I've just finished the fieldwork and breathing a sigh of relief after all the hectic rushing around the country surveying species rich meadows. The fields are mainly in the floodplains of the rivers Thames, Severn, and Derwent. We are looking at various aspects of these species rich communities which used to be a common sight but are now rare, for example what level of water and nutrients do they need/can they withstand. Floodplain meadows are of course subject to occasional flooding indeed they act as flood protection areas for cities such as Oxford, we know these high biodiversity plant communities can withstand a certain amount of winter flooding but what happens when the areas flood in summer when the plants are in full growth like happened in 2007?
The 1300 sample locations have to be surveyed over a short period when all the plants are up and flowering but before they are cut at the end of June. Besides the meadows that we have been recording annually for many years there were several ‘new’ floodplain areas that had not been looked at for 10 years and which proved to be a bit of a challenge. We wanted to record exactly the same 1x1 metre square areas (quadrats) that had been surveyed in the past so that we could see if there had been a change in species composition especially after the severe flooding and lack of hay cut that happened in 2007. The quadrats we record are not marked by anything – the areas are run over by hay cutting equipment and later grazed by animals so we can’t put in above ground sticks and filling each field full of buried metal to mark all 200 squares is not really desirable either. So how do we find them each year and how to rediscover the ones from 10 years ago?
Until this year we had been using theodolite type surveying equipment to accurately measure angles and distances from fixed points, these can position the quadrats to within a few mm if the fixed objects are still present and visible and we can find the ‘origin’ position of the survey. It’s a big ‘if’ when you consider that the origin position is usually a buried dipwell somewhere in the middle of thousands of square metres of waist high grass and that the landscape often changes quite considerably in 10 years. Fences are replaced, trees grow up and obscure reference points, the 10cmx10cm metal lids of the dipwells may be taken away so the metal detector might be of no help in finding them.
We are moving over to a gps based system, its not as accurate as the old system but can usually position the quadrats to within 5cm of where they should be which is fine and is usually significantly quicker as you don’t have to hunt for the fixed points and there is no delicate equipment to carefully set up on a heavy tripod. The gps also gives the locations in latitude/longitude or ordinance survey grid so researchers will be able to go back to those exact positions in future. There is still a bit of a downside to the new system, it may be lighter, quicker and can be one person operated but it does rely on the mobile phone system to get real time differential corrections of the gps signal – this is how it achieves a much better accuracy than a normal hand held gps. Some of our sites have rather poor and intermittent gprs mobile phone coverage which can be very frustrating as the accuracy can go from a couple of cm to a couple of metres and back again as you are walking along so we may even set up our own temporary base stations and use a radio link instead of using the mobile phone for these sites.
What are the results of all this effort by the botanical surveyors and of the chemical analysis of soil and hay, well you will have to wait until at least the autumn for all the data to be typed in and analysed. Just by eye some of the sites looked rather different to normal but this may have been more to do with the lack of a hay cut rather than the water from summer flood itself.
Botanical surveyors setting off to set up quadrats in a flooded meadow beside the Thames in 2008.
Normally the meadows are dry at this time of year so it was interesting trying to identify species of grass under 30cm of river water at this site. The red box contains the ‘total station’ theodolite for comparison with gps at setting out quadrat locations.