Reforestation without biodiversity could create breeding ground for disease: A new study suggests the destruction of forests in favor of palm oil plantations and monoculture reforestation could be increasing risk of the emergence of zoonotic diseases such as covid-19, The Guardian reports. “Reforestation can increase biodiversity loss when forest expansion is made at the expense of grasslands, savannas, and open-canopy woodlands,” the study states. Reforestation correlated most strongly with disease outbreaks in areas with more grassland and less tropical climates, including the United States and Europe.

What do you mean planting trees could be bad? The issue is monoculture, or the cultivation of a single crop. A range of species and habitats are required to filter diseases in a biodiverse environment. When forests are replaced with monoculture plantations, specialist species die off in favor of generalists like rats and mosquitoes, resulting in a loss of natural disease regulation, the study suggests.

The study used data from the WHO, World Bank, FAO and Gideon epidemic database to examine the correlation between trends for forest cover, plantations, population and disease around the globe. It surveyed the period between 1990-2016, covering 3.8k outbreaks of 116 zoonotic diseases (transferred from animals) and 1.9k outbreaks of vector-borne (carried by mosquitoes, ticks and flies) diseases.

But correlation is not causation: The authors do not rule out the fact that other factors, such as climate change disruption, may be involved in the development of diseases, but point to the link between land use change and epidemics through several case studies. Deforestation in Brazil increases the risks of malaria, while loss of forests in West Africa has been identified as a factor in the development of Ebola.

Palm oil plantations are one of the major drivers of deforestation: The US Food and Agriculture Organization found that forests had decreased in size by 800k square kilometers since the 1990s, while the study found that nearly a quarter of global forest loss occured due to an increased demand for beef and palm oil, which require cutting down forests to build plantations or rear livestock.

So why don’t we just boycott palm oil? Despite its issues as a monoculture crop contributing to deforestation, palm oil is the most versatile and efficient of all vegetable oils, contributing 35% of global vegetable oil yield through only 10% of the land used for vegetable oil crops. Any alternative would require four to ten times more land, according to the WWF. Palm oil is used in almost 50% of all packaged consumer goods found in a supermarket — ranging from peanut butter to deodorant — and is critical to the GDP of emerging economies, with millions of small farmers relying on it for their livelihoods. Indonesia and Malaysia make up over 85% of global supply, but there are 42 other countries that produce it.

What can be done? Further studies are planned to unpack the correlation between deforestation and disease, and to potentially predict future outbreaks. As individual consumers, the WWF suggests that those who can should invest in smallholder programmes and sustainable landscape initiatives, and following the RSPO production standard and best practices for sourcing palm oil to shift consumption towards a sustainable palm oil industry.