TY  - JOUR
A1  - Irob, Katja
A1  - Blaum, Niels
A1  - Baldauf, Selina
A1  - Kerger, Leon
A1  - Strohbach, Ben
A1  - Kanduvarisa, Angelina
A1  - Lohmann, Dirk
A1  - Tietjen, Britta
T1  - Browsing herbivores improve the state and functioning of savannas
BT  - A model assessment of alternative land-use strategies
JF  - Ecology and evolution
N2  - Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle-dominated land use to one dominated by comparatively specialized browsers and usually native herbivores. However, the consequences for ecosystem properties and processes remain largely unclear. We used the ecohydrological, spatially explicit model EcoHyD to assess the impacts of two contrasting, herbivore land-use strategies on a Namibian savanna: grazer- versus browser-dominated herbivore communities. We varied the densities of grazers and browsers and determined the resulting composition and diversity of the plant community, total vegetation cover, soil moisture, and water use by plants. Our results showed that plant types that are less palatable to herbivores were best adapted to grazing or browsing animals in all simulated densities. Also, plant types that had a competitive advantage under limited water availability were among the dominant ones irrespective of land-use scenario. Overall, the results were in line with our expectations: under high grazer densities, we found heavy bush encroachment and the loss of the perennial grass matrix. Importantly, regardless of the density of browsers, grass cover and plant functional diversity were significantly higher in browsing scenarios. Browsing herbivores increased grass cover, and the higher total cover in turn improved water uptake by plants overall. We concluded that, in contrast to grazing-dominated land-use strategies, land-use strategies dominated by browsing herbivores, even at high herbivore densities, sustain diverse vegetation communities with high cover of perennial grasses, resulting in lower erosion risk and bolstering ecosystem services.
KW  - browsing
KW  - ecohydrology
KW  - land use
KW  - plant community
KW  - savanna
KW  - wildlife
KW  - management
Y1  - 2022
U6  - https://doi.org/10.1002/ece3.8715
SN  - 2045-7758
VL  - 12
IS  - 3
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Falk, Thomas
A1  - Kirk, Michael
A1  - Lohmann, Dirk
A1  - Kruger, Bertus
A1  - Hüttich, Christian
A1  - Kamukuenjandje, Richard
T1  - The profits of excludability and transferability in redistributive land reform in central Namibia
JF  - Development Southern Africa
N2  - Policies which redistribute property rights to land can improve the well-being of rural households and can have overall growth effects. In many cases, however, land reforms are driven mainly by politically justified objectives. Under such circumstances, little emphasis is placed on whether and, if so, how property rights can increase productivity. Following 18 years of land reform implementation in Namibia, we evaluated 65 beneficiaries in Namibia. We assess to which degree land rights affects their farm income. The study focuses on Namibia’s two main commercial land reform instruments, namely the Farm Unit Resettlement Scheme and the Affirmative Action Loan Scheme. We find evidence that the majority of land reform projects are not profitable. Further, our study confirms the importance of the right to restrict land access compared with the right to transfer. The long-term leasehold contract seemingly provides sufficient incentives to make productive use of the land.
KW  - Redistributive land reform
KW  - property rights
KW  - farm productivity
KW  - pastoralism
KW  - Namibia
Y1  - 2017
U6  - https://doi.org/10.1080/0376835X.2016.1269633
SN  - 0376-835X
SN  - 1470-3637
VL  - 34
SP  - 314
EP  - 329
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - GEN
A1  - Synodinos, Alexios D.
A1  - Eldridge, David
A1  - Geißler, Katja
A1  - Jeltsch, Florian
A1  - Lohmann, Dirk
A1  - Midgley, Guy
A1  - Blaum, Niels
T1  - Remotely sensed canopy height reveals three pantropical ecosystem states
BT  - a comment
T2  - Ecology : a publication of the Ecological Society of America
Y1  - 2017
U6  - https://doi.org/10.1002/ecy.1997
SN  - 0012-9658
SN  - 1939-9170
VL  - 99
IS  - 1
SP  - 231
EP  - 234
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Synodinos, Alexis D.
