Tessema Zewdu | Haramaya university (original) (raw)

Papers by Tessema Zewdu

Research paper thumbnail of Influences of Tree Species and Canopy Cover on Aboveground Biomass Yield and Ground Cover of Herbaceous Plants in Eastern Oromia, Ethiopia

American Journal of Agriculture and Forestry, 2021

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Research paper thumbnail of Improving the Quantity and Quality of Forages Produced from Intercropping of Faba Bean (Vicia faba L.) with Forage Oats in Lemo District, Hadiya Zone, Ethiopia

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Research paper thumbnail of Эндоназальная инфракрасная термометрия в диагностике аллергического воспаления слизистой оболочки полости носа у пациентов с бронхиальной астмой

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Research paper thumbnail of Effect of range land vegetation degradation on livestock and socio-economics status of the pastoralists, Afar regional state, Northern Ethiopia

The objectives of the study were to assess current vegetation diversity in the rangeland and its ... more The objectives of the study were to assess current vegetation diversity in the rangeland and its effect on the livestock and socio-economics of the pastoralists. Vegetation data were collected from 72 sample plots laid on the four transects. The size of the main plot was 20 m x 20 m for tree species. Socio-economic data were analyzed using SPSS version 21 software packages. A total of 75 species of vascular plants belonging to 60 genera and 26 Families were identified from 72 plots. Fabaceae and Poaceae were found to be the dominant families. The Shannon diversity index of the vegetation was 2.10, and evenness index was 0.50, total basal area calculated was 3.25 m2/ha for tree plants species. These studies indicated that most tree species were identified to have poor regeneration status, while shrub species had good regeneration status; which means expansion of unpalatable shrub species and the indicator of bush encroachment in the study area. In the study area, rangeland vegetation...

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Research paper thumbnail of Ultrafine particles, blood pressure and adult hypertension: a population-based survey in Northeast China

Environmental Research Letters, 2021

The toxicity of ultrafine particles (UFPs) on blood pressure (BP) has not been well studied. We a... more The toxicity of ultrafine particles (UFPs) on blood pressure (BP) has not been well studied. We aimed to evaluate the associations of long-term UFP exposure with different components of BP and the risk of prehypertension/hypertension. We included a total of 24 845 Chinese adults (18–74 years old) in a cross-sectional survey (Liaoning province, China). The 4 year (2006–2009) average concentrations of UFP was estimated using a chemical transport model. We measured systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and pulse pressure (PP), prehypertension and hypertension. We used a generalized linear mixed model to examine the associations while controlling for important individual covariates. One unit (1 μg m−3) increase in UFP was associated with an increase in SBP of 1.52 mm Hg [95% confidence interval (CI): 0.48–2.55], DBP of 0.55 mm Hg (95% CI: 0.01–1.08) in DBP, MAP of 0.92 mm Hg (95% CI: 0.23–1.61) and PP of 0.62 mm Hg (95% CI: 0.05–1.20...

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Research paper thumbnail of Plant phenotypic plasticity in a changing climate

Trends in Plant Science, 2010

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Research paper thumbnail of Computing Good Allocations for Combinatorial Optimization Games

The Department of Management Science, 2004

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Research paper thumbnail of Chemical composition, dry matter production and yield dynamics of tropical grasses mixed with perennial forage legumes

To evaluate the dry matter (DM) yield, relative yield, relative total yield, aggressivity index a... more To evaluate the dry matter (DM) yield, relative yield, relative total yield, aggressivity index and relative crowding coefficient, stability and chemical composition of grass-legume mixtures, an experiment was conducted in a randomised complete block design with 3 replications. Chloris gayana, Panicum coloratum, Phalaris aquatica, Desmodium uncinatum and Medicago sativa were planted as both pure stands and grasslegume mixtures in the first week of June 1996 to give 11 treatments, and observations continued for 3 years. The highest DM yields were obtained from pure Chloris and Panicum plus 4 mixtures: Chloris-Medicago, Chloris-Desmodium, Panicum-Medicago and Panicum-Desmodium mixtures, with 13–15 t/ha per year in Years 2 and 3. Phalaris and its mixtures yielded well in the first year, but declined steadily after that. The relative total yields of mixtures were greater than ‘unity’, indicating that the DM yields of mixtures were higher than those of an average of the pure stands. The ...

