nology 145 (2007) 325–333www.elsevier.com/locate/revpalbo

Review of Palaeobotany and Paly

Pollen analysis of spider webs from Yunnan, China

Xiao-Yan Song a,b,f, S. Blackmore c, S. Bera d, Cheng-Sen Li a,e,⁎

a State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, Chinab Shanxi Agricultural University, Shanxi, 030801, China

c Royal Botanic Garden Edinburgh, 20a Inverleith Row, Edinburgh EH3 5LR, UKd Department of Botany, University of Calcutta, Kolkata, 700019, India

e Beijing Museum of Natural History, Beijing, 100050, Chinaf Graduate School, Chinese Academy of Sciences, Beijing, 100039, China

Received 19 August 2006; received in revised form 16 January 2007; accepted 16 January 2007Available online 26 January 2007

Abstract

This study concerns the palynological analysis of 19 spider webs, which were collected from the northwestern, central andsouthern parts of Yunnan, China. Pollen grains and spores of 20 taxa belonging to 16 families were recorded from northwesternYunnan and 28 taxa from 23 families from central Yunnan. Spider webs from southern Yunnan yielded 28 taxa belonging to 25families from Mengla County, 38 taxa in 34 families from Wangtianshu Garden and 11 taxa representing 10 families fromXishuangbanna Botanical Garden. The pollen grains and spores extracted from spider webs reflect the distinct characteristics of theregional vegetation which changes from north to south Yunnan. This demonstrates the potential of spider webs as a natural trap forthe study of modern pollen rain.© 2007 Elsevier B.V. All rights reserved.

Keywords: spider webs; natural pollen trap; Yunnan; China

1. Introduction

Natural traps such as surface soils, moss and lichencushions, leaves and bark have been widely used instudies on modern pollen rain (Faegri et al., 1989;Groenman-vanWaateringe, 1998). Spider webs can alsobe regarded as a kind of natural trap, with the potentialto provide a record of modern pollen rain and itsdispersal and deposition in a particular geographicalarea (Bera et al., 2002). Spider webs have also proved to

⁎ Corresponding author. State Key Laboratory of Systematic andEvolutionary Botany, Institute of Botany, Chinese Academy ofSciences, Beijing, 100093, China. Fax: +86 10 62593385.

E-mail address: lics@ibcas.ac.cn (C.-S. Li).

0034-6667/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.revpalbo.2007.01.001

be a useful indicator of environmental chemistry andhave applications in cave environmental studies (Hoseet al., 2002). In the present paper, we analyzed the pollengrains and spores extracted from samples of spider webscollected in Yunnan Province, China. The resultsdemonstrate a reliable relationship between the localvegetation and the palynological data obtained from thespider webs.

2. Material and localities

Nineteen samples of spider webs were collected fromYunnan Province, China (Fig. 1). Four samples werecollected in January 2005 in Lijiang County, northwest-ern Yunnan (Lasn-1: 26°52′N, 100°09′E; altitude:

Fig. 1. The location of sampling sites. A: The location of Yunnan Province of China, B: the sampling sites in Yunnan Province LS: Lashi Lake,XT: Xintuan Reservoir, WB: Wenbi Reservoir, HLT: Heilongtan, XSBN: Xishuangbanna Botanical Garden, WTS: Wangtianshu Botanical Garden,ML: Mengla County.

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2424 m.s.l.; Wbhn-1, Wbhn-2: 26°49′N, 100°12′E;altitude: 2370 m.s.l.; Xtn-1: 26°55′N, 100°19′E;altitude: 2461 m.s.l.). In April 2005, 15 samples werecollected: two from Heilongtan, Kunming, centralYunnan (25°1′N, 102°41′E; altitude: 1980 m.s.l.) and13 from localities in the southern part of Yunnan. Thelatter comprised four from the tropical rain forest area ofXishuangbanna Botanical Garden (21°41′–21°55′N,101°15′–101°25′E; altitude: 592 m.s.l.), five fromMengla County (21°09′–22°23′N, 101°05′–101°50′E;altitude: 786 m.s.l.) and four from WangtianshuBotanical Garden (21°25′–21°38′N, l01°34′–101°52′E; altitude: 750 m.s.l.).

