Saqib Kamran·Shujaul Mulk Khan·Zeeshan Ahmad·Amjad Ur Rahman·Majid Iqbal·Fazal Manan·Zahoor Ul Haq·Saif Ullah

Abstract Graveyards or sacred groves are often places of natural vegetation protected by spiritual believers because of their sacred beliefs and indigenous culture.A study of graveyards was conducted to determine their role in species conservation,community formation,and associated indicators and species composition using multivariate statistical approaches.It was hypothesized that variations in the age of graveyards would give rise to diverse plant communities under the impact of various edaphic and climatic factors.Quantitative ecological techniques were applied to determine various phytosociological attributes.All the data were put in MS Excel for analysis in PCORD and CANOCO softwares for cluster analysis(CA),two-way cluster analysis(TWCA),indicator species analysis and canonical correspondence analysis. CA and TWCA through Sorenson distance measurements identified five major graveyard plant communities: (1) Ficus-Bougainvillea-Chenopodium; (2) Acacia-Datura-Convolvulus; (3) Ziziphus-Vitex-Abutilon; (4) Acacia-Lantana-Salsola;and(5)Melia-Rhazya-Peganum.Species such as Capparis decidua,Herniaria hirsuta,Salvadora oliedes and Populus euphratica were only present inside graveyards rather than outside and advocate the role of graveyards in species conservation.The impact of different environmental and climatic variables plus the age of the graveyards were also assessed for comparison of plant communities and their respective indicator species.The results indicate that higher chlorine concentration,age of graveyards,low soil electrical conductivity,lower anthropogenic activities,higher nitrogen,calcium and magnesium concentrations in the soil,and sandy soils were the strong environmental variables playing a significant role in the formation of graveyard plant communities,their associated indicators and species distribution patterns.These results could further be utilized to evaluate the role of edaphic and climatic factors,indicator species and conservation management practices at a greater scale.

Keywords Graveyards/Sacred groves·Plant communities·Multivariate statistical techniques·Indicator species·Edaphic factors·Conservation·PCORD software

Introduction

Sacred groves in Pakistan are places of natural vegetation protected by spiritual believers due to their indigenous cultures and sacred beliefs(Gopal et al.2018).These religious mystical places were created in memory of their warriors and heroes,and conserved by the local societies through their sacred spirits.These graveyards have a significant contribution in the preservation of unique types of flora and fauna(Sen and Bhakat 2012).People abstain from cutting trees and shrubs and do not allow their cattle to graze in graveyards.These exhibit abundant and protected flora due to their spiritual purity and protection(Sen and Bhakat 2012).These holy sites have been major reservoirs of diverse plant species and have protected several threatened,rare,aromatic,medicinal and economically important species for many generations(Gadgil and Vartak 1976;Bhagwat and Rutte 2006;De Lacy and Shackleton 2017a).The impact of sacred groves in terms of phytodiversity and conservation has also been accepted by developed countries and non-Muslim communities(Ramanujam and Cyril 2003).Muslim graveyards are thought to be secure habitats for a variety of plants and animals.They often have conserved a region’s vegetation because of their isolation from human habitations,and hence may be models for research on species conservation(Khan et al.2015;Jackson and Ormsby 2017).

Religious and spiritual values are more conspicuous in terms of culture ecosystem services in these sacred sites.The conservation of sacred sites due to their integral cultural value contributes to conservation of biodiversity that ultimately makes them repositories of bio-cultural diversity(Gopal et al.2018).A review of the literature revealed very little about the biodiversity of Muslims sacred groves(Ahmed et al.2009;Ishii et al.2010;Siraj et al.2010;Bharathi and Prasad 2017;Jackson and Ormsby 2017;Waikhom et al.2018).Although some research on the subdomains of floristic communities is available,but there is a lack of comprehensive studies of graveyard vegetation in relation to environmental factors.The decay of human bodies continuously adds nutrients to the soil in these groves,and it is crucial to assess the influence of various edaphic and other associated environmental variables on the vegetation dynamics of these habitats.

