Foredune psammophilous communities and

coastal erosion in a stretch of the Ligurian sea

(Tuscany, Italy)

Andrea Bertacchi,

Marco Alberto Luca Zuffi,

Tiziana Lombardi

Article

First Online:

16 June 2016

DOI: 10.1007/s12210-016-0543-5

Cite this article as:

Bertacchi, A., Zuffi, M.A.L. & Lombardi, T. Rend. Fis. Acc. Lincei (2016).

doi:10.1007/s12210-016-0543-5

Abstract

Italy sandy coasts are characterised by a great diversity of habitats and, at the same time, many of

these coastal stretches are in erosive condition. Therefore, it is important to understand, in areas

where marine erosion is particularly strong, which are the most vulnerable and most threatened

habitats. The paper sets out data from the survey of foredune habitats (annual vegetation of drift

lines, embryonic dunes, mediterranean white dunes, sensu Directive 92/43/EEC) in the San Rossore

Estate sandy coast (Northern Tuscany, Italy) strongly subjected to erosion. The surveys, in addition

to updating the information collected, aim to point out the arrangement of these habitats in relation

to coastal retrogradation and foredune erosion, in order to identify appropriate management tools

for mitigating disturbance factors. The surveys, conducted in the field and by photo-interpretation,

revealed the presence of foredune plant communities hardly referable, from the phytosociological

point of view, to known associations of neighboring coasts. The Cakile maritima plant communities

of annual vegetation of drift lines, the Elymus farctus/Othantus maritimus phytocoenosis of

embryonic dune and the Ammophila arenaria/Euphorbia paralias communities of white dunes, are

markedly altered in their floristic composition; the coverage and distribution of the different plant

communities are in a highly differentiated manner according to erosion gradients. The

understanding of dynamics of alteration of psammophilous plant communities in relation to coastal

erosion may suggest potential aid in the management actions aimed at containing the

transformations or and/or useful for the restoration of the same habitats.

Keywords

Habitats Coastal erosion Dunes Psammophilous vegetation Tuscany

1 Introduction

Coastal erosion is a widespread problem at the regional and global scale, impacting about 70 % of

the Earth’s sandy beach environments (Bird 1985; O’Riordan 1995; Zhang et al. 2004; Pranzini et

al. 2015) and it looks increasingly linked to the global warming process (Cazenavel and Le

Cozannet 2014; IPCC 2013). In this context, the plant communities of sandy beaches and dune

systems are found in habitats particularly vulnerable to coastal erosion (Feagin et al. 2005;

Schlacher et al. 2008; Doody 2013), making them particularly worthy of attention and protection in

order to avoid the habitats destruction, biodiversity alterations and loss of key ecosystem functions

(Van der Meulen and Udo de Haes 1996; Van der Maarel 2003; Provoost et al. 2004; Lucrezi et al.

2014).

Italy has a coastline of about 7500 km, of which approximately 47 % is represented by hard and soft

rock coasts and 53 % by sandy coasts and the phenomenon of coastal erosion affects, to different

degrees, around 42 % of sandy coasts (Valpreda and Simeoni 2003; GNRAC 2006; EUROSION

2007). These environments, where non-processed by human activities, are characterised by a great

diversity of habitats (sensu Directive 92/43/EEC) often along a well-defined zonation from annual

vegetation of drift lines (H1210) mainly characterized by Salsolo Kali-Cakiletum maritimae Costa

et Manz 1981, corr. Riv-Mart. et al. 1992, the community of embryonic dune (H2110) mainly

featured by Echinophoro spinosae-Elymetum farcti Géhu 1987, the white dune (H2120)

characterized by Echinophoro spinosae-Ammophiletum australis (Br.-Bl. 1933) Géhu, Rivas-

Martinez & R. Tx. 1972 in Géhu et al. 1984, the mosaic of annual herbs and perennial shrubs in the

fixed dune (H2210, H2230, H2240) and, finally, on the top of fixed dune, Juniperus spp community

(H2250) (Pignatti 1993; Macchia et al. 2005; Acosta et al. 2007; Carranza et al. 2008; Biondi and

Blasi 2009; Prisco et al. 2012).

Many studies have focused on the arrangement of the plant communities on the dunes as result of

the different environmental and geomorphological features of the beach-dune system (Géhu et al.

