Work Package 1:
Savanna Dynamics and Global Change
Savanna Dynamics and Global Change
30 researchers
COORDINATORS Patrick Duncan (UPR 1934 CNRS, Chizé) and Jeremy Midgley (Botany department, University of Cape Town)
Savannas are
multi-state systems, and the ecological drivers which cause savannas to change
from one state to another (fire, large herbivores wild and domestic etc.) are
beginning to be understood. The
scientific aims of this WP are to contribute to improving our understanding of
impact of global change on processes controlling a few model
savanna systems (Hwange and Kruger in
particular). As a contribution to the science-policy interface for sustainable development the aim is to
use this knowledge to model the systems, and to build scenarios as a basis for
management decisions.
Project
1 : The impact of ecosystem engineers, fire and large herbivores, on
plant-soil interactions and biogeochemical cycles.
Participants : Jacques Gignoux, Luc Abbadie, Sébastien
Barot, Jean-Christophe Lata (CNRS
UMR 7618, Paris), Simon Chamaillé-Jammes (CNRS UMR 5175 Montpellier), Hervé Fritz (CNRS UMR 5558 Lyon), William Bond (University of Cape Town).
In savannas the functioning of the
nutrient cycles is highly modified by fire, grazers and browsers. Grazing lawns
concentrate heavy grazing pressures, making them a useful system for the study of
these interactions. A PhD (O. Bonnet) enabled us to show that large grazers (in
particular, white rhinos) are able to consume the primary production
immediately so no standing crop accumulates. This functioning is interrupted
during dry spells and is activated by rainfall, including during the dry
season. Other work (L. Abbadie, X. Le Roux) includes measurements of the
effects of selective grazing on the microbial community and other soil
properties in Hluhluwe-iMfolosi Park where exclosures show major or little
effect on the nitrogen and carbon cycle respectively. This GDRI allowed us to
submit a research proposal on carbon allocation under various regimes of
climate, fire and herbivory to the French Agence
National de la Recherche; South African sites play an important role in the
project.
The understanding of the impact of
large herbivores and fire on grasses (biomass, production, species composition
and quality as a food resource), has improved greatly. In particular, the
nitrogen cycle in savannas is now relatively well understood; however, the
phosphorus cycle is less well known. Recent results show that complex
interactions between these cycles are the rule: grasses are limited by
phosphorus under acacia trees and by nitrogen in open areas. Mycorrhizae are
known to play an important role in the phosphorus cycle, and have rarely been
studied in savannas. Our objective for the future will be to better document
the nitrogen and phosphorus cycles in savannas, using the gradients of grazing
/ browsing intensity, fire frequency and intensity, rainfall and soil nutrient
retention ability available in parks such as Hluhluwe-iMfolosi and Kruger. This
involves (1) characterization of the main microbial functions encountered under
various environmental conditions (e.g. nitrification, denitrification, nitrogen
fixation), (2) assessment of the phosphorus cycle, including the incidence of
mycorhizae, (3) evaluation of plant allocation strategies for carbon, nitrogen
and phosphorus (3) modelling the coupled carbon, nitrogen and phosphorus
cycles.
Project 2 : Factors controlling large herbivore populations: direct and indirect
effects of predation in the context of resource constraints.
Participants: Simon
Chamaillé-Jammes (CNRS UMR 5175
Montpellier), Hervé Fritz,
Jean-Michel Gaillard, Christophe Bonenfant (CNRS UMR 5558 Lyon), Patrick Duncan (CNRS Chizé), Michel de Garine-Witchatitski, Mathieu Bourgarel (Cirad), Elissa Cameron,
André Ganswindt (MRI, Univ. Pretoria), Norman Owen-Smith (Univ. of Wits), David
Ward, Adrian Shrader, Rob Slotow (Univ. Kwazulu-Natal).
This project studies the complex interaction between habitat quality,
climate, pathogens and predation on herbivore abundance, and the cascading
effects on vegetation. We particularly rely on the Hwange Environmental
Research for Development programme (HERD) based on an exceptional, long term,
cooperation between the Zimbabwe Parks and Wildlife Management Authority, two
French organizations the Cirad and the CNRS, the universities of Harare and Bulawayo
and two research/conservation programmes (Painted Dog Conservation and Hwange
Lion Research, WildCru, Oxford University). This site (Hwange) and the
surrounding forestry and communal areas, is currently under evaluation by the
CNRS as an “Observatoire Homme-Milieu/Zone
Atelier”. This Project currently has a Postdoc in Wits (S. Grange), 7 PhD
students; an MPhil student Bulawayo University (NUST).
