Page 4 of 5

Re: Stages of earthworm invasion

Posted: Sat Dec 06, 2014 2:01 pm
by RayA
Lee Frelich wrote:Joe:

That's right in western MA its unlikely that there would be native earthworms except in a few very sheltered places, they certainly wouldn't be all over the landscape. There are a number invasion fronts of earthworms in MA, such as along the creek right outside Bob Leverett's house.

Here are some photos I took in the woods behind Bob's home in early September of this year, showing the earthworm damage front there. The land slopes gently down to a brook. Near the margins of the brook, where it's too wet for the worms, there's green herbaceous plant growth; a few yards away, upslope, where it's drier, there's virtually nothing green on the forest floor. It's pretty dramatic, and was a real eye-opener for me:
Along stream, few or no worms. Woods in the background are worm-damaged.
Along stream, few or no worms. Woods in the background are worm-damaged.
Stream is to the left. Green plants survive near stream. <br />No green plants left on the right side of photo, where worm damage is.
Stream is to the left. Green plants survive near stream.
No green plants left on the right side of photo, where worm damage is.
Upslope from the stream, no green plant life, and almost no leaf litter left.
Upslope from the stream, no green plant life, and almost no leaf litter left.
No duff layer left, just oak leaves on mineral soil here.
No duff layer left, just oak leaves on mineral soil here.
A worm, and &quot;soil&quot; that's nothing but worm castings (excrement).
A worm, and "soil" that's nothing but worm castings (excrement).

Re: Stages of earthworm invasion

Posted: Sun Dec 07, 2014 7:49 am
by Joe
Ray, when you say, "Upslope from the stream, no green plant life, and almost no leaf litter left"---- isn't it possible that other variables are also at work upstream, such as, possibly, heavy deer grazing?

Are those non native worms chewing up all the ground vegetation?

Strange, but the "forestry community" talks a lot about invasive species but never mentions worms- at least not in this state. If it's really that big a threat, they need to learn about it.

So, is it inevitable that these species will spread over most of the land?
Jo

Re: Stages of earthworm invasion

Posted: Sun Dec 07, 2014 1:07 pm
by RayA
Joe,

I'm not the expert, by any measure, on this topic... just found out about it recently (from Bob). But my understanding from what I've read is that the worms move very slowly, on the order of feet per year. The glaciers eliminated any worms that might have been here, and when the ice retreated, the worms to the south could then advance northward. But they can't migrate fast enough to keep up with the retreating glacier. But they've been introduced into various locations by man's activities, eg, moving soil during construction, shipping nursery products, fishing bait, etc, etc. Once introduced to a site, they'll slowly spread from there. That's why there isn't a problem yet in all areas, but there doesn't appear to be a way to get rid of them once they arrive, so they'll continue to slowly spread.

As far as the situation behind Bob's house goes, I'm sure there could be other factors at work too (I'll leave that for Dr Frelich or others to address more), but there's no doubt worms are present, and the conditions Lee has described are visible. Deer, to my knowledge, don't eat the duff layer out of existence, and that's what you see in the highly damaged areas. Most of the leaf litter is gone; the worms destroy the forest floor layer, leaving only the most recently fallen leaves, with mineral soil directly below them. If oaks are present, their leaves are among the least tasty and will be the last to be eaten. Since the duff layer is the primary rooting zone of plants, including tree seedlings, they're seriously affected when the duff is gone.

Bob has become familiar with the signs of worms' presence, and can now recognize them in various places, and points them out. Stream corridors are likely areas for worm damage due to the release of bait worms. And there's an interesting "mustard test" described by Lee that you can do to verify worm presence.... mix a little yellow mustard powder in a couple quarts or so of water and slowly pour it on suspect ground; if worms are there, they'll come right to the surface to escape the irritant. Bob and I did that at his location, so I could see it work, and it did. Several worms came right out of the ground, post haste. I have a short video clip of it.

Re: Stages of earthworm invasion

Posted: Sun Dec 07, 2014 1:22 pm
by dbhguru
Joe,

Deer browse aftermath is fairly easy to distinguish from earthworm impact. Let's get together sometime soon and we can show you clear examples of earthworms at work in ways we don't like. They are not forest friends. If you google "damage caused by earthworms", you'll see plenty of references to studies that document the changes caused by earthworms. Bad new! We'll have to leave it to you to figure out why recognition and understanding of earthworm impact has been slow to spread within the timber community. I know that Dr. Lee Frelich demonstrated the presence earthworms in the forest to some of the Minnesota State forestry folks. They become believers afterward. However, nobody has a remedy.

In terms of tree growth, my understanding is that they eat the fine roots and retard growth, but they don't kill trees.

Bob

Re: Stages of earthworm invasion

Posted: Sun Dec 07, 2014 2:41 pm
by Joe
Well, if it's really a big problem, long term, and of course we must be thinking long term, then we need to inform the Mass. forestry community- but of course, they don't listen to me. (ha, ha, ha) But I'll find a way to get the word out- and yes, Bob, I'll have to drop by sometime so you can show me the problem near you- maybe this coming spring. Once I really see it, I'll understand it better. I have seen forests where the ground seemed amazingly bare- never thinking it could be due to worms. In fact, on one property with bare soil. I also noticed an over abundance of invasive plants, following a timber harvest I did some years ago. Maybe there is a relationship here? The invasive plants can more easily penetrate the forest when the ground is bare due to worms?
Joe

Re: Stages of earthworm invasion

Posted: Sun Dec 07, 2014 8:59 pm
by RayA
Joe,

I'd guess that if worms were present in the plot that was harvested, even many invasives might not be able to thrive there. Just a guess. But I'm never wrong. I thought I was once, but that was a mistake.

