The last time I visited the old-growth stand of eastern hemlocks at Snyder-Middleswarth Natural Area, in central Pennsylvania’s Bald Eagle State Forest, the hemlocks were succumbing to a wooly adelgid infestation, and I figured they’d all be dead in a few years. That was early June 2007. My hiking buddy Lucy and I felt we should go back five years later and see what was taking the hemlocks’ place.

What we didn’t expect was that a few of the ancient hemlocks would appear untouched. Were these individuals blessed with some form of resistance to the invasive scale insects — or were they just lucky?

In general, though, 80-90 percent of the hemlocks were dead or almost dead, as expected. We were pleased to see their place was being taken more often than not by yellow birch, a long-lived tree already present on the site. Though the stand could no longer be characterized as old-growth, the forest as a whole retained many old-growth characteristics, especially (of course) large standing and fallen dead trees, but also deep moss and a diverse understorey.

The continued presence of a rare shrub called hobblebush testified to the relative absense of deer in the heart of the natural area — a very fortunate circumstance indeed. Further along, as the ravine grew less steep and more accessible to deer, we began to notice fewer shrubs and more red maple.

As in 2007, we were struck by the profusion of hemlock varnish shelf fungi and their attendant beetles, eating and mating with abandon. This time I also spotted a couple of the marvelously spiked horned fungus beasts, though I didn’t manage to get a good photo of them.

We were too late for most of the spring wildflowers, but the partridgeberry was just coming into bloom.

And whereas last time we found some weird fern galls, this time Lucy spotted some white galls on rhododendron leaves that were new to both of us.

“Swift Run” had struck us as a misnomer last time, but yesterday it was running very high, and was full of tannic foam as a result. I couldn’t resist eating a fingerful of foam, and was disappointed to find that it tasted of nothing but forest soil.

But mostly what caught our eye were the dead hemlocks.

As they shed their bark, they appear raw and red as fresh meat,

and up close one can see that numerous insects or insect larvae have been having a field day with them.

Death in a forest can be both fruitful and beautiful. We were relieved and impressed to see that the heart of this untouched preserve retained its garden-like qualities,

though the occasional lichen-draped branch fallen from a dead hemlock crown offered a sober reminder of how much biodiversity could be lost if the adelgid invasion does eventually result in 100% mortality of canopy-height hemlocks.

But the ravine still rings with winter wren and hermit thrush song, and given how rapidly the adelgid-created openings are filling in with yellow birch, it’s a safe bet that while the wildlife composition will change somewhat, Snyder-Middleswarth will remain a refuge for forest-interior species for decades if not centuries to come.

Watch the slideshow.

A large black snake lay motionless on the moss beside the trail just past the signboard for the Snyder-Middleswarth Natural Area. My hiking buddy and I had driven over this past Saturday afternoon to pay homage to one of Pennsylvania’s most spectacular old-growth remnants before it is altered forever. The air was crystal-clear, adding to the cathedral-like effect of shafts of sunlight reaching down through the canopy.

Just past the snake we began to find spectacular, red and orange polypores — the hemlock varnish shelf…

and the fungus beetles known as Megalodacne heros, colored to match. Those that weren’t busy eating were busy mating, true to their family name Erotylidae, and some managed both at the same time.

In fact, things are looking very good for hemlock varnish shelves and the beetles that love them at Snyder-Middleswarth for a decade or more to come. That’s because the hemlock trees are dying,

300-year-old giants falling victim to an insect barely bigger than the point of a pencil, the hemlock woolly adelgid. Their egg masses are often compared to the ends of cotton q-tips, an image more in keeping with the kinds of places where human beings go to die.

The eastern and Carolina species of hemlock are especially vulnerable, though occasional individuals do show resistance. It may take a century or more for their native predators and diseases to catch up with the adelgids and bring them more into balance with the eastern forest ecosystem, though they will probably always remain an outbreak insect. In a few centuries, we may have new old-growth hemlock forests in Pennsylvania.

But in the meantime, another climax species — yellow birch — seems poised to take over at Snyder-Middleswarth. Almost every fallen hemlock log we saw bore a thick fur of birch seedlings. Forest ecologists refer to these as nurse logs, which is a bit misleading: birches and other tree seedlings prefer to sprout on logs not because they are fertile nurseries — they aren’t — but because they offer relatively sterile refuges from soil microbes inimical to seedling growth.

The word seems to have gotten out that the giants are dying — that’s the only way we could account for the dearth of visitors on a perfect Saturday afternoon in early summer. We walked slowly along the trail above the inaptly named Swift Run, looking at everything and listening to the songs of hermit thrushes and winter wrens. In three hours, we only heard a couple planes go over. It’s a deep ravine far from any highways — one of the quietest spots in all of central Pennsylvania.

I renewed my acquaintance with several plants that I don’t get to see too often, including starflower (Trientalis borealis) and mountain holly (Ilex montana). And we encountered botanical oddities like the fern fist above, one of several we found, probably the result of some wasp or another hijacking the ferns while they were still unfurling in order to make gall-like brood chambers from the crippled fronds. (If anyone has a better guess, I’d like to hear it.)

But mostly what caught my eye were the dead and dying hemlocks. I know that new hemlock seedlings will sprout up after the adelgid population crashes, and some of them may even survive future outbreaks. But it will be a long time before the forest once again has trees with this much character and presence.

It was 7:00 o’clock by the time we made our way back to the parking area. Much of the ravine was already in shadow. I turned around for a last, long look at hemlocks bathed in cathedral light.

Slideshow.