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Research paper thumbnail of Casa 2018 T4 CP FR Vdef

Crédit Agricole, Feb 14, 2019

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Research paper thumbnail of Inter-connection Between El-Niño-Southern Oscillation Induced Rainfall Variability, Livestock Population Dynamics and Pastoralists Adaptation Strategies in Eastern Ethiopia

Journal of environment and earth science, 2017

Extreme climatic events significantly limit livestock performance in semiarid tropics. We assesse... more Extreme climatic events significantly limit livestock performance in semiarid tropics. We assessed the effect of El-Nino-Southern Oscillation (ENSO) rainfall variability episodes on livestock population dynamics of pastoral communities in Shinile zone of eastern Ethiopia. Rainfall and ENSO data from 1984-2015 were collected from the National Meteorology Agency of Ethiopia and National Oceanic and Atmospheric Administration, respectively. Future rainfall trend was predicted with MarkSim (RCP 4.5 General Circulation Model). Livestock population was collected from Ethiopian Central Statistical Agency and the respective study zone. The analysis of rainfall data revealed that there was higher inter-annual rainfall variability under pastoral communities during studied years. Cattle and sheep had positively associated (P 0.05). Cattle mortality and off-take rate had a significant negative relationship with ENSO rainfall variability. Hence, ENSO rainfall variability has affected livestock p...

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Research paper thumbnail of In sacco dry matter and nitrogen degradation and their relationship with in vitro dry matter digestibility of Napier grass (Pennisetum purpureum Schumach.) as influenced by height of plant at cutting

Australian Journal of Agricultural Research

In vitro dry matter digestibility (IVDMD) as well as in sacco rumen dry matter degradability (DMD... more In vitro dry matter digestibility (IVDMD) as well as in sacco rumen dry matter degradability (DMD) and nitrogen degradability (ND) studies of Napier grass (Pennisetum purpureum) were carried out using a 3 3 factorial experiment arranged in a randomised complete block design with 3 replications. The treatments were 3 levels of nitrogen (N) fertiliser (0, 46, bacterium Synergistes jonesii is known to degrade these compounds and inoculation of the bacterium into the rumen protects cattle against mimosine and DHP toxicity. We report on the development, production, and storage of an in vitro, fermentor-based, mixed bacterial inoculum, which includes S. jonesii, for administration to cattle. This technique may be applicable to the production and delivery of other live, anaerobic, bacterial inocula for use in animal agriculture.

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Research paper thumbnail of Rangeland water requirement satisfaction index under rainfall variability and predicting future rainfall scenarios: implication for availability of feed resources

Ecological Processes

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Research paper thumbnail of Changes in vegetation structure and aboveground biomass in response to traditional rangeland management practices in Borana, southern Ethiopia

African Journal of Range & Forage Science

This study aimed to determine vegetation structure, species diversity and aboveground herbaceous ... more This study aimed to determine vegetation structure, species diversity and aboveground herbaceous biomass and browse yields in Borana rangelands of southern Ethiopia. Sampling through random allocation of quadrats within replicated sample plots was undertaken in communally grazed areas, grazing enclosures and rangelands managed by prescribed fire for five years and grazed only post-fire during dry seasons. A total of 57 herbaceous species (24 grasses and 33 non-grasses) and 39 woody species (12 trees and 27 shrubs) were identified. Of the 24 grass species identified, 16.7% were highly desirable, 62.5% desirable and 20.8% less desirable by grazers. Biomass of both trees and shrubs was significantly higher (p < 0.001) in grazing enclosures than in other treatments, whereas herbaceous vegetation biomass was higher, but not significantly, in prescribed fire managed rangeland units. Importantly, fire-managed areas also contained the highest densities of some of the most desirable grassland species, including Cenchrus ciliaris, Chrysopogon aucheri and Digitaria milanijiana. We conclude that in the absence of fire, the increasing prevalence of enclosures in Borana pastoralist systems may be encouraging the proliferation of woody shrubs and trees at the expense of more desirable pasture species.

