Soil contains one fourth of the global carbon pool. It is also the most biologically diverse component of our planet with a wide array of living organisms of different sizes whose functional value includes cycling of nutrients and soil structure modifications that influence soil fertility and water retention, among others.
These attributes are telling of the potential and significant role that soil plays with regard to increasing soil carbon storage and reducing carbon emissions, both contributing to mitigate climate change; as well as increasing food production. Unfortunately, the role that soils play has not been well recognized and valued enough to feature prominently as other elements such as forests and agriculture in climate and environmental debates.
To raise this issue and bring evidence to the fore, ICRAF’s scientist, Dr Edmundo Barrios led a session on Plant-Soil Feedbacks and Adaptation to Climate Change at the 8th Ecosystem Services Partnership conference.
Dr Edmundo noted that significantly more effort and attention is focused on above-ground biodiversity and its management, while ignoring the below ground biodiversity which drives essential ecological functions benefiting life forms. “New molecular tools are increasingly showing us that what we see above the soil in terms of biodiversity is just the tip of the iceberg, a huge biodiversity lies belowground,” said Dr Edmundo. “without the functions provided by soil organisms, life would become unsustainable for different plants, insects, animals, -even human-beings.”
Using research conducted in agricultural landscapes in Eastern Africa, Dr Edmundo explained various biological functions of the soil ecosystem, and raised concern that these functions were increasingly being undermined by practices such as agricultural intensification that solely depends on fertilizers and other agrochemicals to enhance soil fertility and production. “This is because with increased agricultural intensification comes associated a reduced biological capacity for system self-regulation and this makes agricultural systems more vulnerable to environmental changes” he said. He recommends including trees with different characteristics in agricultural landscapes as they provide a sheltering role to different types of soil organisms, particularly during periods of climatic stress, thus protecting the functional diversity required to resume ecosystem functions once the stress period has concluded.
Dr Katarina Hedlund of Lund University, Sweden further expanded on this argument with evidence from several countries across Europe. She emphasized the fact that ‘belowground natural capital shapes aboveground diversity and ecosystem functioning.’ Dr Katarina said that considerable effort had been made in their study to identify and classify the different species important for soil functions and that these species were declining on soils where extensive and intensive crop and animal rotation was practiced. This, in-turn, leads to loss of soil carbon and nitrogen, followed by lower yields. “The loss of these components cannot be replaced by chemicals and fertilizers which instead have a long-term effect of depleting soil nutrients and increasing resistance to pests,” she said.
Tree fed rain
During the session, Dr Meine vanNoordwijk said that linked to the issue of biological soil function is emerging evidence on biological rain generation, which is rain that comes from forests and trees. While this maybe a common known traditional fact among communities, Dr Meine said that the scientific community has long ignored it, claiming lack of data for evidence. But this is changing. “New evidence on credible mechanisms for forest and tree effects on rainfall is emerging,” said Dr Meine.
Explaining the concept in a newly published policy brief, Dr Meine and others explain that there is evidence to show that forests and trees can trigger rainfall by ‘releasing ice nucleating bacteria and volatile organic carbon compounds.’ However, systematic comparison between vegetation types and species has yet to be conducted. Observations made to this effect include cases where change in forest cover in one region has affected rainfall patterns in another.
According to Dr Meine, this evidence has implications for climate change discussions whose focus has been on the importance of forests for carbon at the international scale. “This evidence should prompt a shift in climate thinking and debates. With evidence that forests and trees are important for rainfall, it calls for discussions and agreements not just at the UN global level but even more important across regions,” he said.
Based on follow-up discussions, participants attending the session noted the interdependence of biological functions in the soil and trees, with Dr Meine highlighting that trees provide a buffer for soil and ground water.
And perhaps a key takeaway home message should be the importance of linking science with local knowledge in the management of ecosystem services.
Background information on the session
In the final session of ESP'7 in Costa Rica, soil biodiversity and functions was identified as a critical knowledge gap in the study biodiversity and ecosystem services. This year the Global Soil Biodiversity Initiative (GSBI) was invited to join forces with the Thematic Working Group 2 ‘Biodiversity and Ecosystem Services’ to start addressing this knowledge gap. The GSBI was formed at RIO+20 in 2012 to generate scientific knowledge, create awareness, and drive action towards the management of soil biodiversity to enhance ecosystem services.
A GSBI sponsored TWG2 session entitled 'Plant-soil feedbacks and adaptation to climate change' co-hosted by Edmundo Barrios and Katarina Hedlund (Lund University, Sweden) was held in ESP’8 at Stellenbosch, South Africa on Monday 9 November.