Monthly Archives: June 2013

MORE ON THE HEATHLAND CONSERVATION GRAZING DEBATE

   Twenty years ago I carried out research into the effects of grazing on habitats for Natterjacks at Woolmer, and the results for them were positive. Very high density grazing by highland cattle resulted in poaching and trampling which helped break up ground encrusted by the alien moss Campylopus introflexus, giving small toadlets access to the soft sand beneath in which to burrow and escape predators and desiccation (Denton & Beebee, 1997). At the same time the cow dung was colonised by a dung beetle fauna of 12 Aphodius species, including the nationally scarce A.coenosus (Denton, 1997), a very rapid positive increase in overall biodiversity.

   However exclosures were also erected to measure the effects of slightly lower density cattle grazing with and without supplementary rabbit grazing. At ground level 20 years on there is structurally no measurable difference. A similar overall result as that found at Cavenham Heath (Bullock & Pakeman, 1997)

Livestock’s preference for Salix and Populus species is implicated as a threat to several RDB lepidopteran species at sites on heaths (Mark Parsons pers. comm.).  Other examples of local biodiversity destruction include devastation of isolated Alder Buckthorn Frangula alnus, and Broom Cytisus scoparius stands which were already highlighted as important in commissioned invertebrate surveys.

    From a floristic and structural standpoint it can be argued that the cattle have locally had a positive effect around Woolmer Pond and other Molinia dominated wet areas. This is good news for Natterjacks and although it is supposed to be bad news for competing Common Toads B.bufo, they are actually increasing! On the downside Harvest Mice Micromys minutus and Water Vole Arvicola terrestris were present before the grazing scheme started. The former is certainly unlikely to thrive in short Molinia. The later appears to have disappeared, possibly coincidentally, but Mink Mustela vison has yet to be reported from Woolmer Pond.  The cattle may also help check the dominance of Crassula helmsii, which has become established in every water body with pH >5 on West Woolmer Forest (26 to date), but the impact of hard grazed Crassula lawns on native flora is still unknown.  However key areas of Sphagnetum supporting the RDB1 spangled water beetle Graphoderus zonatus, as well as dozens of other Notable insects and spiders, and a delicate well-structured bog community with abundant Sundews Drosera sp., etc. have been seriously degraded, indeed locally reduced to black churned peat. A similar outcome was observed at Churt Flashes in Surrey where an introduction programme was carried out for this beetle in the late 1990s, only for the essential Sphagnum rafts to be destroyed by wallowing cattle.

  Further evidence that sphagnetum and bog pool habitats are particularly vulnerable comes from Folly Bog, Surrey. Here amongst much positive grazing effort, a period of overgrazing in 2009 resulted in significant damage. Just three years on in autumn 2012, despite repeated warnings that the cattle should be removed before they had a negative impact, sphagnetum supporting the only extant population of the RDB mire specialist rove beetle Erichsonius ytenensis (which had not been recorded anywhere in the world since 1938, and in the UK since 1913) was damaged by over grazing. I had kept the capture details vague (Denton, 2012), as I was concerned that the site may be damaged by collectors!

    One of the few pertinent studies using replicated sampling albeit of effects of sheep grazing on moths of  upland acid grasslands showed that overall diversity and abundance was greatly reduced by increasing grazing pressure (Littlewood, 2008).

 RE-WILDING AND THE NEW FOREST MODEL

    The Vera Model seems to have taken centre stage, its pros and cons have been well documented in BW (Hodder et al, 2009, Vera, 2009), but in my experience, amongst existing heathland managers it is seen as a green light to graze away, despite remaining a hypothesis, based on findings from a site that is younger than I am, and from most images I’ve seen of it in rather worse condition. A site from which we are told ‘countless species of wild animal and plant’ exist simply because of Greylag Geese Anser anser.  Yet the images show landscapes which seem amenable to making a very full species count!