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Research paper thumbnail of Perception and attitude of pastoralists on livestock-wildlife interactions around Awash National Park, Ethiopia: implication for biodiversity conservation

Ecological Processes, 2017

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Research paper thumbnail of Tree species determine soil seed bank composition and its similarity with understory vegetation in a semi-arid African savanna

Ecological Processes, 2017

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Research paper thumbnail of Effect of tree species on understory vegetation, herbaceous biomass and soil nutrients in a semi-arid savanna of Ethiopia

Journal of Arid Environments, 2017

Abstract The effect of tree species on understory vegetation, herbaceous biomass and soil nutrien... more Abstract The effect of tree species on understory vegetation, herbaceous biomass and soil nutrients were studied in a semi-arid savanna of Ethiopia. Twenty large trees, from each of the species: Acacia robusta, Ziziphus spina- christi, and Balanites aegyptiaca , a total of 60 trees, and 480 samples were used for measuring understory vegetation, herbaceous biomass, and soil nutrients during the study. The inside tree canopies had a higher speciesdiversityand plant abundance than the outside tree canopies. Acacia robusta had a higher number of species and plant abundance in the understory vegetation compared to other tree species. The biomass yield of herbaceous vegetation under the inside canopies of A. robusta was higher than the canopies of other tree species. Similarly, most soil nutrient contents were higher under A. robusta than other tree species, and the inside canopies had a higher soil nutrient contents compared to outside tree canopies. Hence, the presence of larger trees in semi-arid African savannas confirmed to maintain more species composition and diversity of understory vegetation, higher herbaceous biomass and improved soil nutrients. Therefore, conservation of larger tree species is crucial for proper utilization and ecological stability of semi-arid African savannas under the changing climate and global warming.

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Research paper thumbnail of Effect of host diversity and species assemblage composition on bovine tuberculosis (bTB) risk in Ethiopian cattle

Parasitology, Jan 30, 2017

Current theories on diversity-disease relationships describe host species diversity and species i... more Current theories on diversity-disease relationships describe host species diversity and species identity as important factors influencing disease risk, either diluting or amplifying disease prevalence in a community. Whereas the simple term 'diversity' embodies a set of animal community characteristics, it is not clear how different measures of species diversity are correlated with disease risk. We therefore tested the effects of species richness, Pielou's evenness and Shannon's diversity on bovine tuberculosis (bTB) risk in cattle in the Afar Region and Awash National Park between November 2013 and April 2015. We also analysed the identity effect of a particular species and the effect of host habitat use overlap on bTB risk. We used the comparative intradermal tuberculin test to assess the number of bTB-infected cattle. Our results suggested a dilution effect through species evenness. We found that the identity effect of greater kudu - a maintenance host - confounde...

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Research paper thumbnail of Mechanisms of bush encroachment and its inter-connection with rangeland degradation in semi-arid African ecosystems: a review

Journal of Arid Land, 2016

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Research paper thumbnail of Soil seed bank dynamics under the influence of grazing as alternative explanation for herbaceous vegetation transitions in semi-arid rangelands

