Italy: Dune Restoration on the Coast of the Tyrrhenian Sea

Project Stage:
Completed

Start Date:
1995-06-25

End Date:
2000-06-25

Primary Causes of Degradation

Degradation Description

European sandy coastlines are everywhere under threat of extensive erosion (e.g. van der Maarel 1979; Anon. 1998; De Lillis 1998; Dean & Dalrymple 2002), in particular along the Mediterranean coastlines. Here ca. 75% of the sandy coasts are presently degraded (Géhu 1985; Salman & Strating 1992).

The series of mobile dunes on the Tyrrhenian coastline of Lazio, along the Roman littoral facing the high tide mark is virtually absent. Along this coastline the elements of the various plant associations are forced back to the next belt, where they are thus overlapping and compressed along a narrow and not very high dune system.

Extensive human activities in littoral areas are widespread, and the factors causing disturbance are of a various nature. In fact, from the twentieth century onwards a strong intensification of human activities has been registered. This includes cattle grazing, farming, tourism, road construction and expansion, reforestation and agriculture.

Reference Ecosystem Description

Along the shoreline of the Italian peninsula, under natural conditions, there is a succession of various plant associations from the outermost dune belts, directly subject to the action of the sea, to the more sheltered inner ones (Lucchese & Pignatti 1990; Vagge & Biondi 1999). Starting from the sea, the first community is represented by the Salsolo kali-Cakiletum maritimae (Rivas-Martínez et al. 1992), barely inside the high tide mark, followed on the embryonic dunes by the Sporobolo-Elymetum farcti (Géhu et al. 1984), on the shifting dunes by the Echinophoro spinosae-Ammophiletum arundinaceae (see Géhu et al. 1984), and in the interdunal spaces with accumulation of organic matter by the Crucianellion maritimae (Braun-Blanquet 1933). This pioneer vegetation is followed on the consolidated dunes by pioneer macchia with junipers: Asparago acutifolii-Juniperetum macrocarpae (Bolós 1962; typus Géhu et al. 1990).

Project Goals

–To build up dune belts along the coast, located between the high water mark and the macchia vegetation behind this (consolidated dunes)
–To determine the optimal distance from the sea for planting Ammophila littoralis on the dunes which had been built up
–To verify the sustainability of restoration management approaches

Monitoring

The project does not have a monitoring plan.

Description of Project Activities:
In June 1995, 40 dunes were built up, accumulating sand on a base of dry trunks and branches of Quercus species occurring in the estate; these dunes were shaped according to the more or less elliptical morphology of the already existing ones. The sand used, of equal grain size, was taken from the sandy area immediately inland in order to avoid the presence of seeds from other vegetation types. The 40 built-up dunes formed three belts located at different distances from the high water mark: 14 at a distance of < 40 m (33 - 40 m) from the sea, 15 at a distance of 40 - 70 m, and 11 at a distance of > 70 m (70 - 86 m). In January 1996 20 individuals of Ammophila littoralis, taken from the neighbouring dunes, were transplanted on each of 38 built-up dunes, and distributed evenly over their surface. In order to compare both the evolution of the morphology and the natural colonization of the plant species in the absence of the stabilizing species, A. littoralis was not transplanted on to the last two dunes, at a distance of < 40 m from the sea. The phenology of the main species of the natural dune system was followed by means of monthly observations, from June 1995 until October 1996, in order to identify their growth and reproductive phases. At the same time the fruits were collected and the seeds at various stages of maturation were isolated. In October 1996 and in February, April and June 1997, germination trials were carried out on the main species present: Ammophila littoralis, Anthemis maritima, Cyperus capitatus, Cakile maritima, Elymus farctus and Pancratium maritimum - to verify the reproductive capacity of the seeds of each species. The change in height and area of each dune, the survival of A. littoralis, the change in cover, the appearance of new shoots and, lastly, the establishment of new species were monitored after 1 yr, 2 yr and 5 yr from the starting phase. The cover of A. littoralis was measured as percentage of the surface covered in a grid-plot with eight subplots of 0.25 m2 each.

