Invasive Species

February 2021

Invasive species can wreak havoc on ecosystems and ecological processes, but they are not going unchallenged.  This month we feature a scientist who has been fascinated by insects for his whole life, research that aims to improve detection by establishing how invasive species spread, and how 100 national experts partnered to author a comprehensive state-of-the-science synthesis on invasive species ecology and impacts.

Environmental Education

Forestcast artworkThe Forestcast podcast Season 1: Balance and Barrier is a special six-part series on one of the most significant environmental threats to our forests, and the scientists studying and combating these threats.

Listen and Subscribe

Featured Scientist

Nathan Havill

Nathan HavillAs a small child growing up in Michigan, Nathan Havill collected insects. Today, people from all over the world are sending insects to him to study – mostly adelgids, tiny insects related to aphids. As a Research Entomologist with the Northern Research Station’s lab in Hamden, Connecticut, Havill’s work focuses on the evolutionary history of pest insects, their host trees, and natural enemies.

Beginning with his Ph.D. dissertation, Havill’s research has addressed some of the fundamental unknowns about hemlock woolly adelgid: Where did the invasive forest insect that is decimating hemlock trees in the Eastern United States and Canada originate? Did it come from China or Japan via the Western United States? Through genetic analysis, Havill determined that hemlock woolly adelgid is actually native to the West Coast, that hemlock adelgids in the Eastern United States came directly from Japan and, astonishingly, originated with a single clone.

Havill defines a great day in the lab as “when you find an unexpected result that leads to exciting new ideas.” Studying adelgids has led to more than one great day for Havill, including the identification of a previously unrecognized species of hemlock tree on a tiny Korean island, and more recently, the discovery of a previously unknown species of fly that is an adelgid predator. Havill also led a team that discovered that some species related to balsam woolly adelgid were in fact genetic hybrids, helping scientists and land managers better understand their risk as pests.

While he would prefer that the HWA had never ventured outside of its native range, he is nevertheless fascinated by what has become his favorite insect group. “You might think they don’t look like much, but they have such strange and interesting biologies,” he said.

Havill’s interest in nature is a family tradition. His grandfather was once the chairman of the Council on Environmental Quality and president of the National Audubon Society. His wife is an evolutionary biologist, and their 6-year-old daughter’s career goal is currently to be a “butterfly scientist.”

Whether he is working in the field, on a hike with his family, or even watching television, insects are never far from Havill’s thoughts. For example, “…when I watch the Tour de France and the race reaches the Alps, the footage always shows bicycles racing through the forest,” Havill said. “Instead of watching the race, my mind often wanders to those forests and the fascinating insects they must harbor.”

More about Nathan Havill >>

Featured Research

Invasive Species Range Shift

Composite image showing four invasive species affecting US forests.The key to reducing the risk of invasive species spread lies in vigilant efforts at detecting insects early, but several factors make developing models for early detection of invasive species challenging. Research by a Northern Research Station scientist and collaborators was aimed at improving models predicting how invasive insects spread through invaded territory to facilitate early detection and control efforts.

“One of the critical assumptions in invasive species models is that the species is in equilibrium with its environment, but invasive non-native species are typically in disequilibrium with their environment,” said Research Entomologist Melody Keena.  “In addition, two forms of sampling bias can produce poorly predictive models.”

Scientists used different modeling approaches to guide surveying and monitoring areas under threat of invasion to aid in finding infestations as soon as possible. They also studied the distribution of a variety of invasive species to identify potential for range expansion by comparing the niche the species occupied in its native habitat versus introduced habitats. Research demonstrated that most of these species showed climatic niche shifts in their invasive range and had not yet fully occupied the available niche within the invaded range.

“Using this information along with some of the other spatial and temporal predictive models that were also developed through this research collaboration will improve our ability to predict the spread dynamics of invasive species in the infested range and design short- and long-term management strategies for the invasive species,” Keena said.

More information on Assessing Niche Shifts and Conservatism by Comparing the Native and Post-Invasion Niches of Major Forest Invasive Species. >>

Featured Partnership

Synthesis of Invasive Species Research for the U.S. Forestry Sector

The planning team for the invasive species stakeholder workshop that brought together dozens of leading experts to develop the outline, content, and process for the National Assessment.

Natural resource managers across the Nation now have access to the most cutting-edge science behind invasive species ecology and impacts, as well as practical management guidelines, thanks to a new comprehensive science synthesis, Invasive Species in the Forests and Grasslands of the United States.

Led by Northern Research Station Research Entomologist, Therese Poland and a team of 5 co-editors, along with over 100 national experts, including 75 Forest Service scientists, contributed to synthesizing the latest research on addressing the environmental challenges presented by invasive species. This included research from a wide range of natural science and social science fields.

Invasive species are among the top threats to biological diversity in the world. “With ever-increasing world trade and travel, the introduction and establishment of invasive species has also increased, wreaking havoc on ecosystems and ecological processes.” states Poland.

The synthesis includes input from nongovernment organizations, academic institutions, professional organizations, private corporations, and state and federal agencies representing public, private, and tribal interests.  “We brought experts from diverse fields of study together to understand how invasive species of all taxonomic groups – insects and pathogens, plants, vertebrates, and aquatic organisms – impact habitats in forests, rangelands, and grasslands of the United States,” explains Poland.  

As human behavior influences the processes that drive invasive species introduction and spread, a multi-disciplinary approach incorporating social and ecological dynamics is necessary for facilitating a better understanding of invasive species management. “Invasive species not only impact natural environments, they affect a wide range of ecosystem services that underpin human well-being,” said Vanessa Lopez, Invasive Plant and Biological Control National Program Manager for State and Private Forestry. “This requires researchers to take a collaborative, multidisciplinary approach.”

This comprehensive review will be a valuable resource for scholars, policy makers, and natural resource managers and practitioners.

View or download Invasive Species in Forests and Rangelands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector >>

Last updated: 02/02/2021