Shrub Layer:  An Empty Niche?  

TOPIC: Shrub-layer an empty niche?
== 1 of 8 ==
Date: Sat, Dec 6 2008 10:07 am
From: "Ryan McEwan"
Hi all,
So one thing I work on is trying to understand WHY invasive plants are able
to acquire habitat space so readily. There are a number of
that has been postulated to explain the invasion of shrubs (honeysuckle,
privet, etc) into forest understories is "the empty niche hypothesis" which
suggests that the eastern deciduous forest does not have a substantial shrub
layer, and thus the invasive species can waltz right in.
Do y'all buy this?
An potentially interesting corollary hypothesis I have is that the shrub
layer of the eastern deciduous forest is underdeveloped because the forest
itself (over most of its spatial extent) passed through a period of
intensive disturbance (humans with chain saws, ~1890-1940). Tree
species recovered from this via stump sprouts, seed banks, etc...but, the
shrub layer is less resilient and has not recovered as rapidly. Thus the
"empty niche" (if one exists) is a reflection of human disturbance, rather
than the natural state of the system.
Do y'all buy this?
I think my corollary hypothesis can be addressed somewhat simply by asking:
"Is the shrub layer of old-growth forests better developed (more species
rich, etc) than that of second-growth forests?"
Any thoughts?

== 2 of 8 ==
Date: Sat, Dec 6 2008 10:45 am
From: "Edward Frank"
Some interesting ideas. I am not a forest ecologist, but a geologist with an interest in trees. It has been my personal experience that the shrub layer is not as thick in old growth forests as it is in logged or disturbed forests. I am not sure about the diversity, but they are generally fewer in number in old growth. I would attribute this to the thicker and more closed canopy in many of the old growth forests as opposed to the more open and sporadic canopy of the disturbed forests. This is effect is exacerbated by the removal of evergreens and there replacement by hardwoods in many of these timbered areas.
It strikes me that the understory/shrub layer in the disturbed forests consists of more opportunistic species that thrive in the light. This includes both shrubs and small trees. In the old growth forests the floor is more open and the shrub layer consists of more shade tolerant species and shade tolerant small trees. Invasive species tend to be more prevalent in disturbed forests than in old growth. I take that to mean that they are typically more opportunistic and light loving species that can compete with the native species in these timbered and disturbed situations, whereas they do not do as well and are not as competitive with the more shade tolerant species in old growth forest.
I have not done any systematic analysis of the differences, but this is my impression, and I acknowledge it could be erroneous.
Ed Frank

== 3 of 8 ==
Date: Sat, Dec 6 2008 1:03 pm
From: Lee Frelich
Eastern deciduous forests on good sites have a high leaf area index, and
thus relatively little light getting through to the forest floor, and a lot
of extremely shade tolerant tree seedlings and saplings, so that shrubs
cannot compete very well.
Invasion by buckthorn, privet, Japanese barberry, tatarian honeysickle,
etc. is probably more vigorous in forests invaded by European earthworms
(and now Asian earthworms as well), because the worms make an ideal seedbed
for the shrubs, and although this part of their impacts is not as well
studied, probably also increase light levels by making the soils drier so
that the canopy is not as dense, and by killing much of the seedling and
sapling layer (in conjunction with deer). The worms also change the
mycorrhizal community so that it is less favorable to native trees and the
non native shrubs are adapted to the presence of the worms (having
co-evolved with them). Human disturbance also creates opportunities for
shrubs, but these areas usually also have the exotic earthworms.
In northern MN forests, the opposite happens. People have suppressed
disturbances (fires) that used to keep native shrubs at bay, and we now
have 100 million acres of the native shrub beaked hazel. These forests are
on shallow soils, however, and don't have the high leaf area index of
deciduous forests on good sites.

