Saturday, 19 January 2013

Just how fast can pondweeds travel?

The pondweeds that turned up in the field ponds, discovered at the end of the harvest when the ponds were accessible after a summer behind the thickets of oil seed rape (Blog, 12th Jan), were unexpected. I should not be surprised: much of my work on ponds has been teetering along that tricky line trying to work out if the animals and plants are where they are because of some reliable rules, a response to measurable, describable influences such as nutrient levels in the water or the presence of a predator... or perhaps they are where they are just as accidents of history. I am reassured ponds remain full of surprises. Just how fast can plants arrive in a pond or wetland? My favourite example, albeit just a one off anecdote, is from Aberlady Bay, on the south coast of the Firth of Forth east of Edinburgh. In 1989 a pond was scraped out of the sandy wet grasslands, intended to encourage wading birds. You can see the raw sand of the pond on the day it was dug.
The following day I was back on the reserve and walked up to the pond to take some more photographs. In the shallows were conspicuous rafts of feathers, and, tangled in amongst the preening debris, stems and clumps of aquatic plants. Not plants that grew around the edge of the pond which had been dug out in the middle of a grass sward, but new plants, plants i could not recall growing on teh site at all. The plants seemed to have been carried in by birds within twenty four hours. By the summer of 1990 the scrape was choked with a glorious mess of aquatic plants and teeming with invertebrates, even though the sand sides remained exposed and bare. None of the plants had been introduced by the reserve team. That is how fast plants can travel.

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