The brook glides over brown shale and tumbles over gray sandstone boulders, filling the forest with the sounds of rushing water. Standing next to it, I smell the fresh, earthy scent rising from its turbulent water. The air is still and mosquitoes float around me, ready to bite.
One of New Jersey’s rainiest Junes in decades has brought Tillman Brook to life, and a thunderstorm last night has energized an already exuberant flow. At 10 in the morning, the skies have not yet cleared and here, 750 feet above sea level, I am in the clouds, surrounded by fog and a light drizzle. The rocks and rhododendron leaves and fern fronds are still glossy and wet from last night’s rain.
I am at the bottom of a ravine whose modest topography is covered with trees that have lived undisturbed for over a century and a half. In that time they have achieved an impressive size, reaching over 100 feet into the forest canopy on trunks nearly 4 feet thick.
The eastern hemlocks are the most attractive trees here, with their rich brown bark and their branches that cast a deep shade onto the forest floor; their dark conical crowns remind me of cold snaps and quiet snowfall.
Contrary to what you might expect from this scene, Elizabeth and I are in the New Jersey Highlands, a small part of the Appalachian Mountains that happens to fall within the state’s borders. We are in Tillman’s Ravine, to be precise, and our straight-line distance from Newark is only 45 miles.
I’d first read about Tillman’s Ravine in Plant Communities of New Jersey, which praised it as an enchanting and easily accessible example of an eastern hemlock – northern hardwood forest. Such forests have a broad range, but in this part of the country they are restricted to low spots on steep, north-facing slopes or to cool, moist ravines like this one.
Later, while adding to the list of old growth forests on Wikipedia, I learned that about 25 acres of the ravine were only selectively logged in the past and are otherwise an extremely rare example of old-growth forest in New Jersey.
The promise of seeing a locally rare ecosystem in pristine condition was too much for me to resist, and so here we are on a drizzly Thursday morning, making a stop on our way between family we’re visiting in New Jersey and Pennsylvania.
Tillman Brook began carving this ravine out of Kittatiny Ridge’s west slope when the Pleistocene ice sheet retreated some 15,000 years ago. The ice was followed by tundra and boreal forest as it moved north, before eastern hemlock and its associates moved in to stay about 8,000 years ago. Hemlock thrived here for thousands of years until its population crashed from a disease or a fungus, perhaps, 4,800 years ago. The tree virtually disappeared from its range in a matter of decades, and its population only recovered after 2,000 years.
The hemlocks here are threatened again today, this time by the hemlock woolly adelgid (that’s uh-DELL-jid), a sap-eating bug from Asia that was first introduced to the eastern United States in the 1950s and has so far weakened and killed hemlocks throughout half their range.
Once a stand of hemlocks becomes infested, the adelgid feeds on the tender shoots of new growth, resulting in a vicious circle of growth and attack that steadily weakens the trees. Although tree deaths in a stand might start and stop from year to year because of the growth-attack cycle, the effects of infestation are cumulative, and trees might start dying after just 3 years.
The adelgid reached New Jersey in the mid 1980s, and, in 1988, the state began monitoring several wild hemlock stands as part of its response. By 2003 the adelgid had killed all of the hemlocks in one of the monitored stands, coincidentally named Shades of Death.
The hemlocks in Tillman’s Ravine were first infested in 2000, but so far few of them have been killed. It turns out that hemlocks near water sources are more resilient to adelgid infestation and trees near the bottom of a slope or near a stream tend to be the healthiest in infested stands. If high soil moisture or proximity to a water source prolongs a hemlock’s life in the face of an infestation, it might even allow a hemlock to survive. But no one knows for sure yet.
I walk next to Tillman Brook and a light rain has started to fall. Maybe the hemlocks next to the water will survive the adelgid. For my part, I hope that these trees, which have for centuries graced this brook, will continue to grace it for a few more.