== 4 of 8 ==
Date: Sat, Dec 6 2008 3:35 pm
From: "Steve Galehouse"
I think another aspect concerning the proliferation of alien species in the
shrub layer could be lack of predation or control by their naturally
associated pests and diseases---the privets and buckthorns made it over to
North America, put perhaps whatever insects pests of fungal diseases that
kept them in check in their native areas didn't. Also, the exploding deer
population throughout the Northeast and Midwest may have more of an impact
on the native shrub layer, less so on alien shrubs---I would presume a
whitetail deer would prefer browsing on shrubs and trees with which it has

 == 5 of 8 ==
Date: Sat, Dec 6 2008 5:59 pm
From my western experience, when a population explodes, the pressure on the understory eventually will end discrimination for natives, to most anything that might provide sustenance, native or not. I imagine deer in the East may not be that much different than deer in the West, but I'm no wildlife biologist. I do recall that deer in the Quabbin are quite happy to browse on young oak, but quickly go on to other browse when oak offerings are gone. Deer exclosures in the Quabbin allowed oaks to regenerate with high success due to the advance regeneration that their advanced root structure allowed. Would Pennsyvania be that much different?

== 6 of 8 ==
Date: Sat, Dec 6 2008 5:59 pm
From my western experience, when a population explodes, the pressure on the understory eventually will end discrimination for natives, to most anything that might provide sustenance, native or not. I imagine deer in the East may not be that much different than deer in the West, but I'm no wildlife biologist. I do recall that deer in the Quabbin are quite happy to browse on young oak, but quickly go on to other browse when oak offerings are gone. Deer exclosures in the Quabbin allowed oaks to regenerate with high success due to the advance regeneration that their advanced root structure allowed. Would Pennsyvania be that much different?

== 7 of 8 ==
Date: Sat, Dec 6 2008 6:14 pm
I'll take a stab at your corollary hypothesis...IMHO, most old-growth forest ecosystems will have a naturally more diverse horizontal and vertical diversity in their understory, as a fuller range of disturbances has offered up opportunities for a wider diversity of pioneering species to enter, to enter into an already rich seed bank; similarly, the vertical or structural diversity will also be more present, as the forbs/shrubs competition has had time to sort out acceptable light/soil/moisture relationships. This accumulating diversity over time lends resilience to the ecosystem, and a subsequent richness of response to disturbances, of varying frequency and intensity.

== 8 of 8 ==
Date: Sat, Dec 6 2008 9:32 pm
From: Beth Koebel
I don't agree with the first hypothesis, "the empty niche hypothesis".  I am a firm believer that nature would have filled all the niches with an appropriate species.  As time slowly changed so does the species in each niche.
I do like your second hypothesis of since the intensive disturbance of mankind that the shrub layer couldn't recover faster than the invasive shrubbery.  I also like your idea on how to go about proving this theory.

TOPIC: Shrub-layer an empty niche?
== 1 of 2 ==
Date: Mon, Dec 8 2008 1:58 pm
From: Carolyn Summers
Unfortunately, deer have also become an agent of disturbance. It is logical
that they prefer many native shrubs to the exotics. Just over the last 10
years, I have seen two common species gradually being eliminated from my
hemlock woods ­ hobblebush, Viburnum lantanoides and Ilex montana, mountain
winterberry. I could name others, but these two seem hardest hit.
Carolyn Summers

== 2 of 2 ==
Date: Mon, Dec 8 2008 5:41 pm
I guess in retrospect, I could shorten my previous answer to less than ten words:
A disturbance is a disturbance is a disturbance.
Man as an indigenous people were a disturbance. A person today, if careless, can be a disturbance. People as a society today, with the advantage of technology, are a disturbance. Weather events are disturbances, and changes in climate are disturbances.
They all create opportunities for a pioneering species to enter, whether the pioneering species is a native, an unwanted opportunistic alien invader, or a desirable non-native replacement for a native that no longer can adapt to the unnatural range of variation caused by climate change.
It's probably not the issue so much that invasives occupy disturbed habitat so quickly, but how well it reproduces once it gets established. When invasives are out competed by the natives, invasives are not as much as a problem, say, as when the natives are outcompeted, and extinguished.

