How can we assess the impacts of invasive species in LIISMA?

What’s the difference between a tomato plant and knotweed? Well, many things– one is welcome in your backyard garden for delicious snacks, while the other is likely an unwelcome nuisance. Neither plant is native to North America, but tomato plants impact our health and economy positively and pose no ecological harm. Knotweed, on the other hand, presents numerous negative impacts; factsheets will tell you that this aggressive plant outcompetes native vegetation and increases soil erosion. Invasive species as a whole are defined by the negative impacts they pose to either the environment, economy, or human health. 

But how do researchers know those impacts? And when a new non-native species arrives on Long Island, how can we tell if it leans knotweed or tomato, with negative impacts, or neutral-positive ones? Our friends at the New York Invasive Species Research Institute (NYISRI) held a workshop last August discussing how scientists and managers can get at this question: the sentinel approach.

The sentinel approach is nothing new – it has been used for decades in biosurveillance, as trees were planted in areas where they did not originate and monitored to assess what insects might attack them. That data could then be used to prevent the introduction of those threatening insects. However, this approach of installing a sentinel organism in a set of chosen environments and tracking it through time has applications beyond pest surveillance.

Researchers with NYISRI and the Blossey Lab at Cornell University have used the sentinel approach in myriad ways, including to study deer browse pressure, the effectiveness of deer management methods, and the impacts of both widespread and emerging invasive species. How does it work?

Suppose we’d like to better understand the impact that holly osmanthus (Osmanthus heterophyllus) poses on the environment. We already know that this species, still in the horticulture trade, escapes from backyard plantings into natural areas on Long Island– but what impact is it having once it’s there? We can start by assessing a common assumption that invasive plants outcompete native ones. Choosing a few study locations that contain holly osmanthus, we can plant native plants strategically around holly osmanthus, and track those individual native plants over years. Measuring survival, height, and other factors specific to the native plants, we can gather real data on the impact of one emerging invasive species on the ecosystem.