3. Local vegetation

There are considerable differences in both climateand vegetation between the south and north of theYunnan Province. The standard reference work for

classifying the vegetation of Yunnan is best understoodin terms of the vegetation map (Fig. 2) which recognizesthree major regions: tropical monsoon forest, subtrop-ical evergreen broad-leaved forest and alpine vegetationof Qinghai–Tibet plateau. Each of these is divided into anumber of geographical zones and then further sub-divided into domains and subdomains which representdistinctive types of natural forest recognized by thepresence of key taxa (Writing Group of YunnanVegetation, 1987). Lijiang County is located withinthe subdomain of Pinus yunnanensis forest and Picea–Abies forest of north Yunnan (Fig. 2). Kunming City issituated within the subdomain of Cyclobalanopsisglaucoides forest, Castanopsis orthacantha forest andP. yunnanensis forest in central Yunnan (Fig. 2). Thesubdomains in which Lijiang County and Kunming Cityare located both belong to the domain of semi-humidevergreen broad-leaved forest and P. yunnanensis forestof central and eastern Yunnan (Writing Group of

Fig. 2. Vegetational regionalization of Yunnan Province. Explanation of Fig. 2 (regionalization of Yunnan vegetation) (Writing Group of YunnanProvince, 1987; Xu et al., 2004): (I) region of tropical monsoon forest, rain forest, (IA) subregion of monsoon forest, rain forest of western China,(IAi) zone of northern tropical seasonal rain forest and semi-evergreen monsoon forest, (IAi-1) domain of seasonal rain forest and semi-seasonalevergreen monsoon forest found in inter-montane basins of western and southwestern Yunnan, (1b) subdomain of Terminalia myriocarpa andPometia tomentosa forest, Semecarpus albescens and Phoebe nanmu forest found in inter-mid-montane basins of northern Xishuang Banna, (II)region of subtropical evergreen broad-leaved forest, (IIA) subregion of semi-humid evergreen broad-leaved forest of western China, (IIAi) zone ofsubtropical monsoon evergreen broad-leaved forest of southern plateau, (IIAii) zone of subtropical evergreen broad-leaved forest of northern plateau,(Aii-1) domain of semi-humid evergreen broad-leaved forest and Pinus yunnanensis forest of central and eastern Yunnan, (1c) subdomainP. yunnanensis forest and Picea–Abies forest of Northwestern central Yunnan, (III) region of alpine vegetation of Qinghai–Tibet Plateau.

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Yunnan Vegetation, 1987). Within this domain, sixaltitudinal vegetation belts are recognized (WritingGroup of Yunnan Vegetation, 1987; Table 1).

Xishuangbanna Botanical Garden, WangtianshuBotanical Garden and Mengla County are located inthe same subdomain of Terminalia myriocarpa andPometia tomentosa forest and Semecarpus albescensand Phoebe nanmu forest which are found in inter-mid-montane basins of north Xishuang Banna (Fig. 2). Inthis subdomain three altitudinal vegetation belts arerecognized (Writing Group of Yunnan Vegetation, 1987;Table 2).

4. Methods

The samples of spider webs were treated withconcentrated hydrochloric acid to dissolve the meshes.The superfluous materials in the solution were removedwith a strainer. Samples were washed several times withdistilled water to remove acid. The residue was mixedwith 10 ml conc. HF and kept for 2 days to removesilica. After washing and centrifuging, the residue wastreated with acetolysis mixture (acetic anhydride andconcentrated sulphuric acid in v/v=9:1). Finally theacetolyzed samples were kept in 50% glycerine jelly and

Table 1The altitudinal distribution ranges of main modern vegetation types inthe domain of semi-humid evergreen broad-leaved forest and Pinusyunnanensis forest of central and eastern Yunnan (Writing Group ofYunnan Vegetation, 1987)

