Deciphering interactions between climate, carbon, biodiversity and livelihoods in East
African mountains
Rob Marchant, Claudia Capitani, Philip Platts, Dereje Denu, Mathew Mathayo Mpanda, Dickens
Odeny, Peter Omeny, Tadesse Woldemariam Gole, Joyce Ininda, Faith Karanja, Ensermu
Kelessa, Chris Oludhe, Geoffrey Mwchala, Geroge Ogutu, Philip Omondi, Amos Majule, Marion
Pfeifer and Fergus Sinclair
During the last four decades, cumulative CO2 emissions from forest loss and other land use
changes have increased by 45%, with commensurate impacts on global climate and
biodiversity, as well as more localised impacts on ecosystem goods and services such as
hydrological functioning, soil conservation and forest products. Half of the African population,
and most priority sites for conservation, are concentrated in mountain and coastal regions.
Research on the interactions between mountain biodiversity, carbon storage and local
livelihoods under environmental change is, therefore, crucial.
It is challenging to understand how and why climates are changing at local scales, and how
climate models can be used to provide useful information for a range of stakeholders (national
level policy developers through to households), particularly in mountain areas where
environmental gradients are steep and where large and local scale drivers interact to greatly
influence climate variability, and associated uncertainty in projections. Addressing the lack of
high-resolution, regionally-focused climate projections for Africa, we constructed ‘AFRICLIM’
climate ensembles from a range of global climate models, spatially downscaled by regional
climate centres (CORDEX initiative), and then by bias-correction against high-resolution
baselines. Comparing historical runs with remotely-sensed and in situ weather records across
East Africa revealed that unimodal rainfall patterns are better captured than the bi-modal rainfall
regimes of the equatorial sub-region.
These uncertainties notwithstanding, spatially downscaled projections for the CHIESA transects
indicate that by mid-century, mean annual temperatures could be 1.8–2.4°C warmer in the Taita
Hills, 1.9–2.6°C warmer in Mount Kilimanjaro, and 2.3–3.0°C warmer in the Jimma Highlands.
Mean annual rainfall is projected to increase in Taita but to remain similar for Kilimanjaro and
Jimma, but with high model uncertainty (Figure 1). The projections indicate an increase in
climatic extremes, seasonally and annually, compounded by increased uncertainty around the
timing of these events. In participatory scenario analysis, local stakeholders in Taita envisaged
solutions for possible changes in rainfall and temperature, mainly targeting improved water
retention and usage. These farmers are most concerned by increasing variability and
unpredictability of climatic events, as opposed to steady changes in these parameters.
The spatial distributions of tree biomass, soil organic carbon and soil nutrients, plant, bird and
butterfly diversity were studied across ~150 1-ha plots: 29 in Jimma, 75 in Kilimanjaro and 48 in
Taita. The plots span a range of land use / land cover types, including natural or degraded
forest, semi-managed coffee forest (SMCF), mixed agroforestry systems, woodland, pasture,
low-intensity cropland, and plantation. Carbon assessments highlight the importance of
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agroforestry systems for climate change mitigation, in both the above- and below-ground carbon
pools. For example, trees in Jimma Highland’s SMCFs store 62±25 (mean±SE) AGC t.ha-1,
compared with 82±32 t.ha-1 in adjacent natural forests (Figure 2). Other land use types, such as
woodland, pasture and cropland, store significantly less carbon. Diversity among all growth
forms of plant is highest in SMCFs, partly due to degradation in the natural forests. Butterfly
diversity is highest in the natural forests, especially among habitat specialists. Similarly in Taita,
bird and butterfly diversity among habitat specialists is highest in the forests, while overall
diversity, driven by generalist species, is highest in the agroforest and low-intensity cropland
systems. Future loss of trees from these landscapes can, however, be expected to impact
negatively on biodiversity and, particularly in Kilimanjaro, has been linked with reductions in soil
fertility.
To ensure future safeguarding of biodiversity, carbon storage, and other ecosystem services,
we suggest that traditional coffee farmers be supported during times of yield loss or failure in the
market price of coffee, to lower the risk of conversion to cropland. Tree planting is encouraged
as part of an integrated management system, to increase carbon storage and to improve soil
fertility, as well as to facilitate pest control and pollination services. Increased tree cover has the
additional benefit of regulating hydrological flows, and reducing air temperatures locally and
regionally, helping to mitigate some of the projected impacts of climate change. Surveying over
500 sites across East African biomes, we document a predictable relationship between
vegetation canopy structure and its impact on local land surface temperature - a beneath the
canopy cooling effect, whereby dense vegetation may reduce microclimatic in the understory by
several degrees Celsius, compared to open lands. Indeed, it remains unclear to what extent
locally perceived changes in recent climate are a function of broad-scale processes (e.g. global
warming) as opposed to local and regional changes in land use.
Participatory scenario analysis in Taita found that local stakeholders, on the one hand,
acknowledged the negative effects of deforestation in water catchment areas, and the need for
increased forest cover; on the other hand, they could not envisage alternative economic
activities to farming, which is expected to expand in line with local population increase.
Reconciling these apparently opposing trajectories is a major challenge for conservation of the
forest resource that underpins local food security, environmental regulation and connects with
global issues of climate regulation.
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Figure 1. Changes in rainfall as predicted by one regional model compared to satellite-derive
rainfall. While coastal Eastern Africa is predicted to get broadly wetter, the Ethiopian Highlands
are predicted to have a reduction in annual rainfall and also experience significant changes in
the seasonal distribution of this rainfall (right). Platts PJ, Omeny PA, Marchant R (2015).
AFRICLIM: high-resolution climate projections for ecological applications in Africa. African
Journal of Ecology 53, 103-108.
Figure 2. Left: Distribution of vegetation plots (1 ha) along a 23.6 km transect in the Jimma
Highlands, southwest Ethiopia, part of the Eastern Afromontane Biodiversity Hotspot. Right:
Aboveground live carbon storage across land use / land covers types. Traditionally managed
coffee forests retain 75% of carbon, compared with natural forests. Plant and animal diversity
is high is both systems compared to other land use types. Plantations store the most carbon,
but the trees are harvested at maturity and the stands retain minimal biodiversity.
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