Spontaneous flora of the Rila Monastery (Bulgaria)

Abstract

The spontaneous flora of the largest and most popular Rila Monastery, symbol of Bulgaria, included in the UNESCO World Heritage list was investigated during 2008–2012. The objectives of the study were to explore species composition and to characterize the plants spontaneously spread in the inner court of the monastery. The total number of the found vascular plants is 110 species from 43 families and 94 genera. The analysed group included predominantly native species, perennial plants – hemicryptophytes (61 species; 58.65%). The most common species were classified into three groups: (1) species, typical for the rocks flora; (2) common species with wide ecological amplitude and high colonization possibilities; and (3) species, typical for the flora surrounding the monastery. Frequently found species were Sclerochloa dura, Poa annua, Polygonum aviculare, Plantago major, Trifolium repens, Agrostis capillaris, Geum urbanum and Stellaria media. The distribution of the species is a result of specific ecological conditions, such as soil moisture and quantity, lightening of the site area during the day, exposition and intensity of use. The anemochoric woody species (Acer pseudoplatanus, Acer heldreichii, Fraxinus excelsior, and Ulmus glabra) found in the court as seedlings were also observed on the walls and roof of the Hrelyo's Tower, which can cause severe damage to the buildings and problems for the conservation of the archaeological monuments.

Keywords:

• ecology
• flora
• pavements
• Rila
• species distribution

Introduction

The study of the flora in archaeological places (ruines, castles), architectural and touristic complexes (walls and pavements) is of great importance for the maintenance and preservation of the monuments. Moreover, these places are suitable to study plant invasions and anthropogenic influence. Investigations on the peculiarities of urban flora and vegetation revealed a high species diversity and a dynamic development of vegetation.[1] Floristic data about archaeological and touristic places in Bulgaria are very scarce,[2–5] mainly related to low altitudes. Rila Monastery is the largest Eastern Orthodox monastery and a symbol of Bulgaria. It was founded in the tenth century AD and has become a spiritual, educational and cultural centre of Bulgaria. Since 1983 the monastery has been included in the list of World Cultural Heritage of UNESCO. Rila Monastery, Hrelyo's Tower and the monastery buildings were declared a group of architectural, artistic and historical complex of national importance. Rila Monastery is attractive and important in a role of sustainable tourism and welcomes around a million visitors every year.

Data about the spontaneous flora in the area of the Rila Monastery and the neighbouring most visited by tourist places are sporadic.[6,7] Although in the montane region street and wall flora resemble rocks flora and do not form important singular habitat,[8] its investigation is necessary in order to prevent the natural flora from the influence of invasive plants species. Vascular plant colonization is essentially conditioned by the adaptability of the species and the efficiency of their mode of reproduction.[9] This survey is designed to detect the species that contribute mostly to anthropophytization of the flora and appeared potential threat for the cleanliness of the nature. Such knowledge are critical to the choice of appropriate preventive and eradication methods of these species.

The aim of the study was to investigate the spontaneous flora with the cultivated ornamental plants of the different parts (sites) in the inner court of the Rila Monastery in order to: (1) evaluate similarity between sites; (2) estimate the relative importance of particular factors on species composition; (3) evaluate the anthropogenic impact on the studied flora; and (4) evaluate the potential role of the invasive plants on the natural flora.

Materials and methods

Study area and data collection

The highest mountain on the Balkan peninsula located in south-western Bulgaria, Rila Mts., forms a separate floristic region in the Bulgarian flora with many relict and endemic species.[10,11] This mountain is considered one of the important biodiversity hot spot places in the mountain areas on the Balkan peninsula on global level, since 100 endemic taxa are recorded.[12] The Rila Monastery is situated in the western part of the mountain at 1147 m above sea level (a.s.l.) (42°07′58.88″N, 23°20′22.62″E) in the beech vegetation belt.[13] It is surrounded by an old forest of Fagus sylvatica, mixed with Abies alba, Picea abies, Acer pseudoplatanus, Acer heldreichii, Sorbus aucuparia, Carpinus betulus, Fraxinus excelsior, etc. A territory of 250,000 m² around the Rila Monastery was declared in 2000 as the Rila Monastery Nature Park.

The mountain is situated in the transitional zone between the moderate-continental and continental-mediterranean climate.[14,15] The climate in the area of the monastery is montane. The lowest measured air temperature is approximately −25 °C at the end of January and the highest does not exceed 36 °C in July. The mean annual precipitation is between 1000 and 2200 m a.s.l. varies from 1050 to 1200 mm.[15]

The monastery complex occupies an area of 8800 m² and is rectangular in form, centred around the inner court (3200 m²) where the Hrelyo's Tower and the main church are situated.[16] For the aim of the study, the inner court of the monastery was divided into four sites, more or less equal in size, following the four corners of the court and the geographic directions (Figure 1). The court is paved with different in size and form sienite and granite cobblestones, and pavement made by round river stones with large joints and definite dip for water drainage. The joints vary in width 5–10 cm.

