You may be right on the first two questions. In many years to come, the native environment could adapt and the invasive plant might eventually develop diseases and predators, however, we're talking about years, and years, and years and not tens of years. In the meantime the invasive plant will have done so much damage to the ecosystem, that many of the native plants that used to exist there, no longer do, and there is no native environment left to coexist with. Under no circumstances can invasive plants be considered harmless.

Some plants that are invasive in one region are not in others. For instance, the Tropical Soda Apple which is a horrible invader in Florida is not invasive in more temperate climates. Have you ever traveled in the South and seen whole forests engulfed by Kudsu? Waterways in the Northeast have been totally taken over by Purple Loostrife. Privet and Japanese Honeysuckle are also outcompeting native plants in my region and that is just to name a few.

There are varying degrees of invasive, with "noxious" being the worst. Be sure to check the USDA Invasive Plant list for your state if you have any doubt about the invasiveness of any plant you introduce into your garden or natural area.

The link below to a Nature Conversancy site is very good.

Here is a link that might be useful: Nature Conservancy on invasive plants

The answer to all of your questions is yes.

You have to take into account the modivations of the people theat create 'invasive' plant lists. Many of them believe that US wild spaces should be exaclty the same as the day european settlers set foot in the new world. They don't take into account that the environment changes.

You also have to take into account definitions which in many ways are economically influenced. If a plant competes with crop plants it is considered a noxious weed even if the 'noxious weed' is native.

Disease and pests eventually do catch up with non-native plants. If you look at Pinus sylvestris and other non-native pines that are on some states invasive lists, pine wilt which is caused by a nemotode that native pines are resistant to are infecting non-native species in at an increased rate. Whether or not non-native pines eventuall form a resistance is a matter of evolution at work.

In many years to come, wouldn't the native environment gradually adapt to compete with the invasive plant?

Perhaps it would and perhaps it would not. Each species in the native environment that suffered competition from the non-native species would react in its own way. Some might evolve to co-exist, others might evolve to out-compete the non-native and others might become extinct. However, each of these evolutionary trends might require thousands of generations to evolve. In many cases the native plants might not have enough time to evolve. That would depend on how invasive or how quickly the non-native plant spreads and how competitive it is, on how rare the native species is, etc.

Wouldn't the invasive plant gradually develop diseases and predators in the new environment?

The answer is perhaps. It depends on whether there are generalist diseases and predators present in the new environment that can adapt quickly to the new species. Those diseases may not be strong enough to keep the new species in check. However, a plant species is not necessarily kept in check by a few diseases and herbivores; it may require a wide range of different diseases, herbivores and the competitive effects from a number of other species. For new diseases to be able to infect the introduced species requires either natural genetic variability or new mutations that allow the new disease to infect, grow and reproduce in the non-native species. This may occur or it may not and it may take a long time, hundreds of years to happen.

And lastly, wouldn't the invasive plant gradually adapt to the native environment, and start coexisting with native plants, and become harmless?

No. A species survives by out-competing other species, by producing more offspring, by spreading to new locations, etc. Species do not evolve to become less competitive or less successful. The affected native species would have to evolve to become more competitive.

Garden escapes may occur at any time. Quick action to prevent such escapes from spreading are required to avoid the possible extinction of native species. Natural communities can be a delicate balance of many species which may be severely affected by one introduced non-native species; valuable and rare native species may be driven to extinction if new non-native species are allowed to escape.

thank you ammaad for the inclusion of: "evolutionary trends". I might add: "evolutionary trends operating under contemporary conditions..."
my speculative answers to your questions are:1)doubtful;
2)perhaps;3)no

some rather interesting online peer-reviewed investigations can be found at:
"PLoS Biology"(Public Library of Science)Search Engine (suggest keywords:'global change');
"Blackwell Synergy Global Change Biology"-(journal);
"The Royal Society" http://www.royalsoc.ac.uk/ (keywords:"global change")
and
plantstress.com/

goodness,admmad;
It appears that I misspelled your name.please excuse...

Some native species undoubtedly would adapt to compete more effectively, and some native pests would eventually adapt to attack widespread invasive species. This usually takes a lot of time, though, at least time measured on a human level. Before the native species have time to adapt, quite a few of them might become extinct from having to compete with a new species that has no diseases or natural predators.

