STRUCTURE AND SPECIES DIVERSITY OF BROMUS ERECTUS GRASSLANDS OF BIANCANABADLANDSAuthor(s): Simona MACCHERINI, Alessandro CHIARUCCI, Vincenzo DE DOMINICISReviewed work(s):Source: Belgian Journal of Botany, Vol. 133, Fasc. 1/2 (2000), pp. 3-14Published by: Royal Botanical Society of BelgiumStable URL: http://www.jstor.org/stable/20794459 .Accessed: 29/02/2012 04:40

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Belg. Journ. Bot. 133 (1-2) : 3-14 (2000)

STRUCTURE AND SPECIES DIVERSITY OF BROMUS ERECTUS GRASSLANDS OF BIANCANA BADLANDS

Simona MACCHERINI, Alessandro CHIARUCCI & Vincenzo DE DOMINICIS

Dipartimento di Scienze Ambientali, Univerist? degli Studi di Siena, Via RA. Mattioli 4,1-53100 Siena, Italy

Summary. ? Species richness, diversity and structure were studied in Bromus erectus

grasslands on the top of biancana landforms of the Orcia Valley, Tuscany (central Italy). Three

community types were recognized : uneven B. erectus grasslands on less stable morphologies, and compact B. erectus grasslands and B. erectus grasslands colonized by Spartium junceum scrub, both on more stable morphologies. The main difference between them was a dramatic

decline in species richness and diversity from the former to the latter. The number and cover of

annual herbs, many of which are low-growing species (e.g. legumes and graminoids), also

decreased significantly in the same order. The frequency of B. erectus was constant (100%) in

all three types of community, whereas percentage cover increased sharply (54.2 vs. 85.5%) between uneven and compact grasslands, remaining high in the scrub communities (83.8%). Cover of phanerophytes showed low values in the uneven and compact grasslands, but reached

80% in the scrub communities. The increase in cover of B. erectus caused the disappearance of

species typical of the pioneer vegetation of Pliocene clay soils with Artemisia cretacea.

Colonization of the compact grasslands by 5. junceum induced a reduction in grassland species of the class Festuco-Brometea. The implications of these findings for the conservation of B.

erectus grasslands and biancana badlands are discussed.

Key words. ? Grasslands, Bromus erectus, Spartium junceum, species richness, community struc ture.

Nomenclature. ? Pignatti (1982)

INTRODUCTION

Under the regulation of the European Union that establishes a common framework for the con

servation of wild animal and plant species and nat

ural habitats (92/43/ECC, Rom?o 1996), semi-nat ural dry grasslands on calcareous substrate are

classified as habitats of Community importance. Because of the changes in land use, the area of semi-natural grasslands is decreasing across the

whole of Europe (van Dijk 1991). Increasing dominance of invasive or aggressive grass species and shrub invasion of these species-rich communi ties result in reduced species richness (see Dzwonko & Loster 1998). Many authors have described the detrimental impact of dominant

grass species on species richness and diversity, particularly for the chalk grasslands of western

Europe dominated by Brachypodium pinnatum (see Hurst & John 1999).

4 BELGIAN JOURNAL OF BOTANY 133

Changes in land management, from grazing to cultivation, and the abandonment of traditional

management led to a reduction in the surface area of biancane, peculiar erosion forms of clay areas

of central Italy. Consequently, the perennial grass lands dominated by Bromus erectus, growing in different geomorphological situations of the bian cana landscape under traditional management, were significantly reduced in the last decades or

they evolved into shrubland (Chiarucci et al.

1995b). In 1995, a nature reserve was established in the Orcia Valley (southern Tuscany) to preserve the biancana landscape and its peculiar vegetation types. Although B. erectus is not rhizomatous and

consequently is a less effective dominant than other species, e.g. Brachypodium pinnatum (Grime et al. 1988), it is reported that a relaxation of grass land management may result in the formation of

dense, species-poor swards (Grime et al. 1988, Dierschke & Engels 1991).

The present paper aims to analyse the effects induced by dominance of Bromus erectus and by shrub invasion on species diversity and composi tion of dry grasslands, with a reference to the man

agement strategies for the conservation of Bromus erectus grasslands of the biancana badland.

