Letter-to-the-Editor: Modelling the multi-functionality of
African savanna landscapes under global change
Reimund P. Rötter 1*, Simon
Scheiter2, Munir P. Hoffmann3,1,
Mirjam Pfeiffer2, William C.D.
Nelson1, Kingsley Ayisi4, Peter
Taylor5 , Jan-Henning Feil6, Sara
Yazdan Bakhsh6, Johannes
Isselstein7, Anja Lindstädter8,9,
Kai Behn8, Catrin Westphal10, Jude
Odhiambo5, Wayne Twine11, Ingo
Grass12, Paolo Merante1, Gennady
Bracho-Mujica1, Thomas Bringhenti1,
Sala Lamega7, Issaka Abdulai1, Quang
Dung Lam1, Mina Anders10, Valerie
Linden5, Sina Weier5, Stefan
Foord5, Barend Erasmus13
1 University of Göttingen, Tropical Plant Production
and Agricultural Systems Modelling (TROPAGS), Germany
2 Senckenberg Biodiversity and Climate Research Centre
(SBiK-F), Germany
3 AGVOLUTION GmbH, Germany
4 University of Limpopo, South Africa
5 University of Venda, South Africa
6 University of Göttingen, Department of Agricultural
and Rural Economics, Germany
7 University of Göttingen, Grassland Sciences, Germany
8 University of Bonn, Institute of Crop Science and
Resource Conservation, Germany
9 University of Potsdam, Germany
10University of Göttingen, Functional
Agrobiodiversity, Germany
11University of Witwatersrand, South Africa
12University of Hohenheim, Germany
13University of Pretoria, South Africa
*Corresponding author: Reimund P. Rötter (email:
reimund.roetter@uni-goettingen.de)
Short running title: Modelling African savanna
multi-functionality
Acknowledgments: This work was conducted within the South
African Limpopo Landscapes Network - SPACES2: SALLnet project (grant
number: 01LL1802A) funded by the German Federal Ministry of Education
and Research (http://www.bmbf.de/en/).
Abstract (245 words)
Quantifying how multiple ecosystem services and functions are affected
by different drivers of Global Change is challenging.
Particularly in African savanna regions, highly integrated land-use
activities created a landscape mosaic with flows of multiple resources
between land use types. A framework is needed that quantifies the
effects of climate change, management and policy interventions on
ecosystem services that are most relevant for rural communities, such as
provision of food, feed, carbon sequestration, nutrient cycling and
natural pest control. In spite of progress made in ecosystem modelling,
data availability and stakeholder interactions, these elements have
neither been brought together in an integrated framework, nor evaluated
in the context of real-world problems. Here, we propose and outline such
framework as developed by a multi-disciplinary research network, the
Southern African Limpopo Landscapes network (SALLnet). Components of the
framework such as the crop model APSIM and the vegetation model aDGVM2
had already been parameterized and evaluated using data sets from
savanna regions of eastern, western and southern Africa, and were
fine-tuned using novel data sets from Limpopo. A prototype of an
agent-based farm household model was developed using comprehensive farm
survey information from the Limpopo Province of South Africa. A first
test of the functionality of the integrated framework has been performed
for alternative policy interventions on smallholder crop-livestock
systems. We discuss the versatile applicability of the framework, with a
focus on smallholder landscapes in the savanna regions of southern
Africa that are considered hotspots of global change impacts.
Keywords: African savanna; ecosystem services; food security;
integrated modelling; land use systems
Problem statement and challenges (words: 1986)
Various recent publications have indicated that accelerated global
change and its negative impacts on terrestrial ecosystems in southern
Africa urgently demand for quantitative assessment and modelling of a
range of ecosystem services (Conway et al., 2015; IPCC, 2019;
Chaplin-Kramer et al., 2019) on which rural communities depend.
Information is needed on how these Ecosystem Services (ES) can be
enhanced through sustainable land management interventions and enabling
policies (Rötter et al., 2005; Sikora et al., 2020). Yet, it has also
been claimed that, to date, the required systems analyses, data and
tools to quantify important interactions between biophysical and
socio-economic components, their resilience and ability to contribute to
livelihood needs do not exist (Midgley & Bond, 2015; Sikora et al.,
2020). We disagree, but acknowledge that building an appropriate
integrative modelling framework for assessing the multi-functionality of
savanna landscapes is challenging. Yet, in this Letter-to-the-Editor we
show that a number of suitable modelling components and required data
already exist and can be mobilized and integrated with emerging data and
tools to provide answers to problem-driven questions posed by
stakeholders on land management and policy issues.
High population growth, persistent low agricultural productivity and
poverty, severe land degradation and high climate variability, among
others, have already led to a decline of essential ES in many regions of
Africa. The situation is particularly critical in the savanna regions of
southern Africa, which are considered hotspots of global change impacts
that lead to a deterioration of ES (Conway et al., 2015; IPCC, 2019;
Sikora et al., 2020). Accelerated climate change is putting additional
pressure on their multi-functionality (Conway et al., 2015; Midgley &
Bond, 2015). ES such as provision of food, feed, fuel, carbon
sequestration, nutrient cycling, habitat quality, pollination and
natural pest control are under threat (IPCC, 2019; Sikora et al., 2020).
