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Healthy forests, healthy people – and healthy ticks?
The hills are alive in Northwest Connecticut, but it’s not all birdsong and snowdrops: the blacklegged tick has shaken off its winter torpor, and now crawls in droves through the understory, spreading disease and myths in equal measure.
Dr. Scott Williams, Chief Scientist and Head of the Department of Environmental Science and Forestry at the Connecticut Agricultural Experiment Station (CAES), a state organization spearheading research on tick-borne diseases, dismissed two commonly held misconceptions about the tiny, dangerous insect: “They don’t fly. They don’t drop out of trees.” Williams advised that rather than worry about the branches overhead, think low and keep your ankles covered. “They crawl up from the ground for the most part, or [from] a few inches off the ground.”
Demystifying tick behavior and pathogen transmission yields surprising insights into how to manage disease levels in our region: in a healthy forest, more ticks might actually equal less disease, Williams explained.
Debunking Myths
Blacklegged ticks (also widely known as deer ticks) and Lyme disease are commonly misunderstood components of the New England forest, starting with the illness’ origin story. Conspiracy theories abound speculating where it began, with an especially persistent and oft-debunked claim that it leaked from a government research facility on Plumb Island.
But reputable research has shown that the disease has been circulating in the northern hemisphere for millennia. One of the bacterium responsible for causing Lyme disease, Borrelia burgdorferi, was detected in Ötzi the Iceman, a 5,000 year-old mummy found in the Eastern Alps in the 1990s. A study conducted by the Yale School of Public Health in 2017 traced B. burgdorferi back to North American forests of 60,000 years ago, meaning the bacterium was resident in our woods long before the earliest human inhabitants arrived.
Closer to home
Deer ticks and Lyme disease are as Connecticut as New Haven pizza, with one of our picturesque coastal towns lending its name to the ailment after a cluster of cases there in the 1970s lead to its identification as a unique condition. The state remains positioned in the very heart of tick country, and the Icebox of Connecticut, which previously benefitted from the protection of its harsh winters, is losing its defenses as the cold season continues to warm up.
“We’re not trying to scare people from being outside, we’re trying to educate people on when the various stages [of ticks] are active – what’s tick habitat and what’s not,” Williams said. For instance, a field of high grass, commonly regarded as a tick haven, is actually largely inhospitable to the bugs, as they desiccate quickly in a dry environment. “That’s kind of a desert for ticks,” Williams explained.
The most “ticky” habitat “is really that edge where your lawn meets the forest,” he said, and when it comes to getting bitten, it’s often a matter of timing.
When to watch out
While adult deer ticks are active now, Williams explained that May, June, and early July are the months when most infections occur since that’s when both humans and the nymphal stage of deer ticks are likely to be active outdoors. Although the adult ticks wandering the undergrowth and brush now can certainly transmit the pathogen, it’s the nymphs that are “the really problematic guys,” Williams said, in part because they are small and hard to detect, and also because in spring, “human activity and tick activity in the nymphal stages coincide.”
A white-tailed deer in the forest. Photo: Mike Zarfos
Host competency and the dilution hypothesis
Active ticks, active humans, and an abundance of both yield higher bite rates, thus contributing to more infections. However, Williams explained that the species present in an ecosystem can have significant impacts on the spread of tick-borne pathogens to humans.
A surplus of white-tailed deer upon the landscape, for example, is often thought to correlate to more tick-borne illness. While a large deer population will often support a high concentration of ticks, deer are a “dead-end host” for the bacterium, meaning they don’t transfer the pathogen back into the ticks.
Mice, however, are “competent hosts.” The concept of host competency is the ability of a reservoir host species (animals that carry and spread disease-causing pathogens) to infect the ticks with pathogens, which small rodents are highly adept at whereas larger animals are less so. When deer are plentiful on a landscape, “you typically have high tick abundances with lower infections with the various pathogens,” Williams said.