METHODS

Study area

The study area is located at Podere Beccanello

(Fig. 1), in the upper Orcia valley, central Italy, and has

already been subject to geomorphological and geob otanical research (AA.VV. 1997). Its area is about 20 ha,

half of which is occupied by biancane. Biancane (plural for biancana) are small domes up to 20 m high, sur

rounded by nearly horizontal pediments that may extend

up to 15 m from the biancana slopes. Biancane may be

isolated, but usually occur in groups (Guasparri 1978). The processes leading to their formation are related to

specific meteorological conditions and to a land use not finalized to conservation (Calzolari et al. 1996).

Altitude ranges from 330 to 430 m. According to Thornthwaite & Mather (1957), the climate is transi

tional between subhumid and subarid, with moderate summer drought ; mean annual temperature is between

12.6 and 14.4 ?C and mean annual rainfall between 671

and 835 mm (Colica 1993).

The sedimentary lithology consists of Pliocene marine clays, rich in salts such as NaCl, CaC03 and sul

phates. Morphologically, the area is a remnant of a high

ly dissected, 20% slope facing SSW, of which the Man cane and gullies are the main features (Calzolari &

Ungaro 1998). The biancane are classified on the basis of their morphological stability, which depends on local factors : the different types reflect different evolutionary stages with a trend from the taller "bean" forms to the

terminal "souffl?-like" or "cone" forms (Calzolari &

Ungaro 1998). The part of the area without biancane has been reshaped several times since the 1920s, and is at

present partly cultivated and partly set aside. The bian

cana fields were grazed by sheep since from 1826 to about 1980 (Calzolari et al 1996).

Sampling

Different successional vegetation stages can be

found on the top of the bean biancana forms. Thirty

quadrats (2 m 2 m) were selected within each of three

vegetation types, differing in structural features :

i) uneven B. erectus grasslands on less stable morpholo

gies (data collected in June 1996), characterised by fre

quent small mass movements, like creeping, mudflows

and small landslides, as shown by large cracks and steps

(Calzolari et al. 1993) ; ii) compact . erectus grass lands and iii) B. erectus grasslands colonized by Spartium junceum scrub, both on more stable morpholo

gies, characterised by steps due to small mass move

ments (Chiarucci et al. 1995a). These three community

types belong to the alliance Bromion erecti (order Brometalia erecti) and can be interpreted as a succes

sional pathway : uneven grasslands > compact grass lands > scrub communities. More details of the vegeta tion of the study area are given by Chiarucci et al

(1995b). In each plot, the presence of all vascular plant

species was recorded and their cover accurately estimat

ed. Since the cover was estimated for each species, strat

ification or multiple layering of dense growth may lead to total cover values exceeding 100% (Kent & Coker

1992).

Data analysis

Species richness values of the three vegetation

types were compared by different approaches : /) the mean number of species per plot, //) the total number of

species recorded in the 30 plots of each type and ///) an estimated value of the species pool, i.e. the set of species which inhabits a community type (Zobel 1992, Eriksson

DIVERSITY OF BROMUS ERECTUS GRASSLANDS 5

Fig. 1. ? Beccanello farm : biancana field.

1993), i.e. our vegetation types ; species pool richness were estimated by second-order jackknife estimator

(Palmer 1991), using the program Estimates (Colwell 1997). Species diversity was calculated using the Bulla (1994) index of diversity (D) and differentiation diversi

ty, using Whittaker's measure (Whittaker 1960).

Community structure was investigated by compar

ing number of species and cover of the following life form groups : annual and perennial graminoids, legumes and forbs, chamaephytes and phanerophytes.

The relationships between species richness and

) B. erectus cover and ii) total cover in each plot were

examined using linear and potential regression. Differences in ecological and structural features

between the community types were analysed by Kruskal-Wallis analysis of variance by ranks. When the

null hypothesis was rejected, the non-parametric Tukey test (P < 0.05) was used for multiple comparisons (Camussi ?tf a/. 1995).

RESULTS

Species diversity and community attributes

Total cover showed a significant, obvious, increase from uneven grasslands to compact grass lands and scrub communities, were vegetation lay ering produced a total cover largely exceeding 100% (Table 1).

Uneven grasslands showed the highest species richness, both as mean species richness per plot and total species number per 30 plots, fol lowed by compact grasslands and scrub communi ties (Table 1). According to the second-order jack knife estimated values, 87.0% of the species pool of the uneven grasslands was sampled in the thirty plots, whereas the proportions of the species pool sampled in compact grasslands and in scrub

6 BELGIAN JOURNAL OF BOTANY 133

communities were of 69.2 and 74.6% (Table 1).