• Site 1: It is situated in front of the Samokov door (entrance B) and around Hrelyo's Tower (app. 908 m²). This is the northern part of the court, unshaded, with high and intermediate use.

• Site 2: It is situated behind the church in front of the Monastery Museum (app. 712 m²). This is the eastern part of the court where one of the two fountains are situated, forming a microhabitat with some hygrophytes (Juncus bufonius, Juncus compressus, Carex sp.). Most of the site is a shaded area with intermediate use. Ornamental trees, shrubs and herbs are planted in this site.

• Site 3: This is the southern part of the court with 770 m². The second fountain is found here and, like in site 2, several ornamental plants are found. This is a territory with an intermediate and low use by the visitors. The southern corner of the court is a shaded area, while the area around the southern wall of the church is unshaded.

• Site 4: It is situated in front of the main entrance (Dupnitza door) of the monastery (app. 810 m²), covered with the biggest granite cobbles. This is the western part of the court, intensively used by the visitors. This is unshaded area.

Figure 1. Map of the first floor and inner court [16] with study sites of the Rila Monastery.

This study was conducted during 2008–2012. The floristic list (except Bryophyta) is arranged in alphabetical order of the taxa (Table 1).

Table 1. List of spontaneously spreading taxa in the inner court of the Rila Monastery and their frequency (numbers in brackets).

