Gestion des pelouses dunaires de la réserve biologique
de la Côte d’Opale
The dune grasslands of the Opal coast biological
Reserve
Monitoring and management methods to ensure
long-term conservation
Frantz VEILLE, Françoise DUHAMEL & Christophe BLONDEL
Atelier international sur les dunes de Dunkerque - 12 au 14 juin 2018
Presentation of the site
Biogeographical situation and context
-> Sandy coastline of north-west France : dune complex of the Picardy maritime plain, Pas-de-Calais department (Opal coast)
-> The national forest is entirely located on the communal territory of Merlimont
-> This forest is classified as a mixed biological reserve for an area of 456,96 ha
Management objectives
1 – Preserve or restore habitats having a rich patrimonial value
active conservation habitat management
Managed Biological Reserve Zone
2 - Preservation and study of evolutionary processes (dune dynamics and forest vegetation dynamics)
=> non-interference
Biological wilderness area : 76 ha
MIXED STATE BIOLOGICAL RESERVE OF THE OPAL COAST _________________________________ Managed Reserve / Integral Zoning Map
Managed Reserve zone
Zone-reserved area
Perimeter of the biological reserve
Interest of the site
Geomorphological originality
=> The dune massif of MERLIMONT is the perfect example of dunes of Picardy morphology
External cord
Interdunal depression
Inner cord
Black dune
White dune
Sea schore
Interdune sandy plain Inner dune complex
Dry mesophilous sand + slack (fresh water
from the dune aquifer) + slack (fresh water
from the dune aquifer)
Wet interdunal plain
External dune complex
Coastal dune
Inner coastline
Interest of the site Spontaneous vegetation dynamics
=> one of the rare French coastal sites where natural dune and forest dynamics are exercised
1947 1979 2009
Interest of the site
=> Exceptional biological and ecological
wealth: the diversity of habitats is the source of a diversity and originality of phytocenotic, floristic, faunistic and mushrooms species without equivalent at European level
• 12 generic habitats, including 2 priority habitats (nearly 90% of the site's surface area)
• 50 elementary Habitats
• 80 vegetation communities
are from the European directive " Habitats, Fauna, Flora "
Beach
White dune (Ammophila arenaria subsp. arenaria) Grasslands Mesophilous meadows Grasslands and edge grassland Fallow land and ruderal vegetation
Thicket of the dune
Aquatic vegetation
Different hygrophilic vegetation Hygrophilic vegetation Swamp vegetation Tall herbs (« Mégaphorbiaies ») Wet meadow Reeds Humid forest Softwood Anthropogenic environments Recent work area Habitat mosaic
Type habitat
Simple habitat
Reserve perimeter Patch
Phytocenotic diversity of the grey dunes of the Picardy maritime plain
Bryolichenic grasslands of Koelerion albescentis
• Tortulo ruraliformis - Phleetum arenarii
• Community of Carex arenaria and Asperula cynanchica
• Festuco filiformis - Galietum maritimi
• Community of Carex arenaria and Poa pratensis subsp. latifolia
Annual grasslands of Thero-Airion
Dune hems of Galio littoralis - Geranion sanguinei
Phytosociological monitoring Context
Monitoring of grasslands and dune marsh set up in 2000 with
surveys until 2013 (five staggered readings for each habitat type)
Device with 32 permanent plots for xerosera or mesosera and 32 for hygrosera, with targeted objectives per plots block
Difficulties in implementing or respecting management methods (control, mowing, rabbit grazing with or without mowing)
Evolution of grasslands mowed regularly
R² = 0,4833
R² = 0,4918
0 %
10 %
20 %
30 %
40 %
50 %
60 %
70 %
80 %
90 %
100 %
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Mesoxerophilous dune grasslands - Regular mowing plots (P4c) Evolution of coverings of meadows or grasslands taxa and hems taxa
rec. de taxons de prairies et de pelouses
rec. de taxons d'ourlet au sens large
Tendance linéaire rec. taxons de prairies et de pelouses
Tendance linéaire rec. taxons d'ourlet au sens large
Evolution of grasslands mowed irregularly
R² = 0,0199
R² = 0,0487
0 %
10 %
20 %
30 %
40 %
50 %
60 %
70 %
80 %
90 %
100 %
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Mesoxerophilous dune grasslands - Irregular mowing plots (P1) Evolution of coverings of meadows or grassland taxa and hems taxa
rec. de taxons de prairies et de pelouses
rec. de taxons d'ourlet au sens large
Tendance linéaire rec. taxons de prairies et de pelouses
Tendance linéaire rec. taxons d'ourlet au sens large
Evolution of unmanaged grasslands
R² = 0,8705
R² = 0,3061
0 %
10 %
20 %
30 %
40 %
50 %
60 %
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Mesophilous vegetation - Reference plots Evolution of coverings of meadows or grassland taxa and hems taxa
rec. taxons fourrés et forêts
rec. de taxons de prairies et de pelouses
