By LESLIE BISHOP, guest columnist
Hemlocks are not common trees of our Indiana forests. Yet, not far from my house, there is a small population of Eastern hemlock.
In all of Indiana, there are less than 20 small isolated stands of hemlock, and they are all glacial relicts — populations that are left over from the time when glaciers covered much of North America.
Hemlocks and other conifers were a common component of the vegetation following the retreat of the last glacier around 10,000 years ago. After the glacier retreated, the climate became warmer and drier, and the ancient conifer forests were gradually replaced by the deciduous forests we know today.
But in some isolated places, hemlocks were still able to thrive. Now, in Indiana, we find hemlocks only in our wettest and coolest habitats, on the north-facing slopes of deep-cut ravines or box canyons and on steep, rocky bluffs along streams and rivers.
[sc:text-divider text-divider-title=”Story continues below gallery” ]And so, it is amazing that right here in Brown County we can visit hemlocks that represent a population that has endured for thousands of years!
On Christmas day, we hiked into the Trevlac Bluffs Nature Preserve on the historic Yellowwood Trail. We followed the meandering trail through a mature forest where shagbark hickory and white oak trees towered above us. A pileated woodpecker pounded an old beech tree; otherwise, all was silent. The fall leaves now form a thick blanket on the ground, and at times the trail disappeared.
When we reached the bluffs, we lingered to admire the hemlock trees. Hemlocks cling to the cliff edge and seem to march down the steep bluff, which rises 200 feet above Bean Blossom Creek. The graceful, long arms that drape from the dark trunks of the larger hemlocks gave me a strange sense of belonging.
I came of age in the Tennessee mountains, where hemlocks were plentiful and created a comforting canopy of green. I found a branch on the ground. I crushed and smelled the leaves. Oh, that smell.
The smell transports me to my college days at the University of Tennessee where I spent my weekends hiking the trails of Great Smoky Mountain National Park. There, the Eastern hemlocks line steep banks along cool mountain streams. The smell evokes rhododendron and mountain laurel, the welcoming feel of rustic trail signs, and the carefree explorations of a girl with field guides in hand.
Now, the hemlocks of the Smoky Mountains are under siege, as are all the hemlocks throughout the eastern United States. The hemlock wooly adelgid, an invasive insect from Japan, has killed thousands of trees across the range of Eastern hemlock from New England to the southern Appalachian Mountains, and its range is expanding.
The adelgids are small, aphid-like insects that pierce the leaves with their mouthparts and suck the sugars from the tree. Infected trees die within four to 10 years. Despite efforts to control the adelgids with insecticide and natural predators (a beetle species), the hemlocks continue to suffer.
Luckily, so far there is no evidence that the wooly adelgids have reached Indiana. But if it ever does, the isolation of the remnant populations of hemlocks could play a role in the survival of hemlocks in Indiana.
We continued on the trail which took us up and down slopes and ravines to another area of the bluffs with hemlocks. The winter landscape is stark, yet beautiful. The rugged terrain, the leafy trails, and the smell of hemlock leaves jog old memories as well as create new ones.
Leslie Bishop is a Brown County resident and retired biology professor from Earlham College. She can be reached through the newspaper at [email protected].
