Contain those Crawlers! Invasive Earthworms in Our Forests - What's the big deal about earthworms again?
Beneficial here – detrimental there: European earthworms decrease species diversity in North America
Another study on invasive earthworms has been released and this time from the German Centre for Integrative Biodiversity Research. What's interesting is that they use the same tunnel vision narrowed focus on just one simple subject without using peripheral view of other related contributors or lack of them within the forest biodiversity. This has been done in the other studies where researchers failed to even consider the lack of other biological controls which may have been missing in those specific study areas. I've written about this previously in the two articles before where the presence of earthworm predators such as hedgehogs, moles, various birds, etc might be missing.
Many native plants cannot thrive under these unusual circumstances, which is why the species diversity of the forest understory is decreasing. Wherever the worm creeps, the goblin fern (Botrychium mormo), for example, has become rare. Other plants are also threatened by the earthworm invasion, such as the largeflower bellwort (Uvularia grandiflora), the Japanese Angelica Tree (Aralia elata), . . . . . "
|Image: Invasive Species of sussex County, New Jersey|
Japanese Angelica Tree (Aralia elata)
|Photo by Paul Ojanen (University of Minnesota)|
Zoom in Link of Green Forest Understory
|Photo by Scott L. Loss (Oklahoma State University)|
Zoom in Link to bare Forest Understory
I first have to question the two radically different locations taken by one guy from Oklahoma in the south and the other guy's photo presumably in Minnesota in the north. How can you make a comparison ? The forest tree and plant diversity could be completely different. Also interesting is when you click on the zoom link of the supposedly bare forest understory in the bottom photo which magnifies the situation greatly, you see that this is actually Springtime. Not Fall or Winter. There is indeed leaves and other forest liter and numerous maples seedling are popping up everywhere. It just doesn't flow with their written narrative. They also mentioned how earthworm infested forests hurt the understory plants during summer or even drought periods. But that doesn't even jive with what Todd E. Dawson, formerly an associate professor at Cornell found when researching a natural phenomena called "Hydrailic Lift & Redistribution" of water from deeply rooted Sugar Maples to other smaller plants in the forest understory. It just seems to me lately that much of science is dropping the ball in research when they practice a narrowed worldview of tunnel vision on a specific subject. Ecosystems are driven by multiple factors, not just one. Here is the Cornell study:
The other thing that doesn't fit their narrative of the disappearance of Sugar Maples in many areas are that they are being replaced by another invasive, Norway Maples (Acer platanoides). Norway Maple is extremely tolerant of shade and therefore thrives and out competes wonderfully with Sugar Maple. But they don't even attempt to reference this and they should have. For example, here is a Wikepedia piece on Norway Maple's invasiveness and how it can be a major cause of depleted forest understories.
"The roots of Norway maples grow very close to the ground surface, starving other plants of moisture. For example, lawn grass (and even weeds) will usually not grow well beneath a Norway maple, but English Ivy, with its minimal rooting needs, may thrive. In addition, the dense canopy of Norway maples can inhibit understory growth. Some have suggested Norway maples may also release chemicals to discourage undergrowth, although this is controversial. Acer platanoides has been shown to inhibit the growth of native saplings as a canopy tree or as a sapling. The Norway maple also suffers less herbivory than the sugar maple, allowing it to gain a competitive advantage against the latter species."Did you notice that Norway Maple is very shallow rooted and outcompetes other plants for moisture ? Do you know why ? Like other trees here in Sweden and other Scandinavian countries where I live, they are all often shallow rooted because it rains incessantly here. If there is a month or so of no rain, it is very common to see these shallow rooted trees turn brown and eventually die if they don't receive moisture quickly. The often easily tumble over n a bad windstorm. So it makes sense that because of centuries of such habitat where constant rain is the norm, these trees have developed specific epigenetic induced characteristics which allow them to succeed in there particular Scandinavian and Siberian environment. Therefore in another foreign environment, their shallow roots desperately suck up as much water as possible in their new less wet environment. They have not had as much time to engineer themselves the way Sugar Maple also has an extensive spreading root system, but has numerous sinker roots for which it can tap into deeper subsoil layers for moisture capture. In the Oklahoma photo above which shows the supposedly bare understory, you can also see grasses in the background and they explain this in the report.
Grasses also grow well in invaded forests because their fine roots can quickly absorb soil nutrients, particularly nitrogen, and can tolerate summer droughts. Moreover, earthworms eat small seeds of certain plant species and thus directly influence the composition of the forest understory.
Something Else of Important Note on the two Photos above - They've recycle from another article back in 2012Back in 2012 in the Smithsonian Blog, they were blaming Earthworms for the decline in Ovenbirds. Birds from the Midwest who make nests on the ground with twigs which create an over-like structure. I've never seen Earthworms devour twigs and sticks, but that's what they say. Take a look below of the photos by Scott L. Loss again.
|Images by Scott L. Loss|
SMITHSONIAN INSIDER: "EARTHWORMS TO BLAME FOR DECLINE OF OVENBIRDS IN NORTHERN MIDWEST FORESTS, STUDY REVEALS"
One last puzzling photograph from the article
|(photo: Simone Cesarz)|
European earthworms of the species Lumbricus terrestris
This picture above was a pazzle to me. It looked staged. Someone took a handful of earthworms and dumped them on top of some forst litter. But the idea was that the earthworms were removing the forest litter completely. I would have muched rather seen a photograph inside the forest canopy which they said had no understory plants because of earthworms, then digging a hole in this bare canopy to reveal all those earthworms. At the same time, show a photo of a hole being dug within a forest rich in understory plants and the lack of any earthworms. Does that make sense to anyone else ?
And yet another important dilemma. Migration of all lifeforms [not just earthworms] northward because of Climate Change
|Image - University of Washington|
interactive map shows where animals will move under climate change
|Image - AllPESTS.ORG|
I suppose what puzzled me most was the absence of any talk about lack of earthworm predators in general. Many creatures eat earthworms. Small snakes, moles, toads, numerous birds, ants, mites, centipedes, etc, etc, etc. But again, no mention of whether or not they even bothered to look for these and if absent, why ? Were any of the earthworm infested locations ever improved by the reintroduction of any of these predators ? We'll never know. Almost every negative research paper I've ever read never once addresses these major topics. Here are a couple more interesting links for reading.