1984; Doing 1985; Hesp 1991; Barbour 1992; Vagge and Biondi 1999; Acosta et al. 2007; da Silva

et al. 2008; Lomba et al. 2008; Maun 2009; Miller et al. 2010; Isermann 2011; Fenu et al. 2013;

Tissier et al. 2013). In this context, some studies have focused on the effects of coastal erosion on

psammophilous communities of the foredunes, investigating individual species or the plant

communities and their habitats (Roman and Nordstrom 1988; Costa et al. 1996; Feagin et al. 2005;

Ciccarelli 2014; Bitton and Hesp 2013; Martins et al. 2014).

In the wake of these researches, this study has the purpose to investigate the arrangement of the

associations characterizing the foredune habitats (H1210, H2110, H2120), to different degree of

coastal erosion of a stretch of coastline affected by an ancient, important erosive process in the

northern part of Tuscany.

2 Study area

In Italy mainland coast of Tuscany represents an example of great interest, both from the point of

view of the number of habitats that can be found along the coast (Vagge and Biondi 1999; Bertacchi

et al. 2010; Viciani et al. 2014) and from the huge phenomenon of erosion, which interests the 36 %

of sandy coasts (GNRAC 2006). In this context, one of the coastal areas most affected by erosion is

that of the San Rossore Estate (part of Regional Park of Migliarino San Rossore Massaciuccoli),

near the town of Pisa, northern Tuscany, northern-central Italy.

The study area (43°43′38″N; 10°16′48″E) (Fig. 1), is represented by a stretch of sandy coast about

12 km long, between the mouths of the two major rivers of Tuscany, the Serchio and Arno rivers,

affected by an important erosion pattern. This process started at the end of the 19th century, after an

uninterrupted accretion of the coast from Roman times (Ceccarelli Lemut et al. 1994), and it

resulted in a retreat of the shoreline up to a maximum of 400 m, during the time span 1938–2011

(Anfuso et al. 2011) and, for the same historical period, an overall loss of about 260 hectares of

surface area (Bini et al. 2008). This destructive phenomenon occurred in an environmental context

of great naturalistic value. The area is in fact characterized by a large number of habitats of high

biodiversity value (Tomei et al. 2004), and it was designated in 2004 as the UNESCO Biosphere

Reserve “Selva Pisana”.

Fig. 1

Geographic position of the study area

The annual average rainfall (1997–2010) was 773 mm, with the highest rainfall recorded in autumn,

and an annual average temperature of 14.4 °C, with maximum value close to 30 °C during August.

The ombrothermic diagram extracted from the data shows a period of summer drought and water

shortages from June to September (data from the “San Piero a Grado” weather station, 43°40′33″N;

10°20′8″E). According to the bioclimatic classification of Rivas-Martinez and Rivas-Saenz (2015),

the area has a Mediterranean macrobioclimate, with an upper Mesomediterranean thermotype and a

lower sub-humid ombrotype.

The beach and dunes of S. Rossore Estate, although they constitute only a small fraction of the

Estate (about 109 ha, 2.4 % of the total area), are of great interest. The interest of beach and dunes

of S.Rossore Estate is not only due to the presence of psammophilous habitats of preservation

importance, but also because, unlike the neighboring coastal areas, the access to them is forbidden

to the public and, therefore, may represent a study area without direct anthropic interference.

During previous surveys on the dune vegetation it emerged an anomalous zonation and a marked

fragmentation of some vegetal communities, with some species that were particularly scattered and

rarefact, especially if compared to the neighboring areas (Bertacchi et al. 2009; Sani et al. 2010;

Bertacchi and Lombardi 2014a). Our research has been aimed at underlining any relationships

between the intensity of the coastal erosion, expressed by beach retrogradation and disappearance of

the dune belt, and the typology and coverage of the vegetal communities.

3 Methods

The study regarded the entire foredune area—the portion of the beach-dune profile that extended

from the mean tide line to the top of the frontal dune (Barbour 1992), and its width varied between

20 and 100 m, depending on the studied sectors (Fig. 2).

Fig. 2

Transect arrangement in two eroded stretch of studied area (dashed line foredune limits)

The study as a whole was conducted on psammophilous habitats and consisted of the following

stages.