Vegetation type Altitude(m)

Main elements ofvegetation

1. Shrub–grassland savanna b1300 Sophora viciifolia,Pyracantha fortuneabaComm.

2. Semi-humid evergreenbroad-leaved forest orPinus forest

1600–2500 Castanopsis,Cyclobalanopsis,Lithocarpus,(Cyclobalanopsisglaucoides, Castanopsisdelavayi, Castanopsisorthacantha), Pinusarmandii and Pinusyunnanensis

3. Montane mossy evergreenbroad-leaved forest

2400–2900 Lithocarpus craibianus,Pinus armandii and Alnusnepalensis etc. Ferns andmoss increase.

4. Tsuga forest andevergreen coniferousbroad-leaved mixed forest

2700–3000 Tsuga dumosa, Quercusguayavaefolia,Quercuslongispica, Abies ernestiiand Pinus yunnanensis

5. Picea and Abies forest 3100–4200 Abies georgei, Abiesdelavayi, Picealikiangensis andAbies forrestii

6. Alpine shrubbery andalpine grassland

4000–4700 Ericaceae (Rhododendroncephalanthum,R. adenogynum,R. traillianum andR. fastigiatum)

Table 2The altitudinal distribution ranges of the main modern vegetation typesin the subdomain of Antiaris toxicaria, Pouteria grandifolia,Canarium album forest and Ficus altissima–Chukrasia tabularisforest found in inter-mid-montane basins of southern Xishuangbanna(Writing Group of Yunnan Vegetation, 1987)

Vegetation type Altitude(m)

Main elements ofvegetation

1. Seasonal rain forest orsemi-evergreen seasonalrain forest

b800–900 Antiaris toxicaria, Pouteriagromdifolia, Canariumalbum, Terminaliamyriocarpa, Pometiatomentosa, Parashoreachinensis, Ficus altissima,Chukrasia tabularis

2. Mountain rain forest 800–1000 Alstonia pachycarpa,Paramichelia baillonii

3. Mountain monsoonevergreen broad-leavedforest

N1000 Castanopsis, Lithocarpus,Lauraceae, Theaceae

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mounted on glass slides for light microscopic observa-tion. In total, 2773 pollen grains and spores wereobserved. Most of samples contained over 200 grains,but some of them far fewer. Palynomorphs wereidentified by comparison with a series of monographsand atlases (IB-CAS, 1976; IBSCIB-CAS, 1982; Wanget al., 1995). All samples are stored in the Institute ofBotany, Chinese Academy of Sciences, Beijing.

5. Results

5.1. Northwestern Yunnan

Four samples from northwestern Yunnan were notparticularly rich in pollen grains and spores and in onesample they were entirely lacking. The three samples thatdid contain pollen and spores yielded 20 taxa represent-ing 16 families, predominantly of arboreal pollen whichaccounted for 50.9% of the pollen/spore content insample Lasn-1, 62.6% in Wbhn-1 and 72.0% in sample

Xtn-1. The most abundant pollen in the three samples isthat of Alnus (Lasn-1: 43.0%, Wbhn-1: 32.0%, Xtn-1:54.0%). Pinus pollen grains are also present insignificant amounts (Lasn-1: 6.1%, Wbhn-1: 15.8%,Xtn-1: 6.0%). Herbaceous taxa are fairly well repre-sented (Lasn-1: 49.1%, Wbhn-1: 36.9%, Xtn-1: 24%),especially Artemisia (Lasn-1: 45.6%, Wbhn-1: 35.1%,Xtn-1: 14.0%). Pollen grains of Tsuga, Betula, Poaceae,Gesneriaceae, Verbenaceae and Compositae are presentat very low percentage (Wbhn-1: 0.5%, Xtn-1: 4.0%).No spores were recovered from Lasn-1 (Fig. 3, Table 3).