Ecological Modelling, 2016

Ecological studies have frequently stressed that the availability of seeds in the soil is importa... more Ecological studies have frequently stressed that the availability of seeds in the soil is important for the recovery of semi-arid rangelands. However, the crucial role of soil seed banks has not been incorporated into rangeland models to understand vegetation states and transitions in semi-arid rangelands. We developed and evaluated a novel model to show that the availability of seeds in the soil seed banks as a function of plant cover can trigger transitions from perennial to annual grasses and from annual grasses to bare soil with increasing grazing pressure. The model indicates that when grazing pressure is low, a high cover of perennial grasses and a large soil seed bank of these grasses may be present, whereas annual grasses with their seeds in the soil appear with increasing grazing. When grazing pressure further increases, vegetation cover and the soil seed bank size decline. We found that the positive feedback between plant cover and the size of the soil seed bank depends on seed traits, i.e., longevity and germination rate. This positive feedback is an alternative explanation for a sudden vegetation changes in rangelands, which are often explained by the positive feedback between plant cover and the infiltration rate of rain into the soil. In contrast to this latter positive feedback, our model can explain shifts in vegetation from perennials to annuals and vice versa on different soil types, which are often seen in semi-arid rangelands. Our model contributes therefore to the understanding of vegetation dynamics for the proper management and possible restoration of degraded semi-arid rangelands.

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Research paper thumbnail of Changes in grass plant populations and temporal soil seed bank dynamics in a semi-arid African savanna: Implications for restoration

Journal of environmental management, Jan 26, 2016

The re-colonization or recovery of grass species after disappearance due to heavy grazing depends... more The re-colonization or recovery of grass species after disappearance due to heavy grazing depends on the presence of persistent soil seed banks that might be accumulated over time from the aboveground vegetation. Moreover, successful plant recruitment is a function of seed production, seed germination and seedling survival, which can be mechanistically understood through studying the life cycle processes of grass species populations under field conditions. Therefore, we studied the number of germinable seeds, species richness and life-forms in the soil seed banks under light and heavy grazing conditions, and the changes in grass species populations in a semi-arid savanna of Ethiopia. Accordingly, a total of 103 species (15 perennial and 29 annual grasses, 6 legumes, 52 forbs and 1 woody species) emerged from the soil samples collected. Lightly grazed sites had a higher seed density compared with heavily grazed sites. The seed density increased over the first three months of soil sam...

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Research paper thumbnail of Influences of Tree Species and Canopy Cover on Aboveground Biomass Yield and Ground Cover of Herbaceous Plants in Eastern Oromia, Ethiopia

American Journal of Agriculture and Forestry, 2021

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Improving the Quantity and Quality of Forages Produced from Intercropping of Faba Bean (Vicia faba L.) with Forage Oats in Lemo District, Hadiya Zone, Ethiopia

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Эндоназальная инфракрасная термометрия в диагностике аллергического воспаления слизистой оболочки полости носа у пациентов с бронхиальной астмой

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Research paper thumbnail of Effect of range land vegetation degradation on livestock and socio-economics status of the pastoralists, Afar regional state, Northern Ethiopia

The objectives of the study were to assess current vegetation diversity in the rangeland and its ... more The objectives of the study were to assess current vegetation diversity in the rangeland and its effect on the livestock and socio-economics of the pastoralists. Vegetation data were collected from 72 sample plots laid on the four transects. The size of the main plot was 20 m x 20 m for tree species. Socio-economic data were analyzed using SPSS version 21 software packages. A total of 75 species of vascular plants belonging to 60 genera and 26 Families were identified from 72 plots. Fabaceae and Poaceae were found to be the dominant families. The Shannon diversity index of the vegetation was 2.10, and evenness index was 0.50, total basal area calculated was 3.25 m2/ha for tree plants species. These studies indicated that most tree species were identified to have poor regeneration status, while shrub species had good regeneration status; which means expansion of unpalatable shrub species and the indicator of bush encroachment in the study area. In the study area, rangeland vegetation...