TOPIC: Shrub-layer an empty niche?
== 1 of 1 ==
Date: Tues, Dec 9 2008 7:03 am
From: pabigtrees
In the East I have observed and studied this exact topic. As a land
manager for a private landowner, it was my responsibility to get rid
of invasives (talk about job security) I started to notice that the
areas that were heavily infested with exotic species had been
disturbed at some recent point. Agriculture was the biggest
disturbance. Some of the wooded sections were farm fields and had
been let go 100 years ago or less. These fields that now have 30"
poplar and ash still retain the high PH levels that the farmers
created through liming or incorporting sea shells. The successionary
native tree species moved in easily along with the invasive shrubs.
(Eleagnus, Rosa, Lonicera, Euonymus, etc) The original ephemeral
layer and shrub layer were completely removed by the act of farming
these fields. Some areas were left untouched due to slope or rocks.
These areas maintained their ephemeral layer and their native
hardwood canopy, but the native shrubs were few and far between. The
only native shrub present is Lindera benzoin which is not prefered to
white tail deer. I agree with Ed that old growth areas tend to have
little shrub layer due to competition and lack of light.
One area I focused on was an old field that ended at an old stone
wall. The field contained red maple, white ash, black cherry, tree of
heaven, bird cherry, and tulip poplar and had been "let go" about 50
years ago. The forest floor is covered in honeysuckle vine,
multiflora rose, burningbush and spicebush and garlic mustard. The
deer population is heavy. The PH of the old field is 7.2. This all
stops abruptly at the stone wall, like a line drawn in the sand. The
other side of the wall is a steep slope with rock. The trees are well
over 150 years old. Black, white, chestnut and red oak. Black gum,
Hickory, White ash, and some sassafrass and dogwood cover the area.
Not one invasive tree on this side of the wall. The shrub layer is a
heavily browsed layer of Pinxter bloom, lowbush blueberry, mountain
laurel, and witchhazel. The ground is covered with moss and spotted
wintergreen. A cat brier sneaks through here and there. The PH is
Disturbance, deer, and availability of seed sources are to blame. One
good thing is that the Native hardwoods seem to be inching their way
back into the old fields. The Bitternut Hickory seems to be the most
prolific, as the deer don't like to eat it OR rub it with their
antlers. One other native that seems to be getting a foothold is
american holly. Deer leave it alone.
I often wonder if time is the answer to invasives. In two hundred
years will the trees shade out the shrubs again? Only if the deer are
controlled in my opinion. This has caused me to start hunting again
four years ago. I have removed twelve deer from my neighborhood in
that time, mostly does.

TOPIC: Shrub-layer an empty niche?
== 1 of 7 ==
Date: Wed, Dec 10 2008 7:15 am
From: Kouta Räsänen
Scott & ENTS,
An interesting topic and discussion! I would like to comment only
> I often wonder if time is the answer to invasives.  In two hundred
> years will the trees shade out the shrubs again?
Remember that in two hundred years any given area has probably a
different climate. This allows more and more exotics to enter to
natural ecosystems as the native species are not anymore the "best
adapted" for the area they historically occupy.
Kouta from Germany

== 2 of 7 ==
Date: Wed, Dec 10 2008 8:50 am
From: Elisa Campbell
Somewhat on this topic, I came across a refernce to a fairly short
article on the effects of an overabundance of white tailed deer.
Overview Paper: Impacts of White-tailed Deer Overabundance in Forest
By Thomas Rawinski, USDA Forest Service
Land managers, especially in southern New England, need to recognize
that deer are exacerbating invasive plant problems, while also seriously
degrading native forest vegetation. Integrating aggressive deer
population control measures into land management programs holds great
promise in restoring these forests.
The paper can be found at
Thomas J. Rawinski, Author and Botanist
USDA Forest Service
Durham Field Office, N A State & Private Forestry
Phone: 603-868-7642

