I'm not sure that the previous posts have addressed the original question about the extent of "artificial" wetlands in today's landscape. The best way to try to determine the extent of these wetlands may be to compare pre-settlement vegetation community maps with existing land use maps. I'm not sure if Pennsylvania has these maps available, but Michigan does have pre-settlement maps available which were created based on the General Land Office Survey notes from the early 1800's. This may be the best method of comparing pre-settlement (pre-European) wetlands with existing wetlands. Someone proficient in GIS could probably figure this out without too much work.
With regard to species diversity in "artificial" vs. "natural" wetlands, 150 years is more than enough time for a wetland to become highly diverse, depending on the surrounding seed source. I would venture to say that the diversity of existing wetlands, (artificial or not) is more likely determined by its proximity to adjacent existing wetlands and to existing invasive species populations. I would be interested to hear others thoughts on this point. Ellery Troyer -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[EMAIL PROTECTED] On Behalf Of Amartya Saha Sent: Thursday, April 10, 2008 9:30 AM To: [email protected] Subject: Re: [ECOLOG-L] wetland acreage To add to the thread, I suppose these dams are no more than 150 years old at most ? So the wetlands created by placing the dam are not very old, thereby quite possibly not as species-rich as a natural wetland Furthermore, the original (pre-dam) ecosystem being a running water system, its restoration can have greater ecological value, since there are few locations on the landscape where streams can naturally exist., ie, basically along local topographic lows. There is also the river continuum concept whereby removal of artificial barriers to water flow can have an impact far beyond the immediate stream reach. However its possible that these particular artificial wetlands could be important sites of refuge for wetland spp that managed to arrive there -- as Sharif mentions, it would be good to actually examine the wetlands in question, and then decide. Generally speaking, stream restoration could provide more ecological diversity, as its technically easier to create a wetland elsewhere (in theory at least), but the benefits and costs could vary from case to case. Cheers Amartya Sharif Branham wrote: > Hello Andy, > > I think the question should be about the quality of the wetlands that are being replaced. Wetlands that are created as a result of roads or other engineered surfaces are not equal to a natural wetland as far as habitat value is concerned. One could do an analysis of the wetland that is to be displaced by breaching the dam to see if the quality of the habitat that will be lost is equal, less than or greater than the habitat that will be enhanced by breaching the dam. You could consider the quantity and diversity of the species that benefit from each habitat type. You could even look at ecological services being provided by the wetlands versus what will be gained by breaching the dam. I hope that helps you get at the essence of the argument. > > Sharif> Date: Wed, 9 Apr 2008 12:50:53 -0400> From: [EMAIL PROTECTED]> Subject: [ECOLOG-L] wetland acreage> To: [email protected]> > I have been discussing the merits of stream restoration with some > colleagues and I've been fussing over the potential loss of wetlands > as a result of the removal of dams. My stream-oriented friends have > been asking why I've been worried about the loss of what amounts to > artificial wetlands in the first place? Aside from the fact that > they're typically considered jurisdictional, it got me wondering if > we (collectively) have any idea whatsoever how many wetlands in the > landscape are artificial? In other words, how many wetlands exist > because of human activities, such as roads, railroads, and the like? > (Let's keep mitigation, stormwater, and treatment wetlands out of the > discussion for now.) Anyone have a clue?> > Thanks.> > Andy Cole> > > > Charles Andrew Cole, Ph.D.> Associate Director> Center for Watershed Stewardship>! Penn State University> 301a Forest Resources Laboratory> University Park, PA 16802> 814-865-5735> [EMAIL PROTECTED]> > http://www.larch.psu.edu/watershed/home.html > _________________________________________________________________ > Use video conversation to talk face-to-face with Windows Live Messenger. > http://www.windowslive.com/messenger/connect_your_way.html?ocid=TXT_TAGL M_WL_Refresh_messenger_video_042008