Species richness was significantly negatively cor

related with the cover of the dominant species, i.e. Bromus erectus (Fig. 2a), and with total cover

(Fig. 2b). The Bulla index of species diversity showed a

pattern resembling that of species richness, where as differentiation diversity had an inverse pattern,

being highest in scrub communities (Table 1).

Community structure

The number and cover of annual herbs, many of which are low-growing species (e.g. legumes and graminoids), decreased sharply with increas

ing total cover (Table 2). The pattern of perennial herbs was less linear : their number decreased with

increasing total cover but the number of forbs

increased from uneven to compact grasslands and the number of graminoids and legumes decreased with increasing total cover. The cover of perennial graminoids, except Bromus erectus, decreased in

compact grasslands, increasing again in scrub

communities, whereas the number perennial forbs was constant in the first two types and decreased

slightly in scrub communities (Table 2). Number and cover of phanerophytes was highest (up to

80%) in scrub communities.

Floristic composition

The frequency of Bromus erectus was con

stantly 100% for all community types and its per centage cover increased sharply from uneven

grasslands (54.2%) to compact grasslands (85.6%), and scrub communities (83.8%) (Table 3). Aster linosyris, Carex fiacca and Phleum bertolonii also characterised the herba ceous cover of scrub communities ; these species in addition to Onobrychis viciifolia and Dactylis hisp?nica were also the most abundant in compact grasslands. Where the dominance of B. erectus was lower (in uneven grasslands), Avena fatua, Dactylis hisp?nica, Hedysarum coronarium and

Onobrychis viciifolia were the most abundant

species. The uneven grasslands had many exclusive

species, some of which had a high frequency. Most of them were annuals (e.g. Medicago minima,

Catapodium rigidum and Trifolium scabrum). The

compact grasslands and the scrub communities had few exclusive species, which achieved low values of frequency and cover, especially in the first community type. Pyrus amygdaliformis, Crataegus monogyna, Rosa canina and Juniperus communis were found only in the scrub communi

ties, where Spartium junceum had a cover of about 77%.

Table 1

Comparison of community attributes of the three vegetation types. Values are means, denotes

the probability of differences (Kruskal-Wallis test) between community types, different letters indicate

significant differences (p < 0.05) based on non-parametric Tukey tests

Uneven

grasslands

Compact

grasslands

Scrub

Cover of species (%) Species richness (# species/4 m2) Total number of species Second order jackknife estimation of species Diversity (D) Differentiation diversity

77.4A

24.4A

87

100.0 12.6A

3.57

100.7B

14.4B

67

96.9

8.6B

4.65

174.9C

9.2C

46

61.6

6.4 c

5.00

DIVERSITY OF BROMUS ERECTUS GRASSLANDS 7

40 80 120 160

Total Ground Cover (%)

200 240

Fig. 2. ? Relationship between species richness and a) Bromus erectus cover and b) total cover with a fitted linear regression (2a) and a fitted potential regression curve (2b). Circles : uneven grasslands, triangles : compact grasslands ; squares : scrub com

munities.

8 belgian journal of botany 133

Table 2

Comparison of community structure of the three vegetation types. Values are means, denotes the probability of differences (Kruskal-Wallis test) between community types, different letters indicate

significant differences (p < 0.05) based on non-parametric Tukey tests

Uneven

grasslands Compact

grasslands

Scrub

Number of species

Annual graminoids Annual legumes Annual forbs

Total annual herbs

Perennial graminoids (not B. erectus) Perennial legumes Perennial forbs

Total perennial herbs

Chamaephytic species Phanerophytic species

Cover of species

Annual graminoids Annual legumes Annual forbs

Total annual and biennal herbs

Perennial graminoids (not B.erectus ) Perennial legumes Perennial forbs

Total perennial herbs

Chamaephytic species Phanerophytic species

2.1A

4.9a

7.2a

14.3a

3.3a

1.5a

4.1a

9.8a

0.5a

0.1a

3.0a

3.1a

2.5a

8.6a

6.36a

3.5a

4.5a

68.5a

0.2

0.02a

0.4B

1.3B

3.1B

4.8B

3.1B

1.1B

4.3B

9.4B

0.3a

0.2a

0.2B

0.5B

1.7B

2.4B

4.60B

2.5B

5.5a

98.P

0.2

0.04a

0.4B

0.1C

0.9C

1.3C

2.0C

0.3C

2.7C

6.0C

0.3a

1.9B

0.1B

0.03c

0.7C

0.8C

5.24c

0.2C

4.0B

93.3C

0.5

80.4B

DISCUSSION

Species diversity

The increase in total cover observed between uneven and compact grasslands, essentially due to the increase in cover of Bromus erectus (54.2 vs.

