Posted by Graeme Lyons , Sunday, 31 May 2015 17:02
This summer another battle is unfolding above the streets of Lewes. On one side, Malling Down with its steep sided Combe and scrubby Green Pits and on the other Southerham Farm, with its secluded valleys and ludicrously named Bible Bottom. Yet which one is 'better' for invertebrates? There is only one way find out! FIGHT! Well, no. Actually it's to carry out a repeatable and standardised survey that can inform the management of these two superficially similar yet surprisingly different sites. That's exactly what we are doing this year and we have recently completed the third visit...
Once a month from March until September we are recording all the species we can find within six discrete areas (three on Malling and three on Southerham). We always record for the same time across all six areas. The sites are very rich, particularly in scarce weevils, and the total number of species recorded so far stands at 293! Above is the smart but diminutive (3mm) weevil Tychius schneideri. It only feeds on Kidney Vetch which is abundant at Southerham on Bible Bottom but mostly missing from Malling (conversely Malling has all the Common Rock-rose). So how do the two sites compare? So far Malling is winning with 201 species and Southerham is on 179 species. This difference is likely to be down to the lack of scrub at Southerham but that's not to say we want Southerham covered in scrub (but some scrub is good). A better way to compare the site's qualities for invertebrates would be to compare the proportion of species with conservation statuses but that will have to wait until the survey is completed. Remarkably, only 87 (30%) of the species were recorded on both Malling and Southerham (so not that similar after all or just an example of how hard invertebrates are to find? Or how many species recorded occur at very low densities?). Out of the six sites, the Green Pits at Malling is currently coming out best of all with 102 species. It has the most scrub of all the plots, the least amount of south facing slope BUT a hugely varied topography. It's an old quarry on the north of the site.
Perhaps the most extraordinary difference is the abundance of the RDB Carthusian Snail at Southerham which has so far not been recorded at all from Malling. In many parts of Southerham it's the most abundant snail and was recorded in all three plots there during the first visit. The sites are only separated by a few hundred metres of golf course!
Also as Southerham lacks Common Rock-rose, it also lacks the Cistus Forester that's present at Malling Down. Both sites are covered in Knapweed though but it's only Bible Bottom at Southerham that has the Scarce Forester that feeds on the Knapweed!? So which site will come out on top? I believe Malling will end up with more species but Southerham is likely to have a higher proportion of scarce species and species associated with chalk-grassland. We'll have to wait and see though!