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Research paper thumbnail of Ultrafine particles, blood pressure and adult hypertension: a population-based survey in Northeast China

Environmental Research Letters, 2021

The toxicity of ultrafine particles (UFPs) on blood pressure (BP) has not been well studied. We a... more The toxicity of ultrafine particles (UFPs) on blood pressure (BP) has not been well studied. We aimed to evaluate the associations of long-term UFP exposure with different components of BP and the risk of prehypertension/hypertension. We included a total of 24 845 Chinese adults (18–74 years old) in a cross-sectional survey (Liaoning province, China). The 4 year (2006–2009) average concentrations of UFP was estimated using a chemical transport model. We measured systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and pulse pressure (PP), prehypertension and hypertension. We used a generalized linear mixed model to examine the associations while controlling for important individual covariates. One unit (1 μg m−3) increase in UFP was associated with an increase in SBP of 1.52 mm Hg [95% confidence interval (CI): 0.48–2.55], DBP of 0.55 mm Hg (95% CI: 0.01–1.08) in DBP, MAP of 0.92 mm Hg (95% CI: 0.23–1.61) and PP of 0.62 mm Hg (95% CI: 0.05–1.20...

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Research paper thumbnail of Plant phenotypic plasticity in a changing climate

Trends in Plant Science, 2010

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Computing Good Allocations for Combinatorial Optimization Games

The Department of Management Science, 2004

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Chemical composition, dry matter production and yield dynamics of tropical grasses mixed with perennial forage legumes

To evaluate the dry matter (DM) yield, relative yield, relative total yield, aggressivity index a... more To evaluate the dry matter (DM) yield, relative yield, relative total yield, aggressivity index and relative crowding coefficient, stability and chemical composition of grass-legume mixtures, an experiment was conducted in a randomised complete block design with 3 replications. Chloris gayana, Panicum coloratum, Phalaris aquatica, Desmodium uncinatum and Medicago sativa were planted as both pure stands and grasslegume mixtures in the first week of June 1996 to give 11 treatments, and observations continued for 3 years. The highest DM yields were obtained from pure Chloris and Panicum plus 4 mixtures: Chloris-Medicago, Chloris-Desmodium, Panicum-Medicago and Panicum-Desmodium mixtures, with 13–15 t/ha per year in Years 2 and 3. Phalaris and its mixtures yielded well in the first year, but declined steadily after that. The relative total yields of mixtures were greater than ‘unity’, indicating that the DM yields of mixtures were higher than those of an average of the pure stands. The ...

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Research paper thumbnail of Casa 2018 T4 CP FR Vdef

Crédit Agricole, Feb 14, 2019

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Inter-connection Between El-Niño-Southern Oscillation Induced Rainfall Variability, Livestock Population Dynamics and Pastoralists Adaptation Strategies in Eastern Ethiopia

Journal of environment and earth science, 2017

Extreme climatic events significantly limit livestock performance in semiarid tropics. We assesse... more Extreme climatic events significantly limit livestock performance in semiarid tropics. We assessed the effect of El-Nino-Southern Oscillation (ENSO) rainfall variability episodes on livestock population dynamics of pastoral communities in Shinile zone of eastern Ethiopia. Rainfall and ENSO data from 1984-2015 were collected from the National Meteorology Agency of Ethiopia and National Oceanic and Atmospheric Administration, respectively. Future rainfall trend was predicted with MarkSim (RCP 4.5 General Circulation Model). Livestock population was collected from Ethiopian Central Statistical Agency and the respective study zone. The analysis of rainfall data revealed that there was higher inter-annual rainfall variability under pastoral communities during studied years. Cattle and sheep had positively associated (P 0.05). Cattle mortality and off-take rate had a significant negative relationship with ENSO rainfall variability. Hence, ENSO rainfall variability has affected livestock p...