  Whitmoor Common in Surrey is one of only two extant sites in southern Britain for the lovely caddis fly Hagenella clathrata a BAP species dependent on Molinia litter in small pools, sheltered by tussocks. Many of the key breeding areas for the caddis have been grazed hard and are no longer suitable, and the only remaining breeding area is overgrown by a dense stand of 2m high birch scrub. Alas the strategy of using cattle to control said scrub had resulted in limited browse damage of the birch, and devastation of the underlying essential Molinia habitat that was only stopped by intervention of entomologists, insisting on the removal of the stock. The other site on Chobham Common has just been ring fenced and grazed, without even leaving any exclosures for monitoring the response of Hagenella or any other plant or animal.

   Indeed the irony is that grazing increases the amount of nutrient (Nitrogen) on nutrient poor soils, and removes the litter layer which sequesters nutrients (ie Molinia thatch), thus increasing the rate of succession to woodland (Jofré & Reading, 2012).

   The response is all too often a disingenuous claim that the prevention of woodland encroachment was never promised by grazing. This is simply not the case, the MoD site managers prime motives are to keep sites suitable for training and wildlife, and from day one grazing was sold as an essential tool to do this. Given the paucity of hard ecological evidence, any suggestion of naiveté on the part of site managers (who don’t claim to be ecologists) is grossly unfair.

   The Amphibian and Reptile Conservation Trust have a long and unmatched track record of heathland management for rare reptiles, and have been very effective at maintaining key reptile foci in excellent condition using manual and mechanical clearance.

    It is no coincidence that the same foci are hotspots for invertebrates as well, with sites like Hankley and Witley Commons having amongst the richest aculeate Hymenopteran faunas in the country.

   Trying to increase overall floristic diversity is dependent on exposing an existing viable seed bank (i.e. Starfruit Damasonium alisma), or more likely, through colonisation from other sites. In a fragmented landscape, without some intervention the goal of seeing key species return to sites may require considerable patience, or simply remain a pipe dream.   The botanical evidence is strongly supportive of grazing, but in a world where the threat of invasive species grows daily, the goal of bringing back lost species, could well be outweighed by losses through stock spreading problem taxa such as Crassula helmsii.

   Many if not all the heaths now coming into grazing have been nutrient enriched by woodland succession and atmospheric deposition. Conditions are thus not the same as in the past. Restoration grazing then should be regarded as a different beast to maintenance grazing.

    The reply is invariably ‘these things take time’, and you can’t make an omelette…? Maybe so but surely those entrusted with managing some of the finest remaining wildlife habitats in the country ought to consult and get an educated prediction of what they expect to bring back, and what they might lose. In many heated discussions about the need for such a shopping list, the best defence I have heard is ‘well our botanist says it looks nice’. Ecology is a nebulous subject, but this is hardly a scientific approach. 

     The excuse used to be, ‘well we have to rely on farmers to provide stock and they don’t do what they are told’. Today several wildlife trusts have their own herds and herdsman yet little has changed, and the sickening sight of bald, flowerless trampled ground which was the year before blossom rich and humming with invertebrates (and crawling with herptiles) is all too familiar. Indeed in many cases grazing schemes are so out of control that the claim is all too often that the desired results (whatever they maybe) can be achieved simply through how the sites look to the individual grazing officers!

