Summary description of the project objectives
Tropical forest-savanna transitions are regions where tropical forests and savannas converge and both
exist as discrete “patches” under similar climatic conditions (Veenendaal et al. 2014). They are often
referred as “Zones of Tension” (ZOT), following Clements’ concept of the ecotones as zones of tension
(Clements 1905). Tropical forests and tropical savannas are the two most biodiverse biomes of the world
(Bass et al. 2010) and account for 60% of all terrestrial gross primary productivity (Beer et al. 2010).
Therefore, any shifts in their distributions will have important consequences on local, regional and global
carbon balances (Field et al 1998; Sitch et al 2003), climate feedbacks (Malhi et al 2008; Better et al 2008),
and on potential tipping points (Mace et al. 2014).
Most studies use global models or remote sensing approaches that represent the transition from forest to
savanna as a competition between a few functional groups (often just two groups: tropical grasses and
tropical trees). There is plenty evidence that the transition between tropical forest and non-forest biomes
is not gradual, but a threshold phenomenon between two stable states that can occur at the same level of
rainfall (de L. Dantas et al. 2013). The switch between these two stable states has been suggested to be
primarily mediated by fire (Hirota et al. 2011, Lehmann et al. 2011, Staver et al. 2011), although soil,
climate, light, and herbivory also have a key role in this transition (Lehmann et al. 2014, Veenendaal et al.
2014).
This project aimed at gathering a detailed ecological and ecophysiological data for understanding the
dynamic processes operating at tropical forest-savanna transition, at a number of sites of Brazil and
Africa. The study was framed in the context of the forest-savanna fire thresholds from a functional trait
perspective, with the aim of testing and further developing the role of fire and its interaction with drought
and resources availability.
Description of the work
The project conducted detailed plot surveys to quantify
functional diversity, and manipulative experiments to
understand and quantify seedlings responses to fire,
drought, light and nutrient availability. The study areas
were located in Nova Xavantina (Brazil) and Kogyae Strict
Nature Reserve (Ghana) (Figure 1). In each area, a number
of plots (four in Brazil and three in Ghana) were sampled
along a forest-savanna transitions for the functional traits Figure 1. Location of the study areas and
described in Table 1. Fieldwork was conducted in 2014.
sampled plots at each site. Source: Google Maps®.
Two manipulative experiments (one field based at Kogyae, and the other at a greenhouse in Wageningen,
Netherlands) we also performed in 2014 and 2015. The field manipulative experiment conducted at
Kogyae look at differences in survival and establishment of five forest tree species in different vegetation
Leaf Traits
Photosynthetic performance
Branch Traits
Twig specific density
Plot Traits
Leaf Area Index
Specific leaf area
Twig dry mass,
Regeneration
Leaf dry mass
Wood anatomy (vessel area, fiber area)
Crown depth
Leaf saturated mass
Wood density
Crown volume
Leaf fresh mass
Leaf area to sapwood area ratio
Leaf thickness
Bark thickness
Leaf nutrients: N, P, K, Ca, Mg, S
Bark density
Leaf osmotic potential (using osmometer)
Vessel length
Leaf turgor loss point (selected species)
Native hydraulic conductivity
Leaf venation
Twig nutrients: N, P, Ca, Mg, K
Branch architecture
Table 1. List of functional traits collected within this Project at seven permanent 1- ha plots (four in Brazil, three in
Ghana).
types (forest, transition, savanna). The greenhouse experiment tested the effects of water availability and
fire on a set of 27 African species ranging from wet forest to dry savanna.
Main results achieved
Through the campaigns and experiments we have gathered a large database on functional diversity along
forest-savanna transitions of both adult and juvenile tree species. At the adult level, we have gathered an
exhaustive forest-savanna functional trait dataset (see summary list of traits collected on adult trees
representing up to 80% of the plot’s basal area at each permanent plot) that will enable us to scale from
individual traits to ecosystem functioning properties, such as primary productivity and nutrient cycling. At
the time of this report results are still preliminary and a set of scientific publications is under preparation.
A Special Issue in a high-impact scientific Journal will be published during 2016.
The field manipulative experiment in Ghana led to two MSc thesis (Anabel Cardoso, U. Oxford and J.
Medina-Vega, Wageningen University) and a publication is currently under review at a scientific journal.
The greenhouse experiment allowed us to test a new methodology for applying fire treatments on
ecological research under experimental conditions. The experiment was harvested at the end of
November 2015.
Expected final results and their potential impact and use

A Special Issue in a high-impact scientific Journal will be published during 2016.

A new methodology for performing fire treatments on manipulative greenhouse experiments.

An extensive characterization of the functional diversity in forest-savanna transitions for use in
Dynamic Vegetation models,.

Dataset to be incorporated in global datasets such a TRY and GEM.

Accurate information of the vulnerability of these transitions to ongoing changes in climate and
fire regimes.
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