	Sites (frequency)
Taxa	1	2	3	4	Status	Life cycle	Life forms	Life strategy	Reprodu-ctions	Dispersal mode	Geoelement
Aspidiaceae
Dryopteris filix-mas (L.) Schott.		+(1)			Ap	per	H	C	spv	ane	Boreal
Athyriaceae
Cystopteris fragilis (L.) Bernh.		+(1)			Ap	per	H	C	spv	ane	Kosm
Polypodiaceae
Polypodium vulgare L.		+(1)			Ap	per	H	C	spv	ane	Boreal
Spermatophyta
Aceraceae
Acer pseudoplatanus L.		+(1)			Ap	h2	M	C	s	ane	EurMed
A. heldreichii Orph. ex Boiss.		+(1)			Ap	h2	N,M	C	s	ane	Balk
Amaranthaceae
Amaranthus retroflexus L.	+(1)			+(1)	Inv	ann	T	CSR	s	ane; hyd; epi	Kosm
Apiaceae
Anthriscus sylvestris L.	+(3)		+(1)	+(3)	Arch	bi-per	H	CS	s	epi;dys;	Eur
Heracleum sibiricum L.		+(1)	+(1)		Ap	bi-per	H	C	sv	ane	EurAs
Myrrhoides nodosa (L.) Cann.				+(1)	Ap	ann	T	CS	s	epi; ane	EurAs
Pastinaca hirsuta Panc.	+(1)				Ap	per	H	CS	sv	ane	Balk
Araliaceae
Hedera helix L.		+(3)	+(4)		Ap	h1	N	CS	sv	epi	EurAs
Asteraceae
Achillea millefolium L.	+(3)	+(3)	+(1)		Ap	per	H	CR	sv	ane	EurSib
A. pannonica Scheele				+(1)	Ap	per	H	C	sv	ane	Pann-Balk
Artemisia vulgaris L.	+(1)				Ap; Inv	per	H	CSR	sv	ane	SubBoreal
Bellis perennis L.		+(2)			Ap	per	H	CS	sv	auth	EurAs
Matricaria discoidea DC.	+(2)			+(2)	Inv	per	T	CSR	sv	ane; epi; auth	EurAs
M. chamomilla L.	+(3)				Ap;Inv	ann	T	CSR	sv	ane; epi	EurAs
Crepis conyzifolia (Gouan)A.Kern.	+(2)				?	per	H	CS	sv	ane; epi; auth	SubMed
Hieracium murorum L.			+(1)	+(1)	Ap	per	H	CS	sv	ane; auth	SubMed
Lapsana communis L.				+(3)	Ap;Inv	ann	H	CS	sv	ane	EurSib
Leontodon hispidus L.	+(1)		+(1)		Ap	per	H	CSR	sv	ane	EurMed
Mycelis muralis (L.) Dum.	+(1)	+(3)			Ap	per	H	CS	sv	ane	Med
Petasites albus (L.)Gaertn.	+(1)	+(1)			Ap	per	H	CS	sv	ane; epi; auth	EurPont
Senecio rupestris Waldst. & Kit.	+(1)			+(1)	Ap	per	T,H	CSR	s	ane	SubMed
Tanacetum corymbosum (L.) Sch.Bip.	+(1)				Ap	per	H	CS	sv	ane; epi; auth	EurMed
Tanacetum vulgare L.				+(1)	Ap;Inv	per	H	CS	sv	ane; epi; auth	EurSib
Taraxacum officinale Weber	+(3)		+(3)	+(3)	Ap	per	H	CSR	sv	ane; epi; auth	EurMed
Tussilago farfara L.		+(3)	+(3)		Ap;Inv	per	H	CSR	sv	auth	EurAs
Betulaceae
Corylus avellana L.			+(1)		Ap	h1-h2	N	C	s	ane; epi	Med-CAs
Boraginaceae
Echium vulgare L.	+(1)		+(1)		Ap;Inv	bi-per	H	CSR	sv	epi	EurAs
Pulmonaria rubra Schott				+(1)	Ap	per	H	C	sv	myr	Carp-Balk
Brassicaceae
Alliaria petiolata (M.Bieb.) Cavara & Grande				+(2)	Ap	ann-bi	H	CS	s	ane	EurAs
Berteroa incana (L.)DC.	+(2)				Ap	ann-per	H, T	CS	s	ane	sPont
Capsella bursa-pastoris (L.) Medik.	+(3)			+(3)	Ap	ann-bi	T	CSR	s	auth	Kosm
Cardamine pectinata Pall. ex DC.	+(1)				Ap	ann-bi	H	CS	s	auth	SubMed
Rorippa sylvestris (L.) Besser			+(1)		Ap	per	H	C	sv	auth	EurAs
Campanulaceae
Campanula rapunculoides L.				+(1)	Ap	per	H	C	sv	auth	Eur
Caryophyllaceae
Arenaria serpyllifolia L.	+(3)			+(3)	Ap	ann-bi	T, H	SR	s	?	EurAs
Cerastium fontanum Baumg.	+(2)	+(2)			Ap	per	T	SR	sv	ane;hyd	Eur
Herniaria glabra L. subsp. nebrodensis Jan ex Nyman	+(2)	+(2)		+(2)	Ap	ann-bi	T, H	SR	sv	?	Eur-Cauc-OT
Herniaria hirsuta L. subsp. Hirsuta	+(2)	+(2)		+(2)	Ap	ann-bi	T, H	SR	sv	?	EurAs
Sagina procumbens L.	+(4)	+(3)		+(2)	Ap	per	Ch	SR	sv	ane	Boreal
Spergularia rubra (L.) J.Presl & C.Presl	+(3)	+(2)	+(2)	+(3)	Ap	ann	T, H	SR	s	ane	SubBoreal
Stellaria media (L.)Vill.	+(3)	+(4)	+(4)	+(3)	Arch	ann-bi	T, H	SR	sv	ane	Kosm
Chenopodiaceae
Chenopodium album L.	+(1)			+(1)	Arch	ann	T	CSR	s	ane; anthr;hyd	Kosm
Cyperaceae
Carex sp.			+(1)	+(1)		per	H	CS	sv	auth
Convolvulaceae
Convolvulus arvensis L.	+(3)				Ap	per	H	SR	s	end; auth;	Kosm
Crassulaceae
Sedum album L.		+(4)	+(3)		Ap	per	Ch	CS	sv	myr; hyd; auth	SubMed
S. acre L.	+(3)				Ap	per	Ch	CS	sv	myr; hyd; auth	EurMed
Dipsacaceae
Knautia drymeia Heuff.		+(1)		+(1)	Ap	per	H	C	sv	epi	Alp-Carp-Balk
Fabaceae
Coronilla varia L.	+(1)				Ap	per	H	C	?	epi; ane; auth	EurMed
Medicago lupulina L.		+(2)			Arch	ann-bi	H	CSR	sv	ane; auth	EurAs
M. minima (L.) Bartal.	+(3)				Ap	ann	T	CSR	sv	epi; ane; auth	EurAs
Melilotus officinalis (L.) Pall.	+(1)				Arch	bi	H	CS	s	ane; auth	EurAs
Robinia pseudoacacia L.			+(1)		Inv	h2	M	CS	s	ane	N Am
Trifolium medium L.			+(3)	+(3)	Ap	per	H	CSR	sv	ane; epi	EurSib
T. repens L.	+(4)			+(4)	Ap	per	H	CSR	vvs	ane; epi	EurSib
T. pratense L.	+(3)				Ap	per	H	CSR	sv	ane; epi	SubBoreal
Geraniaceae
Geranium macrorrhizum L.		+(2)			Ap	per	H	C	sv	auth; epi	EurMed
G. pusillum L.	+(2)	+(3)			Arch	ann-bi	T,H	C	sv	auth; epi	EurMed
G. robertianum L.		+(1)		+(1)	Arch	ann-bi	T,H	C	sv	auth; epi	SubBoreal
Hypericaceae
Hypericum perforatum L.			+(1)		Ap	per	H	CS	sv	ane	Kosm
Juncaceae
Juncus bufonius L.		+(2)	+(2)		Ap	ann	T,H	CS	sv	ane; epi	SubBoreal
J. compressus Jasq.		+(2)	+(2)		Ap	per	H	CS	sv	ane; epi	EurAs
Luzula sylvatica L.				+(1)	Ap	per	H	C	sv	myr	Eur
Lamiaceae
Ballota nigra L.	+(3)		+(2)		Ap	per	Ch,H	CSR	sv	epi	EurMed
Clinopodium vulgare L.	+(1)				Ap	per	H	CS	sv	ane; epi; auth	SubBoreal
Lamium purpureum L.		+(3)			Arch	ann	T,H	CSR	s	auth	EurMed
Prunella vulgaris (L.) L.			+(2)		Ap	per	H	CSR	sv	hyd;epi; dys; auth	Kosm
Liliaceae
Allium flavum L.		+(2)			?	per	G	CS	ssv	end	Med
Malvaceae
Malva sylvestris L.			+(1)		Ap	ann-per	H	CS	sv	auth	Kosm
Onagraceae
Epilobium roseum Schreb. subsp. subsessile (Boiss.) P.H.Raven	+(3)			+(2)	Ap	per	H	C	sv	ane	Eur-OT
Oleaceae
Fraxinus excelsior L.	+(1)				Ap	h2	M	C	s	ane	EurMed
Papaveraceae
Chelidonium majus L.	+(1)	+(2)	+(1)		Ap	per	H	CSR	s	myr	EurAs
Plantaginaceae
Plantago lanceolata L.	+(3)			+(3)	Ap	per	H	CSR	sv	auth	Kosm
P. major L.	+(3)	+(3)	+(4)	+(3)	Ap	per	H	CSR	sv	auth	Boreal
Poaceae
Agrostis capillaris L.		+(4)		+(3)	Ap	per	H	CS	vvs	ane	Boreal
Dactylis glomerata L.			+(1)	+(1)	Ap	per	H	CSR	vvs	ane; epi	EurAs
Festuca pratensis L.				+(1)	Ap	per	H	C	vvs	ane	Boreal
Hordeum murinum L.	+(2)			+(2)	Ap	ann	T, H	CS	s	ane	Boreal
Lolium perenne L.				+(3)	Ap	per	H	CS	vvs	ane	EurAs
Poa annua L.	+(4)		+(3)		Ap	ann	T, H	CSR	s	ane	Kosm
P. bulbosa L.	+(2)		+(1)		Ap	per	H	CSR	vvs	auth	EurAs
P. nemoralis L.	+(1)		+(3)	+(2)	Ap	per	H	C	vvs	ane	Boreal
Sclerochloa dura (L.)P.Beauv.				+(4)	Ap	ann	T	CS	sv	ane	EurAs
Polygonaceae
Rumex acetosella L.	+(3)			+(3)	Ap	ann	H, G	CS	s	auth	EurSubMed
Polygonum aviculare L.	+(4)	+(3)		+(3)	Ap	ann	T	CSR	s	?	Kosm
Primulaceae
Primula veris L.			+(1)	+(1)	Ap	per	H	CSR	sv	ane	EurMed
Ranunculaceae
Clematis vitalba L.	+(1)			+(1)	Ap	h1	N	CS	s	ane; auth; epi	Eur
Ranunculus repens L.		+(2)	+(3)		Arch	per	H	CSR	sv	epi	SubMed
Rosaceae
Crataegus monogyna Jacq.	+(1)				Ap	h1	N	C	s	end	SubBoreal
Fragaria vesca L.		+(2)			Ap	per	H	CSR	sv	end; epi; auth	SubBoreal
Geum urbanum L.		+(4)	+(2)	+(3)	Ap	per	H	CSR	ssv	epi	SubBoreal
Potentilla argentea L.		+(2)			Ap	per	H	CS	sv	ane; myr; end	Pont
P. reptans L.		+(2)			Ap	per	H	CS	vvs	ane; myr; end	Kosm
Prunus cerasifera Ehrh.				+(1)	Ap	h2	M	CS	sv	end; anthr	EurAs
Rosa canina L.			+(1)		Ap	h1	N	CS	vvs	auth; end	SubMed
Rubus sp.		+(1)			Ap	h1	S	CS	vvs	auth; end
Sorbus aucoparia L.	+(1)	+(1)			Ap	h1	M	C	s	end	SubBoreal
Scrophulariaceae
Antirrhinum majus L.			+(1)		Ap	per	Ch	CSR	sv	ane	Med
Veronica arvensis L.	+(3)	+(1)	+(1)	+(3)	Arch	ann	T	SR	s	ane; auth	EurSib
Ulmaceae
Ulmus glabra Huds.	+(1)				Ap	h2	M	C	ssv	ane	EurMed
Urticaceae
Urtica dioica L.		+(2)	+(1)		Ap	per	H	CSR	vvs	ane	Boreal
Violaceae
Viola odorata L.	+(1)				Ap	ann-bi	H	CS	sv	myr	EurMed