85.6%), causes a decrease in species richness and

diversity. Similar changes induced by increase in abundance of the dominant species have been observed in other overgrown European grasslands (Wells 1971, Rusch 1988, Bobbink & Willems

1087, 1991, 1993, Dierschke & Engels 1991, Mitchley & Willems 1995, Hurst & John 1999). The cover of tall species reduces penetration of

light, impeding the development of short lived and/or light-demanding species (Kull & Zobel

1991, Mitchley & Willems 1995, Zobel et al

1996, Hurst & John 1999) and produces a thick

layer of litter which inhibits seed germination and establishment of seedlings (Hurst & John 1999). As shown by Chiarucci et al (1995a), coloniza tion by Spartium junceum further reduces diversi

ty and species richness in Bromus erectus grass lands. Other authors (Hobbs & e 1986, Rejm?nek & Rosen 1988, Davies & Waite 1998) have reported similar findings after colonization of

grasslands by woody species, and ascribe the effect to a decrease in the amount of light reaching the ground. Spartium junceum, a species with pho tosynthesizing stems which only bear leaves in

spring (Pignatti 1982), hardly ever achieves high cover values.

Community structure

The increase in cover of Brachypodium pin natum and Br?mus erectus observed in calcareous

DIVERSITY OF BROMUS ERECTUS GRASSLANDS

Table 3

Species frequency and cover in the three vegetation types

Uneven grasslands

Frequency Cover Compact grasslands

Frequency Cover

Scrub

Frequency Cover

Hypericum perforatum I 0.01

Parapholis strigosa I 0.01 Veronica arvensis I 0.01

Arahis sagittata I 0.02 Artemisia cretacea I 0.02

Bellardia trixago I 0.02

Carlina corimbosa I 0.01

Echium vulgare I 0.01

Hordeum maritimum I 0.02

Lactuca saligna I 0.01

Malope malacoides I 0.04

Medicago orbicularis I 0.01

Carduus nutans I 0.01

Filago germanica I 0.01

Aegilops geniculata I 0.05 Melilotus sulcata I 0.03 Astragalus monspessulanum I 0.32

Bromus hordeaceus I 0.17

Bromus madritensis I 0.06

Podospermum laciniatum I 0.05

Plantago maritima I 0.14

Tordylium apulum I 0.04 Trifolium angustifolium I 0.08

Medicago minima II 0.12

Catapodium rigidum II 0.04 Trifolium scabrum II 0.09

Crepis vesicaria III 0.2

Hedysarum coronarium III 1.75

Sonchus oleraceus I 0.01

Centaurium pulchellum I 0.01

Potentilla hirta I 0.01 Dorycnium hirsutum I 0.03

Geranium dissectum I 0.02

Vfcw hybrida I 0.01 Leontod?n villarsii I 0.01 P?<2 sylvicola I 0.01

Trifolium stellatum I 0.04 Phalaris coerulescens I 0.13

Bupleurum b?ldense I 0.01

Parentucellia viscosa II 0.03 P/crw echioides II 0.07 Phleum ambiguum II 0.08 Hippocrepis unisiliquosa III 0.15 Brachypodium distachyum III 0.21 Trifolium echinatum III 0.51 Trifolium campestre III 0.32 y/c/? safr'va III 0.39

Scorpiurus muricatus III 0.53

Trifolium lappaceum IV 0.74 Sherardia arvensis IV 0.28

Einum strictum subsp.

corymbulosum V 0.16

Coronilla scorpioides

II

I

0.02

0.02

0.02

0.04

0.04

0.02

0.03 0.02

0.01 0.06 0.04

0.01

0.02

0.03

0.02

0.01

0.07

0.1

0.05

0.1

0.11 0.04

0.08

0.01

10 BELGIAN JOURNAL OF BOTANY 133

Uneven grasslands

Frequency Cover Compact grasslands

Frequency Cover Scrub

Frequency Cover

Ornithogalum pyrenaicum I 0.01 Pulicaria dysenterica I 0.01 Lotus corniculatus I 0.02 Orchis coriophora I 0.02 Anth?mis tinctoria I 0.03 Hieracium piloselloides I 0.03 Cuscuta epithymum I 0.1 Inula viscosa I 0.06