== 3 of 7 ==
Date: Wed, Dec 10 2008 10:05 am
From: Elisa Campbell
more on deer and invasives (this one concludes that to encourage native
plants, the invasives must be removed):
Tuesday, August 5, 2008 - 1:30 PM
COS 40-1: Interactive effects of white-tailed deer and invasive
plants on temperate deciduous forest native plant communities
Norman A. Bourg1, William J. McShea1, and Chad M. Stewart2. (1)
Smithsonian Institution - National Zoological Park, (2) Indiana
Department of Natural Resources
The relationship between white-tailed deer (Odocoileus virginianus)
populations, herbivory and invasive species proliferation has received
little study, despite its potential impacts on native biodiversity and
natural areas management. To address this important ecological issue, we
initiated a controlled field experiment in 2005 at three high deer
density study sites in mid-Atlantic temperate upland deciduous forest
(Conservation and Research Center, Front Royal, VA; Great Falls National
Park, VA; and the Goldmine tract of the Chesapeake and Ohio Canal
National Historical Park, MD). Following initial baseline vegetation
surveys (all herbaceous plants and woody plants ? 30 cm in height) of
333 4x4-meter randomly located plots, control, deer exclusion (fenced)
and invasive species removal (hand pulling) treatments were applied in a
2x2 factorial design at each of the study sites. Plots were resurveyed
in 2007 to estimate the understory vegetation response in terms of
native species richness, diversity and woody stem counts. Response
variables were analyzed as mixed-model repeated measures analyses of
covariance using SAS version 9.0 software.
The forest understory plant community responded positively after 1.5
years of exposure to the experimental treatments, and the non-woody
components were largely responsible for the significant changes thus
far. Native herbaceous species richness increased significantly at two
of the three study sites, with the invasives removal treatments having
the greatest response. Significant increases in native forb species
diversity occurred at the same sites, with the invasives removal
treatments again showing the largest increases but mainly in plots that
also had high initial invasive species cover. Woody species richness,
diversity and stem numbers displayed significant relationships with the
canopy species richness covariate and showed increasing trends at all
sites over time, but significant treatment effects did not appear by
2007. The results for non-woody native plants, particularly in those
plots that were treated with hand-pulling of invasives only, support the
conclusions that invasive plant cover negatively impacts their survival
and that collateral damage to native species did not occur. The similar
response in the invasives removal treatments indicates the primary
inhibitor for most non-woody natives is the presence of invasive plants
and not deer herbivory. Detection of significant treatment effects on
woody species may occur after a scheduled plot resurvey in 2009,
although positive trends were documented here. Deer management, such as
fenced exclusion or population reduction, in the absence of invasive
plant removal, may therefore be insufficient to promote restoration of
the native plant community.

== 4 of 7 ==
Date: Wed, Dec 10 2008 10:21 am
I know Tom Rawinski. He is a fine scientist and he is clearly stating what many of us realize is the biggest problem to forest regeneration - overabundance of deer. What has been amazing to me is the lack of foresight in DCR's implementation of Green Certification. Unless DCR incorporates real deer population controls into their expanded timber harvesting operations, the deer population is just going to grow larger. It is a no-brainer, but DCR plows on with their plans to expand harvesting, oblivious to invasives and deer. Go figure. When talking to DCR people, I have to bite my tongue a lot these days, but duh!

== 5 of 7 ==
Date: Wed, Dec 10 2008 10:38 am
From: Elisa Campbell
and moose ...

== 6 of 7 ==
Date: Wed, Dec 10 2008 10:48 am
There is no doubt that the spread of certain invasive species is accelerated
by white tail deer. In the Appalachians Microstegium vimineum, Japanese
stiltgrass is changing the condition of the "natural" hardwood forest faster
than researchers can keep up with the evolving idea of what a "natural" forest
or "natural" regeneration is likely to be defined as in the future.
Invasive plants are showing up in tracts of woodland where nothing more than
a stream passing through the property is a part of the disturbance regime.
In so many forested situations I have encountered, the invasive species are
not filling in a vacant niche...they are replacing a dynamic and diverse
forest understory comprised of hundreds of native plant species per acre with a
green desert that consists of a dozen or less of the most persistent native
plants fighting for space against the overwhelming assault of non resident alien
invaders that are capable of altering their adopted environment to suit
their needs while producing prodigious amounts of seed that enjoy extremely high
germination rates in the absence of fertility depleting microorganisms that
keep resident plan populations in balance.
Again, the changes being wrought on our forests by climate change and
nonnative plants, insects and diseases is validating the ENTS historical mission of
documenting what a "natural" forest is by today's definition.