Ecological Outcomes Achieved

Eliminate existing threats to the ecosystem:
Germination rate and time was largely different among the species examined. In some species, such as C. capitatus, C. maritima and A. littoralis, germination ranged between 20 and 30%, and took from two up to five weeks. It reached 60% in P. maritimum, the species that took longest (almost seven weeks) to germinate. E. farctus exhibited the highest germination rate, 80%, but its seeds had the shortest germination time, just two weeks. The survival rate of individuals of A. littoralis, between January 1996 and February 2001, changed from 96 to 66%, on the dunes closest to the sea; at a distance between 40 and 70 m it decreased fairly slowly during the first year (99%) up to 74%, that is the highest survival rate registered in 2001 and, lastly, on the dunes furthest inland, more than 70 m from the sea, it remained at 100% until June 1997, after which it decreased to 60% in 2001. The average cover of A. littoralis also changed in time according to distance from the high water mark: in the first six months, from December 1996 to June 1997, the cover increased, especially on the dunes more than 70 m from the sea where it reached an increment of 50%. However in the next four years the trend changed and in February 2001 the cover tended to be highest, although not significantly, at the intermediate distance. Over the latter period the cover tended to decrease slightly on the dunes at a distance of less than 40 m and more markedly on the dunes at more than 70 m ; the cover was quite constant, between 25 and 30%, on the dunes at intermediate distance from the sea (40 m < d < 70 m). Between October 1996 and February 2001 the average number of vegetative shoots for each dune increased progressively: from 11 to 53 in those nearest to the sea, from 9 to 38 in those located at a greater distance, while the number increased from 10 to 56 in those located at the intermediate distance. The number of new shoots was lowest on the dunes at more than 70m), though not significantly. During the five years of observation the number of species that colonized the new dunes increased progressively from 7 (June 1996) to 16 (July 2000). These were autochthonous species, germinated from the seeds occurring in the sand used for building up the dunes. The two dunes where A. littoralis did not occur show a smaller number of species than the others: two germinated in June 1997: Cakile maritima and Raphanus raphanister ssp. landra, and six in July 2000: Elymus farctus, Anthemis maritima, Eryngium maritimum, Cyperus capitatus, Sporobolus pungens and Crucianella maritima. In June 2001 the average number of species on each dune belt was highest (6.6) at the greatest distance from the sea (d > 70 m) and lower in the other dune belts (4.6, d < 40 m; 4.2, 40 m < d < 70 m). At the same time the total plant cover varied between 15 and 60% with an average of 28.6% and was composed mainly of A. littoralis. A. littoralis was the dominant species with 25% of the cover; among the species that germinate after planting Ammophila, only Anthemis maritima, Elymus farctus and Echynophora spinosa reached fairly high cover values. The range of the frequency of the species, from 3 to 90%, is very great: there are species present only on a few dunes (C. maritima, S. kali, S. pungens), whereas other species are widely represented (A. maritima, E. farctus, E. maritimum). The morphological characteristics of the dunes, the height and the surface particularly, showed a progressive change over time. The height decreased progressively in all the three belts. In July 2000 the height of the dunes located more than 70 m from the sea was about 60% of the initial one, that of the dunes closest to the sea was 50%, and that of the dunes located between 40 and 70 m from the sea was 49%. In the two control dunes, i.e. without A. littoralis, the height progressively decreased until July 2000 when it reached 47% of its initial value; the height of the control dunes was very similar to that of the dunes located in the belt < 40 m from the sea. In the course of time the surface area of the dunes tended to increase due to the accumulation of sand at the sides of each dune. The surface area of the dunes at more than 70 m from the sea changed from 25 m2 to 34 m2 and, similarly, in the dunes located in the belt between 40 and 70 m from the sea the area increased from 27 m2 to 35 m2, that is, by ca. 30%. However, at a distance of less than 40 m the surface did not change because at this distance the accumulation of sand at the sides was offset by their partial destruction by the tides; consequently the average area remained 29 m2 the whole time.

Factors limiting recovery of the ecosystem:
The belt closest to the sea, in spite of the progressive increase in the number of shoots, showed a decrease of the survival rate of A. littoralis, due above all to the violent coastal storms which have partly destroyed some of these dunes, so that the cover showed small fluctuations only. It is noteworthy that no increase in dune height can yet be observed, five years after the transplantation, probably because the cover reached by A. littoralis is still inadequate, even though relatively extensive.

Socio-Economic & Community Outcomes Achieved

Key Lessons Learned

The fast growth rate of transplanted Ammophila littoralis shoots, and the resultant increase in cover, highlights the potential of this species to facilitate the restoration of sandy coast environments. It is well known that A. littoralis forms a barrier that blocks the transport of wind-blown sand so that, at the base of the aerial shoots, and therefore also on the surface of the dune, new sand grains are deposited. By this mechanism, a close link is established between the dune systems and A. littoralis: the dune grows by constant deposition of sand grains, and at the same time, it stimulates the development of new roots and of the soil fauna (van der Putten et al. 1989), which are essential for maintaining the survival and the vigour of this species (Hope-Simpson & Jefferies 1966; Eldred & Maun 1982).

