Article by Kelly French

If you work in the forest products industry or are a forest landowner or recreationist, odds are you have seen your fair share of white-tailed deer while spending time in the woods. There is a very large population of these deer in Maine and throughout the Northeastern United States – and their presence poses many threats to forest communities. One of the most significant and detrimental impacts of white-tailed deer is the effect of deer browse on understory vegetation and tree regeneration in Maine’s forests. As such, many landowners and forest managers are seeking efficient ways to reduce deer browse impacts on their lands.

Since red oak is a preferred food source for white-tailed deer, successfully regenerating red oak can be challenging when facing increased browse pressure from growing deer populations. Furthermore, climate change is driving shifts in suitable habitats for North American tree species, which may lead to increased competition for red oak seedlings from a variety of other species in the understory. As such, it is important to mitigate stress for seedlings whenever possible to encourage the recruitment of mature oak trees into the forest. To help inform potential mitigation strategies, over the last year, we studied the efficacy of large-scale fenced deer exclosures and a sheep-fat-based deer repellent called Trico* at reducing deer browse of red oak seedlings at the Holt Research Forest.

Pictures from left to right: fenced deer exclosures, transplanted red oak seedlings marked with pin flags for experimentation, Trico-sprayed red oak seedling in the Fall of 2021.

After transplanting 240 red oak seedlings to plots within HRF in 2021, we observed and measured them until the end of the summer in 2022 to quantify how well the deer browse-repellent Trico and the exclosures worked at reducing browse effects. We found that Trico was the most effective treatment – with only around 16% of seedlings showing browse by the end of the experiment, compared to control seedlings (which had no treatment) at 38.1% and seedlings grown in the fenced exclosure at 24.2%. While, in theory, fenced exclosures should prevent high rates of browse, we found they are easily damaged due to falling trees and debris, which can allow white-tailed deer in, along with other herbivorous wildlife.

Evidence of deer browse in control, fenced exclosure grown, and Trico-sprayed seedlings in July 2022.

Deer management is a complex ecological challenge that may require various interactive solutions in the face of changing climates and shifting tree habitats. If you want to learn more about Trico as a potential strategy for your property, please visit

Similar Posts