Are Roadsides a Safe Haven for Woody Plant Encroachment?

roadside with trees growing in ditch

Nebraska has nearly 96,000 miles of roadways throughout the state. A mixture of county, state, and federal entities maintain the corridors that service the state’s 531 municipalities across its 93 counties. The Nebraska Department of Transportation actively manages invasive woody species on state highways, while many rural roads in Nebraska are managed by counties or private landowners and receive sporadic invasive tree management.

Biome-level attention to woody encroachment was slow to develop. However, major advancements in understanding and modeling the spread are providing new tools for natural resource managers to protect grasslands. Utilizing resilience theory, we can model varying outcomes that may help bring resources to address this issue to the appropriate scale.

How We Apply Resilience

Lessons from resilience theory tell us that landscapes are complex and don’t exist in isolation. When attempts to mitigate invasive or problematic species occur in patchworks (i.e., only on state-supported highways), it becomes of matter of responding to a symptom without addressing the underlying condition. This isn’t just ineffective financially, the continued encroachment of problematic species over time and space (resilience slow-changing variable), an entire landscape can be pushed to its limits.

Assessing the return on investment for such a reactive approach is increasingly important. When we talk about protecting grasslands on a large scale, we need to calculate how much funding is available, how efficiently can it be utilized, and what is the long-term funding commitment? These answers lie at the heart of addressing woody plant encroachment: a landscape-level approach.

What We Learned: Landscape-level Approaches

Applying techniques from biology, we have been able to reveal not only how juniper species spread but the conditions in which it thrives. Eastern redcedar seed, for example, has been shown to travel anywhere from 650’ to over .5 miles through bird dispersal. Using these as guides, we went to work assessing juniper encroachment in a 15,000-acre area in the Denton Hills grasslands in southeast Nebraska.

Assuming that all resources were targeted to address privately-owned fields, which were kept clear of all reproducing cedar trees, there still would exist significant habitat suitable for seed-producing eastern redcedar trees. This means that long-term, returns-on-investment in grassland and forest management are much lower. It also means that grassland recovery efforts are increasingly problematic because there is no coordinated effort to eliminate seed sources within the tree’s dispersal range.

What is Next?

In natural resource management, coordination of activities is essential to achieving practical on-the-ground results. Because of the total amount of right-of-way corridors in the state, this lesson applies here. Developing a coordinated approach among private landowners, counties, and state is part of the equation for reducing the vulnerability of grasslands and forests to eastern redcedar pressure.

Read More About Our Research