Lathyrus nissolia I 0.05

Dorycnium pentaphyllum I 0.62 subsp. herbaceum

Sanguisorba minor I 0.06

subsp. muricata

Brachypodium rupestre Lonicera caprifolium Juniperus communis

Pyrus amygdaliformis Crataegus monogyna Rosa canina

Quercus pubescens I 0.01 Teucrium polium I 0.03 Ornithogalum pyramidale I 0.01 Teucrium chamaedrys I 0.01

Dactylis hisp?nica V 3.46 V 1.04 Bromus erectus V 54.17 V 85.5 Phleum bertolonii V 1.93 V 1.66 Aster linosyris V 2.56 V 3.65 Hypochoeris achyrophorus V 0.71 I 0.06 Avena fatua IV 2.42 II 0.16 Blackstonia perfoliata IV 0.13 III 0.3 Onobrychis viciifolia IV 1.29 V 1.81 Galium verum III 0.93 V 0.43 Geropogon glaber III 0.12 I 0.02 Allium cirrhosum III 0.07 II 0.08 Koeleria splendens III 0.52 III 0.35 Plantago lanceolata III 0.23 I 0.05 Daucus carota III 0.2 III 0.25 Pallenis spinosa II 0.22 I 0.02 Scabiosa columbaria II 0.32 I 0.13 Vicia tenuissima II 0.11 I 0.02 Carthamus lanatus II 0.09 II 0.17 Carex fiacca II 0.24 III 1.45 Convolvulus arvensis II 0.04 I 0.12 Thymus longicaulis II 0.1 II 0.15 Xeranthemum cylindraceum II 0.11 II 0.27 Trifolium ochroleucum I 0.17 I 0.04 Stachys heraclea I 0.03 II 0.18 Picris hieracioides I 0.01 II 0.1 Prunella laciniata I 0.03 I 0.04 Prunus spinosa I 0.01 I 0.01 Cirsium arvense I 0.01 I 0.01 Rhinanthus alectorolophus I 0.01 I 0.19 Spartium junceum I 0.01 I 0.04 Scorzonera glastifolia I 0.01 II 0.19 Eryngium campestre I 0.01 III 0.25

I I I I I II I I I I

IV V II IV I II I I II I I I I II I I I II V II I I I I I I I I I

V II I

0.26

0.02

0.01

0.06

0.03

0.02 0.17

0.29 0.87 2.12

0.05

0.18 0.03

0.25 0.31 83.83 1.47

2.26

0.01

0.14

0.08

0.11

0.45

0.02 0.01 0.07 0.01 0.37 0.02 0.01 0.01 0.11

3.36 0.36

0.07

0.01

0.04

0.06

0.16 0.02

0.03

0.03

0.03

76.83 0.27 0.06

DIVERSITY OF BROMUS ERECTUS GRASSLANDS 11

grasslands causes a substantial decrease in low

growing species and generally represses forb cover more than graminoid cover (Dierschke & Engels 1991 for B. erectus, Hurst & John 1999 for B. pin natum). Here we found that the number and cover

of shorter annual herbs decreased substantially with increasing cover of B. erectus and following colonization by S. junceum. However, the cover of

perennial forbs was similar in all three types of

community and forb richness increased slightly between uneven and compact grasslands.

The least vulnerable species, in terms of per

centage cover, to increasing abundance of Bromus erectus were Phleum bertolonii, Carex fiacca, Aster linosyris, Onobrychis viciifolia and Dactylis hisp?nica, but the latter two were much affected

by colonization by S. junceum. The resistance of Carex fiacca to increases in tall-growing species has already been observed in Brachypodium pin natum (Bobbink & Willems 1987, Hurst & John

1999) and Bromus erectus grasslands (Wells 1971, Dierschke & Engels 1991). Indeed, in Italy

Carex fiacca is found in many different types of

vegetation, ranging from grassland to forest com

munities (Pignatti 1982). Colonization of grasslands by S. junceum

seems to be quite rapid in the biancana badlands

(De Dominicis 1980), certainly faster than pedoge netic evolution (Chiarucci et al. 1995b), and was

presumably favoured in the study area by the ces

sation of grazing. The invasion and spread of

woody species in these grasslands occur unevenly ; in fact, substantial differences in shrub cover can be observed between biancane of the same form,

managed in the same way. Similar observations have been made in B.

erectus grasslands abandoned for 20 years : some

plots showed shrub development and others only dense cover of B. erectus without shrubs

(Dierschke & Engels 1991).