Note: Abbreviations and symbols: Status (affiliation to geographical-historical groups): Ap – apophyte, Arch – archaeophyte, Inv – invasive; life forms: Ch – chamaephyte, G – geophyte, H – hemicrytophyte, T – terophyte, M – megaphanerophyte, N – nanophanerophyte; S – hemiphanerophyte; life cycle: per – perennial, ann – annual, bi – biennial, h1 –shrub, h2 – tree; life strategy: C – competitor, S – stress tolerator, R – ruderal; types of reproduction: s – seed, sv – seed and vegetatively, ssv – mosty by seed, rarely vegetatively, vvs – mosty vegetatively, rarely by seed, spv –spores and vegetatively; dispersal mode: ane – anemochory, auth – autochory, anthr – anthropochory, dys – dyszoochory, end – endozoochory, epi – epizoochory, hyd – hydrochory, myr – myrmecochory, (?) – unknown; geolement: Boreal; SubBoreal; Eur – European; Eur-As – Euroasiatic; EurSib – Eurosiberian; Eur-OT – European-oranoturranean; Med – Mediterranean; Med-CAs –Mediterranean-central Asiatic; SubMed –SubMediterranean; EurSubMed – European-submediterranean; Eur-Cauc-OT – European-caucasus- oranoturranean; EurPont –European-pontian; Pont – pontic; Pann-Balk – Pannonian-Balcanian; Balk – Balkanian; Carp-Balk – Carpatobalkanian; Alp-Carp-Balk – Alpo-Carpato-Balkanian; Kosm – cosmopolitian.