A1  - Tietjen, Britta
A1  - Lohmann, Dirk
A1  - Jeltsch, Florian
T1  - The impact of inter-annual rainfall variability on African savannas changes with mean rainfall
JF  - Journal of theoretical biology
N2  - Savannas are mixed tree-grass ecosystems whose dynamics are predominantly regulated by resource competition and the temporal variability in climatic and environmental factors such as rainfall and fire. Hence, increasing inter-annual rainfall variability due to climate change could have a significant impact on savannas. To investigate this, we used an ecohydrological model of stochastic differential equations and simulated African savanna dynamics along a gradient of mean annual rainfall (520–780 mm/year) for a range of inter-annual rainfall variabilities. Our simulations produced alternative states of grassland and savanna across the mean rainfall gradient. Increasing inter-annual variability had a negative effect on the savanna state under dry conditions (520 mm/year), and a positive effect under moister conditions (580–780 mm/year). The former resulted from the net negative effect of dry and wet extremes on trees. In semi-arid conditions (520 mm/year), dry extremes caused a loss of tree cover, which could not be recovered during wet extremes because of strong resource competition and the increased frequency of fires. At high mean rainfall (780 mm/year), increased variability enhanced savanna resilience. Here, resources were no longer limiting and the slow tree dynamics buffered against variability by maintaining a stable population during ‘dry’ extremes, providing the basis for growth during wet extremes. Simultaneously, high rainfall years had a weak marginal benefit on grass cover due to density-regulation and grazing. Our results suggest that the effects of the slow tree and fast grass dynamics on tree-grass interactions will become a major determinant of the savanna vegetation composition with increasing rainfall variability.
KW  - Rainfall variability
KW  - Savanna-grassland bistability
KW  - Stochastic differential equations
KW  - Coexistence mechanisms
KW  - Fire
Y1  - 2017
U6  - https://doi.org/10.1016/j.jtbi.2017.10.019
SN  - 0022-5193
SN  - 1095-8541
VL  - 437
SP  - 92
EP  - 100
PB  - Elsevier Ltd.
CY  - London
ER  - 
TY  - JOUR
A1  - Lohmann, Dirk
A1  - Guo, Tong
A1  - Tietjen, Britta
T1  - Zooming in on coarse plant functional types-simulated response of savanna vegetation composition in response to aridity and grazing
JF  - Theoretical ecology
N2  - Precipitation and land use in terms of livestock grazing have been identified as two of the most important drivers structuring the vegetation composition of semi-arid and arid savannas. Savanna research on the impact of these drivers has widely applied the so-called plant functional type (PFT) approach, grouping the vegetation into two or three broad types (here called meta-PFTs): woody plants and grasses, which are sometimes divided into perennial and annual grasses. However, little is known about the response of functional traits within these coarse types towards water availability or livestock grazing. In this study, we extended an existing eco-hydrological savanna vegetation model to capture trait diversity within the three broad meta-PFTs to assess the effects of both grazing and mean annual precipitation (MAP) on trait composition along a gradient of both drivers. Our results show a complex pattern of trait responses to grazing and aridity. The response differs for the three meta-PFTs. From our findings, we derive that trait responses to grazing and aridity for perennial grasses are similar, as suggested by the convergence model for grazing and aridity. However, we also see that this only holds for simulations below a MAP of 500 mm. This combined with the finding that trait response differs between the three meta-PFTs leads to the conclusion that there is no single, universal trait or set of traits determining the response to grazing and aridity. We finally discuss how simulation models including trait variability within meta-PFTs are necessary to understand ecosystem responses to environmental drivers, both locally and globally and how this perspective will help to extend conceptual frameworks of other ecosystems to savanna research.
KW  - Traits
KW  - Dryland
KW  - Degradation
KW  - Shrub encroachment
KW  - Simulation
KW  - Eco-hydrological model
KW  - EcoHyD
Y1  - 2018
U6  - https://doi.org/10.1007/s12080-017-0356-x
SN  - 1874-1738
SN  - 1874-1746
VL  - 11
IS  - 2
SP  - 161
EP  - 173
PB  - Springer
CY  - Heidelberg
ER  - 
TY  - JOUR
A1  - Guo, Tong
A1  - Weise, Hanna
A1  - Fiedler, Sebastian
A1  - Lohmann, Dirk
A1  - Tietjen, Britta
T1  - The role of landscape heterogeneity in regulating plant functional diversity under different precipitation and grazing regimes in semi-arid savannas
JF  - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog
N2  - 1. Savanna systems exhibit a high plant functional diversity. While aridity and livestock grazing intensity have been widely discussed as drivers of savanna vegetation composition, physical soil properties have received less attention. Since savannas can show local differences in soil properties, these might act as environmental filters and affect plant diversity and ecosystem functioning at the patch scale. However, research on the link between savanna vegetation diversity and ecosystem function is widely missing. 2. In this study, we aim at understanding the impact of local heterogeneity in soil conditions on plant diversity and on ecosystem functions. For this, we used the ecohydrological savanna model EcoHyD. The model simulates the fate of multiple plant functional types and their interactions with local biotic and abiotic conditions. We applied the model to a set of different landscapes under a wide range of livestock grazing and precipitation scenarios to assess the impact of local heterogeneity in soil conditions on the composition and diversity of plant functional types and on ecosystem functions. 3. Comparisons between homogeneous and heterogeneous landscapes revealed that landscape soil heterogeneity allowed for a higher functional diversity of vegetation under conditions of high competition, i.e. scenarios of low grazing stress. However, landscape heterogeneity did not have this effect under low grazing stress in combination with high mean annual precipitation. Further, landscape heterogeneity led to a higher community biomass, especially for lower rainfall conditions, but also dependent on grazing stress. Total transpiration of the plant community decreased in heterogeneous landscapes under arid conditions. 4. This study highlights that local soil conditions interact with precipitation and grazing in driving savanna vegetation. It clearly shows that vegetation diversity and resulting ecosystem functioning can be driven by landscape heterogeneity. We therefore suggest that future research on ecosystem functioning of savanna systems should focus on the links between local environmental conditions via plant functional diversity to ecosystem functioning.