Floristic composition

Species exclusive to the uneven grasslands of the biancana badlands include annual grasses, such as Aegilops geniculata, Hordeum maritimum, and

legumes, such as Medicago minima and Trifolium

scabrum, typical of pioneer vegetation with Artemisia cretacea on Pliocene clay soils. This

type of vegetation is encountered on soils high in

salt, low in moisture and with elevated dynamics, such as those of the sedimentation pediments of biancane or the more eroded slopes of calanchi

(Branconi et al. 1979, Chiarucci et al. 1995b, Maccheresti et al. 1998).

The compact grasslands are characterized by the presence of Dorycnium pentaphyllum and Lotus corniculatus, indicator species of grasslands on more stable and evolved badland soils (Biondi et al. 1986).

Colonization of compact grasslands by Spartium junceum leads to a decrease in grassland species from the class Festuco-Brometea, with the

disappearance, for example, of Hippocrepis unisiliquosa, Potentilla hirta, Trifolium campestre and Vicia hybrida. The decrease of species typical of open grassland has also been reported after col onization of European calcareous grasslands by woody species (Rejmanek & R?sen 1988, 1992, Kull & Zobel 1991, Davies & Waite 1998, Dzwonko & Loster 1998). Spartium junceum scrub communities had high frequencies of Pyrus amygdaliformis, Crataegus monogyna, Rosa cani na and Juniperus communis, indicating a dynamic process towards mature scrub communities of the alliance Pruno-Rubion ulmifolii (De Dominicis et

al. 1991). However in this area, more evolved scrub has

preferentially been found where there is moisture, such as at the foot of slopes and along impluvium lines (Chiarucci et al. 1995b).

Implications for conservation

To maintain the composition and species rich ness of semi-natural grasslands, a return to tradi tional methods of land use or their optimization has been suggested in many different situations

(Bobbink & Willems 1988,1991,1993, Dierschke & Engels 1991, Mitchley & Willems 1995, Zobel et al. 1996, Dzwonko & Loster 1998). These methods favour the formation and subsequent colonization by herbaceous species of gaps caused

by different management activities (Rusch 1988,

12 BELGIAN JOURNAL OF BOTANY 133

1992, Rusch & Fernandez-Palacios 1995, Zobel et al 1996).

In the management of biancana badlands, however, it is not only necessary to maintain

species diversity, but also to ensure the conserva tion of these landforms. Morphological stability of the biancane is positively correlated with plant cover (Calzolari et al. 1993, 1997) and inappro priate management of the latter may trigger ero

sion, deep infiltration of water and soil movement

(Torri et al. 1994). Clearing, grazing and burning, which limit the dominance of Bromus erectus and

Spartium junceum shrubs, may accelerate the evo lution of biancane towards the terminal souffl? like and cone forms.

An intermediate level of disturbance is there fore necessary to maintain a sufficient degree of

plant cover and to avoid dynamic evolution of veg etation towards closed scrub communities.

ACKNOWLEDGEMENTS

This research was supported by the National Research Council of Italy. The authors thank Dr.

Ermanno Busoni, Dr. Dino Torri and Dr. Costanza

Calzolari (CNR-IGES, Florence, Italy) for useful infor mation on geomorphology.

REFERENCES

AAVV, 1997. ? Badland processes and significance in

changing environments : Guide for the excursion.

In : Rodolfi G, & Torri O. (eds.) : Fourth

International Conference on Geomorphology.

Suppl. Geograf. Fis. Dinam. Quat. III, T.2 : 151

166.

Biondi E., Ballelli S., Allegrezza M., Guitian J., &

Taffetani F., 1986. ? Centaureo bracteatae

Brometum erecti ass. nova dei settori marnoso

arenacei dell' Appennino centrale. Doc. Phytosoc. 10: 117-126.

BoBBPNK R., & Willems J. H., 1987. ? Increasing domi

nance of Brachypodium pinnatum (L.) Beauv. in

chalk grasslands : a threat to a species-rich

ecosystem. Biol. Conserv. 40 : 301-314.

Bobbink R., & Willems J. H., 1988. ? Effects of mana

gement and nutrient availability on vegetation structure of chalk grassland. In : During H. J.,

Werger M. J. A., & Willems, J. H. (eds.)

Diversity and pattern in plant community,

pp. 183-193.