== 7 of 7 ==
Date: Wed, Dec 10 2008 12:29 pm
As a vegetation program manager for several years at the Grand Canyon, we concluded that unless one was able to handpull evasives in their first season there, handpulling alone didn't guarantee full protection. Once invasives provide input into the seedbanks, they are much more difficult to eradicate.

TOPIC: Shrub-layer an empty niche?
== 1 of 1 ==
Date: Wed, Dec 10 2008 8:18 pm
From: "Steve Galehouse"
Russ, ENTS-
Not to be a heretic, but I think we have to realize we humans are as much
agents of dispersal of plant species as are birds, squirrels, wind patterns,
etc. Were it not native in my area, I think any of the Smilax species would
be considered invasive, as well as Viburnum acerifolium and Vaccinium
stamineum. The "alien" barberries, buckthorns, burning bushes and the rest
that have become naturalized are now effectively native species--just
because we can document how they came here from distant origins, doesn't
mean they don't belong here in the grand scheme. We don't know how "native"
species expanded their ranges, but I'm sure many did so with the help of
human influence(agriculture). I also think that observing and recording the
shrub layer of the forest, without taking in to account the herbaceaous
layer, is limiting the mix of the forest community.

TOPIC: Shrub-layer an empty niche?
== 1 of 13 ==
Date: Thurs, Dec 11 2008 7:28 am
From: "Ryan McEwan"
In my view, the term "invasive" really refers to life history
characteristics (dispersal, reproduction, growth characteristics) whereas
"native" refers to where a species was...basically... prior to the
"Columbian Exchange." I think your argument highlights the importance of
recognizing that there are "non-native invasive species" and also non-native
species that have "naturalized." The naturalized species are innocuous
members of an ecological community, the invasive species have
significant impacts on biodiversity and ecosystem function (think of the
forest floor under Lonicera).
I imagine that if you focus on life history traits, some native species are
"invasive," but, most deciduous forest shrub-layer species don't fall into
that category in my view- Smilax, Viburnum, Lindera, etc., just dont
have the same impact on biodiversity and ecosystem function as invasives
such as Lonicera or Ligustrum. What about Rhododendron, though? I think
it is an interesting case...and maybe Kalmia in some settings, I am sure
there are others I am not thinking of.
The other really important thing to keep in mind is that native weeds should
not be considered "invasive" if they are part of an ephemeral community.
Think of poke (Phytolacca) has all the features of an "invasive"
species, but it does NOT form a persistent is ephemeral,
holding the niche for a brief time. Ultimately, I think native weeds might
be the key for management of need something aggressive to
hold those disturbed areas until you can get the forest floor in place and
some shade from the canopy. Native "weeds" like Phytolacca, Rubus,
Eupatorium rugosum, maybe even Acer negundo, and others, might be very
helpful in that context.

== 2 of 13 ==
Date: Thurs, Dec 11 2008 8:11 am
From: "Edward Frank"
Are you saying that Rhododendron and Mountain Laurel are a native invasive in some conditions as opposed to the "normal" forest components? If so in what circumstances is this the case? It always struck me as a core component of the forest rather than something that should not be there.
The definitions you provided are useful in these types of discussions on the list to make sure everyone is starting from the same basic perspective. The idea of native placeholders to help prevent the establishment of non-native invasives is interesting.
I am wondering about what you think concerning the replacement of native grasses by invasive ones in some settings. this is a big problem in some patches of open prairie in the mid west. Another example is from some of the Allegheny River Islands, portions of the islands were open grassy areas. These have since been replaced by Japanese Stiltgrass. This may be do to the damming of the river upstream preventing the annual or at least frequent flooding of the islands. (The presumption being that the flooding was more favorable to the native species than it is to the invasives.) The same can be said for the invasive multiflora roses, the Knotweed, etc. The only areas in portions of the island not covered by the invasives, and still retaining a semblance of native species are areas still being flooded. The point being that changes in the natural processes of flooding, fire, etc, may actually result in less "disturbance" of the area and promote the rise of invasives. Some types of disturbances are needed to maintain the natural succession cycles and interrupting them may result in the invasion of both exotics and atypical native species. Obviously the grassy areas do not have shrub layer, but the process could be analogous to those affecting forest settings.
Join the Primal Forests - Ancient Trees Community at:

