Some of Pennsylvania’s iconic tree species might not survive climate change

Tens of thousands of acres of mountain maple, American beech, balsam fir, paper birch, and quaking aspen that produce some of Pennsylvania’s most vibrant spring, summer, and fall scenes are at risk because of climate change, according to a state agency.

“Our climate may warm too quickly for these species to adapt before dying out,” the Pennsylvania Department of Conservation and Natural Resources (DCNR) wrote in a recent blog post. The post suggests a new strategy for forest management, including shifting to “change resilient” trees.

That’s no small statement for an agency in charge of overseeing 2.2 million acres of state forests and 121 state parks. Not only that, the DCNR advises owners of 15 million acres of private forests.

A year ago, the DCNR issued a climate change adaptation plan in a report that detailed the issues the state’s forests face with rising temperatures, more frequent storms, and overall wetter years. The plan was the result of a collaboration with 80 DCNR staff working with the Northern Institute of Applied Climate Science.

“There is certainly change we are already starting to see,” said Greg Czarnecki, the climate change and research coordinator for the DCNR and an author of the report.

The report found that since the early 20th century the commonwealth has seen a temperature increase of 1.8 degrees Fahrenheit. Winter temperatures have seen the fastest rise, increasing 1.3 degrees Fahrenheit per decade from 1970 to 2000 in the Northeastern U.S., according to the report.

The temperature rise coincides with the onset of fossil fuels as the nation’s primary energy source.

Moreover, the Northeast has seen an increase in the frequency of very hot days, higher annual precipitation, and heavy storms. In fact, many areas of Pennsylvania set records in 2018 for the number of days of rain and total annual rainfall. This year is on track to be another wet one.

Warming tends to promote nonnative species over native, scientists are finding.

Many trees native to Pennsylvania can’t thrive in continually soggy conditions. The American mountain ash is one such species, so biologists believe it no longer makes sense to keep planting them. Rather, the commonwealth should look to plant climate-resilient trees, mostly more southern species such as sycamore, hackberry, box elder, and Eastern redbud.

But Pennsylvania’s forests aren’t just a collection of trees — they are complex ecosystems. Climate change will negatively affect rare species of wildlife, foster an increase in pests and invasive species, as well as fragment existing habitats, the report states. And all these factors influence what types of trees thrive.

For example, the emerald ash borer, a beetle native to Asia and first seen in the United States in 2002, has already destroyed tens of millions of ash trees in 35 states and is likely to do even more damage than initial modeling suggested. Infestations have been found in Pennsylvania and New Jersey.

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It is just one of several invasive pests that attack trees.

Czarnecki notes that the eastern hemlock, Pennsylvania’s state tree, has long been under attack by the woolly adelgid, a relative of the aphid. But warmer weather has allowed the insect to spread from the southern part of the state to the north and west.

“When you talk about the adelgid, it’s a good example of how climate change leads to other stressors for trees,” Czarnecki said.

Philadelphia’s tree population is also at risk. The city is warming up, especially in the winter, and getting wetter, according to a separate report for the city issued by the Urban Forestry Climate Change Response Network. Philly is also surrounded by tidal waterways, including the Delaware River, and the report found that by 2080, sea levels in the region could rise from 1 to 4½ feet.

All those factors will affect trees, the report states.

In the area around Philadelphia, black cherry, eastern white pine, sweet birch, and white ash are all likely to decline. Northern catalpa, Japanese maple, gray birch, and American beech are all also moderately or highly threatened, that report states.

Growers ought to be thinking of picking fungal- and disease-resistant trees, the DCNR advises.

“Wise choices for replacements could be part of the solution to ensure that our forests remain healthy, viable, and productive,” the DCNR’s blog post states.