Drier tropical forest at risk of biodiversity homogeneisation with droughts
Th Ecosystems Lab at the University of Oxford, www.oxfordecosystems.org, has been dedicated to carry fieldwork and collect plant functional trait and vegetation census in the most hidden places in the tropical forests arround the world. Our paper now published in Nature Communications, https://rdcu.be/b5o5A, makes use of such great data combined with that of the great database of ForestPlots.net to investigate how a changing climate affects tropical forest in West Africa.
All images with credit to Yadvinder Malhi
Our study involved working in the field for six months with over thirty Ghanaian researchers and students to collect detailed information on the functional traits from leaves and wood of 299 trees from 94 distinct species. At each site the trees had to be climbed on what was difficult conditions in order to collect leaves for analysis.
The research was carried out over multiple forest monitoring plots ranging from dense wet tropical rainforest to dry forest and savanna. Many of these plots have been monitored for decades by our local partners and collaborators in Ghana from the SCIR, www.csir.org.gh , and the Forestry Commision, www.fcghana.org and by our coolaborators in the UK as Sophie Fauset from Plymouth University (www.plymouth.ac.uk/staff/sophie-fauset).
We found that climate impacts differ between wetter and drier tropical forests in West Africa. Forests with an already drier climate undergo greater biodiversity loss when confronted with further drought. This finding goes contrary to expectation as it has been thought that drier
forests would already be more adapted to drought, and therefore more able to cope with climate change. Conversely, the biodiversity of wetter tropical forests did not appear to be impacted by the warming climate thus far, and even increased under drier conditions. However, this may be because these forests have greater reserves of moisture stored in their trunks and soils, which can be drawn upon to cope with dry periods.
Our hope is to contribute with practitioners and give more insights to understand which parts of the forest run greater risk of biodiversity loss and need enhanced protection efforts. Since drier tropical forests may be at greater risk due to climate change they may also be less resilient to additional anthropogenic impacts, leading to further forest degradation.
The study contributes to an ongoing debate about whether drier forests have adapted over time to drought conditions, and are therefore more resilient to future change. The findings show that the opposite is true: drier forests in West Africa are already at the limit of their adaptation, existing on the edge of a tipping point and at risk of losing further species. Wetter forests appear more resilient thus far, but how long this resilience can continue as the climate keeps warming and drying remains uncertain.
Drier tropical forests are home to a number of plants that are important for local livelihoods and human health. Among these threatened species are Strombosia pustulata, a hard, termite-resistant wood valued for construction, and Terminalia superba, a timber species also used in traditional medicine to treat wounds, sores and malaria.
According to the UN, over 1 million animal and plant species are now threatened with extinction, more than ever before in human history. By distinguishing between the impacts of climate change
on wetter and drier tropical forests, our study supports global efforts to understand and slow this rapid biodiversity loss.
Our work has been possible thanks to all collaborators from Ghana and also to the funding from the Netherlands Organisation for Scientific Research (NWO) under the Rubicon programme (019.162LW.010), European Rsearch Council (ERC) grants, grants from the Royal Society‐Leverhulme Africa Capacity Building Programme, from the Natural Environment Research Council (NERC) and from Royal Society Research Fellowship to the authors of the study.