(Fig. 3):

Fig. 3

Measurements made on studied sandy coast: be beach erosion width; bw beach width; fw foredune

width; de dune erosion width; wd white dune width; ed embryonic dune width; vdl vegetation drift

line width; fc foredune cacumen; t transect

3.1 Physical elements surveys

By layering by GIS MapInfo ® the aerialphotos (WMS Geoscope Service, Regione Toscana), we

reconstructed the changes of the coast line and, conseguently, of beach width (beach erosion)

comparing the shape of 2003 with 2015. Through the analysis of the DTM Lidar model (Digital

Terrain Model by elaboration of Light Detection And Ranging data, Geographical Service, Regione

Toscana), integrated by field surveys, we verified the presence/absence of the dune belt and its

height, as well as the width of the survived and disappeared foredune (2003–2015) (dune erosion);

3.2 Vegetation surveys

We carried out 75 transects, perpendicular to the shoreline, 10 metres wide, deep as the foredune, at

intervals of 100 m over the north-central sector of the investigated coast. Along these lines, we

recorded the presence/absence and width of the various plant communities. The plant communities

have been investigated by the phytosociological method of Braun-Blanquet (1983), which allowed

their subsequent habitat reference. The southern sector of the estate coast (about 4 km) was not

investigated, because it has been recently affected by measures of coastal defense, that have heavily

altered the natural environment. Psammophilous coastal vegetation, according to the different plant

associations identified, was typified by the categories described by the Habitats Directive (Directive

92/43/EEC, MD 20th January 1999) and their diagnostic species (Carranza et al. 2008; Biondi and

Blasi 2009; Biondi et al. 2012; Prisco et al. 2013). For the purposes of processing gathered data, we

considered as “key” habitats the following ones: 1210—annual vegetation of drift lines; 2110—

embryonic shifting dunes; 2120—shifting dunes along the shoreline with Ammophila arenaria

(white dunes).1 Nomenclature of vascular species is according to the “Flora d’Italia” (Pignatti 1982)

and to the “An annotated checklist of the Italian vascular flora” (Conti et al. 2005)

3.3 Statistical analyses

A multivariate analysis procedure, using Syntax software (Podani 2001), according to the “UPGMA

cluster algorithm analysis” and applying the Bray/Curtis coefficient of similarity, was carried out

for the data recorded during the vegetation surveys. We ran all other analyses with IBM SPSS

21.0.0.0. release (64 bit version). All physical and vegetational data were statistically processed

according to non parametric and parametric statistics. Physical data set has been controlled for

normality and homoscedasticity with Kolmogorov–Smirnov test.

Physical elements-beach width, height and width of the dune—and the width of key habitats have

been considered as ordinal or nominal factors and treated with non parametric statistics. The

physical elements that are linearly distributed have been treated with parametric statistics. Given the

different nature and origin of recorded data, we carried out a non parametric bivariate correlation

(Spearman ρ), using all habitat types, dune erosion, beach erosion and dune height. This correlation

has been aimed at highlighting relevant descriptive bivariate correlation before using multivariate

approach of all the considered variables.

To describe and explain the patterns of relationships between the abiotic and biotic components of

this coastal system, we grouped the entity of dune erosion (2003–2015 loss of width in meters)

width in four different classes (ranked as 0–1 m = 1; 1.1–10 m = 2; 10.1–20 m = 3; >20 m = 4) and

we ran: (1) one way ANOVA, between each habitat width and dune erosion width rank, (2)

multivariate general linear model, with the width of each habitat and dune height as dependent

variables, dune erosion rank as fixed factor, and beach width as covariate, and the interaction

between dune erosion rank and beach width.

4 Results

4.1 Physical elements

To better understand the geomorphological dynamic of this area, it must be reported that starting

from 1954 to date, the disappearance of the coastal line ranges from 45 m to about 300 m width

(Bini et al. 2008; Anfuso et al. 2011; Bertacchi and Lombardi 2014b). In this historical scenario, in

the span covered by this investigation (2003–2015), erosion has worked on 84 % of the considered

detecting points, varying from a minimum of 2 m to a maximum of 84 m; in 8 % records, the coast

appears in equilibrium and, in the remaining part, in a light accreting, even if this latter

phenomenon is largely determined by localized artificial cliff. From DTM LIDAR data analysis, we

recorded the erosion pattern of the dunal relief (width of dune collapsed 2003–2015) in 68 %

percent of the measured points, with erosion widths ranging from a minimum of 4 to a maximum of

over 40 m. The field survey of the dunal cacumen found, at the present, minimum values of 0.5 m

and maximum of 8 m, with more than 70 % of less than 4 m height (Fig. 4a).

