Managing Forests for Water: Challenges in the Anthropocene

Forests are experiencing rapid changes in climate, disturbance regimes, invasive species, human population growth, and land use, and new management approaches may be required. Photo by Sarah Farmer, U.S. Forest Service.
Forests are experiencing rapid changes in climate, disturbance regimes, invasive species, human population growth, and land use, and new management approaches may be required. Photo by Sarah Farmer, USFS.

Humans are enmeshed in an ancient and intricate relationship between forests and water, and as the impacts of climate change are felt across the globe, the relationship will become increasingly important.

A special issue of the journal Forests, titled Forest Management and Water Resources in the Anthropocene, examines the interactions between forests, water, climate change, and humans. The issue was developed and edited by U.S. Forest Service Southern Research Station (SRS) scientists Ge Sun and Jim Vose, and covers topics such as soil moisture, wildfire, streamflow, land use, and modeling studies. The special issue includes an article Sun and Vose wrote on how emerging global threats interact with forest water resources and ecosystems.

“Decades of research has provided a depth of understanding on the relationships among forests and water,” says Vose. “However, the rapid changes in climate, disturbance regimes, invasive species, human population growth, and land use expected in the 21st century are likely to create substantial challenges for watershed management.”

The changes have been so swift and sweeping that a number of scientists agree that Earth has entered a new epoch, the Anthropocene. The proposed epoch is dominated by humans, and characterized by human impacts to the environment, including drastic increases in the amount of atmospheric carbon dioxide and subsequent changes in climate.

“Changes in the earth’s climate have significant impacts on forest water resources. Climate change is hydrological change,” says Vose, who is a project leader at the SRS Center for Integrated Forest Science. Climate change affects the amount of rainfall and snowfall that forests receive, and also affects the timing of precipitation. In addition, extreme weather events – and the very high or very low stream flows that they cause – are becoming more common.

Climate change also directly affects how plants grow and use water, and could indirectly contribute to fire, insect outbreaks, tree death, and sea level rise. The interactions between these changes are complex and very difficult to predict.

Forested watersheds have been studied for decades, but the knowledge and tools developed in the past were based on historical observations that may not reflect the future. “A key question is whether existing strategies for protecting water resources will be relevant to future conditions,” says Sun, who is a research hydrologist at the SRS Eastern Forest Environmental Threat Assessment Center. “Managers need flexible tools that account for thinning, prescribed fire, and other management strategies.”

Forested watersheds are a critical source of clean drinking water. Land managers, city planners, and policymakers across the globe are working to ensure that people – especially those who live in large cities – have adequate and reliable water resources. The world population is projected to swell to 9.6 billion by 2050, and most of that growth will be in cities.

Across the globe, about half of all forests have already been cut down as a result of urbanization and human population growth. Each year, an additional 16 million hectares — over 39.5 million acres — of the remaining forests are lost. At the same time, people are realizing the value of forests as sources of clean water, food, medicines, timber and other products, and recreational, cultural, aesthetic, and spiritual benefits. The economic value of ecosystem goods and services provided just by tropical and temperate forests is estimated at more than $23 trillion each year, and on a global scale, forests store almost half of all terrestrial carbon.

Over the coming decades, decisions about whether to manage forests for drinking water or for carbon storage will require careful consideration of the trade-offs. “The forestry community is facing large global environmental and socioeconomic challenges, and it will be difficult to ‘manage’ our way out of threats,” says Vose. “New approaches that focus on anticipating and guiding ecological responses to change are urgently needed.”

Read the full text of the article.

For more information, email Jim Vose at jvose@fs.fed.us

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