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Research paper thumbnail of In sacco dry matter and nitrogen degradation and their relationship with in vitro dry matter digestibility of Napier grass (Pennisetum purpureum Schumach.) as influenced by height of plant at cutting

Australian Journal of Agricultural Research

In vitro dry matter digestibility (IVDMD) as well as in sacco rumen dry matter degradability (DMD... more In vitro dry matter digestibility (IVDMD) as well as in sacco rumen dry matter degradability (DMD) and nitrogen degradability (ND) studies of Napier grass (Pennisetum purpureum) were carried out using a 3 3 factorial experiment arranged in a randomised complete block design with 3 replications. The treatments were 3 levels of nitrogen (N) fertiliser (0, 46, bacterium Synergistes jonesii is known to degrade these compounds and inoculation of the bacterium into the rumen protects cattle against mimosine and DHP toxicity. We report on the development, production, and storage of an in vitro, fermentor-based, mixed bacterial inoculum, which includes S. jonesii, for administration to cattle. This technique may be applicable to the production and delivery of other live, anaerobic, bacterial inocula for use in animal agriculture.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Rangeland water requirement satisfaction index under rainfall variability and predicting future rainfall scenarios: implication for availability of feed resources

Ecological Processes

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Changes in vegetation structure and aboveground biomass in response to traditional rangeland management practices in Borana, southern Ethiopia

African Journal of Range & Forage Science

This study aimed to determine vegetation structure, species diversity and aboveground herbaceous ... more This study aimed to determine vegetation structure, species diversity and aboveground herbaceous biomass and browse yields in Borana rangelands of southern Ethiopia. Sampling through random allocation of quadrats within replicated sample plots was undertaken in communally grazed areas, grazing enclosures and rangelands managed by prescribed fire for five years and grazed only post-fire during dry seasons. A total of 57 herbaceous species (24 grasses and 33 non-grasses) and 39 woody species (12 trees and 27 shrubs) were identified. Of the 24 grass species identified, 16.7% were highly desirable, 62.5% desirable and 20.8% less desirable by grazers. Biomass of both trees and shrubs was significantly higher (p < 0.001) in grazing enclosures than in other treatments, whereas herbaceous vegetation biomass was higher, but not significantly, in prescribed fire managed rangeland units. Importantly, fire-managed areas also contained the highest densities of some of the most desirable grassland species, including Cenchrus ciliaris, Chrysopogon aucheri and Digitaria milanijiana. We conclude that in the absence of fire, the increasing prevalence of enclosures in Borana pastoralist systems may be encouraging the proliferation of woody shrubs and trees at the expense of more desirable pasture species.

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Research paper thumbnail of Perception and attitude of pastoralists on livestock-wildlife interactions around Awash National Park, Ethiopia: implication for biodiversity conservation

Ecological Processes, 2017

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Tree species determine soil seed bank composition and its similarity with understory vegetation in a semi-arid African savanna

Ecological Processes, 2017

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Research paper thumbnail of Effect of tree species on understory vegetation, herbaceous biomass and soil nutrients in a semi-arid savanna of Ethiopia

Journal of Arid Environments, 2017

Abstract The effect of tree species on understory vegetation, herbaceous biomass and soil nutrien... more Abstract The effect of tree species on understory vegetation, herbaceous biomass and soil nutrients were studied in a semi-arid savanna of Ethiopia. Twenty large trees, from each of the species: Acacia robusta, Ziziphus spina- christi, and Balanites aegyptiaca , a total of 60 trees, and 480 samples were used for measuring understory vegetation, herbaceous biomass, and soil nutrients during the study. The inside tree canopies had a higher speciesdiversityand plant abundance than the outside tree canopies. Acacia robusta had a higher number of species and plant abundance in the understory vegetation compared to other tree species. The biomass yield of herbaceous vegetation under the inside canopies of A. robusta was higher than the canopies of other tree species. Similarly, most soil nutrient contents were higher under A. robusta than other tree species, and the inside canopies had a higher soil nutrient contents compared to outside tree canopies. Hence, the presence of larger trees in semi-arid African savannas confirmed to maintain more species composition and diversity of understory vegetation, higher herbaceous biomass and improved soil nutrients. Therefore, conservation of larger tree species is crucial for proper utilization and ecological stability of semi-arid African savannas under the changing climate and global warming.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Effect of host diversity and species assemblage composition on bovine tuberculosis (bTB) risk in Ethiopian cattle

