J Coasl Conserv (2010) 14:139-151 DO! 10.1007/sl 1852-009-0(172-9
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Topsoil inversion as a restoration measure in sand dunes| h early results from a UK field-trial
M. Laurence M. Jones ■ Kim Norman • Peter M. Rliind
Received: 7 April 2009/Revised: 13 September 2009/Accepted: IS September 2009/Published online: 9 October 2009 C: Springer Science + Business Media B V. 2009.
Abstract Over-stabilisation and cutrophication affect many dune systems in north-west Europe. This leads to lower diversity of typical dune species and an accumulation of soil nutrients. Existing management techniques to remove excess nutrients include mowing, with removal of cuttings, and turf stripping. A new restoration technique called topsoil inversion or deep ploughing may also be able to counter some of the negative effects of eutrophicatiou. It simulates the burial of established soils with fresh mineral sand, by inverting the soil profile. A trial was earned out on two small blocks of eutrophic dune grassland in North Wales, UK. Nutrient-rich surface soils were buried beneath mineral sub-sand using a double-bladed plough, designed to plough to depths of up to 100 cm. Results show that the organic soil horizons were buried to a depth of 80 cm, and covered with 40-50 cm of mineral sand. The pH and organic matter of the surface layers became comparable to those of mobile dunes. Fifteen months after ploughing, bare sand cover was still 70-90%, but significant sand loss through wind erosion resulted in a thinning of the mineral sand over-burden, leavimi the buried omanic lavcr closer to
M. L. M. Jones ^ Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road.
Bangor LL57 2UW North Wales. UK
c-mail: LJiojceh .ac.uk U
K. Norman
BMP Billiton, Field Study Centre, Unit 1, Station Road. Talacre. Flintshire CHS 9RD North Wales, UK
P. M. Rliind
Countryside Council fot Wales, Maes-y-Ffynnon, Penrhosganiedd.
Bangor LL57 2DW North Wales. UK
the surface. Natural vegetation colonisation was slow, with the first surviving plants observed after 8 months. The majority of species present at 15 months were present before ploughing and had regenerated from rhizomes or root fragments. The effect of excluding disturbance caused by rabbits, people and dogs was assessed within fenced areas. After II months, vegetation cover was greater in the fenced areas than in plots exposed to disturbance, therefore disturbance replaced physical conditions as the dominant influence on plant growth and establishment. These early results suggest the trial has been partially successful, but that topsoil inversion could be combined with other methods such as turf stripping or by stabilisation of the ploughed surface by planting with pioneer species, depending on the ultimate'restoration goal.
Keywords Eutrophication ■ Deep ploughing ■ Succession Colonisation • Grassland • Rabbits
Introduction
Many dune areas in the UK and in North-Wesl Europe are
currently over-stabilised and show low: levels of natural
mobility (Rhind_et al. 2007, Provoost et al. 2009).fin an
over-stabilised dune system, most of the dunes are covered'3
by well-established grassland or scrub vegetation and areas_
_of bare sand or pioneer vegetationAare rare or absent. [As a
result the land-forms'Sire static, no new features are being''
formed and existing dunes are not migrating. The situation
at Newborough Warren, a iarge dune system in North
Wales, where the amount of mobile and open dunes has
'declined from 75% in 1951 to less than 6% in 1991 (Rliind
et al. 2(X)J) is typical of dunes in much of England and
Wales.iThe over-stabilisation niav be a result of manv, often --.1 -A
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disturbance (Ranwell and Boar 1986) of (he leading dunes for sea defence
co-occurring, factors. These include natural successiotial development of both vegetation and soils (Jones et al. 2008; Packham and ^jllis 1997"); reductions in managed grazing (Doody 1989); rabbit population crashes due to disease; application of conservation measures such as erection of fences, planting Ammophila, and layiiigjof brash to prevent
ificial stabilisation easures (Westhoff
989);/vchanging climatic conditionlfjreducing natural mobility (Arens el al. 2004; Arens ffnd Geelen 2006; Hugenholtz and Wolfe 2005; Jones« al. 2009); and 'nutrient enrichment from a range offsources including amiospheric deposition (Jones et al. 2004; Kooijman et al. 199R)./groundwater (Jones et al. 2006; Stuyfzand 1993; van Dijk 1989) ancflocalised enrichment from nitrogen-fixers-(Stewart and Pearson 1967; Stuyfzand 1993).[Land management practices such as agricultural improvement have also historicallytbeen practiced on some hind-dune areas, and these are sometimesTncorporated within designated sand dune nature reserves or protected sitesfieadin<z to inherited
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eutrophication problems. [Irrespective of the source of
nutrients, eutrophication raises issues for the maintenance of typical sand dune habitats whic    re naturally nutrient-
poor (Willis and Yemm 1961).] Eutrophication pan adversely impact many parts of the system. Evidence'suggests that nutrients from atmospheric depositio/Nncrease the growth of graminoids and nitrophilous species/S'educing plant diversity (Jones et al. 2004; Kooijman el al. 1998; Plassmann et al.. 2009; Remke et al. 2009, van den Berg et al., 2005). Soil characteristics such as C:N ratio and available nitrogen can belltered (Jones et al. 2004). and N deposition may be one factoraccelerating soil development in dunes (Jones et al. 2008).Jin" the long-term, soi! N enricbmenfAlcads tu increased vegetation growth widi typical dune species'outcompeted by faster growing nilro-philesresulting in loss of diversity and conservation value.