Tendance linéaire rec. taxons de fourrés et forêts
Tendance linéaire rec. prairies + pelouses
Long-term management recommendations
1- Conservation of the typical well-structured grasslands of Koelerion albescentis in connection with rabbit populations
=> no management if rabbits remain abundant
=> regular mowing in the event of regression or disappearance of rabbit populations (Tortulo ruraliformis - Phleetum arenarii)
=> regular mowing or extensive grazing with very low load for other fixed sand grasslands
2 - Restoration of hemmed or shrubby grasslands
=> manual removal or brushing according to the type and state of grasslands
=> then annual mowing for several years
=> return of rabbits, extensive grazing or continuation of regular mowing in subsequent years
Towards a regional protocol for the evaluation of the conservation status of dune grasslands
Methodology adapted from MNHN national documents Criteria or indicators to be recorded at the mapped polygon * Vegetation structure
* Woody cover (%)
* Floristic composition
- % of typical habitat species (0-4, 5-8, > ou = 9)
- number of ruderal or nitrophilic species (0-1, 2-4, > ou = 5)
- recovery of invasive alien specie (0, < ou = 10%, > 10%)
- overlaying of the bryolichenic stratum (< ou = 50%, >50%)
* Faunal composition (yet to be defined)
Towards a regional protocol for the evaluation of the conservation status of dune grasslands
*Degradations
- Overgrazing
- Plowing of the soil by wild boars
- Compacting (passage of machines)…
More general information at site level
* Evolution of the habitat surface
- Progress
- Stability
- Moderate regression (< -10%)
- Significant decrease (> -10%)
* Degradation not observed at the polygon scale
- Human overfrequentation
- Artificial plantations...
Dune grasslands management Of the 460 ha of the reserve:
-> dunes dry to mesophilous representing an area of more than 165 ha, distributed in the external and internal dune complex.
-> distribution of major vegetation types: 36 ha of dune grasslands (2016 mapping), 101 ha of dune shrubs, 18 ha of woodland associated with 10 ha of bare sands.
Distribution of vegetation structures in the 165 ha of dunes
dry to mesophilous of the biological reserve
10,0 ha
36,0 ha
101,0 ha
3,0 ha
15 ha
0,0 ha
20,0 ha
40,0 ha
60,0 ha
80,0 ha
100,0 ha
120,0 ha
su
rface
Type of vegetation structure
bare sand
lawn
dune
hardwood
softwood
Dune grasslands management Dune grasslands restoration actions depending on five main criteria:
Habitat type
State of conservation
Topography
Structure of the colonizing vegetation
Financial resources allocated annually to the site
=> From these parameters, four methods are chosen to carry out the restoration work
Dune grasslands management
• Method 1: manual pull-out technique
Hoe work with export on a tarpaulin of the removed vegetation
State of conservation of the environment: scattered colonizing vegetation or in the form of small spots, covering less than 25% of the surface to be restored
Type of environment targeted: mainly moss grasslands (habitat 2130* : Tortulo ruraliformis - Phleetum arenarii (Massart 1908) Braun-Blanq. & De Leeuw 1936)
Cost: between 4000 à 6000 € ht/ha
Top photo: before works, beginning of colonization by Pine tree (Pinus nigra subsp. laricio) and the Sea buckthorn (Hippophae rhamnoides subsp. rhamnoides) _ 2015
Bottom photo: grubbing-up of sea buckthorn trees with the association « les Blongios » _ 2013
Vegetation status after dry grasslands restoration
« Stone curlew (Burhinus oedicnemus) » grasslands area
* Context
Scattered recolonization shrubs < 1 m high and heterogeneous topography
Mowing in November every two years
* Flora and vegetation observed
Tortulo ruraliformis - Phleetum arenarii on dry mounds (23 taxa), with nitrophilic veil and shrub growth in 2018
Mesophilous dune grassland and meadow in "dry" depressions (to be surveyed in June 2018)
* Objective
Maintenance of current management
Dune grasslands management
• Method 2 : brushcutter
Work with a brushcutter with vegetal export
State of conservation of the environment: large spots of dune shrubs (< 0.5 ha) within grasslands, on uneven or flat areas
Type of environment targeted: reopening of dune grasslands with mosses in the process of advanced colonization
Cost: between 2500 and 3500 € ht/ha
Photography during the building site, with cutting of the stains of colonization by the Sea buckthorn (Hippophae rhamnoides subsp. rhamnoides) _ 2004
Type of vegetation before work
Brushcutter work
Dune grasslands management • Method 3: restoration over two years, with
gyrocrushing accompanied by manual mowing
Crushing in year n and mowing in year n+1 with brushcutter, with vegetal export
State of conservation of the environment : large areas of dense shrubs (< to 1 m high), on a flat surface.
