting depth between the different families. These
results suggest that, during the dry season, there is no
competition for resources between families but there is
competition between species. We conclude that the
adaptation to using shallow water, coupled with
susceptibility to drought of adult short lived Aizoaceae
may be a, mechanism for the diversification of this
family.
Keywords d18O d2H Water source
Dwarf succulents persist in the arid Succulent Karoo despite the low-water storage capacities of ... more Dwarf succulents persist in the arid Succulent Karoo despite the low-water storage capacities of their contracted leaves and stems that are inadequate for enduring severe and prolonged drought. We examined the contribution of non-rainfall moisture (fog, dew, water vapour) to the water budgets and relative abundance of two endemic dwarf succulents Agyroderma pearsonii and Cephalophyllum spissum. Non-rainfall moisture was measured with automated lysimeters containing bare quartz-gravel soils and
introduced A. pearsonii and C. spissum individuals at hourly intervals spanning an 8-month wet winter to dry summer period. Total non-rainfall atmospheric moisture intercepted by the bare quartz-gravel substrate of 1376 mm, of which water vapour adsorption contributed 562 mm, fog 782mm and dew 34 mm, was virtually equivalent to the rainfall amount of 1427 mm. Agyroderma pearsonii intercepted 2284mm of non-rainfall moisture of which water vapour adsorption contributed 1171 mm, fog 1044mm and dew 69 mm. This was nearly three times the non-rainfall amount of 887mm y1 intercepted by C. spissum, of which water vapour contributed 443 mm, fog 413mm and dew 31 mm. The greater quantity of non-rainfall moisture intercepted by A. pearsonii corresponded with its threefold greater leaf abundance and twofold greater canopy cover than that of C. spissum. We conclude that non-rainfall moisture, especially the absorption of atmospheric water vapour by soils and its uptake
by the extensive network of superficial roots of dwarf quartz-field succulents are vital in sustaining their growth and survival and in determining their distributions and relative abundance.
KEY WORDS fog; dew; water vapour; dwarf-succulent; inland-arid; interception
a b s t r a c t Stem diameter variations relative to atmospheric vapour pressure deficits and the... more a b s t r a c t
Stem diameter variations relative to atmospheric vapour pressure deficits and the corresponding differences
in pre-dawn and late dusk foliar organic acids were measured in 4 evergreen and 2 partly drought
deciduous succulent shrubs. These methods were compared at two arid South African sites in distinguishing
CAM and C3 photosynthetic modes. Changes in stem diameter were continuously recorded at
2 h intervals using linear variable differential transducers, known as stem diameter variation sensors.
Annual data collected over varying climatic conditions revealed that rapid changes in the stem diameter
in response to vapour pressure deficit concurred with typical foliar acid trends expected for CAM and C3
photosynthetic modes. Nocturnal foliar acidification, which typifies the CAM mode, was predominant in
evergreen shrubs Cephalophyllum framesii, Ruschia bolusiae, Ruschia stricta and Zygophyllum cordifolium
whilst C3 mode was prevalent in drought deciduous Lycium cinereum and Tripteris sinuata. Diurnal trends
in foliar acidification concurred with the predicted patterns in stem diameter variations for CAM and C3
modes, thus confirming the potential application of stem diameter sensors in distinguishing CAM and C3
modes in arid environments. Daily amplitudes in stem diameter were significantly reduced by nocturnal
fog and dew precipitation in a C3–CAM shrub. This supports earlier studies that the CAM mode in facultative
and CAM-cycling plants does not only conserve water, but may also aid in water absorption. Stem
microvariation changes revealed CAM–C3 variations that were concealed when measuring CAM activity
from total foliar acids. This technique may be very important considering that even the dependable
carbon isotope technique under-estimates the number of CAM-equipped plants in natural systems.