The reservoir host species of B. burgdorferi that actually infects the ticks with the pathogen are small rodents, especially the white-footed mouse which is common to the Litchfield Hills. When fewer deer, and other medium sized mammals, are available, Williams explained that the ticks will then be forced to feed primarily on mice, which will support a smaller population of ticks within which the pathogen is much more concentrated.
CAES team conducts Lyme disease research with mice in Woodbury. Photo: Mike Zarfos
Healthy forests, healthy people
In a healthy ecosystem with a spectrum of animal species, ticks aren’t forced to rely on these highly competent hosts for a blood meal. Williams explained that this scenario, in a species-diverse forest, describes what disease ecologists call the dilution hypothesis: “with a diversity of animals, you’re going to see less infection in the ticks because they have so many options to feed.”
The loss of forest diversity can have the opposite effect, Williams said, which is happening across the Northeast due to development and the incursion of invasive species. Several years ago, Williams conducted research on the correlation of Japanese barberry, an invasive shrub, with tick populations; some of the work was done at Great Mountain Forest with the help of GMF forester Jody Bronson. The study found that the dense tangle of undergrowth created by the proliferation of the shrub caused a humid microclimate that not only provided great tick habitat, but enabled them to remain active throughout the day.
Normally, the moisture-dependent ticks might be inactive under a pile of leaves during the heat of the day, Williams said. But the microclimate created by the “monoculture” of invasive brush growth means ticks continue looking for a host “pretty much 24 hours a day.” He clarified that this was not specific to Japanese barberry, but any plant that grows in a monoculture tangle, “which is pretty much what invasives do in our neck of the woods.”
“What we’re trying to push is a healthy, diverse forest, and that’s very applicable to Great Mountain Forest,” Williams said. The goal, he continued, is responsible management: “If you have a healthy, diverse, well-managed forest, you’re going to have a diverse array of wildlife, and as a result you’re going to have a healthier tick population with lower pathogen infection. That’s kind of the bottom line.”
Where Are Our Winters
Winters in the Ice Box of Connecticut have been getting warmer, and this one is no exception. While the mercury did drop at times, data from the GMF weather station through February this year reveals a familiar trend: above-average temperatures and below-average snowfall.
GMF Property Manager and Head Weather Observer Russell Russ said that “the figures tell a pretty good story— or a bad story if you love snow.” Since 1998 annual (especially wintertime) temperatures have increased at the GMF weather station, while snowfall totals have decreased.
These trends have impacted long-cherished winter recreation opportunities in the Northwest Corner in tangible ways, shortening the Nordic and alpine ski season and eliminating ice fishing on certain lakes in especially warm years. Climatic changes have also had profound impacts on the ecology of forests—many of which researchers are just starting to understand.
The weather station and warming winters
The GMF weather station, known as Norfolk 2SW, is a National Weather Service (NWS) Cooperative Weather Observer Station. It is one of 165 stations in Connecticut which the NWS uses to catalog weather records, and has been used to record weather observations every day since January 1, 1932.
Russ is GMF’s lead weather observer, a position he took over from his father, Forest Manager Darrell Russ, in 2003. He has contributed an additional 22 years of weather data to GMF’s and the NWS’ records, building on the over five decades of readings provided by his father.
After Russ compiled data from the 93 complete annual records since 1932, he found that 10 of the 12 warmest winters on record at Norfolk 2SW were logged since the year 2000. 2024 holds the title as the warmest with an average annual temperature of 48.6ºF, 3.6ºF above the 89-year average of 45ºF from 1932-2020. 2023 and 1998 are tied in third place at 48.4F.
While this winter may have felt frigid at times compared to recent years, the data indicates that monthly averages have remained high, ranging from 5.3ºF warmer than normal in November to 0.2ºF above average in January.
No snow, no grow?
Temperatures this winter have at least stayed closer to normal than many recent years, however snowfall has lagged far behind. Only 38.4 inches have accumulated as of March 1, while the weather station normally averages 65.1 inches through February.