^ Removing soil nutrients is a pre-requisite for restoration of infertile habitats on eutrophic soils (Bradshaw 1996; J^an^s_and_Gough 1989).[However, there.ate relatively few techniques available for managing eutrophication. Adverse effects on vegetation composition can bePcountered by managed grazing whiclAkeeps fast-growing species in check an ows light-dependeiit species to^persist. However, grazing itself does not remove nutrients from low fertility systems (Perkins 1978). Supplementary winter feeding of stock may even/*exacerbate the problems by introducing extra nutrients in (he fodder material Mowing does^Vemove nutrients, but only if cuttings areM-emoved from site or burnt (Bakker et al. 2002). Removal of dungTs possible, but is labour-intensive. Chemical remedialion^s possible in some soils (Mams 2002). Iri dune systems, immobilisation or re-creating earlier successional stagesHs another way to remove nutrients. Large scale remobilisatioti
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schemes have, for example, been conducted jn the Netherlands (Arens et al. 2004; Arens^and Geelen 2006). However, in the UK there has beenlittle dlmand among site managers for similar action. Furthermore public perception, encouraged by decadds of conservation effort aimed at preventing disturbance, seesrnobility as undesirable. Such schemes are alsonimited by the small size of many UK sand dune sites or their proximity to urbanised areas.|Therefore, the potential for large-scale destabilisation in the UK isnimited and disturbance techniques such as turf stripping, also called sod cutting, have so far beenlapplied on a smaller scale—typically less than 0.5 ha. Turf Stripping has> been practiced extensively in the Netherlands, primarily as a dune slack restoration tool (Grootjans et al. 2001; Grootjans et al. 2002), and in restoration of other habitats in Europe including saltmarsh. beathlands and wet meadows (Allison and Ausden 2004; Tallowin and Smith 2001). Turf-stripping is/\fficient but time-consuming and requires somewhere, usually off-site, toAlump the stripped material, making stripping of large areas expensive. An alternative ista bury the nutrients w-situ. which is the approach taken'with lopsoil inversion._
Topsoii inversion, also called deep ploughing, is a techniquejdeveloped in Denmark in'the 1990s where it was original I yfused in forestry planting to^bury the weed seed-bank and suppress competition for newly planted trees (Matthesen and Damgaard 19Q7).fsince then its use has^ widened into the area of conservation management principally in the restoration of sites impaetcofty eutrophication. The basic principle is tdrnvert the soil profile to a target depth of up to 100 cm so that nutrient-rich surface soil together with the unwanted seedbanlfis buried under infertile mineral sub-soil.[similar techniques have been used recently, described (variously as deep-cultivation, to 40 cm (Pywel) et al. 2002), or deep-ploughing, to 30 cm (Allison and Ausden
1004). [However, topsoii inversion as described above
operateAo a greater depth, typically 50-70 cm or deeper. and is^considered a different technique (Glen 2008). |ln dunes it can be seen as sbiulating rapid burial of a soil surface by blown sand. It differfjfrorn the natural process in that the existing soil profile is'inverted rather than buried. Therefore, in common with other mechanical techniques such as turf-stripping and re-profiling of dune slacks halters the soil horizon structure and ma\^hama";e. features of archaeological or geoniorphological interest. )lt isApotentially a useful technique in over-stabilised systems where, natural burial by sand is unlikely to occufand is an alternative to large-scale destabilisation of natural dune features which may not be^ippmpriate on small sites, or those, close to built-up areas.
The vegetation re-colouisation of disturbed bare sand is Hovemed'by physical and chemical soil characteristics, availability of propagules. and is also influenced by disturbance (Packham and Willis 1997). Despite regular outbreaks of