Bryophytes are included in the total number of species of the study flora. The ornamental plants and bryophytes are listed separately (Table 2).

Table 2. List of bryophytes and ornamental plants found in the inner court of the Rila Monastery.

Bryophytes	Ornamental plants
Homalothecium sericeum (Hedw.) Schimp. (Brachyteciaceae)	Chamaecyparis lawsoniana (A. Murray) Parl. (Cupressaceae)
Ceratodon purpureus (Hedw.)Brid. (Ditrichaceae)	Picea abies (L.) H.Karst. (Pinaceae)
Encalypta streptocarpa Hedw. (Encalyptaceae)	Picea pungens Engelm. (Pinaceae)
Orthotrichum anomalum Hedw. (Ortotrichaceae)	Pseudotsuga menziesii (Mirbel) Franco (Pinaceae)
Tortula muralis Hedw. ssp. muralis (Pottiaceae)	Sequoiadendron giganteum (Lindl.) Buchholz (Taxodiaceae)
Weissia controversa Hedw. (Pottiaceae)	Citrus limon (L.) Burm.f. (Rutaceae)
	Nerium oleander L. (Apocynaceae)
	Rosa sp. (Rosaceae)
	Syringa vulgaris L. (Oleaceae)
	Calendula officinalis L. (Asteraceae)
	Leucanthemum vulgare L. (Asteraceae)
	Sedum maximum (L.) Suter (Crassulaceae)
	Geranium macrorhyzum L. (Geraniaceae)
	Pelargonium peltatum (L.) L'Hér. (Geraniaceae)
	Pelargonium zonale (L.) Aiton (Geraniaceae)
	Aquilegia vulgaris L. (Ranunculaceae)
	Antirrhinum majus L. (Scrophulariaceae)
	Petunia hybrida (Solanaceae)
	Tropaeolum majus L. (Tropaeolaceae)
	Viola hybrida (Violaceae)
	Phoenix dactylifera L. (Palmae)

The distribution of the taxa in the sites, life forms, life cycles, reproduction, dispersal mode and geoelement of the species, except Bryophyta, are also given (Table 1). Information concerning life forms of the taxa and their reproduction mode was taken from the literature sources.[17] Life strategies were classified following Grime.[18] The data on the biology of the species, such as mode of reproduction, dispersal of diaspores, were compiled from the available sources [17–21] and personal observations. The frequency of occurrence in the sites is given in a four-scale gradient [21]: (1) presence in small scattered spots; (2) presence in a few, rather large spots or in spots of medium size, easily overlooked at a rapid passage through the collection site; (3) presence locally in parts of the site; (4) presence impossible to be overlooked, appearing almost over the collection site.

The floristic analysis is presented after Assyov and Petrova.[22] The geographical and historical classification (status) of the flora follows the data provided by different Bulgarian authors.[23–25] The terminology is based on the definitions proposed by Pyšek et al.[26] Plant nomenclature follows Košuharov [27], and Tutin et al.[28,29]

Data analyses

The indexes of total anthropophytization and archaeophytization [30] were calculated, (1) $I_{\text{An}}=\left(\text{An}/\text{Sp}+\text{An}\right)100\%$(1) (2) $I_{\text{Ar}}=\left(\text{Ar}/\text{Sp}+\text{Ar}\right)100\%$(2) where An is the number of anthropophytes; Ar is the number of archaeophytes and Sp is the number of spontaneophytes.