== 3 of 13 ==
Date: Thurs, Dec 11 2008 11:03 am
From: "Ryan McEwan"
I don't have a well developed idea about "native invasives." I am
actually skeptical of the concept. I don't think of Rhododendron and
Mountain Laurel as invasive, they came to mind as I was thinking
about native shrubs that have a major impact on biodiversity and ecosystem
function...Rhododendron certainly does in some areas. Its an impactful
shrub, which I think is interesting, but really wouldn't go much beyond
that- "interesting" particularly when thinking about the idea of an "empty
niche." There have been a numbers of papers on Rhododendron dynamics,
disturbance, etc. I think several papers from Coweeta...I don't know that
literature at all.
I think your comments about the grasses are right on. Disturbance (in all
its forms) interacts quite directly with invasion in many systems.
Sometimes removing disturbance causes the invasion, sometimes introducing
disturbance facilitates invasion.
As the responses to my first email have nicely suggested, the invasion
process is complexity piled on complexity piled on complexity.

== 4 of 13 ==
Date: Thurs, Dec 11 2008 12:12 pm
From my perspective, the phrase "native invasive" is a contradiction in terms, and should be discontinued immediately, lest it gain coinage by being "Google-able"....;>}
A species native to the area or region (limits defined by vector capability, watershed, etc.) taking hold in a recent disturbance would come under the broad category of a pioneering species (a phrase used by many to describe species like aspen (in the west...;>)) which often takes hold in recent disturbances (like burns, blowdowns, etc.), lives a relatively short life while other more shade tolerant species get established and eventually dominate (or at least come to maturity).
While my understanding of the eastern disturbance ecology is limited, my thinking is that laurel and rhododendron are native species that 'pioneer' well, after some kind of disturbance. My recall of rhododendron patches is that the tend to occupy the lower reaches, which I suspect might be the result of moving water events? Burns? In any case, they seem to take hold and sustain themselves for some time.
I was asked once 'what is a weed'? My off the cuff, non-academic reply was any plant that I didn't want there...I love looking down on a mosaic of vegetation that includes rhododendron while in flower, but it would quickly attain "weed" status, at exactly the point I had to traverse it.

== 5 of 13 ==
Date: Thurs, Dec 11 2008 12:20 pm
Your comments about invasive grasses set me to thinking...some of what you were saying has to do with the relative periodicity of the disturbances...if their return cycles go outside of their natural range of variation, the site may become more susceptible to invasives...flood events are perfect vectors for many species and are indiscriminant to the native/invasive seeds carried.

== 6 of 13 ==
Date: Thurs, Dec 11 2008 1:01 pm
From: "William Morse"
this discussion has moved on an interesting tangent to the original
post. There is a new book out on the number of north american species
introduced to China and their impacts..its huge. i don't have the
title infront of me now but north american crayfish spread a crayfish
virus to Europe and wiped out nearly the entire European crayfish
fauna and amphipods from Midwest have nearly wiped out native
amphipods in the British Isles...the story simply points out that the
exchange of species non-native to a location are happening globally,
not just here...but the impacts are no less significant. Travis

== 7 of 13 ==
Date: Thurs, Dec 11 2008 1:15 pm
From: "Edward Frank"
I was thinking more along the line of periodic flooding being a controlling factor in which species survive in a niche rather than a vector for seed dispersal. Dale and I were talking about a paper on the Allegheny River Island stuff we are doing. There are several distinct zones as you move upward in elevation from the normal river level to higher grounds. on the lowest levels you find species that tolerate frequent floods sycamores, silver maples, black willow. A little higher you begin to get more black locust, hawthorn and basswood, A little higher and you get red oaks added to the mix, some hickory and butternut. This progression represents the frequency of flooding for those different elevations. Finally at the highest elevations in areas that are flooded only in the couple hundred year range you can pick up pines and hemlocks and a much wider diversity of species. The major and most noxious invasives are limited in number or absent from the areas that are flooded every year or at least every other year. At higher elevations which flood less frequent;ly, thanks to the wondrous Kinzua Dam the invasive multiflora roses and knotweed are the only species that seem to be present in the understory of trees in many areas. Certainly you are not getting any regeneration of the trees in these areas.