The present study also shows the strong consolidation potential of A. littoralis for dune build-up: survival of the tufts of A. littoralis transplanted can exceed 70% and cover reached after 5 yr in the belt between 50 and 70 m from the sea is high (40%), though still lower than on natural dunes (Pignatti et al. 2001).

If survival, cover and the number of growth shoots are taken into account, the belt between 40 and 70 m appears the most suitable one to guarantee the effectiveness of restoration techniques such as those performed in this study, since those closest to the sea are damaged by coastal-storms, and those furthest from the sea did not guarantee a favourable habitat as the survival rate and the number of new shoots of A. littoralis highlights.

The morphological characteristics of the dunes, shaped by simultaneous erosion and accumulation of grains of sand, become gradually modified: in all three of the belts considered, a reduction is noted in the height as well as an increase in the surface area. In some cases, the dunes examined actually tend to lose their initial elliptical shape due to the direction of the dominant winds, and they become crescent shaped. On the dunes furthest inland, where the grains of sand carried by the wind are most often deposited, the reduction in height is less marked.

Colonization by new species is relatively rapid and takes place with species such as Anthemis maritima,
Cakile maritima, Elymus farctus (= Agropyron junceum), Cyperus capitatus (= C. kalii), Ononis variegata and Eryngium maritimum, which play a role – albeit a secondary one – in the deposition of sand (Pignatti 1993). This indicates a progressive development towards populations similar to natural ones. Prevalent among these species are those of the associations Sporobolo-Elymetum and Cakiletum, whereas the species established subsequently pertain mainly to Ammophiletum and Crucianelletum. This gradual and directional process is in accordance with the natural dune colonization: the rapid establishment of pioneer species on the embryonic dunes is followed by a slower colonization by the species of the mobile dunes.

The recolonization process presently underway at the study site is reflected in the establishment of a progressively larger number of species, up to the present number (16), on the dunes where individuals of A. littoralis have been transplanted. It is also of importance that the number of species increases with increasing height of the dunes from 20 to 150 cm; possibly this increase causes the development of a microclimatic gradient and the existence of more niches. The dunes where the number of species is highest are those furthest from the sea, more than 70 m, probably due to seeds incoming from the dune belt behind.

However, the cover of E. farctus, greater than that of other species, and on average greater than in the natural dunes further back (Pignatti et al. 2001), indicates an as yet relatively early phase of the succession. In comparison with the natural dunes of Castelporziano, where ca. 26 species have been observed (Anzalone et al. 1990; Pignatti et al. 2001), the colonization that has so far occurred amounts to some 60% of the species that characterize these environments. Still lacking, compared with the natural dunes behind them, are the following species: Pancratium maritimum, Pseudorlaya pumila, Daucus carota ssp. maritimus, Medicago marina, Lotus cytisoides and, on the dunes furthest from the sea, Silene colorata, Vulpia membranacea, Juniperus oxycedrus, Senecio leucanthemifolius and Sagina maritima. These are species linked with a certain degree of soil evolution and typical of stabilized dunes and of inter-dune spaces with accumulations of organic matter. In the two dunes without any A. littoralis, instead, the colonizing process by new species is much slower; at present it is equal to 30%, demonstrating that the presence of A. littoralis favours the settlement of new species.

Cakile maritima and Elymus farctus often occur in the built-up dunes closest to the sea, while in those situated furthest inland Anthemis maritima, Eryngium maritimum and Ononis variegata become established. In particular plant species referred to the Sporobolus-Elymetum farcti, which precedes the Ammophiletum in the series of mobile dunes, have mainly become established in the tongues of dune decay or in the spaces left free by the death of individuals of A. littoralis planted, and even between the dunes. This leads to a gradual modification in the structure of the built-up dunes which, at times, tends to merge with the natural dunes or to assume an aspect similar to them.

In conclusion, although at the present stage the dune system being built up is still too young to show evident effects on shoreline erosion, the data seem to indicate the effectiveness of the “˜soft techniques’ applied for the environmental restoration of this stretch of the Tyrrhenian sea coast. The results emphasize both the vitality of the rhizomes and the enormous potential of vegetative reproduction of A. littoralis. In general, for measures of this type, it seems in any case necessary to create a seed bank of the local autochthonous species and to set up a nursery in situ in order to guarantee the availability of seedlings and to minimize the negative effects of the method of collecting rhizomes in the field.

Sources and Amounts of Funding

This project was conducted with financial support from the National Academy of Sciences, under the “˜Environmental Survey’ carried out in the Presidential Estate of Castelporziano (Roma, Italy).

Other Resources

De Lillis, M. et al., 2004. Sustainability of sand dune restoration along the coast of the Tyrrhenian sea. Journal of Coastal Conservation 10: 93-100.

M. De Lillis
E-mail delillis@unimol.it

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