Fig. 4

a Pattern of the coastal line dynamics and dune erosion (2003–2015) along the 75 transects made (Y

axis/m; positive values: retrogradation, negative values: progradation). b Recorded decreases in

dune width 2003–2015 (dune erosion) and habitats width (2015), along the 75 transects made (Y

axis/m)

4.2 Vegetation

Phytosociological surveys on the foredune and subsequent multivariate data analysis allowed to

identify five communities (Fig. 5; Table 1). These communities are mainly arranged in a

discontinuous zonation, vegetation of driftline, embryonic dune, white dune, from the sea towards

the interior, although with highly variable width and floristic traits largely dissimilar from the

corresponding psammophilous communities of the closely neighboring coasts (Sani et al. 2010;

Bertacchi and Lombardi, 2014a).

Fig. 5

Cluster analysis of psammophilous communities (157 relevés); a Salsolo-Cakiletum; b S. versicolor

groupments; c O. maritimus groupments; d Echinophoro-Ammophiletum/Euphorbia facies; e

Echinophoro-Ammophiletum/Ammophila facies

Table 1

Table of most representative phytosociological relevés (H1210 Salsolo Kali-Cakiletum maritimae;

H21010a Spartina versicolor groupments; H2110b Otanthus maritimus groupments; H2120A

Echinophoro spinosae- Ammophiletum arundinaceae facies a Euphorbia paralias; H2120B

Echinophoro spinosae- Ammophiletum arundinaceae facies a Ammophila arenaria)

Relevés n° 1 5 22 35 40 2 3 4 26 29 68 7 9 11 16 17 6 8 10 13 18 54 56

Area (sq) 50 20 10 10 50 25 30 20 30 20 25 25 60 50 30 40 25 60 50 30 30 50 40

Height (m) 0,5 0 0,5 0,5 0,5 1,5 2 2 1 1 0,5 2 2 3 8 3 2 2 3 5 6 3 3

Coverage (%) 20 10 30 10 10 30 40 30 20 30 20 40 80 80 60 80 40 80 80 80 60 20 80

Species n° 7 5 6 4 5 8 5 7 6 4 4 8 6 7 5 6 12 12 14 11 12 6 8

Cakile maritima Scop.-

T scap 1 1 1 + + + . + r . . r . + . . . . . . . . .

Salsola kali L.-T scap + r + r + . . . . . r . . . . . . . . . . . .

Xantium italicum

Moretti-T scap + . + . + . . . . . . . . . . . . . . . . . .

Spartina versicolor

Fabre-G rhiz . . . . . 1 + 1 . . . + 1 + . + . . . r + . +

Elymus farctus (Viv.)

Runemark ex Melderis-. + . . . + + . r . . r . . . . . . . . . . .

Relevés n° 1 5 22 35 40 2 3 4 26 29 68 7 9 11 16 17 6 8 10 13 18 54 56

G rhiz

Otanthus maritimus (L.)

Hoffmanns. & Link-Ch

suffr

. . . . . + . + 1 1 2 . . . . . . . . . . . .

Eryngium maritimum

L.-G rhiz 1 + . . . 1 + + + . . . 2 + 1 2 . . . . . . 1

Ammophila arenaria

(L.) Link subsp.

australis (Mabille)

Lainz-G rhiz

. . . . . . + + . + . + 1 + 1 + 3 5 1 3 5 2 4

Euphorbia paralias L. (1)

-Ch frut + r + 1 + + . . + + + 3 3 4 3 2 . + 1 + . + +

Anthemis maritima L.-H

scap . . . . . . . . . . . . . . . . . . + . . . .

Echinophora spinosa

L.-H scap . . . . . . . . . . . . . . . . + . . + . . .

Others . . . . . . . . . . . . . . . . . . . . . . .

Atriplex latifolia

Wahlenb.-T scap . r + . . . . . . . . . . . . . . . . . . . .

Calystegia soldanella

(L.) R. Br.-G rhiz . . . . + 1 + + . . . . . . . . + . . + + . .

Euphorbia peplis L.-T

rept . . . . . . . . . . . . . . . . . . + + . 1 .

Polygonum maritimum

L.-H rept r . r . . . . . . + . . . . . . . . . . . . .

Crithmum maritimum

L.-Ch suffr . . . . . . . . . . . . . . . . + . . . + . .