Bobbink R., & Willems J. H., 1991. ? Impact of differ

ent cutting regimes on the performance of

Brachypodium pinnatum in Dutch chalk grass land. Biol. Conserv. 56 : 1-21.

Bobbink R., & Willems J. H., 1993. ? Restoration man

agement of abandoned chalk grassland in the Netherlands. Biodiv. Conserv. 2 : 616-626.

Branconi S., De Dominios V., Boscagli A., & Boldi L., 1979. ? La vegetazione dei terreni argillosi

pliocenici della Toscana meridionale. I.

Vegetazione pioniera ad Artemisia cretacea. Atti

Soc. Tose. Sci. Nat. Mem. serie B, 86 : 163-183.

Bulla L., 1994. ?An index of evenness and its associ

ated diversity measure. Oikos 70 : 161

Calzolari C, Ristori J., & Sparvoli E., 1993. ? Soils

of the "biancane" badlands of the Orcia Valley

(Tuscany, Italy. ?

distribution, characteristics and

genesis in the Beccanello farm area. Quaderni di

Scienza del Suolo, Firenze 5 : 119-142.

Calzolari C, Torri D., Colica A., Del Sette M., 1997. ? Podere Baccanello study area. In : Rodolfi G.

& Torri D. (eds.) : Badland processes and signif icance in changing environments. Fourth

International Conference on Geomorphology :

Guide for the excursion. Suppl. Geograf. Fis.

Dinam. Quat. III, T.2 : 160-161.

Calzolari C, Torri D., Del Sette M., Maccherini S., Bryan R., 1996. ? Evoluzione dei processi di

erosione su biancane : il caso delle biancane de La

Foce (Val d'Orcia Siena). Atti del Convegno SISS

"Contributi della scienza del suolo allo studio e alla difesa dei territori montani e collinari". 17-19

Giugno 1996, Milano (Italia), Boll. Soc. Ital Sci. Suolo, N.S. 8 : 185-203.

Calzolari C, Ungaro F., 1998. ? Geomorphic features

of a badland (biancane) area (central Italy. ?

characterisation, distribution and quantitative spa tial analysis. Catena 31 : 237-256.

Camussi A., M?ller F., Ottaviano E., Sari Gorla M., 1995. ? Metodi statistici per la sperimentazione

biologica. Zanichelli, Bologna. Chiarucci A., Bonini I., Maccherini S., & De Domini

cis V, 1995a. ? Influence of colonizing Spartium

junceum scrub on B. erectus grassland in biancana

badlands of the Orcia valley, Tuscany. Arch.

Geobot. 1: 47-54.

Chiarucci A., De Dominicis V, Ristori J., & Calzola

ri C, 1995b. ? Biancana badland vegetation in

relation to soil and morphology in Orcia Valley,

DIVERSITY OF BROMUS ERECTUS GRASSLANDS 13

central Italy. Phytocoenolog?a 25 : 69-87.

Colica A., 1993. ? Processi erosivi in calanchi e bian

cane e loro implicazioni per le opere di conser

vazione nell'alta Val d'Orcia (Siena). Tesi di

Dottorato, Universit? degli Studi di Firenze. Colwell R. K., 1997. ? EstimatesS : Statistical estima

tion of species richness and shared species from

samples. Version 5. User's Guide and applica tion published at : http://viceroy.eeb.uconn.edu/ estimates.

Davies A., & Waite S., 1998. ? The persistence of cal

careous species in the soil seed bank under devel

oping and established scrub. Plant Ecol 136 : 27 39.

De Dominicis V, 1980. ? L'evoluzione della vege tazione sui suoli argillosi pliocenici della Toscana.

Giorn. Bot. Ital. 114 : 104.

De Dominicis V, Loppi S., & Chiarucci A., 1991. ?

Vegetation dynamics on Pliocene clayey soils of

Tuscany (Italy). Proc. 34th IAVS Symp. "Mechanisms in vegetation dynamics". 26-30

August 1991, Eger (Hungary), F. Horv?t (ed.), pp. 63-64.

Dierschke H, & Engels M., 1991. ? Response of a

B. erectus grassland (Mesobromion) to abandon

ment and different cutting regimes. In : G. Esser

& D. Overdieck (eds.) : Modern Ecology : basic

and applied aspects pp. 375-397. Elsevier,

Amsterdam.

Dzwonko Z. & Loster S., 1998. ? Dynamics of species richness and composition in a limestone grassland restored after tree cutting. /. Veg. Sci. 9 : 387-394.