Interesting results have
been obtained on an ‘ecosystem engineer’, the elephant, whose populations are
increasing in many protected areas in Southern Africa. In Hwange our work
showed that the increase was limited by food resources, whose access is
constrained by the availability of surface-water. High elephant densities do
not always cause shifts in vegetation communities, and no impact on
medium-sized herbivores was detectable.
We have
recently focused the program on innovative research on direct and indirect
effects of predation. For instance our work on the interaction of resource
availability and anti-predator behaviour has shown that the use of habitat of
seven species of herbivores is strongly affected by the risk of predation, in
the short and medium term. In the period 2011-4, this result will be pursued
through the project “Landscape of fear and the use of landscape resource
heterogeneity by ungulates of different body sizes. Testing new hypotheses on
ungulate species coexistence” (funded by the French Agence National pour la Recherche). A PhD (F.
Barnier) and a postdoc (M. Valeix) have been recruited. We
are running a design a medium-scale field experiment to investigate
behavioural adjustments medium-sized herbivores make when forced to make a
trade-off between resource quality and predation risk. We also rely on GPS
collars to document the locations of herbivores and predators simultaneously
and how both use the various habitats. More than 60 GPS collars are thus
currently deployed in Hwange (on 3 species of predators, 5 herbivores). We
intend to link with South African research groups working in smaller reserves
to replicate this study and assess the generality of our findings. This will
create a strong incentive to build a ‘community-of-practice’ research network
working on the behaviour and dynamics of large mammals.
Project 3 :
Scenario building for sustainable use and conservation
of natural resources: modelling the dynamics of complex, spatially organised
systems, with special emphasis on
interactions between wildlife and people around protected areas
Participants: Hervé Fritz (UMR 5558 CNRS Lyon), Luc Doyen (MNHN Paris), J Manjegwa, B.
Mukamuri (CASS, University of Zimbabwe), A. Binot, M De Garine-Wichatitsky, M-N De Wisscher, E.
Etter (CIRAD-Agir), P. Mundy, E. Mwenje (NUST, Bulawayo), Shakkie Kativu (TREP,
University of Zimbabwe), A. Murwira (Geog. & Env. Sci, University of
Zimbabwe), Graeme Cumming (Univ. Cape Town)
In savannas the
distribution of vegetation, risk of predation and disturbance are major drivers
of animal movements, and the complexity of the systems is even greater when
dealing with a mosaic of protected areas and agricultural land: the
spatio-temporal organisation of land use types as well as ecological processes
may be central in allowing the various components of the system to coexist. The
edge of Protected Areas (PAs) is therefore a perfect laboratory to study the
determinants and conditions that can allow for the sustainability of an
integrated wildlife-human system.
The
new framework of this Project will integrate complementary initiatives to link
research-policy in order to better manage the interface between PAs and their
peripheries (e.g. HERD programme, the AIRD inititiave on research and PAs
management, CIRAD's network of research platforms). The main study objects will
be socio-ecological systems that rely to a large extent on ecosystem goods and
services, in order to produce wealth and improve standard of living of the
inhabitants. It thus appears that our system is defined by a set of components
that can be most interestingly in interaction, through a pluridisciplinary
approach (ecology, political science and economics). The main objectives will
be to understand the determinants of coexistence between humans and wildlife at
the periphery of PAs, and the sustainability of these integrated systems. As an
attempt to produce tools for scenario-building, the results of field studies
will be integrated in co-viability models, or used for role-game scenario
planning exercises.
During
the GDRI 191 we launched two main studies which should provide case studies for
the work in 2011-2014. The first model on the Hwange systems shows that the
spatial arrangement of the park, safari and communal areas is crucial for the
viability of a large elephant population, lucrative trophy hunting and
sustainable meat production, and that environmental stochasticity strongly
decreases the number of viable scenarios (PhD of C. Guerbois). We then
developed a study to model the spatial coexistence of buffaloes and cattle at
the periphery of protected two areas (Hwange and Gonarezhou - PhD of E.
Miguel).With the objective of developing bio-economical models for integrated
and sustainable management of African wildlife including protected areas, we will now
integrate the socio-economic component of one of our long-term sites (Hwange)
in a model of the complex dynamics of this system.
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