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Brown County Hills - Species Spotlight

Yellowwood Trees

The Ogle Hollow Nature Preserve within Brown County State Park is a great place to see good examples of Yellowwood trees in their natural (if mysterious) setting.

The interpretive trail (.75 mile, strenuous hike) through the nature preserve highlights 22 tree species that are typical of the Big Woods. Ask for directions at the park entrance.

The following piece was written for the first Understory newsletter for the Brown County Hills.

The Yellowwoods of Brown County

If you had to write a mystery novel about trees, the yellowwoods of Brown County would make great central characters. Not only are they beautiful and rare, but no one really knows how they got here — or whether they will survive.

Related to black locust and redbud trees, yellowwoods can grow to a height of 50 feet. In late spring or early summer, they produce beautiful bundles of white pea-like flowers. They can reproduce from seeds held in flattened brown seedpods – but also send up sprouts from their roots (and often resprout after being blown or cut down).

But the amazing thing about yellowwoods is the mystery they create. Hank Huffman, a former biologist with the Indiana Division of Nature Preserves (and probably the leading expert on the Yellowwood in Indiana), tries to unravel the mystery.

In the mid-1980s, Hank did extensive fieldwork which identified a number of unknown stands of Yellowwood in Brown County State Park and Yellowwood State Forest. He found that the stands were always situated on northeast-facing slopes at the head of steep ravines. Also, he found that many stands seemed to be missing a generation. There were mature trees and small sprouts — but no teenagers!

His study also highlighted the obvious mystery: Why are these forests the yellowwood’s only home in Indiana? Is Brown County the last stand of a previously widespread population — or the first toehold for an expanding species?

“The yellowwood is trying to tell us a story”, says Huffman. He theorizes that northeast-facing slope locations coincide with “shadow pockets” – places that direct afternoon sunlight can’t reach in early spring. This may prevent the yellowwood (which is more widely distributed further south) from ending its winter dormancy too early – saving it from late frosts.

Likewise, Huffman is pretty sure he knows why yellowwoods from the 1970s and 1980s are missing. White-tailed deer were absent from the late 1800s until 1934 when they were reintroduced. Through the 1950s and 1960s, deer populations grew unchecked on state lands and peaked in the late 1970s. During Huffman’s field work, he noticed plenty of evidence of deer browsing on yellowwood trees. He doesn’t think it’s coincidence that there’s a conspicuous lack of yellowwood saplings of the age that corresponds to the worst deer overpopulation.

According to Huffman, the evidence so far seems to be consistent with an expanding range. Studies of prehistoric climate and ecology have shown no signs of yellowwood trees this far north in early post-glacial times, which suggests that local yellowwoods were established no earlier than a few thousand years ago. But why do we have a few thousand yellowwoods in Brown County – and nowhere else for a hundred miles around? And, how did this stand first get established? Huffman thinks that future genetic studies might give us clues to help solve the mystery. But for now the trees seem to be withholding the full story. We should be careful not to destroy the evidence.

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