Eriksson O., 1993. ? The species-pool hypothesis and

plant community diversity. Oikos 68 : 371-374. Grime J. P., Hodgson J. G, & Hunt R., 1988. ?

Comparative plant ecology. A functional approach to common British species. Unwin Hyman, London.

Guasparri G., 1978. ? Calanchi e biancane nel territo

rio senese : studio geomorfologico. L'Universo

58 : 97-140. Hobbs R. J., & Mooney . A., 1986. ?

Community

changes following shrub invasion of grassland.

Oecologia 70: 508-513.

Hurst A., & John E., 1999. ? The biotic and abiotic

changes associated with Brachypodium pinnatum dominance in chalk grassland in south-east

England. Biol. Conserv. 88 : 75-84.

Kent M., & Coker P., 1992. ? Vegetation description and analysis : a practical approach. John Wiley and Sons, Chichester.

KuLL ., & Zobel M., 1991. ? High species richness in

Estonian wooded meadow. Veg. Sci. 2: 711

714.

Maccherini S., Chiarucci A., & De Dominicis V., 1998. ? Plant communities of the Radicofani calanchi

(southern Tuscany). Atti Mus. Stor. nat. Maremma

17 : 91-108. Mitchley J., & Willems J. ., 1995. ? Vertical canopy

structure of Dutch chalk grasslands in relation to their management. Vegetatio 117 : 17-27.

Palmer M. W, 1991. ? Estimating species richness :

the second-order jackknife reconsidered. Ecology 72: 1512-1513.

Pignatti S., 1982. ? Flora d'Italia. Edagricole Bologna. ' 3 voll.

Rejm?nek M., & Ros?n E., 1988. ? The effects of colo

nizing shrubs (Juniperus communis and Potentilla

fruticosa) on species richness in the grasslands of

Stora Alvaret, ?land (Sweden). Acta Phytogeogr. Suec. 76 : 67-72.

Rejm?nek M., & Ros?n E., 1992. ? Influence of colo

nizing shrubs on species-area relationships in

alvar plant communities. /. Veg. Sci. 3 : 625-630.

Rom?o C, 1996. ? Interpretation manual of European Union habitats. Directorate General XI

"Environment, Nuclear Safety and Civil

Protection" of the European Commission,

Bruxelles.

Rusch G., 1988. ? Reproductive regeneration in grazed and ungrazed limestone grassland communities

on ?land. Preliminary results. Acta Phytogeogr. Suec. 76: 113-124.

Rusch G., 1992. ? Spatial pattern of seedling recruit

ment at two different scales in a limestone grass

land. Oikos 65 : 433-442. Rusch G., & Fern?ndez-Palacios J. M., 1995. ? The

influence of spatial heterogeneity on regeneration

by seed in a limestone grassland. /. Veg. Sci. 6 :

417-426.

Thornthwaite C. W. & Mather J. R., 1957. ?

Instructions and tables for computing poten tial ?vapotranspiration and water balance.

Drexel Inst. Techn. Lab. of Climatology, 10, 3, Centerton.

Torri D., Colica A., & Rockwell D., 1994. ?

Preliminary study of the erosion mechanism in a biancana badland (Tuscany, Italy). Catena 23 :

281-294.

van Dijk G., 1991. ? The status of semi-natural grass lands in Europe. In : Goriup P. D., Batten L. A. &

Norton J. A. (eds.). The conservation of lowland

14 BELGIAN JOURNAL OF BOTANY 133

dry grassland birds in Europe, pp. 15-36. JNCC Pubi., Newbury.

Wells T. C. E., 1971. ?A comparison of the effects of

sheep grazing and mechanical cutting on the structure and botanical composition of chalk

grassland. In : Duffey E., (ed.), The scientific

management of animal and plant communities for

conservation, pp. 497-515. Blackwell Scientific

Pubi., Oxford.

Whittaker R. H., 1960. ? Vegetation of the Siskiyou

mountains, Oregon and California. Ecol Monogr. 30 : 279-338.

Zobel M., 1992. ? Plant species coexistence - the role

of historical, evolutionary and ecological factors.

0/^65: 314-320. Zobel M., Suurkask, M., R?sen E. & P?rtel M., 1996.

? The dynamics of species richness in an exper

imentally restored calcareous grassland. J. Veg. Sci. 7 : 203-210.

Manuscript received 15 February 2000.