KW  - Plant functional type
KW  - Trait diversity
KW  - Ecosystem functioning
KW  - Plant coexistence
KW  - Soil texture
KW  - Ecohydrological model
Y1  - 2018
U6  - https://doi.org/10.1016/j.ecolmodel.2018.04.009
SN  - 0304-3800
SN  - 1872-7026
VL  - 379
SP  - 1
EP  - 9
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Falk, Thomas
A1  - Lohmann, Dirk
A1  - Azebaze, Nadege
T1  - Congruence of appropriation and provision in collective water provision in Central Namibia
JF  - International journal of the commons
N2  - Achieving cooperation in natural resource management is always a challenge when incentives exist for an individual to maximise her short term benefits at the cost of a group. We study a public good social dilemma in water infrastructure provision on land reform farms in Namibia. In the context of the Namibian land reform, arbitrarily mixed groups of livestock farmers have to share the operation and maintenance of water infrastructure. Typically, water is mainly used for livestock production, and livestock numbers are subject to high fluctuations due to the given environmental conditions. Our paper assesses how alternative payment systems with differing congruence of provision and appropriation support the cooperation in the group given the ever-changing equilibria. In a first step, we conducted an exploratory overview of the social-ecological system of central Namibian land reform projects. The Social Ecological System (SES) Framework served as a guideline for this assessment (Ostrom 2009). Taking the complexity of the cooperation situation into account, in the second step we designed a role-play that is based on a social-ecological simulation model. The role-play simulates the real-life decision situations of land reform beneficiaries wherein equilibria are permanently changing. This approach helped us to not only better understand the cooperation challenges of Namibian land reform beneficiaries, but also supported stakeholders in their decision making and institution building. Our study provides evidence to support that land reform beneficiaries increase their contributions as they own more livestock and as other group members increase their payments. Nevertheless, only groups with relatively homogeneous livestock endowments manage to agree on payment rules. Interestingly, the dominant rule is an "equal payment per farmer" and not a "payment per head of livestock", though the latter would imply a higher congruence of provision and appropriation.
KW  - Land reform
KW  - Namibia
KW  - participatory ecological-economic modelling
KW  - public good
KW  - role play
KW  - savanna rangeland
Y1  - 2016
U6  - https://doi.org/10.18352/ijc.583
SN  - 1875-0281
VL  - 10
SP  - 71
EP  - 118
PB  - Brill
CY  - Urtrecht
ER  - 
TY  - JOUR
A1  - Guo, Tong
A1  - Lohmann, Dirk
A1  - Ratzmann, Gregor
A1  - Tietjen, Britta
T1  - Response of semi-arid savanna vegetation composition towards grazing along a precipitation gradient-The effect of including plant heterogeneity into an ecohydrological savanna model
JF  - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog
N2  - Ecohydrological models of savanna rangeland systems typically aggregate plant species to very broad plant functional types (PFTs), which are characterized by their trait combinations. However, neglecting trait variability within modelled PFTs may hamper our ability to understand the effects of climate or land use change on vegetation composition and thus on ecosystem processes. In this study we extended and parameterized the ecohydrological savanna model EcoHyD, which originally considered only three broad PFTs (perennial grasses, annuals and shrubs). We defined several sub-types of perennial grasses (sub-PFTs) to assess the effect of environmental conditions on vegetation composition and ecosystem functioning. These perennial sub-PFTs are defined by altering distinct trait values based on a trade-off approach for (i) the longevity of plants and (ii) grazing-resistance. We find that increasing grazing intensity leads to a dominance of the fast-growing and short-lived perennial grass type as well as a dominance of the poorly palatable grass type. Increasing precipitation dampens the magnitude of grazing-induced shifts between perennial grass types. The diversification of perennial grass PFTs generally increases the total perennial grass cover and ecosystem water use efficiency, but does not protect the community from shrub encroachment. We thus demonstrate that including trait heterogeneity into ecosystem models will allow for an improved representation of ecosystem responses to environmental change in savannas. This will help to better assess how ecosystem functions might be impacted under future conditions. (C) 2016 Elsevier B.V. All rights reserved.