All plant species have specific micro habitats in which they live and complete their life cycles(Berg et al.1994;Gao et al.2017;Das et al.2018;Li et al.2018).Species vary with variations in habitats and are present in abundance around a particular set of environmental conditions(Mota et al.2017).There are several biotic and abiotic factors that affect plant diversity and sometimes lead to their vulnerability,especially in species which have narrow ecological amplitudes. There is a connection between variation in species and abiotic factors such as habitat heterogeneity, topography, elevation, latitude, environmental stresses and age of substrates(Mota et al.2017).Other non-living factors which affect plant growth and abundance are soil chemistry, soil temperatures, air movements,evaporation,and variations in slope and aspect(Butler et al.1986;Chaparro et al.2012).Climate change contributes to rises in temperature,increases the chances of floods and drought that ultimately alter physical conditions in ecosystems,which affects species composition,distribution patterns, and abundance. Humans also create ecological disturbances in the form of population increases,urbanization,over-use of natural resources,and industrialization that contribute to climate change(DeFries et al.2005;Monteiro et al.2017).

To assess these varied impacts,multivariate statistical techniques provide an efficient way to reduce the complexity inherent in natural vegetation and to detect important environmental factors that explain this complexity(Khan et al.2016;Iqbal et al.2018).These techniques distinguish the patterns in species to species environmental relationships. They help in generating hypotheses about the structure and significance of indicators of these special sites and sets of environmental variables(Beals 1984;Anderson et al.2006).They reduce the complexity of data by summarizing the ecological information in low dimensional space by bringing plant species with similar requirements together in bi-plots,a type of exploratory graph used in statistics.Thus,they provide not only an understanding of patterns of diversity at local and regional scales but also environmental gradients and their impact on species distributions and diversity.

In this study,it was hypothesized that variations in the age of graveyards or sacred groves would result in unique species and diverse plant associations or communities under the impact of various edaphic and climatic factors.The study aimed to explore the role of graveyards in phytodiversity and conservation of vegetation.The main objectives were to quantify and classify the vegetation into communities,identify indicators of each community and evaluate distribution patterns under the impact of edaphic,climatic and age factors in the district Bannu of Pakistan.The findings may be used as baseline data in finding indicator species of a particular region,and in identifying plant associations as influenced by edaphic and other climatic factors for better conservation management.

Materials and methods

Study area

The district of Bannu is located in the Khyber Pakhtunkhwa(KP)province of Pakistan,32°43′-33°06′N latitude and 70°22′-70°57′E longitude,covering an area of 1227 km2(Fig.1).The area has four distinct seasons,winter from November to February with minimum and maximum temperatures of 5°C and 26°C respectively;spring from February to April;summer from mid-April to the end of August;and,a short autumn season.May and June are dry and hot while July and August are moist and the hottest months of the year.Minimum and maximum temperatures during summer are 26°C and 40°C,respectively. The maximum amount of rain occurs in August(111.4 mm).

Fig.1 Study area representing sampling stations with special reference to elevation zones

Methods

Quantitative ecological techniques via quadrat method were used for data collection of species and environmental variables.A total of 210 quadrats(plots)were established in 20 different(60% of the total)graveyards at each Union Council(UC)of Bannu,Pakistan.Size of the quadrats for trees,shrubs,and herbs were 30×30 m,5×5 m and 1×1 m,respectively.Phyto-sociological attributes,i.e.,density,frequency,cover,relative density,relative frequency,relative cover and Important Values(IV)were measured for each of the plant species at each graveyard.Diameters of the tree species were measured at breast height using the formula, Basal Area=[(Diameter at Breast Height/2)2×3.143 or πr2].Plant specimens were collected and labeled,placed between sheets of newspapers and pressed(Khan et al.2012;Ahmad et al.2016a).Once the specimens were appropriately dried and mounted on standard herbarium sheets,they were identified using Flora of Pakistan and other available literature.Specimens were deposited in the Herbarium of Quaid-i-Azam University,Islamabad,Pakistan.GPS was used for elevation,longitude and latitude measurements.

