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May 2012

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From:
John Pogacnik <[log in to unmask]>
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John Pogacnik <[log in to unmask]>
Date:
Wed, 30 May 2012 08:48:18 -0400
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I have seen a decline in Ovenbirds up here in Lake County also.  I firmly believe that earthworms, and deer, are the culprits.  If you have the "bad" species of earthworms present you can have some major problems.  We have now documented around 17 species of earthworms up here in Northeast Ohio.  Of these, 2 are Asian and the rest European.  There are no native species here.  Not all species are a major problem.  Only a handfull are creating the major problems.  The nightcrawler is one of the worst followed by the two Asian species. The first thing to understand about earthworms is how they are disrupting a forest.  Earthworms feed on the leaf litter in the forest.  A good forest should a layer of freshly fallen leaves with layers of older leaves and partially eaten leaves.  This is the area where you find forest macroinvertebrates.  This is also a nursery for native plants.  If you scrape away the leaves the ground is fibrous with a lot of organic matter.  A forest with a severe worm problem only has the previous year's leaves with nothing but old leaf petioles and bare ground underneath.  A lot of these areas will have no leaf cover by mid summer.  Needless to say no leaf cover means no forest invertebrates, no small mammals, and no forest regeneration.  Earthworms alter forest
ecosystems in many ways; they increase soil nitrogen levels, disrupt plant
mycorrhizae, modify microflora composition, remove the soil’s O horizon,
increase nutrient cycling rates, and decrease leaf litter, to name a few.  Another problem is invasives thrive in areas with worms.  It makes sense.  Most of the plants come from areas where these invasive worms are part of the ecosystem.   If you have worm problems, you don't lose your mature plants, you just see much less additional native plant regeneration.  In many of our parks we are seeing little or no maple regeration in areas with 80-90% maple overstory.  In areas that we do see maple seedlings there is a nice layer of duff.  Now couple the lack of regeneration and the browsing of the mature plants by deer, you get what is called forest decline syndrom.  There is basically a loss of plants annually.  The deer are eating more plants than are added every year through regeneration.   Up here in our parks I have yet to find an area without any earthworms.  Some areas are just not as bad as others.   Some of the worst areas are basically woodland desererts.
 
Worms have a negative affect on ground nesting birds.  In areas with severe worm numbers you have a decrease in vegetative cover and a lack of forest invertebrates.  The forest invertebrates is what many of our forest birds are feeding on.  This spring while doing surveys I noted the variety of forest invertebrates in areas where there was a good duff layer with a nice mix of wildflowers and areas with worms and invasives.  There was a huge difference. If you are doing breeding bird surveys this summer, I think it would be worthwhile to check the condition of the forest floor where you have ground nesters such as ovenbirds and hermit thrushes present.  I looked at areas where we had hermit thrush nests last year and all sites had minimal worm problems with a good duff layer.  It isn't hard to determine if you have worm problems.  At this point in the season all areas should have a layer of leaves that fell last year.  Scrape away that top layer of leaves  You should see layers of old leaves and decaying leaves and humus below.  If you see only newly fallen leaves and nothing but leaf petioles under them and mineral soil you have a problem.   it would be interesting to see if there is a definite correlation. Earthworms have probably been in a lot of these areas for years.  The increase in deer has accelerated the problem in many areas.  It is definitely something to keep an eye on.  For those interested, the Cleveland Museum of Natural History's Conservation Symposium this year will deal with Forest Management.  There will be a a talk on earthworms and there will also be a workshop on how to judge an area in minutes on how invaded it is.  They developed and are using this system in Minnesta.  I have used their criteria when I am out doing various surveys.  It is a quick and easy method to determine on a level of 1-5 how invaded an area is.  This can be valuable whan doing surveys of just about anything forest related.  Here is a link to the symposium. http://www.cmnh.org/site/conservation/conservationsymposium.aspx
 
 One other thing.  When you remove invasives from an area that is invaded by worms, there is going to be very limited regeneration of native species.  That is why in many cases when the invasives are removed, more invasives take their place.  there are sonme species that seem to spread in worm areas.  Ash, Jack-in-the pulpit, Pennsylvania sedge are just a few.  We need to get out into these areas and see what else is "worm tolerant".   It might make a difference in areas to plant native plants that will spread and flourish in these areas, especially finding bird-friendly species to plant.  It would be nice to have a lot of eyes out there seeing what we can find out.  For more info on worms check out: http://www.nrri.umn.edu/worms/
John Pogacnik

                                          
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