Type of environment targeted: young dune shrubs
Gyrocrushing cost: between 500 and 700 € ht/ha
Cost of exporting mowing: between 1000 and 2000 € ht/ha
General photography before and after work : Sea buckthorn vegetation (Hippophae rhamnoides subsp. rhamnoides)
Photography before works (2015)
Photography after work (2018)
Dune grasslands management
Example: restoration over two years, with gyrocrushing accompanied by manual mowing
Vegetation structure before work (2015)
Restoration of the grasslands after the gyrocrusher has passed
through it (2017)
Restoration after the passage of the mowing exporter (2018)
Vegetation status after dry grasslands restoration
Undergrowth cleared in September 2016 using method 3 * Contexte
Young shrubs < 1 m from Ligustro vulgaris - Hippophaetum rhamnoidis typicum with clearings, on mounds and dry slopes
Poorly organic sandy soils
Mowing with a brushcutter in 2017
* Flora and vegetation observed
In 2017, semi-ruderal dune meadow of Carici arenariae - Calamagrostietum epigeji
En 2018, mosaic with hem (Hieracium umbellatum and Carex arenaria dune community) and Koelerion albescentis hemmed dune grasslands
* Objectives
Maintenance of annual export mowing
Soil « étrépage » tests on Carici arenariae - Calamagrostietum epigeji
Semi-ruderal dune meadow of Carici arenariae - Calamagrostietum epigeji mosaic with hem (Hieracium umbellatum and Carex arenaria dune community) and Koelerion albescentis
hemmed dune grasslands in May 2018
Dune grasslands management
• Method 4: exclusively mechanical restoration
Crusher with vegetal export and tractor for stump crusher
State of conservation of the environment: large areas of dense shrubs (> 1 m high) on a flat surface.
Type of environment targeted: mature dune shrubs with small trees
Cost: 5000 € ht / ha
Photographs during the two phases of the project: crusher with vegetal export and tractor for stump grinder (2017)
Dune grasslands management
example : restoration with crusher (with vegetal export) and tractor for stump crusher (2017)
Restoration area after work
(September 2017)
Restored area, first year of vegetation
(May 2018)
Vegetation status after dry grasslands restoration
1 - Mesophilous shrubs brushcutted in September 2017
* Context
Ligustro vulgaris - Hippophaetum rhamnoidis shrubs too dense, already high (1 to 2 m) and
heterogeneous topography (subassociations typicum and eupatorietosum cannabini)
Organic sandy soils in depressions
* Flora and vegetation observed
Pioneer grasslands and meadows taxa (Koelerion albescentis et Carici arenariae - Arrhenatherion elatioris)
Taxa of annual nitrophilic hems (Galio aparines - Alliarietalia petiolatae)
Wasteland taxa (Artemisietea vulgaris)
* Objective
Mowing and collecting slash in 2019
Vegetation status after dry grasslands restoration
2 - Mesoxerophilous shrubs brushcutted in September 2017 * Context
Dense shrubs of Ligustro vulgaris - Hippophaetum rhamnoidis typicum with Sambucus nigra on drier slope
Poorly organic sandy soils
* Flora and vegetation observed
Pioneer dune grasslands well present (Koelerion albescentis)
Annual nitrophilic hem taxa of Claytonio perfoliatae - Anthriscetum caucalidis
Sporadic taxa of dune wastelands (Cynoglosso officinalis - Oenotheretum glaziovianae)
* Objective
Mowing and collecting slash in 2019
Dune grasslands management
Example : maintenance by a manual tear-off
Before restoration in october 2013 After restoration in december 2013 In may 2018, before the next maintenance work planned in the
autumn
Dune grasslands management
Example of maintenance work by mowing with a brushcutter and vegetable export
Maintenance by biannual mowing since restoration work in 2004
before after
Grasslands, meadows and dune shrubs mosaic in May 2018
Conclusion
Since 1999, different techniques have been implemented to restore the grasslands of the European directive “Habitats-Flora-Fauna”.
As soon as shrubs structures are reached, the floristic surveys, after restoration, show above all a return of mesophilous meadows in the medium term.
Consequently, to ensure long-term conservation of dune grasslands, priority is given to the conservation of 34 ha existing areas, mainly by grubbing up sea buckthorn (method 1).
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