Sunday, June 30, 2019

Rare Plants Inhabit Adirondack Ice Meadows

Now that the weather has finally warmed up, we can appreciate ice a little more. Among other things, ice greatly improves summertime drinks, and an icy watermelon is hands-down better than a warm one. And in this part of the world, ice also provides us with unique wildflower meadows.

Along stretches of riverbank in the Southern Adirondacks, rare Arctic-type flowers are blooming now in the fragile slices of native grasslands that are meticulously groomed each year by the scouring action of ice and melt-water.

Known as ice meadows, these habitats are few and far between in the world. They are found almost exclusively near the headwaters of rivers which originate in mountainous terrain; in New York State this includes the St. Regis, Sacandaga, and Hudson Rivers. In these habitats, ice mounds up along the banks to depths of between three and five meters each winter.

Obviously, such quantities of ice will compress the plant community on the shoreline. The ice also takes a long time to melt, leading to a truncated season with unusually cold soils for ice-meadow inhabitants.

For these reasons, as well as the fact that inundation kills the roots of most tree species within about ten days, native trees cannot develop in ice meadows. The groundcover species which do survive and thrive there are adapted to extreme short seasons. According to the SUNY College of Environmental Sciences and Forestry’s New York Natural Heritage Program, thirteen rare plants are found on New York’s ice meadows, though not all occur at every site.

Dwarf cherry (Prunus pumila var. depressa), New England violet (Viola novae-angliae), and auricled twayblade (Neottia auriculata) are among the plants a visitor might see. Personally, I’d like a glimpse of something called the many-headed sedge (Carex sychnocephala), but only if accompanied by a team of martial-arts experts. In addition to these boreal plants, other native wildflowers like tall cinquefoil (Drymocallis arguta), bastard toadflax (Comandra umbellata), and thimbleweed (Anemone virginiana) often add to the profusion of summer blooms in an ice meadow.

The processes which account for the formation of ice meadows are not completely understood. It was often thought that slushy ice called frazil was responsible for scouring the riverbanks, but the deposition of frazil ice is not particularly violent or forceful. Frazil is formed when turbulence entrains very cold air – usually below 16 F (-9 C) – into near- freezing water. This results in rod-shaped ice crystals that often coalesce into loose clumps. When they float at the surface they look much like chunks of snow.

An unusual feature of frazil as compared to solid ice is that it can get sucked under the ice covering a stretch of river and “hang up” on a rock, snag or other feature. This can quickly lead to a “hanging dam” in the water under the ice which can drastically raise the water level in a matter of hours.

Frazil ice is known to occasionally form in many rivers and good-size streams in NYS, but it only accumulates enough to alter riparian habitat in a few locations. The shape of a riverbed, rate of elevation change, and size and nature of its watershed probably also influences the genesis of ice meadows.

North Creek resident and lifelong naturalist Evelyn Greene has spent countless hours observing ice meadows, especially during winter. She suggested to me that the scouring action of water, a force which after all has carved gorges such as the Grand Canyon, is mainly responsible for the ice meadows. She says that ice sometimes does get pushed along the riverbed, but this happens rarely. She points out that being under flowing water for more than a month per year leaches out nearly all available nitrogen from ice-meadow soils. Since the plant community is one which is common to the thin, nutrient-poor, acidic soils at high elevations, I would call that a confirmation.

Greene also notes that ice-out conditions have changed in recent decades, with multiple significant thaws during winter becoming common. She says that most often now there is a thermal ice-out, and that dynamic ice-outs, where ice may get pushed along the riverbed, have become the exception.

An Adirondack Park ice meadow can be seen from Warren County’s Hudson River Recreation Area. Other ice meadows can be found in the Silver Lake and Hudson Gorge Wilderness Areas.

The New York Natural Heritage Program lists “trampling by visitors” as a threat to ice meadows, so please be careful not to step on any vegetation.

In a region characterized by long winters, it can be refreshing to enjoy mountains of ice, or at least the results thereof, in short sleeves.

Photo courtesy Evelyn Greene.

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Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.You can read more of his work at or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World

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