5.2. Central Yunnan

Two samples from Heilongtan yielded abundantpollen grains and spores with 28 taxa representing 23families being present. Among them, trees and shrubsdominate (Hltn-1: 93.1%, Hltn-2: 88.8%), especiallyPinus (Hltn-1: 90.1%, Hltn-2: 58.3%). Herbaceous taxaare present in moderate amounts (Hltn-1: 6.7%, Hltn-2:11.2%), with Artemisia pollen again representing themost abundant herbaceous taxon (Hltn-1: 3.2%, Hltn-2:2.9%). Pteridophyte spores (Pteris: 0.3%) were onlyrecorded in Hltn-1. The pollen grains of tropical andsubtropical plants belonging toMyrtaceae, Elaeagnaceaeand Pittosporaceae were recorded (Table 3). The taxarecorded from the spider webs from central Yunnan werefound to be richer than those from northwestern Yunnan.

5.3. Southern Yunnan

Two of the four spider webs taken from tropical rainforest in Xishuangbanna Botanical Garden yielded

Fig. 3. The percentage comparison of pollen and spores from spider web samples in Yunnan, China.

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pollen grains and spores representing 11 taxa from 10families. The present plants were Pinus, Dichapetalaceae,Leguminosae, Malvaceae, Artemisia, Convolvulaceae,Melastomaceae, Rubiaceae, Pteris and Selaginellaceae.

Pollen and spores of 28 taxa belonging to 25 familieswere retrieved from five spider webs from MenglaCounty in the southern part of Yunnan. Among these,trees and shrubs pollen are abundant (Mln-1: 79.0%;Mln-3: 92.2%). The assemblage in Mln-1 is character-ized by a high percentage (58.9%) of Myrsinaceaepollen. In Mln-3, the abundance of Loranthaceae pollen(73.3%) is followed by Meliaceae (12.5%) and Bigno-niaceae (4.7%). Herbs (Mln-1: 21.1%; Mln-3: 7.8%) aremainly represented by taxa of Compositae. In Mln-5,trees and shrubs values reach 95.5% with a frequentrepresentation of Sonneratiaceae (60.8%) followed byMalvaceae (20.1%) and Myrsinaceae (5.0%). Lorantha-ceae, Meliaceae, Rutaceae, Samydaceae and Theaceaepollen are also recorded. Herbs (4.0%) are moderatelyrepresented with Poaceae, Compositae and Gesneria-ceae. Spores belong to ferns of the Gymnogrammaceae;their relative abundance reaches 0.5%. Mln-2 and Mln-4did not yield significant amounts of pollen grains orspores. In Mln-2, among the recorded taxa, herbsdominated (68.9%) over trees and shrubs (29.5%).Spores of Gymnogrammaceae are also found (1.6%).In Mln-4, only 2 pollen grains of Theaceae were found.No pteridophyte spores were recovered from Mln-1,Mln-3 and Mln-4 (Fig. 4, Table 3).

Thirty eight taxa representing 34 families wereidentified in 4 samples from Wangtianshu BotanicalGarden, making these the most diverse spider webrecords. Pollen and spores were not abundant in Wtsn-2and Wtsn-4, but included 14 angiosperm taxa in 13families, 1 gymnosperm taxon in 1 family and 1 family ofpteridophytes. In Wtsn-1, trees and shrubs pollenamounted for 59.3% of the total, consisting mainly of

Malvaceae (17.4%), Oleaceae (14.0%) and Quercus(5.8%). The non-arboreal pollen component of 40.7%was dominated by Gesneriaceae (36.1%). In Wtsn-3,percentages of tree and shrub pollen reach 97.4%with theremaining 2.4% herbaceous plants mainly consist ofGesneriaceae (1.8%). In this sample, pollen of Euphor-biaceae dominates (up to 84.8%) followed in abundanceby Castanopsis (5.4%) and Samydaceae (4.4%). Pollengrains of many tropical and subtropical plant taxa such asAnacardiaceae, Bombaceae, Ebenaceae, Combretaceae,Guttiferae, Tetracentraceae, Flacourtiaceae and Pittospor-aceae were present in low frequencies. In Wtsn-2 andWtsn-3, pteridophyte sporeswere recorded and accountedfor 3.6% and 0.2%, respectively (Fig. 3, Table 3).