Helichrysum stoechas

(L.) Moench-C suffr . . . . . . . . . . . + + + + 1 . . 2 . . . +

Lagurus ovatus L.-T

scap . . . . . . . . . . . + . . . . + . . . + . .

Pancratium maritimum

L.-G bulb . . . . . . . . . . . . . + . . + . + + . . +

Silene colorata Poir.-T

scap . . . . . . . . . . . + . . + + . r + + + . +

Crepis vesicaria L.-T

scap/H bienn . . . . . . . . . . . . . . . . . + . + . . .

Hypocheris radicata L.-

H ros . . . . . . . . . . . . . . . . + . + . . . .

Phleum arenarium L.-T

scap . . . . . . . . . . . . . . . . . . . . + . .

Plantago coronopus L.-

T scap/H bienn . . . . . . . . . . . . . . . . + + + . + . .

Urospermum

dalechampii (L.) Smidt-. . . . . . . . . . . . . . . . . + . . . + .

Relevés n° 1 5 22 35 40 2 3 4 26 29 68 7 9 11 16 17 6 8 10 13 18 54 56

T scap

Bromus madritensis L. -

T caesp . . . . . . . . . . . . . . . . . . + . + . +

Vulpia membranacea

(L.) Link.-T caesp . . . . . . . . . . . . . . . . . . . r . . .

Glaucium flavum L.-H

scap . . . . . . . . . . . . . . . . . . . . . . .

Malcolmia ramosissima

(Desf.) Gennari-T scap . . . . . . . . . . . . . . . . + + . + . . .

Silene otites (L.) Wibel-

H ros . . . . . . . . . . . . . . . . + + . . . + .

Erianthus ravennae (L.)

Beauv.-H caesp . . . . . . . . . . . . . . . . r + . . r . .

In the first five relevés Euphorbia paralias specimens are only one year seedlings

First visible/recordable strip, when present, was referred to association Salsolo Kali-Cakiletum

maritimae Costa et Manz. 1981, corr. Riv-Mart. et al. 1992 (H1210—Annual vegetation of drift

lines); this is followed by a particularly narrow strip, often absent, occasionaly composed by

Spartina versicolor groupments and Otanthus maritimus groupments with a very low presence of

Elymus farctus. These communities complex, are referable to the alliance Agropyrion juncei

(R.Tüxen 1945 in Br.-Bl. and R.Tüxen 1952) Géhu, Rivas-Martínez and R. Tüxen1972 (H2110—

Embryonic shifting dunes) but never to characteristic association Echinophoro spinosae-Elymetum

farcti Géhu 1987. Anyway, considering their marked rarefaction, these groupments, in the

subsequent data analysis in relation to erosion, were considered as a single vegetational unit.

Proceeding inward, two plants communities are sequentially detected and these are referred to two

facies of the Echinophoro spinosae- Ammophiletum arundinaceae Géhu, Rivaz-Martinez et

R.Tuxen 1972, in Géhu et al. 1984, (H2120—Shifting dunes along the shoreline with Ammophila

arenaria -white dunes). The two facies of association, Echinophoro—Ammophiletum facies a

Euphorbia paralias, Echinophoro—Ammophiletum facies a Ammophila arenaria, being spatially

well differentiated, have been considered separately in the subsequent data analysis in relation to

erosion (H2120A and H2120B).

The distribution of the several psammophilous communities was really different: H1210 was found

in 68 % times, H2110 in 24 % times, H2120A and H2120B in 64 % and in 76 % times,

respectively. Also when regarding to the phytocenosis width along the foredune we recorded highly

different values both within and among them: H1210: 1–15 m; H2110: 0.2–0.5 m; H2120A: 1–

15 m; H2120B: 1–30 m. (Fig. 4b).

4.3 Coastal erosion—habitats

In 2015, beach and dune erosion were normally distributed (Kolmogorov–Smirnov test, Z = 0.577,

P = 0.916 and Z = 1.277, P = 0.077, respectively) and ranged 27.1 ± 23.4 m (n = 75) and

14.1 ± 13.8 (n = 75). On the contrary, dune height and the habitat variables were not normally

distributed (all Kolmogorov–Smirnov test, with P < 0.05 to P < 0.005). The Spearman correlation

index showed different values, depending on the the physical aspect and vegetational type:

1. (a)

we found a highly significant correlation between beach erosion and dune erosion

(ρ = 0.750) (Table 2);

Table 2

Non parametric bivariate correlation (Spearman ρ) on all 75 investigated transects

