Had things gone another way, Vermont would be a vastly different ecological community today. It’s likely that continued warming and increased precipitation would have brought other now-extinct species like the short-faced bear, giant ground sloth (Megalonyx spp.), and giant beaver (Castoroides ohioensis) into Vermont, just as it eventually would bring moose, white-tailed deer, and black bears. But things did not go that way, and within the first 2,000 years of humans arriving in North America over 35 genera (~50 species) of large mammals went extinct across the continent. The same pattern followed in South America. North America lost lions, cheetahs, camels, horses, and giant versions of everything from skunks to armadillos.
Alfred Russel Wallace wrote of these extinctions: “We are in an altogether exceptional period of the earth’s history. We live in a zoologically impoverished world, from which all the hugest, and fiecest, and strangest forms have recently disappeared…Yet it is surely a marvelous fact…this sudden dying out of so many large mammalia, not in one place only, but over half the surface of the globe” (from The Geographical Distribution of Animals, 1876). A century later, Paul Martin had more data and further concluded that in the absence of keystone megafauna species, the ecosystems of today are in a state of disarray. Their extinctions put a finality to the ecosystem changes that had started when megafaunal populations collapsed 14,800 to 13,700 ya. Trees like Kentucky coffeetree and osage orange (Maclura pomifera) relied on these now extinct megafauna for dispersal and scarification of their seeds (as did avocado with gomphotheres in South America). Absent their mutualists, the range and abundance of these trees has dwindled markedly. Without large carcasses to scavenge, California condors, dire wolves, and a host of land snails died off (a small population of condors survived). Mammoths grazed in the winter by using their tusks to scrape away snow and exposing low lying vegetation, which also exposed the soils to colder winter temperatures and deepened the layer of permafrost. Without large grazers trampling down vegetation and maintaining permafrost, the grasslands of the north were replaced by woody shrubs and conifers. The cold, dry conditions that dominated these boreal forests slowed the decomposition of the woody plant biomass, increasing fuel and resulting in more frequent and severe fires (source). Novel plant communities emerged in this strange land (where ash grew alongside hophornbeam, elm, spruces, and larches: source).
Archaeologists tend to fall into two main camps for the cause of these megafaunal extinctions: overkill (the hypothesis first put forth by the paleobiologist, Paul Martin that suggests overhunting by newly arrived humans caused a critical and irreversible decline in many large mammals) and a series of abrupt and rapid changes in climate. Both likely played a key role in the demise of gomphotheres, glyptodons, and stilt-legged horses (Haringtonhippus spp.), though which played the more dominant role is still up for debate (I tend to lean towards the overkill hypothesis).
When small bands of Clovis people first arrived in Vermont after the cold and dry Younger Dryas period, around 11,000 years ago, they were just in time to see the last vestiges of tundra retreat into Canada and up into our higher elevations. They also witnessed (or precipitated) the extinction of New England’s remaining Pleistocene megafauna and likely hunted whales and seals along the shores of the Champlain Sea which filled much of the Champlain Valley. Their population was small, nomadic, and sparse, likely less than 10 people per 100 square kilometers, and concentrated down in the Champlain Valley and Connecticut River Valley. These are the ancestors of the Abenaki, who have continuously occupied this land for 11,000 years. Their culture would shift and adapt as the climate, forests, and animals changed through the millenia.