6. Discussion

The pollen and spore assemblages recovered fromspider webs are strongly dominated by pollen of trees,shrubs and herbs, whereas pteridophyte spores are eitherabsent or are present in very low frequency (Fig. 4,Table 3). It is not clear why pteridophyte sporesoccurred so sporadically.

The localities of Yunnan where the spider webs werecollected are situated at quite different latitudes andaltitudes. As a consequence, the local vegetation is alsovery different in each of the three regions. The pollen andspore taxa analyzed from the spider webs reflect the localvegetation of the collection site. The diversity of tropicaland subtropical plant taxa is more pronounced in southernYunnan than in central and northwestern Yunnan and theoverall vegetation of southern Yunnan is richer (Fig. 4).

Lijiang County belongs to the subdomain of Pinusyunnanensis forest and Picea–Abies forest, but thepollen found from the spider webs in Lijiang showed thatthe pollen of Alnus is predominant in the local pollenrain. The reason is that Alnus nepalensis has been

Table 3Comparative account of spore-pollen taxa retrieved from spider webs at different locations in Yunnan Province (Wu, 1991; Mabberley, 1997)

Taxa Vegetation categories Lash-1 Wbhn-1 Xtn-1 Hltn-1 Hltn-2 Bnn-3 Bnn-4 Wtsn-1 Wtsn-2 Wtsn-3 Wtsn-4 Mln-1 Mln-2 Mln-3 Mln-4 Mln-5

Abies T ⁎ +Pinus T + ++ + +++ +++ # # + # ⁎ + # ⁎ ⁎

Tsuga T + ⁎

Acanthaceae ST + ⁎ # +Alnus T +++ ++ +++ ⁎ + + #Anacardiaceae ST ⁎

Araliaceae ST +Artemisia T +++ ++ ++ + + # + ⁎ # ++ # ⁎

Betula W + + + ⁎ + + # +Bignoniaceae ST # +Bombacaceae ST ⁎

Caprifoliaceae T ⁎ ⁎

Caryophyllaceae T ⁎

Castanopsis W ⁎ # + # + #Celtis W ⁎

Chenopodiaceae W + ⁎

Combretaceae ST ⁎

Compositae W ⁎ + ⁎ + # + # ⁎ + # +Convolvulaceae W +Corylus T + ⁎

Cruciferae W +Dichapetalaceae ST #Ebenaceae ST ⁎

Elaeagnaceae W ⁎

Ericaceae W ⁎ ⁎

Erythroxylaceae ST ⁎

Euphorbiaceae W ⁎ ⁎ + +++ ⁎

Fagaceae W ⁎

Flacourtiaceae ST +Gesneriaceae W + ⁎ + + + # # ++ # + # # ⁎ +Guttiferae ST ⁎ +Ilex ST ⁎ + #Juglandaceae W ⁎ + ⁎

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Leguminosae W ⁎ #Loranthaceae ST +++ +Malvaceae W ⁎ # ++ # ⁎ ++Melastomataceae ST # #Meliaceae ST + ++ +Moraceae ST ⁎

Myrsinaceae ST ⁎ +++ +Myrtaceae ST ⁎ + ⁎

Oleaceae W + ++ ⁎ +Papilionaceae W # ⁎ #Pittosporaceae ST + #Plantaginaceae W ⁎

Poaceae W + + ⁎ # ⁎ # ⁎ +Polygonaceae WQuercus T ⁎ ⁎ + ⁎ #Rubiaceae W ⁎

Rutaceae W + # ⁎ +Samydaceae ST + + +Sonneratiaceae ST +++Sterculiaceae ST #Tetracentraceae ST ⁎

