Scientists say that climate change is disrupting the biological cycles of plants and animals.
By Mike Lynch
Scientist Curt Stager walks along the edge of the woods, his flashlight shining into the shallow water of a leafy, roadside pool on a dark night in Paul Smiths. It’s late April, and he’s out looking for spotted salamanders, wood frogs, and spring peepers that have migrated to shallow vernal pools to breed. After poking around for a minute, he lets out an excited shout: “There’s a salamander! There he is! He’s early!”
In the water is a dark, four-inch-long creature with bright yellow spots. In the same pool not far away, wood frogs float on the surface. In another week, pools like this will be a filled with breeding frogs and salamanders, which will leave behind egg sacks that hatch into larvae.
Spotted salamanders spend most of the year underground, so seeing them is rare except during these annual breeding migrations. Their journeys are triggered by the first rains of spring.
The salamander migration is one of countless biological cycles that occur because of seasonal changes in sunlight, precipitation, and temperature, among other factors. Other cyclical events include the blooming of flowers, the budding of trees, bird migrations, the re-emergence of bears from hibernation, and the changing of leaves in fall. Often phenomena are synchronous, such as pollinating insects hatching at the same time flowers bloom.
The study of these seasonal phenomena is called phenology. It’s a field that is drawing attention these days, because scientists say that global climate change is altering nature’s clock and throwing phenomena out of synch, which could have serious consequences for flora and fauna and their ecosystems.
The Adirondacks’ migrating birds are among the wildlife that could be put at risk by phenological changes. At the Crown Point Birding Station, for example, early waves of yellow-rumped warblers sometimes return in spring before the hawthorn trees have budded. Gordon Howard, the banding station’s coordinator, said this is bad news for the warblers because their main source of food at Crown Point is the larvae of winter moths, which in turn rely on the fresh leaves of the hawthorns for sustenance.
“We came here last year, and the leaves weren’t even out on the trees,” said Gary Lee, a retired forest ranger and co-author of the guidebook Adirondack Birding. “Without those leaves on the trees, the food isn’t here for the birds.”
In some other recent years, Howard noted, the insects have hatched before the warblers returned. Howard, who has volunteered at the station since 1984, just started noticing these changes a few years ago.
Wildlife Conservation Society ecologist Michale Glennon and her intern Madeleine Rubenstein reviewed the scientific literature and found plenty of evidence that timing mismatches such as Howard has observed are affecting birds in Europe (where more research has been done), and Glennon believes similar changes are likely occurring here.
In a report issued in January, Glennon and Rubenstein say bird migrations are believed to be triggered by seasonal cues at their winter grounds, such as day length and temperature. Yet these cues offer no information about the conditions on their breeding grounds. And different parts of the globe are being affected differently by climate change.
Glennon said birds that travel the farthest are believed to be most vulnerable. Long-distance migrants that breed in the Adirondacks include the yellow-bellied flycatcher, palm warbler, Tennessee warbler, and the olive-sided flycatcher. The flycatcher has one of the longest migrations of any bird, spending its winters in South America.
“The thought is if they are somewhat evolutionary-constrained in terms of when they’re coming back, there’s a possibility that they get here too late because other factors that have controlled their food sources have already occurred, like it got warm earlier and therefore the bugs they needed [hatched already],” Glennon said.
Although birds probably adapted to disruptions in the past, those changes were gradual. It’s the pace of change occurring now that has scientists worried.
“Birds have adjusted for millions of years,” Howard said. “It’s like, can they adjust fast enough? Can they adapt fast enough?”
Scientists say climate change has been occurring for at least a century. Between 1895 and 2011, average annual temperatures in the Northeast increased by nearly two degrees Fahrenheit and the average annual precipitation increased by about fi ve inches, according to the 2014 National Climate Assessment.
Temperatures are expected to rise faster this century. If carbon-dioxide and other greenhouse gas emissions continue to increase, a warming of 4.5 to ten degrees Fahrenheit is projected by the 2080s. If current emission rates are reduced substantially, the temperature is projected to increase three to six degrees.
Ezra Schwartzberg, an entomologist, is one of the many scientists trying to determine what such a drastic rise in temperature will mean for plants and animals. He is the manager of Intervale Lowlands, a private nature preserve outside Lake Placid where he has begun monitoring phenological changes. His work at Intervale builds off his graduate work.
At the University at Wisconsin at Madison, Schwartzberg studied the relationship between emerging forest tent caterpillars and birch and aspen trees in Wisconsin and Minnesota. The research on the species—which are found in the Adirondacks as well—took place over two years starting in 2011. The caterpillars lay eggs on birch and aspen twigs. After the insects hatch, they feed on emerging buds to survive.
“They don’t have the option to crawl down that tree and crawl over to another tree and start eating something else,” Schwartzberg said. “They rely on that food source being right there where they need it.”
Using a controlled environment, Schwartzberg exposed the species to three scenarios: one at ambient conditions, one with temperatures raised about three degrees Fahrenheit, and one with temperatures raised about six degrees. Schwartzberg found that the trees were more sensitive than the insects to the heat change, and so their buds emerged before the larvae hatched. Instead of feeding on freshly emerging buds, the caterpillars had to eat tougher, woody buds that had started developing toxic defenses.
Schwartzberg said it’s diffi cult to duplicate this kind of study because it relies on controlled environments and is very expensive. But he’s still interested in the timing of life-cycle processes. At Intervale Lowlands, he and the landowner, Larry Master (who is an Explorer board member), created a phenology trail a few years ago where seasonal changes are recorded. Over time, they expect to be able to detect changes in phenology.