Cluster analysis using Euclidean distance and unweighted pair-group means average was used as the computational criteria to determine the similarities between sites on the bases of frequency of species.

Pearson correlations between species composition (transformed to 1 for presence) and life cycle, life strategy, reproduction, dispersal mode, light regime and intensity of use were also performed. All statistics were performed using StatSoft-Statistica 7 program.

Results and discussion

Species composition

The total number of vascular plants (including Bryophyta) growing spontaneously on the pavement court in the monastery was 110 species from 43 families and 94 genera (Table 1). Bryophyta were 5.45%, Pteridophyta - 2.73% and the rest (91.82%) were representatives of seed plants. Magnoliopsida (dicotyledons) was the prevailing group with 31 families, 75 genera and 87 taxa. The most numerously represented families were: Asteraceae (17 species), Rosaceae (9), Poaceae (9) and Fabaceae (8). The high proportion of Asteraceae species confirmed previous data provided for the spontaneous flora in some cities in Bulgaria,[2,3,5,31] Poland,[19] Belgium,[32] Greece [33] and Turkey.[34,35] This proportion is related to high species number in Central Europe [36] and the remarkable success of Asteraceae family in terms of dispersal and establishment. Moreover, the biological characteristics of many species from these families (i.e. the ability to use various dispersal routes) predisposes them to spread and to occupy new diverse habitats.[36] A few species are very common, but 86.5% of the taxa are recorded in only one or two sites. The most important species in terms of their frequency are Sclerochloa dura, Poa annua, Polygonum aviculare, Plantago major, Trifolium repens, Agrostis capillaris, Geum urbanum and Stellaria media.

The comparison of the life form spectrum showed a predominance of herbaceous perennial plants – hemicryptophytes (60 species; 57.69%) over other life forms in all sites; followed by therophytes – hemicryptophytes (12; 11.54%), therophytes (11; 10.57%), etc.

The proportion of the woody species (megaphanerophytes, nanophanerophytes and hemiphanerophyte) was also well presented (13; 12.5%). The highest number of the nanophanerophytes was characteristic for site 3. Poorly represented were the chamaephytes (4, 3.85%) and geophytes (1, 0.96%). The species composition found in the study area resembled the floristic composition of pavements in other European regions.[33,37] This biological spectrum is also a reflection of the species composition of the Bulgarian flora.[38]

The high number of perennials in urban areas can be related to their ability to produce vegetative propagation organs.[32] Most of the vegetative reproducing species (T. repens, Potentilla reptans, Lolium perenne, A. capillaris, P. bulbosa, Urtica dioica) were very frequent in the study sites. These species occupy places with wide joints and soil. In these places the number of annuals is low. One of the frequently appearing annuals was P. aviculare. This species is also capable to colonize rapidly trampled places near to walking paths, where it often forms long and narrow or irregular patches.[39] P. aviculare is more competitive in comparison with other annual or annual–biennial weed species like Chenopodium album and S. media. While Ch. album was rarely found, S. media was a very frequent in all sites, mainly in semi-shaded and more humid places. The rare appearance of the ruderal Ch. album can be related to the montane climate and the higher altitude where its survival and growth is reduced, particularly under cool soil conditions.[40] Some of the more frequently found perennials on the pavements, such as P. major, T. repens, Taraxacum officinale, Ranunculus repens, Tussilago farfara are known to tolerate compacted and poorly aerated soils.[32] The perennial species Anthriscus sylvestris, a plant of moderately disturbed habitats and edges in moist or mesic sites,[41] was also well presented. It is widely distributed in the natural flora of the mountain up to 1500 m a.s.l.

The flora of the pavements in places intensively used by visitors (sites 1 and 4) was poorly presented. On such trampled areas more often are found S. dura and Sagina procumbens, but rarely P. annua and P. aviculare. The first species is known to invade and rapidly colonize disturbed sites, such as fairground and athletic fields.[42] This species is able to compete with other weedy species in severely trampled areas. The frequency of this plant, predominantly in sites 1 and 4, can be related to the mode of dispersal, which appears to be either by plant fragmenting or by the entire inflorescence.[43] S. procumbens was also found in the crevices of the low part (up to 50 cm) of the walls of the Hrelyo's Tower, the church, etc. (sites 1 and 2).

The geoelement characteristics of the plants growing on the pavement court revealed that the Euro-Asiatic (29; 27.88%) and European (19; 18.27%) plants were the most well-presented group. The studied flora was also characterized by a high percentage of Boreal (9; 8.65%), sub-Boreal (10; 9.62%) and cosmopolitan species (13; 12.5%) from one hand and low participation of Mediterranean–sub-Mediterranean species (10; 9.62%) on the other. The Balkan, Pontic and Oriental-Turanean species were few. This distribution of the geoelements on the pavements was similar to that reported for the Nature Reserve Rilomanastirska gora, Kirilova Poljana locality.[7] The reasons for such similarity were the ecological conditions (mountainous climate, altitude, exposure) and intensity of use by man.