Of course, this is part of how evolution operates, with some species out-competing others. The major difference between the current invasive situation and the whole previous history of life is probably one of scale. Human transport is able to move many organisms around the world much, much faster and in much, much larger numbers than any natural process could. Without humans, it would be very unlikely for a plant (or animal, or fungus, or bacteria, or amoeba) that is native to Europe to quickly move to North America, South America, Australia, or Eastern Asia. Using natural processes, it would take hundreds of thousands or millions of years for a particular species to move across such distances, and it would move slowly enough that the local species would have much more time to adapt to it. Humans, on the other hand, can introduce a species into many different locations on multiple continents within a few years, whether intentionally or unintentionally. In addition, many of invasive species thrive in conditions that humans and domesticated animals create, such as cutting down and tearing up native vegetation over large areas, or grazing large areas. This makes for a more lopsided version of the usual evolutionary process, with the odds stacked much more heavily in favor of some of the introduced species and much more heavily against the older, established, native species.

Harold,

Eventually a new equilibrium will always be established. The question is always, "At what cost?" The new equilibrium may take longer than a human lifetime to achieve. True invasives (as in plants that actually displace natives vs. plants that naturalize, but don't crowd out native species) change everything in an ecosystem.

I have a perspective on this that have roots in a subject not welcome on these boards so I will leave it to you to find an answer to the question.

Ryan

an equilibrium? Could you give me a hint of credible sources (biology based)?Why the continued loss of biodiversity?

There seems to be some misconceptions about what makes a plant a "noxious" weed. Each state has the authority to determine what plants are deemed noxious, and this action is carried out often by the state's dept. of agriculture, usually with input from a weed management advisory board. Our board is made up of state legislators and ag industry representatives. Economic impacts of the plant are the primary concern. Here in Idaho, the majority of noxious weeds are toxic to livestock. Some are crop pests and a few infest lakes and streams. All noxious weeds are introduced. There are no native noxious weeds, even though some native plants may become crop pests or are harmful to livestock. Once a plant is deemed noxious, the state has the authority to require landowners to manage the weed on thier property. This seems to be rarely enforced around here. The major emphasis is on education and economic incentives.

I realize this is a little off topic from the original post. I hope it is helpful.

Surely invasive plants will eventually blend into the ecosystem. Whether it's natural enemies catch up to it or new ones adapt, any plant that is abundant is going to become a good food source for something else. All plants were new at one time.

This is such a good topic. There's so much debate of the definition of terms: native, weed, and invasive. And it varies from botanists to horticulturists to taxonomists to agrarians to... It really warrants discussion.

While you may eventually find an equilibrium between an introduced species and its new habitat, it's doubtful that an equilibrium would establish between the introduced species and the native species it supplants (bad pun). So many microniches and urban and suburban borders make it more difficult for the spread of native plants, and much easier for the introduction of foreign ones.

Each microhabitat in which a native species is 'successfully removed' represents a loss of genetic diversity within that particular species, and of course, the more limited your genetic material, the more vulnerable you are to disease and predators.

As an example, if you are a plant species with a slow maturity and/or reproductive cycle like Maryland's native persimmon, living in a very specific environment (brackish swamp), and a well-adapted invasive, like the common reed (aka 'phragmites'), comes along--without intervention your resources are going to get used up and your population will have a difficult time recovering.

I've heard arguments that this is just accelerated 'fittest of survival,' but as Springa7 mentions, our scale of international trade and potential for introduction of species is unprecedented.

Researchers have found that islands are terrific models for this line of inquiry and there are several books on the subject. One of my favorites is Song of the Dodo: Island Biogeography in the Age of Extinction. It's not hardcore data, but more essay format.

**In reply to Botanybob's comment that 'all noxious weeds are introduced,' it seems to depend on which group you're asking. I recently read that natives can be considered noxious--for instance, in a recently disturbed area. Cattails were given as an example. Got the info from this website on plant management in Florida wetlands:
http://aquat1.ifas.ufl.edu/guide/invplant.html

--Sara

Environment wouldnt compete with the new plant, environment is not a living being. Here environment I guess you mean by the native pests, and decease causing bactaria and all, in that means wat you said is right...