“What we see at Intervale Lowlands is likely to be more indicative of the Adirondacks’ response to climate change as compared to studies performed elsewhere,” Schwartzberg said.
Intervale also has trail cameras that enable Schwartzberg and Master to keep track of another animal at risk from phenological disruption: the snowshoe hare. Hares are especially vulnerable to predators; most are killed within three years. To camouflage themselves, the animals have evolved to change their coat from brown to white as winter approaches. This annual change takes place over a period of weeks and is believed to be triggered by the length of daylight and other factors. In the Adirondacks, winters are beginning later, meaning some hares may turn white before snow blankets the landscape. As a result, hares may become more conspicuous to predators. They also will be at risk if, as predicted, the Adirondacks experiences more winter thaws.
Perhaps the most obvious sign that the seasons are changing in the Adirondacks is in ice data. Lake Placid residents have recorded ice-in and ice-out dates on Mirror Lake since 1903. An analysis by Stager and three colleagues for the Adirondack Journal of Environmental Studies found signifi cant changes in the ice-in dates between 1903 and 2008. The data show Mirror Lake ice is forming fourteen to fifteen days later and melting three to four days earlier than in the past.
The State University College of Environmental Science and Forestry has long-term lake-ice records for five lakes (Wolf, Deer, Arbutus, Catlin, and Rich) on its Huntington Wildlife Forest in Newcomb. Four scientists reviewed the dates of ice formation on the lakes from 1975 to 2007 for a 2012 report in the journal Climate Change. The data showed that median ice-in dates for all five lakes shifted from November 28 to December 9, while the median ice-out dates shifted from April 28 to April 23. The ice season decreased on all five lakes, with the largest decrease, twenty-one days, occurring on Wolf Lake.
A shorter ice season could alter a lake’s ecology. It means more sunlight reaches the water, lengthening the growing season of aquatic plants and raising water temperature. Combined with higher ambient air temperatures, these changes could make lakes less suitable for cold-water species such as brook trout and lake trout.
Andrew Richardson, who teaches biology at Harvard University, has studied climate change in forests across the Northeast and found that spring is coming earlier to low-elevation deciduous forests.
“If you look over the last fifteen years, spring is seven days earlier now than it was in 2000,” Richardson said. “That’s based on both ground observations of phenology and using satellite remote sensing across the Northeast, in the eastern deciduous forest.”
Richardson said 2010 and 2012 were the earliest springs on record in the Northeast (from Pennsylvania to Canada), but such early springs are projected to be the norm by the end of the century. In the Adirondacks, a string of eighty-degree days in 2012 led to extremely early ice-out dates. Mirror Lake in Lake Placid experienced ice-out on March 23, the earliest date ever recorded there.
In a 2012 article in Global Change Biology, Richardson and his colleagues noted that a serious frost can occur even after such warm weather, leaving plants and animals at risk. He predicted that the occurrence of a frost after leaf-out is likely to become more common.
In 2010, despite the extremely warm spring, temperatures dropped below freezing between May 9 and May 11, causing damage to trees, ranging from mild leaf damage to complete defoliation of the canopy. Trees at Huntington Forest, which was monitored for the paper, sustained significant damage.
Although trees have evolved to handle frosts, Richardson said early springs followed by serious frosts are not good for their long-term health. If these weather patterns persist, it could put forests at risk.
“The tree can handle the stress, but then it’s in a weakened state,” Richardson said. “It’s drawn down its reserve and will be more susceptible to other stress events.”
Gary Lee, who lives in Inlet, believes tree swallows also are harmed by big shifts in spring temperatures. In recent years, he said, the swallows have been hit hard by cold spells after arriving in spring.
“They set up their nest, and then you get these cold spells—unusual cold spells,” he said. “You get snow in the end of May and sometimes in June, and you lose the whole age class. You lose those babies.”
Early warm spells also could lure amphibians out of hibernation. If cold returns, they would be exposed and hungry. The resultant stress could compromise their immune systems, making them vulnerable to disease.
Another concern for amphibians is that climate-change models predict an increase in both intensive rainstorms and droughts. Heavy rains can cause temperatures to drop in breeding pools, slowing the development of young amphibians. On the other hand, droughts could cause pools to dry up, causing the amphibian and insect eggs to die. Moreover, herpetologist David Patrick said if temperatures rise during winter, as predicted, the region may see less snowfall.
“Without deep snowpack to recharge these wetlands, there’s a greater risk of eggs being left high and dry,” Patrick said. “This happened last year where I found thousands of wood-frog egg masses above the water line.”
Stacy McNulty, a scientist with the Adirondack Ecological Center in Newcomb, believes amphibian populations stand a better chance in the Adirondack Park than in most places—at least in the near future. Not only are there innumerable vernal pools in the Park, but the habitat around the pools, where the amphibians live most of the year, is protected. She said species reliant on vernal pools are more vulnerable in developed areas where the landscape is fragmented.
But McNulty also noted that scientists are still trying to get a handle on phenological changes. That’s why she, Stager, and other scientists have been collecting data on nature’s cyclical events, recording when frogs call in the spring, when lilacs bloom, and when migrating birds arrive on their breeding grounds. They hope the data eventually will allow them to better understand how plants and animals will react.
“It’s very complicated,” McNulty said. “We’re hoping that with this phenology data, it will at least help us understand what’s going on now.”
Watch a video related to phenology in the Adirondacks.