Southern Africa has also been identified as a hotspot for biodiversity,
whereby agricultural expansion is seen as a key driving force for the
declining species diversity (IPBES, 2018). The projected doubling of the
African human population by 2050 and the climate change-induced
increased frequency of extreme droughts underline the urgency of
science-informed assessments as a prerequisite for identifying
sustainable land management options (IPCC, 2019; Sikora et al., 2020).
About 70% of the population of southern Africa relies on agriculture.
Most of them are smallholders of which about 94% depend on rainfed
agriculture. Around 16% of the rural population has been characterized
as “food insecure” during the last five years (Sikora et al., 2020).
Climate variability, climate change, changes in land-use, technological
advances, institutional and policy constraints as well as the current
status of ES determine whether and to what extent the most relevant
sustainable development goals (SDGs) can be achieved, specifically, No
poverty (1), Zero hunger (2), Clean water (6), Climate action (13) and
Life on land (15). Southern African savanna landscapes are composed of
arable land, rangelands and orchards/homegardens and host unique nature
parks (Midgley & Bond, 2015; Sikora et al. 2020; IPBES, 2018), which
are, however, excluded here from our analysis. Rural livelihoods,
especially those of smallholders, who commonly perform mixed
crop-livestock farming largely depend on the ES these three major land
use types provide. Smallholders in the region are highly diverse in
terms of resource endowments such as land and water. The generally huge
yield gaps (with yield levels at 20% of the attainable), food
insecurity and shrinking land holdings call for radical changes in land
use policies and management to avoid societal unrest growing in the
future. In national plans on sustainable development, sustainable
intensification (Cassman & Grassini, 2020) of these systems, not
surprisingly, has the highest policy priority (Sikora et al., 2020). It
is seen as an important means to provide incentives to the younger
farmer generation, boost agricultural development and to set land aside
for nature conservation.
A broad range of management interventions has been suggested for
promoting sustainable intensification (Cassman & Grassini, 2020),
including cereal intercropping with legumes, site-specific fertilizer
application and irrigation. Most experimental studies on testing such
interventions have just looked at impacts on dry matter production and
yield, but a few also looked at other ecosystem functions such as carbon
sequestration and water and nutrient use efficiency. Yet, to date no
study has looked in an integrated manner at the complexity of
smallholder systems with a broad range of interacting ES at the
landscape level.
There is an urgent need to develop and apply an appropriate analytical
framework to assess the current status of ecosystems and their
functions. Land management interventions must be identified that can
reverse the decline of ES and work towards the achievement of the SDGs
in the face of climate change and other global change processes such as
population growth and biodiversity decline.
Available and emerging data and tools
On that background, the Southern African Limpopo Landscapes network
(SALLnet) set out to perform field studies, develop and apply systems
approaches and modelling tools to gain a deeper understanding of the
interactions and multi-functionality of different land use types (arable
land, tree orchards/homegardens, rangelands) and develop sustainable
land management scenarios jointly with stakeholders.
Process-based (eco-)systems modelling for crops and rangelands offers
the option to conduct scenario analyses in order to examine the
interaction between management and environment for given crop and
rangeland systems (e.g. Hoffmann et al., 2018; Pfeiffer et al., 2019).
These models generate output on dry matter production, crop yield, water
and nitrogen dynamics, carbon sequestration and vegetation dynamics.
Output of crop and livestock models can be combined (Dscheemaker et al.,
2014) whereby livestock models generate data on meat and milk, depending
on age, gender, etc. Farm level economic modelling (Reidsma et al.,
2015; Rötter et al., 2016) allows for the ex-ante evaluation of
the outcomes of different scenarios of land use management and enabling
policies including proposed risk management strategies at regional level
(Reidsma et al., 2015; Rötter et al., 2005, 2016).
The process-based crop model APSIM (Akinseye et al., 2017; Hoffmann et
al., 2018; Holzworth et al., 2014), and the vegetation models
aDGVM/aDGVM2 (Scheiter & Higgins, 2009; Scheiter & Savadogo, 2016;
Scheiter et al., 2018) had been previously parameterized and tested for
crop and rangeland systems in several savanna regions of western,
eastern and southern Africa. Based on comprehensive groundwork such as
agronomic trials on water conservation and irrigation, integrated
nutrient management, new crop cultivars and crop rotations (e.g.
Hoffmann et al. 2020), drought or grazing experiments in rangelands
(e.g. Pfeiffer et al., 2019) it was possible to further extend modelling
capabilities for crops and rangelands and evaluate them for the Limpopo
region in South Africa. For example, in addition to the simulation of
carbon sequestration, dry matter production and water fluxes, the
trait-based aDGVM2 vegetation model can now also simulate vegetation
dynamics as a function of specific local management actions such as
grazing and fuelwood harvesting. This makes it suitable for the
simulation of rangeland dynamics (Scheiter et al., 2019, Pfeiffer et
al., 2019).