Dune

eight

(m)

H1210

width

(m)

H2110

width

(m)

H2120 A

width

(m)

H2120 B

width

(m)

Beach

erosion

width (m)

Dune

erosion

width

(m)

Dune

eight (m)

Spearman

ρ 1.000 0.196 0.227* 0.141 0.561** −0.347** –0.427**

Sig. (2-

code) – 0.093 0.050 0.228 0.000 0.002 0.000

n 75 75 75 75 75 75 75

H1210

width

(m)

Spearman

ρ 0.196 1.000 0.309** 0.818** 0.537** –0.414** –0.514**

Sig. (2-

code) 0.093 – 0.007 0.000 0.000 0.000 0.000

n 75 75 75 75 75 75 75

H2110

width

(m)

Spearman

ρ 0.227* 0.309** 1.000 0.524** 0.459** –0.417** –0.605**

Sig. (2-

code) 0.050 0.007 – 0.000 0.00 0.000 0.000

n 75 75 75 75 75 75 75

H2120 A

width

(m)

Spearman

ρ 0.141 0.818** 0.524** 1.000 0.660** –0.367** –0.596

Sig. (2-

code) 0.228 0.000 0.000 – 0.000 0.001 0.000

n 75 75 75 75 75 75 75

H2120 B

width

(m)

Spearman

ρ 0.561** 0.537** 0.459** 0.660** 1.000 –0.504** –0.710**

Sig. (2-

code) 0.000 0.000 0.000 0.000 – 0.000 0.000

n 75 75 75 75 75 75 75

Beach

erosion

width

(m)

Spearman

ρ

–

0.347**

–

0.414**

–

0.417** –0.367** –0.504** 1.000 0.750**

Sig. (2-

code) 0.002 0.000 0.000 0.001 0.000 – 0.000

n 75 75 75 75 75 75 75

Dune

erosion

width

(m)

Spearman

ρ

–

0.427**

–

0.514**

–

0.605** –0.596** –0.710** 0.750** 1.000

Sig. (2–

code) 0.000 0.000 0.000 0.000 0.000 0.000 –

n 75 75 75 75 75 75 75

Significant values are represented by * (alpha <0.05) and ** (alpha <0.005)

2. (b)

we found a negative correlation between the dune erosion and each habitat, even with

differences among habitats (H1210, ρ = −0.514; H2110, ρ = −0.605; H2120A, ρ = −0.596

and H2120B, ρ = −0.710), while beach erosion and dune height slightly correlated only with

H2120B (Table 2).

3. (c)

among habitats, the stronger correlation was between H2120A and H1210 and all the others,

(ρ = 0.818). Correlations between the other habitats were not significant (Table 2).

Considering the dune erosion as the most important geomorphological factor acting on shaping the

development of detected habitats, we grouped the entity of dune erosion in four different classes (0–

1 m = 1; 1.1–10 m = 2; 10.1–20 m = 3; >20 m = 4). It was tested separately for each habitat (e.g.

vegetation width), with One Way Anova. The results show a progressive and statistically significant

decrease in the width of all the different habitats assessed according to the increased erosion of the

dune belt (Fig. 6).

Fig. 6

Trend of width averages (m) of the different habitats for the four considered classes of dune erosion

with One way analysis of variance (ANOVA) between each habitat depth and dune erosion depth

rank

The multivariate GLM found a marked significant effect of erosion dune on three habitats, not on

H1210 and a marginal effect on the dune height. Beach erosion had no effect on all the considered

variables. The interaction between beach and dune erosion provided marked effects only on the

dune eight, and no effect on habitats (Table 3).

Table 3

Multivariate general linear model of effects and interaction of erosive patterns on the biotic and

abiotic features of the coastal system (on the four dune erosion selected classes)

Factor Dependent variable F Probability

Dune erosion

H1210 2.159 0.101 NS

H2110 22.738 <0.0001**

H2120 A 4.282 0.008**

H2120 B 12.492 <0.0001**

Dune height 2.844 0.044*

Covariates

Beach erosion

H1210 0.505 0.480

H2110 0.008 0.930

H2120 A 1.889 0.174

H2120 B 0.046 0.831

Dune height 0.101 0.751

Interactions

Beach erosion × Dune erosion

H1210 0.678 0.568 NS

H2110 0.374 0.772 NS

H2120 A 1.820 0.152 NS

H2120 B 1.836 0.149 NS

Dune height 4.204 0.009**

Significant values are represented by * (alpha < 0.05) and ** (alpha < 0.005)