    Recent survey at Bourley Woods on the Hampshire/ Surrey border (Denton, 2011), found a diverse set of habitats on former heathland, dominated by plantation woodland with lakes managed as a fly fishery. The fishermen keep the margins open and scrub free to allow room for casting, and as a consequence the margins are locally dominated by a luxuriant and very species rich fen edge plant community which inturn supports a superb fauna (including and the Small Red Damselfly Ceriagrion tenellum, and the first county record for the nationally scarce reed beetle Donacia thallasina in over a century). The drier areas are also very rich with hundreds of Southern Marsh Orchids Dactylorhiza praetermissa, and thriving Adder and Grass Snake populations etc.  The report pointed out that this habitat was in fine condition and would be vulnerable to damage from grazing stock. Yellow Loosestrife Lysimachia vulgaris (host of several nationally scarce invertebrates) abounds around the lake shore and this plant is highly prized by hungry cattle. Despite the advice, cattle were let loose before a management plan was completed, and made straight for the fen edge with predictable effects. Bourley is a place that can be easily subdivided without any serious impact on vistas, simply because there aren’t many in woodland. It is also worth noting that other ponds on adjacent land to Bourley Woods have Crassula helmsii, and cattle (which are used to graze on both areas) are a likely vector for this highly invasive weed, which if established in the large water bodies would undoubtedly have a serious impact on both the fishery and biodiversity, and ultimately result in control measures which would be extremely costly.  Clearly this is a case of grazing very much out of control!

    It is not just on heathland. Newdigate clay pits abounded with Grass Snake Natrix natrix, and all the common amphibians, yet key critical terrestrial habitat for the Great Crested newt Triturus cristatus (which in the planning system would have to be mitigated against if damaged) has been removed by grazing cattle. Why? What was the grazing brought in for, a simple enough question?? Site manager said for ‘scrub control’ clearly unaware of importance of scrub to the GCN. The site is still covered in scattered scrub, which I know from experience could quite easily have been controlled manually (slowly and surely) with little more than a bow saw, some gloves, and the devastating sacrifice of a few square metres for a bonfire site!

    The draw of purple heather rolling uninterrupted to the horizon is peculiarly addictive in Britain. Perhaps the fear of bandits and highwaymen having somewhere to lurk runs deep, and open means safe. Whatever the reason, it is fair to say that emphasis on maintaining vast open tracts of heather dominated heath remains very strong for many site managers. In biodiversity terms this is far from optimal as the assemblage associated with such areas is limited and resilient. Of the 133 UKBAP species associated with lowland heath, less than 10% are in any way associated with dwarf-shrub, or ericoid heath (Webb, et al, 2010).

   It is interesting that the Vera model converts have so little faith in the theory that they cut down scattered oaks on heathland, almost as a priority. Why aren’t scattered oaks left to develop into the pasture woodlands of tomorrow?? Key Purple Emperor Apatura iris master trees were felled on Ash Ranges in Surrey, yet bizarrely a mature Eucalyptus was left nearby.

      The holistic approach is beguiling, and for key vertebrates such as birds which require large territories, big is beautiful, but a comparison of Dorset heathlands showed that somewhat counter-intuitively, heathland fragmentation is actually a positive for many invertebrates (Webb, 1990). The edge effect is clearly essential for many species of aculeate Hymenoptera which forage for food in richer habitats but return to disturbed sandy sites for nesting. In simple terms a sandpit surrounded by miles of heather dominated heath will support less species of bees and wasps, than one close to a range of flower rich verge or ruderal habitats. Indeed disturbed heath edge habitats are critically important for many phytophagous invertebrates, which do not occur on mature Callunetum.

   A counter to the positive of the edge effect is that on smaller blocks the remaining open habitats are exposed to a much greater input of unwelcome seed sources (especially pine and birch, but Gaultheria also increasing as a problem). They can also attract very high density usage by dog walkers, with disastrous impact for ground nesting birds, and Adders Vipera berus often an early casualty.

 A BETTER MODEL: EELMOOR MARSH, NORTH HAMPSHIRE

    Managed for over a decade with cattle and Przewalski’s Horses Equus ferus przewalskii, this site is perhaps the best example of what can be done with appropriate grazing in support of extensive manual and mechanical woodland and scrub control. It doesn’t come cheap, and has a budget many other sites currently could only dream of, but the effects of the grazing are carefully monitored by both botanists and entomologists. Their feedback is essential to fine tune the regime (by adjusting grazing density) in light of regular monitoring. As a result (and combined with other management), the site remains a botanical haven which has abundant nectar/host plant sources for an equally important invertebrate assemblage, as well as supporting abundant reptile and amphibian populations.

