Research
Studying the 55 acres we protect
The Demarest Nature Center is a 55-acre preserve of meadows, forest and wetlands in the middle of a suburban borough — which makes it a useful place to study how a small woodland holds up under pressure. This page collects the research we publish about the preserve, along with the interactive tools that go with it.
Deer Population
The animal you are most likely to spot at the nature center is the white-tailed deer. DNC trustees estimate between 30 and 50 deer living within our 55 acres — roughly 135 to 225 deer per square kilometer. Research compiled across multiple forest studies finds that a forest understory can only regenerate at densities below about 10 deer per square kilometer.
The understory — the layer of shrubs, wildflowers and saplings closest to the ground — is where much of a forest’s biodiversity lives, and it is also where deer do most of their foraging. At current densities, seedlings are eaten before they can take root. The full article traces what follows from that:
- The pollinator problem. The wildflowers and low shrubs deer eat are the early-spring food supply for bees and butterflies. In heavily grazed forests, bumblebee visitation drops measurably.
- The front yard effect. The browsing does not stop at the preserve’s edge. Hydrangeas, hostas, arborvitae and daylilies are favorites, and even “deer-resistant” plantings are no longer a sure thing.
- Lyme disease. Deer are the primary reproductive host for the black-legged tick. New Jersey ranked fourth in the nation for Lyme disease cases in 2023, and Bergen County records confirmed cases every year.
- Road safety. Bergen County consistently ranks among the top New Jersey counties for deer-vehicle collisions, with hundreds of crashes recorded each year.
- What comes next. Ecologists call this an overshoot. Left unmanaged, the herd settles at a permanently degraded equilibrium — but with effective management, studies suggest meaningful vegetation recovery is possible within a decade.
The Interactive Model
To see how those pieces fit together, we built a working simulation of the preserve: Demarest Deer Population — Interactive Explorer. It is the page the QR code in the Summer 2026 newsletter points to.
The model tracks two stocks — the size of the herd and the quality of the vegetation — and lets you move six sliders to see how they interact over time: starting herd size, birth rate, natural death rate, managed removal rate, vegetation regrowth rate, and how much browsing damage each deer does. Set the removal rate to zero and the herd drifts toward a degraded equilibrium where the vegetation never recovers. Raise it, and both the herd and the forest floor find a healthier balance within years rather than decades.
Three tabs: Simulation for the sliders and charts, Analysis for the feedback loops and parameter sources, and Model Structure for a diagram of how the stocks and flows connect.
The model runs entirely in your browser — nothing to install, and it may take a few seconds to load the first time.
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Our research and feature stories are published twice a year in Demarest Nature News. Past issues are free to read, and members receive every issue.