Soil samples were collected from each graveyard and their physiochemical properties were assessed and quantified.Soil pH was measured using 1:5 water suspensions.Electrical conductivity (EC) and total dissolved solids(TDS)were calculated with 1:5 soil water suspensions using an electrical conductivity meter (Rhoades 1996;Ahmad et al.2016b).Organic matter was measured by the Walkley-Black procedure (Nelson and Sommer 1982).Soil texture was calculated by using a hydrometer(Iqbal et al.2018).Carbonate,bicarbonate,chlorine and calcium+magnesium contents were calculated according to Khan et al.(2016).

Data analyses

All species and environment data were prepared in MS Excel sheets for quantitative traits such as density and relative density,frequency and relative frequency,and cover and relative cover using various formulae.Data sets were analyzed using multivariate statistical techniques using software PC-ORD version 5 and CANOCO version 4.5.Data on the presence or absence(1,0)for all species were prepared according to software requirements and treated in PC-ORD V5 for classification of plants into communities.Plant species with similar floristic composition or habitat using cluster analysis(CA)and two-way cluster analysis(TWCA)were grouped together in different sub-clusters. Indicator species of each graveyard community were identified through indicator species analyses(ISA)of PC-ORD.Species area curves(SAC)were constructed using Sorensen Distance Measurements to determine whether the sampling size was adequate or not.A canonical correspondence analysis(CCA),a utility for environmental gradient measurements using the CANOCO software version 4.5,was used to determine the effects of the variables.

Results

A total of 81 plant species belonging to 71 genera were recorded in 210 quadrats of the graveyards,28(33% )were trees,11(14% )shrubs and 42(53% )herbs(Fig.2).The family Poaceae was the most abundant(9 spp.;20% of total vegetation),followed by the Fabaceae and Asteraceae families (6 spp. each). The dominant life form was phanorophytes(32 spp.;39% of total vegetation)followed by therophytes (24 spp.; 30% ). Microphylls were the dominant leaf form(33 spp.;41% ),followed by nanophylls(18 spp.;23% )(Appendix S1).

Classification of graveyards vegetation into plant communities

Cluster and two-way cluster analyses

Cluster analysis using PC-ORD grouped the graveyard vegetation into five major graveyard habitat/community types,clearly observed in the dendograms(Figs.3,4).The two-way cluster analysis(TWCA)demonstrates detailed distribution patterns of different species at each sample station.Each black dot shows the presence of a species and a white dot the absence(Fig.4).The details of the five habitat/community types are as follows:

Fig.2 Distribution of trees,shrubs and herbs in the graveyards of the District Bannu,Pakistan

Ficus religiosa-Bougainvillea spectabilis-Chenopodium murale community

This graveyard vegetation community is represented by a total of 18 stations with Ficus religiosa,Bougainvillea spectabilis and Chenopodium murale as top indicator species(Fig.5).These species were indicators of high soil chlorine concentrations and youngest graveyard age.Salvadora oleoides,Capparis decidua and Prosopis juliflora were dominant,while Acacia nilotica,Morus nigra and Populus alba were rare.Dominant shrubs were Calatropis procera and Withania somnifera and rare shrubs were Ricinus communis and Datura alba.The herb layer was dominated by Cynodon dactylon,Avena sativa and Chenopodium album while Dactyloctenium aegyptium,Sisymbrium irrio and Euphorbia helioscopia were rare herbs compared to other communities due to variations in edaphic factors and the young age of the graveyard.

This community has mainly developed on loamy,clay soils with pH from 6.8 to 8.5,demonstrating distinctly neutral and alkaline pedology.The electrical conductivity(EC)of the soils ranged from 38 to 400 μm/cm,total dissolved solids (TDS) 35-280 mg/L, carbonates 0.4-2.6 mEq/L, bicarbonates 1.5-7.3 mEq/L, chlorine 0.7-35.4 mEq/L,calcium+magnesium 1.6-36.8 mEq/L,organic matter 0.08-0.69% ,and nitrogen levels from 0.005 to 0.03% .

