Newswise — A collaboration of scientists has developed one of the first models to assign a dollar value to the loss or gain of species in an ecosystem. The new work offers an economic argument for preserving biodiversity. The findings were published Wednesday (April 5) in Science Advances.
“It’s long been thought that biodiversity is valuable, but it’s been hard to quantify that value in monetary terms,” said Bruce Hungate, lead author and director of the Center for Ecosystem Science and Society at Northern Arizona University. “We tackled this by blending models of ecology and economics to make explicit, quantitative estimates about the value of species richness for carbon storage, one of the many ways species in nature provide value to people.”
To build the model, the researchers first had to identify some measurable service of biodiversity that society has priced. While biodiversity provides many valuable services, concern about climate change has led economists to put a dollar value on the abatement of climate-warming carbon emissions (ranging between roughly $40 and $400 per metric ton). Now there’s a $175 billion global carbon market that pays for activities that remove carbon from the atmosphere.
Biodiversity could enter the game through a 4-billion-year-old form of carbon storage from plants: photosynthesis. Plants absorb carbon dioxide for energy and growth, storing the carbon in their leaves, stems and roots and later transferring it to the soil through decay. The key is to link biodiversity and carbon storage in a quantitative way. So researchers asked if changing the number of plant species in an ecosystem affects the amount of carbon that ecosystem stores over time.
The National Socio-Environmental Synthesis Center (SESYNC) convened the team of scientists, which included economists and ecologists. They analyzed data from two long-term experiments in Minnesota grasslands that measured how plant and soil carbon changed with the number of plant species in a plot. Modeling results over 50 years, they estimated the “marginal” increase in carbon storage, or how much additional carbon is stored for each species added to the mix.
They found that each additional species in a grassland plot increased the plot’s overall carbon storage, on average. One reason for this gain may be that new species fill different niches, yielding more overall growth.
With more species came diminishing returns in cumulative carbon storage. A change from five to six species stored almost 10 times more carbon than a change from 15 to 16 species, showing the biggest benefit came from adding species to the least diverse plots.
At small scales, such as one hectare, going from one to two plant species in a 50-year time period would store an additional 9.1 metric tons of carbon, potentially saving $804.55 per hectare based on a mid-range estimate ($137 per metric ton) of the social cost of carbon. At larger scales, cost savings could hypothetically be significant. For example, adding just one species to the 12.3 million hectares of cultivated lands restored to grasslands by the U.S. Department of Agriculture’s Conservation Reserve Program could save more than $700 million. The biggest cost savings come from restoring the most degraded, species-poor lands.
"This is one of the first studies to estimate the monetary value of species loss, since most studies of the monetary value of biodiversity have focused on habitat loss,” said Paul Leadley, professor at the University of Paris-Saclay, who was not involved in the study. "Demonstrating the monetary value of biodiversity for carbon storage is important for communicating with many policymakers, but biodiversity underpins many additional services such as wood production and recreation, and for some people, biodiversity has value that you can't put a price on."
The dollar amounts provided in the study are underestimates, because biodiversity confers value in many ways beyond storing carbon.
“Biodiversity means products like wood, food and fuel, and services like recreation, water purification and flood protection, all of which could be quantified using our approach,” Hungate said. “Money is a language that speaks, and showing the economic value of biodiversity underscores the importance of conservation and the policies that support it.”
While the value of biodiversity is more complex than just one economic measure, this new research takes a bold step toward understanding its value, he said.
Director, The Center for Ecosystem Science and Society