 WHERE DO WE GO FROM HERE? Of course grazing is a useful, in many areas essential tool, but all tools need to be used properly. The assumption that summer grazing by cattle will control key problem species like birch and bracken shows astonishing naiveté as our Woolmer friends demonstrate every year. It is probably impossible to overgraze a site for Natterjacks, so continued need for manual scrub control on west Woolmer Forest is evidence enough that cattle are no panacea.

   Trying to control bracken by cattle grazing is akin to using napalm to control daisies in one’s lawn. The New Forest still abounds with dense bracken stands emerging erect and vigorous from heath grazed so hard that it resembles the used pitches on the square at the Oval. Alas with the withdrawal of Asulam, physical cutting/ trampling is likely to become the only alternative means of control, and the temptation to use livestock will increase. If re-wilding is the way forward then surely Wild Boar Sus scrofa and its descendents have a role to play here.

 FENCING, TETHERING AND ANIMAL WELFARE

 I visited Dry Sandford Pit last year, as its name implies it is a post industrial site, yet one of timeless beauty, and with luxuriant fen and lovely Corallian exposures, providing excellent habitat for aculeate Hymenoptera. Yet the peace was interrupted by the hammering and chain-sawing of a gaggle of ‘conservationists’ erecting a hideous fence, slap bang across this gem of a site. If this is cost effective habitat management, I despair. A pony or goat tethered at intervals for a few days each year would surely do the job without ruining the aesthetic joy of the place. Electric fencing would also have suitable, and only a temporary blot on the landscape.

    ‘Oh we can’t tether animals, they might choke themselves’. Anyone been to Harlow lately? This urban fringe Common is grazed flat by dozens of tinker ponies all tethered and individually watered, and all continuously harassed by poorly controlled dogs, but it works here!

   NE looked into the cost effectiveness of employing shepherded stock, but the results have not been made available. What is s odifficult about using a horse/cow on a tether for local mosaic creation/ scrub management? On small sites this can be very effective. A tethered mature horse can clear mix herbs/ and seriously strip light scrub over an area of 50m² in under 8 hours.

REFERENCES

Bullock, J.M. & Pakeman, R.J. 1997. Grazing of lowland heath in England: Management methods and their effects on heathland vegetation. Biological Conservation 79: 1-13.

Denton, J. 1997. Recent records of notable Coleoptera on heathland. Coleopterist 6, 68-70.

Denton, J. 2011. Invertebrate Survey of Bourley Woods. Unpublished report.

Denton, J.S. & Beebee, T.J.C (1997) Habitat occupancy by juvenile natterjack toads on grazed and ungrazed heathland. Herpetological Journal. 6: 49-52.
 Jofré, G.M.  & Reading, C.J. 2012. An assessment of the impact of grazing on reptile populations. ARC Research report, 12/01.

 Littlewood, N.A. 2008. Grazing Impacts on moth diversity and abundance on a Scottish Upland Estate. Insect Conservation ad Diversity. 1, 151-160.

 Newton, A.C., Stewart, G.B., Myers, G, Diaz, A, Lake, S, Bullock. J.M., & Pullin, A.S. 2008.Impacts of grazing on lowland heathland in north-west Europe: A systematic review of the evidence. Biological Conservation, 142, 935-947.

 Webb, J.R., Drewitt, A.L. & Measures, G.H. 2010. Managing for species: Integrating the needs of  England’s priority species into habitat management. No.1. Report. Peterborough, Natural England.

 Webb, N.R.  1990. Changes on the heathlands of Dorset, England. Between 1978 and 1987. Biological Conservation, 51, 273-286.

 Vera, F.W.M. 2009. Large-scale nature development- the Oostvaardersplassen. British Wildlife, 20 (5) Special supplement, 28-37.