Re: Stages of earthworm invasion

Posted: Mon Dec 08, 2014 5:15 am
by DougBidlack
Joe,

I think I recall Lee saying that earthworms and deer do favor invasive plants which are mainly from Europe and Asia. My understanding is that the elimination of the duff layer by the earthworms and the living plants by deer clears a path for invasion by Eurasian species which are adapted to an environment with earthworms and little to no duff plus the deer tend to avoid eating many of these invasives while gobbling up the native flora. Real bad combination.

Doug

Re: Stages of earthworm invasion

Posted: Tue Mar 01, 2016 3:05 pm
by wisconsitom
Really got to wonder about some of this: Why should there be a result skewered toward Eurasian invasives when nearly every silvics manual for native N. American tree species states that bare mineral soil is required for seed germination? Where my land is, it took forest fires in the 1930s to clear away the duff thereby allowing for the stand of Thuja that now completely dominates much of the stand. In that case, it was fire. But why should not other ground-clearing disturbances not also work the same magic? I've got to admit to a great deal of skepticism regarding this invasive earthworm hypothesis. And too, if earthworms were present in the north prior to the last ice age, should not whole vast plant community systems be in existence-or at the least, nearby-capable of coexisting with the worms?

Finally, the matter of soil types. Here in Wisconsin, wherever there is a loamy, richer soil, agriculture dominates. Yet I hear concern for the forests of the northern part of the state, but these forests-if you'll allow for some oversimplification-are occurring on sand, gravel, and various admixtures of the two. Not good earthworm habitat, yet all the worry. I'm having a really hard time wrapping my head around what I view as large inconsistencies in this thing.

Also had a guy give a talk at one of our arborist's conferences. His description of the mechanism by which earthworms increased soil bulk density was unsatisfying and left me wondering if it is even really so. That was a few years ago and I wish I could remember the particulars better. But I do remember walking away, talking to one of my peers, and the two of us not agreeing as to whether this fellow, within his presentation, had really offered any solid evidence that soil bulk density was necessarily increased following "invasion". To my mind, it had not been. He simply stated it to be so. I don't see how the creation of a vast network of mini-tunnels in the ground would do such a thing, especially as organic material was brought down a bit lower into the profile. That doesn't add up to evidence as far as I can see.

Re: Stages of earthworm invasion

Posted: Tue Mar 01, 2016 7:00 pm
by dbhguru
Tom,

You make some good points. The Earthworm threat is not uniform. Soil types matter a lot. However, more generally, the damage European and Asian earthworms are causing is now well studied by scientific researchers in the Midwest and Northeast. It's past the doubting stage. I see earthworm damage here in Massachusetts and participated in a study by Brown University documenting the damage they do. But again, the impact they have definitely varies depending on soil type. It certainly isn't uniform. BTW, the change in soil chemistry and compaction is explained in research papers by Dr. Lee Frelich, Director of the Center For Forest Ecology at UMN. I'll see if I can get you some of the latest results.

I realize that the damage done by non-native earthworms it is still hard to wrap one's head around. I'm sure if I told the fishing community in my native South that night crawlers are not good for the native plant communities, the first thing they would do would be to laugh uproariously. The second thing they would do would be to use me for fish bait - even though the evidence of damage would be all around them. Accepting the dual personalities of earthworms (garden usually good, forests bad) is still a hard thing to accept.

Here is a lightweight discussion of the earthworm situation intended for the general public.

http://www.dnr.state.mn.us/invasives/te ... index.html

Bob

Re: Stages of earthworm invasion

Posted: Wed Mar 02, 2016 9:14 am
by wisconsitom
Thanks Bob. I have seen some of Dr. Frelich's work. I'm certainly willing to concede that the problem may lie between my two ears, but this is not the first I've heard of this, as referenced in my post above. Ironically perhaps, considering my doubting stance here, the land I bought to grow trees and forest on is at the very turning point between the good, fertile, clay and silt-based stuff of southern WI and the generally poor, acidic and sandy/gravelly stuff of the north. I'm right inbetween. This was by design, as I wanted to end up in what I call "the cedar belt" which is that part of this state where Thuja occidentalis makes its best growth. I succeeded on that, but in doing so, ended up in an earthworm area. Indeed, the field that we are restoring to forest was alfalfa when we bought the place, so it is of substantially decent ag quality. These are the signposts of an earthworm-ridden soil. I suppose much of my woods is of a type that does not readily show us the damage, since so much of it is swamp conifer. We've got broadleaved trees there-paper birch is numerous, as are balsam poplar, some sugar maple, black ash, and a smattering of others, but it's just not the classic "hardwood stand" whereby worm effects are most readily observed. All of which is a long way to say...........I don't know!