== 8 of 13 ==
Date: Thurs, Dec 11 2008 1:56 pm
From: "Edward Frank"
I am in complete agreement about the term Native Invasive. It is an oxymoron and should be abandonned. The concept trying to be expressed is interesting however. Consider that something might cause the explosive increase in the number of one native species to the detriment of others that would normally be expected in an area. In other examples a single species may be present in greater numbers than in the adjacent areas because of some specific type of disturbance. This condition may persist for a long time or be relatively ephemeral min nature. In this regard I am thinking of the Marion Brooks Natural Area in PA. Here the location was logged, then a massive fire burnt the area destroying most of the organic material and soil structure. the area was pioneered by white birch. This occurred 80 or 90 years ago and the area persists as a stand of almost pure white birch. other species are not recolonizing the area as might be expected in a normal disturbed region.
Another example to a degree might be patches of forests that have limited species diversity because of alleopathy of some of the species present. If some of these limited areas were to expand it would be an invasive-like effect that limited the diversity of species present in the area compared to the normal forest.
I guess I am just rambling at this point.

== 9 of 13 ==
Date: Thurs, Dec 11 2008 3:31 pm
From: Lee Frelich
Ed, Don:
I find the term native invasive useful and will continue to use it in
publications (along with exotic invasive and exotic non-invasive). Native
invasive is particularly useful for species like Carex pensylvanica, that
have expanded their niche to exclude most other native species permanently
over vast areas in the absence of disturbance, but that happened to be
preadapted to the disappearance of certain mycorrhizae from the soil.

== 10 of 13 ==
Date: Thurs, Dec 11 2008 4:03 pm
From: "Edward Frank"
Ok Lee whatever you say,

== 11 of 13 ==
Date: Thurs, Dec 11 2008 6:40 pm
Of course you can do what you wish without any sayso from me.
But perhaps you could explain how this differs from any native species competing with other natives when faced with an opportunity brought about by a disturbance, whether natural or, presumably in the specific case you refer to, by man's introduction of non-native earthworms(?)?Your offered example is so specific. I believe Ed and I were discussing a much more general scenario, where we were worried that such a usage was likely to introduce confusion into a topic already becoming fraught with new terminology to the lay public (non-native, alien invader, invasives, etc.)

== 12 of 13 ==
Date: Thurs, Dec 11 2008 8:22 pm
From: Carolyn Summers
Hi Lee,
You are a scientist and I am not, but it does seem to me an accurate term,
speaking as a lay person. It is the earthworms that are the invaders, no?
The sedge is on its home turf and is merely taking advantage of favorable
conditions created by the earthworm to expand its niche at the expense of
other natives. If something native expands its niche that is just an
expansion, but if a plant is introduced from another continent that truly is
an invasion. Why not refer to these problems as native monocultures, since
the problem is not the existence of the plant, but rather the absence of
Carolyn Summers
63 Ferndale Drive
Hastings-on-Hudson, NY 10706

== 13 of 13 ==
Date: Fri, Dec 12 2008 2:05 am
From: Kirk Johnson
Native grape vines act like an invasive in some cases in the right
conditions if you ask me. Almost as bad as certain exotic vine species. I
always cut out grape vines if they start growing on my property. I don't
like them that much.
Kirk Johnson

TOPIC: Shrub-layer an empty niche?
== 1 of 4 ==
Date: Fri, Dec 12 2008 2:05 am
From: Kirk Johnson
Native grape vines act like an invasive in some cases in the right
conditions if you ask me. Almost as bad as certain exotic vine species. I
always cut out grape vines if they start growing on my property. I don't
like them that much.
Kirk Johnson

== 2 of 4 ==
Date: Fri, Dec 12 2008 5:10 pm
From: Lee Frelich
You are right, its not the mere existence of the plant (Penn sedge) that is
a problem, the problem is that it takes on the same characteristics as
exotic invasive species with regard to the scale of its spread, preventing
(perhaps permanently) the other native species from recovery.

