Saturday, 6 October 2018

Bath Nats Primrose Hill 16th September 2018


Report of visit to Primrose Hill 16th September 2018
A group of four revisited Primrose Hill to repeat the biodiversity measurements begun in 2012.  It was an autumn day after a dry summer which will have not helped the growth of our target organisms.  There were many visitors to the site (plus dogs).  We found that there had been much clearing of the undergrowth and dead wood with the brush wood burnt and the larger pieces stacked as in good practice so passage though the wood was easy.  We recorded the presence or absence of so-called lower plants (bryophytes, lichens and fungi) in 20 x 4 m radius circles.  The position of the circles was determined by our random generator (Alan R).  One unexpected complication was that despite notices at the gateway asking people to take their dog faeces home with them it was almost impossible not have them in our circles so pollution we thought might be high!  This is not the only place in Bath where this happens (try the Linear Pathway!) but it was I thought the worst.
The site was established in 2000 on an arable field so we would expect that there would not be any bryophytes lichens and fungi on site (or at least not woodland ones) so starting from zero we have data from 12 and 18 years after establishment.  We did not expect to find any real rarities but you never know.  In fact we did find some less common bryophytes such as Cololejeunea minutissima (Minute Pouncewort) a tiny epiphytic liverwort growing on Field Maple and Fissidens incurvus  (Short-leaved Pocket-moss) on soil.  Surprisingly a small piece of stone lying on the surface yielded two species not encountered anywhere else in our sampling: Tortula muralis (Wall Screw-moss) and Eucladium verticillatum (Whorled Tufa-moss) the latter of which is very small. For comparison we have data from an 18 year old coppice at Lower Woods, an ancient woodland site In Gloucestershire.
Below are the different scores from these three samples:

    Primrose Hill 2012                     Primrose Hill 2018                         Stanley 2000
Species Richness             4                                                        16                                      17
Simpson’s Index of
Evenness                           2.99                                                  9.69                                   17.62
Species Conservation
Value Index (rarity)         2 (=/-0)                                             2.75 (+/-0.75)                   4.04 (+/-1.53)
Frequency (colonies)      40                                                     115                                    244
Nitrogen Index
(pollution)                         6.2                                                    4.94                                   4.68
The picture emerging from this is that after a time sites are colonized by common species and that the distribution of these colonies increases in time. Rarer species are part of this colonization. There is some amelioration of the nitrogen pollution from the arable field but the dogs are doing their best to slow this down. Stanley is similarly dogged by dogs.
We will be repeating this in the future when this will become an increasingly fascinating experiment.  We have several other sites under observation that we hope to visit in the future.
May thanks to Alan and Marion Rayner for their unflagging enthusiasm with identifying  “lower plants” and Kate for her care recording of the field data

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