5 Discussion

The phytosociological surveys on this streatch of coast confirm the trend to a floristic

impoverishment of plant communities and the prevalence of certain species already highlighted by

surveys made in 2005 by Sani and Tomei (2006) for the interely coast of San Rossore. The

associations here idenfied in our investigation showed, in almost all cases, a marked physiognomic

and floristic difference with respect to the associations detected in the sandy shores of the

neighboring Tyrrhenian dune environments (Vagge and Biondi 1999; Acosta et al. 2003; Bertacchi

et al. 2009; Bertacchi and Lombardi 2014a), and to the rest of the same habitat of continental and

mediterranean bioclimatic regions of Italy (Prisco et al. 2012).

When considering habitat 1210, which association of reference is the Salsolo Kali-Cakiletum

maritimae Costa et Manz 1981, we detected a substantial conformity with data present in literature

(Table 1). The other habitats display, on the contrary, different scenarios. Habitat 2110 is

represented here only by plant communities generically related to the Agropyrion juncei, but,

however, without any trace of the more representative association Echinophoro spinosae-Elymetum

farcti Géhu 1987, common in coastal areas next to the area studied as, in the same way in the

absence of disturbance, in the rest of the Italian sandy shores (Vagge and Biondi 1999; Biondi and

Galdenzi 2014). In each case, here, for this habitat we wish to emphasize: (1) the extreme scarcity

of the characteristic species Elymus farctus; (2) the absence of the other diagnostic species

Echinophora spinosa (Table 1); (3) the presence of Spartina versicolor, that can be attributed to

high capability of colonization by S.versicolor of disturbed sand wet environments (Bertacchi and

Lombardi 2014c), as, on the other hands, the presence in other relevés, of Othantus maritimus, that

can indicate a step of stabilization (Biondi and Galdenzi 2014); d- anyway the high thinness of

embryonic strip (max 0.5 m) and its overall scarcity (24 % of the total points collected) (e.g. Figs. 4,

5), can indicate a high vulnerability of this habitat to the erosive dynamics.

In the case of Ammophila arenaria white dune (habitat 2120), phytosociological data collected

showed the presence of two groupments, interpreted as facies of association Echinophoro spinosae-

Ammophiletum arundinaceae Géhu, Rivaz-Martinez and R.Tuxen 1972 in Géhu et al. 1984, and in

no case, it never finds the association in its floristic entirety. In fact, in one case (e.g. H2120A,

Table 1) there is a belt, placed always in catenal contact with the embryonic dune or, where absent,

with that annual vegetation of drift lines, characterized by the marked presence of Euphorbia

paralias. E. paralias is a diagnostic species of Echinophoro spinosae- Ammophiletum

arundinaceae, but, here, it formed monophytic plant communities (e.g. Fig. 7a), physiognomically

separated from the subsequent Echinophoro spinosae- Ammophiletum arundinaceae. This last

facies is instead characterized by the almost total absence of Echinophora spinosa, a other

diagnostic species of the association (Table 1) (Biondi et al. 2012; Acosta and Ercole 2015),

common in coastal areas next to the area studied, and the almost exclusive presence and coverage

by Ammophila arenaria. These vegetation features are evidently the symptom of environmental

changes, linked to changes of non-anthropogenic source (as mentioned above, the entire stretch of

studied coastline is under full protection with total access restriction) but, obviously, to marine

erosive action.

Fig. 7

Outline of the most recurrent forms of marine erosion on the stretch of coast studied (a no erosion;

b moderate; c pronunced; d strong) and correlated vegetation landscape (for numerical code, see

Materials and Methods)

The correlation analysis (Spearman ρ) between physical factors (beach erosion, dune erosion, dune

height) and habitats showed that dune erosion has the highest correlation especially as regards

habitats 2110 and 2120B (Tables 2). The different intensity of dune erosion (decrease of dune belt

width 2003–2015) markedly influenced (ANOVA analysis) the reduction of phytocoenoses, as well

as the dune system reduction, with a differentiated vulnerability (Figs. 6, 7; Table 3).