== 3 of 4 ==
Date: Fri, Dec 12 2008 5:19 pm
From: Lee Frelich
In some sense Penn sedge is not different from other native species. For
example, birch after forest fires can take over a million acres in the
boreal forest. However, these birch don't alter the historic successional
pathways like Penn sedge. The later successional species can still get back
in, unlike Penn sedge that expands rapidly and alters the environment in
such a way that other native species are excluded. We know that most native
plant species can persist and recover to some extent after earthworm
invasion if Penn sedge doesn't take over.
I have not had problems explaining the concept of native invasive species
to the public.

== 4 of 4 ==
Date: Fri, Dec 12 2008 11:59 pm
I recognize your use of 'native invasive' serves you well, and presumably in an academic environment. I understand that doing an internet search such as Google often yields a fair number of hits, and their value academically is questionable.
That said, out of curiousity, I Googled "native invasive". Out of the first 100 hits, two specifically referred to the usage that you have explained.
The other ninety-eight were "non-native invasive" hits.
Don't get me wrong, I'm all for elevating the standards of ENTS members understanding of the world around us. My only point was, and at this point I apologize as I've already belabored the point too long, I worry about the likelihood of confusion it's use will generate in the lay the Grand Canyon, we strove everyday to get the message out to our public, and we never felt our job was done...

== 2 of 2 ==
Date: Sat, Dec 13 2008 7:07 pm
From: James Parton
Kirk, ENTS,
Poison Ivy also acts as an invasive. Often overgrowing trees along
clearings. It makes measuring girth on some trees difficult,
especially in summer.
James Parton

TOPIC: Shrub-layer an empty niche?

== 4 of 9 ==
Date: Sun, Dec 14 2008 9:47 am
From: James Parton
Though I have been measuring trees for less than a year, I have found
that winter is definitly easier to find the highest point. It would
seem that in summer that the trees would actually be a little taller,
with the leaves being on them, except for evergreens, of course!
On Dec 14, 12:22 pm, wrote:
>     On the short daylight hours of winter, what does one do with one's time? Why, Bob, you say, what a silly question! Why, measure trees of course.  And, that folks is exactly what I've been doing, but with a specific purpose in mind. I am comparing summertime with wintertime measurements of trees in our wooded lot. One tree occupied the spotlight this morning - the Monica Tuliptree. In summer, the crown is full and prevents full laser penetration to the higher, farther twigs. This is the rule rather than the exception with tuliptree and makes the species difficult to measure to the absolute top.
>      My summer measurements of the Monica tuliptree range from 121 to 123 feet, depending on my exact location, with 123 utilizing the most optimistic readings from my instruments. Today's winter measurement were taken from the second floor of our home, looking out a window that provides an unobstructed view of both base and crown.  At the point of measurement, I was 43.5 feet above the base of the tree. The height I got (with repetition) was 125.4 feet. By being at a higher location than on the deck by 10 feet and shooting in the winter, I am able to see twigs farther into the crown and hit higher points. BTW, I used both the Prostaff 440 and Prostaff 550 and got measurements that were in agreement.
>       In our discussions about tree measuring, we have often acknowledged that winter is the best time to measure hardwoods and I can certainly verify that. Monica's tuliptree gets frequent re-measurements and is one of several dozen trees I use to keep tabs on the range of readings I can get from casual measurements taken at different times of the year.
>       The wintertime measurement of Monica's tuliptree puts the slender tree in the 125 Club. It shares this distinction with 3 other trees, two white pines and another tuliptree. Altogether, there are 6 trees on Monica's property that exceed 120 feet in height. None of our surrounding neighbors with private property can lay claim to the same. Not bloody bad, folks. Not bloody bad.
> Bob