Prototype agent-based bio-economic models (Rötter et al., 2016) are
currently being tested in three subregions of Limpopo with explicitly
different agricultural risks. These models are based on new farm survey
information collected from villages along a climatic gradient and can be
applied to examine the economic performance of different farm types and
analyse the effects of policy interventions on management decisions from
the farm household level to the regional scale.
Towards an integrated modelling framework and relevant
use-cases on sustainable land management
Based on considerations such as data availability and agro-ecological
diversity we have chosen the province of Limpopo to develop and
operationalize an integrated modelling framework for multi-functional
savanna landscapes. The Limpopo region is highly diverse in terms of
biophysical conditions, biodiversity and land use, and comprises some of
the former homelands of the Republic of South Africa. It is
characterised by a high climatic variability (CV of seasonal rainfall in
many areas > 25%), poverty (headcount 11.5% in 2016) and
food insecurity (12.9%) as well as by a high level of land inequality
– and as such is quite typical for many other regions in southern
Africa (Sikora et al., 2020). Therefore, it truly is a hotspot of global
change impacts and appealing for generalising the findings for similarly
managed ecosystems in southern Africa.
For making the modelling framework complete for numerous potential
applications, it is necessary to combine available data and tools with
new or emerging state-of-the-art databases. The latter include high
resolution remote sensing products (land use data), iSDA digital soil
map, IoT (Internet of Things)-based micro-climate maps, rapid plant
health detection by smartphones, new regional climate modelling
products, and additional biophysical modelling components such as the
hydrological model SWAT (Arnold et al., 1998) and the LIVSIM (LIVstock
SIMulator) model (Van de Ven et al., 2003).
Fig. 1 illustrates how the data and model components already developed
can be supplemented with additional tools and integratively linked to
quantify interactions between different land use types, management
decisions, and environmental change from the field- to the
landscape-level.
INSERT Fig. 1
However, before coupling models or combining their outputs within such
analytical framework, its components need to be tested with local data
and use-cases. Based on discussions with stakeholder platforms
established by SALLnet, the following relevant use-cases have been
defined, most of which have relevance for the wider domain of southern
African savanna landscapes:
- Sustainable management of smallholder crop-livestock systems
- Potential of deficit irrigation for sustainable intensification of
maize-based systems for so-called “emerging farmers”
- New crops for filling the winter livestock feed gap
- Sustainable management of macadamia orchards
With a systems perspective in mind, we compiled the tools and defined
data flows necessary for quantifying the crucial ecosystem services
(Fig. 1) for different alternative management interventions and policy
views. In doing so, we especially focused on use-cases I, II and III
(above). Work on these is currently in progress for Limpopo, utilizing
supportive tools such as sensitivity analysis and expert judgements to
check the plausibility of results.
The purpose of the framework is to ex-ante assess what effects
sustainable intensification measures such as improved management
practices (see above) and enabling policy interventions (such as
investments in agricultural extension services, irrigation or
communication infrastructure) could have. The framework examines the
effects of such interventions on interactions between land use types and
the ecosystem services they provide from plot to landscape scale - and
thus on the functioning of the whole land use system. Such land use
optimisation has to be done in a spatially explicit manner and with a
long-term perspective, and should allow to quantify potential trade-offs
and synergies between short-term economic viability and long-term
ecosystems functioning.
Outlook
Our integrated modelling framework and systems approach to analyzing the
multi-functionality of savanna landscapes contains several novelties.
Here we emphasise two aspects: (i) closing the missing link between
biophysical analysis, farm level decision-making and policy intervention
scenarios, and (ii) developing and evaluating the framework jointly with
stakeholders and a multi-disciplinary team with problem-oriented
use-cases.
We propose the following steps for developing, evaluating and
operationalising such framework for any given savanna region in southern
Africa:
- Monitoring and assessing spatio-temporal patterns of ecosystem
functions and services at landscape level
- Developing a framework linking crop, livestock and rangeland systems
with farm-economic models enabling integrated analyses
- Using assembled field experimental, survey and monitoring data as well
as advanced sensitivity analysis and expert knowledge to evaluate the
framework
- Perform land management and policy scenario analyses for alternative
interventions as jointly defined with stakeholders
Research opportunities to extend the applicability of the framework lie
in: further model-data fusion, integration of high-resolution remote
sensing, soil and micro-climate sensor data, as well as distinct
improvements of crop and vegetation models, in particular for capturing
the impacts of climate extremes and elevated CO2.
Likewise, extended (agent-based) model capabilities incorporating
insights into human decision behaviour under risk/uncertainty, and their
use in sensitivity analyses and for alternative stakeholder-defined
scenarios will allow us to better explore sustainable land use options.