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Don’t Blame Bambi

Zoe Clemmons, Rocky Mountain Research Station
April 28, 2020

Deer grazing in West Virginia forest opening.
Deer grazing in West Virginia forest opening. USDA Photo/Brice Hanberry

Deer often get blamed for declines in forest structure, particularly oak hardwood and pine forests of the Eastern United States, mainly because of their propensity to munch on tree seedlings.

However, scientists Brice Hanberry, of the USDA Forest Service’s Rocky Mountain Research Station and Marc Abrams, from Pennsylvania State University, decided to explore whether white-tailed deer populations are a key driver in changing eastern forests. Based on their research, it appears that deer are not the culprits.

At the local level, deer have the potential to decrease survival, growth, and reproduction of tree seedlings and saplings. However, broader trends in eastern forests are entirely different.

Ecologists recognize that eastern forests are changing from historic conditions and are becoming more densely packed with trees. Increased deer densities are often blamed for forest declines, while studies show trees are capturing more growing space and replacing grasses, herbs, and forbs. This conundrum piqued the interest of researchers.

So, what is the relationship between deer and trees at the larger scale?

Rather than focusing on seedling survival, Brice and Marc used stocking – which measures how many trees are in an area, the diameter of trees, and the space a tree uses – to help assess impacts of browsing by white-tail deer on forest structure.

Using tree survey data, they compared forest stocking data to deer population densities from over 2000 counties throughout the eastern U.S. Additionally, using current tree surveys and historical records they examined trends in tree species preferred by deer.

Forest in Missouri after thinning by prescribed fire, demonstrating a more open canopy and typical historical forest structure.
Forest in Missouri after thinning by prescribed fire, demonstrating a more open canopy and typical historical forest structure. USDA Photo/Carter Kinkead

Researchers found white-tail deer have not reduced tree densities at landscape scales across the Eastern U.S. In fact, they propose other management influences and fire exclusion have had bigger impacts. 

This research prompts us to ask new questions about hunting management and forest wildlife habitats. Eastern pine and oak forests used to be more open with herbaceous plants in the understory. These understory vegetation layers provided habitat for birds and pollinators. Increased stocking can change this habitat, leaving less room for these creatures to make their home.

Additional research may help find answers to what is driving forest change and offer new ways of looking at forest health. Also, further research can propel scientists and land managers to look for new solutions for managing healthy forests--getting Bambi off the proverbial hook.