Trees all over the world have commercial value as suppliers of food, wood, and other marketable products. However, they are also enormously important in terms of supplying ecosystem services that benefit humans and other living organisms. Their “hidden” value lies in providing such essential functions as sequestering and storing greenhouse gases, filtering pollutants from the air, adding aesthetic beauty and recreational potential to landscapes and providing habitats for countless other species.
Newly published research asks how the non-market value of trees in the U.S. (excluding Hawaii and Alaska) compares to their commercial value, and whether the tree species that provide the greatest benefits are under significant threat due to climate changes. The authors of the article in the open-access journal PLOS Sustainability and Transformation, include Jeannine Cavender-Bares and Stephen Polasky from the University of Minnesota, St. Paul, U.S., and their colleagues.
Previously, the service value of the trees growing in forests and plantations in the U.S. was not known. However, the concept that trees provide ecosystem services to people allows researchers to quantify the value of these services in monetary terms. The researchers decided to synthesize existing sources of data to assess the annual net monetary value of five key ecosystem services that are provided by 400 species of trees across the U.S.
They considered only the value of climate regulation through carbon storage, the value (in terms of human health benefits) of filtering particulate matter from the air, and the value of producing wood products, food crops and Christmas trees. Spatially explicit information, by species, was available for these five ecosystem services.
The researchers quantified the net value of these five tree-related ecosystem services by calculating the value of benefits provided and subtracting the direct costs incurred to produce these services. In addition, they mapped the regions where trees are most threatened by pests and pathogens, climate change and the threat of more frequent fires. In this way they were able to identify locations across the U.S. where the services provided by important tree lineages are likely to be most threatened in future.
The researchers found that, between 2010 and 2012, the value of these five ecosystem services generated by trees totaled $114 billion annually. Carbon storage in tree biomass made up 51 percent of the net annual value, while preventing human health damages via air quality regulation contributed another 37 percent of the annual value. The remaining 12 percent of the net annual value came from provisioning services.
Trees in the pine and oak families were the most valuable, generating $25.4 billion and $22.3 billion in annual net benefits, respectively. Trees in these two lineages are widely distributed across the U.S. and occupy a diversity of ecological niches. Pines were most valuable because of their wood that fetches a high price and is used in the manufacture of many different products. Oaks, on the other hand, were most valuable in terms of providing climate and air quality regulation services.
Interestingly, trees in the U.S. provided more value in terms of their climate and air quality regulating services than they did in terms of commercial products. However, the majority of the tree species face threats from climate change, and populations will find themselves outside the range of tolerable environmental conditions in future, as the climate alters. In addition, the species most valuable for carbon storage will be most threatened by increasing fire frequency and the most valuable tree species overall will be most threatened by pathogens and pests.
“The fact that tree lineages have evolved to inhabit different ecological niches across the continent is important for sustaining the ecosystem services that we depend on for our life support systems,” said Cavender-Bares. “These benefits from trees, however, are increasingly at risk.”
“Our research team found that climate change threatens nearly 90 percent of tree species, while pests and pathogens put 40 percent of the combined weight of all U.S. trees at risk. We also found that the species and lineages of greatest ecosystem service value are the most at risk from pests and pathogens, climate change, and increasing fire exposure.”
The study had several limitations that likely contributed to an undervaluation of ecosystem services since the researchers did not have access to data for many ecosystem services such as erosion control, flood regulation, and shade-related energy savings. Future studies may provide more accurate estimates of the monetary value of these benefits.
“This study shows that the ‘hidden’ value of trees – the non-market value from carbon storage and air pollution filtration – far exceeds their commercial value,” said the researchers. “Sustaining the value of trees requires intentional management of forests and trees in the face of myriad and simultaneous global change threats. Our study provides information and an approach that can contribute to precision forestry practices and ecosystem management.”