A recent press release from the University of Lund includes a confusing contradiction. Summarising Dr. Geraldine Thiere's recent doctoral dissertation, Biodiversity and Ecosystem Functioning in Created Agricultural Wetlands, the release claims that on one hand natural wetlands are not more biodiverse than recently dug ponds, on the other hand that biodiversity in wetlands increases with age. Both statements can't be true.
After I had written to Dr. Thiere she kindly clarified the matter for me. It turns out that arguably neither of the two contradictory statements is true.
To begin with, Thiere hasn't studied any natural wetlands.
"I actually compared the diversity and composition of created wetlands with old ponds in the agricultural landscape. These ponds were 50 to 100 years old and stem from clay diggings mÃ¤rgelhÃ¥lor; they are at least semi-natural systems. There was no difference between the diversity and composition of macroinvertebrates in created wetlands and old ponds.
It is a bit complicated to compare created wetlands to real, natural wetlands; partly because there are so few left in the agricultural landscape, partly because the wetlands created today are not neccessarily similar to the wetlands that were once lost. Created wetlands are most alike to small ponds (dammar); natural wetlands on the other hand may not have a permanent water surface (more like a mosse)."
Secondly, the increase in biodiversity over time that she has documented occurred over a period of only six years.
"Wetland age seems to 'enhance' macroinvertebrate diversity, i.e. older wetlands (in my case 5-6 years) hosted more macroinvertebrate species than younger wetlands (they also hosted different species combinations). ... natural wetlands are present in the landscape for a long time, and the question is if created wetlands (even 6 year old ones) come even close to the natural diversity."
Yes, that's the question. Maybe a wetland hits maximum biodiversity already within a few years of its creation. Or maybe an artificial wetland remains relatively poor compared to natural wetlands even after a hundred years. But that's not the question Geraldine Thiere's research was designed to answer.