The Revenge of the Ash – a challenge to restoration

The people in this photo started cutting brush in Blue Star Woods last summer. As stewards of this degraded wet woods, they have a challenge to face. Big portions of the understory are solid stands of young ash trees.

The bonfire burns evil brush, but killing brush is
just the first step.

Yes, our mature ash trees in this region are rapidly dying of an invasive Eurasian disease (due to the emerald ash borer). Yes, this plague is an ecological tragedy for some rich woods where many ash species are an ancient part – and for many animals that depend on those species.

Yes but, many of us are happy to see the wretched ash die in our oak woods, prairies, and wetlands where they had become one of the worst problem invasives (because of the absence of natural fire).

But do you recognize what’s in the foreground here? Seedling ash. This pest doesn’t seem inclined to go away without a struggle. Let’s brace ourselves for a new (if temporary) problem.

Many plants have a survival mechanism that tells them, “Tree, wake up! If you’re dying, at least put out as much seed as you can.” The ash are doing this. In one beautiful, rich wetland, a couple decades into restoration, thousands of ash seedlings suddenly appeared. They’d been only a very minor problem for years. Now suddenly there were half a dozen ash seedlings in every square foot.

We wondered, what’s happening suddenly after all these years? Would they just magically go away. But no, soon they were four or five feet high; they needed control. It would be a gigantic job, but that area had populations of four threatened plant species. We had contractors cut each little trunk and apply Round-up to each little stump. (Some believe that Round-up hurts the surrounding plants less than Garlon.) Indeed, the threatened plants came back robustly (see below). Whew!

Prairie white-fringed orchids (in cages to protect them from the deer) and scores of other rare species were nearly shaded out by dense green ash saplings after near-by trees (dying from the ash borer) put all their last energies into reproduction. 

 

When thickets of young ash are this dense, few other seedlings can compete.

The photo on the right is a close-up of ash seedlings at Blue Star Woods. Grim, no? What should be done with them? From a quick evaluation, I suspect that Blue Star may in part have been swamp white oak (Quercus bicolor) woodland. Mixed with the oak areas were patches that seemed like they could have been wet prairie or sedge meadow. Little surviving herb vegetation was still apparent in most areas.

For Blue Star, if there are resources to deal with the ash seedling areas at all, perhaps foliar spraying is the answer. In this case (unlike the orchid pond, where the competition had had years to kill off the later-emerging seedlings) repeat herbiciding may be needed for two or three growing seasons.

Consider a third site. At the ephemeral Oak Pond, mature green ash had long ago shaded out the herbs. Many years back we girdled the ashes, and they all died without the spectacular flush of seedlings. Perhaps in important areas it might be good to girdle dying ash so that they won’t leave yet another huge problem in their wake?

As Daniel Suarez of Plants of Concern wrote: I've seen explosions of ash seedlings in a flat woods, completely shading out a large population of the state-threatened Dwarf Raspberry (Rubus pubescens). I imagine dealing with ash seedlings will become a priority for most stewards before long... Is there some way we can get a number of stewards to document what, if anything, happens to ash seedlings at their sites after prescribed fire?"