Climate change poses risk to wild food plants in southern Africa

High levels of climate warming could shrink the geographic range of two-thirds of wild-harvested food plant species in southern Africa.

In the article, “Climate change risk to southern African wild food plants”, recently published in Regional Environmental Change, the University of Cape Town’s (UCT) Carina Wessels and her co-authors focus on the links between climate change, traditional knowledge, food security and wild-harvested food plants.

Wessels, who at the time was affiliated with the African Climate and Development Initiative (ACDI), collaborated on the study with Dr Christopher Trisos of the Climate Risk Laboratory at the ACDI and Dr Cory Merow, a quantitative ecologist from the University of Connecticut’s Department of Ecology and Evolutionary Biology.

Understanding the impact of change

Wild-harvested food plants are important ingredients in the diets of millions of people, especially during times of hardship when staple crops fail. Although they contribute to food security in southern Africa, little is known about the risk that climate change poses to these edible plants, with most studies thus far describing the impact of climate change on food security in terms of the prospects for agriculture (mainly major crops) and fisheries.

Wessels and her co-authors considered the climate change risk to 1 190 wild food plant species (including the num-num, the sour fig, rooibos and the marula fruit) used by 19 native language groups in the region.

In the future, already water-stressed countries in the region like Botswana are likely to become even hotter and drier and, ultimately, more water-stressed.

“Our aim was to determine where wild food plants occur and whether these plants are threatened by climate change,” Wessels says. “We also wanted to know whether the areas where these plants grow overlap with regions of projected crop yield loss (under climate change).”

“People living in rural areas use wild-harvested food plants to supplement their diets, especially during times of hardship when staple crops fail,” Trisos says. But, due to climate change, many people living in the central parts of the region may soon be left without this nutritional safety net.

The researchers’ approach allowed them to generate new knowledge that can inform timely responses in a climate-altered future.

The data underlying the projections

The researchers used a recently published list of 1 740 southern African edible plant species to identify wild-harvested food plant species. This inventory, the most comprehensive of its kind yet, shows that edible plant use patterns differ between 19 indigenous cultural and language groups in the region.

Wessels and her co-authors included wild food plants that are used as snacks, cooked as vegetables or ground as flour (among other uses) in their analysis. They also considered those plants used as famine food (food eaten during famine conditions to avoid starvation).

They employed historical climate data (including averages for 30-year periods), future climate scenarios (including projected averages for 20-year periods), environmental data (including soil information) and species distribution modelling to inform their work.

A warming climate creates winners and losers

The team considered two future greenhouse gas scenarios. In both, the future looks hotter for native wild food plants.

In the low emissions scenario (RCP 2.6), by 2081–2100, global warming is likely to have stayed below 2°C higher than pre-industrial levels (before 1850). The high emissions scenario (RCP 8.5) represents a future in which we will have experienced more than 4°C of global warming by the end of this century.

“There is a mix of winners and losers in a world that is up to 2°C warmer (than pre-industrial levels),” Trisos says. “If we allow warming beyond this threshold, however, there will be more losers than winners.”

Their results show the ranges of 40% of wild food plant species will likely shrink by 2060–2080 in the low emissions scenario. Roughly six out of every ten wild food species, however, are expected to expand their range.

This picture is reversed in the high emissions scenario: 66% of wild food plant species are projected to experience range reductions, and only 34% range increases.

Climatic conditions are expected to decrease species richness the most in southern Africa’s northeastern parts in this scenario – causing the local extinction of more than 200 species. Local species losses of more than 50% are foreseen for most of Botswana.

In contrast, increases are projected for both crop yield and wild food plant species richness in the southern and eastern parts of southern Africa (including parts of the Western Cape, Eastern Cape, KwaZulu-Natal and Mpumalanga).

Intersecting climate risks

Climate change, Trisos stresses, poses a fundamental threat to the places, species and cultural processes that people rely on for their livelihoods.

“Our research identified large regions in which both crop yields and wild food plants are at risk,” Trisos explains. Among these are South Africa’s North West and Free State provinces and parts of northern Namibia.

In the high emissions scenario, maize, sorghum and wild food plants will be most at risk along the northeastern border between South Africa and Botswana.

Some ethnic and language groups using wild food plants are expected to be more negatively affected by climate warming than others. Geographic range decreases are projected for over 76% of species used by the Southern Sotho, 71% of species used by the Xhosa and 74% of species used by the !Xóõ from the Kalahari region.

Rooting climate adaptation

In the future, already water-stressed countries in the region like Botswana are likely to become even hotter and drier and, ultimately, more water-stressed. The situation increases the urgency of implementing effective plans for increasing local resilience.

“Our results point to the vast pool of traditional knowledge of food systems that we could potentially use in regional adaptation responses,” Trisos says. “We need to look beyond conventional crops to the exceptional diversity of wild food plants.

The use of traditional knowledge (for adaptation) is potentially a key strength of African communities.”