The prevalence of competitor and stress-tolerant type (CS type; 38 species) and competitor, stress-tolerant and ruderal type (CSR type; 32 species) of Grime's life strategies over competitor type (C type; 24 species) in the described flora reflects the habitat conditions as an anthropogenically influenced area. In such habitats the number of ruderals is increased. Nine species are included in the group of the stress-tolerant and ruderal type (SR) and only Achillea millefolium is presenting competitor and ruderal (CR) life-strategy group. The probability of the reproduction success in disturbed habitats of the ruderals is associated to a short life-span and self-pollination.[18] The relation between life strategies found in the studied flora was confirmed by the preference of high number of species with generative-vegetative (58; 55.77%) and vegetative-rarely generative (11; 13.56%) mode of reproduction. Only G. urbanum, Allium flavum and U. glabra prefer seed and rarely vegetative reproduction. The trade-off between vegetative propagation and generative reproduction is expected as a flexible adaptation to the habitat conditions within the species.[18] The number of species reproducing by seeds (28; 26.92%) was also well presented. The success of these species in a competitive environment is associated with the size and number of produced seeds: a high number of small seeds improve the species dispersal ability at the expense of the ability of the seedlings to get established successfully.[44] The spontaneously spreading plants in the monastery court use several different ways of dispersion of propagules. A species dispersal ability is largely determined by its seed characteristics that allow it to sample a wide range of environments and colonize places where it will be competitively dominant.[44] The highest number of anemochoric species (34; 32.69%) was related to the species composition of the flora: prevailing of the species from the Asteraceae and Poaceae families. The woody species (A. pseudoplatanus, A. heldreichii, F. excelsior, U. glabra) found in the court as seedlings are also anemochoric. These species were also observed on the walls and roof of the Hrelyo's tower and can cause severe damages to the buildings. Tree species, due to the expansion of their root systems, are considered hazardous for the architectural monuments, having the highest hazard index (H index).[9]

Species with diverse spreading strategies (40 species) in the studied flora were comparatively high in number. Obviously, this helps them to spread, migrate and settle on new habitats.[20] Species, spreading in zoochoric or anthropochoric ways, were found on places, most often used by the visitors, a fact, confirmed by previous authors.[19] The number of species with myrmeko-, epi- and endochorous mode of distribution was more or less equal. The autochorous species (13; 12.5%) also formed a significant group.

Most of the studied species were apophytes (82; 78.85%). The archaeophytes were 10 species (9.62%). The calculated index of total archaeophytization of the flora was 9%, whereas the index of anthropophytization was 45.99%. The richest in anthropophytes families in Bulgaria are Asteraceae, Poaceae, Fabaceae, Brassicaceae, Chenopodiaceae, Caryophyllaceae, Polygonaceae, Scrophulariaceae and Amaranthaceae.[23] The same families were rich in anthropophytes in this study. Species Amaranthus retroflexus, Artemisia vulgaris, Matricaria discoidea, M. chamomilla, Lapsana communis, Tanacetum vulgare, T. farfara, Echium vulgare, Alliaria petiolata, Berteroa incana, Capsella bursa-pastoris, Arenaria serpyllifolia, Spergularia rubra, S. media, Ch. album, Convolvulus arvensis, Medicago lupulina, M. minima, Melilotus officinalis, Robinia pseudoacacia, Geranium pusillum, Hypericum perforatum, Ballota nigra, Lamium purpureum, Malva sylvestris, Chelidonium majus, Plantago lanceolata, P. major, Hordeum murinum, L. perenne, Poa annua, Sclerochloa dura, Rumex acetosella, Polygonum aviculare, Prunus cerasifera, Antirrhinum majus and U. dioica found in the studied flora are part of the alien flora of Europe.[45,24] These species are 5.02% (37 species) of terrestrial magnoliophyta alien species provided for Bulgaria (736) according to DAISIE European Invasive Alien Species Gateway.[46] The species A. retroflexus, R. pseudoacacia, M. discoidea, H. murinum, P. cerasifera, and Ch. album are part of the most widespread (150) alien plant species in Europe.[45] R. pseudoacacia (native to North America), A. retroflexus, and M. discoidea (South America) are included in top 100 alien species in Europe, according to DAISIE European Invasive Alien Species Gateway.[46]

Data analyses in the study area

Although the sites are neighbouring each with an approximately equal territory they show some specifics in species diversity. The cluster analysis (Figure 2) demonstrated that two clusters (A and B) are formed at a linkage distance around 17. The highest similarity was shown between sites 2 and 3 as the Euclidean distance is the shortest.

Figure 2. Cluster diagram showing the groups of similarity among sites.