Acacia senegal-Datura alba-Convolvulus arvensis community

A total of 12 stations were clustered in this graveyard community.The most characteristic species were Acacia senegal,Datura alba and Convolvulus arvensis(Fig.6).These were indicator species of comparatively lower soil EC,younger graveyards,low anthropogenic pressures and moderate grazing pressures(Table 1).The dominant tree species were Capparis decidua,Salvadora oleoides and P.juliflora,whereas Dalbergia sissoo,Populus euphratica and Ziziphus nummularia were less abundant.The shrub layer was dominated by Calotropis procera and Vitex trifolia mixed with rare shrubs of Datura alba.In addition to C.dactylon,Plantago ovata and Medicago polymorpha were dominant herbs and Fumaria indica,Conyza bonariensis and Euphorbia helioscopia were rare herb species.The pH ranged from 7.1 to 8.1 and the soil texture was loamy to silt clay.Soil organic matter varied from 0.29 to 0.69% ,soil nitrogen 0.001-0.03% ,EC 42-300 μm/cm,TDS 29.4-210 mg/L, carbonates 0.2-2.4 mEq/L, bicarbonates 1.1-3.6 mEq/L,chlorine 0.5-4.8 mEq/L,and calcium+magnesium 2.5-32.5 mEq/L.

Fig.3 Five major graveyard plant communities based on cluster analysis using PCORD V5

Ziziphus spina-Vitex trifolia-Abutilon indicum community

A total of 11 stations form this graveyard community.The main indicator species were Ziziphus spina-christi,Vitex trifolia and Abutilon indicum under the impact of higher nitrogen concentrations and greater grazing pressures,compared to others habitats(Table 1,Fig.7).The dominant trees and shrub species included S.oleoides,P.dactylifera,P.alba and Calotropis procera.Rare trees and shrubs were Eucalyptus camaldulensis,Morus nigra,Parkinsonia aculeata and Withania somnifera,all having minimum important value index(IVI).Desmostachya bipinnata,C. dactylon and Parthenium hysterophorus were dominant herbs;Solanum nigrum,Sisymbrium irio and Conyza bonariensis were rare herbs.Soils exhibit silt and clay textures with pH ranging from 6.7 to 8.3, carbonates 0.6-1.4 mEq/L, bicarbonates 2.3-4.1 mEq/L, chlorine 0.3-23.5 mEq/L, calcium+magnesium 1.6-16 mEq/L,organic matter 0.08-0.86% ,nitrogen 0.003-0.012% , EC 35-320 μm/cm and TDS 28-224 mg/L.

Acacia nilotica-Lantana camara-Salsola foetida community

This graveyard association included a total of 17 stations.The most common indicator species were A.nilotica,Lantana camara and Salsola foetida under the influence of a sandy soil and a graveyard over one hundred years old(Table 1,Fig.8).The dominant tree species were Capparis decidua,Prosopis juliflora and Z.nummularia.However,Ziziphus sativa,Ficus racemosa and Nerium oleander were rare.W.somnifera,Agave salmiana and Datura alba were dominant shrubs while Ricinus communis,Opuntia stricta and Withania coagulans were rare with less IVI.The dominant herbs were C.dactylon,P.hysterophorus and Avena sativa.Rare herbs were Polygonum aviculare,Melilotus indicus and Dactyloctenium aegyptium,based on IVI.The difference in species composition and distribution from other communities was due to the sandy soil and old age(above hundred)of the graveyards.Soil pH ranged from 6.7 to 8.0,EC 30-380 μm/cm, TDS 26.6-266 mg/L, carbonates 0.2-1.6 mEq/L, bicarbonates 1.0-4.2 mEq/L, chlorine 0.5-27.3 mEq/L, calcium+magnesium 1.2-12.5 mEq/L,organic matter 0.09-0.48% and nitrogen 0.004-0.024% .

Fig.4 Two-way cluster dendrogram showing distribution of 81 species in 70 plots of the graveyards measured using the Sorenson method

