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Wednesday, January 8, 2014

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?"


  1. Stephen,

    Your ash dilemma reminds me of the thick stand of maple seedlings visible all around the historical entrance to Deer Grove. Initially, this carpet of maple seedlings looked scary to me. However, the FPD then burned a similar looking area at Deer Grove and the result was no more maple seedlings. Are burns being conducted at Blue Star? Do prescribed burns not kill the ash seedlings?



  2. I agree with your observations about dying ash at times producing a dense colony of young ash seedling. I have seen this phenomena at several sites along the North Branch. At Watersmeet, we have been cutting and herbiciding one of these beds for several years. New seedlings are not quite as dense as in your photos from Blue Star, but young ashes have reappeared after treatment, I think because seeds remained in the area to produce multiple year crops of young ashes. The plan is to continue to cut and herbicide these new plants as they appear until the seed bed is exhausted. As with your orchid pond situation, there were other desirable plants in the area, so foliar spraying was not a good option. The area where the ash seedlings are present is very wet, with swamp milkweed, water hemlock, and winged loosestrife, so prescribed burning would be difficult under a number of weather conditions.

    Within the northern flatwoods community at Watersmeet, black ashes were once common, growing with swamp white oak, musclewood, skunk cabbage, and extensive stands of marsh marigolds. The loss of these black ashes, which are conservative trees that belonged in this space, to an invasive species (the emerald ash borer) from Europe and Asia saddens me. I am attempting to save all the young black ash in the hopes that one of these trees might show resistance to this insect and survive. But so far, even very black young ashes eventually show signs of borer infestation and die. The blue ash is another very conservative ash species that I believe should be saved in the few places where it is found.

    I have not seen profuse ash seedlings produced by dying black ash. All the big flushes of young ashes seem to be from dying green ash.

  3. My experience overlaps somewhat with that of James and Eileen. Yes, fire seems to kill most tree seedlings up to some age. But after that, many species just re-sprout. I wonder what that critical age (or size?) is. It would be useful to know.

    Yes, the ash beds of all three areas discussed are in wet areas where good conditions for fire are rare. To make it worse, there's little fuel. Grasses and oak leaves burn easily. Maple and ash leaves will rarely burn except during brief periods in fall - and in some years the length of that period seems to be zero.

    1. Although the soil moisture determines the vegetation type for the range of fire intervals, the soil moisture does not determine the fire return interval or intensity. Indeed, some of our wetlands have the most densely packed fuel and burn the hottest. It is not entirely the wetness that is causing difficulty in conducting prescribed burns. It is a lack of sunlight and wind to dry the fuel. In the case of Blue Star, it is also the elimination of vegetation that provides quality fuel, which has most likely been caused by a long absence of fire. The problem of too little sunlight and wind can both be solved by additional canopy thinning. The problem of a lack of vegetation to provide fuel is a more difficult problem, as those species are likely excluded until the seedlings are controlled.

  4. It's interesting to think about trying to girdle all of the larger green (weedy) ashes as an attempt to prevent them from masting. What kind of impacts would it have on populations of emerald ash borer if their most abundant food source (green ash) was taken away? Would it slow their spread? Could they find the isolated, rarer ash species?

    I've seen explosions of ash seedlings in a flatwoods, completely shading out a large population of the state-threatened Dwarf Raspberry, Rubus pubescens. I image dealing with ash seedlings will become a priority for most stewards before long. It's not an envious task, though, as hundreds can grow within a small area.

    Is there some way we can get a number of stewards to just document what, if anything, happens to ash tree seedlings at their site after a prescribed fire passes through? It wouldn't necessarily be a formal experiment, but if many participated by sharing their observations, perhaps some kind of trend indicating a critical age or size may emerge?


  5. Ash seedlings can be a problem, but the solution depends very much on the situation. In Miami Woods they are consumed by the excessive deer population, not a condition I would wish on other stewards. Fire is certainly a good solution where there is sufficient fuel. In areas with high quality forbs, careful hand application of glyphosate based herbicide is probably best. But where few forbs are present I wouldn't hesitate to use Garlon at 1.5% spray early in the growing season or bark application without cutting. The grasses and sedges may be set back a bit by Garlon, but they will recover. The borers seem to be getting pretty much all above one inch in diameter.