Parasitology, Jan 30, 2017

Current theories on diversity-disease relationships describe host species diversity and species i... more Current theories on diversity-disease relationships describe host species diversity and species identity as important factors influencing disease risk, either diluting or amplifying disease prevalence in a community. Whereas the simple term 'diversity' embodies a set of animal community characteristics, it is not clear how different measures of species diversity are correlated with disease risk. We therefore tested the effects of species richness, Pielou's evenness and Shannon's diversity on bovine tuberculosis (bTB) risk in cattle in the Afar Region and Awash National Park between November 2013 and April 2015. We also analysed the identity effect of a particular species and the effect of host habitat use overlap on bTB risk. We used the comparative intradermal tuberculin test to assess the number of bTB-infected cattle. Our results suggested a dilution effect through species evenness. We found that the identity effect of greater kudu - a maintenance host - confounde...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Mechanisms of bush encroachment and its inter-connection with rangeland degradation in semi-arid African ecosystems: a review

Journal of Arid Land, 2016

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Soil seed bank dynamics under the influence of grazing as alternative explanation for herbaceous vegetation transitions in semi-arid rangelands

Ecological Modelling, 2016

Ecological studies have frequently stressed that the availability of seeds in the soil is importa... more Ecological studies have frequently stressed that the availability of seeds in the soil is important for the recovery of semi-arid rangelands. However, the crucial role of soil seed banks has not been incorporated into rangeland models to understand vegetation states and transitions in semi-arid rangelands. We developed and evaluated a novel model to show that the availability of seeds in the soil seed banks as a function of plant cover can trigger transitions from perennial to annual grasses and from annual grasses to bare soil with increasing grazing pressure. The model indicates that when grazing pressure is low, a high cover of perennial grasses and a large soil seed bank of these grasses may be present, whereas annual grasses with their seeds in the soil appear with increasing grazing. When grazing pressure further increases, vegetation cover and the soil seed bank size decline. We found that the positive feedback between plant cover and the size of the soil seed bank depends on seed traits, i.e., longevity and germination rate. This positive feedback is an alternative explanation for a sudden vegetation changes in rangelands, which are often explained by the positive feedback between plant cover and the infiltration rate of rain into the soil. In contrast to this latter positive feedback, our model can explain shifts in vegetation from perennials to annuals and vice versa on different soil types, which are often seen in semi-arid rangelands. Our model contributes therefore to the understanding of vegetation dynamics for the proper management and possible restoration of degraded semi-arid rangelands.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Changes in grass plant populations and temporal soil seed bank dynamics in a semi-arid African savanna: Implications for restoration

Journal of environmental management, Jan 26, 2016

The re-colonization or recovery of grass species after disappearance due to heavy grazing depends... more The re-colonization or recovery of grass species after disappearance due to heavy grazing depends on the presence of persistent soil seed banks that might be accumulated over time from the aboveground vegetation. Moreover, successful plant recruitment is a function of seed production, seed germination and seedling survival, which can be mechanistically understood through studying the life cycle processes of grass species populations under field conditions. Therefore, we studied the number of germinable seeds, species richness and life-forms in the soil seed banks under light and heavy grazing conditions, and the changes in grass species populations in a semi-arid savanna of Ethiopia. Accordingly, a total of 103 species (15 perennial and 29 annual grasses, 6 legumes, 52 forbs and 1 woody species) emerged from the soil samples collected. Lightly grazed sites had a higher seed density compared with heavily grazed sites. The seed density increased over the first three months of soil sam...

Bookmarks Related papers MentionsView impact