Melia azedarach-Rhazya stricta-Peganum harmala community

A total of 12 stations clustered together formed this graveyard community.The top indicators included Melia azedarach,Rhazya stricta and Peganum harmala and were indicators of higher calcium and magnesium concentrations and high anthropogenic pressures(Table 1,Fig.9).Moreover,dominant tree and shrub species were P.juliflora,Capparis decidua,Ziziphus nummularia,Calotropis procera,W.somnifera and Vitex trifolia.Rare trees and shrubs were P.dactylifera,S.oleoides,Melia azedarach,W.coagulans and Datura alba.The dominant herbs were C.dactylon,D.aegyptium and Dichanthium annulatum,and rare herb species were Ranunculus muricatus,Salsola foetida and Melilotus indicus based on IVI.Soil pH ranged from 7.2 to 8.8,EC 30-300 μm/cm,TDS 21-220 mg/L,organic matter levels ranged from 0.4 to 0.5% ,nitrogen 0.025-0.022% , carbonates 0.2-2.4 mEq/L, bicarbonates 1.7-5.2 mEq/L, chlorine 0.3-10.5 mEq/L, and calcium+magnesium 2.7-42.8 mEq/L.

Role of graveyards in plant conservation

Fig.5 Data attribute plot(left to right)of Ficus religiosa,Bougainvillea spectabilis and Chenopodium murale showing their position relative to various environmental variables following CAA

Fig.6 Data attribute plot of(left to right)Acacia senegal(1st indicator species),Datura alba(2nd indicator species)and Convolvulus arvensis(3rd indicator species)showing their distribution in relation to different environmental factors after CCA

A total of 81 plant species from 34 different plant families have been conserved and safeguarded in these graveyards.A comparison of vegetation inside and outside the graveyards showed that Capparis decidua,Herniaria hirsute,Salvadora oliedes and P.euphratica were only present inside graveyards.Similarly,species such as Acacia modesta,Acacia senegal,Abulotion indicum,Solanum nigrum and Parkinsonia aculeata were rarely found in the wild but were conserved in these graveyards in considerable numbers.Populous euphoratica was reported for the first time from the study area and is a new record to theregional flora;it was also protected within these graveyards habitats.Abutilon indicum(an extremely rare species in Pakistan)and Solanum nigrum(rare species in the study area)were also observed in satisfactory numbers in these graveyards.These sacred groves/graveyards also conserved very large,mature trees as well;for example,two individuals of Ficus religiosa with diameter at breast height(DBH)of 9.7 m and 9.1 m,one individual of Tamarix aphylla with a DBH of 3.4 m and two individuals of Ficus elastica with DBH of 6.5 m and 5.8 m(Fig.10).Thus,graveyards represent a less disturbed location for plant species and an ideal place for natural conservation.

Table 1 Information on the top three indicator species of each community

Fig.7 Data attribute plot of Ziziphus spina-christi,Vitex trifolia and Abutilon indicum under the influence of edaphic and other climatic factors

Fig.8 CCA bi-plot of Acacia nilotica,Lantana camara and Salsola foetida indicator species in relation to various environmental variables

Fig.9 Data attribute plot(left to right)of Melia azedarach,Rhazya stricta and Peganum harmala in relation to different environmental variables

Discussion

Fig.10 Old tree individuals with their DBH

The vegetation in graveyards or sacred groves is considered least disturbed due to the sacred nature of these sites.These microhabitats have great potential for the conservation of flora as well as fauna due to their cultural and religious significance(Sen and Bhakat 2012).They exhibit unique ecological amplitudes due to a combination of inorganic and organic sedimentology and edaphology,the influence of soils on living things,and hence give rise to a variety of plant species and unique plant communities.A total of 81 species belonging to 34 families were recorded from 20 different(60% of the total)graveyards in the District of Bannu.Although there is no comprehensive ecological study available on graveyards except for a few inventories,the adjacent areas exhibit more or less the same number of species as graveyard vegetation.For example,72 and 67 plant species were reported from various graveyards of Peshawar and Kohat districts,respectively(Shah 2013;Khan et al.2015).These sacred groves were mostly dominated by Capparis decidua and Prosopis joliflora due to mesic conditions as compared to this study.The shrub layer was dominated by Calatropis procera because of high soil chlorine concentration and climatic variability.Cynodon dactylon and Desmostachya bipinnata were dominant herbs of the region.These were also reported by Chaghtai et al.(1978,1983),Hussain et al.(1993)and are widely distributed in other graveyards of Pakistan.De Lacy and Shackleton(2017b)reported on species richness,composition and structure of 139 tree and shrub species from 35 sacred groves of Grahamstown,South Africa.The most dominant species were Cupressus sempervirens followed by Cupressus glabra and Cupressus macrocarpon.Sacred places are natural refugia for species biodiversity in both urban and rural areas and maintained by different cultures throughout the world.Gopal et al.(2018)worked on wild and cultivated plant species of 69 sacred places in the megacity of Bengaluru,India,and evaluated biological relationships,cultural features and parameters related to the urban matrix and type of sacred sites.A total of 121 species were reported,dominated by Ficus religiosa and Azadirachta indica.Among the documented 34 plant families,Poaceae,Fabaceae,Amaranthaceae and Asteraceae were the most dominant.Microphylls,plants with one single unbranched leaf vein,were dominant followed by the nanophyll leaf form,leaves ＜25 mm long.A high percentage of microphylls were the result of dry climatic conditions.Microphylls and nanophylls are representative of hot climatic conditions(Velázquez et al.2016).Cold,dry climates are favorable for small leafed species,whereas moist,warm conditions are favorable for larger leaves species(Harrison et al.2010).Furthermore,the appearance of small leaves is related to the preservation of moisture as well an ecological adaptation to unfavorable and harsh conditions in the study area.While only one species of megaphylls was recorded in the study region,Shah(2013)reported that microphylls and nanophylls were dominant leaf spectra in Peer Taab Graveyards and Dheri Baba hill Gohati of Pakistan.