Even with no dune erosion, habitat 2110 already has shown extremely low values in both thickness

and presence, while the habitats 1210 and 2120A and 2120B have shown a variable thicknesses (7

to 10 m). This is likely due to past -undetectable-fluctuations of erosive processes, not followed by

a re-colonization of this habitat. H2120 (A and B) appeared only altered in its floristic component

(Tables 1), but not in its thickness and coverage (cf. Figs. 4b, 6, 7). Where erosion has ranged

between 1.1 and 10 m (class 2), all habitats drastically has decreased in thickness, with highest

decrease in H2110 and H2120B. The third class of erosion (10–20 m) displayed a pattern not

dissimilar from the previous class. When the dune belt has decreased more than 20 m, H1210,

H2120A and B, have reduced their thickness to less than 2 meters while H2110 has disappeared

(Figs. 6, 7; Table 3). When considering all variables and factors (multivariate GLM), it emerged a

strong effect of dune erosion on three out of four habitats (not on H1210), particularly high for

H2110 and H2120B (Table 3). Beach erosion variability did not affect habitats nor dune height. The

interaction dune erosion x beach erosion had a significant effect only on the dune height. Habitat

1210, that is composed by pioneer and annual species, actually reflects a low vulnerability, and it is

present in each case. It is absent just where erosion prevents the deposition of organic debris, to

which this habitat is ecologically linked (e.g. Fig. 7b) (Pignatti 1993; Vagge and Biondi 1999;

Acosta et al. 2007). Habitat 2110 it is almost surely the more critically endangered habitat, both in

terms of floristic composition -the characteristic association Echinophoro-Elymetum has never been

found- and of its presence and overall coverage, often close to zero even at the first class of erosion

(no erosion).

This marked sensitivity appears in line with that has already been reported for the Iberian peninsula

(Lomba et al. 2008) and for the Thyrrenian coast of north and central Italy (Ciccarelli 2014; De

Luca et al. 2011; Attorre et al. 2013). Habitat 2120, divided into its two main components,

dominated by Euphorbia paralias (H2120A) and Ammophila arenaria (H2120B) respectively,

shows a significantly high vulnerability to erosion dune since the second class of erosion (1.1–

10 m). Although still significantly present along this coast (70 % of cases) when the retreat of the

coastline cause the dune belt collapsing, the habitat 2120B tends to disappear on a wider scale and

more rapidly than the other habitats. So, the persistence of the habitat 2120 found here and in other

Tyrrhenian coastal sectors under strong erosion (Ciccarelli 2014) can be explained by a temporary

presence linked to the hindmost habitat position to the coastline.

Our data support the strong correlation among erosion, species composition and distribution of

psammophilous plant communities, as reported for other phytogeographical contexts than those of

the interior Mediterranean (Roman and Nordstrom 1988; Feagin et al. 2005; Martins et al. 2014;

Bitton and Hesp 2013). Moreover, from what we observed, it is possible to emphasize that the most

useful geomorphological element to investigate the effects of erosion on psammophilous plant

communities is represented by dune belt, as noted by Lomba et al. (2008) and by crossing of

vegetation data with the diachronic investigation of integrity/width of dune. The measurement of

the coast line retreat alone, does not take into account the possibility of scraping of dune belt and

the dispersing the sands on a similar surface.

Finally, it seems extremely important how to detect flora alteration in the different dune habitats.

For example, the great diffusion of Euphorbia paralias, which had a strong seeds spreading and a

good buoyancy in sea water (Heyligers 2002), if compared to species characterised by the rhizomes

spread as E. farctus and A. arenaria (Maun 2009), can indicate a phase of extreme instability of the

dune system.

The survey carried out by us has underlined, due to the important erosion phenomenon on the

investigated coast, the risk of the loss of much of the dune environment and psammophilous

communities related thereto. The current trend of erosion shows no horizontal recession of sands

and, consequently, seems no longer allowing inland translocation of psammophilous communities,

determining, therefore, the progressive disappearance of all types of dune vegetation. Each time the

monitoring of plant communities and the dune morphology reveals similar dynamic, the

consolidation of the dune by plants implantation or wooden fences appears consequently useless.

Coastal protection like detached breakwaters aimed at containing the offshore transport of sand

sediment can be effective, although sometimes with reversed responses (Bowman and Pranzini

2003).

Footnotes

1

These habitats represent the typical phytocenotic contingent of beaches and foredune systems for

the italian sandy coasts (Acosta and Ercole 2015).

Acknowledgments

This study was financially supported by grants from University of Pisa (Ricerche Geobotaniche in

ambito Mediterraneo).

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