With a punctuality that SEPTA might envy, the annual “peak” foliage show is arriving in the Philadelphia region. And given the weather forecast, this weekend it could well coincide with peak traffic on the trails, some of which have suffered for wear from their newfound popularity.

The coronavirus that has affected about every aspect of our lives has generated such a stampede on local trails that some state parks have asked people to please, please, go somewhere else.

That mass march began early in the spring when the pandemic first celebrated its triumph over normality. An Inquirer analysis of foot and bike traffic on some of the region’s most heavily used trails showed that the surge continued through September.

For example, nearly 27,000 hikers and bikers last month used the Chester Valley Trail, which crosses Montgomery and Chester Counties, about double the September 2019 total, according to Delaware Valley Regional Planning Commission data. That was the case even though September 2019′s weather overall was warmer and drier.

Fortunately, with the Fairmount Park System, the sprawling Circuit Trails network, and the legions of woods, forests, and byways, the region is generously veined with more than enough trails to accommodate those heading outdoors for a sanity break.

The weather this weekend should be ideal for admiring leaves that have yielded to the same pigments that color pumpkins, apples, and corn. Saturday afternoon should be balmy and sunny, and after a front routs this tepid, humid air mass, Sunday will be a textbook autumn day with sun and highs in the 50s.

Peak foliage now animates just about all of Southeastern Pennsylvania, the state Department of Conservation and Natural Resources reported in its Thursday update. The only exceptions were the lower-elevation areas of Philadelphia and Delaware County.

Forester Ryan Reed, the report’s author, said that’s a function of being close to the Delaware River and the preponderance of non-native trees. Those trees constitute one reason that considerable remnants of the foliage season often linger well into November, arborists say.

So just what is ‘peak’?

It isn’t as though nature has an on-off switch. “There is a very ‘non-linear’ nature to how fall color progresses,” Reed said.

The region has a “rolling peak,” said Bill Trescott, arborist with the Mount Cuba Center in Hockessin, Del., near the Chester County border.

A frog in a pond reflecting autumn foliage at the Mt. Cuba Center in Delaware.
Shelly Silva/Mt. Cuba Center
A frog in a pond reflecting autumn foliage at the Mt. Cuba Center in Delaware.

Foliage color is driven primarily by light changes, but the differing elevations in the region create “micro-climates” and subtle temperature differences that affect leaf fall. A leaf-denuding hard frost on a hill might spare trees rooted a few hundred feet lower.

It is impossible to predict precisely when trees will shed their leaves, and no hard data are available about how that changes from year to year, but Trescott said he has noticed that show has been lingering longer over his 35 years at Mount Cuba.

That likely is tied to the fact that first-frost dates have been arriving later, likely tied to worldwide warming. And that’s partly due to the region’s tree population, said Bill Cullina, executive director of the University of Pennsylvania’s Morris Arboretum, which includes non-native species such as Asian maples that hold their leaves longer.

“This is the one reason fall color is stretched out around here,” he said. In addition, local trees such as the elms, tulip poplars, and beeches are late leaf-droppers.

The oaks typically are last, and Trescott says he has seen oak leaves hang tough into December.

Where to go?

For walkers and cyclists looking to avoid the crowds, “When they go matters. Where they go matters,” said Gail Farmer, executive director of Wissahickon Trails.

Her office is on Morris Road in Ambler at the trailhead of the heavily used Four Mills Nature Reserve. Less than a mile-and-half away on Butler Pike is the far-lesser-trodden 2.4-mile trail system of Willow Lake Farm Preserve, next to a homely drugstore parking lot. On one of the the most spectacular afternoons of the season earlier this month, it was absolutely empty.

When he has hiked, John Boyle, who is research director of the Bicycle Coalition of Philadelphia, has been partial to the Franklin Parker Preserve near Chatsworth, in Burlington County, and the Ted Stiles Preserve near Washington Crossing in Mercer County.

Among the lesser-used paths recommended by Circuit Trails are the Tacony, Pennypack, and the K&T Trail, which is part of the Delaware River Trail.

To get an idea for the optimal time to head out there, the Delaware Valley Regional Planning Commission database has trail traffic broken down by 15-minute increments, along with archival data, based on surveys by its automated counters.

For those who have more interesting pastimes than poring through data, Boyle has this time-saver: “If you go early, especially during the week, you can walk or bike any path in the region.”