GMF weather observer Russell Russ poses after 24 inches of snow fell in October 2011.
Low snow years are becoming increasingly commonplace at GMF, which on average receives nearly 90 inches of snowfall. Last winter totaled only 45.5 inches of snow between October and May, making it the 6th least snowy winter in Norfolk 2SW’s records, while all similarly low-snow years have occurred in the past several decades. By contrast, only one of the top 15 snowiest years in Russ’ data archive came after the early 1980s – a particularly snowy 1995-1996 season.
Lower snow yields and warmer temperatures mean that a persistent winter snowpack blanketing the forest floor in Northwest Connecticut may be reduced or eliminated entirely, a scenario which could have negative impacts on forest ecosystems. Research within the past two decades has highlighted how the cold season is “functionally important” to the growing season, according to a 2012 study on snowpack decline and its repercussions in a New Hampshire Forest.
Long thought to be a “dormant season,” winter sees the active continuation of nutrient exchange between roots and soils, a process aided by the insulation of a robust snowpack. Kept at or above freezing, nutrients such as nitrate and phosphate circulate within root systems, keeping trees healthy. A thin or absent snowpack combined with cold temperatures, which has occurred extensively this winter, can freeze soils and interrupt this process. Key species of the New England forest, such as sugar maple and yellow birch, are particularly susceptible to deep freeze-thaw cycles like those of December and January this season. According to a more recent study on the impacts of climate change on winter-dependent biomes, a “deep and long-lasting snowpack drives water and nutrient availability at the start of the growing season.”
Another paper on increased winter runoff events emphasizes that “the synchrony of spring nutrient availability and nutrient uptake” – meaning when spring thaw and plant growth occur simultaneously – is important for natural ecosystems. The paper also finds that midwinter thaws “pose an ongoing and increasing risk to water quality in snow-covered regions,” but that further research is required to identify specific dangers.
Impacts from reduced snowpack and warmer temperatures extend beyond plants to which animal species may thrive in our woodlands. In several instances, white-tailed deer have been shown to succeed in landscapes with reduced snowpack, replacing moose as the dominant browsing species in winter. Different herbivores favor different tree species, so a shift in which herbivore is more common can lead to cascading impacts on forest plant communities, according to the 2024 paper.
Finally, the livelihood and function of a working forest may be altered by diminished snowfall. The 2012 study predicts the maple sap-harvesting season to be shortened by half and the sap yield reduced “by 20% or more” by the end of the century in New England. The paper also anticipates an earlier and prolonged mud season, potentially affecting winter timber harvests which benefit from frozen and snow-covered roads to protect soils from compaction and erosion.
Ice out
Reduced ice cover on lakes and ponds is “a key indicator of changing winter climate globally,” states the 2024 study, and this is consistent with GMF’s water bodies. Russell Russ has tracked ice-in and ice-out dates since 2000, and maintains that lakes and ponds are freezing over about two weeks later than in “the old days,” and melting about two weeks earlier.
Tobey Pond with open water in January, 2025. Photo: Alec Linden.
Northern lakes normally experience “inverse stratification” during normal ice cover, when colder water rises to near the surface ice and warmer water sinks beneath. Alternatively, when ice is absent from the surface, these lakes often stratify with warmer water layering above cooler water. Reduced ice cover disrupts the normal circulation of nutrients throughout the lake as the seasons change.
The 2024 study notes that these changes may affect phytoplankton, which serve as the base of the aquatic food webs. One report shows that a specific species of phytoplankton, the diatom Discostella stelligera, has become increasingly abundant – even dominant – in northern lakes. Diatoms are an important component of lake food chains, so the drastic shift in species profile may have cascading ramifications for these ecosystems.
The aquatic life of our lakes is dependent on ice cover, just as the flora and fauna populating the forested landscapes of the Northwest Corner rely on snow cover. As these features of the landscape melt away, researchers are realizing that many surprises are in store as the cold winters of memory fade into the past.