Here is a link that might be useful: http://c.1asphost.com/Sanganagouda/forum/

There was a series of TV shows about dinosaurs a few years ago in which computer generated dinosaurs were put into taped backgrounds. The makers of the show said it was difficult to find good settings. For instance, they would see a beautiful cypress, but at the base of the tree there would be grass.

As I understand it, grass evolved near the end of the dinosaur era. Since then the invasive plant has spread across the planet. Many predators have evolved to eat it. Diseases have evolved to attack it. And, yet, great plains of the stuff exist. A new equilibrium has been reached.

In 50 million years will a new invasive plant be innocuous or omnipresent? It could be either.

By the way, I think sangam mistakenly posted the following link on the 'beyond NPK' discussion.

Here is a link that might be useful: Georgia invasives

Pickwick,

equilibrium in the population of any living thing is reached when the number of individuals dying is approximately equal to the number being born. This might not happen until a monospecific community has reached a climatic or geographical barrier, but it will happen eventually (this worst-case scenario has, thankfully, never been realized).

Ryan

...,contemporary conditions/trends....
Ryan ; request references .... more emphasis in the realm of plant sciences and biotic/abiotic inputs, appreciated...
Suggest providing "http:/"; within your post; keywords or keyword phrases within science portal references; library call numbers or ISBN and/ or authors and so forth....
thanks...

prickwick,

the definition I used (or an approximation thereof) can be found in any textbook that addresses evolutionary biology. I'm sure you have a local library.

Ryan

....specific references/textbooks requested....as I thought this forum speciffically emphasizes science over philosophy,personal observations,and ego.... wish to further understand the formulation of your thinking under contemporary conditions (and the impacts/implications of emerging nations including issues beyond CO2 and increased temperatures....)

Pickwick (I'm very sorry for the misspelling, it was an accident!),

Only a few examples come immediately to mind: Achillea millefolium which the "Jepson Manual" (1996, third edition, page 189) notes was introduced to Calfornia and is somewhat invasive in some locations and stable in others (it is so stable on the Channel Islands that it is treated by some publications as native).

There is also widespread disagreement on the status of Fragaria chiloensis which is found along the west coast of North America, coastal South America and Hawaii.

It either evolved independently in at least two locations- South American Coast and North American Coast - or it developed in one area and was transported elsewhere. It is stable (i.e. has reached equilibrium) in at least some places in both North and South America. (Jepson Manual, 1996, third edition, page 952)

Ryan

...hello Ryan;I am reminded of several themes...I find Luis Villareal's article "Are Viruses Alive" presented in the December 2004 publication Of Scientific American rather profound suggesting the revisitation by molecular biologists working with viruses (with current tools of analysis)reviewing works published sixty plus years ago-for example:the evolutionary role of viruses in the web of life...Therefore the integration of biological systems (i.e.)surely involves a multi -disciplinary approach: integrations and contributions of a vast number of scientists' original works disciplined in specific fields and how these ideas are continually peer reviewed and weighed....so for another example,the roles of symbiotic rhizospheric inter-relationships with plants within a community (i.e.)what environmental imputs decrease population densities inducing/contributing to stresses/effects...((i.e.)"Toxicological Benchmarks for Contaminants of Potential Concern for Effects on Soil Litter Invertibrates and Heterotrophic Proceses:1997 Revision:R.A.Efroymson;M.E.Will;G.W.Suter)... inhibiting some means to compete with invasives possessing superior genetic and physiological traits(ie.reproductive versatility)...or review the behaviour and documentation of say:Cadmium(plantstress.com/ )is a good start:"Studies on Cadmium Toxicities in Plants:A Review" P.Das; S. Samantarray;G.A.Rout;Journal of Environmental Pollution;Vol.98;No.1;1997);Mercury,Perchlorates with regards to uptake studies...( work aquatic plants,for one example:(Lemnaceae) and its role and function within food chains;or the required health of vectors of pollinators/seed dispersal organisms...
The development of a contextual view takes time,as well as the continued ability to read scientific papers...)I am humbled...References suggested here are only a start and not meant to be used to formulated an opinion...for confirmations,cross references, ponderance,and deference to specialists are important to me...