Cluster analyses(CA)and TWCA,using PCORD software,classified all the locations and plant species into five major graveyard communities or associations under the influence of different environmental factors.The names of these communities were based on indicator species analyses.Our results are in close harmony with Ali et al.(2017)who reported five types of graveyard communities in the Malakand Division, Pakistan using multivariate statistics.In the current study,graveyard or sacred groves were dominated by Capparis decidua, Salvadora spp.along with Prosopis joliflora,Cynodon dactylon and Desmostachya bipinnata.Similar results were also reported by Chaghtai and Yusaf(1976).Capparis decidua,Prosopis joliflora,Cynodon dactylon,Desmostachya bipinnata and Cenchrus ciliaris were the most common plant species in graveyards of Peshawar(Chaghtai et al.1978).

Soils play a key role in the establishment of plant species(Schluter 2001).There is a strong interrelationship between soil and vegetation(Li et al.2008).The soils of the graveyards in this study were mostly clay loams with pH from neutral to alkaline.Adjacent regional graveyards had sand loamy alkaline soils(Hussain et al.1993).This study also focused on the effect of ecological variables such as phosphorus contents,EC,pH,organic matter and nitrogen levels.Nitrogen,calcium,magnesium,soil texture,anthropogenic pressures and grazing pressures have significant impacts upon plant species distribution,composition and formation in different graveyard communities.Similarly,Ali et al.(2017)evaluated environmental gradients such as elevation,slope,silt/sand/clay ratios,pH,and organic matter,nitrogen,phosphorous and potassium contents,and found that they were significantly correlated with the distribution of species and communities after CCA using the CANOCO software.These statistical techniques were also used by Khan et al.(2013,2014),Ali et al.(2017).Grazing and human pressures were higher in urban than in rural areas.Current graveyard vegetation was more natural than vegetation outside the graveyard sites.Molnár et al.(2017)reported that floristic composition and vegetation of graveyards were more natural than vegetation of nearby regions,and more protected by the local people due to their sacred beliefs and indigenous culture.

Conclusion

Graveyards or sacred groves play a major role in plant phytodiversity and species conservation,especially rare or mature species.The age of graveyards,lower soil electrical conductivity,lower anthropogenic pressures,higher soil levels of nitrogen,calcium and magnesium and sandy soils were major factors which played significant roles in species distribution,community formation and the presence of indicator species.Electric conductivity(EC)is an important indicator of soil health.It affects plant nutrient availability,crop yields and crop suitability.CA,TWCA and ISA using PCORD are useful tool for phytosociological classification and analysis of graveyards flora. This phenomenon could further be expanded to evaluate role of the edaphic and climatic factors,identification and role of indicator species in conservation management practices in the field of vegetation ecology.The concept of privileges to sacred groves can further be used to save threatened flora via community involvement.