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Researchers investigate impacts of climate change on rare tropical plants

View from the one of the 'sky islands' of the Eastern Arc: the Uluguru Mountains. Credit: Rob Marchant

Research led by the University of York has found that the impacts of climate change on rare plants in tropical mountains will vary considerably from site to site and from species to species.

While some species will react to climate change by moving upslope, others will move downslope, driven by changes in seasonality and water availability. The researchers believe that this predicted variation, together with the long-term isolation and relative climatic stability of the mountains, may shed light on historical processes behind current patterns of biodiversity.

The study, published in the journal Ecography, focussed on the Eastern Arc Mountains of Tanzania and Kenya, home to some of the oldest and most biodiverse habitats on Earth. Thousands of plant and animal species live in this chain of increasingly fragmented patches of forest, woodland and grassland, many hundreds of which are found nowhere else.

The mountains are home to two of the species in the BBC’s top ten new species of the decade: the grey-faced sengi (or elephant shrew) and the Kipunji monkey – the first new genus of monkey to be discovered since the 1920s.

Image: The Eastern Arc Mountains study region in Tanzania and Kenya, consisting of 13 distinct ranges (a.k.a. blocs). Adjacent highlands have different geological substrates and have climatic regimes influenced more by the Great African Lakes or the intertropical convergence (a band of thunderstorms that circle the globe near the equator) than by the Indian Ocean. Credit: Phil Platts
Image: Begonia poculifera Hook. f. (Begoniaceae), Nawenge Forest Reserve, Mahenge Mountains, R. Gereau 6890. This species is mostly distributed in forests of West and Central Africa, but also occurs in the Eastern Arc Mountains – evidence of an ancient pan-African forest belt. Credit: C. Davidson, copyright www.floraoftheworld.com
Image: Moss-covered trees in the Uluguru Mountains intercept moisture carried on Indian Ocean trade winds. Credit: Rob Marchant
Image: Watercolour of Impatiens ulugurensis Warb. (Balsaminaceae), endemic to the Uluguru Mountains. Common name: Busy Lizzie. Artwork by Riziki Kateya, a Tanzanian botanical artist trained at the Royal Botanic Gardens Kew. Thanks to Colin Watkins for providing the image

In addition to being crucial for biodiversity conservation, the value of the mountains is increasingly being realised as important to the national development of Tanzania, providing food and fibres, clean water and climate stability.

The researchers used regionally downscaled climate models based on forecasts from the Max Planck Institute (Hamburg, Germany), combined with plant specimen data from Missouri Botanical Garden (St. Louis, USA), to show how predicted climate change could impact rare plant distributions differentially across the Eastern Arc Mountains.

We considered the possibility that plants might migrate rapidly to keep pace with 21st century climate change, and found that sites with many rare species are characterised by climates significantly more likely to remain accessible to those plants in the future

Dr Phil Platts

Lead author Dr Phil Platts, from the University of York’s Environment Department, said: “We explored the hypothesis that mountain plants will move upslope in response to climate change and found that, conversely, some species are predicted to tend downslope, despite warmer annual conditions, driven by changes in seasonality and water availability.”

Although patterns of change are predicted to be complex, the authors note that their findings link with theories of past ecosystem stability.

Dr Platts said: “We considered the possibility that plants might migrate rapidly to keep pace with 21st century climate change, and found that sites with many rare species are characterised by climates significantly more likely to remain accessible to those plants in the future. This fits with the idea that similar processes in the past underlie the patterns of biodiversity and endemism (organisms unique to a certain region) that we observe today: during glacial-interglacial cycles, old evolutionary lines were able to maintain populations in sites such as the Eastern Arc, while facing extinction elsewhere.”

Professor Neil Burgess, co-author and Chief Scientist at the UNEP World Conservation Monitoring Centre, added a cautionary note: “For many organisms, effective dispersal has been massively curtailed by human activity, and so their future persistence is far from certain. Especially on lower slopes, climate-induced migrations will be hampered by fragmentation and degradation of the habitat mosaic.”

The researchers warn of the problems of using larger-scale, global climate models to assess localised impacts of climate change. They say that two thirds of the modelled plant species are predicted to respond in different directions in different parts of their ranges, exemplifying the need for a regional focus in climate change impact assessment.

“Conservation planners, and those charged more broadly with developing climate adaption policy, are advised to take caution in inferring local patterns of change from zoomed perspectives of broad-scale models,” said Dr Platts.

The study emphasises the importance of seasonality and moisture, rather than altitude and mean temperature, for determining the impacts of climate change on mountain habitats in tropical regions.

Co-author Roy Gereau, from the Missouri Botanical Garden’s Africa and Madagascar Department, said: “This study demonstrates the enormous potential of carefully curated herbarium data, combined with climatological information, to elucidate fine-scale patterns of species distribution and their differential changes over time.” Future work will investigate a wide range of climate models and emissions scenarios, as well as DNA sequencing of selected plant species.

Co-author Dr Rob Marchant, from York’s Environment Department, said: “What is clear from the current study is that effective conservation must operate at a landscape level, taking into account the spatial variation in how ecosystems and people have responded to previous episodes of rapid change.”

Further information

  • The paper, “Spatial heterogeneity of climate change in an Afromontane centre of endemism”, is published online in Ecography. 
  • The authors are Philip J Platts (Environment Department, University of York; Zoology Department, University of Cambridge), Roy E Gereau (Africa and Madagascar Department, Missouri Botanical Garden, St Louis), Neil D Burgess (UNEP-WCMC, Cambridge; WWF-US, Washington DC; Biology Department, University of Copenhagen) and Rob Marchant (Environment Department, University of York).
  • The research was funded by the Marie-Curie programme of the European 6th Framework (MEXT-CT-2004-517098), with additional support from the Leverhulme Trust (www.valuingthearc.org), the Ministry for Foreign Affairs of Finland (www.chiesa.icipe.org) and the British Institute in Eastern Africa (www.biea.ac.uk).The work was led by the York Institute for Tropical Ecosystems (www.york.ac.uk/environment/research/kite), which explores ecosystem dynamics, climate change and human impacts in tropical Africa.
  • The Missouri Botanical Garden maintains the publicly accessible database TROPICOS (www.tropicos.org), on which all of the plant species distributional data used in these analyses are stored.
  • More information on the University of York’s Environment Department at www.york.ac.uk/environment.
  • More information on the BBC’s top ten new species of the decade.