KW  - Plant functional types
KW  - Trait heterogeneity
KW  - Rangeland management
KW  - Precipitation gradient
KW  - Livestock
KW  - Ecosystem functioning
Y1  - 2016
U6  - https://doi.org/10.1016/j.ecolmodel.2016.01.004
SN  - 0304-3800
SN  - 1872-7026
VL  - 325
SP  - 47
EP  - 56
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Lohmann, Dirk
A1  - Falk, Thomas
A1  - Geissler, Katja
A1  - Blaum, Niels
A1  - Jeltsch, Florian
T1  - Determinants of semi-arid rangeland management in a land reform setting in Namibia
JF  - Journal of arid environments
N2  - To assess the ecological and economic implications of the redistributive land reform in semi-arid Namibia, we investigated to what extent land reform beneficiaries adjust herd size and herd composition according to environmental (rainfall, vegetation) and economic variables (herd size, financial assets, running costs). We performed model-based role-plays with Namibian land reform beneficiaries, simulating 10 years of rangeland management.
 Our study revealed that the farmers surveyed mainly manage their herds according to their economic situation (herd size and account balance) but do not take environmental variability (rainfall and vegetation) into account. Further, our results indicate that, due to financial pressure, farmers are not able to apply their desired management strategies, and that owners of small farms face a higher risk of economic failure. However, farmers apply rather conservative and constant stocking rates and will thus, given the current economic limitations, likely not contribute to semi-arid savanna degradation.
 We conclude that land reform beneficiaries need support to be able to apply straightforward and efficient management strategies. This could be achieved by facilitating cooperation between small farming businesses and by supporting initial investment in productive cattle herds at the time of redistribution of the land.
KW  - Dry land degradation
KW  - Semi-arid savanna
KW  - Land reform
KW  - Rangeland management
KW  - Simulation model
KW  - Role-play
Y1  - 2014
U6  - https://doi.org/10.1016/j.jaridenv.2013.10.005
SN  - 0140-1963
SN  - 1095-922X
VL  - 100
SP  - 23
EP  - 30
PB  - Elsevier
CY  - London
ER  - 
TY  - JOUR
A1  - Lohmann, Dirk
A1  - Tietjen, Britta
A1  - Blaum, Niels
A1  - Joubert, David Francois
A1  - Jeltsch, Florian
T1  - Prescribed fire as a tool for managing shrub encroachment in semi-arid savanna rangelands
JF  - Journal of arid environments
N2  - Savanna rangelands worldwide are threatened by shrub encroachment, i.e. the increase of woody plant species at the cost of perennial grasses, causing a strong decline in the productivity of domestic livestock production. Although recent studies indicate that fire might be of great importance for semi-arid and arid savanna dynamics, it is largely not applied in the management of semi-arid rangelands especially with regard to woody plant control. We used the eco-hydrological savanna model EcoHyD to simulate the effects of different fire management strategies on semi-arid savanna vegetation and to assess their longterm suitability for semi-arid rangeland management. Simulation results show that prescribed fires, timed to kill tree seedlings prevented shrub encroachment for a broad range of livestock densities while the possible maximum long-term cattle densities on the simulated semi-arid rangeland in Namibia increased by more than 30%. However, when grazing intensity was too high, fire management failed in preventing shrub encroachment.
 Our findings indicate that with regard to fire management a clear distinction between mesic and more arid savannas is necessary: While the frequency of fires is of relevance for mesic savannas, we recommend a fire management focussing on the timing of fire for semi-arid and arid savannas. (C) 2014 Elsevier Ltd. All rights reserved.
KW  - Acacia mellifera
KW  - Bush encroachment
KW  - Dry land degradation
KW  - Rangeland management
KW  - Simulation model
KW  - Southern Africa
Y1  - 2014
U6  - https://doi.org/10.1016/j.jaridenv.2014.04.003
SN  - 0140-1963
SN  - 1095-922X
VL  - 107
SP  - 49
EP  - 56
PB  - Elsevier
CY  - London
ER  -