The high per cent of perennial and species with all three life strategies – competitor, stress tolerant and ruderals, were found in all studied sites. Intensity of use is the major factor affecting species composition on pavements mainly in site 1 (0.33; p < 0.001, Table 3) showing lower similarity with other sites. The same factor as well as joint width and paver type were considered important for the weed incidence on pavements.[32] The calculated high index of similarity between sites 1 and 4 was owed to the intensive regime of use and light regime, whereas similarities between sites 2 and 3 can be related to more humid and shaded areas. The annual and biennial weeds were considered to rely on humid germination conditions and are more abundant in shaded pavements.[32] Significant correlation between species composition and life cycle was found only in site 3. Indeed, species composition on pavement in site 1 had a lower significant correlation coefficient with life strategy and life cycle. Light regime and dispersal mode do not correlate significantly with species composition in all sites.

Table 3. Pearson correlation coefficient between species composition in sites and life cycle, life strategy, reproduction mode, light regime and regime of use.

	Life cycle	Life strategy	Reproduction mode	Dispersal mode	Light regime	Regime of use
Site 1	−0.25*	−0.32**	−0.22*	0.07	−0.01	0.33***
Site 2	−0.01	0.06	0.06	−0.19	0.19	−0.02
Site 3	0.25*	−0.31**	0.19	−0.04	0.17	0.02
Site 4	−0.25*	−0.06	0.04	−0.07	0.10	0.18

Note: ***p < 0.001; **p < 0.01; *p < 0.05.

Ornamental plants

The plants used for decoration in the monastery court are listed in Table 2. They are present in the interior of a monastery as mobile or fixed flowerpots or laid-out on the ground. Usually in Orthodox monasteries ornamental plants are dislocated round the main architectural structures of the yard: the gate, the faucet (fountain), the wall and the stairs.[47] The cultivated roses (Rosa sp.) and Syringa vulgaris in the Rila Monastery court are grown near the southern sunny wall of the church in the middle of the court. The trees Sequoiadendron giganteum, Pseudotsuga menziesii, Picea pungens, Chamaecyparis lawsoniana were planted there together with P. abies, which is typical for the natural vegetation of the mountain.

The monasteries were always considered as the most secure and reliable place for the introduction of flowers. The ornamental plants introduced in the Rila Monastery court originate from North America, Asia and the Mediterranean. The species Leucanthemum vulgare, Aquilegia vulgaris, Pelargonium zonale, P. peltatum, Petunia hybrida, Sedum maximum, Calendula officinalis, Tropaeolum majus, Geranium macrorrhizum and Antirrhinum majus are plants considered typical for the interior in other Bulgarian monasteries.[47] The mediterranean shrub Buxus sempervirens, which is also typical for the yards in other Bulgarian monasteries,[47] was not found here. The cultivated mediterranean plants were presented by few species (Nerium oleander, Citrus limon). The main reason for this was the higher altitude and the long winters, which are not suitable for the growth of these xerothermic plants. It is difficult to say if G. macrorrhizum and Hedera helix are planted as ornamentals or are self-populated in the court because of their natural distribution close to the monastery. The species A. majus was found only outside the study area, on the nearest wall north from the monastery. The same species is typical for the walls of many urban floras in Bulgaria and other European countries.

Conclusions

The frequency analyses showed that the most common species on the pavement court of the Rila Monastery can be classified into three groups: (1) species typical for the rocks flora as it was considered flora of pavements and walls (Sedum sp. dev., A. serpyllifolia; S. rubra); (2) common species with a wide ecological amplitude and high colonization abilities (P. major, S. media, P. aviculare, H. murinum, A. capillaris, U. dioica, C. bursa-pastoris, T. farfara); and (3) species typical for the surrounding areas (Knautia drymeia, Cardamine pectinata, Hieracium murorum, Myrrhoides nodosa, Pastinaca hirsuta, Corylus avellana, A. heldreichii, F. excelsior). The high percentage (90%) of accidental species that were recorded in one or two sites only with very rare occurrence indicated the influence of the surrounding flora on the species composition. Comparisons between the sites give reason to consider the distribution of the species as a result of some specific ecological conditions like soil moisture and quantity, lightening of the site area during the day and intensity of use. On pavements with wide joints and high amount of soil, a more dense and diverse plant cover appears. The study flora consisted predominantly of heliophilous to shade-tolerant plants, which indicated moderate to warm habitat and semi-dry to freshly moist soils. Some species distributed in the court (F. excelsior, A. pseudoplatanus, A. majus, H. helix) were also observed on the monastery walls and Hrelyo's tower. These species have a deteriogenic effect and may cause serious problems for the conservation of the archaeological monuments. Possible escape of the alien species outside of the studied area is dangerous to the native flora if it contributes to the expansion of invasive species. For this reason weed prevention measures and weed control is likely to be the most effective strategy for the cleanliness of the surrounding native flora.

Acknowledgements

We would like to express our thanks for the taxonomic determinations of bryophytes to Ass. Prof. Dr A. Ganeva.

Disclosure statement

No potential conflict of interest was reported by the authors.