@article{SynodinosTietjenLohmannetal.2018,
  author    = {Synodinos, Alexis D. and Tietjen, Britta and Lohmann, Dirk and Jeltsch, Florian},
  title     = {The impact of inter-annual rainfall variability on African savannas changes with mean rainfall},
  series = {Journal of theoretical biology},
  volume    = {437},
  journal   = {Journal of theoretical biology},
  publisher = {Elsevier Ltd.},
  address   = {London},
  issn      = {0022-5193},
  doi       = {10.1016/j.jtbi.2017.10.019},
  pages     = {92 -- 100},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{SynodinosTietjenJeltsch2015,
  author    = {Synodinos, Alexios D. and Tietjen, Britta and Jeltsch, Florian},
  title     = {Facilitation in drylands: Modeling a neglected driver of savanna dynamics},
  series = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog},
  volume    = {304},
  journal   = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0304-3800},
  doi       = {10.1016/j.ecolmodel.2015.02.015},
  pages     = {11 -- 21},
  year      = {2015},
  abstract  = {Our current understanding regarding the functioning of the savanna ecosystem describes savannas as either competition- or disturbance-dependent. Within this generalized view, the role and importance of facilitation have been mostly neglected. This study presents a mathematical model of savannas with coupled soil moisture-vegetation dynamics, which includes interspecific competition and environmental disturbance. We find that there exist environmental and climatic conditions where grass facilitation toward trees plays an important role in supporting tree cover and by extension preserving the savanna biome. We, therefore, argue that our theoretical results in combination with the first empirical studies on the subject should stimulate further research into the role of facilitation in the savanna ecosystem, particularly when analyzing the impact of past and projected climatic changes on it. (C) 2015 Elsevier B.V. All rights reserved.},
  language  = {en}
}