Forest Health Monitoring

FoHVOS staff began implementing our Forest Health Monitoring program in 2006 at multiple FoHVOS preserves, partner properties, and private lands throughout the Hopewell Valley. To date, we have performed forest health monitoring methods at 23 properties. Additionally, the same protocols have been adopted and performed at many other sites statewide, providing a robust picture of New Jersey forest health trends in the last decade.

Field Methods

Designed to measure changes in native plants (favored by deer) and non-native plants (not favored by deer), our methods involve estimating native and non-native cover of trees, shrubs, wildflowers, and grasses. Our data allow us to analyze long-term trends in forest health in relation to deer overabundance and invasive species.

Our goal is to decrease the harmful ecological impacts that overabundant deer have on forest health. Comparing our measured native plant cover before and after initiation of deer management, we see a strong positive relationship between the amount of native cover at a given site and the amount of time since deer management began. These data suggest that our management programs have been beneficial for forest health at our preserves. While we have had a positive impact on our preserves, this only accounts for a small portion of land. The bigger picture is that our deer management programs cannot have an effect at the broader level of all of Hopewell Valley.

Please reach out if you are interested in starting your own forest health monitoring or deer management program! We are happy to provide guidance and support.

Deer have favorite foods too—and they tend to be native plants!

Maple-leaf Viburnum is a favorite deer food. It is uncommon to find fruiting individuals in the Hopewell Valley because they are heavily browsed.

FoHVOS, Mercer County Park Commission, and independent botanists evaluate a vegetation plot.

FoHVOS actively conducts Forest Health Monitoring protocols at 15 sites in the Hopewell Valley, including FoHVOS preserves, other open space, and private lands. These sites have either very poor (less than 20%; red) or poor (21-50%; yellow) native cover. While conditions are improving as DMP’s continue, all sites have yet to reach the goal of 70% native cover

Trends in Forest Health

On average, native shrub cover has improved over time, partly in thanks to deer management programs. Still, most preserves have a long way to go until we can reach goals of 70% native cover. Below shows the change in percent native shrub cover for all monitored properties.

Above: Details of results at Heritage, Nayfield and Thompson Preserves—note that recovery is often delayed for many years before positive results become noticeable. For example, we began deer management at the Thompson Preserve in 2007, when native cover was only 13%. We observed a small decrease in native cover 5 years later, and it wasn’t until 2016 that we were able to measure a large improvement. It can take many years for land to recover from deer overabundance.