Theaceae ST # +Ulmus T +Urticaceae W ⁎

Verbenaceae ST ⁎ + ⁎ # ⁎

Athyriaceae W #Gymnogrammaceae W ⁎ + # ⁎

Polypodiaceae W #Pteris W + ⁎ ⁎

Selaginellaceae W #Temperate zone taxa 3 7 4 5 7 1 2 4 2 3 1 2 3 2 0 3Widespread taxa throughout

Yunnan3 7 8 9 11 3 5 6 7 12 2 5 7 5 0 6

Tropical and Subtropical taxa 0 2 1 2 3 0 2 6 3 9 3 2 1 5 1 8Total taxa 6 16 13 16 21 4 9 16 12 24 6 9 11 12 1 17

#: the pollen or spore percentage is very low, ⁎: the pollen or spore percentageb1%, +: the pollen or spore percentage between 1% and 10%, ++: the pollen or spore percentage between 10% and 40%,+++: the pollen or spore percentageN40%, T: the temperature zone taxa, ST: the tropical/subtropical taxa, W: widespread taxa throughout Yunnan.

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Fig. 4. The composition of pollen assemblages extracted from spider webs from Northern, Central and Southern Yunnan and grouped in threecategories: temperature zone taxa, widespread taxa found throughout Yunnan and tropical/subtropical taxa.

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increasing in abundance as a consequence of disturbanceto the original forests (Writing Group of YunnanVegetation, 1987). Kunming City belongs to thesubdomain of Cyclobalanopsis glaucoides forest, Casta-nopsis orthacantha forest and P. yunnanensis forest. Thepollen assemblage extracted from the spider webs inHeilongtan showed that pollen of Pinus is predominantin the local pollen rain, as the parent plant is the localvegetation.

Xishuangbanna Botanical Garden, Wangtianshu Bo-tanical Garden and Mengla County all belong to thesame subdomain, which is characterized by plants suchas Antiaris toxicaria, Pouteria gromdifolia, Canariumalbum, Parashorea chinensis, Chukrasia tabularis,Paramichelia baillonii, Castanopsis, Lithocarpus, Laur-aceae and Theaceae (Table 2). The pollen extracted fromthe spider webs in this area reflected the most commongenera and families of this subdomain (Fig. 4, Table 3).

In Wangtianshu Botanical Garden, Parashoreachinensis (Family Dipterocarpaceae) grows abundant-ly, but pollen of this dominant forest tree was notfound in the spider web samples collected from thislocality. Probably this is because the spider webs werecollected in April which is well ahead of the mainflowering period for Parashorea in May and June (Liet al., 1990). The spider webs we investigated arepresumed to be less than a year old and to have beenproduced after the end of the flowering season in lateJune. In this case, these spider webs were producedafter late June, their age being less than one year.

7. Conclusions

1). Spider webs can be regarded as a natural trap foratmospheric pollen rain and the pollen assemblagethat can be extracted from them reflects the local

vegetation near the sampling sites although pteri-dophyte spores appear to be under-represented.

2). The particular characteristics of individual spiderwebs can vary significantly in terms of theirposition, size and age and such differences can beexpected to be reflected in the pollen assemblagethat is trapped and retained. Other local factorssuch as wind speed and humidity will also affectthe retention of pollen grains and spores in webs.This makes it difficult to determine precisereasons why any particular web may or may notyield an informative record of the pollen rain andfurther research into these factors is required. It istherefore most appropriate to regard spider websas an additional or supplementary natural trapwhich can be used alongside more establishedmethods in studies of modern pollen rain.

Acknowledgements

We are very grateful for the help of Professor Nai-Qiu Du, Drs. Yi-Feng Yao, Hong-En Jiang and Ya-QinHu from the Institute of Botany, Chinese Academy ofSciences for providing helps in this work. The study wassupported by the National Basic Research Program ofChina (# 2004CB720205) and the National NaturalScience Foundation of China (# 30530050).

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