[APWG] NEWS: Invasive Species Widespread, but Not More Than at Home

Mon Mar 14 10:06:12 CDT 2011

Hi Wayne
I agree with your comments. Some people consider most exotic plants as invasive in all situations regardless of where they occur. This includes many roadside weeds that survive in a hostile, manmade environment that many native plants cannot tolerate but these plants are only rarely found 100 yards away from the highway. At least that has been my observation here in upstate NY where I often wander off the road to see how far the invasive plants that dominate the roadside may be found. I read here that Portland, Oregon has an ordinance requiring the extermination of certain exotic plants, seemingly because they present a threat to the native ecosystem of the city of Portland?   I am all in favor of protecting undisturbed ecosystems and other places of native biodiversity from exotic weeds but I wonder how many truly "undisturbed ecosystems" still exist in most of the US. I have been pleased to note on this list serve that the tone of the posts is moving more towards learning and understanding the processes that lead to weed invasions and then designing a carefully calculated approach to dealing with them as some of the posters here have done.
Bob

From: apwg-bounces at lists.plantconservation.org [mailto:apwg-bounces at lists.plantconservation.org] On Behalf Of Wayne Tyson
Sent: Friday, March 11, 2011 5:08 PM
To: apwg at lists.plantconservation.org
Subject: Re: [APWG] NEWS: Invasive Species Widespread, but Not More Than at Home

Yes, it would be interesting. For some reason, many people in the alien bashing business seem reluctant to discuss the difference between "invasive" plants that are largely restricted to disturbed sites and which do not "spread" significantly into or within undisturbed ecosystems (and when they do, attempting to understand that in those cases that the presence of the alien or other colonizing species within "undisturbed" ecosystems is possibly due to small areas of disturbance [e.g., gopher mounds] within them, or other relatively short-term phenomena that shift localized habitat factors in favor of the alien/colonizing species) and those which progressively invade undisturbed ecosystems. It appears that Sahara mustard belongs in the latter group, but disturbance magnifies the effect, particularly to the casual observer.

I also would be interesting to know (I haven't read the paper; no doubt it provides this information) in which of these general categories (I am calling them "obligate ruderals" and "true invasives," but am willing to consider other, better terms) those included in the study fall. Some alien species fall into both categories, still others might be considered mere waifs.

All species are likely to perform best (be most successful) where conditions favoring their requirements are all present at the right times, and will be less successful in more marginal habitats.

I have recently suggested that disturbances connected with control measures such as pulling and trampling, not the mention the use of vehicles, tend to favor many colonizing species, so won't repeat those remarks here.

I look forward to all comments, especially those revealing my errors.

WT

----- Original Message -----
From: Marc Imlay<mailto:ialm at erols.com>
To: apwg at lists.plantconservation.org<mailto:apwg at lists.plantconservation.org>
Sent: Friday, March 11, 2011 2:41 AM
Subject: Re: [APWG] NEWS: Invasive Species Widespread,but Not More Than at Home

It would be interesting to know if the only 2.5 sites per species in home ranges were natural sites or unnatural disturbed sites without competition from native species. Native Switch Grass has been found invasive in America in unnatural habitats but not in natural habitats and is a new invasive in Europe.

Marc Imlay, PhD,
Conservation biologist, Park Ranger Office
(301) 442-5657 cell
Marc.Imlay at pgparks.com<blocked::mailto:Marc.Imlay at pgparks.com> ialm at erols.com<mailto:ialm at erols.com>
Natural and Historical Resources Division
The Maryland-National Capital Park and Planning Commission
www.pgparks.com<http://www.pgparks.com/>

-----Original Message-----
From: apwg-bounces at lists.plantconservation.org [mailto:apwg-bounces at lists.plantconservation.org] On Behalf Of Reinhart, Kurt
Sent: Thursday, March 10, 2011 11:59 AM
To: apwg at lists.plantconservation.org
Subject: Re: [APWG] NEWS: Invasive Species Widespread,but Not More Than at Home

Okay, I'll bite & also do some shameless self promotion.

A contrary view to Firn et al. is provided using a single species (a prominent invasive tree species) that was carried out across 40 total populations with slightly more than half in its native range and nearly half in its non-native range in Reinhart et al. (2010, New Phytologist http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2009.03159.x/abst
ract).  This study concluded that measures of local relative abundance were considerably greater in the non-native than native ranges.  This study may not seem like a direct comparison because the main topic relates to Enemy release but comparable data are in the supplement (which apparently hasn't been read by many).  Others have made similar observations though often without quantitative evidence for species like spotted knapweed, garlic mustard, etc.

Firn et al's ELE study's main advantage over Reinhart et al.'s is their use of considerably more species (26 species, 12 grass and 14 forb
species) at 39 sites.  They concluded species have similar levels of abundance in native vs. non-native ranges.  A conclusion from their paper is that many of the grasses were common at home and away while many of the forbs were rare at home and away.  However based on information in their supplement, I calculated that on average they have measurements for only 2.5 sites per species in home ranges and 7.6 sites per species in exotic ranges.  Sampling more species per region is valued because many species have incredibly large distributions and local abundances are variable throughout.  Sampling broadly is necessary to avoid forms of regional sampling bias though researchers have to balance logistics (also see Adams et al. 2009 as an example of an extensive sampling network
(http://www.plantecology.org/Full%20text%20papers%20and%20abstracts/2009
%20papers/Adams%20Bioinvasions%202009.pdf).  Firn et al. help avoid this limitation by looking at numerous species though more than half represent relatively minor invasions.

I think what we would mostly like to know is what traits/processes/interactions can we attribute to the success of the most invasive species and whether their abundances, effects of enemies, etc. differ at biogeographical scales.  Following the rule of 10s, these species represent the most improbable invasion scenarios.  So we shouldn't be too surprised if such rare events can never be predicted without the benefit of hindsight.  However, I wouldn't be surprised if further studies, focusing on highly invasive species which are the exceptions, reveal that most/many are cases where the species attain greater levels of local abundance/dominance in their non-native than native ranges.  My 2 cents.  You decide.

Kurt Reinhart

  31. NEWS: Invasive Species Widespread,        but Not More Than at
Home
      Range (Olivia Kwong)
Message: 31
Date: Thu, 3 Mar 2011 08:27:30 -0600 (CST)
From: Olivia Kwong <plant at plantconservation.org>
To: apwg at lists.plantconservation.org
Subject: [APWG] NEWS: Invasive Species Widespread,      but Not More
Than
        at Home Range
Message-ID:
        <Pine.LNX.4.64.1103030826390.1121 at cpanel1-bb.epconline.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed

http://www.sciencedaily.com/releases/2011/03/110301111459.htm

Invasive Species Widespread, but Not More Than at Home Range

ScienceDaily (Mar. 1, 2011) -- Invasive plant species have long had a reputation as being bad for a new ecosystem when they are introduced.

Stan Harpole, assistant professor of ecology, evolution and organismal biology at Iowa State University, is founding organizer of a team of more than 70 researchers working at 65 sites worldwide that tested that assumption.

See the link above for the full article text.

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